Urban flood simulation based on porosity and local time step

doi:10.3785/j.issn.1008-973X.2020.03.023

Journal of ZheJiang University (Engineering Science)

2020, Vol. 54

Issue (3): 614-622 DOI: 10.3785/j.issn.1008-973X.2020.03.023

Hydraulic Engineering

Urban flood simulation based on porosity and local time step

Wei LI(

),Ji-yu ZOU,Peng HU*(

)

Ocean College, Zhejiang University, Hangzhou 310058, China

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Abstract

A well-balanced shallow water model of anisotropic porosity was developed under the framework of finite volume method, in order to increase the computational efficiency of urban flood simulation. The high-resolution Harten-Latex-van Leer-Contact (HLLC) approximate Riemann solver which could automatically capture shockwaves and discontinuities was used for flux computation, together with the local time step technique for time updating. The application to classic idealized urban floods shows that the represent model can accurately reproduce the complex hydrodynamics of urban floods and increase the computational efficiency markedly: the anisotropic porosity method reduces the requirement of local grid refining around obstructions and increases the computational efficiency by an order of magnitude; the local time step technique allows each grid to use a relatively large time step and reduces the temporal iteration, and further saves the computation cost by about two to three times.

Key words： anisotropic porosity shallow-water equation urban flood simulation local time step finite volume method

Received: 11 April 2019 Published: 05 March 2020

CLC:

TV 131.2

Corresponding Authors: Peng HU E-mail: lw05@zju.edu.cn;pengphu@zju.edu.cn

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Cite this article:

Wei LI,Ji-yu ZOU,Peng HU. Urban flood simulation based on porosity and local time step. Journal of ZheJiang University (Engineering Science), 2020, 54(3): 614-622.

URL:

http://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2020.03.023 OR http://www.zjujournals.com/eng/Y2020/V54/I3/614

基于孔隙率和局部时间步长的城市洪水模拟

为提高城市洪水模拟的计算效率，在有限体积法框架下，基于能自动捕捉激波、间断的高精度Harten-Latex-van Leer-Contact （HLLC）近似黎曼算子，并结合局部时间步长技术，建立满足静水平衡特性的各向异性孔隙率浅水模型. 经典城市洪水模拟结果表明，所建立的模型能够精确模拟洪水传播过程的复杂流动现象，并能显著提升计算效率：孔隙率方法降低了建筑物周围网格加密的要求，能使计算效率提升一个数量级；局部时间步长技术让每个网格采用尽可能大的时间步长，减少了循环次数，可进一步提升计算效率约2.0~3.0倍.

关键词： 各向异性孔隙率, 浅水方程, 城市洪水模拟, 局部时间步长, 有限体积法

Fig.1 Conceptual model diagram of porosity in triangular cell

Fig.2 Experimental set-up and dimensions for idealized urban floods

Fig.3 Diagram of mesh types for each test calculation case in building area

Fig.4 Water depth evolution over time（balance case 1）

Fig.5 3D view of water level and bed topography at different times（balance case 2）

Fig.6 Comparison of water depth contours between case C_C and P_RN at experimental time of 10 s

Fig.7 Water depth against time at different gauges for idealized urban flood experiment

Fig.8 Water depth profiles along longitudinal street of y=2 m at different times for idealized urban flood experiment

Fig.9 Flow velocity profiles along longitudinal street of y=2 m at different times for idealized urban flood experiment

Fig.10 Acceleration rate of computation time for each approach at different maximal updating levels of local time step (LTS)

Tab.1 Comparison of errors between calculated and measured values by different solutions


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