ANALYSIS OF FLUID STRUCTURE INTERACTION FSI DE TO OIL HAMMERING IN A

Abstract

The objective of the present study is to model mathematically the combination of Fluid Structure Interaction (FSI) due to Oil hammering, write a computer code against a mathematical model and then experimentally verify this model for a hydraulic system. The hydraulic system under investigation is a mobile crane. Also the study involves the destructive testing of the hydraulic system to optimize the thickness of tubes used for the flow of Fluid (oil) and experimentation for optimizing the number of clamps for holding the fluid lines. The mathematical model presented here is the modified form of A.S. Tijssiling model (A.S. Tijssiling, 2007). In which he assumes pressure head while in this research pressure generated by a hydraulic pump driven by an electric motor is assumed. The model developed is one-dimensional quasi-static based on oil hammering and beam theories. The three interaction mechanisms such as friction coupling, poisson coupling and junction coupling are taken into account. The friction coupling represents the mutual friction between liquid and pipe. While the poisson coupling relates the pressure in the liquid to the axial stresses in the pipe through the radial contraction and the expansion of the pipe wall. It is he named after Poisson in connection with the his contraction coefficient and is associated with the breathing or hope mode of the pipe. The poison leads to the precursor waves. Junction coupling act as a specific point in a pipe system such as unrestrained valves, bends and tees. The Mac Cormac’s scheme is used as a discritization tool for the solution of the given model. The experiment has been carried out by making a hydraulic circuit which consists of an electric motor hydraulic pump lines or tubes, directional control valve and hydraulic jack. This experiment is similar to the experiment by Body and Fan of University of Dundy, UK (A.S. Tijssiling, 2007) whose apparatus consist of an isolated parts of a pipe system closed at end and connected with a tank situated at a height H. Also Optimization of thickness of the tubes used for fluid flow is optimized by conducting destructive bursting testing of the lines. At the moment, the pipes thickness installed on the existing system are suggested on the basis of experience. The experiments show that the thickness of the tubes used for the fluid flow is over vii designed and weight and cost of the system can be reduced by using tubes of smaller thickness. Optimization of the number of clamps used for securing the fluid lines to the system and controlling the axial and flexural vibrations is carried out. Currently the number of clamps used is suggested on the basis of experience. The experiments show that the number of clamps used on the current system under production is too high and their number can be halved while maintaining a reasonable level of safety. In summary the research study has resulted in the development of mathematical model for investigating the FSI in a oil based hydraulic system, developed an efficient code for easy use of the mathematical model for future researchers. The knowledge gained by the development of the FSI model for the hydraulic system would be critical for designing of future higher capacity hydraulic systems. Experiments were conducted and the mathematical model was found to be within 10% error range. Also experiments were conducted on optimizing the number of clamps needed to mount a hydraulic system’s lines. Moreover thickness of the tubes needed to handle the pressure flow has also been optimized.