Evaluation of forming limit in viscous pressure forming of automotive aluminum alloy 6k2 1 -T4 sheet
conective tissue结缔组织(留学生英语备课资料)
Chapter 5. Connective TissueConnective Tissue: IntroductionThe different types of connective tissue are responsible for providing and maintaining the form of organs throughout the body. Functioning in a mechanical role, they provide a matrix that connects and binds other tissues and cells in organs and gives metabolic support to cells as the medium for diffusion of nutrients and waste products.Structurally, connective tissue is formed by three classes of components: cells, fibers, and ground substance. Unlike the other tissue types (epithelium, muscle, and nerve), which consist mainly of cells, the major constituent of connective tissue is the extracellular matrix (ECM). Extracellular matrices consist of different combinations of protein fibers (collagen, reticular, and elastic fibers) and ground substance. Ground substance is a highly hydrophilic, viscous complex of anionic macromolecules (glycosaminoglycans and proteoglycans) and multiadhesive glycoproteins (laminin, fibronectin, and others) that stabilizes the ECM by binding to receptor proteins (integrins) on the surface of cells and to the other matrix components. In addition to its major structural role, molecules of connective tissue serve other important biological functions, such as forming a reservoir of factors controlling cell growth and differentiation. The hydrated nature of much connective tissue provides the medium through which nutrients and metabolic wastes are exchanged between cells and their blood supply.The wide variety of connective tissue types in the body reflects variations in the composition and amount of the cells, fibers, and ground substance which together are responsible for the remarkable structural, functional, and pathologic diversity of connective tissue.The connective tissues originate from the mesenchyme, an embryonic tissue formed by elongated undifferentiated cells, the mesenchymal cells (Figure 5–1). These cells are characterized by oval nuclei with prominent nucleoli and fine chromatin. They possess many thin cytoplasmic processes and are immersed in an abundant and viscous extracellular substance containing few fibers. The mesenchyme develops mainly from the middle layer of the embryo, the mesoderm. Mesodermal cells migrate from their site of origin in the embryo, surrounding and penetrating developing organs. In addition to being the point of origin of all types of connective tissue cells, mesenchyme develops into other types of structures, such as blood cells, endothelial cells, and muscle cells.Figure 5–1.Embryonic mesenchyme.Mesenchyme consists of a population of undifferentiated cells, generally elongated but with many shapes, having large euchromatic nuclei and prominent nucleoli which indicate high levels of synthetic activity. These cells are called mesenchymal cells. Mesenchymal cells are surrounded by an extracellular matrix which they produced and which consists largely of a simple ground substance rich in hyaluronan (hyaluronic acid). This section is stained with Masson trichrome which stains collagen fibers blue and the lack of collagen in mesenchyme is apparent. X200.Cells of Connective TissueA variety of cells with different origins and functions are present in connective tissue (Figure 5–2 and Table 5–1). Fibroblasts originate locally from undifferentiated mesenchymal cells and spend all their life in connective tissue; other cells such as mast cells, macrophages, and plasma cells originate from hematopoietic stem cells in bone marrow, circulate in the blood, and then move into connective tissue where they remain and execute their functions. White blood cells (leukocytes) are transient cells of most connective tissues; they also originate in the bone marrow and move to the connective tissue where they reside for a few days, then usually die by apoptosis. Figure 5–2.Lineages of connective tissue cells.This simplified representation of the connective tissue cell lineage includes cells from the multipotential embryonic mesenchyme cells and hematopoietic stem cells of bone marrow. Dottedarrows indicate that one or more intermediate cell types exist between the examples illustrated. The cells are not drawn in proportion to actual sizes, eg, adipocyte, megakaryocyte, and osteoclast cells are significantly larger than the other cells illustrated.Table 5–1.Functions of connective tissue cells.FibroblastsFibroblasts synthesize collagen, elastin, glycosaminoglycans, proteoglycans and multiadhesive glycoproteins. Fibroblasts are the most common cells in connective tissue (Figure 5–3) and are responsible for the synthesis of extracellular matrix components. Two stages of activity—active and quiescent—are often observed in these cells (Figure 5–3b). Cells with intense synthetic activity are morphologically distinct from the quiescent fibroblasts that are scattered within the matrix they havealready synthesized. Some histologists reserve the term fibroblast to denote the active cell and fibrocyte to denote the quiescent cell.Figure 5–3.Fibroblasts.Connective tissue where parallel bundles of collagen are being formed.(a): Fibroblasts typically show large active nuclei and eosinophilic cytoplasm tapering off in both directions along the axis of the nucleus, a morphology usually called "spindle-shaped." The nuclei (arrows) are clearly seen, but the cytoplasmic processes resemble the collagen bundles (C) that fill the extracellular matrix and are difficult to distinguish in H&E-stained sections. (b): Both active and quiescent fibroblasts may sometimes be distinguished, as in this section of dermis. Active fibroblasts are large cells with large, euchromatic nuclei and basophilic cytoplasm, whereas inactive fibroblast or fibrocytes are smaller with less prominent, heterochromatic nuclei. The very basophilic round cells in (b) are leukocytes. BothX400.H&E.The active fibroblast has an abundant and irregularly branched cytoplasm. Its nucleus is ovoid, large, and pale-staining, with fine chromatin and a prominent nucleolus. The cytoplasm is rich in rough ER, and the Golgi apparatus is well developed. The quiescent fibroblast or fibrocyte is smaller than the active fibroblast and is usually spindle-shaped. It has fewer processes; a smaller, darker, elongated nucleus; and more acidophilic cytoplasm with much less RER.Fibroblasts synthesize most components of connective tissue ECM, including proteins, such as collagen and elastin, which upon secretion form collagen, reticular, and elastic fibers, and the glycosaminoglycans, proteoglycans, and glycoproteins of the groundsubstance. Fibroblasts are targets of various growth factors that influence cell growth and differentiation. In adults, fibroblasts in connective tissue rarely undergo division; mitosis can resume when the organ requires additional fibroblasts as in wound healing.MEDICAL APPLICATIONThe regenerative capacity of the connective tissue is clearly observed when tissues are destroyed by inflammation or traumatic injury. In these cases, the spaces left after injury to tissues whose cells do not divide (eg, cardiac muscle) are filled by connective tissue, which forms a scar. The healing of surgical incisions depends on the reparative capacity of connective tissue. The main cell type involved in repair is the fibroblast.When it is adequately stimulated, such as during wound healing, the fibrocyte reverts to the fibroblast state, and its synthetic activities are reactivated. In such instances the cell reassumes the form and appearance of a fibroblast. The myofibroblast, a cell with features of both fibroblasts and smooth muscle cells, is also observed during wound healing. These cells have most of the morphological characteristics of fibroblasts but contain increased amounts of actin microfilaments and myosin and behave much like smooth muscle cells. Their activity is responsible for wound closure after tissue injury, a process called wound contraction.AdipocytesAdipocytes (L. adeps, fat, + Gr. kytos, cell) are connective tissue cells that have become specialized for storage of neutral fats or for the production of heat. Often called fat cells, they have considerable metabolic significance and are discussed in detail in Chapter 6.Macrophages & the Mononuclearphagocyte SystemMacrophages were discovered and initially characterized by their phagocytic ability. They have a wide spectrum of morphologic features that correspond to their state of functional activity and to the tissue they inhabit.In the electron microscope, macrophages are characterized by an irregular surface with pleats, protrusions, and indentations, a morphologic expression of their active pinocytotic and phagocytic activities. They generally have a well-developed Golgi apparatus, many lysosomes, and rough ER (Figure 5–4).Figure 5–4.Macrophage ultrastructure.Characteristic features of macrophages seen in this TEM of one such cell are the prominent nucleus (N) and the nucleolus (Nu) and the numerous secondary lysosomes (L). The arrows indicate phagocytic vacuoles near the protrusions and indentations of the cell surface. X10,000.Macrophages derive from bone marrow precursor cells that divide, producing monocytes which circulate in the blood. These cells cross the wall of venules and capillaries to penetrate the connective tissue, where they mature and acquire the morphologic features of macrophages. Therefore, monocytes and macrophages are the same cell in different stages of maturation. Macrophages are also sometimes referred to as "histiocytes."Macrophages are distributed throughout the body and are present in most organs. Along with other monocyte-derived cells, they comprise a family of cells called the mononuclearphagocyte system (Table 5–2). All are long-living cells and may survive for months in the tissues. In most organs these cells are highly important for the up-take, processing, and presentation of antigens for lymphocyte activation. The macrophage-like cells have been given different names in different organs, eg, Kupffer cells in the liver, microglial cells in the central nervous system, Langerhans cells in the skin, and osteoclasts in bone tissue. However, all are derived from monocytes. The transformation from monocytes to macrophages in connective tissue involves increases in cell size, increased protein synthesis, and increases in the number of Golgi complexes and lysosomes. A typical macrophage measures between10 and 30 m in diameter and has an oval or kidney-shaped nucleus located eccentrically.Table 5–2.Distribution and main functions of the cells of the mononuclear phagocyte system.MEDICAL APPLICATIONWhen adequately stimulated, macrophages may increase in size and are arranged in clusters forming epithelioid cells (named for their vague resemblance to epithelial cells), or several may fuse to form multinuclear giant cells. Both cell types are usually found only in pathological conditions.Macrophages act as defense elements. They phagocytose cell debris, abnormal extracellular matrix elements, neoplastic cells, bacteria, and inert elements that penetrate the organism. Macrophages are also antigen-presenting cells that participate in the processes of partial digestion and presentation of antigen to other cells (see Chapter 14). A typical example of an antigen-processing cell is the macrophage present in the skin epidermis, called the Langerhans cell (see Chapter 18). Althoughmacrophages are the main antigen presenting cells, under certain circumstances many other cell types, such as fibroblasts, endothelial cells, astrocytes, and thyroid epithelial cells, are also able to perform this function. Macrophages also participate incell-mediated resistance to infection by bacteria, viruses, protozoans, fungi, and metazoans (eg, parasitic worms); in cell-mediated resistance to tumors; and in extrahepatic bile production, iron and fat metabolism, and the destruction of aged erythrocytes.When macrophages are stimulated (by injection of foreign substances or by infection), they change their morphological characteristics and metabolism. They are then called activated macrophages and acquire characteristics not present in their nonactivated state. These activated macrophages, in addition to showing an increase in their capacity for phagocytosis and intracellular digestion, exhibit enhanced metabolic and lysosomal enzyme activity. Macrophages also have an important role in removing cell debris and damaged extracellular components formed during the physiological involution process. For example, during pregnancy the uterus increases in size. Immediately after parturition, the uterus suffers an involution during which some of its tissues are destroyed by the action of macrophages. Macrophages are also secretory cells that produce an impressive array of substances, including enzymes (eg, collagenase) and cytokines that participate in defensive and reparative functions, and they exhibit increased tumor cell–killing capacity.Mast CellsMast cells are large, oval or round connective tissue cells, 20–30 m in diameter, whose cytoplasm is filled with basophilic secretory granules. The rather small, spherical nucleus is centrally situated and may be obscured by the cytoplasmic granules (Figure 5–5).Figure 5–5.Mast cells.Mast cells are components of loose connective tissues, often located near small blood vessels (BV). (a): They are typically oval-shaped, with cytoplasm filled with strongly basophilic granules. X400. PT. (b):Ultrastructurally mast cells show little else around the nucleus (N) besides these cytoplasmic granules (G), except for occasional mitochondria (M). The granule staining in the TEM is heterogeneous and variable in mast cells from different tissues; at higher magnifications some granules may show a characteristic scroll-like substructure (inset) that contains preformed mediators such as histamine and proteoglycans. The ECM near this mast cell includes elastic fibers (E) and bundles of collagen fibers (C).The secretory granules are 0.3–2.0 m in diameter. Their interior is electron-dense and heterogeneous. Mast cells function in the localized release of many bioactive substances with roles in the inflammatory response, innate immunity, and tissue repair.Because of their high content of acidic radicals in their sulfated glycosaminoglycans, mast cell granules display metachromasia, which means that they can change the color of some basic dyes (eg, toluidine blue) from blue to purple or red. The granules are poorly preserved by common fixatives, so that mast cells are frequently difficult to identify. Mast cell granules contain a wide variety of paracrine compounds that promote different aspects of a local inflammatory response. A partial list of important molecules released from these granules includes:§Heparin, a sulfated glycosaminoglycan that acts locally as an anticoagulant§Histamine, which promotes increased vascular permeability and smooth muscle contraction§Serine proteases, which activate various mediators of inflammation§Eosinophil and neutrophil chemotactic factors which attract those leukocytes§Leukotrienes C4, D4, and E4(or the slow-reacting substance of anaphylaxis, SRS-A) which also trigger smooth muscle contraction.Mast cells occur in many connective tissues, but are especially numerous near small blood vessels in skin and mesenteries (perivascularmast cells) and in the mucosa lining digestive and respiratory tracts (mucosal mast cells). The average size and granular content of these two populations differ somewhat.Mast cells originate from progenitor cells in the bone marrow. These progenitor cells circulate in the blood, cross the wall of venules and capillaries, and penetrate connective tissues, where they proliferate and differentiate. Although they are in many respects similar to basophilic leukocytes, they have a separate stem cell. Release of the chemical mediators stored in mast cells promotes the allergic reactions known as immediate hypersensitivity reactions, because they occur within a few minutes after penetration by an antigen of an individual previously sensitized to the same or a very similar antigen. There are many examples of immediate hypersensitivity reaction; a dramatic one is anaphylactic shock, a potentially fatal condition. The process of anaphylaxis consists of the following sequential events: The first exposure to an antigen (allergen), such as bee venom, results in production of the IgE class of immunoglobulins (antibodies) by plasma cells. IgE is avidly bound to the surface of mast cells. A second exposure to the antigen results in binding of the antigen to IgE on the mast cells. This event triggers release of the mast cell granules, liberating histamine, leukotrienes, ECF-A, and heparin (Figure 5–6). Degranulation of mast cells also occurs as a result of the action of the complement molecules that participate in the immunological reaction cited in Chapter 14. Histamine causes contraction of smooth muscle (mainly of the bronchioles) and dilates and increases permeability (mainly in postcapillaryvenules). Any liberated histamine is inactivated immediately after release. Leukotrienes produce slow contractions in smooth muscle, and ECF-A attracts blood eosinophils. Heparin is a blood anticoagulant, but blood clotting remains normal in humans during anaphylactic shock. Mast cells are widespread in the human body but are particularly abundant in the dermis and in the digestive and respiratory tracts.Figure 5–6.Mast cell secretion.Mast cell secretion is triggered by re-exposure to certain antigens and allergens. Molecules of IgE antibody produced in an initial response to an allergen such as pollen or bee venom are bound to surface receptors for IgE (1), of which 300,000 are present per mast cell. When a second exposure to the allergen occurs, IgE molecules bind this antigen and a few IgE receptors very rapidly becomecross-linked (2). This activates adenylatecyclase, leading to phosphorylation of specific proteins and (3) entry of Ca2+ and rapid exocytosis of some granules (4). In addition, phospholipases act on specific membrane phospholipids, leading to production and release of leukotrienes (5). The components released from granules, as well as the leukotrienes, are immediately active in the local microenvironment and promote a variety of controlled local reactions which together normally comprise part of the inflammatory process called the immediate hypersensitivity reaction. ECF-A, eosinophil chemotactic factor of anaphylaxis.Plasma CellsPlasma cells are large, ovoid cells that have a basophilic cytoplasm due to their richness in rough ER. The juxtanuclear Golgi apparatus and the centrioles occupy a region that appears pale in regular histologic preparations (Figure 5–7).Figure 5–7.Plasma cells.Plasma cells are abundant in this portion of an inflamed intestinal villus. The plasma cells are characterized by their abundant basophilic cytoplasm involved in the synthesis of antibodies. A large pale Golgi apparatus (arrows) near each nucleus is the site of the terminal glycosylation of the antibodies (glycoproteins). Plasma cells can leave their sites of origin in lymphoid tissues, move to connective tissue, and produce the antibodies that mediate immunity. X400 PT.The nucleus of the plasma cell is generally spherical but eccentrically placed. Many of these nuclei contain compact, peripheral regions of heterochromatin alternating with lighter areas of euchromatin, a configuration that can give the nucleus of a plasma cell the appearance of a clock-face. There are few plasma cells in most connective tissues. Their average lifespan is short, 10–20 days.MEDICAL APPLICATIONPlasma cells are derived from B lymphocytes and are responsible for the synthesis of antibodies. Antibodies are immunoglobulins produced in response to penetration by antigens. Each antibody is specific for the one antigen that gave rise to its production and reacts specifically with molecules possessing similar epitopes (see Chapter 14). The results of the antibody-antigen reaction are variable. The capacity of the reaction to neutralize harmful effects caused by antigens is important. An antigen that is a toxin (eg, tetanus, diphtheria) may lose its capacity to do harm when it combines with its respective antibody.LeukocytesConnective tissue normally contains leukocytes that migrate from the blood vessels by diapedesis. Leukocytes (Gr. leukos, white, + kytos), or white blood corpuscles, are the wandering cells of the connective tissue. They leave blood by migrating between the endothelial cells lining capillaries and postcapillaryvenules to enter connective tissue by a process called diapedesis. This process increases greatly during inflammation, which is a vascular and cellular defensive reaction against foreign substances, in most cases pathogenic bacteria or irritating chemical substances. The classic signs of inflammation were first described by Celsus in the first century as redness and swelling with heat and pain (ruboret tumor cum calore et dolore). Inflammation begins with the local release of chemical mediators of inflammation, substances of various origin (mainly from local cells and blood plasma proteins) that induce some of the events characteristic of inflammation, eg, increase of blood flow and vascular permeability, chemotaxis, and phagocytosis.MEDICAL APPLICATIONIncreased vascular permeability is caused by the action of vasoactive substances; an example is histamine, which is liberated from mast cells and basophilic leukocytes. Increases in blood flow and vascular permeability are responsible for local swelling (edema), redness, and heat. Pain is due mainly to the action of chemical mediators on nerve endings. Chemotaxis (Gr. chemeia, alchemy, + taxis, orderly arrangement), the phenomenon by which specific cell types are attracted by some molecules, is responsible for the migration of large quantities of specific cell types to regions of inflammation. As a consequence of chemotaxis, leukocytes cross the walls of venules and capillaries by diapedesis, invading the inflamed areas.Leukocytes do not return to the blood after arriving in connective tissue except for the lymphocytes. These cells circulate continuously in various compartments of the body: blood, lymph, lymphatic organs, and the interstitial fluid of connective tissue. Lymphocytes are particularly abundant in the connective tissue of the digestive tract.A detailed analysis of the structure and functions of leukocytes and lymphocytes is presented in Chapters 12 and 14.FibersThe connective tissue fibers are formed by proteins that polymerize into elongated structures. The three main types of connective tissue fibers are collagen, reticular, and elastic fibers. Collagen and reticular fibers are both formed by the protein collagen, and elastic fibers are composed mainly of the protein elastin. These fibers are distributed unequally among the types of connective tissue and the predominant fiber type is usually responsible for conferring specific properties on the tissue. CollagenThe collagens constitute a family of proteins selected during evolution for the execution of several (mainly structural) functions. During the process of evolution of multicellular organisms, a family of structural proteins was selected by both environmental influences and the functional requirements of the animal organism and developed to acquire varying degrees of rigidity, elasticity, and strength. These proteins are known collectively as collagen, and the chief examples among its various types are present in the skin, bone, cartilage, smooth muscle, and basal lamina. Collagen is the most abundant protein in the human body, representing 30% of its dry weight. The collagens are produced by several cell types and are distinguishable by their molecular compositions, morphologic characteristics, distribution, functions, and pathologies. More than 20 types of collagen have been identified and designated with Roman numerals; the most important of these are listed in Table 5–3. They are classified into the following four categories according to their structure and general functions.Table 5–3.Collagen types.[ 1 (I)]2[ 2 (I)]300-nmmolecule,67-nm bandedfibrils[ 1 (II)]3300-nmmolecule,67-nm bandedfibrils[ 1 (III)]367-nm bandedfibrils[ 1 (V)]3390-nmmolecule,N-terminalglobular domain1 (XI)] [2 (XI)] [3 (XI)]300-nm molecule[ 1 (IX)] [ 2 (IX)] [ 3 (IX)] 200-nm molecule[ 1 (XII)]3LargeN-terminaldomain;interacts withtype I collagenXIV [ 1 (XIV)]3LargeN-terminaldomain;cross-shapedmolecule[ 1 (VII)]3450 nm,globular domainat each end[ 1 (VII)]2[ 1(IV)]Two-dimensional cross-linkednetworkCollagens that Form Long FibrilsThe molecules of long fibril–forming collagens aggregate to form fibrils clearly visible in the electron or light microscope (Figure 5–8). Collagen type I is the most abundant and has a widespread distribution. It occurs in tissues as structures that are classically designated as collagen fibers forming structures such as tendons, organ capsules, and dermis.Figure 5–8.Type I collagen.Molecules of type I collagen, the most abundant type, assemble to form much larger structures. (a): TEM shows fibrils cut longitudinally and transversely. In longitudinal sections the fibrils display alternating dark and light bands that are further divided by cross-striations and in cross-section the cut ends of individual collagen molecules can be seen. Ground substance completely surrounds the fibrils. X100,000. (b):In H&E stained tissues, type I collagen fibrils can often be seen to aggregate further into large collagen bundles (C) of very eosinophilic fibers. Subunits for these fibers were secreted by fibroblasts (arrows) associated with them. X 400.Fibril-Associated CollagensFibril-associated collagens are short structures that bind the surfaces of collagen fibrils to one another and to other components of the ECM. Molecules in this category are also known as FACIT collagens, an acronym for "fibril-associated collagens with interrupted triple helices."Collagens that Form Anchoring FibrilsAnchoring collagen is type VII collagen, present in the anchoring fibrils that bind the basal lamina to reticular fibers in the underlying connective tissue (Figure 4–2). Collagens that Form NetworksAn important network-forming collagen is type IV collagen, whose molecules assemble in a meshwork that constitutes a major structural component of the basal lamina.Collagen synthesis, an activity once thought restricted to fibroblasts, chondroblasts, osteoblasts, and odontoblasts, has now been shown to occur in many cell types. The polypeptides initially formed on ribosomes of the rough ER are called procollagen chains, which intertwine in ER cisternae to make triple helices. Every third amino acids in the chains is glycine; two other small amino acids abundant in collagen are hydroxylated post-translationally to form hydroxyproline and hydroxylysine. Many different chains have been identified, encoded by related genes and varying in length and amino acid sequence.The triple helix of chains forms a rod-like procollagen molecule, which in type I and II collagen measures 300 nm in length and 1.5 nm in width. Procollagen molecules may be homotrimeric, with all three chains identical, or heterotrimeric, with two or all three chains having different sequences (Figure 5–9). Different combinations of the many procollagen chains in procollagen molecules are largely responsible for the various types of collagen with different structures and functional properties. In collagen types I, II, and III, collagen molecules aggregate and become packed together to form fibrils. Hydrogen bonds and hydrophobic interactions are important in the aggregation and packing of these subunits. In a subsequent step, this structure is reinforced by the formation of covalent cross-links, a process catalyzed by lysyl oxidases.Figure 5–9.。
英语翻译
P86It is estimated that more than 50 per cent is liquid line in the petroleum and gas pipeline system ,the remainder gas .Pipeline size is governed by the amount of material to be transported through the line .lines may vary anywhere from a diameter of 3 or 4 inches for the liquid collection lines to 48 inches for the gas trunk lines .the oil lines tend toward the smaller sizes ,the gas toward the larger.据估计，在石油和天然气管道系统中，超过50％是液体，其余的气体。
管道的尺寸是通过线路输送的材料的输送量来控制的。
线路在任何地方都可能会发生用于液体收集线直径为3或4英寸变成48英寸的气体干线。
油线趋向于更小的尺寸，气体朝向较大尺寸。
P91Filtration is one of the most common applications of the flow of fluids through packed beds.as carried out industrially,it is exactly analogous to the filtrations carried out in a chemical laboratory using a filter paper in a funnel. The object is still the separation of a solid from the fluid in which it is carried. In every case , the separation is accomplished by forcing the fluid through a porous membrane. The solid particles are trapped within the pores of the membrane and build up a layer on the surface of this membrane. The fluid, which may be either gas or liquid, passes through the bed of solids and through the retaining membrane.过滤是流体通过填充层流动的最普遍的应用之一。
计算流体力学(CFD)文档——8. Turbulence modelling
=
w≡
u
2
¡
Then the eddy viscosity (turbulent stress ÷ mean velocity gradient) is
t≡
/ ∂U ∂y
=(
u
2
¡
)
×
y
u¡
= ( u¡ y)
Hence, in the log-law region,
t = u¢ y
(6)
8.2.3 General Stress-Strain Relationship
Relate this to the expressions for representative shear stress ( − uv ) and normal stress ( − u 2 ) above.
8.2.4 Other Turbulent Fluxes
It is common to assume a gradient-diffusion relationship between turbulent fluxes and the
The kinematic eddy viscosity t = t/ has dimensions of [velocity] × [length], which suggests
that it be modelled as
t = u0l0
(9)
On physical grounds, u0 should be a velocity scale reflecting the magnitude of turbulent
viscous stress and velocity gradient. In simple shear,
专业英语整理
专业英语整理Part1 生药部分TERMINOLOGY部分要求的词汇中药Traditional Chinese Medicines中药材Chinese Materia Medica (CMM)Traditional Chinese Medicinal MaterialsChinese Crude Drugs中草药Traditional Chinese Medicinal HerbsChinese Herbal Medicines ; (Herbal Medicines:草药）药用植物学Medicinal Plants民间药物Folklore Medicaments （Folk Herbs：草药）Indigenous（本土的）Drugs 中成药Traditional Chinese Patent Medicines中药制剂Chinese Medicinal Preparations药用植物学Pharmaceutical Botany生药学Pharmacognosy（药用植物分类学Pharmaceutical Plant Taxonomy）植物化学Phytochemistry植物化学分类学Plant Chemotaxonomy药用植物志Flora of Medicinal Plants中药药剂学Traditional Chinese Pharmaceutics中药炮制学Science of Processing Chinese Crude Drugs（显微生药学Microscopical Pharmacognosy）本草学herbals药典pharmacopoeiaStrengthening basic researches on Chinese Medicinal Plants and its relations to realizing the modernization of CMM 加强中国药用植物基础研究及其与中药现代化的关系一．词汇记载be recorded来源derived from（卫生事业health care , health undertakings明显的副作用：inciting side-effects疗效reliable therapeutical effectstherapeutic [,θerə'pju:tɪk] adj. 治疗(学)的;疗法的；对身心健康有益的）二．句子（中医药的健康理念和临床医疗模式体现了现代医学的发展趋势。
(最新整理)USP-1092-溶出度试验的开发和验证(中英文对照版)
（1092）(完整)USP-1092-溶出度试验的开发和验证(中英文对照版)（1093）（1094）（1095）编辑整理：（1096）（1097）（1098）（1099）（1100）尊敬的读者朋友们：（1101）这里是精品文档编辑中心，本文档内容是由我和我的同事精心编辑整理后发布的，发布之前我们对文中内容进行仔细校对，但是难免会有疏漏的地方，但是任然希望（(完整)USP-1092-溶出度试验的开发和验证(中英文对照版)）的内容能够给您的工作和学习带来便利。
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（1103）（1104）溶出度试验的开发和验证【中英文对照版】INTRODUCTION前言Purpose目的The Dissolution Procedure： Developmentand Validation <1092〉 provides a comprehensive approach covering items to considerfor developing and validating dissolution procedures and the accompanyinganalytical procedures。
It addresses the use of automation throughout the testand provides guidance and criteria for validation. It also addresses thetreatment of the data generated and the interpretation of acceptance criteriafor immediate— and modified-release solid oral dosage forms。
密封装置的种类及作用
/
hydraulic machinery such as hydraulic jacks, hydraulic lifting platform and the seal between the cylinder and piston engine, this chapter focuses on the rotary dynamic seal.
1、垫片密封
1
1, the gasket seal
/
垫片密封是静密封中最常用的一种形式。在两连接件的密封面之间垫上不同材质的 密封垫片，然后拧紧螺纹或螺栓，使垫片产生弹性和塑性变形，填塞密封面的不平处，达到 密封的目的。
The sealing gasket seal is still the most commonly used one kind of form. In two different fittings between the sealing surface of mat material of sealing gaskets, then tighten the screw or bolt, the gasket produce elastic and plastic deformation, filling sealing surface unevenness, achieve the purpose of sealing
密封装置主要用来保持系统的密封性，是保障系统工作的先决条件。因此，必须经常保 证密封装置在系统的工作压力和可能遇到的温度范围内，才能具有良好的密封性。根据工作 条件的不同，在液压系统和冷气系统中使用的密封装置通常可分为两种密封形式：一种为动 密封装置，一种为静密封装置。这两种密封装置各具有什么样的结构和特点呢？以下是对这 两种密封装置的分别介绍：
viscosity in
Dynamic effects of a step-wise increase in thermal conductivity and viscosity in the lowermost mantleJohn B.Naliboff1and Louise H.Kellogg1Received9January2006;revised8March2006;accepted15March2006;published19April2006.[1]We present numerical models of mantle convection incorporating changes in viscosity and thermal conductivity at depth.Increasing the viscosity and/or thermal conductivity by a factor of5at depths below2000km increases the size and stability of thermal upwellings. Decreasing the thermal conductivity beneath2000km,in contrast,has comparatively little effect on thermal upwellings.Increases in viscosity and/or thermal conductivity close to a factor of5beneath2000km may tend to counteract the tendency of the post-perovskite phase transition to decrease the size and stability of thermal upwellings.We also find that varying viscosity and thermal conductivity beneath2000km affects basal heat fluxes and mantle geotherms,which should have strong implications for the stability of the post-perovskite phase change near the core-mantle boundary(CMB).Citation:Naliboff,J.B.,and L.H.Kellogg(2006),Dynamic effects of a step-wise increase in thermal conductivity and viscosity in the lowermost mantle, Geophys.Res.Lett.,33,L12S09,doi:10.1029/2006GL025717.1.Introduction[2]Recent experiments by Badro et al.[2003]suggest that a transition from a high-spin to a low-spin state occurs in Fe2+in magnesiowu¨stite(Mw)between60–70GPa and in perovskite(Pv)between60–70Gpa and again at120GPa [Badro et al.,2004].Additional work by Lin et al.[2005] and Speziale et al.[2005]confirms the spin transition in magnesiowu¨stite,while Li et al.[2004,2005]confirm the transition in perovskite.Such a transition could increase both the radiative thermal conductivity of material[Sher-man,1991]and the viscosity,as a result of Fe partitioning dominantly into the Mw phase[Badro et al.,2003].In contrast,Lin et al.[2005]observe a qualitative decrease in the radiative thermal conductivity in conjunction with a high-spin to low-spin transition in Mw.The spin transition in magnesiowu¨stite is gradual due to its temperature and pressure dependence[Badro et al.,2003;Sturhahn et al., 2005],and Fe2+in perovskite may exhibit a mixed high-spin and low-spin state under conditions between the first tran-sition(70GPa)and the second transition(120GPa)[Badro et al.,2004].Thus,both the depth at which material properties change,and the magnitude of any changes remain uncertain.[3]First principle calculations and high-pressure and high-temperature experiments on perovskite have lead to the discovery of a transition to a post-perovskite phase (PPv)with a strong positive Clapeyron slope above the CMB near the top of the D00region[Murakami et al.,2004; Tsuchiya et al.,2004;Oganov and Ono,2004].The depth of this transition corresponds to the pressure range found for the second high-spin to low-spin transition in perovskite [Badro et al.,2004;Lin et al.,2005].The transformation to the post-perovskite structure may help influence the style of convection within the Earth’s mantle;if the transition has a strong,positive Clapeyron slope,flow in the region is destabilized and upwellings become smaller and more time-dependent[Nakagawa and Tackley,2004;Matyska and Yuen,2005].Heat flow out of the core also increases but lower mantle temperatures decrease due to faster core cooling rates[Nakagawa and Tackley,2005].Matyska and Yuen[2005,2006]also show that radiative thermal conduc-tivity can produce large-scale upwellings despite the influ-ence of a positive Clapeyron slope for the PPv transition. Such large-scale upwellings are consistent with seismic observations[Romanowicz and Gung,2002].[4]Previous studies have shown how viscosity increases in the lower mantle[Hansen et al.,1993;van Keken and Yuen,1995;Hunt and Kellogg,2001],depth-dependent thermal expansivity[Hansen et al.,1993],or variable thermal conductivity[Dubuffet et al.,1999;Dubuffet and Yuen,2000]can increase the size of upwellings or length-scale of convection in the lower mantle.Also,Montague and Kellogg[2000]showed how elevating the thermal diffusivity in a compositionally dense D00region could suppress internal convection in the D00layer.In this paper we examine how stepwise increases in thermal conductivity [Sherman,1991]and viscosity[Badro et al.,2003],as well as stepwise decreases in thermal conductivity[Lin et al., 2005]affect convective flow and the size and stability of thermal upwellings.Unlike Montague and Kellogg[2000], we do not consider compositional variations,because we wish to isolate the effects of the spin transition.2.Numerical Models[5]To investigate the effects of varying thermal conduc-tivity and viscosity in the deep lower mantle,we use a modified version of the2-D mantle convection code Con-Man[King et al.,1990],which solves the classical-Boussi-nesq equations for the conservation of mass(rÁu=0), momentum(Àr P+rÁt+RaT k^=0),and energy((@T/@t) +uÁr T=rÁ(k r T)+H)for an incompressible,Newtonian fluid,where u is velocity,T is temperature,P is pressure,t is the deviatoric stress tensor,Ra is the thermal Rayleigh number,k^is a unit vector in the radial direction,k is the thermal diffusivity,H is the internal heating parameter,and there is no adiabatic heating and cooling or viscous dissipa-tion.Our computational domain contains1000horizontalGEOPHYSICAL RESEARCH LETTERS,VOL.33,L12S09,doi:10.1029/2006GL025717,2006 1Geology Department,University of California,Davis,California,USA.Copyright2006by the American Geophysical Union.0094-8276/06/2006GL025717$05.00nodes and100vertical nodes,and has an aspect ratio of 10Â1.The top and basal surfaces are free-slip with no accumulation of stress,with periodic boundary conditions on the side walls.The model is heated both from below and within and cooled from above(Table1).[6]Viscosity follows an Arrhenius law:m¼m i exp E*þV*zTþT*ÀE*þV*z oT1þT*where the index i refers to the upper mantle(i=0above 660km),middle mantle(i=1between660and2000km) or lowermost mantle(i=2below2000km).The maximum variation of viscosity due to temperature is approximately a factor of100;we limit the variations in viscosity in order to preserve a mobile surface lid.The viscosity increases by a factor of30at660km and also increases at2000km in selected models(Table2),creating a viscosity peak in the mid-lower mantle.The thermal conductivity varies only with depth(Table2and Figure1b).[7]We do not account separately for variations in radiative and lattice thermal conductivity;we change only the thermal diffusivity(Table2)to represent variations in thermal conductivity.Because k total=k radiative+k lattice,and as the lattice thermal conductivity is not expected to increase with the spin transition,jumps in k total in our models represent correspondingly larger magnitude jumps in radiative thermal conductivity.3.Results[8]Figure2shows temperature fields snapshots.The reference model(m2/m1=1and k2/k1=1)develops multiple, fairly mobile,thermal upwellings and downwellings (Figure2a).Increasing the viscosity and thermal conduc-tivity at2000km(Figures2b and2c)increases the size and stability of the thermal upwellings.The higher temperature in these plumes may influence the stability of the post-perovskite phase[Hernlund et al.,2005;Wookey et al., 2005].Increasing thermal conductivity,but not viscosity,at 2000km(Figures2d and2e)increases the plume size and possibly their stability.Notably,the change in material properties at2000km appears to offer only minor resistance to flow of material across this depth,visible as some buckling in the downwellings.No thermal boundary layer develops in the interior of the model(Figure3b).[9]Decreasing the thermal conductivity beneath2000km (Figures2f and2g)produces a moderately time-dependent flow similar to that in Model1with the number of plumes increasing slightly,but only minor changes in the size of theTable1.Input Values and ParametersQuantity Symbol Value Thermal Rayleigh number Ra1Â107 Activation volume V*0.5 Activation energy E*2 Reference depth z o0.1 Temperature offset T*0.25 Internal heating number H10 Surface temperature T o0 Basal temperature T11Table2.Model Viscosity and Thermal Conductivity Structurem i k m2/m1k2/k1 Depth660km m0=1k0=1--660<Depth2000km m1=30k1=1--Depth>2000kmm2k2m2/m1k2/k1 Model130111 Model260222 Model3150555 Model430212 Model530515 Model6300.810.8 Model7300.510.5Figure 1.Depth profiles of(a)horizontally averaged viscosity and(b)thermal conductivity for models1–7. Figure2.Snapshots of non-dimensional temperature fields for(a)m2/m1=1and k2/k1=1,(b)m2/m1=2and k2/k1=2, (c)m2/m1=5and k2/k1=5,(d)k2/k1=2,(e)k2/k1=5, (f)k2/k1=0.8and(g)k2/k1=0.5.Each temperature image is a representative snapshot of the given model at a state of thermal equilibrium.thermal rge cold regions can be observed accumulating at the base of the model.[10]The basal heat flux increases with thermal conduc-tivity beneath 2000km (Figure 3a),but this effect is reduced when the viscosity also increases.With a 20%decrease in thermal conductivity at 2000km depth (k 2/k 1=0.8)the basal heat flux shows little change,while a 50%decrease in thermal conductivity (k 2/k 1=0.5)reduces the basal heat flux.[11]Increasing thermal conductivity alone produces hot-ter geotherms than increasing both viscosity and thermal conductivity,while decreasing the thermal conductivity produces similar (k 2/k 1=0.8)or cooler (k 2/k 1=0.5)geo-therms than Model 1(Figure 3b).Furthermore,varying the viscosity and/or thermal conductivity significantly changes temperatures in the D 00region.Because the stability of the PPv phase is strongly temperature-dependent [Hernlund et al.,2005;Wookey et al.,2005],increases in the thermal conductivity and subsequent increases in temperature may reduce the occurrence of PPv.4.Discussion and Conclusions[12]Increases in plume size and stability associated with increases in viscosity and thermal conductivity could coun-teract the pattern of smaller and more time-dependent plumes induced by the exothermic PPv phase transition,perhaps producing intermediate sized plumes in combination with the PPv phase transition.Although this idea needs to be investigated by including the density crossover associated with the PPv in future calculations,the generation of large superplumes structures may require other mechanisms like variable radiative thermal conductivity [Matyska and Yuen ,2005]or compositional heterogeneity [Wen ,2001;Ni et al.,2002;Tackley ,2002;Trampert et al.,2004;McNamara andZhong ,2005;Nakagawa and Tackley ,2005;Tan and Gurnis ,2005].Although increasing thermal conductivity produces larger plumes,the associated increase in heat flux could act in concert with PPv to destabilize the dense piles [Nakagawa and Tackley ,2005],and thus require a higher chemical density contrast or viscosity to stabilize chemical piles.Chemically dense regions above the CMB should play a significant role in limiting heat flux out of the core if thermal conductivity increases by a factor of 2Âor 5Â[Montague et al.,1998;Montague and Kellogg ,2000],although decreases in thermal conductivity should reduce the need for a hot,dense layer limiting the core heat flux.[13]The steep geotherms in the lowermost mantle ob-served for elevated viscosity and thermal conductivity in Figure 3b should decrease the probability that a geotherm intersects the PPv phase transition;conversely,models with decreasing thermal conductivity are more likely to cross into the PPv stability field.If the geotherms do indeed steepen significantly,the PPv stability may become limited to cold downwelling regions,instead of both cold and average mantle geotherms [Hernlund et al.,2005;Wookey et al.,2005].Our models do not include adiabatic heating or cooling;the addition of the adiabatic temperature gradient to our geotherms should enhance this steepening effect in the D 00region.However,increases in the basal heat flux may drop lower mantle temperatures through time,resulting in more post-perovskite,as pointed out by Nakagawa and Tackley [2005].Van den Berg et al.[2005]also demonstrate enhanced core and mantle cooling for strongly radiative thermal conductivity.Studies taking into account core cool-ing with changes in viscosity and thermal conductivity are needed to resolve this issue.[14]All of the results discussed to this point reflect varia-tions in viscosity and thermal conductivity at 2000km,whichrepresents the depth at which Fe 2+in magnesiowu¨stite should be in a complete low-spin state [Badro et al.,2003;Lin et al.,2005].However,since Fe 2+in perovskite may not be in a complete low-spin until the D 00region [Badro et al.,2004;Li et al.,2004,2005],thermal conductivity and viscosity may vary both at 2000km and near 2600km.Recent experiments on the partitioning of Fe between Mw,Pv,and PPv indicate that variations in the partition coefficients do not occur until the D 00region,and both increasing Fe in Mw [Murakami et al.,2005]and increasing Fe in PPv [Mao et al.,2005;Kobayashi et al.,2005]are reported for the region.These results highlight the need for a more complete understanding of material properties in the deep lower mantle guided by thelocation of the Fe 2+spin transition in both magnesiowu¨stite and perovskite.Future work should also explore the interac-tion of these transitions with possible chemical density variations in the mantle.[15]Acknowledgments.This work was supported by NSF EAR-0126281.We thank Magali Billen,Qing-zhu Yin,and Donald Turcotte for helpful discussions about the models,and Ctirad Matyska and A.P.van den Berg for constructive and insightful reviews.We also thank the conveners of the International Workshop on the Post-Perovskite Phase Transition in the Earth’s Deep Mantle and the NSF for providing conference travel support.ReferencesBadro,J.,G.Fiquet,F.Guyot,J.P.Rueff,V .V .Struzhkin,G.Vanko,and G.Monaco (2003),Iron partitioning in the Earth’s mantle:Toward a deep lower mantle discontinuity,Science ,300,177–189.Figure 3.(a)Non-dimensional basal heat flux versus change in thermal conductivity at 2000km depth.Open circles represent models where only thermal conductivity varies at 2000km,while filled circles represent models where viscosity and thermal conductivity increase at 2000km.(b)Non-dimensional mantle geotherms for models 1–7.Badro,J.,J.P.Rueff,G.Vanko,G.Monaco,G.Fiquet,and F.Guyot (2004),Electronic transitions in perovskite:Possible non-convecting layers in the lower 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齿轮泵简介(中英对照)
Gear pumpChinese Name: gear pumpName: gear pumpDefinition: rely sealed in a housing of two or more gears, the work space is generated in the process of mutual engagement volume change to liquid delivery pump.Applied disciplines: mechanical engineering (a subject); drive (two subjects); hydraulic transmission (two subjects)The gear pump is to rely on the change and moving of the working volume of the pump cylinder and the ring gear formed between rotary pumps for conveying liquid or so pressurized. Form two closed space by two gears, pump, front and rear cover, when the gear is rotated, the gear is disengaged from the side of the space volume grew larger, forming a vacuum, the liquid suction, the gear meshing side of the volume of the space from large small, while the liquid squeeze into the pipeline to go. The suction chamber and the discharge chamber is spaced by two gears meshing line to. The outlet pressure of the gear pump is entirely dependent on the size of the pump source resistance.The concept of the working principle of the gear pump is very simple, i.e. in its most basic form is the same as the two dimensions of the gear in a close fit within the housing.The engagement rotation, the interior of the housing is similar to the "8" shape, the two gears are mounted on the inside, the outsidediameter of the gear, and both sides of the housing close fit. From the extruder, the material in the suction port into the middle of the two gears, and to fill this space, the rotation direction of the housing with the teeth movement, and finally discharged in the two toothing.Speaking in terminology, gear pump, also called a positive displacement device, i.e. as a cylinder bore of the piston, when one tooth into the fluid space of another tooth, the liquid is mechanically squeezed row out. Because the liquid is incompressible, so the liquid and the tooth at the same time can not occupy the same space, so that the liquid has been excluded. This phenomenon continuously occurs due to the continuous engagement of the teeth, and, therefore, at the outlet of the pump provides a continuous excluded volume pump per revolution, the same amount of discharged. With the uninterrupted rotation of the drive shaft, the pump also continuously discharged fluid. The pump flow is directly related to the speed of the pump.In fact, in a pump with a small amount of fluid loss, which makes the efficiency of the operation of the pump can not reach 100%, because these fluids are used to lubricate bearings and gears on both sides, and the pump body can never be a clearance fit, so can not make 100% offluid from the outlet, so asmall amount of fluid loss is inevitable. However, the pump or can run well, can still reach an efficiency of 93% to 98% for most of the extrudate,.Viscosity or density changes in the process fluid, the pump will not be much of an impact. If there is a damper, for example in theoutlet side accommodates a strainer or a limiter, the pumps will pushfluid through them. If the damper changes in their work, i.e., if the filters become dirty, clogged, or the back pressure of the limiter, the pump will continue to maintain a constant flow rate, until the device of the weakest parts of the mechanical limit is reached (usually equipped with a torque limiter).The rotational speed of a pump, in fact, is limited, which mainly depends on the process fluid, and if the transmission is oil, the pump can be rotated at high speed, but when the fluid is a high viscosity of the polymer melt body, this restriction will be substantially reduced.Promote the highly viscous fluid to enter the intake port side of the two tooth space is very important, if this space is not filled, then the pump would not discharge the flow of accurate, so the value of PV (pressure x velocity) is another limiting factor, and is a process variable. Because of these limitations, the gear pump manufacturer will provide a range of products of different specifications and displacement (for each revolution of the amount discharged). These pumps will be compatible with the specific application process to make the system optimal capacity and price.PEP-II of the pump gear and shaft are of integrally quintana hardened process, to obtain a longer working life. "D" type bearing a combination of forced lubrication mechanism, so that the polymer via a bearing surface, and returns to the inlet side of the pump, in order to ensure effective lubrication of the rotation shaft. This feature reduces the possibility of retention and degradation of polymers. Precision machining of the pump shaft exact fit, to the bearings and gears of the "D" type can ensure that the gear shaft is not eccentric, to prevent thegear wear. The Parkool sealed structure with PTFE lip seal a water-cooled sealed together. Such seals do not actually touch the surface of the shaft, its sealing principle is that the polymer is cooled to asemi-molten state and form a self-sealing. May also be used Rheoseal sealing it in a reverse spiral groove seal sheet processing, the polymer can be anti pressed back imported. For ease of installation, the manufacturer to design an annular bolt mounting surface to enable the flange installation cooperating with other devices easier, which makes the manufacture of the cylindrical flange. PEP-II gear pump with heating element matches with the specifications of the pump, available to users matching, which can ensure the rapid heating and heat control. Different pump body heating mode, the damage to these components only a board, independent of the entire pump.The gear pump is driven by a separate motor, effectively blocking the upstream pressure pulsation and flow fluctuations. Gear pump outlet pressure pulsation can be controlled within 1%. In the extrusion production line using a gear pump, and can improve the speed of flow rate output, and to reduce theshearing of the material in the extruder and residesThe external gear pump is the most widely used as a gear pump, the general gear pump is usually refers to external gear pump. Its structure is shown in Figure 5-14, the main drive gear, driven gear, pump, pump cover and safety valve. The sealed space gear pump pump, pump cover and gear constitute studio. Two gear axle are fitted respectively in the two bearing bore of the pump cover, out of the pump body, the driving gear shaft driven by the motor rotation. External gear pump is simplestructure, light weight, low cost, reliable work, a wide range of applications.Gear pump working, driving wheel with the motor to rotate and drive the driven wheels to follow the rotation. When the suction chamber side of the meshing teeth gradually separate, the volume of the suction chamber is increased, the pressure is reduced, put the liquid suction pump suction human tube; suction liquid two routes in the alveolar gear pushed onto the discharge chamber. Liquid into the discharge chamber, since the two gear teeth continuously engaged, liquid is squeezed from the discharge chamber into the discharge pipe. Driving gears and driven gears are constantly rotating, the pump can be continuous suction and discharge liquid.Equipped with a safety valve, a pump, conveying the liquid may be automatically open the top valve, so that the high pressure liquid is returned to the suction pipe when the discharge pressure exceeds a predetermined pressure.The internal gear pump, the inner gear, by a pair of mutually meshing and the middle of the crescent-shaped member, the pump casing and the like. The crescent-shaped member is spaced from the suction chamber and a discharge chamber. When the pinion gear is rotated, a partial vacuum is formed, in the place of the gear is disengaged, the liquid being sucked A pump filled with the suction chamber interdental, and then along the inner and outer sides of the two routes of the crescent-shaped member into the discharge chamber. In place of the tooth into engagement, the liquid present in the interdental is extruded while the feed discharge tube.Gear pump with self-priming capability, flow and discharge pressure independent pump casing, suction valve A and the discharge valve has a simple structure, uniform flow, reliable, low efficiency, noise and vibration, easy wear, used to transport non-corrosive, non-solid particles and various oils with lubricating ability, the temperature is generally not more than 70 '° C, such as lubricating oil, edible oil. The general flow range of 0.045 ~ 30ms / h, pressure range of 0.7-20MPa, working speed 1200-4000r/min.Structural featuresGear ninety people advanced level of new technology - dual arc sine curve tooth arc. Involute gear, the most prominent advantages Tooth Surface gear meshing process there is no relative sliding tooth surface wear, and stable operation the trapped fluid phenomena, low noise, long life, high efficiency.The pump to get rid of the shackles of the traditional design into a new area in the design, production and use of the gear pump.The pump has a differential pressure relief valve as overload protection, safety valve total reflux pressure pump rated discharge pressure of 1.5 times. Allows discharge pressure range in accordance with the actual need to be adjusted separately. But this safety valvefor not reducing valve long-term work, the need to separately install the pipeline.The shaft end seal design for the two forms, a mechanical seal, a packing seal, can be determined according to the specific use conditions and user requirements.Operation and maintenance, start:Gear pumps(1) before the start of check all pipe flange joint tightness.(2) coupling plate moving without friction and collision sound.(3) The first time you start the pump should be injected into the transmission fluid.(4) before the start of fully open suction and discharge valve in the pipeline, the non-closing valve starts.(5) Verify that the motor rotation direction, start the motor.2, Parking:(1) Turn off the motor.(2) Turn off the pump inlet and outlet valves.Common faults can not discharge(1) failure phenomenon: the pump can not dischargeGear pump the whole picture (3) the cause of the malfunction: a rotating in opposite directions; b, suction or discharge valve closed; c, the entrance no material or pressure is too low; d, the viscosity is too high, the pump can not bite materialCountermeasures: a, confirm the direction of rotation; confirm valve is closed; c, check valves and pressure gauges; d, check theliquid viscosity, low speed according to the speed ratio of the flow, if flow is insufficient flowsInadequate flow(2) failure phenomenon: pump flow the lack KCB300 gear pumpThe cause of the malfunction: a, inhalation or discharge valve closed; b, low inlet pressure; c export pipeline blockage; d, stuffing box leakage; e, the speed is too lowCountermeasures: a confirmation whether the valve is closed; b, the check valve is open; c confirm excretion is normal; d, fastening; drain large leak affecting production, should stop operation, demolition inspection; e, check the pump shaft speed ;Abnormal sound(3) failure phenomenon: abnormal soundThe cause of the malfunction: a coupling the the eccentric big or poor lubrication b, motor failure; abnormal c reducer; to poor installation d seal at; e shaft deformation or wearCountermeasures: a look for positive or filling grease; b, check the motor; c, check the bearings and gears; d, check the seal; e, parking disintegration of inspectionCurrent is too large(4) failure phenomenon: the current to excessive gear pump seriesThe cause of the malfunction: a outlet pressure is too high; b, the melt viscosity is too large; poor c, shaft seal assembly; the d shaft or bearing wear; e, motor failureCountermeasures: a to check downstream equipment and piping; b testing viscosity; c, check the seal properly adjusted; d, parking after checking hand drive cars are overweight; e, check the motorPump suddenly stopped(5) failure phenomenon: the pump suddenly stoppedThe cause of the malfunction: a power outage; b, motor overload protection; c coupling damage; d, the outlet pressure is too high, the chain reaction; e pump, biting into the anomaly; f, shaft and bearing adhesive stuck Countermeasures: a, check the power;, check the motor; c, f turning to open the safety cover, turning checks; d check the instrumentation interlock system; e, after stopping, reversing turning confirmed; confirmSeal oil spill(6) failure phenomenon: sealing oil spillCause: a shaft seal is not adjusted, seal wear between fine c mechanical seal dynamic friction surface of the stationary ring with bad four spring relaxation Countermeasures: a re-adjustment of b, the rightamount tighten the gland bolts or replace the seals, c, replace the dynamic and static ring or reground, four replacement springOther phenomena1 causes(1) internal and external rotor backlash too the suction pressureoil chamber interoperability. Significantly reduce the volumetric efficiency, the output flow is not enough;②axial clearance is too large;③the suction line junction surface Mifengbuyan the other reasons, so that the pump into the air, effective suction flow reduction;④Suction poor. As a result of the oil viscosity is too large, the oil filter clogged by dirt as a result of the inhalation flow reduction;⑤relief valve stuck in the half-opening position, part of the pump to the flow back to the tank through the relief valve, and making the traffic into the system is not enough. At this time accompanied by a failure do not increase the system pressure.2, Remedy①replace the inner and outer rotor, the tooth side of the gapwithin a predetermined range (typically less than 0.07 mm);②both ends of the grinding pump surface, to ensure that after the assembly of the rotor inside and outside the axial gap in the range of0.02 ~ 0.05mm; (3) replacing defective suction pipe seal, bandaged pipe fittings threaded portion and then tighten fittings with Teflon tape;(4) appropriate viscosity oil, washing oil into the oil filter to make oil-absorbing smooth. And, where appropriate, to increase the oil absorption diameter;⑤repair relief valve, to exclude relief valve shorted fuel tank caused the pump effectively reduced flow phenomenon.Edit this paragraph the trapped oil phenomenon gear pump to a smooth work, the degree of coincidence of the gear must be greater than 1, so there are always two pairs of gears engaged simultaneously, and a part of the oil is siege surrounded by a closed cavity in the two pairs of teeth between. This closed cavity begins with the rotation of the gear is gradually reduced, and later gradually increased. Closed chamber volume decreases causes trapped fluid by squeezing generate high pressure, and is extruded from the gap, leading to fluid heating, and to enable the parts to subject to additional loads; while the increase in volume of closed chamber also caused a partial vacuum, and dissolved in the oil in the gas separation, the occurrence of the cavitation. These will generate a strong vibration and noise, which is a gear pump phenomenon of trapped oil.HarmThe radial imbalance force is large enables the shaft bending, the tooth tip in contact with the housing, while the accelerated wear of the bearings and reduce the life of the bearing.EliminationMethod to eliminate the trapped oil, usually in the both sides of the cover open unloading groove, so that the volume of the closed chamber is reduced through the left unloading groove communicates with the oil pressure chamber, the volume increases when the unloading tank with the suction chamber through the right side connected.Feasible circuit performance to improve the performance of gear pumpGear pumps due to the structural constraints of the fixed displacement gear pump is generally considered only for the constant flow hydraulic source. However, the accessories and threaded coupling combination valve program is effective for improving its functionality, reduce system cost and improve system reliability and, therefore, the performance of the gear pump approachability expensive, complex piston pump.Mounted directly on the pump control valve, eliminating the need for tubing between the pump and the directional valve, to thereby control the cost. Fewer fittings and connectors to reduce the leak, and to improve reliability. And the pump itself valve can reduce the loop the loop pressure to improve theperformance of their work. Here are some of the basic functions of the gear pump can improve the loop, some of which is proved to be feasible practice basic loop, and some of the innovative research.Uninstall loopUninstall components will combine high flow pump with low-power single-pump. The liquid from the two gear pump due to the structural constraints of the fixed displacement gear pumps usually considered only for the constant flow hydraulic source. However, attachments andthreaded coupling combination valve program to enhance its functionality, reduce system cost and improve system reliability to be effective, therefore, gear pumps, fixed displacement due to structural constraints, usually considered only for constant flow gear pump hydraulic source to use. However, the accessories and threaded coupling combination valve program is effective for improving its functionality, reduce system cost and improve system reliability and, therefore, the performance of the gear pump approachability expensive, complex piston pump. Performance accessible expensive, complex piston pump. The outlet, until it reaches a predetermined pressure, and (or) traffic. At this time, the large flow pump put flow from the outlet is recycled to the inlet, thereby reducing the output flow of the pump system, the upcoming pump power is reducedto just above the desired value of the high-pressure part of the work. The percentage depends on the flow rate decreases not uninstall displacement ratio of total displacement. Combination or threaded coupling unloading valve to reduce or eliminate the pipes, channels and accessories, and other possible leaks.Easiest unloading member by manual manipulation. Spring unloading valve is turned on or off, when a manipulation of the signal to the valve, the valve off state is switched. Leverage or other mechanical agencies is the easiest way to manipulate this valve.Guidance and control (pneumatic or hydraulic) unloading valve is an improvement of the mode of operation, because such valves can be remotely controlled. Its greatest progress is a solenoid valvecontrolled by an electrical or electronic switch, it is not only the available remote control available microcomputer automatic control, generally considered this simple unload technology is the application of the best case.The artificial manipulation uninstall components commonly used in large flows and fast action to be large flows and reduce the flow loop for precise control, such as rapid telescopic boom circuit need for fast action. Unloading valve of the circuit shown in Figure 1 without the manipulation of the signal effect, the large flow loop always output. For a normally open valve, in the normal state the loop will output a small flow.Pressure sensing unload valve is the most common solution. As shown in Figure 2, the spring action of the unloading valve is in its flow position. Circuit pressure relief valve preset value is reached, the relief valve to open, the uninstall switch valve in the hydraulic and under to its small flow position. Thepressure sensing uninstall circuit used for the trip to their fast, low speed high pressure fluid supply of the hydraulic cylinder when the end of the trip. Pressure sensing unloader valve base is basically a reach system pressure and unloading automatically uninstall components, generally used for the splitter mileometer and hydraulic vise.Unloader valve is the flow sensing uninstall loop pressure to the large flow position by a spring. The fixed orifice size of the valveflow to determine the optimum speed of the engine required. If theengine speed exceeds this optimum range, the throttle orifice pressure drop will increase, which will unload valve shift to small flow position. High flow pump adjacent elements made of the size of the maximum flow throttle, therefore circuit energy consumption less smooth and low cost. Typical applications of this loop, the loop defining flow rates up to an optimum range in order to improve overall system performance, orqualified machine during traveling at high speed loop pressure. Commonly used in the garbage carrying trucks.Pressure flow sensing the uninstall circuit of unloading valve is pressed to the large flow position by a spring, whether it reaches a predetermined pressure or flow, will uninstall. Idling or normal operating speed, the equipment can be used to complete the high-pressure job. This feature reduces the unnecessary traffic, and therefore reduces the required power. Because such a circuit having a wide range of load and speed changes, Guchang for excavation equipment.With power integrated pressure sensor the uninstall circuit, by two minor changes in the pressure sensing uninstall pump, two sets of pumps driven by the same prime mover, Guidance and control unload signal to accept another uninstall pump each pump. Such sensing mode called interactive sensing, it enables a set of pump to work under highpressure and the other set of pump work in a large flow. Two reliefvalve is adjusted according to each special loop pressure to make one or two pumps to uninstall. This program has reduced power requirements, and therefore inexpensive prime mover of the small capacity can be used.The load sensing Uninstall loop. When the load-sensing signal tothe main control valve control chamber (lower chamber), the pump flow rate through valve 1, a valve 2 rows back to the tank; when the load-sensing signal is applied to the control valve, the liquid supply pumpto the loop; When the pump output pressure exceeds a predetermined value when the pressure of the load sensing valve, the pump only to loop work flow, throttle position bypass back to the tank and the excess flow through the valve.Gear pumps and piston pump with load sensing element with low cost, the ability of anti-pollution and low maintenance requirements of the advantages. Priority flow controlRegardless of the speed of the gear pump, the size of the work pressure or slip traffic, value flow control valves total guarantee the equipment required for the flow. In this circuit shown in Figure 7, the output flow of the pump mustbe greater than or equal to the time passage required flow, the secondary flow can be used with or back to the tank. Once setpoint flow valves (proportional valve), the primary control and hydraulic pump combined, eliminating piping and to eliminate the external leakage, and therefore reduce the cost. Typical applications of the of such gear pump loop truck crane can frequently be seen on the steering mechanism, which eliminates the need for a pump.Load sensing function and setting of the flow control valve is aflow control function is very similar: that is, regardless of the speed of the pump, pressure or slip the pumping required flow size, offer flow. But only through a port to the primary oil line to provide the requiredflow until the maximum adjustment value. This circuit can replace the standard flow control loop for maximum output flow. No-load circuit pressure is lower than the set value once the flow control program, so the loop temperature rise is low, no-load power consumption. Loadsensing column flow control valve with a flow control valve, a typical application of the power steering mechanism.Bypass flow controlBypass flow control, regardless of the speed of the pump or thelevel of pressure of work, the total pump to the system at a predetermined maximum value for the fluid, the excess the part row back to the tank or pump inlet. This scenario limits the flow into the system, so that it has the best performance. The advantage is, to control the maximum adjustment flows through a circuit scale and reduce costs; the pump and valve integrally, and through the pump bypass control, so that the circuit pressure is reduced to a minimum, thereby reducing the pipeline and its leakage.The bypass flow control valve in the group with limited work flow (speed) range load sensing control valve with design. Such type of gear pump circuit commonly used to limit the hydraulic control so that the engine up to the optimum speed Spam delivery truck or power steering pump circuit can also be used in a fixed mechanical device.Dry suction valveThe dry suction valve is a pneumatic control hydraulic valve, which is used to pump oil into the throttle, only minimal flow (<18.9t/min) through the pump when the equipment's hydraulic-load; while the loadfull flow suction pump. Shown in Figure 10, this circuit may be omitted between the pump and prime mover clutch, thereby reducing the cost, and also reduces the load power consumption, a prime mover of power due to the minimal flow through the loops to maintain the device. In addition, to reduce the noise of the pump in the no-load. Dry suction valvecircuit switching hydraulic system can be used in any vehicle driven by an internal combustion engine, for example, the garbage loading trucks and industrial equipment.Hydraulic pump program selectionCurrently, the working pressure of the gear pump is nearing piston pump, the combination of load sensing program offers the possibility of variable gear pump, which means the original clear boundaries betweenthe gear pump andpiston pump change management increasingly blurred a.Reasonable to select one of the determinants of the hydraulic pump program, the cost of the entire system, expensive piston pump, gear pump, with its lower cost, simple circuit, filtration requirements and low, as many applications as practicable options.Edit this paragraph, motor characteristics G5, GPC4 series gear pump, GM5, GMC4 series gear motor introduction in the United States Vickers (VKS), technical prominent features:Compact structure, small size, light weightBy the aluminum alloy before the cover, the intermediate, the rear cover, gear alloy steel and aluminum alloy pressure plate component parts, the front, within the press fitted in the rear cover two DU bearings, for DU material is ideal for the gear pump bearing materials, can greatly improve the life of the gear pump.2. Reliable workThe pressure plate is the main element of the radial and axial pressure compensation, can reduce the bearing loads and automatic adjustment of the gear shaft to the gap, thus effectively improving the performance and operational reliability of the gear pump; GM5, GPC4 series of gear motors can provide single rotation without front bearing, double rotation without front bearing and single-spin to the band front bearing double spin with the front bearing four structure type, with front bearing gear motor can withstand radial forces and axial force .3 high-speed, pressureSpeed high from 3000 to 4000 rev / minute, the theoretical torque 17N.m (Newton meters) ~ 64N.m up to 20-25MPa.4. Connection method is applicable to imports of machinery and construction machineryMeet SAE and National Standard GB mounting flange and shaft extension, oil inlet and outlet ports connected line. Widely used in automobiles, tractors, construction machinery, agricultural machinery and other mechanical hydraulic system。
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Abstract: A ductile fracture criterion is introduced into numerical simulation to predict viscous pressure forming limit of the automotive body aluminum alloy 6k21-T4. The material constant in the ductile fracture criterion is determined by the combination of the viscous pressure bulging (VPB) test with numerical simulation. VPB tests of the aluminum alloy sheet are camed out by using various elliptical dies with different ratios of major axis to minor axis@), and the bugling processes are simulated by the aid of the finite element method software LS-DYNA3D. On the basis of the stress and strain calculated from numerical simulations, the forming limits of bulging specimens obtained are predicted by the ductile fracture criterion, and compared with experimental results. The fracture initiation site and the minimal thickness predicted by the ductile fracture criterion are in good agreement with the experimental results.
Table 1 Chemical composition of 6k21-T4 aluminum alloy (mass fraction, %)
a1[13] also carried out calculations for various strain paths from balanced biaxial stretching to uniaxial tension of aluminum alloy sheets and predicted the forming limit diagrams. JAIN et a1[20] predicted the forming limit of AA6111-T4 sheet by means of various ductile fracture criterion and assessed the applicability of the different fracture criteria. In this study, VPB tests of the automotive aluminum alloy 6k21-T4 sheet are carried out with various strain paths and the processes are simulated by the finite element code LS-DYNA3D. A ductile fracture criterion is applied to predict the forming limits of VPB specimens.
and higher spring-back. The forming limit of the sheet metal is predicted by the onset of localized necking in the conventional approaches[8-11]. In case of aluminum alloy with lower ductility, fracture offen occurs before necking instability. So, the conventional approaches don't fit for prediction of the forming limit of aluminum alloy sheet. Because ductile fracture criteria have been widely used in the bulk forming process, they are recently introduced into the forming limit prediction in sheet metal forming processes [ 12-16]. In the ductile fracture criterion, the occurrence of ductile fracture is usually estimated by the stress and strain during forming. The distributions and the histories of stress and strain are calculated by finite element analysis of sheet metal forming. The forming limit can be predicted by the combination of finite element analysis with the ductile fracture criterion. TAKUDA et al[ 171 successfully predicted the forming limits in deep drawing of the Fe/Al laminated composite sheets by using Oyane criterion (one of ductile fracture criteria) [ 181. Axisymmetric bore-expanding was simulated by the rigidplastic finite element method. The fracture initiation site and the critical stroke were predicted by means of the ductile fracture criterion[l9]. TAKUDA et
iysxbi
Evaluation of forming limit in viscous pressure forming of automotive aluminum alloy 6k2 1-T4 sheet
WANG Zhong-jin(E,%&)', LI Yi(% @)',LIU Jian-guang($U@%)', ZHANG Yi-he(?&x?U)*
Available online at
Science Press
Transactions of Nonferrous Metals Society of China
Trans. Nonferrous Met. SOC. China 1 7(2007) 1 169-1 174
1. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
2. Research and Development Center, China FAW Group Corporation, Changchun 130011, China
Corresponding author: WANG Zhong-jin; Tel: +86-451-86418643; E-mail: wangzj@hit. edu. cn
Байду номын сангаас
1170
WANG Zhong-jin, et al/Trans. Nonferrous Met. SOC. China 17(2007) silicone rubber. The flow stress vs. strain rate curve of the viscous medium is shown in Fig. 1.
Key words: aluminum alloy sheet; viscous pressure forming limit; ductile fracture criteria; finite element analysis
1 Introduction
Mass reduction is one of the key problems in the automotive industries. With the lower density and good mechanical properties, aluminum alloy becomes the ideal material to replace heavier materials in the car. However, aluminum alloy has poorer room-temperature formability than steel. This can result in restrictions in part geometry, then limiting automotive design[ 11. Therefore, the new technology that can improve the formability of aluminum alloy sheet is required. Viscous pressure forrning(VPF) is a new sheet flexible forming technology. The previous investigations show that VPF can improve the sheet formability[2-71. VPF uses a semi-solid, flowable, highly viscous and strain rate sensitive macromolecule polymer (called viscous medium) as the forming flexible-punch. Because of high viscosity and strain rate sensitivity, the viscous medium can produce a non-uniform pressure field adaptively to the deformation of the sheet metal and improve the stress distribution of the sheet to reduce spring-back of formed panels. So VPF is in favor of forming the aluminum alloy sheet with lower ductility