• Proceedings of the KSME Conference
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• 2001.06d
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• pp.1001-1007
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• 2001

Hydrogen fueled engine with dual injection can achieve high power and high efficiency simultaneously. In this study, the suitable compression ratio of hydrogen fueled engine with dual injection were investigated including performance of this engine according to variation of compression ratio. As results, it was found that the suitable compression ratio of that was about CR=11, and torque and thermal efficiency increased by 6% and 7% respectively.

• International journal of advanced smart convergence
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• v.6 no.1
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• pp.68-75
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• 2017

In this paper, a particular application of digital photos, remote sensing, remote shooting air moving, high-resolution and high compression of medical images required by remote shooting of JPEG2000 standard applied in the field of hardware design, production was implemented. JPEG2000 standard for image compression using the software implementation of the processing speed is very slow compared to conventional JPEG disadvantages, and also the standard of JPEG2000 DWT (Discrete wavelet transform) to improve the level of compression for image data if processing speed is a phenomenon that has degraded. In order to solve these JPEG2000 compression / decompression groups were designed and applied. In this paper, the optimal JPEG2000 compression / reservoir hardware by changing the level for still image compression, faster computation speed and quality has shown improvement.

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.596-603
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• 1998

The entry compression wave, which is generated at the entrance of the tunnel, is almost always associated with the pressure transients in the tunnel as well as the impulse noise at the exit of the tunnel. It is highly required to design the train nose shape that can minimize such undesirable phenomena. The objective of the current work is to investigate the effects of the train nose shape on the entry compression wave. Numerical computations were applied to one-dimensional unsteady compressible flow in high-speed railway train/tunnel systems. A various shape of train noses were tested for a wide range of train speeds. The results showed that the strength of the entry compression wave is not influenced by the train nose shape, but the time variation of pressure in the entry compression wavefront is strongly related to the train nose shape. The current method of the characteristics was able to represent a desirable nose shape for various train speeds. Optimum nose shape was found to considerably reduce the maximum pressure gradient of the entry compression wave.

• Geomechanics and Engineering
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• v.2 no.4
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• pp.303-319
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• 2010

The effect of grain crushing on the deformation of sand in 1D compression and 1D creep at high stresses was investigated theoretically and experimentally. An approach was proposed to formulate the process of grain crushing in sand in accordance with the laws of fracture mechanics and energy conservation. With this approach, the relation between the void ratio and the amount of grains crushed in 1D compression was derived. Laboratory test data were used to verify this derived relation. In addition, it was observed that there are similarities in evolution of grain size distribution in 1D compression and 1D creep tests. This implies that the changes in microstructure in sand under 1D compression and 1D creep are comparable.

• International Journal of Concrete Structures and Materials
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• v.4 no.1
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• pp.63-68
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• 2010

With the emergence of ultra-high strength of concrete, the compression lap splice has become an important area of interest. According to ACI 318-08, a compression splice can be longer than a tension splice when high-strength concrete is used. By reevaluating the test results of compression splices and performing regression analysis, a simplified design equation for splice length in compression was developed based on the basic form of design equations for development/splice lengths of deformed bars and hooks in tension. A simple linear relation between $l_s/d_b$ and $f_{sc}\sqrt{f'_c}$ was assumed, and yields good values for the correlation coefficient and the mean and the COV (coefficient of variation) of the ratios of tests to predictions of splice strengths in compression. By including the 5% fractile coefficient of 0.83, a design equation for splice length in compression was developed. The splice length calculated using the proposed equation has a reliability that is equivalent to other provisions for reinforcing bars.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2315-2325
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• 1996

A compression wave is attenuated or distorted as it propagates in a tube. The present study investigated the propagation characteristics of the compression waves which are generated by a train in a high-speed railway tunnel. A Total Variation Diminishing (TVD) difference scheme was applied to one-dimensional, unsteady viscous compressible flow. The numerical calculation involved the effects of wall friction, heat transfer and energy loss due to the friction heat in the boundary layer behind the propagating compression wave, and compared with the measurement results of a shock tube and a real tunnel. The present results show that attenuation of the compression wave in turbulent boundary layer is stronger than in laminar boundary layer, but nonlinear effect of the compression wave is greater in the laminar boundary layer. The energy loss due to the frictional heat had not influence on attenuation and distortion of the propagating compression waves.

• The Korean Journal of Emergency Medical Services
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• v.17 no.2
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• pp.57-64
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• 2013

Purpose : The purpose of the study is to investigate the quality and relevance of back strength or chest compression which is applied by isotonic exercise of hip joint. Methods : Subjects were 37 students who participated in the BLS course and accepted the informed consent from December 7 to 8, 2012. During CPR performance, back strength was measured by the researcher. CPR was used the manikin for practical training with using PC, conducted by standard CPR for 2 minutes, Quality of chest compressions included average chest compression depth, rate, and recoil ratio. Results : Back strength (kg) is related to the chest compression depth (mm) (r =.746, p <.001). The high quality CPR is the most important factor so high quality is full chest recoil of chest compression and chest compression depth (mm) (${\beta}$=.831, p <.001). In this study, chest compression rate and recoil ration were not influenced by back muscle strength. Conclusion : It is necessary to implement the CPR program to improve physical strength and effective performance of CPR.

• Journal of the Korean Society of Clothing and Textiles
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• v.41 no.3
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• pp.420-432
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• 2017

This study examined user needs for compression pant development for women with pes planus in their 50s and 60s. A total of 355 women aged 50 to 69 participated in the survey and interview. Questions were asked if they had pes planus, the using condition of foot orthotic, inconveniences during gait, and wearing condition of compression pants. The results showed that 42 (11.8%) women had pes planus. Orthotic insole and arch support were used most frequently. The most uncomfortable aspect of foot orthotic (n=146) was that it was difficult to use unless they were going outside. Participants with pes planus responded that they felt discomfort on the inner area of propodium, metatarsus, ankle, and knee during gait. The purchase and wearing rate of compression pants were not high; however, compression pants were purchased with specific needs and purposes. Respondents mainly wore the compression pants for sports activities. M size was the most frequently worn size. They preferred high waist type leggings and there was a need to increase the compression strength of the waist, thigh, knee and ankle. Additionally, the ease of donning and doffing were discussed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.5
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• pp.432-438
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• 2003

This paper describes a modified Roebuck compression device as a potential compression device of a rotating cryogenic refrigeration system in superconducting machine such as generator or motor. The conventional cryogen transfer method from stationary refrigeration system to rotating system can be eliminated by an on-board cryogenic refrigeration system that utilizes well-designed multi-stage modified Roebuck compression device. This paper shows basic thermodynamic analysis of modified Roebuck compression device and its application for compressing neon at 77 K with substantial pressure ratio when the rotor diameter is 0.8 m with rotating speed of 3600 rpm. The device does not require any moving part in rotating frame, but two separate thermal reservoirs to convert thermal energy into mechanical compression work. The high temperature thermal reservoir is atmospheric environment at 300 K and the low temperature thermal reservoir is assumed as a liquid nitrogen bath at 77 K. The concept of the compression device in this paper demonstrates its usefulness of generating high-pressure neon at 77 K for rotating J-T neon refrigeration cycle of superconducting rotor.

• Journal of KSNVE
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• v.7 no.6
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• pp.959-966
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• 1997

In general, the booming noise intensity at tunnel exit is strongly related to the gradient of the compression wave front created by high speed train entering the tunnel. This paper presents some results in relation with the compression wave front produced when the high speed train enters a tunnel. Four kinds of tunnel entrance shape with real dimensions were studied to investigate the formation of compression wave front inside tunnel by train entering tunnel. Computations were carried out using three-dimensional compressible Euler equation with vanishing viscosity and conductivity of fluid. According to the results, the flow disturbances occured at tunnel entrance were eliminated by tunnel hood with same cross sectional area. The compression wave front is formed completely at 30-40m from tunnel entrance. The maximum pressure gradient of compression wave front is reduced by 29.8% for the inclined tunnel hood and reduced by 21.5% for the tunnel hood with holes at the top face with tunnel without hood. The length of the inclined hood is 15m and the length of the hood with holes is 20m.