• Structural Engineering and Mechanics
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• 제78권5호
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• pp.585-597
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• 2021

This paper presents a comparative study of analytical method, finite element method (FEM) and Multilayer Perceptron (MLP) for analysis of a contact problem. The problem consists of a functionally graded (FG) layer resting on a half plane and pressed with distributed load from the top. Firstly, analytical solution of the problem is obtained by using theory of elasticity and integral transform techniques. The problem is reduced a system of integral equation in which the contact pressure are unknown functions. The numerical solution of the integral equation was carried out with Gauss-Jacobi integration formulation. Secondly, finite element model of the problem is constituted using ANSYS software and the two-dimensional analysis of the problem is carried out. The results show that contact areas and the contact stresses obtained from FEM provide boundary conditions of the problem as well as analytical results. Thirdly, the contact problem has been extended based on the MLP. The MLP with three-layer was used to calculate the contact distances. Material properties and loading states were created by giving examples of different values were used at the training and test stages of MLP. Program code was rewritten in C++. As a result, average deviation values such as 0.375 and 1.465 was obtained for FEM and MLP respectively. The contact areas and contact stresses obtained from FEM and MLP are very close to results obtained from analytical method. Finally, this study provides evidence that there is a good agreement between three methods and the stiffness parameters has an important effect on the contact stresses and contact areas.

• Composites Research
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• 제33권6호
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• pp.390-394
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• 2020

탄소섬유 스프레드 토우를 제조하는 과정에서 섬유 손상이 발생하며, 이는 스프레딩 과정에서 장비와 섬유 사이 혹은 섬유 간의 마찰로 발생한다. 이로 인해, 재료 및 장비조건에 따라 프로세스 성능에 차이가 발생하고, 제품 물성이 하락한다. 섬유 손상을 최소화하는 것은 스프레드 토우를 제조하는 공정에서 반드시 고려되어야 한다. 본 연구에서는 공기를 이용한 탄소섬유 스프레딩 공정에서 탄소섬유의 필라멘트 수와 사이징 함량, 탄소섬유토우 스프레딩 장비의 공정 변수(초기섬유장력, 열풍온도, 진공압력)를 달리하여 스프레드 토우의 공정성능 변화를 관찰하였다. 탄소섬유 품종에 따른 조건 별 최적조건에서 제조된 샘플을 이용해 인장강도를 평가하여, 탄소섬유의 손상에 따른 기계적 물성 감소를 확인하였다.

• Journal of the Korean Wood Science and Technology
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• 제49권1호
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• pp.14-22
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• 2021

The objective of this study was to investigate the effect of alkali-washing with different sodium hydroxide concentrations on the chemical compositions of steam-treated Betung bamboo strand. Strands were subjected to steam treatment at 126 ℃ for 1 h under 0.14 MPa pressure and followed by washing with 1-5% sodium hydroxide solution for 30 sec. The alteration of structural and non-structural chemical components content of bamboo strands was evaluated. Steam and washing treatments with various concentrations of sodium hydroxide solution considerably reduced the extractive content of bamboo strands, and the cell wall chemical components of the strand in the small degree. FTIR analysis showed noticeable changes in peaks related to hemicellulose and lignin. The relative crystallinity increased significantly after steam and washing treatment with sodium hydroxide up to 3% concentration. SEM Images showed smooth and clean strands surface after washing with 3% sodium hydroxide.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.71-84
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• 2020

In order to improve the performance of marine centrifugal pump, a centrifugal pump whose specific speed is 66.7 was selected for the research. Outlet diameter D2, outlet width b2, blade outlet angle β2, blade wrap φ and blade number z of the impeller were chosen as the variables. The maximum weighted average efficiency and the minimum vibration intensity at the base were calculated as objectives. Based on the Latin Hypercube method, the impeller was numerically optimized. The numerical results show that after optimization, the amplitudes of pressure fluctuation on the main frequency at different monitoring points decrease in varying degrees. The radial force on impeller decreases obviously under off-design flow rates and is more symmetrical during the operation of the pump. The variation of the axial force is relatively small, which has no obvious relationship with the rotating angle of the impeller. The energy performance and vibration experiment was performed for verifying. The test results show that the weighted average efficiency under 0.8Qd, 1.0Qd and 1.2Qd increases by 4.3% after optimization. The maximal vibration intensity at M1-M4 on the pump base reduced from 0.36 mm/s to 0.25 mm/s, decreasing by 30.5%. In addition, the vibration velocities of bracket in pump side and outlet flange also have significant reductions.

• PNF and Movement
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• 제18권3호
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• pp.403-414
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• 2020

Purpose: This study examined how performing chin tuck exercises in supine, sitting, and standing positions affects changes in the muscle activity of the neck and shoulder. Methods: Seventeen men and three women with forward head posture participated in the study. The subjects performed the chin tuck exercise using a pressure biofeedback unit. After determining the ideal order for performing the chin tuck exercise in supine, sitting, and standing positions through randomized controlled trials, muscle activity was measured in the dominant-side sternocleidomastoid, scalenus anterior, upper trapezius, and levator scapulae. Muscle activity was measured three times in each muscle for each position, and the average of the three measurements was used for analysis. Results: In this study, the chin tuck exercise performed in a supine position reduced muscle activity of the sternocleidomastoid, scalenus anterior, upper trapezius, and levator scapulae significantly more than performing the exercise in either sitting or standing positions (p < 0.05). No significant difference in muscle activity was observed when the exercise was performed in a sitting position versus a standing position (p < 0.05). Conclusion: Performing a chin tuck exercise in a supine position is more effective for stabilizing the neck and shoulder than performing it in a sitting or standing position, as it reduces excessive tension and fatigue in the neck and shoulder.

• 한국컴퓨터정보학회논문지
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• 제26권8호
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• pp.113-125
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• 2021

본 연구는 신한복 저고리에 대한 선호도 조사를 통해 추출된 신한복 저고리 디자인을 기본으로 하여 신한복 저고리 원형을 개발하고자 하였다. 본 연구는 선행연구에서 선정된 K패턴을 기본으로 하여 진행되었으며, 외관평가에 대한 분석은 SPSS 27.0 프로그램을 활용하였다. 1차 외관평가 및 의복압 평가 결과, 어깨부위의 수정이 요구되어 어깨끝점을 1cm 줄여 진동둘레를 다시 정리하였다. 소매길이와 둘레의 수정은 소매길이를 1.5cm 줄이고 소매둘레는 양쪽 끝에서 0.5cm씩 줄여 주었다. 2차 평가결과, 저고리길이와 밑단둘레, 소매길이에 대한 수정이 요구되어 앞뒤저고리길이와 소매길이를 1cm 줄여 주었다. 밑단둘레는 프린세스라인에서 각각 0.2cm씩 줄여 총 1.6cm를 줄여 최종 평가에서는 높은 평가를 받았다. 향후 연구에서는 소재별, 길이별, 연령별 패턴 연구를 실시하고 실제 착의실험을 통한 수정사항 도출이 이루어져야 할 것으로 생각된다.

• 한국산업융합학회 논문집
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• 제25권2_1호
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• pp.149-159
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• 2022

Biomass is material that is comprehensive of carbonaceous materials from plants, crops, animals, and algae. It has been used as one of heating fuel since the beginning the emergence of human beings. Since biomass is regarded as carbon-neutral energy source, it has recently been attracting attention as an energy source that can replace fossil fuels. The most widely applied field is distributed power generation, and a method of generating electric power by driving an internal combustion engine with syngas produced by gasifier is chosen. While the composition of the syngas produced in gasifiers changes depending on the air flowing into the reactor, commercialized gasifiers so far do not control the air flowing into the reactor. When the inner pressure in reactor increases, the air sucked into the reactor is reduced. That change of amount of air makes the composition of syngas varied. Those variations of composition of syngas cause the incomplete combustion hence the power output of engine drops, which is a critical weakness of the gasification technology. In this paper, to produce the uniformly composed syngas, PID control is applied. The result was shown when the amount of air into the reactor is supplied with the constant amount using PID control, the standard deviation of caloric values of syngas is around 2[%] of its average value. Meanwhile the gasifier without PID control has the standard deviation of caloric values is around 7[%]. Therefore, Adopting PID control to supply constant air to the gasifier is highly desirable.

• 한국임상수의학회지
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• 제39권3호
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• pp.144-148
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• 2022

A one-year-old spayed female Korean Shorthair cat presented to Kangwon National University Veterinary Hospital with vomiting, weight loss, lethargy, loss of appetite, and polyuria that lasted for more than two weeks. The body condition score, blood pressure, heart rate, and body temperature were abnormally low, and the physical examination findings were consistent with moderate dehydration. Hematological and biochemical tests demonstrated mild azotemia and a low Na:K ratio. Additional abdominal ultrasound imaging revealed reduced size of both adrenal glands. The adrenocorticotropic hormone (ACTH) stimulation test showed decreased post-ACTH cortisol and aldosterone levels and increased endogenous ACTH levels, confirming a diagnosis of primary hypoadrenocorticism. The cat was treated with subcutaneous injections of desoxycorticosterone pivalate (DOCP) and oral prednisolone supplementation, and subsequent electrolyte analysis showed a normal Na:K ratio. Clinical symptoms were also improved in response to treatment. Hypoadrenocorticism in cats is a very rare disease, but it should not be excluded as a potential diagnosis in favor of kidney diseases or other conditions, especially when the Na:K ratio is low. In addition, the prognosis for the disease and the response to DOCP treatment should be further evaluated in cats.

• 한국환경과학회지
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• 제30권12호
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• pp.1053-1065
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• 2021

In this study, the prediction technology of Hydrological Quantitative Precipitation Forecast (HQPF) was improved by optimizing the weather predictors used as input data for machine learning. Results comparison was conducted using bias and Root Mean Square Error (RMSE), which are predictive accuracy verification indicators, based on the heavy rain case on August 21, 2021. By comparing the rainfall simulated using the improved HQPF and the observed accumulated rainfall, it was revealed that all HQPFs (conventional HQPF and improved HQPF 1 and HQPF 2) showed a decrease in rainfall as the lead time increased for the entire grid region. Hence, the difference from the observed rainfall increased. In the accumulated rainfall evaluation due to the reduction of input factors, compared to the existing HQPF, improved HQPF 1 and 2 predicted a larger accumulated rainfall. Furthermore, HQPF 2 used the lowest number of input factors and simulated more accumulated rainfall than that projected by conventional HQPF and HQPF 1. By improving the performance of conventional machine learning despite using lesser variables, the preprocessing period and model execution time can be reduced, thereby contributing to model optimization. As an additional advanced method of HQPF 1 and 2 mentioned above, a simulated analysis of the Local ENsemble prediction System (LENS) ensemble member and low pressure, one of the observed meteorological factors, was analyzed. Based on the results of this study, if we select for the positively performing ensemble members based on the heavy rain characteristics of Korea or apply additional weights differently for each ensemble member, the prediction accuracy is expected to increase.

• 한국지열·수열에너지학회논문집
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• 제17권4호
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• pp.79-90
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• 2021

This paper presents a study to reduce the effect of blast pressure on the blast valves installed in protection tunnels, where the shape of the tunnel entrance and the blast pocket is optimized based on the predetermined basic shape of the protective tunnels. The reliability of the numerical tunnel models was examined by performing analyses of mesh convergence and overpressure stability and with comparison to the data in blast-load design charts in UFC 3-340-02 (DoD, 2008). An optimal mesh size and a stabilized distance of overpressure were proposed, and the numerical results were validated based on the UFC data. A parametric study to reduce the blast overpressures in tunnel was conducted using the validated numerical model. Analysis was performed applying 1) the entrance slope of 90, 75, 60, and 45 degrees, 2) two blast pockets with the depth 0.5, 1.0, and 1.5 times the tunnel width, 3) the three types of curved back walls of the blast pockets, and 4) two types of the upper and lower surfaces of the blast pockets to the reference tunnel model. An optimal solution by combining the analysis results of the tunnel entrance shape, the depth of the blast pockets, and the upper and lower parts of the blast pockets was provided in comparison to the reference tunnel model. The blast overpressures using the proposed tunnel shape have been reduced effectively.