• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.1221-1225
• /
• 2008

In this paper, analysis of pressure and flow characteristics have been performed with a servo valve. A number of servo valve have been used in various applications including the inserting device, bearing transportation and welding machine. By analysis of flow and pressure gradient, technology can be obtained about optimal simulation of high response servo valve for competitiveness. Spool displacement and ratio of inlet/outlet pressure can give big effects to flow and pressure inside servo valve.

• Journal of computational fluids engineering
• /
• v.19 no.4
• /
• pp.20-28
• /
• 2014

An efficient solution algorithm for simulating free surface problem is presented. Navier-Stokes equations for variable density incompressible flow are employed as the governing equation on Cartesian meshes. In order to describe the free surface motion efficiently, VOF(Volume Of Fluid) method utilizing THINC(Tangent of Hyperbola for Interface Capturing) scheme is employed. The most time-consuming part of the current free surface flow simulations is the solution step of the linear system, derived by the pressure Poisson equation. To solve a pressure Poisson equation efficiently, the PCG(Preconditioned Conjugate Gradient) method is utilized. This study showed that the proper application of the preconditioner is the key for the efficient solution of the free surface flow when its pressure Poisson equation is solved by the CG method. To demonstrate the efficiency of the current approach, we compared the convergence histories of different algorithms for solving the pressure Poisson equation.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.17 no.4
• /
• pp.43-48
• /
• 2013

A study is analyzed on the adverse pressure gradient and the transient regime of supersonic diffuser with Computational Fluid Dynamic. The flow field of supersonic diffuser is calculated using Axisymmetric two-dimensional Navier-Stokes equation with $k-{\epsilon}$ turbulence model. The transient simulation is compared in terms of mach number and static temperature of vacuum chamber according to pressure variation of rocket engine combustion chamber. Combustion gas flow into the vacuum chamber during operation of the supersonic diffuser. According to this phenomenon, the pressure and the temperature rise in the vacuum chamber were observed. Thus, the protection system will be necessary to prevent the pressure and temperature rise in the transition process during operation of the subsonic diffuser.

• Steel and Composite Structures
• /
• v.32 no.6
• /
• pp.701-715
• /
• 2019

Using first-order shear deformation theory (FSDT), a semi-analytical solution is employed to analyze creep damage and remaining life assessment of 304L austenitic stainless steel thick (304L ASS) cylindrical pressure vessels with variable thickness subjected to the temperature gradient and internal non-uniform pressure. Damages are obtained in thick cylinder using Robinson's linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The thermo-elastic creep response of the material is described by Norton's law. The novelty of the present work is that it seeks to investigate creep damage and life assessment of the vessels with variable thickness made of 304L ASS using LMP based on first-order shear deformation theory. A numerical solution using finite element method (FEM) is also presented and good agreement is found. It is shown that temperature gradient and non-uniform pressure have significant influences on the creep damages and remaining life of the vessel.

• Journal of Chest Surgery
• /
• v.20 no.1
• /
• pp.30-38
• /
• 1987

Sixty-eight consecutive patients have been subjected to total corrective surgery of tetralogy of Fallot at the Hanyang University Hospital between August 1975 and December 1984. Of these, the pressure of chambers and great arteries were measured, before and immediately following an operation in 39 of the survived group and 11 of the expired group. The values of postoperative peak pressure were correlated with the outcome of the operation. The result are as followings; 1] Compared to the average peak pressure of right atrium in the survived group, 14.46*4.16 mmHg, that in the expired group, 19.36*8.19 mmHg, was significantly lower, 2] Compared to the average systolic pressure of right ventricle in the survived group, 56.72z16.37 mmHg, that in the expired group, 70.45*15.26 mmHg, was significantly lower. 3] Compared to the average systolic pressure of pulmonary artery in the survived group, 33.26*12.95 mmHg, that in the expired group, 37.55*11.63 mmHg, was higher. But the difference was not significant. 4] Compared to the average peak pressure of left atrium in the survived group, 17.41*6.90 mmHg, that in the expired group, 31.18*12.47 mmHg, was significantly higher. 5] Compared to the average systolic pressure of left ventricle in the survived group, 103.82~12.83 mmHg, that in the expired group, 90.55*20.02 mmHg, was significantly lower. 6] Compared to the average value of the right ventricle-pulmonary artery systolic pressure gradient [RV-PA] in the survived group, 24.95a15.44 mmHg, that in the expired group, 35.09*17.01 mmHg, was significantly higher. 7] Compared to the average value of the right ventricle to left ventricle systolic pressure ratio [RV/LV] in the survived group, 0.55*0.15, that in the expired group, 0.80a0.20, was significantly higher. 8] Compared to the average value of the pulmonary artery-left atrium peak pressure gradient [PA-LA] in 15.85x12.29 mmHg that in the expired group, 4.18x6.00 mmHg, was significantly lower. It is, therefore, suggested that in the operating room, PA-LA is as valuable as RV - PA, RV/LV in making important surgical decision and predicting the prognosis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.30 no.3
• /
• pp.123-129
• /
• 2018

In this study, CFD is used to compare and analyze the flow characteristics using reflected pressure wave during the intersection of two trains in straight tunnel. Two tunnels of different lengths; 600 m and 3,400 m were designed and numerical analysis of the flow characteristics of two tunnels carried out by setting the crossing state of the two trains at a constant velocity of 27 m/s form the center of the tunnel. The simulation model was designed using the actual tunnel and subway dimensions The train motion was achieved by using the moving mesh method. For the numerical analysis, $k-{\omega}$ standard turbulence model and an ideal gas were used to set the flow conditions of three-dimensional, compressible and unsteady state. In the analysis results, it was observed that the inside of the long tunnel without interference of the reflected pressure wave was maintained at a pressure lower than the atmospheric pressure and that the flow direction was determined by the pressure gradient and shear flow. On the other hand, the flow velocity in the short tunnel was faster and the pressure fluctuation was noted to have increased due to the reflected pressure wave, with more vortices formed. In addition, the flow velocity was noted to have changed more irregularly.

• Journal of Chest Surgery
• /
• v.12 no.4
• /
• pp.350-354
• /
• 1979

The incidence of congenital aortic valvular stenosis has been known rare, and approximately 3-6% of congenital heart diseases. Recently, we experienced 1 case of congenital aortic valvular stenosis, and which was corrected surgically under extracorporeal circulation successfully. A 11 years old male pt. was admitted to N.M.C. because of dyspnea, dizziness, chest pain and episode of syncope. An auscultation, harsh systolic murmur [Gr. IV/VI] was noted at aortic area and also palpable strong thrill. ECG showed LVH c strain pattern and suspicious LVH finding in simple chest P-A film. In Lt. cardiac catheterization, abrupt pressure change [110mmHg] between LV & Aorta was noted across the aortic valve. And aortic insufficiency was absent, well visualized both coronary arteries and suspicious bicuspid aortic valve in aortography. Valve form was bicuspid, large one was noncoronary cusp and another cusp was Rt. & Lt. coronary cusp which was interpositioned rudimentary commissure. Central aortic orifice was about 5ram in diameter. Valvulotomy was done along the fusioned commissure between noncoronary cusp and Rt. & Lt.coronary cusp, and then short incision was added between Rt. coronary cusp & Lt. coronary cusp. Immediate postoperative course smooth but unknown cardiac arrest was noted in POD second day. Complete recovery was done without sequelae by resuscitation. After operation, clinical symptoms were subsided but systolic murmur [Gr. II/VI] was audible at aortic area, diastolic murmur was absent. ECG showed still remained LVH but much decreased R wave voltage in Lt. precordial leads. Simple chest P-A showed no interval changes compared to preop film. Control Lt. heart catheterization revealed still remained pressure gradient [40ramrig] between LV & Aorta. But much decreased pressure gradient compared to preop pressure gradient [110mmHg].

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2001.10a
• /
• pp.122-127
• /
• 2001

As pipelines are often used to transport gas, oil, water and oil products, there are more than one pipeline installed in the offshore field. The size and space of pipelines are various depending on the design specifications. The pipelines are to be designed and installed to secure the stability to external loads during the installation and operation period. The flow patterns are very complex around the pipelines being dependent on incoming flow velocity, pipelines size and space. To investigate the flow patterns, number of experiment are conducted with visualization equipment in a circulating water channel. The flow motion and trajectory were recorded from the laser reflected particles by camera. From the experiment the flow patterns around spaced pipelines were obtained. Also pressure gradient was measured by mano-meter to estimate the hydrodynamic forces on the behind pipeline. The results show that the various sizes and spaces can be affected in the estimation of external load. The complex flow patterns and pressure gradients can be effectively used in the understanding of flow motion and pressure gradient.

• Journal of computational fluids engineering
• /
• v.20 no.4
• /
• pp.109-115
• /
• 2015

In this study, the Stokes flow in the microchannel is analysed where the semicircular protuberances with constant spacing are attached on the upper and lower walls with staggered arrangement. For the low Reynolds number flow in microchannel, Stokes approximation is used and the periodicity and symmetry of the flow are considered to determine the stream function and pressure distribution in the flow field by using the method of least squared error. As results, the streamline patterns and pressure distributions in the flow field are shown for some specific values of the size and spacing of the protuberances, and shear stress distributions on the surface of semicircular protuberances are plotted. Especially, for an important physical property, the average pressure gradient along the microchannel is obtained and compared with that for the case of in-phase arrangement of the upper and lower protuberances. And, for the small clearance between the protuberances of upper and lower walls or between the protuberances and the opposite wall, the average pressure gradient is derived from the lubrication theory and compared with that of the present study.

• Korean Chemical Engineering Research
• /
• v.48 no.2
• /
• pp.198-204
• /
• 2010

Solids flow characteristics have been determined in a pressurized solids recycle systems of silica sand particles for the application in a pressurized CFB(PCFB). The solids recycle system is composed of a downcomer(0.10 m i.d. 2.25 m high) and a loop-seal(0.10 m i.d.). The silica sand($d_p=240{\mu}m$, ${\rho}_s=2582kg/m^3$) particles were transported at room temperature and system pressure($P_{sys}$) up to 0.71 MPa using air. Solids mass flux($G_s$) increases with increasing system pressure at constant aeration rate. Pressure gradient, solids velocity and actual gas velocity increase with increasing $P_{sys}$ at constant aeration rate. The Pressure drop number($\Phi$) on pressure gradient in downcomer has been correlated with Transportation number(Tr). Pressure drop across the loop-seal increases with increasing of $G_s$ irrespective of variation of $P_{sys}$. The obtained $G_s$ and Transportation number(Tr) have been correlated with the experimental variables.