Shahrood University of Technology Journal of Hydraulic and Water Engineering 2980-986X 2 1 2024 07 01 A Hybrid Solution for Transient Pipe Flow based on Method of Characteristics and Lax-Friedrichs Scheme 13 28 3188 10.22044/jhwe.2024.13086.1015 EN Faeze Khalighi Department of Civil Engineering, Shahrood University of Technology, Shahrood, Iran. Department of Mathematics and Computer Science, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. Ahmad Ahmadi Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, SAR 999077, Kowloon, Hong Kong. Alireza Keramat Civil and Environmental Engineering Department, Hong Kong Polytechnic University, Hong Kong Research Institute for Land and Space, Hong Kong Polytechnic University, Hung Hom SAR 999077, Kowloon, Hong Kong. Arris Tijsseling Department of Mathematics and Computer Science, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. Journal Article 2023 05 06 Method of Characteristics (MOC) has long been an excellent and widely established technique for analyzing transient flow, especially in a single pipeline with constant wave speed. But, this method has some limitations in terms of mesh sizing while studying multi-pipe systems or systems with different wave speeds. More specifically, it needs all pipes to satisfy the Courant number to be unity while the same time step should be chosen for all pipes. With this, one reach in each pipe remains, which does not satisfy the Courant requirement. As one possible remedy to this shortcoming, a hybrid numerical method based on MOC and a two-step variant of the Lax-Friedrichs method (MOC-LF) is suggested in the present study. This method is compared against the conventional MOC scheme, which adapts interpolation for the remaining length per pipe (MOC-MOC). In the approach, two significant effects of FSI in fluid-filled tubes, namely Poisson and junction coupling, are introduced. The computational simulations are carried out for a reservoir-pipe-valve system with instantaneous and gradual closure of the downstream valve. The results of proposed scheme and those of MOC with interpolation are in good agreement with solutions obtained by MOC with a very fine grid, which are taken as a reference. Detailed comparison of the computational methods in terms of error indicates that the proposed MOC-LF can be a good alternative for conventional MOC schemes. https://jhwe.shahroodut.ac.ir/article_3188_d294f43a1f603308fb69db8a69ec8bc6.pdf