Investigation and optimization of ship panel behaviour under underwater explosion by using numerical methods

In parallel with the rapid developments in the the shipbuilding industry for military purposes, the need for analysis of underwater explosion induced shock is increasing with each passing day. Especially projects that are developed for military purposes rely on the principle of confidentiality, therefore, the analysis of these structures with national resources are of utmost importance. In this thesis, strength analysis for the basic structural elements of the ship, the plate structures, are conducted for underwater explosion induced shock loads. A new function is proposed for explosion induced shock pressure profile and compared with existing Cole pressure function. The equations of motion for the laminated composite plate subjected to blast loading are derived by the use of the virtual work principle. The geometric nonlinearity effects are taken into account using the von Karman large deflection theory of thin plates. Approximate solutions are assumed for the space domain and substituted into the equations of motion. The Galerkin Method is used to handle the nonlinear differential equations in the time domain. The solution of dependent and non-linear differential equations are conducted by using MATHEMATICA software. The strength Tsai-Wu and Tsai-Hill failure analyses of three layered composite plate under uniform static pressure load are carried out using the Galerkin method. In addition, a finite element solver, NASTRAN software, is used for static analyzes of the composite plate. Midpoint deformation of the plate, Tsai-Wu and Tsai-Hill failure intensities are validated by comparing Galerkin and finite element methods. Damped and undamped clamped rectangular three-layered composite plate is subjected to blast loading, the geometric non-linear dynamic analyzes are carried out using the Galerkin and the finite element method. For the underwater explosion shock blast pressure load, different than the Cole approach, a new and better function is proposed for the first part and the exponantial decreasing second part of the pressure. Proposed function has been applied dynamically to the composite plate by using MATHEMATICA and ANSYS software. In order to examine the damping effect of the water and to test the accuracy of the proposed pressure function, a MATHEMATICA algortihm has been developed and the results are compared with dynamic finite element software LS-DYNA. In the damped case, the pressure function depends on the x and y dimensions and w' the velocity of the plate. In this case, three variables are available and ANSYS software does not permit to describe three variables at the same time. Therefore, damped analysis cantilever steel plates were analyzed using LS-Dyna software. By analyzing the explosion of 40 gr of TNT on the 0,15 m depth of water, time-dependent changes in the pressure acting on the steel plate are compared. Steel plates are preferred due to the availability of the test results in the literature, e.g.,Ramajeyathilagam K et al. carried out explosion test for steel plates. The explosion analysis of the steel plates are performed by using LS-Dyna software and compared with the experimental results. In the last section, blast loaded laminated composite plates multi objective genetic optimization is carried out. In this context, one of the most successful multi-objective genetic algorithm approaches, Non-Dominated Sorting Genetic Algorithm, is used for optimization. By adding the optimization algorithm to the dynamic solver of underwater blast loaded laminated composite, the stacking sequences, layer orientation angles and thicknesses of each layer that gives the optimum mass and failure intensities (Tsai-Wu theory) are determined. Non-Dominated Sorting Genetic Optimization of the 3, 5, 7 and 9 layer composite plates, which are subjected to 0,15 depth of water and 20 gr TNT explosion induced shock loads, are carried out and Pareto optimal plate geometries are calculated.