(整理)Abaqus截面输出相关.

Defining the surface sectionSection output requests are available only for sections defined using element-based surfaces (see“Element-based surface definition,” Section 2.3.2). Consequently, the sections must be defined using faces of continuum elements although other types of elements (beams, membranes, shells, springs, dashpots, etc.) can be attached to the section.Calculation of accumulated quantities on the section (such as the total force) involves nodal quantities associated with elements on one side of the section only. Therefore, the surface definition should use elements only from one side of the section (the “base elements,” as defined in “Prescribed assembly loads,” Section 32.5.1), thus precisely identifying the side from which accumulated quantities are computed.Since the section usually cuts through the mesh in a typical section output request, automatic generation of the surface cannot be used. Specifying the element faces gives exact control over which element faces formthe surface, which is essential when defining a cross-section through a solid body.You must specify the name of the surface for which output is being requested.Surfaces that are defined in a restart analysis can be used only for section output requests. The newly defined surface cannot be used for any other purpose (such as a contact pair or pre-tension section definition).Use either of the following options: Input FileUsage:*SECTION PRINT, NAME=section_name,SURFACE=surface_name*SECTION FILE, NAME=section_name,SURFACE=surface_nameSelecting the coordinate system in which output is desiredYou can specify the choice of coordinate system in which the section output is desired. By default, thecomponents of vector quantities associated with the section are obtained with respect to the global system of coordinates. Alternatively, you can specify that output is desired in a local system as defined below. Input FileUse either of the following options: Usage:*SECTION PRINT, NAME=section_name,SURFACE=surface_name,AXES=GLOBAL or LOCAL*SECTION FILE, NAME=section_name,SURFACE=surface_name,AXES=GLOBAL or LOCALDefining a coordinate system local to the surface sectionYou can allow Abaqus/Standard to define the local system, or you can specify it directly.Default local systemThe default local system is particularly useful when the section is flat or almost flat. Though it can also be used in the case when the defined surface is curved, the default local system may be irrelevant for such problems.The default system is defined by a straight line in two-dimensional and axisymmetric cases or by a plane in three-dimensional cases, fitted (in a least square sense) through the nodes belonging to the section. The anchor point (origin) of the local system is the centroid of the projection of the surface on the fitted line or plane. The local directions are given by the normal (1-direction) and the tangent direction (the 2-direction in two-dimensional and axisymmetric cases) or the tangent directions (the 2- and 3-directions in three-dimensional cases) to the fitted line or plane. When several straight lines or planes can be fit equally well between the nodes defining the section (for example, a closed circular or spherical surface), the original local directions will be parallel to the global axes.The positive local 1-direction is selected such that it will form an acute angle with the average normal direction to the section, computed by averaging the positive normals to the element faces defining the section. If the average normal direction is zero (a closed surface), the 1-direction will form an acute angle with the global x-axis. If in two-dimensional or axisymmetric cases the 1-direction is within 0.1° of being normal to the global x-axis, it will form an acute angle with the global y-axis. In three-dimensional cases if the 1-direction is within 0.1° of being normal to the global X–Y plane, it will form an acute angle with the global z-axis.In two-dimensional and axisymmetric cases the local 2-direction is obtained by rotating the local1-direction counterclockwise by 90° about the anchor point. For three-dimensional situations the tangent directions of the surface are defined using the Abaqus conventions for local directions on surfaces in space (see “Conventions,” Section 1.2.2).Input File U se either of the following options to useUsage: the default local coordinate system:*SECTION PRINT, NAME=section_name,SURFACE=surface_name, AXES=LOCAL*SECTION FILE, NAME=section_name,SURFACE=surface_name, AXES=LOCALUser-specified local systemA user-specified local system is defined by specifying the origin and the directions of the axes. You can specify the origin (anchor point) by giving a node number or by specifying the coordinates of the anchor point.In two-dimensional and axisymmetric cases the local 2-direction is defined by specifying either a predefined node number or the coordinates of a point (point a) on the local 2-direction. The local1-direction is then obtained by rotating the local 2-axis clockwise by 90° about the anchor point (see Figure 4.1.2–1). If node numbers are used to definethe anchor point or the local directions, they must be connected to the mesh.Figure 4.1.2–1 User-defined local coordinate system.In three-dimensional cases either two predefined nodes or the coordinates of two points can be used to specify the local directions. A rectangular Cartesian coordinate system is then defined by its origin (the anchor point) and these two points. The first point (point a) must lie on the local 2-direction, and the second (point b) must be in the local 2–3 plane on the side of the local 3-direction. Although it is not necessary, it is intuitive to select the second pointsuch that it is on or near the local 3-direction (see Figure 4.1.2–1).If you do not specify the anchor point of the local system, it is taken to be the centroid of the projection of the surface on the fitted line or plane. If you do not specify the directions of the axes, the local system will be anchored at the specified anchor point and its axes will be parallel to the default axes of the projected surface. If neither the anchor point nor the directions are defined, the default local system will be used.In large-deformation analyses the surface section may rotate significantly during the deformation. By default, when output is requested in a local coordinate system, the system rotates with the average rigid body motion of the elements used to define the surface section (i.e., the local system and the output are updated during the analysis). The anchor point and local directions must then be specified relative to the undeformed configuration. You can choose to obtain vector output in the original local coordinate systeminstead. This choice is irrelevant in steps in which geometric nonlinearities are not considered.Input File Usage: Use either of the following options to specify the local coordinate systemdirectly:*SECTION PRINT , NAME=section_name ,SURFACE=surface_name ,AXES=LOCAL, UPDATE=YES or NOanchor point definitionaxes definition *SECTION FILE , NAME=section_name ,SURFACE=surface_name ,AXES=LOCAL, UPDATE=YES or NOanchor point definitionaxes definitionControlling the frequency of outputYou can control the frequency of section output by specifying the output frequency in increments. Unless a frequency of zero is specified to suppress output, the variables will always be output at the last increment of the step.Input FileUsage: Use either of the following options:*SECTION PRINT, NAME=section_name,SURFACE=surface_name, FREQUENCY=n*SECTION FILE, NAME=section_name,SURFACE=surface_name, FREQUENCY=nData file formatPrinted output is arranged in tables. The first line of the table contains the name of the requested output variable (see “Abaqus/Standard output variable identifiers,” Section 4.2.1), and the second line contains the corresponding value. If a section output request is defined without any specified outputvariables, all appropriate variables associated with the current analysis type are outputs.If several section output requests to the data file are encountered in one particular step, separate tables will be created for each request. Each table has a header denoting the name of the section and the name of the surface used. In addition, if the output is requested in a local coordinate system, the global coordinates of the anchor point(会给出local coordinates 的原点在global coordinate 中的坐标) and the cosine directions of the local axes are output.Results file formatSeveral section output records (record numbers1580–1591 in “Results file output format,” Section 5.1.2) are output for each section output request to the results file. The actual collection of records to be written to the results file depends on the number of valid output requests. If a section output requestis defined without any specified output variables, all records relevant to the current analysis type are stored in the results file.Vector output in the sectionVector output associated with section output requests consists of the total force (SOF), the total moment (SOM), and the center of forces (SOCF这是表示一个点). Output variable SOF is computed as a vector sum of the stress-based (internal) nodal forces of the nodes in the surface.Output variable SOM is computed with respect to the origin of the coordinate system considered.Thus, if the output is requested in the global coordinate system, the total moment is computed about the global origin; if the output is requested in a local coordinate system, the moment is computed about the current anchor point of the local system. The coordinates of the current anchor point may change during the analysis if the localcoordinate system is updated. Output variables SOF and SOM are both reported in the coordinate system considered.The center of forces SOCF is computed as the closest point to the centroid of the section through which the total force SOF acts. SOCF is always reported in the global coordinate system. If the total force vector is equal to zero, the centroid of the section is reported as the center of forces SOCF.The total moment vector, SOM, will not necessarily equal the cross product of the center of force vector, SOCF, and total force vector, SOF. Forces acting on two different points of the section may have components acting in opposite directions, such that these force components generate a net moment but not a net force; therefore,the total moment may not arise entirely from the resultant force.Scalar output in the sectionScalar output associated with a section output request consists of the area of the defined section (SOAREA), the total heat flux (SOH) in heat transfer analysis, the total current (SOE) in electrical analysis, the total mass flow (SOD) in mass diffusion analysis, and the total pore fluid volume flux (SOP) in couple pore fluid diffusion-stress analysis. These output variables are computed as the algebraic sum of the scalar internal nodal fluxes (work-conjugate to the associated primary solution variables) of the nodes in the surface. For example, in heat transfer analysis the total heat flux (SOH) is the sum of the NFLUX values at the nodes on the surfaces.Limitations when using section output requests Section output requests are subject to the following limitations:Section output requests are available only for sections defined by an element-based surface. Thus, they can be used only for sections along faces ofcontinuum elements.∙When defining the section, elements on only one side of the section must be used. Abaqus/Standard identifies all elements attached to the surface on this side and computes the section outputvariables as in a free-body diagram.∙ form a closed surface, or be on the exterior of the body. Figure 4.1.2–2 presents some typical cases of valid surfaces. If the section cuts only partially through the mesh, a valid free-body diagram cannot be isolated (see Figure 4.1.2–3) and incorrect answers may be computed.Abaqus/Standard will attempt to identify theinvalid cases and will issue error or warning messages.Figure 4.1.2–2 Valid section definitions.Figure 4.1.2–3 Invalid section definitions.∙Elements attached to the section can be on either side of the surface but must not cross the defined section. Figure 4.1.2–3 presents a few invalid cases. In most cases Abaqus/Standard willsuccessfully identify elements that cross the surface, and warning messages will be issued. The elements will then not be considered in thecalculation of the section variables.∙For section output purposes, Abaqus/Standard will ignore the elements attached to the section for which it cannot establish whether they belong to one side or the other of the section (e.g., SPRING1 elements).∙Section output requests cannot be specified withina substructure.∙Section output requests cannot be specified in random response analyses.∙The total force and the total moment in the section are computed based only on the stresses (internal forces) in the identified elements. Thus,inaccurate results may be obtained if distributed body loads are present in these elements since their effect on the total force in the section is not included. Common examples are the inertial loading in dynamic analyses, gravity loads,distributed body forces, and centrifugal loads. In these cases the total force in the section may depend on the choice of elements used to define the section as illustrated in Figure 4.1.2–4(a).Assuming that gravity loading is the only active load, the element stresses will be different in the two elements. Hence, if the same section is defined first using element 1 and then using element 2, different answers for the total force will be obtained. In a similar way the effects of anydistributed body fluxes (heat, electrical, etc.) prescribed in the identified elements are not included.Figure 4.1.2–4 Total force in the section.Depending on which side of the surface is used to define the section, different answers will be obtained in analyses similar to the caseillustrated in Figure 4.1.2–4(b). Assuming a static analysis with the concentrated loads shown in the figure being the only active loads, a zero total force is reported if the section is defined using element 1 and a nonzero force equal to the sum of the concentrated loads is obtained if the section is defined using element 2.。