Numerical Simulation of Mechanical Characteristics of a Metal Net for Deep-Sea Aquaculture

The investigation on hydrodynamic characteristics of a cage is important for its application in the deep-sea aquaculture in our country.With finite element method,the beam element is used to simulate a three-dimensional metal chain net,and the connector element is introduced as the interaction between metal net lines.A mechanical model for the metal net is constructed to simulate the hydrodynamic characteristics of a metal net subjected to fluid current forces.The static simulation results show that the relative errors of the displacements are 2.13%,4.19%,6.64%,and 11.35% compared with static concentrated load tests under concentrated forces of 20,40,60,and 80 N,respectively.Both the transient hydrodynamic deformations and drag forces of the netting structures under different current velocities are obtained by solving the hydrodynamic equation of the netting structure.The average relative error of the current forces obtained by numerical simulations shows an 8.13%deviation from the drag tests of the metal nets in the tank under five current velocities.The effectiveness and precision of the simulation approach are verified by static and dynamic tests.The proposed simulation approach will provide a good foundation for the further investigation of the hydrodynamic characteristics of deep-sea aquaculture metal cages and the parameter design for the safety of such cage systems.

A Fast Product of Conditional Reduction Method for System Failure Probability Sensitivity Evaluation

Systemreliability sensitivity analysis becomes difficult due to involving the issues of the correlation between failure modes whether using analytic method or numerical simulation methods.A fast conditional reduction method based on conditional probability theory is proposed to solve the sensitivity analysis based on the approximate analytic method.The relevant concepts are introduced to characterize the correlation between failure modes by the reliability index and correlation coefficient,and conditional normal fractile the for the multi-dimensional conditional failure analysis is proposed based on the two-dimensional normal distribution function.Thus the calculation of system failure probability can be represented as a summation of conditional probability terms,which is convenient to be computed by iterative solving sequentially.Further the system sensitivity solution is transformed into the derivation process of the failure probability correlation coefficient of each failure mode.Numerical examples results show that it is feasible to apply the idea of failure mode relevancy to failure probability sensitivity analysis,and it can avoid multi-dimension integral calculation and reduce complexity and difficulty.Compared with the product of conditional marginalmethod,a wider value range of correlation coefficient for reliability analysis is confirmed and an acceptable accuracy can be obtained with less computational cost.