• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.1
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• pp.98-103
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• 2017

In this paper, determination method for drag force and drag coefficient from results of firing test is described. The drag force and drag coefficient are determined through inverse operation of 2-dimensional projectile equation of motion. Determination method was verified by comparing analytical drag coefficient with data from flight test. Analysis of drag coefficient and drag reduction was performed with the data of flight test using artillery projectiles with base bleed unit.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.495-509
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• 2019

The objective of this study is to analyze the compressibility effects of multiphase cavitating flow during the water-entry process. For this purpose, the water-entry of a projectile at transonic speed is investigated computationally. A temperature-adjusted Tait equation is used to describe the compressibility effects in water, and air and vapor are treated as ideal gases. First, the computational methodology is validated by comparing the simulation results with the experimental measurements of drag coefficient and the theoretical results of cavity shape. Second, based on the computational methodology, the hydrodynamic characteristics of flow are investigated. After analyzing the cavitating flow in compressible and incompressible fluids, the characteristics under compressible conditions are focused upon. The results show that the compressibility effects play a significant role in the development of cavitation and the pressure inside the cavity. More specifically, the drag coefficient and cavity size tend to be larger in the compressible case than those in the incompressible case. Furthermore, the influence of entry velocities on the hydrodynamic characteristics is investigated to provide an insight into the compressibility effects on cavitating flow. The results show that the drag coefficient and the impact pressure vary with the entry velocity, and the prediction formulas for drag coefficient and impact pressure are established respectively in the present study.

• Steel and Composite Structures
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• v.44 no.2
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• pp.225-240
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• 2022

Local responses of steel plate-concrete composite (SC) walls under impact loads are typically evaluated using design equations available in the AISC N690s1-15. These equations enable design of impact-resistant SC walls, but some essential parts such as the effects of wall size and shear reinforcement ratio have not been addressed. Also, since they were developed for design basis events, improved equations are required for accurate prediction of the impact behaviors of SC walls for beyond design basis impact evaluation. This paper presents a numerical study to construct a robust numerical model of SC walls subjected to impact loads to reasonably predict the SC-wall impact behavior, to evaluate the findings observed from the impact tests including the effects of the key design parameters, and to assess the actual responses of full-scale SC walls. The numerical calculations are validated using intermediate-scale impact tests performed previously. The influences of the fracture energy of concrete and the conservative aspects of the current design equations are discussed carefully. Recommendations are made for design practice.

• Advances in aircraft and spacecraft science
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• v.9 no.2
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• pp.119-130
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• 2022

Supersonic projectiles like rockets, missiles, or aircraft find various applications in the field of defense. The shape of the wings is mainly designed as wedge shape or delta wings for supersonic vehicles. The study of supersonic flows over the wedges and flat plate delta wings around the large scale of incidence angle is considered in the supersonic projectile. In the present paper, the prime attention is to study the pressure at the nose of the plane wedge over the various Mach number and the various angles of incidence. Ghosh piston theory is used to obtain the pressure distribution analytically, and the results are compared with CFD analysis results. The wedge angle and Mach number are the parameters considered for the research work. The range of wedge angle is 50 to 250, and Mach number is 1.5 to 4.0 are considered for the current research work. The analytical results show excellent agreement with the CFD results. The results show that both the parameters wedge angle and Mach number are influential parameters to vary the static pressure. The static pressure increases with an increase in Mach number and wedge angle.

• Composites Research
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• v.22 no.2
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• pp.18-23
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• 2009

Failure of Kevlar29/Phenolic composite plate under high velocity impact of FSP(Fragment Simulation Projectile) is investigated using a non-linear explicit finite element code, LS-DYNA. Composite laminate and impactor are idealized by solid element and interface between laminas are modeled by tied-break element in LS-DYNA. Interaction between impactor and laminate is simulated face-to-face eroding contact algorithm. When the stress level meets a failure criteria, the layer in the element is eroded. Numerical results are verified by existing test results.

• Structural Engineering and Mechanics
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• v.87 no.2
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• pp.107-116
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• 2023

The three-dimensional Hashin criterion and user subroutine VUMAT were used to simulate the damage in the composite layer, and the secondary stress criterion was used to simulate the interlayer failure of the cohesive element of the bonding layer and the propagation characteristics under the layer. The results showed that when the shear stress wave (shear wave) propagates on the surface of the laminate, the stress wave attenuation along the fiber strength direction is small, and thus producing a large stress profile. When the compressive stress wave (longitudinal wave) is transmitted between the layers, it is reflected immediately instead of being transmitted immediately. This phenomenon occurs only when the energy has accumulated to a certain degree between the layers. The transmission of longitudinal waves is related to the thickness and the layer orientation. Along the symmetry across the thickness direction, the greater is the stress amplitude along the layer direction. Based on the detailed investigation on the impact on various laminated composites carried out in this paper, the propagation characteristics of stress waves, the damage and the destruction of laminates can be explained from the perspective of stress waves and a reasonable layering sequence of the composite can be designed against damage and failure from low velocity impact.

• Structural Engineering and Mechanics
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• v.84 no.2
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• pp.167-180
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• 2022

A strategic structure when exposed to direct hit of conventional bomb/projectile are severely damaged because of large amounts of energy released by the impact and penetration of bomb. When massive concrete slabs suffer a direct hit, the energy released during impact and penetration process are able to easily break up large mass of concrete. When over stressed under such impact of bombs, the concrete structure fails showing brittle behavioural nature. This paper is intended to study and suggest the protective measures for structures used for strategic application by adopting a means to dissipate the large quantum of energy released. To quantitatively evaluate the force, displacement and energy in such scenario, a fine numerical model of the proposed layered structure of different combinations was built in ANSYS programme in which tri-nitrotoluene (TNT) explosive was detonated at penetration depth calculated for GP1000 Lbs bomb. The distinct blast mitigation effect of the proposed structure was demonstrated by adopting various layers/barriers created as protective measures for the strategic structure. The calculated result shows that the blast effect on the structure is potentially reduced due to provision of buster slab with sand cushioning provided as protective measure to the main structure. This concept of layered protective measures may be adopted for safeguarding strategic structures such as Domes, Tunnels and Underground Structures.

• Advances in concrete construction
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• v.16 no.2
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• pp.119-126
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• 2023

Steel fiber reinforced self-compacting concrete (SFRSCC) has good workability such as high flowability and good cohesiveness. The workability, compressive strength, splitting tensile strength, and anti-penetration characteristics of three kinds of SFRSCC were investigated in this paper. The fraction of steel fibers of the SFRSCC is 0.5%, 1.5% and 2.0% respectively. The results of the static tests show that the splitting tensile strength increases with the increase of fraction of steel fibers, while the compressive strength of 1.5% SFRSCC is lowest. It is demonstrated that the anti-penetration ability of 1.5% SFRSCC subjected to a velocity projectile (200-500 m/s) is better than 0.5% and 2.0% SFRSCC according to the experimental results. Considering the steel fiber effects, the existing formula is revised to predict penetration depth, and it is revealed that the revised predicted depth of penetration is in good agreement with the experimental results. The conclusion of this paper is helpful to the experimental investigations and engineering application.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.2
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• pp.161-167
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• 2016

In this study, the effect of wall curvature and post-tension force on impact resistance is evaluated by numerical analysis method. A total of twelve cases with two parameters such as wall shape of flat and curved, and consideration of post-tensioning force were included in this study. A 3D detailed finite element model of commercial passenger plane engine is utilized as projectile. The depths of penetration and central displacement calculated from the numerical simulations were compared and analysed. As the results of the numerical simulations of this study, penetration depth was reduced approximately 60~80% due to the application of post-tension force, but the decrease of maximum central displacement was not remarkable. Also, the effect of curvature was relatively insignificant.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.699-705
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• 2011

High-maneuver missile is a projectile which demands a strong momentum at short time. To produce a necessary thrust for the flight, the gas of high temperature and pressure is generated through explosive combustion of solid propellant, and a great thrust can be obtained by expanding this high temperature and pressure gas. Although the operating time of a rocket motor is less than a few seconds, a failure of part or ablation near the throat of nozzle may take place during the expansion of high temperature and pressure gas for great thrust. In other words, for the precise control of a missile an exact stress analysis considering both, the thermal stress caused by the heat transfer between combustion gas and wall, and the mechanical stress caused by the pressure change in the flow, should be considered first. In this connection, this study investigated the safety, as a point of view of stress and melting point of the material, of the pre-designed thrust generating structure which is subjected to high temperature and pressure as a function of motor operating time.