A Comparative Study on Displacement Response Between Air-Backed and Water-Backed Condition for Flexible Plate Structures Subjected to Underwater Shock Load

2016 ◽  
Author(s):  
Debashis Wadadar ◽  
Asokendu Samanta ◽  
Vighnesh Ambetkar
Keyword(s):  
Virtual Work ◽  
Underwater Explosion ◽  
Stiffened Plates ◽  
Flexible Plate ◽  
Free Standing ◽  
Plate Structures ◽  
Single Degree Of Freedom ◽  
Underwater Blast ◽  
Underwater Shock ◽  
Double Hull

For ships operating in combat situations, estimating the response of the bottom and side shells subjected to non-contact underwater blast load is of paramount importance. The damage severity in underwater explosion (UNDEX) depends not only on the shock factor but also on the type of fluid behind the structure (air or water). The response of a free-standing air-backed (AB) and water-backed (WB) plate has already been studied analytically by Liu and Young [1]. However, analysis for AB or WB conditions for fixed flexible plate structures has not been given due importance. In the present study, the equation of motion for the generalized single degree of freedom (SDOF) model for AB or WB plate, which accounts for its flexibility, is formulated from the principle of virtual work. However, since this model is constructed to have a global overview of the present problem without taking account of its inherent complexities, a detailed numerical investigation using MSC.DYTRAN solver is carried out for bare and stiffened plates. The results obtained from both the analytical model and numerical simulations clearly show significant reduction in displacement in case of WB condition compared to AB condition for equal shock factors. This study emphasizes the fact that WB condition can be used to our advantage in order to reduce damage associated with UNDEX in case of doublebottom or double-hull naval vessels.

scholarly journals Numerical Simulation and Response of Stiffened Plates Subjected to Noncontact Underwater Explosion

2014 ◽  
Vol 2014 ◽  
pp. 1-17 ◽  
Author(s):  
Elsayed Fathallah ◽  
Hui Qi ◽  
Lili Tong ◽  
Mahmoud Helal
Keyword(s):  
Numerical Simulation ◽  
Underwater Explosion ◽  
Design Guidelines ◽  
Nonlinear Finite Element ◽  
Steel Plates ◽  
Stiffened Plates ◽  
Shock Loads ◽  
Floating Structures ◽  
Underwater Shock ◽  
Overall Performance

A numerical simulation has been carried out to examine the response of steel plates with different arrangement of stiffeners and subjected to noncontact underwater explosion (UNDEX) with different shock loads. Numerical analysis of the underwater explosion phenomena is implemented in the nonlinear finite element code ABAQUS/Explicit. The aim of this work is to enhance the dynamic response to resist UNDEX. Special emphasis is focused on the evolution of mid-point displacements. Further investigations have been performed to study the effects of including material damping and the rate-dependant material properties at different shock loads. The results indicate that stiffeners configurations and shock loads affect greatly the overall performance of steel plates and sensitive to the materials data. Also, the numerical results can be used to obtain design guidelines of floating structures to enhance resistance of underwater shock damage, since explosive tests are costly and dangerous.

scholarly journals The Requirement for Hydrostatic Initialisation in LS-DYNA/USA Finite Element Models

2000 ◽  
Vol 7 (2) ◽  
pp. 57-65
Author(s):  
Lloyd Hammond ◽  
Raphael Grzebieta
Keyword(s):  
Finite Element ◽  
Underwater Explosion ◽  
Element Model ◽  
Plate Structures ◽  
Fluid Structure ◽  
The Usa ◽  
Structural Responses ◽  
Fluid Boundary ◽  
Underwater Shock ◽  
Surrounding Fluid

The LS-DYNA/USA (Underwater Shock Analysis) coupled finite element codes are being investigated as a tool for predicting the local response of compliant plate structures subjected to far-field underwater explosion.It had previously been observed in LS-DYNA/USA models that extraneous pressure build-ups emanating from the DAA (doubly asymptotic approximation) boundaries may occur in the surrounding fluid region of the model, which inevitably lead to erroneous modelling of fluid-structure interaction and inaccurate structural responses. These instabilities typically result in divergence of the solution and eventually premature termination of the simulation. After a comprehensive investigation, it was found that the instabilities did not arise if the finite element model was hydrostatically initialised before conducting the LS-DYNA/USA simulation.The purpose of this study is to investigate the need for achieving hydrostatic equilibrium prior to the modelling of the shock wave propagation through the fluid-structure media. The method for achieving static equilibrium with the current version of the LS-DYNA/USA software is presented. The example simulations presented show that the hydrostatic initialisation procedure is effective in removing instabilities occurring at the DAA-fluid boundary, associated with the USA ambient hydrostatic pressure condition.

High Pressure Generation Using Underwater Explosion of a Spiral Explosive in a Conical Vessel

2004 ◽  
Vol 126 (2) ◽  
pp. 258-263
Author(s):  
Toru Hamada ◽  
Shigeru Itoh ◽  
Kenji Murata ◽  
Yukio Kato
Keyword(s):  
Shock Wave ◽  
Characteristic Curve ◽  
Three Dimensional ◽  
Underwater Explosion ◽  
Initial Pressure ◽  
Maximum Pressure ◽  
Underwater Shock Wave ◽  
Expansion Curve ◽  
Underwater Shock ◽  
Manganin Gauge

An explosive configuration was studied so that the underwater shock wave converges at the tip of the explosive, and a three-dimensional spiral configuration was obtained. This spiral configuration need to be analyzed theoretically due to the relation of propagation velocity of underwater shock wave, detonation velocity of the explosive and a configuration of vessel to charge the explosive. In order to study an effect of the convergence, pressure measurement at the spiral center was carried out by using a manganin gauge. Therefore, when SEP was used in this experiment, the maximum pressure value was 17.7 GPa. This maximum pressure value is higher than the pressure value of underwater shock wave generated from the underwater explosion of a straight configuration. Furthermore, this maximum pressure value was higher than C-J pressure of SEP. An initial pressure of underwater shock water shock wave that can obtain from an isentropic expansion curve of SEP and a characteristic curve of water is 5.7 GPa, and C-J pressure of SEP is 15.9 GPa. From the above-mentioned, the effect of spiral convergence could be shown well.

Dynamic performances analysis of hybrid press based on dependent generalized coordinates

2014 ◽  
Vol 229 (12) ◽  
pp. 2187-2194
Author(s):  
Jinliang Gong ◽  
Xiaoming Wang ◽  
Fengan Huang ◽  
Yanfei Zhang
Keyword(s):  
Dynamic Model ◽  
Virtual Work ◽  
Single Degree Of Freedom ◽  
Virtual Work Principle ◽  
Generalized Coordinates ◽  
Hybrid Mechanism ◽  
Adams Simulation ◽  
Angular Velocities ◽  
Dynamic Performances ◽  
Angular Displacements

A kind of multi-link hybrid press mechanism is brought forth. It adopts three motors as actuations to fulfill the single degree of freedom output of end effector. For hybrid press mechanism, the forward kinematics is usually complicated and its numerical solution is computation-intensive and time-consuming. Therefore, the dynamic model is difficult to build up when it needs to analyze the input function’s effect on system dynamic performances. Concept of dependent generalized coordinates is adpoted here and a kind of dynamic modeling method of multi-link hybrid mechanism is presented based on the virtual work principle. The linear and angular displacements of every component can be expressed concisely in the form of dependent generalized coordinates. They are much simpler than that of independent generalized coordinates. Accordingly, linear and angular velocities will be derived by differentiating with respect to displacements. Velocity Jacobian matrix will be simplified under dependent generalized coordinates system and the virtual work principle-based dynamic model will also be simplified accordingly. Then it needs to introduce constraint conditions and multiplier in order to acquire actuation forces. Introduction of the constraints guarantees the real kinetic characteristics of mechanism. In the end, the curves of actuation forces and spherical joints’ inner forces variations are presented using Matlab. By comparing with Adams simulation results, validity of the method has been proved.

Effects of Steel Case on Underwater Shock Wave

2011 ◽  
Vol 52-54 ◽  
pp. 943-948
Author(s):  
Ji Li Rong ◽  
Da Lin Xiang ◽  
Jian Li
Keyword(s):  
Shock Wave ◽  
Peak Pressure ◽  
Underwater Explosion ◽  
Steel Shell ◽  
Cylindrical Charge ◽  
Underwater Shock Wave ◽  
Shock Wave Energy ◽  
Lag Effect ◽  
Underwater Shock ◽  
Different Thickness

The effects of steel case confinement for the aluminized explosive on underwater explosion(UNDEX) were experimentally and numerically investigated. The experimental results using 1kg cylindrical charge cased 6mm steel shell, show that steel case enhance the peak pressure, impulse, shock wave energy and decay time relative to the bare charge. The effect of different thickness of steel case was analyzed. With the increase of the case thickness, the shock wave were enhanced first and weaken later, and there is a lag-effect for the peak pressure of shock wave. There is an optimal case thickness which could maximum enhance the peak pressure. According to dimensional analysis, it's found that the ratio of case mass and charge mass( ) is a better dimensionless parameter to estimate UNDEX for a cased charge.

scholarly journals Fundamental Characteristics of Underwater Shock Wave due to Underwater Explosion of High Explosives.

1996 ◽  
Vol 62 (601) ◽  
pp. 3278-3283
Author(s):  
Shigeru ITOH ◽  
You NADAMITSU ◽  
Akio KIRA ◽  
Shiro NAGANO ◽  
Masahiro FUJITA ◽  
...  
Keyword(s):  
Shock Wave ◽  
Underwater Explosion ◽  
High Explosives ◽  
Underwater Shock Wave ◽  
Underwater Shock

Transverse Vibration of Plate Structures With Elastically Restrained Edges by the Spline/Finite Strip Method

1993 ◽  
Vol 115 (3) ◽  
pp. 295-302 ◽  
Author(s):  
Abdul Hamid Sheikh ◽  
Madhujit Mukhopadhyay
Keyword(s):  
Natural Frequencies ◽  
Stiffened Plates ◽  
Plate Structures ◽  
Finite Strip ◽  
Strip Method ◽  
Finite Strip Method ◽  
Spline Finite Strip ◽  
Elastically Restrained Edges ◽  
Elastically Restrained ◽  
Comparison Of The Results

The newly developed spline finite strip method has been applied to determine the natural frequencies of plates and stiffened plates with edged elastically restrained against translation and rotation. The stiffener has been modelled so that it can be situated anywhere within the plate strip. The formulation has been generalized in such a manner that it can handle general shaped plates and stiffeners having arbitrary orientation and eccentricity. A consistent formulation has been adopted to incorporate the contribution of the edge restraints in the structural stiffness matrix. Numerical examples as available in the literature are solved and the comparison of the results indicates good accuracy of the method. New results in the form of natural frequencies corresponding to the higher modes particularly for plates/stiffened plates with nonclassical boundaries are presented.

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