给排水工程外文翻译

Short and Long Term Advantage roof drainage design performance Decade has witnessed great changes in the design of the roof drainage system recently, particularly, siphon rainwater drainage system has been gradually improved, and there is likely to be the key application. At the same time these changes, urban drainage system design has undergone tremendous changes, because the scope of a wider urban drainage system design for sustainable development, as well as people for climate change flooding more attention. The main contents of this article is how to design roof drainage systems and make a good performance. Special attention is how to get rid of bad habits already formed the design, but also need to consider innovative roof drainage system, such as green roofs and rainwater harvesting systems.

Practical application: In the past few years, the design of the roof rainwater drainage system has undergone tremendous changes. On large buildings, siphon rainwater drainage technology has been very common, as well as green roofs because it is conducive to green development, being more and more applications. Taking into account the ongoing research, this article focuses on how to effectively design a variety of roof rainwater drainage system, and make it achieve the desired design effect.

1. Introduction

In the past decade, the city and the water drainage system design has been widely accepted thinking about sustainable urban drainage system, or the optimal management direction. The main principles of the design of these systems is both a local level in line with the quality of development, but also to create some economic benefits for the investors. This principle has led to the development of new changes in the sump. Although the application of such a device is gradually reduced, but the urban environment relatively high demand areas still require 100% waterproof and rapid drainage, such as the roof. Typically roof drainage system in the design, construction and maintenance has not been given due attention. Although the drainage system investment costs account for only a small portion of the total construction investment, but not able to judge the loss caused by poor design.

There are two different forms of roof drainage system design methods, namely the traditional and siphon method. Traditional systems rely on atmospheric pressure work, the drive ram affected sink flow depth. Therefore, the conventional roof drainage systems require a relatively large diameter vertical drop tube, prior to discharge, all devices must be connected to the groundwater collection pipe network. In contrast, siphonic roof drainage pipe systems are generally designed to full flow (turbulent flow means that require less exhaust pipe), which will form a negative pressure, the larger the higher flow rate and pressure head. Typically siphon system requires less down pipe work under negative pressure to the water distribution network can mean higher altitude work, thereby reducing the amount of underground pipe network.

Both systems consists of three parts: the roof, rainwater collection pipes, pipe network.

All of these elements are able to change the water pressure distribution system.

This section focuses on the role and performance of each part. Due to the principle of siphon system has not been well understood, resulting argument is relatively small, this article will highlight siphon system.

2. Roof

The roof is usually designed by the architect, designer and not by the drainage design. There are three main roof.

2.1 Flat roof

Flat roofs are used in industrial buildings less rainfall regions and countries. This roof is not completely flat, but lower than the minimum roof slope may require. For example, the United Kingdom require maximum slope of 10 °. Setting minimum slope in order to avoid any unnecessary water.

Despite the flat roof if it is not properly maintained will have more problems, but it will reduce the dead zone within the building, and the ratio of sloping roofs in favor of indoor air.

2.2 sloping roofs

Most residential and commercial buildings are pitched roof, inclined roof is the biggest advantage can quickly drain, thereby reducing leakage. In temperate regions, we need to consider carrying roof snow load. Once it rains, rainfall through the sloping roofs can be determined by calculation. When rainfall data can be used, you can use the kinematic theory to solve such problems.

2.3 green roof (flat or inclined)

It can prove roof is the oldest green roofs, including rainfall can reduce or disperse roof planted with plants. It can be planted with trees and shrubs roof garden, it can also be a vegetated roof light carpet. Wherein the latter technique has been widely used. Some of these applications tend to focus on aesthetic requirements and are often used in green development. Since the aesthetic requirements and pressure requirements, as well as green roofs thermal insulation function, reduce the heat island effect, silencer effect, extend the life of the roof.

Green roofs in Germany, the most widely used, followed in North America, but to consider the impact on the aesthetics. Germany is by far the most experienced countries in the 19th century have practical application, then as an alternative to reduce the risk of fire tar roof an option in urban areas. Germany is currently the main research question on the cultivation of other issues to consider smaller cities. A study from 1987 to 1989, was found packed with 70 mm thick green roof can be reduced by 60% -80% of heat loss. In a Canadian work computer model based on the roof indicates that as long as the sump, the area can reach 70% of the roof area can be reduced by 60 percent in one year, the same model was also used for artificial rainfall, which the results indicate that rainfall in the catchment season helps to drain away rainwater.

However, none of these studies show that green roofs can play a useful role in the rainfall season, or how high collection efficiency of water supply. The United States did some tests, as long as the green roofs regular watering, can reduce 65 percent of the runoff in a rainfall. America's most authoritative green roof guidelines by the New Jersey state environmental agencies promulgated. The main

principle is to solve the structural problems of light, and how can the normal drainage after two years.

Rainfall period is based on the probability of failure is determined. The system is typically based on rainfall during rainstorms two minutes, two minutes, have a choice. Although this model will get more traffic, but there is no other better alternative. Studies have shown that the traditional model is applied to study green roofs are premature.

Loss factor than traditional roof records should be small, about 98.7%. Peak flow will be reduced, although not penetrate, the surface roughness but also have a significant impact.

Concentrated rainfall than two minutes for a long time, especially for large roof areas, such as public buildings, commercial buildings, industrial buildings.

Urban drainage design should also consider other factors, for a complex system, a green roof in a rain is not enough. Water flow duration curve shows a longer than traditional systems. And two independent and will affect between is possible, which requires a more precise time period.

3. Rainwater Collector

Basic requirements rainwater collector is designed to be able to accommodate rainfall rainstorms. Although it is possible to make a slightly inclined roof drainage purposes, but the nature of the construction industry and building settlement will become flat roof Typically, the tank is placed in a horizontal, sectional view of the water is outwardly inclined, which the role of hydrostatic.

3.1 drain outlet

Analyzing rainwater collector has sufficient volume is the key to the sump outlet external setting conditions. Also affect the flow rate into the storm water drainage system piping, but also affect the depth of the water catchment. Although the depth of the sump will not bring any particular problems, but too deep can cause excessive sump.

Numerous studies in the 1980s showed that the flow of conventional roof drainage system outlet can be divided into two cases. It depends on the size of the depth and size of the outlet. When the water depth is less than half the diameter of the outlet, the flow of the first type, and the outlet of the flow can be calculated by an appropriate equation; water depth increases, exports are slowly clogging the flow will become another form forms, at the same time, the flow of exports can be obtained through other equations. While conventional roof drainage systems are designed to be free-draining, but may cause limitations encountered in the design of the flow is not free. In this case, it will require additional depth.

Siphon roof drainage systems, the outlet is designed to be submerged stream. In this case, the depth of the outlet of the decision is more complicated, because the design of the sump depends on the flow. Recent studies have shown that conventional roof drainage systems use a variety of non-standard catchment, their depth and height, bigger than the diameter of the outlet. This will eventually result in a siphon effect. For a given catchment, the flow depends on the starting end of the drop tube diameter. A similar phenomenon has also been used to study the standard

catchment, in these circumstances, only limited siphon action occurs within relatively close distance from the exit.

3.2 tank flow classification

In the complex flow sump outlet flow classification, can be seen from Table 2a, the flow will be uniform layering, regardless of whether the same inlet flow. Table 2b and 2c show, export distribution will greatly influence the flow.

When the outlet is not a free jet, sump outlet complex flow classification is difficult to describe. Because each catchment tank pressures are likely to be merged. For example, the siphon tube system design point is at near full jet outlet flow classification depends on the energy loss of each branch.

3.3 hydrostatic sectional

Sump shape of the water surface in the canal can be classified according to the flow equation. In most cases, a low flow rate means that there is less friction loss, if exports are free jet, the friction loss is negligible cross-section through the hydrostatic equation 1 to determine the horizontal distance.

Where Q-- flow (m3 / s)

T- surface width (m)

g- acceleration of gravity (m / s2)

F- flow area (m2)

Equation 1 can not be ignored when the friction required to correct (or very long pipe velocity is large), or not a free jet.

3.4 The current design methods

The previous discussion has highlighted the main factors that should be considered with sink design. However, without the help of a certain number of models, computing hydrostatic sectional roof drainage system, the volume of the sump is possible. This large commercial and manufacturing industry, is a development opportunity, you can merge several kilometers of water routes. Thus, the conventional drainage system sump design methods are mainly based on experience, and assume that exports are free jet.

Sump location in the building, it may cause the example to fail.

Different interface sump

Except in the case cited above, but also allows designers to use empirical data.

3.5 Digital Model

Large number of digital models can be used to accurately describe the flow of any form of catchment tank, regardless of whether the roof flows stable. An example of this model is a combination of roof space model. This model enables users to classify different aspects of the data indicated, includes: details of the rains, the roof surface drainage and other details. Kinematics have also been used to study rainwater tank to flow from the research collection. A typical method is based on open system to solve a basic problem of spatial mobility. This model automatically resolve the sump outlet flow situation, but also to deal with the case of free jet can also be simulated space limited mobility and submerged discharge. Output values include depth and flow rate.

Currently, the model is essentially just a variety of research tools, but also

through practical engineering test. However, we should face up to the various role models.

4 pipe systems group

Composition in the form and scope of the tube group determines the roof drainage system relies mainly on the traditional system or siphon action.

4.1 Traditional stormwater systems

Conventional roof drainage systems, the ground plane is generally vertical pipe-line network, connected to the sump outlet and underground drainage systems, critical systems as well as compensating tube. It should be emphasized that the angle bet ween the ground and the compensating tube is less than 10 °. Capacity of the entire system relies mainly on the outlet tube instead of down.

Flow vertical tube is usually free-flowing, full of only 33%, the efficiency depends on the excess length of the tube. If the drop tube long enough (typically greater than 5m), there may be an annular flow. Similarly, under normal circumstances flow compensation pipe is free-flowing, full of up to 70%. Such designed process both for the design, various equations can also be used.

4.2 Siphon roof drainage system

In contrast with the traditional drainage systems, Siphon roof drainage system relies on air flow outside the system, and the tube is full pipe flow stream.

The designs are usually made on the assumption that the design of heavy rain, the system can quickly siphon discharge rainwater. This assumption allows the application of hydrostatic siphon system theory. Often used steady flow energy equation. While this approach ignores the small amount of energy loss at the entrance, but after the experiment showed that there are still conducive to practical use.

However, steady-state design methods in the siphon system is exposed to rain when the system does not meet the standard requirements or changes in rainfall intensity is large is not applied. In the first case, there will be some mixing of air quality, annular flow occurs. These problems are not integrated in the system when more serious. Because usually designed rains are common, it is clear now design methodology over time may not apply to siphon system. This is a major disadvantage, because the design of the main problem is the noise and vibration problems.

Despite the disadvantages of the prior design approach, but a lot of the world's very few engineering failure reports. When a failure occurs, most likely for the following reasons:

An incorrect understanding of the operation points

Substandard materials list

Installation defects

Maintenance mismanagement

To overcome these disadvantages, we have recently launched a series of research projects, to discuss the siphon system, and the development of digital models. From this work we learn a lot.

In contrast with conventional design methods of some assumptions, siphon system mainly has the following aspects:

1) non-flow system of full flow

2) levels of certain pipe-flowing full pipe flow

3) full pipe flow downstream propagation through a vertical pipe, riser, etc.

4) the inner tube flow occurs over the vertical section, the system to reduce the pressure

5) downward tube is full pipe flow, there will be air lock

6) appears completely siphon action until well into the air system is lower than

a certain level

Table 4a column data indicate that below the design point, the system will siphon unstable flow, depth of the water collecting tank is insufficient to maintain the siphon action. Table 4b show that the unsteady flow in siphon system when it will appear.

Table 5 lists the data output of a digital model. It can be seen that the model can accurately describe the siphon action, siphon and steady state, the data also show that the model can accurately describe the complex siphon action.

5 Conclusion

This article has illustrated the critical roof drainage systems, but these are often overlooked in the urban drainage system design. This article also shows that the design process is a complex process, rely mainly on the performance of exports. The following conclusions are based on the design summed up:

1) Run depend on three interacting parts: the roof, sump, water pipes

2) Green roofs can reduce traffic and beautify the city

3) the export performance of the system is essential

4) siphon drainage system have a greater advantage in large-scale projects, but must be considered high maintenance costs

5) Design siphon drainage system should consider additional capacity and operational issues

Although the green roof is a more attractive option, but the traditional roof of a building in the country will continue to dominate. Green roofs will be gradually developed, and gradually been widely accepted. Similarly, the roof drainage system shown effective that it will continue to play a huge role in the commercial building drainage systems.

Roof drainage system of the greatest threats from climate change, existing systems tend to be not simply aging; rainfall patterns of change will result in inefficient operation, self-cleaning rate will be reduced. Changes in wind speed and the roof will also accelerate the aging of the roof, it is necessary to carry out maintenance. Taking into account the climate change, the increase in materials, roof collected rainwater will be more extensive. Currently, the amount of rain around the globe per person per day 7-300 liters in the UK, with an average consumption of 145L / h / d, of which only about one liter is used by people, about 30 per cent of the toilet, study shows If water shortage, rainwater collected on the roof of developed and developing countries are recommended approach.

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