• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.6
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• pp.1026-1033
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• 2010

The analysis of water-entry impact forces acting on the fin shaft of high speed water-entry body is described. During the entry of high speed body into water, the physical phenomenon and flow properties are analyzed. A proper analysis model is established and the method to estimate the flow force which causes impact torque at the fin shaft is described. It is assumed that the fin shaft is damaged by the force which is induced by contacting with cavity wall. The pressure distribution of fin and the maximum torque are estimated and compared with breaking force. Conclusively, it is hard to resist water-entry impact force in terms of the reinforcement of fin shaft. Additionally safe equipment is essentially required.

• Journal of computational fluids engineering
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• v.4 no.1
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• pp.1-7
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• 1999

The numerical methodology for computing tile impact forces and water entry behaviors of high speed water entry bodies was been developed. Since the present method assumed the impact occurs within a very short time interval. the viscous effects do not have enough time to play a significant role in the impact forces, that is, the flow around a water-entry object was assumed as an incompressible potential flow and is solved by the source panel method. The elements fully submerged into the water are routinely treated, but the elements intersected by the effective planar free surface are redefined and reorganized to be amenable to the source panel method. To validate the present code, it was applied to disk, cone and ogive model and compared with experimental data. Good agreement was obtained. The water entry behavior such as the bouncing phenomena from the free surface was also simulated using the impact forces and two degree of freedom dynamic equation. Physically acceptable results were obtained.

• Ocean Systems Engineering
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• v.8 no.2
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• pp.223-246
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• 2018

In this paper the results of CFD simulations, that were carried out to study the impact pressures acting on a symmetric wedge during water entry under the influence of gravity, are presented. The simulations were done using a solver implementing finite volume discretization and using the VOF scheme to keep track of the free surface during water entry. The parameters such as pressure on impact, displacement, velocity, acceleration and net hydrodynamic forces, etc., which govern the water entry process are monitored during the initial stage of water entry. In addition, the results of the complete water entry process of wedges covering the initial stage where the impact pressure reaches its maximum as well as the late stage that covers the rebound process of the buoyant wedge are presented. The study was conducted for a few touchdown velocities to understand its influence on the water entry phenomenon. The simulation results are compared with the experimental measurements available in the literature with good accuracy. The various computational parameters (e.g., mesh size, time step, solver, etc.) that are necessary for accurate prediction of impact pressures, as well as the entry-exit trajectory, are discussed.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.482-494
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• 2019

In this paper, the oblique water-entry impact of a vehicle with a disk cavitator is studied experimentally and numerically. The effectiveness and accuracy of the numerical simulation are verified quantitatively by the experiments in this paper and the data available in the literature. Then, the numerical model is used to simulate the hydrodynamic characteristics and flow patterns of the vehicle under different entry conditions, and the axial force is found to be an important parameter. The influences of entry angle, entry speed and cavitator area on the axial force are studied. The variation law of the force coefficient and the dimensionless penetration distance at the peak of the axial force are revealed. The research conclusions are beneficial to engineering calculations on the impact force of a vehicle with a disk cavitator over a wide range of water-entry parameters.

• Journal of the Korea Society of Computer and Information
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• v.29 no.4
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• pp.125-134
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• 2024

This study was conducted to verify the impact of social capital on labor market entry for poor and disabled women and to reveal the relationship. In the case of poverty-stricken and disabled women, the reality is that there is very little research on the impact on labor market entry depending on the level and type of social capital that disabled women possess or are involved in for economic activities. Therefore, in this study, we looked at how the level and type of social capital possessed by poor and disabled women affects their entry into the labor market. As a result of the study, the level of social capital of poor and disabled women is larger and the stronger the density, the more labor market they have. It was found to have a very significant impact on market entry, and in terms of social capital type, greater trust and participation were found to have a very significant impact on labor market entry. Based on these research results, major policy implications were suggested regarding the impact of the level and type of social capital of poor and disabled women on their entry into the labor market.

• Management & Information Systems Review
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• v.5
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• pp.185-209
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• 2000

A review of shows that past research has focused predominately on foreign market entry strategy issues in relatively well-established firms. These studies have either ignored venture firms or have failed to treat these firms separately. Only recently, researchers have broadened their search to include aspects of the foreign market investment of the venture. The purposes of this study are to identify and explain the impact factors such as ownership specific advantage, transaction cost, and location specific advantage on the choice of foreign market entry strategy for venture firms. To find the perceived the foreign market entry strategy and determinant factors, 130 venture CEOs from the computer and communications equipment industries were asked to describe their venture's foreign market entry strategy through 17 questionnaire items on competitive method. Using factor analysis, the six determinant factors were categorized. To test the relationships between the foreign market entry strategy and factors such as ownership specific advantage, transaction cost, and location specific advantage, the data collected by questionnaire from 92 ventures. The main results of this research are as follows. First, the factors of ownership specific advantage have partially significant impact on the foreign market entry strategy of venture firms, Second, the factors of transaction cost have significant impact on their foreign market entry strategy. Third, the factors of location specific advantage have significant impact on their foreign market entry strategy. This study has produced evidence to demonstrate that the foreign market entry strategy profile of venture firms can be distinguished from those of relatively well-established firms. An expanded study would allow for stronger conclusions regarding the relative explanatory power of individual variables in the method. Additional research is also needed to examine other determinant variables connecting foreign market entry strategy.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.4
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• pp.71-76
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• 2013

This paper seeks to investigate the effect of technology readiness on the usage of smart entry service. The questionnaires were distributed to passengers who were experience with smart entry service and structural equation modeling was utilized to analyze the data. The results revealed that optimism had a positive impact on perceived usefulness and insecurity had a negative effect on perceived enjoyment. Perceived ease of use had a positive impact on perceived enjoyment, perceived usefulness and intention to use. In addition, perceived usefulness had a positive impact on intention to use. The results from this paper can be used as basic knowledge for developing the smart entry service activation plan.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.191-195
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• 2009

A parametric study for for the water entry of a two dimensional symmetric wedge with deadrise angle of 10 degrees was carried out to find out the most dominant parameter. Water entry problem with constant velocity is simplified as the stationary wedge in the way of the upcoming water surface. The calculated impact loads showed that the effect of the viscosity was not so important in this problem. For a given grid system a suitable time step size can be found. The most sensitive parameter was found to be the grid size.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.4
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• pp.467-473
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• 2017

In this paper, impact characteristics of a water entry gliding vehicle were analyzed using a finite element method. To guarantee the validity of analysis results, a convergence test was performed for several ratios of Euler and Largrange mesh sizes. The impact coefficient was calculated with respect to entry angles and angle of attacks. It can be observed that the impact coefficient was large at a high cross-section gradient and was also affected by cavitation. This study could be useful in the preliminary design stage of a water entry bomb development.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.1-8
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• 2002

When a body enters waters, its original kinetic energy or momentum is distributed among the body and surrounding water in the form of added mass. Due to the transfer of the energy or momentum, the bode is subjected to the hydrodynamic impact forces and acceleration. This impact behavior can be an important criterion of submersible vehicle launched to the air. In this paper, based on Life-boat model, an approximate method is proposed for the evaluation of the forces and responses of cylindrical rigid bode by water entry impact. The impact forces are calculated by yon Karman's momentum theory and motion responses the body, especially acceleration, are calculated by a numerical integration of the motion equations derived by hydrodynamic force equilibrium. The proposed method is expected to be a simple but efficient tool lot the preliminary design or motion analysis of a body subjected to water entry impact.