Ship Motion And System Load Analysis Based On Hydraulic Synchronous Lifting Technology

In recent years, with the development of global low carbon economy, it has been a common view in shipbuilding and shipping industries that vessels will become larger. Because of the increasing number of large tonnage ships, maritime emergency rescue and salvage faces more serious situation. If a large tonnage ship sinks in the main channel or port, it will lead to paralysis of the whole port without sufficient capability of salvage.In order to deal with the possible crisis, the domestic salvage bureaus and enterprises start applying a new technology called hydraulic synchronous lifting to raise the wrecks. However, there are some defects in current application. In the process of salvage, the engineering ships float up and down affected by waves, and wire ropes bear excessive force.Sometimes, the ropes break and it leads to the failure of the whole salvage project.Based on the theory of ship hydrodynamics, this paper calculates the motions, forces and moments of the barge and wreck in hydraulic synchronous lifting system by analyzing mathematical model of random wave, ship motions and system load in time-domain.The first chapter presents research background of ship motions and system load based on hydraulic synchronous lifting technology. This chapter also demonstrates the theoretical significance and practical value of this paper. Meanwhile, this chapter reviews and summarizes the research status of some relevant subjects such as hydraulic synchronous lifting technology application in the case of salvage, modeling ships load and motion characteristics, wave patterns and wave loads, hydraulic synchronous lifting technology on land, ship motions response in waves and ship mooring system dynamic response.The second chapter describes irregular wave with mathematical methods based on the three-dimensional potential flow theory. This chapter also simulates the wave conditions in the ocean, and introduces short term and long term statistics for wave analysis.The third chapter establishes the frequency-domain equations of salvage ship motions and introduces the solution of this equation, especially heave motion solution. Then this chapter calculates the amplitude of a barge’s heave motion under different sea conditions in the hydrodynamic software’HydroStar’according to spectrum analysis.This barge has the capability of 12000 tons lifting buoyancy belongs to Yantai Salvage Bureau.The fourth chapter analyzes the time-domain motions of the salvage ship under wave conditions based on the frequency-domain theory, and establishes the time-domain equations of salvage ship motions. This chapter uses the same barge in the third chapter to calculate its amplitude of heave motion under different sea conditions. The difference is using the mooring analysis software’Ariane’for time-domain calculation. Finally, this chapter compares the results in time-domain calculation with those in spectrum analysis.The fifth chapter analyzes the hydraulic synchronous lifting system’s load in time-domain, which is based on the motion response results of the salvage ship under wave conditions in the third and the fourth chapter. First of all, this chapter analyzes the force and moment on the wreck, then it inputs the motion data of heave and pitch from the calculation results in the fourth chapter. At last, this chapter calculates the hydraulic synchronous lifting system’s load in time-domain by function modules in Matlab. All the calculation functions are based on the theoretical analysis equations. The model of wreck is the Hong Kong bulk carrier ’Bright Century’. The outputs include the heave acceleration of the wreck, the angular acceleration of the wreck and the change of wire ropes’tension. These outputs can provide data reference for development of the wave compensation device on the hydraulic synchronous lifting system. Besides, they are helpful to avoid the problems of salvage ships’fluctuation affected by the wave and excessive force on the lifting ropes.