In the previous paper, the authors proposed a new simulation technique called the "system modal approximation" method (SMA method) for fluid transients in compound fluid-line systems. This technique was able to predict behaviour fast and accurately, and its superiority to other existing methods was verified by simulation and experimental analysis. However, detailed considerations were limited to the cases whose transfer functions of output/input could be approximatede by the second order modes alone. This paper enhances the analytical functions of the SMA method so as to be widely applicable to compound fluid-line systems with various kinds of system compositions and boundary conditions. Specifically, the calculation methods of time response of the required output variable at any points are newly proposed for case (A) whose transfer functions of output/input have to be approximated by the first order modes and derivative element besides second order modes, and (B) whose boundary conditions are given by the relation between pressure and flow-rate. Fluid transients in three kinds of compound fluid-line systems under the several different boundary conditions including the occurrence of column separation are considered. Simulation results based on the methods mentioned above are compared with both the solutions from the method of characteristics and experimental results, and then the usefulness of the generalized SMA method is verified.

Keywords: fluid transients, water hammer, modal approximation, compound fluid-line system, simulation