Journal articles: 'UNDEX'

1

Hsu, Ching Yu, Tso Liang Teng, Cho Chung Liang, Hai Anh Nguyen, and Chien Jong Shih. "The Study on the Dynamic Response of Cylindrical Pressure Hull on the Different Shock Loading Empirical Formula." Applied Mechanics and Materials 799-800 (October 2015): 604–9. http://dx.doi.org/10.4028/www.scientific.net/amm.799-800.604.

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This paper focuses on the comparison between underwater explosion (UNDEX) shock loading empirical formulations. First, the numerical simulations for a cylindrical pressure hull subjected to UNDEX loading were conducted and the results are close to the failure modes shown in experiments of Kwon (1993). Second, the empirical UNDEX loading formula of Cole (1948), Keil (1961) and Shin (1994) used in cylinder subjected to underwater shock loading were compared. The simulation results by using three empirical formulas were compared and Shin’s (or Cole’s) empirical formula was shown to be better than the other empirical formulations when subjected to an UNDEX under the same conditions. The analytical results offer a valuable reference to the research of underwater explosion.

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Du, Zhi Peng, Yu Wang, Yong Chen, and Hong Xing Hua. "A New Type of Rubber Sandwich Coated Onto Ship for the Use of Underwater Explosion Shock Mitigating." Advanced Materials Research 79-82 (August 2009): 291–94. http://dx.doi.org/10.4028/www.scientific.net/amr.79-82.291.

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How to moderate ship the damages caused by the underwater explosion (UNDEX) is of great interest to the modern ship designers. A new type of rubber sandwich with periodic honeycomb core was developed to mitigate the ship shock due to UNDEX. A ship with or without the rubber coat was tested under “near combat conditions” by igniting a 8 kg charge of TNT underwater at varying standoff distances from the ship. The effects of the shocks to ship systems were observed and the responses of the ship were monitored and recorded for each shot. The pressures in the water around the ship were also recorded to explore the fluid-structure interaction and UNDEX shock wave reflection with different targets. Acceleration and strain records indicate that the rubber coat is capable of moderating the high-frequency response excited by shock wave efficiently. Pressure records show that the core crushing and water cavitation promote superior energy absorption that yields an increased resistance to UNDEX.

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Wang, Yuhao, Hongxiao Dong, Tong Dong, and Xiangyun Xu. "Dumbbell-Shaped Damage Effect of Closed Cylindrical Shell Subjected to Far-Field Side-On Underwater Explosion Shock Wave." Journal of Marine Science and Engineering 10, no. 12 (December 3, 2022): 1874. http://dx.doi.org/10.3390/jmse10121874.

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In naval warfare, underwater explosion (UNDEX) shock waves significantly influence the stability and safety of the pressure hull structure of the equipment. This study investigated the unique dynamic buckling of a closed cylindrical shell subjected to a far-field side-on UNDEX shock wave using a three-dimensional numerical simulation based on acoustic–structural arithmetic. In particular, the flow-field response characteristics, plastic deformation, and yield characteristics of the cylindrical shell were determined under the influence of the UNDEX shock wave. Subsequently, the failure mode of the cylindrical shell was analyzed to propose the dumbbell-shaped damage effect. The results revealed that when the UNDEX shock wave encounters a finite cylindrical shell, the fluid exhibits a perturbation such as pressure division, stress wave deflection, and flow in the surroundings of the circular cylinder. However, the fluid cannot produce a sizeable instantaneous displacement that yields certain strong constraints at both ends of the cylindrical shell. These constraints generate an irregular distribution of the flow field pressure, and the cylindrical shell tends to exhibit an “arch” deformation along the direction of shock wave propagation. Owing to the flow surrounding the circular cylinder, a negative pressure zone is generated in the flow field at both ends of the cylindrical shell, which induces a “sucking disc” shape at both ends of the cylindrical shell and ultimately produces a dumbbell-shaped damage effect. The present findings will aid in the structural design and impact resistance of submarines, unmanned undersea vehicles, and additional equipment under the impact load of the UNDEX.

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Sanders, Jacob, Girum Urgessa, and Rainald Löhner. "Literature Review on the Response of Concrete Structures Subjected to Underwater Explosions." CivilEng 2, no. 4 (October 11, 2021): 895–908. http://dx.doi.org/10.3390/civileng2040048.

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This paper presents a review of research on underwater explosions (UNDEX) with a focus on the structural response of concrete or reinforced concrete (RC) structures. First, the physical phenomena of UNDEX and its effects are discussed describing both the theory and considerations of the event. Then a brief description of the standard UNDEX experiment is followed by computational methods that employ governing equations that are used for verification of those methods. Lastly, a discussion on structural response for UNDEX is presented with a particular focus on concrete structures.

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O’Daniel, James L., Theodor Krauthammer, Kevin L. Koudela, and Larry H. Strait. "An UNDEX response validation methodology." International Journal of Impact Engineering 27, no. 9 (October 2002): 919–37. http://dx.doi.org/10.1016/s0734-743x(02)00014-3.

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Wang, Hao, Yuan Sheng Cheng, Jun Liu, and Lin Gan. "The Fluid-Solid Interaction Dynamics between Underwater Explosion Bubble and Corrugated Sandwich Plate." Shock and Vibration 2016 (2016): 1–21. http://dx.doi.org/10.1155/2016/6057437.

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Lightweight sandwich structures with highly porous 2D cores or 3D (three-dimensional) periodic cores can effectively withstand underwater explosion load. In most of the previous studies of sandwich structure antiblast dynamics, the underwater explosion (UNDEX) bubble phase was neglected. As the UNDEX bubble load is one of the severest damage sources that may lead to structure large plastic deformation and crevasses failure, the failure mechanisms of sandwich structures might not be accurate if only shock wave is considered. In this paper, detailed 3D finite element (FE) numerical models of UNDEX bubble-LCSP (lightweight corrugated sandwich plates) interaction are developed by using MSC.Dytran. Upon the validated FE model, the bubble shape, impact pressure, and fluid field velocities for different stand-off distances are studied. Based on numerical results, the failure modes of LCSP and the whole damage process are obtained. It is demonstrated that the UNDEX bubble collapse jet local load plays a more significant role than the UNDEX shock wave load especially in near-field underwater explosion.

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Nguyen, Anh-Tu. "A numerical research on the interaction between underwater explosion bubble and deformable structure using CEL technique." EUREKA: Physics and Engineering, no. 1 (January 19, 2023): 134–51. http://dx.doi.org/10.21303/2461-4262.2023.002637.

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The dynamic process of an underwater explosion (UNDEX) bubble in the vicinity of deformable structures is a complex phenomenon that has been studied by many researchers. The dynamic process of a UNDEX bubble is a complex transient problem that results in a highly distorted bubble and large deformation of the structure. The previous work has introduced various solutions for studying the interaction between the UNDEX bubble and deformable structure. The interaction between the bubble and nearby structures has been widely solved by the combination of the boundary element method (BEM) and the finite element method (FEM). However, this couple requires tight time-step controlling, long-time analysis, and large computer resources. Furthermore, this combination is not widely used as the FEM code in commercially available software for solving UNDEX bubble problems. This paper presents a coupled Eulerian-Lagrangian (CEL) approach in commercial software to deal with the fluid-structure interaction (FSI). The numerical model of a UNDEX bubble is first developed and verified by comparing results with experimental, BEM, and empirical data. Then both bubble behavior and structural deformation are examined in various case studies. The numerical results show that the stiffness of the structure has strongly influenced the bubble behavior and the water jet development. The pressure pulse becomes significantly large as the bubble collapse. Besides, this numerical approach also can reproduce crucial phenomena of a UNDEX bubble, such as the whipping effect and water jet attacks. Although the numerical model is developed using simplified boundary conditions, the proposed approach shows the feasibility of simulating the important features of a UNDEX bubble process as well as the response of nearby structures.

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Elsayed, Fathallah, Li Li Tong, Hui Qi, and Mahmoud Helal. "Finite Element Analysis of Deep Elliptical Submersible Pressure Hull Subjected to a Side-On Non-Contact Underwater Explosion." Applied Mechanics and Materials 578-579 (July 2014): 256–62. http://dx.doi.org/10.4028/www.scientific.net/amm.578-579.256.

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Predicting the dynamic response of a floating and submerged structure subjected to underwater explosion is greatly complicated by the explosion of a high explosive, propagation of shock wave, bubble-pulse, complex fluid-structure interaction phenomena and the dynamic behavior of the floating structures. A numerical simulation has been carried out to examine the behavior of elliptical submersible pressure hull to non-contact underwater explosion (UNDEX) and take the effect of bubble-pulse. The finite element package ABAQUS was used to model the UNDEX and the fluid-structure interaction (FSI) phenomena. The pressure wave resulting from an UNDEX was assumed to be a spherical wave. Plastic strain and the time histories of the wet-surface displacement, velocity and von Mises stress are presented. The analytical results are valuable for designing underwater vehicles to resist UNDEX.

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Nguyen, Anh Tu. "The Application of CEL Technique to Simulate the Behavior of an Underwater Explosion Bubble in the Vicinity of a Rigid Wall." Applied Mechanics and Materials 902 (September 2020): 126–39. http://dx.doi.org/10.4028/www.scientific.net/amm.902.126.

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The dynamic process of an underwater explosion (UNDEX) is a complex phenomenon that involves several facets. After detonation, the shockwave radially propagates at a high speed and strikes nearby structures. Subsequently, bubble oscillation may substantially damage the structures because of the whipping effect, water jet impact, and bubble pulse. This paper presents an application of explicit finite element analyses to simulate the process of an UNDEX bubble in the vicinity of rigid wall, in which the coupled Eulerian-Lagrangian (CEL) approach was developed to overcome the difficulties regarding the classical finite element method (FEM), large deformations, and flow simulation of fluid and gas. The results demonstrate that the method is well suited to manage the UNDEX bubble problem and can be used to model the major features of the bubble dynamics. Furthermore, the behavior of an UNDEX bubble near a rigid wall was also examined in the present study, which showed that the migration of the bubble and the development of the water jet are influenced strongly by the standoff distance between the initial bubble position and the wall. This method can be used in future studies to examine UNDEX bubbles in the vicinity of deformable and complex structures.

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Biglarkhani, Masoud, and Keyvan Sadeghi. "Incremental Explosive Analysis and Its Application to Performance-Based Assessment of Stiffened and Unstiffened Cylindrical Shells Subjected to Underwater Explosion." Shock and Vibration 2017 (2017): 1–17. http://dx.doi.org/10.1155/2017/3754510.

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Incremental explosive analysis (IEA) is addressed as an applicable method for performance-based assessment of stiffened and unstiffened cylindrical shells subjected to underwater explosion (UNDEX) loading. In fact, this method is inspired by the incremental dynamic analysis (IDA) which is a known parametric analysis method in the field of earthquake engineering. This paper aims to introduce the application of IEA approach in UNDEX in order to estimate different limit states and deterministic assessment of cylindrical shells, considering the uncertainty of loading conditions. The local, bay, and general buckling modes are defined as limit states for performance calculation. Different standoff distances and depth parameters combining several loading conditions are considered. The explosive loading intensity is specified and scaled in several levels to force the structure through the entire range of its behavior. The results are plotted in terms of a damage measure (DM) versus selected intensity measure (IM). The statistical treatment of the obtained multi-IEA curves is performed to summarize the results in a predictive mode. Finally, the fragility curves as damage probability indicators of shells in UNDEX loading are extracted. Results show that the IEA is a promising method for performance-based assessment of cylindrical shells subjected to UNDEX loading.

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Mair, Hans U. "Benchmarks for Submerged Structure Response to Underwater Explosions." Shock and Vibration 6, no. 4 (1999): 169–81. http://dx.doi.org/10.1155/1999/743708.

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Benchmarks for submerged structure response to underwater explosions (UNDEX) are compiled. Both analytical and empirical benchmarks are presented; each type has advantages and disadvantages for the purposes of model validation, though no methodology for employing these benchmarks in a model validation effort is proposed. Benchmark computations are also referenced as part of this compilation. Finally, extension of this compilation to the UNDEX response of internal equipment and floating structures, and to hydrodynamic/hydraulic ram problems, is proposed.

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Wu, Zongduo, Zhi Zong, and Lei Sun. "A Mie-Grüneisen mixture Eulerian model for underwater explosion." Engineering Computations 31, no. 3 (April 28, 2014): 425–52. http://dx.doi.org/10.1108/ec-03-2012-0065.

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Purpose – The purpose of this paper is to provide an improved Mie-Grüneisen mixture model to simulate underwater explosion (UNDEX). Design/methodology/approach – By using Mie-Grüneisen equations of state (EOS) to model explosive charge, liquid water and solid structure, the whole fluid field is considered as a multi-phases mixture under Mie-Grüneisen EOS. Then by introducing auxiliary variables in Eulerian model and using mass fraction to establish a diffusion balance, a new improved Mie-Grüneisen mixture model is presented here. For the new reconstructed mixture model, a second order MUSCL scheme with TVD limiter is employed to solve the multi-phase Riemann problem. Findings – Numerical examples show that the results obtained by Mie-Grüneisen mixture model are quite closed to theoretical and empirical data. The model can be also used in 2-D fluid-structure problem of UNDEX effectively and it is proved that the deformation of structure can be clearly described by mass fraction. Research limitations/implications – The FVM model based on mass fraction can only describe the motion of compressible material under impact. Material failure or large deformation needs a modification about the EOS or implementations of other models (i.e. FEM model). Originality/value – An improved non-oscillation Mie-Grüneisen mixture model, which based on mass fraction, is given in the present paper. The present Mie-Grüneisen mixture model provides a simplified and efficient way to simulate UNDEX. The feasibility of this model to simulate the detonation impacts on different mediums, including water and other metal mediums, is tested and verified here. Then the model is applied to the simulation of underwater contact explosion problem. In the simulation, deformation of structure under explosion loads, as well as second shock wave, are studied here.

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Wang, Gong Xian, and Yong Hu. "Advances in Shock Testing Facilities for Naval Shipboard Equipments." Advanced Materials Research 301-303 (July 2011): 1220–25. http://dx.doi.org/10.4028/www.scientific.net/amr.301-303.1220.

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The capability to withstand non-contact underwater explosions (UNDEX) is an important aspect to be emphasized in the design of modern warships, and shock testing is one of the efficient methods to qualify the ability. A brief history on the research of shock testing of naval shipboard equipment as well as major means in evaluating anti-shock performance of warship equipment is introduced first in this paper. Three prevailing shock test methods: UNDEX testing, virtual shock trial and land-based test with shock test machines are presented with the focus on the advances in shock test machines in US and Europe. Comparison of current shock testing facilities is also given. Moreover, some new concepts of shock test machines are reviewed as well, and three major directions of the development of shock test machines are concluded. The first trend is that shock testing machines are required to generate positive and negative shock pulse to simulate real UNDEX environment made up of shock wave followed by bubble pulse and structural whipping. The second is that shock test machines can test heavy equipments, and the last is that shock pulses can be controlled and customized conveniently.

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Helal, Huang, Fathallah, Wang, ElShafey, and Ali. "Numerical Analysis and Dynamic Response of Optimized Composite Cross Elliptical Pressure Hull Subject to Non-Contact Underwater Blast Loading." Applied Sciences 9, no. 17 (August 23, 2019): 3489. http://dx.doi.org/10.3390/app9173489.

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Among the most important problems confronted by designers of submarines is to minimize the weight, increase the payload, and enhance the strength of pressure hull in order to sustain the hydrostatic pressure and underwater explosions (UNDEX). In this study, a Multiple Intersecting Cross Elliptical Pressure Hull (MICEPH) subjected to hydrostatic pressure was first optimized to increase the payload according to the design requirements. Thereafter, according to the optimum design results, a numerical analysis for the fluid structure interaction (FSI) phenomena and UNDEX were implemented using nonlinear finite element code ABAQUS/Explicit. The propagation of shock waves through the MICEPH was analyzed and the response modes (breathing, accordion and whipping) were discussed. Furthermore, the acceleration, displacement and failure index time histories at different locations were presented. The results showed that the greatest acceleration occurred in the athwart direction, followed by the vertical and longitudinal directions. Additionally, the first bubble pulse has a major effect on athwart acceleration. Moreover, the analysis can be effectively used to predict and calculate the failure indices of pressure hull. Additionally, it provides an efficient method that reasonably captures the dynamic response of a pressure hull subjected to UNDEX.

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Kim, Hyeongjun, Gulgi Choi, Yangsub Na, Kyung Hoon Park, and Hyun Chung. "An Experimental Study on UNDEX Characteristics of Airbag Inflators." Journal of the Society of Naval Architects of Korea 54, no. 5 (October 31, 2017): 439–46. http://dx.doi.org/10.3744/snak.2017.54.5.439.

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Kim, Hyunwoo, and Joonmo Choung. "Shock-Resistance Responses of Frigate Equipments by Underwater Explosion." Journal of Ocean Engineering and Technology 36, no. 3 (June 30, 2022): 161–67. http://dx.doi.org/10.26748/ksoe.2022.008.

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Three-dimensional finite element analysis (3D-FEA) models have been used to evaluate the shock-resistance responses of various equipments, including armaments mounted on a warship caused by underwater explosion (UNDEX). This paper aims to check the possibility of using one-dimensional (1D) FEA models for the shock-resistance responses. A frigate was chosen for the evaluation of the shock-resistance responses by the UNDEX. The frigate was divided into the thirteen discrete segments along the length of the ship. The 1D Timoshenko beam elements were used to model the frigate. The explosive charge mass and the stand-off distance were determined based on the ship length and the keel shock factor (KSF), respectively. The UNDEX pressure fields were generated using the Geers-Hunter doubly asymptotic model. The pseudo-velocity shock response spectrum (PVSS) for the 1D-FEA model (1D-PVSS) was calculated using the acceleration history at a concerned equipment position where the digital recursive filtering algorithm was used. The 1D-PVSS was compared with the 3D-PVSS that was taken from a reference, and a relatively good agreement was found. In addition, the 1D-PVSS was compared with the design criteria specified by the German Federal Armed forces, which is called the BV043. The 1D-PVSS was proven to be relatively reasonable, reducing the computing cost dramatically.

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Rong, Ji Li, Da Lin Xiang, and Jian Li. "Effects of Steel Case on Underwater Shock Wave." Applied Mechanics and Materials 52-54 (March 2011): 943–48. http://dx.doi.org/10.4028/www.scientific.net/amm.52-54.943.

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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.

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Lu, Zhaokuan, and Alan Brown. "Application of the Spectral Element Method in a Surface Ship Far-Field UNDEX Problem." Shock and Vibration 2019 (July 25, 2019): 1–16. http://dx.doi.org/10.1155/2019/7463134.

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The prediction of surface ship response to a far-field underwater explosion (UNDEX) requires the simulation of shock wave propagation in the fluid, cavitation, fluid-structure interaction, and structural response. Effective approaches to model the fluid include cavitating acoustic finite element (CAFE) and cavitating acoustic spectral element (CASE) methods. Although the spectral element method offers the potential for greater accuracy at lower computational cost, it also generates more spurious oscillations around discontinuities which are difficult to avoid in shock-related problems. Thus, the advantage of CASE remains unproven. In this paper, we present a 3D-partitioned FSI framework and investigate the application of CAFE and CASE to a surface ship early-time far-field UNDEX problem to determine which method has the best computational efficiency for this problem. We also associate the accuracy of the structural response with the modeling of cavitation distribution. A further contribution of this work is the examination of different nonmatching mesh information exchange schemes to demonstrate how they affect the structural response and improve the CAFE/CASE methodologies.

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XIE, WENFENG, TIEGANG LIU, and YIN-LU YOUNG. "THE EFFECT OF SURFACE CURVATURE ON UNDEX-INDUCED HULL CAVITATION." Modern Physics Letters B 23, no. 03 (January 30, 2009): 253–56. http://dx.doi.org/10.1142/s0217984909018138.

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Hull cavitation evolution induced by an underwater explosion (UNDEX) near a deformable steel structure is numerically investigated using a multiphase compressible fluid solver1-3 coupled with an unsteady one-fluid cavitation model4,5. A series of computations are conducted with varying structure surface curvature. Results suggest that structure surface curvature influence the peak pressures generated from the shock impact and cavitation collapse; a concave-designed surface not only causes local shock focus but also enhances the subsequent cavitation reload.

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Si, Nan, Zhaokuan Lu, and Alan Brown. "Coupling with the Embedded Boundary Method in a Runge-Kutta Discontinuous-Galerkin Direct Ghost-Fluid Method (RKDG-DGFM) Framework for Fluid-Structure Interaction Simulations of Underwater Explosions." Journal of Marine Science and Engineering 9, no. 12 (December 3, 2021): 1375. http://dx.doi.org/10.3390/jmse9121375.

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Solution of near-field underwater explosion (UNDEX) problems frequently require the modeling of two-way coupled fluid-structure interaction (FSI). This paper describes the addition of an embedded boundary method to an UNDEX modeling framework for multiphase, compressible and inviscid fluid using the combined algorithms of Runge-Kutta, discontinuous-Galerkin, level-set and direct ghost-fluid methods. A computational fluid dynamics (CFD) solver based on these algorithms has been developed as described in previous work. A fluid-structure coupling approach was required to perform FSI simulation interfacing with an external structural mechanics solver. Large structural deformation and possible rupture and cracking characterize the FSI phenomenon in an UNDEX, so the embedded boundary method (EBM) is more appealing for this application in comparison to dynamic mesh methods such as the arbitrary Lagrangian-Eulerian (ALE) method to enable the fluid-structure coupling algorithm in the fluid. Its limitation requiring a closed interface that is fully submerged in the fluid domain is relaxed by an adjustment described in this paper so that its applicability is extended. Two methods of implementing the fluid-structure wall boundary condition are also compared. The first solves a local 1D fluid-structure Riemann problem at each intersecting point between the wetted elements and fluid mesh. In this method, iterations are required when the Tait equation of state is utilized. A second method that does not require the Riemann solution and iterations is also implemented and the results are compared.

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Klenow, B., and A. Brown. "Prevention of Pressure Oscillations in Modeling a Cavitating Acoustic Fluid." Shock and Vibration 17, no. 2 (2010): 137–59. http://dx.doi.org/10.1155/2010/904390.

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Cavitation effects play an important role in the UNDEX loading of a structure. For far-field UNDEX, the structural loading is affected by the formation of local and bulk cavitation regions, and the pressure pulses resulting from the closure of the cavitation regions. A common approach to numerically modeling cavitation in far-field underwater explosions is Cavitating Acoustic Finite Elements (CAFE) and more recently Cavitating Acoustic Spectral Elements (CASE). Treatment of cavitation in this manner causes spurious pressure oscillations which must be treated by a numerical damping scheme. The focus of this paper is to investigate the severity of these oscillations on the structural response and a possible improvement to CAFE, based on the original Boris and Book Flux-Corrected Transport algorithm on structured meshes [6], to limit oscillations without the energy loss associated with the current damping schemes.

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Fathallah, Elsayed, Hui Qi, Lili Tong, and Mahmoud Helal. "Numerical Simulation and Response of Stiffened Plates Subjected to Noncontact Underwater Explosion." Advances in Materials Science and Engineering 2014 (2014): 1–17. http://dx.doi.org/10.1155/2014/752586.

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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.

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ZHANG, ZhenHua, XiuFeng HUANG, BangYi HAN, BaoChong REN, Xing JIN, JiHang WU, and YuanXin WANG. "The protective mechanism of pyramid lattice on submarine subjected to undex." SCIENTIA SINICA Physica, Mechanica & Astronomica 51, no. 12 (June 21, 2021): 124606. http://dx.doi.org/10.1360/sspma-2020-0373.

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Kumar, Y. Pawan, N. K. Gupta, Y. Sreenivas Rao, and Bhagirath Kant. "On Shock Response of Marine Sandwich Structures Subjected to UNDEX Loading." Procedia Engineering 173 (2017): 1932–42. http://dx.doi.org/10.1016/j.proeng.2016.12.255.

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Si, Nan, and Alan Brown. "A Framework of Runge–Kutta, Discontinuous Galerkin, Level Set and Direct Ghost Fluid Methods for the Multi-Dimensional Simulation of Underwater Explosions." Fluids 7, no. 1 (December 29, 2021): 13. http://dx.doi.org/10.3390/fluids7010013.

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This work describes the development of a hybrid framework of Runge–Kutta (RK), discontinuous Galerkin (DG), level set (LS) and direct ghost fluid (DGFM) methods for the simulation of near-field and early-time underwater explosions (UNDEX) in early-stage ship design. UNDEX problems provide a series of challenging issues to be solved. The multi-dimensional, multi-phase, compressible and inviscid fluid-governing equations must be solved numerically. The shock front in the solution field must be captured accurately while maintaining the total variation diminishing (TVD) properties. The interface between the explosive gas and water must be tracked without letting the numerical diffusion across the material interface lead to spurious pressure oscillations and thus the failure of the simulation. The non-reflecting boundary condition (NRBC) must effectively absorb the wave and prevent it from reflecting back into the fluid. Furthermore, the CFD solver must have the capability of dealing with fluid–structure interactions (FSI) where both the fluid and structural domains respond with significant deformation. These issues necessitate a hybrid model. In-house CFD solvers (UNDEXVT) are developed to test the applicability of this framework. In this development, code verification and validation are performed. Different methods of implementing non-reflecting boundary conditions (NRBCs) are compared. The simulation results of single and multi-dimensional cases that possess near-field and early-time UNDEX features—such as shock and rarefaction waves in the fluid, the explosion bubble, and the variation of its radius over time—are presented. Continuing research on two-way coupled FSI with large deformation is introduced, and together with a more complete description of the direct ghost fluid method (DGFM) in this framework will be described in subsequent papers.

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Grządziela, Andrzej, and Marcin Kluczyk. "Preliminary Calculations for Minehunter's Genset Foundations." Transactions on Maritime Science 8, no. 1 (April 20, 2019): 54–61. http://dx.doi.org/10.7225/toms.v08.n01.006.

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The requirements for the foundations of naval vessel engines are based on classification rules devised by classification societies or/and military standardization rules. A class guideline was published, defining the requirements, acceptance criteria and machinery seating methods. There is also a schedule of basic calculation procedures for cast resin or rubber chocks which facilitates the process of machinery foundation design, preloading force calculation, the establishment of boundary conditions etc. In case of naval vessels, typical procedures do not meet tactical requirements due to potential explosion loads. Since minehunters are mainly deployed at sea, handling active, naval mines, the shock resistance calculation for the entire machinery, including the Genset, is required. The paper presents preliminary MatLab calculation methods which can be used to analyse the type, number and location of rubber or elastomer chocks. The procedure consists of input data such as UNDEX pressure and technical data of the Genset used in the Polish Navy. Calculation results include the analysis of the dynamic interaction between the Genset and the foundation, as well as the damping effect generated by the UNDEX (UNDerwater EXplosion) shock pulse.

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Park, Il-Kwon, Jong-Chul Kim, Chin-Woo An, and Dae-Seung Cho. "Measurement of Naval Ship Responses to Underwater Explosion Shock Loadings." Shock and Vibration 10, no. 5-6 (2003): 365–77. http://dx.doi.org/10.1155/2003/803475.

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The shock-resistance capability of battle ships against a non-contact underwater explosion (UNDEX) is a very critical factor of survivability. In July 1987 and April 2000, we successfully conducted UNDEX shock tests for a coastal mine hunter (MHC) and a mine sweeper/hunter (MSH) of Republic of Korea Navy (ROKN), at the Chinhae bay, Korea. Test planning for conducting these shock tests included responsibilities, methods, and procedures. Test instruments were developed and tested on a drop shock machine to confirm availability in the actual shock tests with emphasis on shock resistance, remote control and reliability. All vital systems of the ships were confirmed to be capable of normal operational condition without significant damages during the explosion shot. By analyzing the test results, the tactical operational safety zone of the ships in underwater explosion environments was estimated. In this paper, we described the results of measurement of naval ship responses to underwater explosion shock loadings including test planning, sensor locations, data reduction, explosive devices, instrumentation and damage assessments of MSH.

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Si, Nan, Jinwon Park, and Alan J. Brown. "A Direct Ghost Fluid Method for Modeling Explosive Gas and Water Flows." Shock and Vibration 2022 (April 16, 2022): 1–19. http://dx.doi.org/10.1155/2022/1627382.

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This work presents a Direct Ghost Fluid Method (DGFM) as part of a two-fluid numerical framework suitable to model explosive gas and water flows resulting from underwater explosion (UNDEX). Due to the presence of explosive gas and water with shock waves in the modeling domain, classic Eulerian methods with inherent diffusion may not be effective. Numerical diffusion occurs due to nonphysical diffused density at material interfaces, which creates spurious pressure oscillations and significantly degrades the quality of the numerical results. To eliminate or minimize numerical diffusion, sharp interface methods having no mixed elements may be used in multifluid flow computations. The Direct Ghost Fluid Method (DGFM) described in this paper uses direct extrapolation of density (vice pressure) and tangential velocity from real to ghost fluid. The spurious pressure oscillations near the material interface are therefore minimized. One-, two-, and three-dimensional computational fluid dynamics (CFD) solvers that have DGFM as an essential part in their framework to model UNDEX interface conditions are developed, explored, and applied to the simulation of a series of benchmark problems. Excellent agreement is obtained among the simulations, the analytical solutions, and the experiments.

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Grządziela, Andrzej, and Marcin Kluczyk. "Shock Absorbers Damping Characteristics by Lightweight Drop Hammer Test for Naval Machines." Materials 14, no. 4 (February 6, 2021): 772. http://dx.doi.org/10.3390/ma14040772.

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The technical requirements for naval ships machine foundations are far more strict in comparison to merchant’s vessels. These requirements are confirmed in the military standardization of many countries. Underwater Explosion (UNDEX phenomena) detonation pulses, force naval engineers to design and implement different shock absorbers made from a wide variety of materials. This study presents the tests results of typical shock absorber designs made of various types of rubber and elastomers. The initial objective of the study was to determine the energy absorption of shock impacts, the choice of materials capable of operating within the temperature range of 0 °C to 70 °C, resistance to contact with oils and marine fuel, performance at frequencies ranging from 5 to 30,000 Hz, and absorption no less than 40% of harmonic vibration energy. Initial studies conducted on tensile testing machine were used to determine the static and dynamic stiffness of a shock absorbers. Considerations of stiffness coefficient for the linear and nonlinear range is typical for shock pulses. Further tests were carried out on a lightweight drop hammer to determine the characteristics of the damping coefficient for high-speed wave interactions—Shock Response Spectrum (SRS). The final aim of the study was to assess the repeatability of the shock absorbers response to multiple impact loads. Mechanical properties describing possibilities of tested dampers materials to absorb energy of UNDEX were also presented.

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Xu, Liang, and Tiegang Liu. "Modified Ghost Fluid Method as Applied to Fluid-Plate Interaction." Advances in Applied Mathematics and Mechanics 6, no. 01 (February 2014): 24–48. http://dx.doi.org/10.4208/aamm.2012.m50.

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AbstractThe modified ghost fluid method (MGFM) provides a robust and efficient interface treatment for various multi-medium flow simulations and some particular fluid-structure interaction (FSI) simulations. However, this methodology for one specific class of FSI problems, where the structure is plate, remains to be developed. This work is devoted to extending the MGFM to treat compressible fluid coupled with a thin elastic plate. In order to take into account the influence of simultaneous interaction at the interface, a fluid-plate coupling system is constructed at each time step and solved approximately to predict the interfacial states. Then, ghost fluid states and plate load can be defined by utilizing the obtained interfacial states. A type of acceleration strategy in the coupling process is presented to pursue higher efficiency. Several one-dimensional examples are used to highlight the utility of thismethod over looselycoupled method and validate the acceleration techniques. Especially, this method is applied to compute the underwater explosions (UNDEX) near thin elastic plates. Evolution of strong shock impacting on the thin elastic plate and dynamic response of the plate are investigated. Numerical results disclose that this methodology for treatment of the fluid-plate coupling indeed works conveniently and accurately for different structural flexibilities and is capable of efficiently simulating the processes of UNDEX with the employment of the acceleration strategy.

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Li, L.-J., W.-K. Jiang, and Y.-H. Ai. "Experimental Study on Deformation and Shock Damage of Cylindrical Shell Structures Subjected to Underwater Explosion." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224, no. 11 (April 12, 2010): 2505–14. http://dx.doi.org/10.1243/09544062jmes2092.

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The security evaluation of some structures shocked by an underwater explosion (UNDEX) frequently plays a key role in some cases, and it is necessary to accurately predict the damage condition of the structure in an UNDEX environment. This study investigates the dynamic linear and non-linear responses and shock damages of two kinds of submerged cylindrical shell models exposed to underwater spherical trinitrotoluene (TNT) charge explosions in a circular lake. Two endplates and a middle plate are mounted on the cylindrical shells to provide support and to create two enclosed spaces. The two kinds of cylindrical shell models with the same geometry characteristics are unfilled and main hull sand-filled. Fifteen different tests are carried out by changing the TNT explosive weights of 1 and 2 kg, standoff distances ranging from 3 to 0.3 m, and two explosion positions. Measured experimental results are compared with each other, and some transformed data are obtained. A detailed discussion on experimental results shows that the dynamic responses and damage modes are much different, and the main hull sand-filled cylindrical shell is more difficult to be damaged by the shock wave loading than the unfilled model. Edge cracks are mainly observed at the instrument hull of the main hull sand-filled model, but surface tearing and cracks are observed on both the main hull and the instrumental hull of the unfilled model, respectively.

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Lee, Sang-Gab, Jeong-Il Hwon, and Jung-Hoon Chung. "Integrated Structural Dynamic Response Analysis considering the UNDEX Shock Wave and Gas Bubble Pulse." Journal of the Society of Naval Architects of Korea 44, no. 2 (April 20, 2007): 148–53. http://dx.doi.org/10.3744/snak.2007.44.2.148.

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Elsayed, Fathallah, Hui Qi, Li Li Tong, and Mahmoud Helal. "Optimal Configuration for Stiffened Plates under the Effect of Underwater Explosion." Materials Science Forum 813 (March 2015): 161–68. http://dx.doi.org/10.4028/www.scientific.net/msf.813.161.

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The dynamic response of a floating structure subjected to underwater explosion is greatly complicated by the explosion of a high explosive, propagation of shock wave, complex fluid–structure interaction phenomena, and the dynamic behavior of the floating structures. A numerical investigation has been carried out to examine the behavior of stiffened steel plates subjected to shock loads resulting from an Underwater Explosion (UNDEX). The aim of this work is to obtain the optimal configuration to resist underwater shock loading. A non-linear dynamic numerical analysis of the underwater explosion phenomena associated with different geometrical stiffened steel plates is performed using the ABAQUS/Explicit finite element program. Special emphasis is focused on the evolution of mid-point displacements. Further investigations have been performed to study the effect of including material damping and the rate-dependant material properties at different shock loads. The results indicate that stiffener configurations and shock loads affect greatly the overall performance of steel plates and sensitive to the material data.

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LI Haifang, 李海防, 卫伟 WEI Wei, 陈瑾 CHEN Jin, 李旭春 LI Xuchun, and 张佰林 ZHANG Bailin. "Research on soil erosion based on Location-weighted landscape undex(LWLI) in Guanchuanhe River basin, Dingxi, Gansu Province." Acta Ecologica Sinica 33, no. 14 (2013): 4460–67. http://dx.doi.org/10.5846/stxb201212191821.

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WANG, Yu, and ZhenHua ZHANG. "“Blade effect” on the overall damage of hull girder caused by near field undex shock wave." SCIENTIA SINICA Physica, Mechanica & Astronomica 45, no. 5 (April 1, 2015): 054701. http://dx.doi.org/10.1360/sspma2014-00462.

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Shin, Y. S., M. Lee, K. Y. Lam, and K. S. Yeo. "Modeling Mitigation Effects of Watershield on Shock Waves." Shock and Vibration 5, no. 4 (1998): 225–34. http://dx.doi.org/10.1155/1998/782032.

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The object of this analysis is to investigate mitigation effects of watershield on air blast waves. To examine the water mitigation concept, features of the free-field detonation process are studied from a series of one-dimensional simulations using a multimaterial Eulerian finite element technique. Five different shock Hugoniots for water are compared, and the most accurate data are suggested. To verify the numerical procedure, results are compared with available experimental data for UNDEX problem and analytical predictions for air shocks. For the case of contact watershield, the magnitude of peak pressure generally decreases and the shock arrival time increases with increasing thickness of watershield. The total pressure impulse is reduced significantly at near field. Non-contact watershield was also examined, and was found to provide a better design criterion based on the further decay of peak pressure.

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Chen, Yingyu, Xiongliang Yao, and Xiongwei Cui. "A Numerical and Experimental Study of Wall Pressure Caused by an Underwater Explosion Bubble." Mathematical Problems in Engineering 2018 (August 23, 2018): 1–10. http://dx.doi.org/10.1155/2018/6139510.

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The bubble dynamics behaviors and the pressure in the wall center are investigated through experimental method and numerical study. In the experiment, the dynamics of an underwater explosion (UNDEX) bubble beneath a rigid wall are captured by high-speed camera and the wall pressure in the wall center is measured by pressure transducer. To reveal the process and mechanism of the pressure on a rigid wall during the first bubble collapse, numerical studies based on boundary element method (BIM) are applied. Numerical results with two different stand-off parameters (γ=0.38 and γ=0.90) show excellent agreement with experiment measurements and observations. According to the experimental and the numerical results, we can conclude that the first peak is caused by the reentrant jet impact and the following splashing effect enlarged the duration of the first jet impact. When γ=0.38, the splashing jet has a strong impact on the minimum volume bubble, a number of tiny bubbles, formed like bubble ring, are created and collapse more rapidly owing to the surrounding high pressure and emit multi shock waves. When γ=0.90, the pressure field around the bubble is low enough only a weak rebounding bubble peak occurs.

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Xiao, Feng, Yong Chen, Yu Wang, Hongxing Hua, and Dawei Zhu. "Experimental Research on the Dynamic Response of Floating Structures with Coatings Subjected to Underwater Explosion." Shock and Vibration 2014 (2014): 1–13. http://dx.doi.org/10.1155/2014/705256.

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This paper presents an experimental investigation into the dynamic response of three free floating stiffened metal boxes with protective coatings subjected to underwater explosion (UNDEX). One box was kept intact while the other two were, respectively, covered with monolithic coatings and chiral honeycomb coatings. Three groups of live fire tests with different attack angles and stand-off distances were conducted. The acceleration on the stiffener and strain peak on the bottom hull were selected as the major comparative criterions. Test results show that the impulse transmitted to the structure at the initial stage can be reduced, owing to the coating flexibility and fluid-structure interaction mechanism. Consequently, the acceleration peaks induced by both shock wave and bubble pulse were reduced. The shock environment can be more effectively improved by honeycomb coating when compared with monolithic coating. Most of the strain peaks decreased to a certain extent, but some of them were notably manifested, especially for honeycomb coating. The test affirms the fact that soft coating can cause stress concentration on the shell that is in direct contact with the coating due to the impedance mismatch between the interfaces of materials. A softer rubber coating induces a greater magnitude of strain.

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Saffari, Mohsen, Mohammad Kazem Emami Meybodi, Ghader Ghanizadeh, and Harold G. Koenig. "DETERMINANTS OF HEALTH STATUS AMONG PATIENTS WITH KNEE OR HIP OSTEOARTHRITIS: THE ROLE OF DEMOGRAPHIC, CLINICAL AND HEALTH RELATED QUALITY OF LIFE VARIABLES." Journal of Musculoskeletal Research 17, no. 01 (March 2014): 1450004. http://dx.doi.org/10.1142/s0218957714500043.

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Osteoarthritis (OA) is a common chronic disease especially among older adults and has a considerable negative impact on health status (HS). This study investigated associations between demographic, clinical and health related quality of life (HRQOL) factors and the HS of patients with knee or hip OA. We surveyed a convenience sample of 356 patients from two general hospitals in Tehran, Iran. The short form health survey (SF-12), EuroQol (EQ-5D) and a demographic questionnaire were administered. Clinical variables such as body mass undex (BMI), duration of disease and radiographic evidence of the severity of OA were also collected. Two hierarchical regression models identified independent factors related to HS. The mean age of participants was 63.0 (SD, 12.3) and majority were female (90.7%). More than three-quarters were overweight or obese and over two-thirds had an OA severity grade of 3 or 4 based on Kellgren–Lawrence scale. The mean score on the physical and mental components of the SF-12 were 30.50 (SD, 9.63) and 44.38 (SD, 8.64), respectively. The mean scores for HS were 0.47 (SD, 0.34) on the EQ-5D and 63.23 (SD 17.58) on the EQ-VAS. Residence, duration of disease, BMI, OA joint, pain, vitality and mental health (MH) were identified as significant predictors of HS. Future studies are needed to better understand factors that may affect the HS of patients with knee or hip OA.

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Delaney, Danielle. "Under Coyote’s Mask: Environmental Law, Indigenous Identity, and #NoDAPL." Michigan Journal of Race & Law, no. 24.2 (2019): 299. http://dx.doi.org/10.36643/mjrl.24.2.under.

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This Article studies the relationship between the three main lawsuits filed by the Standing Rock Sioux Tribe, the Cheyenne River Sioux Tribe, and the Yankton Sioux Tribe against the Dakota Access Pipeline (DaPL) and the mass protests launched from the Sacred Stone and Oceti Sakowin protest camps. The use of environmental law as the primary legal mechanism to challenge the construction of the pipeline distorted the indigenous demand for justice as U.S. federal law is incapable of seeing the full depth of the indigenous worldview supporting their challenge. Indigenous activists constantly re-centered the direct actions and protests within indigenous culture to remind non-indigenous activists and the wider media audience that the protests were an indigenous protest, rather than a purely environmental protest, a distinction that was obscured as the litigation progressed. The NoDAPL protests, the litigation to prevent the completion and later operation of the pipeline, and the social movement that the protests engendered, were an explosive expression of indigenous resistance—resistance to systems that silence and ignore indigenous voices while attempting to extract resources from their lands and communities. As a case study, the protests demonstrate how the use of litigation, while often critical to achieving the goals of political protest, distorts the expression of politics not already recognized within the legal discourse.

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Lizcová, Zuzana. "Unter Druck." osteuropa 71, no. 4-6 (2021): 147. http://dx.doi.org/10.35998/oe-2021-0031.

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Homanyuk, Mykola. "Unter Besatzung." osteuropa 73, no. 1-2 (2023): 69. http://dx.doi.org/10.35998/oe-2023-008.

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Ščerbakova, Irina. "Memorial unter Druck." osteuropa 70, no. 3-4 (2020): 215. http://dx.doi.org/10.35998/oe-2020-0026.

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Phukan, Jatin. "Inequality in Under-Nutrition among Under-Five Children in Lakhimpur District of Assam." Indian Journal of Pure & Applied Biosciences 10, no. 2 (April 30, 2022): 57–65. http://dx.doi.org/10.18782/2582-2845.8895.

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Children of today are citizens of tomorrow, hence improving nutritional status among children becomes extremely important for all the nations. The raw data collected from the Lakhimpur district reveals that the burden of overall nutritional deficiency among children is still too high; on average, two in every five (37%) children had at least one kind of nutritional deficiency. However, the nutritional status of female children has improved over time compared to the male children, but the overall decline is not satisfactory. We have observed a higher inequality of nutritional deficiency among children in Assam by household wealth status (Gini value= 0.498) compared to the mother's education level (Gini value = 0.067). Therefore, it's an urgent need to expand the scope of the ICDS program to provide mass nutrition and health education by making provisions for home visits and primarily targeting pregnant and lactating mothers.

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Mishra, Alka, and S. L. Swamy S.L. Swamy. "Productivity of Wheat Under Five Promising Populus Deltoides Clones Under an Agrisilviculture Sysytem." International Journal of Scientific Research 3, no. 3 (June 1, 2012): 1–2. http://dx.doi.org/10.15373/22778179/march2014/135.

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Gómez-Rodríguez, Víctor-Gustavo, and Roberto Tolozano-Benites. "LA AUTONOMÍA UNIVERSITARIA A DEBATE." Identidad Bolivariana 6, no. 1 (January 31, 2022): 1–6. http://dx.doi.org/10.37611/ib6ol11-6.

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Academic freedom and institutional autonomy, from all its edges, are not a privilege. Responsible university autonomy is a condition for the development of each institution of higher education and of the country itself. Today there is a debate about what should be the University of the 21st century in Ecuador and what role or roles should be adopted, depending on the autonomy, to each of the actors of the Higher Education System (SES).

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Gallardo, Luis H. "Ryser's conjecture under linear constraints." Algebra and Discrete Mathematics 33, no. 1 (2022): 30–37. http://dx.doi.org/10.12958/adm1791.

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Amin, Tariq, and Prof MC Dubey. "Development of Srinagar under Ashoka." International Journal of Trend in Scientific Research and Development Volume-3, Issue-2 (February 28, 2019): 472–73. http://dx.doi.org/10.31142/ijtsrd21388.

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Dey, Rajiv. "Farmer Distress Under Market Reforms." International Journal of Scientific Research 2, no. 9 (June 1, 2012): 88–89. http://dx.doi.org/10.15373/22778179/sep2013/31.

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Schmidt, Christoph. "Ikonen aus vierfacher Sicht." Jahrbücher für Geschichte Osteuropas 56, no. 4 (2008): 571–80. http://dx.doi.org/10.25162/jgo-2008-0005.

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Journal articles on the topic 'UNDEX'

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