• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.526-544
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• 2021

Based on the potential flow theory, a fully nonlinear numerical procedure is developed with boundary element method to analyze the interaction between a fixed semi-submersible platform and incident waves in open water. The incident wave is separated from the scattered wave under fully nonlinear boundary conditions. The mixed Euler-Lagrangian method is used to capture the position of the disturbed wave surface in local coordinate systems. The wave forces exerted on an inverted conical frustum are used to ensure the accuracy of the present method and good agreements with published results are obtained. The hydrodynamic characteristics of the semi-submersible platform interacting with regular waves are analyzed. Pressure distribution with time and space, tension and compression of the platform under wave action are investigated. 3D behaviors of wave run-ups are predicted. Strong nonlinear phenomena such as wave upwelling and wave interference are observed and analyzed.

• Journal of Korean Society of Steel Construction
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• 제26권2호
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• pp.91-103
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• 2014

High performance steel for bridges(HSB 800) with a minimum tensile stress of 800MPa was recently developed. However, the study for local buckling behavior of plate girders considering interactive effects of flanges and webs is still insufficient. In this study, the flange local buckling(FLB) strength of plate girders with HSB 800 was evaluated by nonlinear finite element analysis. The flanges and webs of plate girders having I-section were modeled as 3D shell elements in the nonlinear analysis. Initial imperfection and residual stress were imposed on the plate girder. The high performance steel was modeled as a multi-linear material. Thus, parametric study of compression flanges with a compact, noncompact and slender web was performed. The flange local buckling behavior of plate girders was analyzed, and the nonlinear analysis results were compared with the nominal flexural strength of both AASHTO LRFD(2012) and KHBDC LSD(2012) codes.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제17권6호
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• pp.18-25
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• 2016

Enhanced tubes are used widely in the evaporators of large tonnage compression-type refrigerators. The evaporators consist of tube bundles, and the refrigerant properties are dependent on the locations in the tube bundles. In particular, the saturation temperatures of low pressure refrigerants (R-11, R-123) are strongly dependent on the locations due to the saturation temperature-pressure curve characteristics. Therefore, for the proper design of evaporators, local property predictions of the refrigerants are necessary. In this study, a computer program that simulates the flooded refrigerant evaporators was developed. The program incorporated theoretical models to predict the refrigerant shell-side boiling heat transfer coefficients and pressure drops across the tube bundle. The program adopted an incremental iterative procedure to perform row-by-row calculations over the specified incremental tube lengths for each water-side pass. The program was used to simulate the flooded refrigerant evaporator of the "T" company operating with R-123, which yielded satisfactory results. The program was extended to predict the performance of the flooded refrigerant evaporator operating with R-11, R-123, and R-134a. The effects of bundle aspect ratio are investigated.

• Journal of Korean Society of Steel Construction
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• 제21권5호
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• pp.471-481
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• 2009

The purpose of this study was to compare and analyze the compression behaviors of SSC (stiffened steel plate-concrete) and NSC (non-stiffened steel plate-concrete) structures, and to identify the effects of the increment in the structural performance of SSC structures. SCC structures are structures that integrate steel plates with line support from ribs (H-shape) and point supports from studs with concretes. On the other hand, NSC structures are structures that integrate steel plates with point supports from studs with concrete. The following results were obtained in this study. First, compared with NSC structures, it was shown that SSC structures have advantages in terms of preventing steel plate buckling and delaying quick destruction through the brittleness of concrete. In addition, the SSC structures showed a 5-28% increment in maximum compressive strength, which far surpassed that shown by the NSC structures.

• KIPS Transactions on Software and Data Engineering
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• 제2권7호
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• pp.495-502
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• 2013

Motion estimation (ME) that limits the performance of image quality and encoding speed has been developed to reduce temporal redundancy in video sequences and plays an important role in digital video compression. But it is computational demanding part of the encoder. Multi-view video is obtained by capturing one three-dimensional scene with many cameras at different positions. ME for Multi-view video requires high computational complexity. To reduce computational complexity and maintain the image quality, a fast motion estimation method is proposed in this paper. The proposed method uses a hierarchical search strategy. This strategy method consists of modified diamond search patten, multi gird diamond search pattern, and raster search pattern. These search patterns place search points symmetrically and evenly that can cover the overall search area not to fall into the local minimum or exploits the characteristics of the distribution of motion vectors to place the search points. Experiment results show that the speedup improvement of the proposed method over TZ search method (JMVC) can be up to 1.2 ~3 times faster while maintaining similar video quality and bit rates.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제33권12호
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• pp.92-100
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• 2005

An aircraft wing or fuselage panel of skin-stringer assembly can fail in a variety of instable modes under compression loads. Instability modes can be buckling of the panel, local buckling of the stringer, flexure, torsion, wrinkle and combined flexural/torsional buckling of the panel assembly. Although researches on these buckling behaviors have been carried out for a long time, there are some difficulties to apply to the practice because of complex theoretical and empirical equations. Accordingly, It is well known that leading aerospace companies are using their own in-house programs for the convenience of practical usage, but our domestic situation is that no such program has been ever developed. In this study a comprehensive program has been developed, which can identify the instability modes and the magnitude of reserve factor of the modes for the skin/stringer panel assembly under compression load. The developed program is based on the theory manual of the Airbus program APA114. For the verification, calculation of the instable reserve factors for the A320 wing panel and A380 low wing panel sections were carried out and compared with results by APA114.

• Korean Journal of Adult Nursing
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• 제15권3호
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• pp.383-392
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• 2003

Purpose: The purpose of this descriptive study was to gain basic data to develop a self-care protocol for the lymphedema patients. Method: The subjects of this study consisted of 115 patients with lymphedema from 8 hospitals and two community health and welfare centers in Busan and Seoul. The data was collected with questionnaire by self reporting of patients between March 2001 and December 2001. Data was analyzed by mean and percentage. Result: For self-care activities in daily life, compliance of 'use skin care preparations', 'use heat and cold', 'protect from local compression on affected limbs', 'protect from insect biting', 'use aids to protect affected limbs', 'take diuretics and take protein diet' did not reach to 50%. For self-care activities related to complex physical therapy, 28.7% of subjects complied with compression garment, 14.8% with manual lymph drainage, and 13.0% with exercise. 20.0% of subjects tried to treat with acupuncture and 13.9% with heat therapy. Conclusion: From this study, it is suggested that patients need to get a self-care education with correct information about self care activities and health care professionals need to develop more convenience self-care techniques of massage and exercise.

• Journal of Institute of Control, Robotics and Systems
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• 제19권7호
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• pp.653-660
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• 2013

This paper deals with the problem of unfairness among uplink TCP (Transmission Control Protocol) flows associated with frame aggregation employed in IEEE 802.11n WLANs (Wireless Local Area Networks). When multiple stations have uplink TCP flows and transmit TCP data packets to an AP (Access Point), the AP has to compete for channel access with stations for the transmission of TCP ACK (acknowledgement) packets to the stations. Due to this contention-based channel access, TCP ACKs tend to be accumulated in the AP's downlink buffer. We show that the frame aggregation in the MAC (Medium Access Control) layer increases TCP ACK losses in the AP and leads to the serious unfair operation of TCP congestion control. To resolve this problem, we propose the TAC (TCP ACK Compression) mechanism operating at the top of the AP's interface queue. By exploiting the properties of cumulative TCP ACK and frame aggregation, TAC serves only the representative TCP ACK without serving redundant TCP ACKs. Therefore, TAC reduces queue occupancy and prevents ACK losses due to buffer overflow, which significantly contributes to fairness among uplink TCP flows. Also, TAC enhances the channel efficiency by not transmitting unnecessary TCP ACKs. The simulation results show that TAC tightly assures fairness under various network conditions while increasing the aggregate throughput, compared to the existing schemes.

• Journal of Korean Neurosurgical Society
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• 제37권2호
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• pp.116-123
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• 2005

Objective: Percutaneous kyphoplasty using a balloon-catheter is an widely accepted method which achieves the restoration of vertebral height and the correction of kyphotic deformity with little complication in osteoporotic vertebral compression fractures. The authors assess the results of 59 patients who underwent kyphoplasty, and analyze the factors that could affect the prognosis. Methods: From December 2001 to May 2003, fifty-nine patients underwent kyphoplasty. The patients included 49 women and 10 men aged 52-85 years. Average t-score on bone marrow density was -3.58. About 7cc of polymethylmethacrylate(PMMA) was injected into the fractured vertebral body using $Kyphon^{(R)}$ under local anesthesia. The vertical height of all fractured vertebrae was measured both before and after surgery. Outcome data were obtained by comparing pre- and post-operative VAS score and by assessing postoperative satisfaction, drug dependency and activity. Various clinical factors were analyzed to assess the relationship with the outcome. Results: The VAS score improved significantly, and the mean percentage of restored vertebral height was 53%. The mean improvement in kyphosis was $3.6^{\circ}$. Eighty-nine percent of the patients gained excellent or good results. Any of the clinical factors including the interval between fracture and operation, the degree of height loss, the degree of the vertebral height restoration or the correction rate of kyphosis did not affect the clinical results. Conclusion: Kyphoplasty is associated with a statistically significant improvement in pain and function with little complication. The clinical results are not affected by any clinical parameters. Further follow-up study is needed to determine whether the restoration affects the long-term clinical results.

• Journal of the Korea Society of Computer and Information
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• 제12권4호
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• pp.87-94
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• 2007

Imbalances in focus, luminance and color between stereo Pairs could cause disparity vector estimation error and increment of transmission data. If the distribution of errors in residual image is large, it may influence to lowering of compression performance. Therefore, in this paper, we propose an efficient balancing method between stereo pairs to reduce the effect. For this, we registrated stereo images using a FFT based method to consider the pixels in the occluded region, we eliminated the pixels of blocks which has large error of disparity vector estimation in balancing function estimation. The balancing function has estimated using histogram specification, local information of target image and residual image between stereo images. Experiments show that the proposed method is effective in error distribution, PSNR and disparity vector estimation. We expect that our method can be improving compression efficiency in stereo coding system.