No abstract

The water entry problem of three-dimensional pounders with different geometric shapes of cube, cylinder, sphere, pyramid, and cone was numerically simulated by the commercial software Abaqus, and the effects of pounder shape and drop height from the free surface of water on deepwater displacement and velocity as well as pinch-off time and depth were investigated. An explicit dynamic analysis method was employed to model fluid-structure interactions using a Coupled Eulerian-Lagrangian (CEL) formulation. The simulation results are verified by showing the computed shape of the air cavity, displacement of sphere, pinch-off time, and depth which all agreed with the experimental results. The results reveal that the drag force of water has the highest and lowest effect on cubical and conical pounders, respectively. Increasing the pounder drop height up to the critical height leads to increased pounder velocity while impacting the model bed and more than the critical drop height has a reverse effect on pounder impact velocity. Pinch-off time is a very weak function of pounder impact velocity; but pinch-off depth increases linearly with increased impact velocity.

In this paper, the crack propagation behavior in flat and stiffened plates with central-cracked is studied based on the theory of linear elastic fracture mechanics and 3D finite-element method. The magnitude and distribution of the stress intensity factor in a 3D stiffened plates are affected by the out-of-plane bending and loading modes. Initially, for validating this method, the behavior of crack propagation in a central-cracked flat plate (unstiffened), followed by the propagation behavior and the crack arrest effects on stiffened plates by stiffeners, as well as the out-of-plane bending effect on the geometry correction function distribution are studied; However, the results are compared with the results of the referenced article. In order to analyze the effect of stiffeners in preventing crack expansion, stiffeners with variable thickness and height were used. It should also be noted that the crack propagation behavior in the stiffened plate is analyzed in two methods. In the first analysis, after the crack tip reaches to the stiffeners, they have not fracture and the crack only expands in the stiffened plate (in the stiffened plate type 1 and 2). In the second analysis, with the crack growth in the stiffened plate and the crack tip reaching to the stiffeners, Also they fractured and cracks in the stiffened plate and stiffeners are propagated (only in the stiffened plate type 2). In both analyses, the magnitudes ​​of the geometry correction function in the middle-plane, the crack arrest effect by the stiffeners (Δβs), and the out-of-plane bending effect (Δβ) were obtained. Then, the changes in these magnitudes ​​were investigated. It was observed that the stiffeners thickness had a negligible effect on the distribution of the geometry correction function and, in general, the stiffeners had a significant role in preventing the crack growth compared to the flat plate, and the more the crack tip is closer to the adjoining stiffeners; the stiffeners effect in the crack arrest will increases. Furthermore, with attention to the geometry correction function that is studied for different crack sizes, it was determined that the geometry correction function and stress intensity coefficient with increasing the length of the crack in the plate, increase.