Research On The Transient Flow Characteristics Of Ship Pipeline Based Under The Action Of Water Hammer

Ship pipeline is an important part of the ship,is the link between the main and auxiliary machinery and the relevant equipment,in order to make equipment operate well and constantly supplement the required fuel,lubricating oil,cooling water and compressed air.As an important part of ship power plant,ensuring the normal operation of cooling water system is an important guarantee for the safe navigation of ships.In the pipeline design of ship cooling water system pipeline,it is usually considered whether the flow of pump and pipeline can meet the requirements of ship design,and how the pipeline is arranged most reasonably,rarely considering the influence of dynamic load of water hammer.However,during the operation of the Marine cooling water system,the transient conditions in the pipeline may be caused by flow blockage due to flow regulation or accidents,as well as valve opening and closing,pump switching and accident stopping of pump.It is easy to produce large water hammer pressure and longtime pressure fluctuation,resulting in water hammer accidents,resulting in the damage of cooling water system pipes and equipment,and ultimately affecting the safe navigation of ships.Therefore,the study on transient flow characteristics of Marine cooling water system is of great significance to provide a basis for system design,pipeline and equipment strength check,and to ensure the safe and stable operation of cooling water system.In this thesis,the cooling water system of a 6500 DWT bulk carrier is taken as the research object to study the transient flow of the cooling water system.The main research contents of this thesis are as follows:(1)AFT Impulse,a water hammer analysis software,is used to create simulation models of the seawater cooling system and high-temperature fresh water cooling system.These models are based on the hydraulic transient flow analysis theory and the structure composition and operating principle of ship cooling water systems.Drawings and pertinent information are used to determine the parameters for each piece of machinery and equipment in the model.In order to select the primary research on closing the valve and stopping the pump conditions,the design must take into account factors like pipe diameter size,system pressure,and a few crucial pump,valve,and cooler aspects.(2)In AFT Impulse software,Newton-Raphson method was used to solve the basic formula of steady-state flow,and stable operating conditions of the system were obtained.Using the characteristic line method,combining the boundary conditions and initial conditions for transient solution,the transient hydraulic calculation results were obtained,the water hammer phenomenon in the cooling water system was explored,and the maximum pressure location of the water hammer phenomenon was obtained,which was an important basis for safety analysis and pipeline design.(3)Increasing the linear closing time of the valve,closing the valve quickly and then slowly in two steps,adding gas accumulator to the pipeline,and other actions can be taken to protect against and positively eliminate water hammer-causing operating conditions,according to the water hammer mechanism.(4)Through the application of FLUENT software,the flow law of butterfly valve internal flow field and the generation of vortex in the pipeline under different opening degrees were analyzed.Based on the dynamic grid,the influence of different closing time of butterfly valve on the water percussion phenomenon in the pipeline was studied,and the effective protection measures against water percussion were proposed.In this thesis,FLUENT and AFT Impulse software are used to obtain the flow field distribution of the valve flow channel area at the micro level,and the numerical distribution of water hammer pressure at the macroscopic level.The results provide useful reference and suggestions for the design and operation management of ship cooling water pipeline system.