Journal of Fluids and Structures 26 (2010) 1123–1141 Investigation of fluid–structure interaction with various types of junction coupling A. Ahmadi, A. Keramat n Civil Engineering Department, Shahrood University of Technology, Shahrood, Iran Received 16 July 2008; accepted 21 August 2010 Available online 20 October 2010 Abstract In this study of water hammer with fluid–structure interaction (FSI) the main aim was the investigation of junction coupling effects. Junction coupling effects were studied in various types of discrete points, such as pumps, valves and branches. The emphasis was placed on an unrestrained pump and branch in the system, and the associated relations were derived for modelling them. Proposed relations were considered as boundary conditions for the numerical modelling which was implemented using the finite element method for the structural equations and the method of characteristics for the hydraulic equations. The results can be used by engineers in finding where junction coupling is significant. & 2010 Elsevier Ltd. All rights reserved. Keywords: Fluid–structure interaction; Piping systems; Water hammer; Junction coupling 1. Introduction Transient flow occurs due to a disturbance in the steady flow, such as valve closing or pump shut-down. It can affect the structural piping system due to interaction between the structure and the contained liquid. In the study of fluid–structure interaction (FSI) in piping systems, the most significant mechanism is junction coupling, as compared with the other coupling mechanisms, namely Poisson and friction coupling (Wiggert and Tijsseling, 2001) in the more flexible piping systems (Heinsbroek and Tijsseling, 1994; Heinsbroek, 1997). Junction coupling takes place at unsupported discrete points of the piping systems such as unrestrained valves, branches, closed ends, pumps, etc. The main concept can be numerically implemented by using appropriate boundary conditions which will mutually relate structural and hydraulic values to each other. FSI in piping systems, considering the effects of column separation, has already been investigated in by Tijsseling (1993). In that study, the method of characteristics (MOC) has been used for numerical modelling of both structural and hydraulic equations. Fan and Tijsseling (1992) have made a study of the simultaneous occurrence of cavitation and FSI. In this research, numerical simulation and experiment concerned a single pipe, while in Tijsseling et al. (1996),a www.elsevier.com/locate/jfs 0889-9746/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfluidstructs.2010.08.002 n Corresponding author. E-mail addresses: a.ahmadi@shahroodut.ac.ir (A. Ahmadi), alireza.keramat@gmail.com, a.keramat@tue.nl (A. Keramat).