• The Journal of the Acoustical Society of Korea
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• v.43 no.3
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• pp.277-284
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• 2024

This study proposes a method to predict noise reduction based on noise-reduction measures, using harmonic response analysis, for transformer design. The dynamic elastic coefficients of the components comprising the actual transformer were determined by manufacturing the materials of the transformer components into simple-shaped specimens, followed by a comparison of the modes between the experiments and the analyses. A finite element model of the transformer was implemented, and harmonic response analysis was performed by deriving the exciting force of the transformer. Subsequently, the theoretical sound power level of the transformer was derived from the results of the harmonic response analysis. Finally, noise reduction measures were established, and the noise reduction amounts were compared between the experiments and the analyses, before and after applying the measures. Through the comparison and analyses of the noise reduction measures, it was confirmed that the trends in the experiments and analyses matched.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.5 s.57
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• pp.109-120
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• 2009

This paper introduces a new method to estimate the loss of prestressing force for the externally prestressing tendon. The proposed method that combines of HGA and FEM is able to identify the lost tensile force of a externally prestressed tendon. The identification variables of the proposed method is a exteranlly prestressed tendon of tension, effective nominal diameter, mass per unit length and Rayleigh damping coefficients. First of all, a finite element model system is constructed to consider the effect of damping, and these variables are identified using inverse analysis technique - updating algorithm. Finally, throughout total 3 cases of numerical tests, the numerical propriety of the proposed method is verified. Here, it is seen that the errors in the estimated variables by the proposed method are about 1% except in the case of Rayleigh damping coefficients.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.4
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• pp.363-371
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• 2023

To construct a ship, blocks of various sizes must be moved and erected . In this process, lugs are used such that they match the block fastening method and various functions suitable for the characteristics of each shipyard facility. The sizes and shapes of the lugs vary depending on the weight and shape of the block structures. The structure is reinforced by welding the doubling pads to compensate for insufficient rigidity around the holes where the shackle is fastened. As for the method of designing lugs according to lifting loading conditions, a simple calculation based on the beam theory and structural analysis using numerical modeling are performed. In the case of the analytical method, a standardized evaluation method must be established because results may differ depending on the type of element and modeling method. The application of this ambiguous methodology may cause serious safety problems during the process of moving and turning-over blocks. In this study , the effects of various parameters are compared and analyzed through numerical structural analysis to determine the modeling conditions and evaluation method that can evaluate the actual structural response of the lug. The modeling technique that represents the plate part and weld bead around the lug hole provides the most realistic behavior results. The modeling results with the same conditions as those of the actual lug where only the weld bead is connected to the main body of the lug, showed a lower ulimated strength compared with the results obtained by applying the MPC load. The two-dimensional shell element is applied to reduce the modeling and analysis time, and a safety working load was verified to be predicted by reducing the thickness of the doubling pad by 85%. The results of the effects of various parameters reviewed in the study are expected to be used as good reference data for the lug design and safe working load prediction.

• The Korean Journal of Rheology
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• v.10 no.4
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• pp.217-226
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• 1998

The anisotropy caused by the fiber orientation, which is inevitably generated by the flow during injection molding of short fiber reinforced polymers, greatly influences dimensional accuracy, mechanical properties, and other quality of the final product. Since the filling stage of the injection molding process plays a vital role in determining fiber orientation, an accurate analysis of flow field for the filling stage is needed. Unbalanced filling occurs when a complex or a multi-cavity mold is used leading to development of regions where the fiber suspension is under compression. It is impossible to make an accurate calculation of the flow field during filling with the analysis assuming incompressible fluid. A mold with four cavities with different filling times was produced to compare the numerical analysis results with the experimental data. There was a good agreement between the experimental and theoretical results when the compressibility of the polymer melt was considered for the numerical simulation. The fiber orientation states for compressible and incompressible fluids were also compared qualitatively as well as quantitatively in this study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.594-600
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• 2021

Curved beam structures are generally used as components in structures such as railroad bridges and vehicles. The stability analysis of curved beams has been studied by a large number of researchers. Due to the complexities of structural components, it is difficult to obtain an analytical solution for any boundary conditions. In order to overcome these difficulties, the differential quadrature method (DQM) has been applied for a large number of cases. In this study, DQM was used to solve the complicated partial differential equations for buckling analysis of curved beams. The governing differential equation was deduced and solved for beams subjected to uniformly distributed radial loads. Critical loads were calculated with various opening angles, boundary conditions, and parameters. The results of the DQM were compared with exact solutions for available cases, and the DQM gave outstanding accuracy even when only a small number of grid points was used. Critical loads were also calculated for the in-plane inextensional buckling of the asymmetric curved beams, and two theories were compared. The study of a beam with extensibility of the arch axis shows that the effects on the critical loads are significant.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.265-270
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• 2013

Strength design for a lightweight bicycle frame made of carbon/epoxy composite laminates was studied using Tsai-Wu's failure criterion. For the design of bicycle frames, reducing the weight of the frame is of great importance. Furthermore, the frame should satisfy the required strength under specific loading cases. In accordance with the European EN 14764 standard for bicycle frames, three loading cases-pedaling, vertical, and level loadings-were investigated in this study. Because of the anisotropic characteristics of composite materials, it is important to decide the appropriate stacking sequence and the number of layers to be used in the composite bicycle frame. From finite element analysis results, the most suitable stacking sequence of the fiber orientation and the number of layers were determined. The stacking sequences of $[0]_{8n}$, $[90]_{8n}$, $[0/90]_{2ns}$, $[{\pm}45]_{2ns}$, $[0/{\pm}45/90]_{ns}$ (n = 1, 2, 3, 4) were used in the analysis. The results indicated that the $[0/{\pm}45/90]_{3s}$ lay-up model was suitable for a composite bicycle frame. Furthermore, the weakest point and layer were investigated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.53-62
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• 1987

High power lasers provide a controllable and precise energy source in surface transformation hardening. A careful control of the process is needed in order that the surface layer of the material reaches the austenizing temperature, but that it does not melt. In order to achieve this the results of theoretical and experimental studies on the laser surface hardening of a medium carbon steel are described. A two-dimensional computer program, which can be used generally for the determination of transient temperature distributions in welding and heat treatment, was established on the basis of the finite element method. For the confirmation of the accuracy of the numerical analysis, a medium carbon steel (SM 45C) of 5mm thickness was heat-treated with a 1kW CW CO$_{2}$ laser machine, while the traverse speed and the distance from the focal point (defocused distance) were varied. Experimental and numerical results showed a similar tendency in correlations between the hardened zone shape and the process parameters. With increasing beam spot diameter the width and depth of the hardened zone increased for relatively small beam spot diameters, but decreased rapidly after reaching the maximum value, while with increasing traverse speed the width and depth of the hardened zone decreased monotonously. Too small beam spot diameters are to be avoided, since the surface melting would lower the surface hardness and produce an uneven surface which may be unacceptable because of the possible requirement for subsequent machining. It could be observed that for a given traverse speed and laser power input there exists a optimal range of the beam spot diameter, which produce a large width of the hardened zone but no melting on the surface.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.3
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• pp.213-220
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• 2000

The method of photoelasticity allows one to obtain principal stress differences and principal stress directions in a photoelastic model. In the classical approach, the photoelastic parameters are measured manually point by point. The previous methods require much time and skill in the identification and measurement of photoelastic data. Fringe phase shifting method has been recently developed and widely used to measure and analyze fringe data in photo-mechanics. This paper presents the test results of photoelastic fringe phase shifting technique for the stress analysis of a circular disk under compression and an edge-cracked plate subjected to tensile load. The technique used here requires four phase stepped photoelastic images obtained from a circular polariscope by rotating the analyzer at $0^{\circ}$, $45^{\circ}$, $90^{\circ}$ and $135^{\circ}$. Experimental results are compared with those or FEM. Good agreement between the results can be observed. However, some error may be included if the technique is used to general direction which is not parallel to isoclinic fringe.

• Journal of Korean Society of Steel Construction
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• v.19 no.6
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• pp.695-702
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• 2007

The Thermal Prestressing Method for continuous composite girder bridges is a new design and construction method developed to induce initial composite stresses in the concrete slab at negative bending regions. Due to the induced initial stresses, prevention of tensile cracks at the concrete slab, reduction of steel girder section, and reduction of reinforcing bars are possible. Thus, the construction efficiency can be improved and the construction can be made more economical. The method for determining the optimum heating region of the thermal prestressing method has not been established although such method is essential for improving the efficiency of the design process. The trial-and-error method used in previous studies is far from efficient, and a more rational method for computing optimal heating region is required. In this study, an efficient method for determining the optimum heating region in using the thermal prestressing method was developed based on the neural network algorithm, which is widely adopted to pattern recognition, optimization, diagnosis, and estimation problems in various fields. Back-propagation algorithm, commonly used as a learning algorithm in neural network problems, was used for the training of the neural network. Through case studies of two-span and three-span continuous composite girder bridges using the developed procedure, the optimal heating regions were obtained.

• The Korean Journal of Air & Space Law and Policy
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• v.5
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• pp.265-301
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• 1993

지난 6월 3일 동경에서 있었던, 아시아 항공/우주법 학술대회 제 3분과에서 영국 Bin Cheng교수의 "The Warsaw System: Mess up, Tear up, or Shore up?"이라는 주제의 논문발표가 있었다. Bin Cheng교수는 특히 유럽의 EC Consultant Paper 와 일본항공사들의 1992년의 무한책임보상주의 채택에 대하여, 마치 무한 책임보상주의의 이론이 승리하였으며, 위의 상황들이 그 시작이라고 단정하였는데 이러한 견해는 아직까지 시기상조라고 생각한다. 본 글에서는 동경회의에서의 Bin Cheng교수의 논문중 특히 10항의 결론 부분을 중점으로 반대되는 의견을 제시하고자 한다. 국제항공사법인 와르소체제가 과연 발전하고 있는 것인가? 퇴보하고 있는 것인가? 와르소체제의 반대론자들은 미국의 소송변호사들, 일본항공사들과 일부 순수이론을 고수하는 학자들로써 이들은 와르소체제로부터의 탈퇴와 무한책임보상주의를 고수하고 있다. EC Consultation Paper (각주 122 참조)에서 보듯이, 비록 항공운송시의 손해배상액이 타 운송시의 손해배상액보다 적기는 하지만 이것이 곧 '무한책임보상주의'를 의미하는 것은 아니다. 미국의 판례중 불법행위로 인한 소송 (Nichole Fortman v. Hemeo Inc.)에서 보면, 작은 창자의 대부분을 병원의 과실때문에 잃은 Brooklin의 한 여인에게 500억 정도의 손해배상이 주어진 것을 보면, 과연 완전 보상에 맞는 무한책임이 과연 항공소송에 적용될 수 있는 것인가를 알아야 한다. 무한책임보상주의는 특히 개발도상국의 항공사들에게 보험료가 너무 과중하고, 와르소협약의 근본목적인 국제항공법의 통일성에 반하고 있기 때문에 국제사회 전반에 적용하기에는 비현실적이다. 와르소체제의 통일 성에 대한 거부는 만약 와르소체제에 버금가는 다른 보상체제가 있는 경우에는 다르지만, 현실적으로는 결국 국제적 혼란만을 야기사킬 것이다. 또한 와르소체제 반대자들은 항공운송인과 승객들의 관계를 갈등관계로 보고 있지만, 근본적으로 와프소협약에서의 항공운송인파 승객들의 관제는 공동이악관계로 보아야 한다. 항공운송사업의 목적도 또한 이윤추구인 바, 승객들이 항공운송인에게 과다한 손해배상을 요구하면, 결국 항공운송인은 승객들의 주머니에서 그 댓가를 찾으려고 할 것이다. 절국 양자의 이익을 보는 것은 소송변호사들 뿐이라고 볼 수 있다. 또한 'Unlimited Liability' 에서 'Unlimited' 란 'Full-Compensation' 을 의미하는 것으로, 'Wilful-Misconduct' 의 경우에는, 'Full-Compensation' 의 개념과 다르게, 그 보상액이 Warsaw협약 제 22조 1항에 적용되지 않는 'No-limited' 의 개념으로 해석하여야 한다. 항공소송의 경우에 통상 'Wilful-Misconduct' 의 경우에 손해배상액이 약 $700,000 인 것을 보더라도 'Full-Compensation'의 의미로 해석할 수 없다. 몬트리올 제 3추가의정서에서 'WilfulMisconduct' 의 개념을 삭제하고자 하는 것은, 이에 대비하여 추가보상제도, 임액수의 종액, 영격책임추의 등의 요소들을 전제로 하고 있기 때문이다. 몬트리올 제 3추가의정서가 최근의 발전적인 손해배상제도인가에 대하여, Bin Cheng 교수는 반대를 하고 있지만, 최선의 제도를 찾는 입장에서 몬트리올 추가 의정서는 여러가지로 부족하다. 그러나, 유한책임제도의 개선, 엄격책임주의의 도입, 빠른 소송타결의 제도, 재판관할권의 확대 그리고, SDR 화폐단위의 채택 등은 헤이그 의정서 이후의 보다 나은 제도적 장치를 하고 있다고 해석하여야 할 것이다. 시대의 변화에 따라 점진적으로 발전된 보상제도를 채택하였다면, 오늘날과 같이 시대에 뒤떨어진 보상체제로 혼란을 겪고 있지 않았을 것이다.