• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2686-2697
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• 1994

When a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel, which causes an impulsive noise. In order to estimate the magnitudes of the noises and to effectively minimize them, the characteristics of the compression wave propagating in a tunnel must be understood. In the present paper, the experimental and analytical investigations on the attenuation and distortion of the propagating compression waves were carried out using a model tunnel. This facility is a kind of open-ended shock tube with a fast-opening gate valve instead of a general diaphragm. One-dimensional flow model employed in the present study could appropriately predict the strength of the compression wave, Mach number and flow velocity induced by the compression wave. The experimental results show that the strength of a compression wave decreases with the distance from the tunnel entrance. The decreasing rate of the wave strength and pressure gradient in the wave is strongly dependent on the strength of the initial compression wave at the tunnel entrance.

• Steel and Composite Structures
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• v.44 no.6
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• pp.883-898
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• 2022

A hollow-core partially-encased composite beam, named HPEC beam, is investigated in this paper. HPEC beam comprises I-beam, longitudinal reinforcement, stirrup, foam formwork, and cementitious grout. The foam formwork is located on both sides of the web, and cementitious grout is cast within the steel flange. To investigate the shear performance of HPEC beams, static loading tests of six HPEC beams and three control beams were conducted. The shear span ratio and the number of studs on the shear behavior of the HPECspecimens were studied. The failure mechanism was studied by analyzing the curves of shear force versus both deflection and strain. Based on the shear span ratio (𝜆), two typical shear failure modes were observed: shear compression failure when 1.6 ≤ 𝜆 ≤ 2; and diagonal compression failure when 𝜆 ≤ 1.15. Shear studs welded on the flange can significantly increase the shear capacity and integrity of HPEC beams. Flange welded shear studs are suggested. Based on the deformation coordination theory and superposition method, combined with the simplified modified compression field model and the Truss-arch model, Modified Deformation Coordination Truss-arch (M.D.C.T.) model was proposed. Compared with the shear capacity from YB9038-2006 and JGJ138-2016, the calculation results from M.D.C.T. model could provide reasonable predictions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.486-493
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• 2000

A theoretical model for the transient performance of vapor-compression air-conditioning system has been developed to evaluate the influence of the refrigerant charge on the system performance. A set of mass and energy equations for the simulation of the heat exchangers and the capillary tube and a polytropic compression model for the compressor are used. The present model successfully predicts the transient behavior of the vapor-compression air-conditioner from the startup. As the refrigerant charge is increased, both the evaporating and condensing pressures increase gradually, and the cooling rate and the COP show a maximum in the range of 0.75-0.8 kg of refrigerant charge. This amount of refrigerant mass is determined to be the optimum charge of the model system. Also, the effect of outdoor air temperature on the optimum refrigerant charge is discussed.

• The Journal of Korea Robotics Society
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• v.17 no.2
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• pp.133-141
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• 2022

This paper introduces model compression algorithms which make a deep neural network smaller and faster for embedded systems. The model compression algorithms can be largely categorized into pruning, quantization and knowledge distillation. In this study, gradual pruning, quantization aware training, and knowledge distillation which learns the activation boundary in the hidden layer of the teacher neural network are integrated. As a large deep neural network is compressed and accelerated by these algorithms, embedded computing boards can run the deep neural network much faster with less memory usage while preserving the reasonable accuracy. To evaluate the performance of the compressed neural networks, we evaluate the size, latency and accuracy of the deep neural network, DenseNet201, for image classification with CIFAR-10 dataset on the NVIDIA Jetson Xavier.

• International Journal of Oral Biology
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• v.34 no.3
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• pp.157-164
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• 2009

We recently described a novel animal model of trigeminal neuropathic pain following compression of the trigeminal ganglion (Ahn et al., 2009). In our present study, we adapted this model using male Sprague-Dawley rats weighing between 250-260 g and then analyzed the behavioral responses of these animals following modified chronic compression of the trigeminal ganglion. Under anesthesia, the rats were mounted onto a stereotaxic frame and a 4% agar solution ($10{\mu}L$) was injected in each case on the dorsal surface of the trigeminal ganglion to achieve compression without causing injury. In the control group, the rats received a sham operation without agar injection. Air-puff, acetone, and heat tests were performed at 3 days before and at 3, 7, 10, 14, 17, 21, 24, 30, 40, 55, and 70 days after surgery. Compression of the trigeminal ganglion produced nociceptive behavior in the trigeminal territory. Mechanical allodynia was established within 3 days and recovered to preoperative levels at approximately 60 days following compression. Mechanical hyperalgesia was also observed at 7 days after compression and persisted until the postoperative day 40. Cold hypersensitivity was established within 3 days after compression and lasted beyond postoperative day 55. In contrast, compression of the trigeminal ganglion did not produce any significant thermal hypersensitivity when compared with the sham operated group. These findings suggest that compression of the trigeminal ganglion without any injury produces prolonged nociceptive behavior and that our rat model is a useful system for further analysis of trigeminal neuralgia.

• Geomechanics and Engineering
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• v.18 no.2
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• pp.121-131
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• 2019

This article discusses the phenomenon of plastic volumetric deformation of naturally structured clays before virgin yielding, i.e., subyielding behavior. A simple approach representing both the compression and shear responses of the clays during subyielding is demonstrated. A new compression model for structured clays based on the theoretical framework of the Structured Cam Clay (SCC) model via incorporation of the subyielding behavior is presented. Two stress surfaces are introduced to distinguish the subyielding and virgin yielding. The hardening and destructuring processes of structured clays under isotropic compression and shear are the focus of this work. The simulations of the compression and shear of eleven natural clays are studied for validation. The proposed work can accurately predict the subyielding behavior of structured clays both qualitatively and quantitatively and can be used for modeling structured clays under compression and shear responses in geological and geotechnical engineering problems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1242-1248
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• 2006

Densification behavior of nanocrystalline titania powder was investigated under cold compaction. Experimental data were obtained under triaxial compression with various loading conditions. Lee and Kim proposed the Cap model by developing the parameters involved in the yield function of general Cap model and volumetric strain evolution under cold isostatic pressing. The parameters in the Drucker/Prager Cap model and the proposed model were obtained from experimental data under triaxial compression. Finite element results from the models were compared with experimental data for densification behavior of nanocystalline ceramic powder under cold isostatic pressing and die compaction. The proposed model agreed well with experimental data under cold compaction, but the Drucker/Prager Cap model underestimated at the low density range. Finite element results, also, show the relative density distribution of nanocystalline ceramic powder compacts is severe compared to conventional micron powder compacts with the same averaged relative density.

• Journal of Biosystems Engineering
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• v.26 no.5
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• pp.449-460
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• 2001

This study was carried out to develop a simulation model with EES(Engineering equation solver) for analyzing the performance of a grain cooler. In order to validate the developed simulation model, several main factors which have affected on the performance of the gain cooler were investigated through experiments. A simulation model was developed in the standard vapor compression cycle, and then this model was modified considering irreversibe factors so that the developed alternate model could predict the actual cycle of a grain cooler. The compressor efficiency in vapor compression cycle considering irreversibility much affected on the coefficient of performance(COP). The COP in the standard vapor compression cycle model was greatly as high as about 6.50, but the COP in an alternative model considering irreversibility was as low as about 3.27. As a result of comparison between the actual cycle and the vapor compression cycle considering irreversibility, the difference of pressure at compressor outlet(inlet) was a little by about 48kPa (8.8kPa), the temperatures of refrigerant at main parts of the grain cooler were similar. and the temperature of chilled air was about 8$\^{C}$ in both. The model considering irreversibility could predict performance of the grain cooler. The theoretical period required to chill grain of 1,383kg from the initial temperature 24$\^{C}$ to below 11$\^{C}$ was about 55 hours 30 minutes, and the actual period required in a grain bin was about 58 hours. The difference between the predicted and an actual period was about 2 hours 30 minutes. The cooling performance predicted by the developed model could well estimate the cooling period required to chill the grain.

• Fibers and Polymers
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• v.7 no.4
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• pp.389-397
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• 2006

The beneficial effects of graduated compression stockings (GCS) in prophylaxis and treatment of venous disorders of human lower extremity have been recognized. However, their pressure functional performances are variable and unstable in practical applications, and the exact mechanisms of action remain controversial. Direct surface pressure measurements and indirect material properties testing are not enough for fully understanding the interaction between stocking and leg. A three dimensional (3D) biomechanical mathematical model for numerically simulating the interaction between leg and GCS in dynamic wear was developed based on the actual geometry of the female leg obtained from 3D reconstruction of MR images and the real size and mechanical properties of the compression stocking prototype. The biomechanical solid leg model consists of bones and soft tissues, and an orthotropic shell model is built for the stocking hose. The dynamic putting-on process is simulated by defining the contact of finite relative sliding between the two objects. The surface pressure magnitude and distribution along the different height levels of the leg and stress profiles of stockings were simulated. As well, their dynamic alterations with time processing were quantitatively analyzed. Through validation, the simulated results showed a reasonable agreement with the experimental measurements, and the simulated pressure gradient distribution from the ankle to the thigh (100:67:30) accorded with the advised criterion by the European committee for standardization. The developed model can be used to predict and visualize the dynamic pressure and stress performances exerted by compression stocking in wear, and to optimize the material mechanical properties in stocking design, thus, helping us understand mechanisms of compression action and improving medical functions of GCS.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.89-98
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• 1997

Compression waves propagating in a high speed railway tunnel impose large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations can cause ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, a steady theory of Chester-Chisnell- Whitham was applied to a simple shock tube with a sudden cross-sectional area reduction to model trains inside the tunnel. The results of the present theoretical analysis were compared with the experiments of the shock tube. The results show that the reflected compression wave from the model becomes stronger as the strength of incident compression wave and the blockage ratio increase. However, the compression wave passing through the model is not strongly dependent on the blockage ratio. The theoretical results are in good agreement with the experiments.