Analysis On Electro-hydraulic Servo Fatigue Test For Sea Pipeline

This paper is based on multi-channel electro-hydraulic servo controlled testing device of deepwater-riser for fatigue developed by Beijing Institute of Petrochemical Technology (BIPT) and Jinan SHIJIN GROUP. This testing system adopts electro-hydraulic technique to operate static and dynamic fatigue test device for oil pipe and pipe joint. The highest frequency during dynamic test is 0.5Hz.Tube pressure pulse frequency of alternating is up to hundreds of thousands of times in the water. We simulate the pressure fluctuations of the media in the overall test pipe. According to the conditions and standard of the test, we determine the host frame, hydraulic system diagram and main system parameters.Owing to the short axial dimension of the testing pipe and short distance away from pulse source, we use the fluctuation method to modeling. The fluctuation method is usually focused on the compressibility of the fluid without considering the flow resistance along the pipe, so the fluctuation method is fit for the wave motion with short distance and less time form pulse source. This method makes the phenomenon of mathematical concepts to solve the time domain is relatively clear. At the same time we take into account the pulse occurs between the source and the pipeline connection will be a small diameter pipeline, so we establish the transmission and reflection model of pressure fluctuation in pipe series and simplify the model after iterative calculation.We use the software Labview which can quickly and accurately display a number of cycles the pipeline at any point within the distribution of pressure fluctuation to calculate the mathematical model. We also write pulse pressure distribution pipeline calculation software with G language belonging to Labview and build specifications convenient to mathematical models. Labview run-time engine as a support needed for stand-alone application running Labview and its engine running include Labview applications and shared libraries built all the necessary libraries and other files. Taking into account the versatility of the software applications we have created a Labview engine installation set-up file. This makes the application of this software has greatly improved in the majority of PC environments.As for the pulsatile flow pressure pipeline analysis, we use computational fluid dynamics software-Fluent to simulate. Fluent is a popular commercial CFD software package in the world. It has a wealth of physical models and advanced numerical methods. We use the dynamic mesh of the model to simulate the flow field boundary movement as the problems changing with unsteady time. Before fixing problem in the calculation of the grid, we must define the movements of the mesh area moving. Fluent provides a UDF definition as a user interface to determine the movement of moving mesh area. The preparation of the UDF must use C language,so we use C language input the form of fluctuating pressure pipeline in the Fluent. According to data of some model parameter values change, we analyzed fluent simulation data on model calculations and theoretical data.We build the system transfer function of the electro-hydraulic controlled system for analysis of dynamic characteristics. Electro-hydraulic servo system has both advantages of electric and hydraulic units. High signal transmission speed and ease of measurement, comparison and correction and big hydraulic output power specially suit the requirements of pulsating fatigue test system.According to the mathematical model of dynamic response analysis of the system stability and dynamic response characteristics to establish compensation.