Study on Buffering Performance of Aluminum Foam during Water-entry Process

The structure will suffer a huge overload, when it enters into water. The buffer head cap can effectively reduce the overload, and the buffer material in the cap is the key to its load reduction performance. In order to study the buffering ability of aluminum foam, an effective numerical simulation method is established in this paper. The numerical simulation method can effectively observe the motion of the structure and the energy absorption process of aluminum foam. It is found that the aluminum foam has strong capacity of buffering and reducing load by comparing with the structure without buffer head cap under the same conditions. In the process of energy absorption deformation, it can effectively protect the projectile from buckling deformation.

2D Ship-Like Section Slamming Pressure Numerical Analysis by Conformal Mapping

In this paper, a method to predict slamming pressures and pressure distribution at the time of water entry for 2D sections is presented. The mathematical model is based on the Schwarz-Christoffel conformal mapping method. This conformal mapping technique has been used to calculate slamming loads during water entry. The pile-up of water during motion is also considered and an alternative pile-up coefficient is assumed against Wagner’s generalized method. A simplified and accurate method is presented, which does not include non-linear terms and jet flow in the calculated pressure distribution on monotonically increasing 2D sections like wedge shapes. Comparison with real ship sections has been done to show accuracy of the results. Finally, a simple yet powerful method is obtained to aid the initial design stage of ships.

NUMERICAL PREDICTION OF SLAMMING LOADS DURING WATER ENTRY OF BOW-FLARED SECTIONS

The two-dimensional water entry of bow-flared sections is studied by using a Multi-Material Arbitrary Lagrangian- Eulerian (MMALE) formulation and a penalty-coupling algorithm. A convergence study is carried out, considering the effects of mesh size, the dimension of fluids domain, and fluid leakage phenomenon through the structure. The predicted results on the wetted surface of a bow-flared section are compared with published experimental values in terms of vertical slamming force, pressure distributions at different time instances and the pressure histories at different points. Comparisons between the numerical results and measured values show satisfactory correlation. An approximation method is adopted to estimate the sectional slamming force showing good consistency for the peak forces.

ASYMMETRICAL WATER IMPACT OF TWO-DIMENSIONAL WEDGES WITH ROLL ANGLE WITH MULTI-MATERIAL EULERIAN FORMULATION

A hydrodynamic study on the asymmetrical water impact of two-dimensional wedges with roll angle is presented. The slam induced loads on the wedges entering calm water with both vertical and horizontal velocities are predicted based on the explicit finite element method. The effects of the horizontal impact velocity and the roll angle are investigated through the predicted results of pressure distribution, pressure variation during the water entry and total impact force, which are also compared with analytical formulations and other numerical calculations. The present method gives reasonable predictions, compared to the numerical and analytical results.

URANS PREDICTION OF THE SLAMMING COEFFICIENTS FOR PERFORATED PLATES DURING WATER ENTRY

The slamming coefficients for perforated plates of various perforation ratios and layout configurations were predicted using Unsteady Reynolds-Averaged Navier-Stokes (URANS) solver STAR-CCM+. The numerical model was validated by comparing with experimental measurements of slamming coefficient for a circular cylinder. The slamming coefficients and free surface profiles of perforated plates were then predicted at full-scale. It was found the air compressibility plays an important role by studying flat plate water entry phenomena. For perforated plates with small gap length/width ratios, the ability of the trapped air to evacuate through the space between the bottom of the plate and free surface is similar. For perforated plates with different gap number at a fixed perforation ratio, the slamming coefficient is increased with the increase in gap length/width ratio. However, a further increase in length/width ratio may impose a negative impact on the escape of trapped air due to the increase of gap number.

Application of geophysical and hydrogeological analyses to predict water and hydrocarbon entry to the T5 Tunnel, west Iran

The Garmsiri Project, including the 4.5 km long T5 Tunnel, is under construction in western Iran. The T5 tunnel passes through the NW-SE trending Emam Hasan Anticline (EHA), perpendicular to the fold axis. The fold is mainly composed of the marlstone and argillaceous limestone layers of Cretaceous to Miocene age, incorporating the Pabdeh-Gurpi Formation, karst limestone of the Asmari Formation, and marlstone and gypsum of the Gachsaran Formation. There was a risk of water entry into the tunnel since it was constructed below the regional groundwater table elevation. In addition the entry of hydrocarbons, in either liquid or vapour phase, to the tunnel was possible due to the presence of numerous active bitumen mines in the vicinity of the anticline. To predict the risk of water or hydrocarbon entry geological and hydrogeological analyses together with the Audio Magnetotelluric (AMT) method were applied. Based on the field works, resistivity and geological cross sections were provided along the tunnel path. Several boreholes were drilled along the tunnel route and watertable elevation, Rock Quality Designation (RQD) and permeability values were measured. To determine a broad range of features related to the anticline, 55 AMT stations were positioned along the tunnel route. Dimensionality analysis confirmed 2D dimensionality of the AMT transfer functions, which allowed to apply the 2D bimodal inversion using a non-linear conjugate gradient algorithm. Integration of the geological and hydrogeological data with the resistivity model resulted in a more detailed geological section along the tunnel, including watertable elevation and identification of highly conductive zones in which bitumen migrated. It was predicted that water entry would be observed through the Asmari Formation and also that elevated H2S concentrations would be encountered during drilling in the anomalous conductive zones. Monitoring results and field observations gained during the tunnel construction were compared by the predictions.