• 한국지반공학회지:지반
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• 제8권2호
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• pp.71-80
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• 1992

정규압밀점토의 거동을 예측하기 위한 새로운 구성방정식이 제안되었으며, 그 골격은 Roscoe 와 Poorooshasb의 증분응력-변형률이론의 기본개념에 근거를 두고있다. 비배수 조건에서의 유효응력경려폰t은 새로운 간극수압계수(C)를 이용하여 유도되었고, 여기 에서 간극수압계수는 표준화묀 간극수압과 응력의 관계에서 직선의 기울기로 표시된다. 비배 수 응력경로와 일정응력비경로(constant stress ratio path)를 따라 발생하는 응력의 증가량을 알게되면, 이때의 체적변형률은 간극비-대수평균 연직 응력(e-dnp) 관계의 선형 특성으로부 터 계산될 수 있다. 또한 Roscoe와 Burland의 수정 Cam-clay 이론에서 유도된 유동법칙(flow rule)을 적용하여 임의 응력점에서의 전단변형률을 예측할 수 있다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2168-2173
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• 2003

Pressure balancing valve is one of important control devices, which is fully automatic and no manual controls, regulating or adjustments are needed. It is typically used to maintain constant temperature of working fluid in power and chemical plants and domestic water supply systems. Pressure balancing valve is composed of body, cylinder and balancing piston. Therefore, the balancing piston shapes are important design parameters for a pressure balancing valve. In this study, numerical and experimental analyses are carried out with two different balancing piston shapes. Especially, the distribution of static pressure is investigated to calculate the flow coefficient($C_v$). The governing equations are derived from making using of three-dimensional Navier-Stokes equations with standard ${\kappa}-{\varepsilon}$ turbulence model and SIMPLE algorithm. Using commercial code, PHOEIC, the pressure and flow fields in pressure balancing valve are depicted.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1552-1564
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• 2002

Meter-in, meter-out and bleed-off circuits are widely utilized in order to adjust the speed of a hydraulic actuator by using a flow control valve and in order to regulate the pressure of a hydraulic volume by using a simple on-off valve. In these circuits, a relief valve serves either to maintain constant system pressure or to protect the system from over-pressure loading. The relief valve of a bleed-off circuit is the second case frequently undergoing on-off action during operation. It makes the analysis of the pressure control characteristics of the circuit highly difficult. In this paper, steady-state flow rate, pressure, heat loss and efficiency of the three circuits are reexamined and basic experiments far obtaining the characteristics of a pump and relief valve are conducted. Finally, simple empirical first-order dynamic models of decreasing and increasing pressure were separately proposed and verified by comparison with experiment. As the result, the basis for the theoretical analysis of the pressure control characteristics of a bleed-off circuit using a simple on-off valve is established.

• Structural Engineering and Mechanics
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• 제58권4호
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• pp.661-676
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• 2016

This paper presents an elastic/plastic model that neglects strain hardening during loading, but accounts for the Bauschinger effect. These mathematical features of the model represent reasonably well the actual behavior of several materials such as high strength steels. Previous attempts to describe the behavior of this kind of materials have been restricted to a class of boundary value problems in which the state of stress in the plastic region is completely controlled by the yield stress in tension or torsion. In particular, the yield stress is supposed to be constant during loading and the forward plastic strain reduces the yield stress to be used to describe reversed yielding. The new model generalizes this approach on plane stress problems assuming that the material obeys the von Mises yield criterion during loading. Then, the model is adopted to describe reversed yielding in thin hollow discs subject to external pressure.

• 한국지반환경공학회 논문집
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• 제7권4호
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• pp.15-24
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• 2006

원형 오픈 케이슨과 원형 수직구에 설치된 흙막이 벽에 작용하는 토압은, 벽체의 변위와 응력해방으로 인한 수평 및 연직 아칭효과로 인하여, 평면 변형조건에서의 옹벽에 작용하는 토압보다는 작은 토압이 발생한다. 원형벽체에 작용하는 토압분포를 조사하기 위해서, 건조한 모래지반에서 깊이에 따른 벽체변형이 균등한 조건의 모형실험을 실시하였다. 벽체 변위, 벽면 마찰, 벽체 형상비 등을 조절할 수 있는 모형 실험 장치가 개발되었고, 모형실험을 통하여 원통형 벽체에 작용하는 토압에 대한 다양한 인자의 영향이 분석되었다.

• International Journal of Automotive Technology
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• 제8권2호
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• pp.165-177
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• 2007

Predictions of diesel particulate filtration are typically made by modeling of a particle collection, and providing particle trapping levels in terms of a pressure drop. In the present study, a series of single channel diesel particulate filter (DPF) experiments are conducted, the pressure traces are inversely analyzed and essential filtration parameters are deducted for model closure. A DPF filtration model is formulated with a non-linear description of soot cake regression. Dependence of soot cake porosity, packing density, permeability, and soot density in filter walls on convective-diffusive particle transportation is examined. Sensitivity analysis was conducted on model parameters, relevant to the mode of transition. Soot cake porosity and soot packing density show low degrees of dispersion with respect to the Peclet number and have asymptotes at 0.97 and $70\;kg/m^3$, respectively, at high Peclet number. Soot density in the filter wall, which is inversely proportional to filter wall Peclet number, controls the filtration mode transition but exerts no influence on termination pressure drop. The percolation constant greatly alters the extent of pressure drop, but is insensitive to volumetric flow rate or temperature of exhaust gas at fixed operation mode.

• Tribology and Lubricants
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• 제22권2호
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• pp.93-98
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• 2006

The numerical analysis of the negative pressure porous gas bearings is presented. The pressure distribution is calculated using the finite difference method. The Reynolds equation and Darcy's equation are solved simultaneously. The air bearing stiffness and damping are evaluated using the perturbation method. Rectangular uniform grid is employed to model the bearing. The vacuum preloading is considered. The pressure in the vacuum pocket is assumed to be a constant negative pressure. The total load, stiffness, damping and flow rate are calculated fur several geometrical configurations and several values of negative pressure. It is found that too large vacuum pocket can result in negative total force.

• 한국정밀공학회지
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• 제28권1호
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• pp.115-122
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• 2011

Recently, we have proposed a hypothesis that spinal structures have a stress sensor driving feedback mechanism, In the human spine, spinal structure could react to modify muscular action in such a way so as to equalize stress at the disc, therefore reduce the risk of injury, In this analysis, abdominal muscle and abdominal pressure, which were not included in the previous study, were added to identify those effects in spine stability during upright stance posture for the case where the intervertebral disc plays the role of mechanoreceptor, The musculoskeletal FE model was consisted with detailed whole lumbar spine, pelvis, sacrum, coccyx and simplified trunk model. Muscle architecture with 46 local muscles containing paraspinal muscle and 6 rectus abdominal muscles were assigned according to the acting directions. The magnitude of 4kPa was considered for abdominal pressure. Minimization of the nucleus pressure deviation and annulus fiber average tension stress deviation was chosen for cost function. Developed model provide nice coincidence with in-vivo measurement (nucleus pressure). Analysis was conducted according to existence of co-activation of abdominal muscle and abdominal pressure. Antagonistic activity of abdominal muscle produced stability of spinal column with relatively small amount of total muscle force. In contrast to the abdominal muscle, effect of abdominal pressure was not clear that was partly depending on the assumption of constant abdominal pressure.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.367-373
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. Activation energy is used as parameter as 10, 20, 27 and 35, and the specific heat ratio and the heat release are fixed as 1.2 and 50. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable pitch at Ea=10, periodical unstable pitch at Ea=20 and 27 and unstable pitch consisting of stable, periodical unstable and weak modes at Ea=35, respectively. In the weak mode, there is no Mach leg on the shock front, where the pressure level is much lower than the other modes. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of these stable and unstable modes. In the stable pitch at Ea=10, the maximum pressure history on the tube wall remained nearly constant, and the steady single Mach leg on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the periodical unstable pitch at Ea=20 and 27 of the maximum pressure history. The high frequency was one cycle of a self-induced oscillation by generation and decay in complex Mach interaction due to the variation in intensity of the transverse wave behind the shock front. Eventually, sequential high frequency oscillations formed the low frequency behavior because the frequency behavior was not always the same for each cycle. In unstable pitch at Ea=35, there are stable, periodical unstable and weak modes in one cycle of the low frequency oscillation in the maximum pressure history, and the pressure amplitude of low frequency was much larger than the others. The pressure peak appeared after weak mode, and the stable, periodical unstable and weak modes were sequentially observed with pressure decay. A series of simulations of spinning detonations clarified that the unsteady mechanism behind the shock front depending on the activation energy.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.367-373
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. Activation energy is used as parameter as 10, 20, 27 and 35, and the specific heat ratio and the heat release are fixed as 1.2 and 50. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable pitch at Ea=10, periodical unstable pitch at Ea=20 and 27 and unstable pitch consisting of stable, periodical unstable and weak modes at Ea=35, respectively. In the weak mode, there is no Mach leg on the shock front, where the pressure level is much lower than the other modes. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of these stable and unstable modes. In the stable pitch at Ea=10, the maximum pressure history on the tube wall remained nearly constant, and the steady single Mach leg on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the periodical unstable pitch at Ea=20 and 27 of the maximum pressure history. The high frequency was one cycle of a self-induced oscillation by generation and decay in complex Mach interaction due to the variation in intensity of the transverse wave behind the shock front. Eventually, sequential high frequency oscillations formed the low frequency behavior because the frequency behavior was not always the same for each cycle. In unstable pitch at Ea=35, there are stable, periodical unstable and weak modes in one cycle of the low frequency oscillation in the maximum pressure history, and the pressure amplitude of low frequency was much larger than the others. The pressure peak appeared after weak mode, and the stable, periodical unstable and weak modes were sequentially observed with pressure decay. A series of simulations of spinning detonations clarified that the unsteady mechanism behind the shock front depending on the activation energy.