• Tribology and Lubricants
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• v.33 no.5
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• pp.207-213
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• 2017

In sliding bearings, viscous friction due to high shear acting on the bearing surface raises the oil temperature. One of the mechanisms responsible for generating the load-carrying capacity in parallel surfaces is known as the viscosity wedge effect. In this paper, we investigate the effect of film-temperature boundary conditions on the thermohydrodynamic (THD) lubrication of parallel slider bearings. For this purpose, the continuity equation, Navier-Stokes equation, and the energy equation with temperature-viscosity-density relations are numerically analyzed using the commercial computational fluid dynamics (CFD) code FLUENT. Two different film-temperature boundary conditions are adopted to investigate the pressure generation mechanism. The temperature and viscosity distributions in the film thickness and flow directions were obtained, and the factors related to the pressure generation in the equation of motion were examined in detail. It was confirmed that the temperature gradients in the film and flow directions contribute heavily to the thermal wedge effect, due to which parallel slider bearing can not only support a considerable load but also reduce the frictional force, and its effect is significantly changed with the film-temperature boundary conditions. The present results can be used as basic data for THD analysis of surface-textured sliding bearings; however, further studies on various film-temperature boundary conditions are required.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.58-62
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• 2001

Aparallel computing environment was constructed based on Windows 2000 operating system. This cluster was configured using Fast-Ethernet system to hold up together the clients within a network domain. For the parallel computation, MPI implements for Windows such as MPICH.NT.1.2.2 and MP-MPICHNT.1.2 were used with Compaq Visual Fortran compiler which produce a well optimized executives for x86 systems. The evaluation of this cluster performance was carried out using a preconditioned Navier-Stokes code for the 2D analysis of a compressible and viscous flow around a compressor blade. The parallel performance was examined in comparison with those of Linux clusters studied previously by changing a number of processors, problem size and MPI libraries. The result from the test problems presents that parallel performance of the low cost Fast-Ethernet Windows cluster is superior to that of a Linux cluster of similar configuration and is comparable to that of a Myrinet cluster.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.157-162
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• 2005

Parallel implementation and performance assessment of the grid assembly in a structured chimera grid approach is studied. The grid assembly process, involving hole cutting and searching donor, is parallelized on the PC cluster. A message passing programming model based on the MPI library is implemented using the single program multiple data(SPMD) paradigm. The coarse-grained communication is optimized with the minimized memory allocation because that the parallel grid assembly can access the decomposed geometry data in other processors by only message passing in the distributed memory system such as a PC cluster. The grid assembly workload is based on the static load balancing tied to flow solver. A goal of this work is a development of parallelized grid assembly that is suited for handling multiple moving body problems with large grid size.

• Journal of the Korean Society of Combustion
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• v.12 no.2
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• pp.20-25
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• 2007

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Hydrogen Fuel is injected in the cavity parallel with air(or nitrogen) flow. The equivalence ratios in this study are 0.132 and 0.447. Experimental measurements use OH-PLIF near the cavity and pressures in the combustor. For parallel fuel injection case, direct fuel add into cavity leads to increase of cavity pressure. And Flame exists just near the bottom wall for low equivalent ratio. There is no flame in the cavity because of no mixing in it. Compared to the inclined fuel injection, ignition delay length is longer for low equivalence ratio in both case. OH distribution is not a single line but a repeatable fluctuation flame structure by turbulence. Pressure distributions have nothing to do with the fuel injection position.

• 한국연소학회:학술대회논문집
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• 2007.05a
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• pp.31-36
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• 2007

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Hydrogen Fuel is injected in the cavity parallel with air(or nitrogen fuel) flow. The equivalence ratios in this study are 0.132 and 0.447. Experimental measurements use OH-PLIF near the cavity and pressures in the combustor. For parallel fuel injection case, direct fuel add into cavity leads to increase of cavity pressure. And Flame exists just near the bottom wall for low equivalent ratio. There is no flame in the cavity because of no mixing in it. Compared to the inclined fuel injection, ignition delay length is longer for low equivalence ratio in both case. OH distribution is not a single line but a repeatable fluctuation flame structure by turbulence. Pressure distributions have nothing to do with the fuel injection position.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.11
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• pp.923-930
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• 2002

Cooling characteristics of a parallel channel with protruding heat sources using convection and conduction heat transfer are studied numerically. A two-dimensional model has been developed for numerical prediction of transient, compressible, viscous, laminar flow, and conjugate heat transfer between parallel plates with uniform block heat sources. The finite volume method is used to solve the problem. The assembly consists of two channels formed by two covers and one printed circuit board which has three uniform heat source blocks. Six different cooling methods are considered to find out the most efficient cooling method in a given geometry and heat sources. The velocity and temperature fields of cooling medium, the temperature distribution along the block surface, and the maximum temperature in each block are obtained. The results are compared to examine the cooling characteristics of the different cooling methods.

• Journal of Electrical Engineering and Technology
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• v.5 no.1
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• pp.45-53
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• 2010

This paper presents an improved parallel particle swarm optimization approach (IPPSO) based decomposed network for economic power dispatch with discontinuous fuel cost functions. The range of partial power demand corresponding to the partial output powers near the global optimal solution is determined by a flexible decomposed network strategy and then the final optimal solution is obtained by parallel Particle Swarm Optimization. The proposed approach tested on 6 generating units with smooth cost function, and to 26-bus (6 generating units) with consideration of prohibited zone effect, the simulation results compared with recent global optimization methods (Bee-OPF, GA, MTS, SA, PSO). From the different case studies, it is observed that the proposed approach provides qualitative solution with less computational time compared to various methods available in the literature survey.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.7
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• pp.36-46
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• 2017

The turbo code, an error correction code, needs a long decoding time since the same decoding process must be repeated several times in order to obtain a good BER performance. Thus, parallel processing may be used to reduce the decoding time, in which case there may be a memory contention that requires additional buffers. The QPP interleaving has been proposed to avoid such case, but there is still a possibility of memory contention when a decoder is constructed using the so-called double flow technique. In this paper, we propose an even-odd cross mapping technique to avoid memory conflicts even in decoding using the double-flow technique. This method uses the address generation characteristic of the QPP interleaving and can be used to implement the interleaving circuit between the decoding blocks and the LLR memory blocks. When the decoder implemented by applying the double flow and the proposed methods is compared with the decoder by the conventional MDF techniques, the decoding time is reduced by up to 32% with the total area increase by 8%.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.4
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• pp.88-95
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• 2013

A new droop control method which can be applied to 3-phase 4-wire uninterruptible power supply is proposed in this paper. The droop control method for parallel operation is very attractive one as UPS parallel operation can be carried out without any data communication devices provided among UPS systems connected, but it reportedly shows a PnP(plug-and-play) problem. A basic reason why a circulating current could flow among parallel-connected UPS systems is clearly investigated as well when droop-controlled-ups systems are operated in the manner of PnP. The proposed algorithm is deduced from the investigated result and is basically structured to keep a balanced frequency and balanced voltage profile against power variation. This paper shows that balanced parallel operation of droop control method can be obtained under unbalanced load as well as balanced load conditions when PnP operation is needed and load change occurs.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.1-8
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• 2013

In nuclear power plant, the reactor cooling system has maintained high-Reynolds-number flow above 1E+07 to cool a heat generated by the reactor. To minimize uncertainty for flow calibration, it is necessary to simulate the high Reynolds' number flow. Y-connection is selected to connect four (4) parallel high flow circulation pumps for maintaining the high flow rate. This paper describes the characteristics for Y-connection by computer flow simulation. It was confirmed through the results that the pressure loss of the Y-connection was lower than that of T-connection. Also as the connection angle of Y-connection was small, as the pressure loss was low.