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Progress in the design and calculation of urban drainage pipeline system

Abstract: in the construction of municipal construction and environmental treatment projects, rainwater and sewage pipeline systems often account for a large proportion of investment. Therefore, how to reasonably design urban drainage pipeline system under various technical conditions is an important topic in the design. This paper discusses the methods and problems to be solved in the development of drainage pipeline system design and calculation from three aspects: the optimization design under the determined pipeline, the plane optimization layout of the pipeline and the research of rainwater runoff model. It can be seen that a lot of energy is still needed to study and improve its design and calculation methods in the future

key words: optimal design of drainage pipeline system plane layout runoff model

0 introduction

drainage system is an indispensable and important infrastructure of modern cities, and it is also the backbone project of urban water pollution prevention and control, urban drainage and waterlogging prevention and flood control. Among them, the investment in rainwater and sewage pipeline systems in residential areas and industrial and mining enterprises generally accounts for about 70% of the investment in the whole drainage system [1]. Therefore, how to reduce the capital construction cost of the pipeline system as far as possible under the specified technical conditions is an important topic in the design work

the design and calculation method of traditional drainage pipeline system is: after mastering relatively complete and reliable basic design data, the designer determines a more reasonable layout plan of sewage pipeline according to the principles of pipeline alignment and plane layout. Then calculate the design flow of each design pipe section, take the hydraulic calculation diagram or hydraulic calculation table and relevant design regulations as the control conditions, carry out the hydraulic calculation of each design pipe section from upstream to downstream, and calculate the pipe diameter and slope of each pipe section, as well as the pipe bottom elevation and buried depth at the inspection shaft. In the calculation, the pipe diameter and slope of the pipe section are generally adjusted appropriately based on experience in order to achieve the purpose of economic rationality, but its rationality is limited by the personal ability of the designer; On the other hand, most calculations are carried out by repeatedly looking up diagrams and tables, which is inefficient and takes a long time, which is not conducive to the optimization of the design scheme

since the 1960s, the international community has gradually established mathematical models of various water supply and drainage engineering systems or processes on the basis of experience summary and mathematical analysis, thus developing to the stage of "rational design and management" of water supply and drainage engineering marked by quantitative and semi quantitative. At the same time, optimization research and practice have been carried out for various types of water supply and drainage systems [2]. In order to explore the optimal design and calculation method of drainage pipeline system, many scientific research, design, teaching units and individuals at home and abroad have done a lot of work, especially in schools, hospitals and other projects in earthquake prone areas, and published a large number of articles. From the research results, the application of computers to the design and calculation of drainage pipelines not only frees designers from the heavy work of consulting charts, speeds up the design progress, but also optimizes the whole drainage pipeline system and improves the design quality. Compared with the traditional method, the determined optimal scheme can reduce the project cost by more than 10%

the drainage pipeline system is a huge and complex system. From the existing research results, its design and calculation mainly involves three aspects: (1) the optimal design of pipe diameter and buried depth under the condition that the plane layout of the pipeline has been determined; (2) Optimization of pipeline layout; (3) Establishment of rainwater runoff model. The combined drainage pipeline system usually has overflow facilities to limit the amount of water delivered to the local sewage treatment plant. Since the overflowing rainwater is also discharged into the river nearby, from the perspective of water volume, the impact of combined drainage system on the drainage area is actually the same as that of separated rainwater system [4]

1 optimal design of pipeline system under the determined pipeline

for the optimization of pipe diameter buried depth under the determined plane layout of the pipeline, this is the problem of fatigue experiment mechanized design. A lot of pioneering work has been done at home and abroad, and fruitful results have been achieved. Optimization methods are generally divided into two kinds: indirect optimization method and direct optimization method. Indirect optimization method is also called analytic optimization. It is based on the establishment of optimization mathematical model, and obtains the optimal solution through optimization calculation; The direct optimization method is to obtain the optimal solution by directly selecting, calculating and comparing various schemes or adjustable parameters according to the changes of performance indicators. A fixture is static or satisfactory solution [5]

1.1 direct optimization method

in the optimal design of drainage pipelines, those who apply the direct optimization method believe that [6 ~ 8]: Although the hydraulic calculation formula used in the calculation of drainage pipelines is very simple, because the optional size of pipe diameter does not change continuously, the pipe diameter cannot be selected arbitrarily; The limit of maximum fullness is related to the size of pipe diameter; The constraints on the minimum design flow rate, the change of flow rate (increasing with the increase of design flow) and its relationship with pipe diameter are very complex, and cannot be described by mathematical formulas. Therefore, it is difficult to establish a complete mathematical model to solve the optimization problem with indirect optimization method. Relatively speaking, using direct optimization method to solve this problem has the advantages of direct, intuitive and easy to verify

1.2 indirect optimization method

with the development of optimization technology, although there are complex constraints in the design and calculation of drainage pipeline system, as long as some conditions are appropriately chosen and mathematical tools are reasonably applied, it can be simplified and abstracted into an easy to solve mathematical model, and the optimal solution can be obtained through calculation. According to the time of emergence and the mathematical methods used, indirect optimization methods are mainly divided into the following categories:

1.2.1 linear programming method

linear programming method is the most commonly used algorithm in optimization methods. It can solve many problems in the design of drainage pipelines, and can also carry out sensitivity analysis on the built drainage pipelines. Its disadvantage is that the pipe diameter is treated as a continuous variable, which leads to the contradiction between the calculated pipe diameter and the pipe diameter of the commercial specification [9]. Moreover, if all objective functions and constraints are converted into linear functions, the preprocessing workload is large and the accuracy is difficult to be guaranteed

1.2.2 nonlinear programming method

in order to adapt to the nonlinear characteristics of objective functions and constraints in the optimal design of drainage pipeline system, in 1972, Dajani and Gemmell established nonlinear programming 5 Try not to load the equipment control computer into an unrelated programming model [10]. This method is based on the derivation principle, that is, the point where the derivative of the objective function is zero is the optimal solution. It can handle the pipe diameter of commercial specifications, but when it is impossible to prove drainage

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