• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.205-210
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• 2006

The impact forces of the highly nonlinear waves are one of the important factors in designing the ocean structures. The impact forces are very difficult to analyze numerically and experimentally because they are impulsive in magnitude and occur instantaneously. In this study the numerical program based on N.S. equations are used to investigate the impact forces of steep waves where the waves are gene rated by the wave maker in the numerical wave basin. The arbitrary steep waves are generated by the superposition of waves of single frequency and the impact forces on vertical cylinder are simulated on the multiblock grids. V.O.F. and the local height function methods are used to track the free surfaces. To validate the numerical analysis the numerical results are compared with the experimental ones and the acceptable agreements are found. It is thought that more studies on the simulations of the incoming breaking waves and the impact forces on the vertical cylinder should be made to obtain the useful results to be applied in the offshore design.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.59-60
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• 2014

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.288-289
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• 2012

• Journal of the Korean Institute of Gas
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• v.18 no.1
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• pp.68-74
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• 2014

In this study, to analyze the impulsive response of a helmet, a simple vibration model is presented. Based upon the experimental data and the simulation results, an equivalent one degree of freedom vibrational system is adapted, and transient impulsive responses are analysed to investigate the influence of engineering parameters such as damping, natural frequency, and impact velocity on the impulsive response of the helmet. Maximum gravitational acceleration reduces as the damping factor value increases. When the damping factor value is around 0.6 or larger, the maximum acceleration does not change. With respect to the natural frequency and the impact velocity, it increases linearly. The relationship between head injury criterion(HIC) and maximum gravitational acceleration is also presented. The scheme of this study is expected to be utilized to economize the design process of high quality helmets.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.9-17
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• 2017

Dynamic mode decomposition (DMD) method was applied for the further study of periodical characteristics of the unsteady shock-induced combustion. The case of Lehr's experiments was numerically simulated using 4 levels of grids. FFT result reveals that almost all the grid systems oscillate at frequencies around 430-435 kHz and the measureed one is around 425 kHz. To identify more resonant modes with low frequencies, DMD method is adopted for 4 grid systems. Several major frequencies are extracted and their damping coefficients are calculated at the same time, which is a quantification parameter for combustion stabilization.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.42.2-42.2
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• 2009

연속주조공정에서 용강의 통로, 산화방지 및 유체 흐름을 용이하게 하는 역할을 하는 다공성 노즐(porous nozzle)은 용강과의 직접적인 접촉으로 인한 화학 반응 및 용강의 침투현상을 방지하기 위해 불활성 가스를 주입하여 청정강을 제조하는데 이용된다. 공정 중 노즐 막힘으로 인한 배압상승과 열충격에 의한 크랙(crack) 발생이 문제되고 있으며 신뢰성 향상 연구가 요구되고 있다. 따라서 본 연구에서는 기공크기와 기공분포가 고온안정성 및 내열충격성에 미치는 영향을 알아보고, 내구성 시험 및 고장분석을 통하여 노즐의 신뢰성 향상 방안을 고찰 하였다. 기공을 제어한 시편을 제조하여 기공분포에 따른 고온안정성을 확인하기 위해 실제 사용 조건인 용강온도($1550^{\circ}C$)와 보다 높은 온도($1700^{\circ}C$)에서 각각 고온 시험을 수행하였다. 열충격을 스트레스 인자로 한 내구성 시험을 수행한 후 고장원인을 분석하였으며 열화정도를 확인하기 위해 열처리 온도에 따른 차압 및 굽힘 강도 변화를 비교하였다. 또한 결정상 분석을 통해 온도에 대한 상변화를 확인하였고, 시편의 표면 및 파단면의 미세구조 분석을 통해 크랙 발생여부를 확인하였다. 다공성 노즐의 기공분포가 균일 할수록 고온안정성 및 내열충격성이 향상됨을 확인하였고, 이를 통해 Porous Nozzle의 열화원인으로 판단되는 기공 크기 및 분포에 따른 크랙 발생에 대해 열응력 고찰을 수행하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1005-1011
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• 2016

The fundamental reason for gear noise is transmission error. Transmission error occurs because of STE (static transmission error) and DTE (dynamic transmission error), while a pair of gears is meshing. These errors are generated by the deflection of the teeth and the friction on the surface of the teeth. In addition, the vibration generated by transmission error leads to excited bearings. The bearings support the shafts, and the noise is radiated after exciting the gear casing. The analysis of the contact stress in helical gear tooth flanks indicates that it is due to impact loading, such as the sudden engagement and disengagement of a gear. Stress analysis is performed for different roll positions, in order to determine the most critical roll angle. Dynamic analysis is performed on this critical roll position, in order to evaluate variation in stresses and tooth contact force, with respect to time. In this study, transmission error analysis was implemented on a spur and helical gear with involute geometry and a modified geometry profile. In addition, in order to evaluate the intensity of impact due to sudden engagement and significant backlash, the impact factor was calculated using the finite element analysis results of static and dynamic maximum bending stresses.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.6
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• pp.659-666
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• 2015

In this paper, various influence factors on the impact-echo test which is an effective method in characterizing defects such as such as the delamination in the concrete structures were studied. The side to thickness ratio(a/h), the relative position of impacting and sensing points over the delamination that have great effects on the flexural and impact-echo(thickness) modes were investigated and examined by the parametric finite element analysis. As a result, the flexural modes dominate in the case of a/h > 2 and the thickness mode was more evident when a/h < 2. With regard to the relative position of impact source and sensing point to the defect, the flexural modes dominate even when either the loading or sensing point was over the delamination defect. However, the thickness mode prevails when both the impacting and sensing points are over the solid region beyond the delamination area.

• Journal of the Korea Institute of Building Construction
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• v.23 no.1
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• pp.11-22
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• 2023

In this work, a depth-by-depth evaluation on the deterioration of concrete is suggested by utilizing disk shaped concrete specimens. Dynamic elastic modulus of cylindrical concrete was measured using a free-free resonance column method and compared with dynamic elastic modulus of disk-shaped concrete measured by impulse excitation technique(IET) and impact resonance(IR). According to the results of the experiment, both IET and IR methods showed a smaller difference in dynamic elastic modulus with smaller deviation in data when thickness of the disk specimen was increased. This trend was more evident from dynamic elastic modulus measured by IR method compared to that measured by IET. Variation in data was also smaller with the IR result. To increase the accuracy of the data, it is recommended to use the IR method for disk specimen with a diameter of 100mm and a thickness of 25mm.

• Journal of Adhesion and Interface
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• v.3 no.3
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• pp.1-6
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• 2002

We invested which is major one in rubber materials design factors affecting on noise and showed the design guide for low noise tire development in this study. Tire noise and impact noise for rubber sheets were tested at anechoic room. Hardness, tensile and dynamic mechanical properties were also measured using the rubber sheets. A major design factor of rubber materials affecting on the tire noise was hardness or 300% modulus. There was also positive correlation between two properties. Therefore, designing rubber materials to have low hardness or 300% modulus can reduce noise.