Dynamic Analysis Of Impact System Of Underwater Pile Driving Hammer And Configuration Optimization Of Anvil

Nowadays,driven pile foundation is the most reliable foundation type for offshore oil and gas platform.As diameter and length of offshore pile are required to be larger,the underwater pile driving hammer with high impact energy is key equipment for building pile foundation.However,underwater pile driving hammer is still blanked in China,it is imminent to develop underwater pile driving hammer for marine mineral resources exploration.This thesis investigated the impact system of the underwater hydraulic pile driving hammer.The axisymmetric dynamical model of impact system was established by numerical method.Numerical results show that the anvil configuration parameters have an important effect on dynamic performances of impact system.The anvil optimal configuration parameters were obtained by the Active-set algorithm based on the dynamic strength optimization model.By the analyzing of underwater pile driving projects,this thesis also proposed the maximum impact energy,suitable pile diameter,and adaptability depth to the underwater environment.Synthesize proposed performance requirements and impact system of pile driving hammer on land,which indicated that impact system of underwater hydraulic pile driving hammer should comprise of ram,anvil,and pile.In underwater environment,double walled hammer shell was designed using diving bell principle.To conserve high impact energy,double acting hydraulic drive option was chosen,to make ram light and small.The option of ram suspension unit and that of anvil shock absorber ring,absorbing impact acting on underwater hydraulic pile driving hammer,were given and general structure plan was achieved.Two dimensional axisymmetric dynamic model of impact system of underwater hydraulic pile driving hammer was established for the dynamic performance optimization of impact system.Based on Lax-Wendroff finite difference method,numerical model of ram and pile were presented with numerical treatments of boundary conditions and numerical model of anvil were presented with numerical treatments of boundary conditions of anvil under curvilinear grid condition.To solve numerical model convergence issue because of the uniformity and orthogonality of anvil body-fitted grids,orthogonal correction algorithm of boundary nodes was developed based on Wei Wenli body-fitted grids generating method.Axisymmetric parameterized model of anvil with quadratic curve profile of the 1200kJ underwater pile driving hammer was established with constant of inner contour line and second-order coefficient of outer contour line as configuration parameters.By numerical simulations of collision for anvil with different configuration parameters,the configuration parameters change of anvil have some effect on transfer efficiency of impact energy,the effect range is about 3%.Moreover,the maximum stress of ram is not affected by the configuration parameters,but those parameters have significant effect on the maximum stress of anvil and pile during collision,the effect range reach to 165.53MPa and 90.77MPa,respectively.The approximate expressions of transfer efficiency of impact energy,the maximum stress in anvil,that in pile and configuration parameters were obtained by radial basis function method.Moreover,optimum model of anvil configuration was established with transfer efficiency of impact energy as target function and anvil and pile maximum stress as constraints.8 optimum models were provided by composing approximate expressions with different radial function.Based on fmincon multi-variable and nonlinear toolbox in MATLAB,the optimum models were solved and 8 optimal results were obtained.All the 8 optimized anvils meet the dynamic strength requirements of 1200kJ underwater pile driving hammer.Coaxial collision of two elastic bars experimental facility was designed to verify the numerical calculation model of ram and pile.The trends of numeric results were identical with the experiment results.The numerical calculation model was established for the impact system of MENCK 1200S underwater pile hammer.The numerical results conform to MENCK simulation data.The dynamic performances of 8 optimal anvils were simulated by the numerical model of impact system.Compared with numerical results,the maximum relative error was 1.7%,which verified the accuracy of the approximate expressions,and optimal configuration parameters of anvil were confirmed.This research investigates reliable numerical model for impact system of underwater hydraulic pile driving hammer and optimal design method for the quadratic curve contour anvil.It also provides one recommend design pattern for the anvil with other smooth curve contour.