• Journal of ILASS-Korea
• /
• v.10 no.1
• /
• pp.10-16
• /
• 2005

To investigate the effect of shockwave on diesel spray characteristics under ultra high pressure injection, the velocity of spray tip and shock wave were investigated using the visualization of spray by schlieren method. Spray characteristics such as the spray radius, height, and droplets size were analyzed. It is found in this study that shock wave, produced by ultra high injection pressure, propagates faster than spray tip. Spray radius of right side of nozzle tip was shorter than that of left side and spray height of right side of nozzle tip was thicker than that of left side. Droplets sue was increased at 414MPa in injection pressure because of pressure gradient between inner and outer of tile spray caused by shockwave.

• Journal of the Korean Society for Precision Engineering
• /
• v.14 no.8
• /
• pp.146-154
• /
• 1997

Solenoid-folw control type ABS is used with a 'dump and reapply' pressure control arrangement instead of using 2/2 (normal open/close) solenoid valves in convensional systems(sol. -sol. control type), a flow control valve is used which replaces the (no) inlet valve. The flow control valve controls fluid flow providing a nearly constant reapply rate( .theta. ) after the dump plase of ABS operation. In this study, to investigate a characteristics of brake pressure by PWM control, test rig was consisted of ABS hydraulic modulator, digital controller, pneumatic power supply and brake master cylinder. For comparison with experi- mental results, system modelling and computer simulation were performed. As a result, experiment results showed fairly agreement with the simulation. Also, it is shown that the pressure gradient (tan .theta. ) is affected by pressure, frequency, duty ratio and expressed with an exponential funtion.

• Proceedings of the Optical Society of Korea Conference
• /
• 2002.07a
• /
• pp.108-109
• /
• 2002

Optical tweezers는 광압(radiation pressure)을 사용하여 입자들을 포획하거나 조절할 수 있다는 점에서 마이크로스케일의 유전체구뿐만 아니라 세포에서도 널리 사용되고 있다. 일반적으로 빛이라는 것은 광자들의 집합체로서 광자의 입자성으로 인하여 외부의 물체와 충돌시 운동량을 전달하게 되고 이것을 광압(radiation pressure)이라고 하며 optical tweezers [1]는 이 광압을 이용한 방법중 하나이다. 레이저빔을 입자에 집속 시켜 주게 되면 입자는 광압에 의해서 gradient force와 scattering force의 힘을 받게 된다. (중략)

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.11a
• /
• pp.301-306
• /
• 1996

To predict the average liquid level under the condition of the countercurrent stratified two-phase flow in a pipe, an analytical model has been suggested. This is made by introducing the interfacial level gradient into the liquid-phase and the gas-phase momentum equations. The analytical method for the gas-phase pressure drop calculation with f$_i$ $\neq$ f$_G$ has also been described using the liquid level prediction model developed in the present study.

• Structural Engineering and Mechanics
• /
• v.26 no.4
• /
• pp.393-408
• /
• 2007

The effects of material nonhomogeneity and nonisothermal conditions on the stress response of pressurized tubes are assessed by virtue of a computational model. The modulus of elasticity, the Poisson's ratio, the yield strength, and the coefficient of thermal expansion, are assumed to vary nonlinearly in the tube. A logarithmic temperature distribution within the tube is proposed. Under these conditions, it is shown that the stress states and the magnitudes of response variables are affected significantly by both the material nonhomogeneity and the existence of the radial temperature gradient.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.10a
• /
• pp.343-344
• /
• 2006

• Journal of Acupuncture Research
• /
• v.25 no.1
• /
• pp.121-130
• /
• 2008

Objectives : Cupping therapy is a stimulation therapy similar to acupuncture and moxibustion with effects that differ depending on the degree of stimulus. To make the strength of the skin objective in cupping therapy for this study, we measured negative pressure in the cupping jar and calculated the expansion rate of the skin. Subjects and Methods : In this study, we experimented with cupping therapy jars made for sale and used in clinics. We studied the pressure in the jars and the changes on the skin surface by measuring properties. We used commercial jars of four different volumes and diameters and tried to discover the properties on the size of the jar. Results : The results of experiment with the cupping therapy are as follows: 1. The lowest pressure in a jar was measured at $-600{\sim}610mmHg$, and the number of operating of vacuum pump for reaching lowest pressure was increased recording where the volume of the jar would be big, but the lowest pressure was not increased recording where the size of that would be big. 2. As the vacuum pump continued to operate, the pressure gradient in the jar got smaller which shows that the expansion rate of the skin was not linear. The pressure gradient shows different operational numbers on the vacuum pump near 0mmHg/operation unrelated to jar volume. 3. When negative pressure worked on the jar, air in the jar decreased. The percentage of air gradually reduced as the negative pressure acted in the jar. For example, the percentage of skin was 37-66% when the negative pressure, reatched -500mmHg. According to out results, different test areas generate different percentages of air in the jar, presumably related to skin elasticity. This phenomenon was most pronounced with the smallest jars. 4. At -500mmHg, the expansion rate of the skin was 1.57-1.9 on the abdomen, and $1.52{\sim}1.68$ on the back. The expansion rate of the skin appeared greater when the jar was relatively small, and it appeared smaller when the jar volume was relatively large relatively.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2002.10b
• /
• pp.85-86
• /
• 2002

For rheology investigation of lubricating oils, first phase diagrams were made from determined free volume based on density measurements and the temperature-pressure relation was estimated using the expansion coefficient of free volume and the temperature-pressure relation of the viscoelastic transition point. Next, the authors proposed the density-pressure-temperature relation and the viscosity-pressure-temperature relation of the tested oils based on the free volume and the phase diagrams. Moreover, it was shown that the Ehrenfest equation or the gradient of the phase diagram is closely related to the expansion coefficient of free volume.

• Geomechanics and Engineering
• /
• v.6 no.5
• /
• pp.503-515
• /
• 2014

On the basis of Hoek-Brown failure criterion, a numerical solution for the shape of collapsing block in the rectangular cavity subjected to seepage forces is obtained by upper bound theorem of limit analysis. The seepage forces obtained from the gradient of excess pore pressure distribution are taken as external loadings in the limit analysis, and the pore pressure is easily calculated with pore pressure coefficient. Thus the seepage force is incorporated into the upper bound analysis as a work rate of external force. The upper solution of the shape of collapsing block is derived by virtue of variational calculation. In order to verify the validity of the method proposed in the paper, the result when the pore pressure coefficient equals zero, and only hydrostatic pressure is taken into consideration, is compared with that of previous work. The results show good effectiveness in calculating the collapsing block shape subjected to seepage forces. The influence of parameters on the failure mechanisms is investigated.

• International Journal of Fluid Machinery and Systems
• /
• v.2 no.1
• /
• pp.1-12
• /
• 2009

Surrogate modeling is applied to a compressor blade shape optimization to modify its stacking line and thickness to enhance adiabatic efficiency and total pressure ratio. Six design variables are defined by parametric curves and three objectives; efficiency, total pressure and a combined objective of efficiency and total pressure are considered to enhance the performance of compressor blade. Latin hypercube sampling of design of experiments is used to generate 55 designs within design space constituted by the lower and upper limits of variables. Optimum designs are found by formulating a PRESS (predicted error sum of squares) based averaging (PBA) surrogate model with the help of a gradient based optimization algorithm. The optimum designs using the current variables show that, to optimize the performance of turbomachinery blade, the adiabatic efficiency objective is improved substantially while total pressure ratio objective is increased a very small amount. The multi-objective optimization shows that the efficiency can be increased with the less compensation of total pressure reduction or both objectives can be increased simultaneously.