• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.557-560
• /
• 2002

In this study, simulation of weak shock waves are peformed by a two-dimensional thermal fluid or compressible fluid model of the lattice Boltzmann method. The shock wave represents an abrupt change in fluids properties, in which finite variations in pressure, internal energies, and density occur over the shock thickness. The characteristics of the proposed model with a simple distribution function is verified by calculation of the sound speeds, and the shock tube problem. The reflection of a weak shock wave by wedge propagating in a channel is performed. The results agree well with those by finite difference method or by experiment. In the simulation of unsteady shock wave diffraction around a sharp corner, we show a flow field of vortical structure near the comer.

• 동력기계공학회지
• /
• 제9권3호
• /
• pp.26-32
• /
• 2005

The volumetric efficiency is significantly affected by the behavior of pressure wave in induction system and exhaust pipe. By the motion of the piston, there exist pressure fluctuation in induction system which produce waves. Waves are propagated along a pipe bi-directional as they propagated through it, making compression wave and rare-faction(expansion) wave. These wave phenomena can affect to the volumetric efficiency. As a method of improvement of the volumetric efficiency, fuel economy and pollutant emission reduction particularly in low engine speeds, a side-branch additional tunable helmholtz resonator on the secondary pipe of intake system is proposed by use of their acoustic vibrations. Some of results are presented which deal with their physical phenomena for the wave action of intake system in a four-stroke three cylinders diesel engine.

• 대한기계학회논문집B
• /
• 제25권6호
• /
• pp.758-765
• /
• 2001

Purpose of the present is to investigate the food configuration at a tunnel entrance for reducing the micro pressure wave that is generated according to train speed. Two configurations were examined for tunnel of 0.5 km length. The experimental results show that a slit cover hood installed at the entrance of the tunnel reduces the maximum micro pressure wave by 41.2%, and a configuration with a slit cover hood installed at the entrance and a 45$^{\circ}$slanted portal at the exit of the tunnel suppresses it by 47.7%.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
• /
• pp.121.1-121.1
• /
• 2014

Recently, much attention has been given to plasma production under liquid and its applications [1]. However, most of plasma production techniques reported so far utilize high voltage dc, ac, rf or microwave power [2], where damage to discharge electrodes and small discharge volume are remained issues. As an alternative of plasma production method under liquid, we have proposed pulsed microwave excited plasma using slot antenna, where damage to the slot electrode can be minimized and plasma volume can be increased. We have also reported improvement of treatment efficiency with use of reduced-pressure condition during the discharge [3]. To realize low pressure conditions in liquid, various alternative technique can be considered. One possible technique is simultaneous injection of microwave power and ultrasonic wave. Ultrasonic wave induces pressure fluctuation with the wave propagation and is so far used for cavitation production in the water. We propose utilization of reduced pressure induced by ultrasonic cavitation for improvement of the plasma production. Correlation between the plasma production and the ultrasonic power will be discussed.

• 대한의용생체공학회:의공학회지
• /
• 제34권1호
• /
• pp.40-45
• /
• 2013

The conventional simulators used the expensive commercial artificial heart with a limited performance, and focused on replicating the heart function. The arterial pressure is the key factor of the cardiovascular disease. The purpose of this study is to develop a simulator focused on the pressure wave. The simulator is composed of a step motor, slider-crank mechanism, piston-cylinder, two check valves, a elastic tube, and two reservoirs. With the changes of design parameters, the functions of the simulator were evaluated. The simulator shows the good agreement of the characteristics of the cardiovascular system.

• Geomechanics and Engineering
• /
• 제5권6호
• /
• pp.595-611
• /
• 2013

This paper presents a three-dimensional (3D) integrated numerical model where the wave-induced pore pressures in a porous seabed around breakwater heads were investigated. Unlike previous research, the Navier-Stokes equation is solved with internal wave generation for the flow model, while Biot's dynamic seabed behaviour is considered in the seabed model. With the present model, a parametric study was conducted to examine the effects of wave and soil characteristics and breakwater configuration on the wave-induced pore pressure around breakwater heads. Based on numerical examples, it was found that the wave-induced pore pressures at breakwater heads are greater than that beneath a breakwater. The wave-induced seabed response around breakwater heads become more important with: (i) a longer wave period; (ii) a seabed with higher permeability and degree of saturation; and (iii) larger angle between the incident waves and breakwater. Furthermore, the relative difference of wave-induced pore pressure between fully-dynamic and quasi-static solutions are larger at breakwater heads than that beneath a breakwater.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2006년도 추계 학술대회논문집
• /
• pp.189-192
• /
• 2006

The numerical simulations on the train entrering a tunnel were performed by solving unsteady axi-symmetric problems. To reduce the effects of the pressure wave generated by the train starting abruptly, several starting method of the train were also examined. The pressure rise by the train entering a tunnel was compared with other results, and similar value was obtained compared with those of previous studies.

• 한국해안·해양공학회논문집
• /
• 제27권5호
• /
• pp.324-338
• /
• 2015

진행파 혹은 임의 반사율을 갖는 부분중복파 혹은 완전중복파-흐름-해저지반의 상호작용에 관한 해석해가 Lee et al.(2014; 2015a; 2015b; 2015c; 2015d) 및 Yamamoto et al.(1978)과 같은 다수의 연구자들에 의해 유도되었으며, 그들은 진동간극수압과 잔류간극수압을 별개로 취급하여 각 파동에 의한 지반응답을 논의하였다. 그러나, 실제 현장이나 실험에서 해저지반내 간극수압은 진동성분과 잔류성분이 별개로 나타나는 것이 아니고 그의 합 (전간극수압)으로 주어지기 때문에 전간극수압의 관점에서 반드시 검토될 필요가 있다. 따라서, 본 연구에서는 진동간극수압과 잔류간극수압뿐만 아니라 전간극수압의 측면에서 파동조건, 지반조건 및 흐름조건의 변화에 따른 지반응답의 변동특성을 논의하였으며, 더불어 이에 따른 액상화의 연직깊이에서 특성변화를 검토하였다. 이로부터 진행파와 순방향의 흐름의 공존장에서는 흐름속도가 증가할수록 무차원진동간극수압이 증가하고, 무차원잔류간극수압은 감소하여 결과적으로 무차원전간극수압이 작아지며, 무차원액상화 깊이도 감소하는 등의 지반응답특성을 확인할 수 있었다.

• 한국전산구조공학회논문집
• /
• 제24권6호
• /
• pp.601-608
• /
• 2011

부유구조체의 설계를 위해서는 파랑하중하에서 부유구조체의 파랑운동 특성과 구조거동에 대한 평가가 요구된다. 부유구조체의 구조거동 평가에서는 파랑하중에 의한 파압분포가 반영되어야 하지만, hydrodynamic 해석모델과 구조해석 모델사이의 파압 연계가 어려워 정확한 구조거동 평가가 어려웠던 문제점이 있었다. 본 논문에서는 파랑하중하에서 대형 부유구조체의 정확한 구조거동 평가를 목적으로 파랑운동-구조거동 통합해석을 실시하였다. AQWA에 의한 hydrodynamic 해석을 바탕으로 부유구조체에 작용하는 파압 분포를 ANSYS Inc.에서 제공하는 Workbench 인터페이스를 이용하여 ANSYS의 구조해석 모델에 연계하였다. 연구결과 본 연구의 파랑운동-구조거동 통합해석은 파랑하중에 의해 부유구조체에 발생하는 파압분포를 구조해석 모델에 정확하게 반영할 수 있어 파랑하중에 의한 부유구조체의 구조거동을 정확하게 평가할 수 있는 것으로 나타났다. 또한, 상부 슬래브의 인장응력은 파랑 입사각 $0^{\circ}$의 경우에 가장 불리하고, 하부 슬래브의 인장응력은 파랑 입사각 $45^{\circ}$의 경우에 가장 불리한 것으로 나타났다.

• Journal of Mechanical Science and Technology
• /
• 제18권9호
• /
• pp.1630-1639
• /
• 2004

The present paper investigated the correlation between the acoustic pressure variations and the augmentation of heat transfer in the ultrasonic induced acoustic fields. The augmentation ratios of heat transfer coefficient were experimentally measured and were compared with the profile of the pressure distribution in the acoustic fields predicted by numerical analysis. For numerical analysis, a coupled finite element-boundary element method (coupled FE-BEM) was applied. The results of the present study reveal that the acoustic pressure is higher near two ultrasonic transducers than other points where no ultrasonic transducer was installed. The augmentation trend of heat transfer is similar with the profile of the acoustic pressure distribution. In other words, as the acoustic pressure increases, the higher augmentation ratio of heat transfer is obtained. Numerical and experimental studies clearly show that the acoustic pressure variations are closely related to the augmentation of heat transfer in the acoustic fields.