• Composites Research
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• 제13권2호
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• pp.40-50
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• 2000

종횡비가 다른 적층복합재료에 경사형 구조를 도입하고, 이것이 일방향으로의 하중을 받을 때의 좌굴특성을 최대화하기 위해서 복합재료의 각 층에서의 섬유부피분율과 두께를 변수로 sequential linear programming method를 이용하여 최적화 하였다. 이로부터 좌굴특성을 최대화 할 수 있는 최적구조를 제안하였다. 적층복합재료는 종횡비의 영향이 커서 종횡비가 1보다 작은 경우는 최외각층의 섬유부피분율을 최대화하는 방향으로 최적화가 이루어졌으나 종횡비가 2인 경우는 각층에서의 섬유부피분율과 두께비가 어느 정도 균형을 이루는 형태로 최적화가 이루어 졌다. 경사형 구조는 전통적인 균일구조의 복합재료에 비해서 섬유부피와 복합재료의 무게 절감에 큰 효과를 가지는 것으로 확인되었다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 1998년도 추계종합학술대회
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• pp.408-413
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• 1998

Electromagnetic wave absorbers for anechoic chamber are needed to broaden the useful frequency bandwidth, reduce the thickness, and decrease the weight. There are various absorbers proposed for the above conditions, but they could not decisively solve it the alone requirements. The Electromagnetic wave absorber made by a conventional ferrite tile has, for example, broadened the useful frequency bandwidth by the way of forming air layer(practically use urethane foam, etc.) on the ferrite tile. Therefore, an air layer is formed between a reflection plate and a sintered Ni-Zn ferrite tile of 7 mm in thickness, which has reflectivity less than -20 dB from 30 MHz to 600 MHz in bandwidth. Accordingly, in this paper, a broadened electromagnetic wave absorber will be designed, which has the reflection characteristics less than -20 dB from 30 MHz to 6000 MHz in the bandwidth. Then we will design a super broadband electromagnetic wave absorber by inserting square Ferrite Cylinders Type with the thickness less than 11 m and with the frequency band from 30 MHz to 6000 MHz under the above tolerance limits. The purpose of this research is on the development of a universal anechoic chamber for measuring radiated electromagnetic wave or immunity of electronic equipments, GTEM-cell, wall material for prevention TV ghost, etc.

• 한국의상디자인학회지
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• 제14권2호
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• pp.89-100
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• 2012

The purpose of this research is to compare the body proportion of the Mongolian and Korean men and women in their 20' s by comparing the characteristics of the body type that uses the body indexes, in order to provide the base data for the increased fit of the apparels. The results are as follows. 1) Histogram of the Rohrer' s Index for the Mongolian men and women in their 20s was examined. the Mongolian men, normal body type took up 48.0% while small body type comprised 50.0% and obese body type comprised 2.0%. the Mongolian women, normal body type comprised 61.5%, small body type comprised 22.1% and obese body type comprised 16.4%. 2) The body proportion of Korean men has 1:1.62 with upper body and low body part on a waist basis, and Mongolian men has 1:1.65. Thus Mongolian men has longer pan of lower body than Korean men. 3) Mongolian women has longer part of lower body and has higher rates of hip height, crotch height, knee height than Korean women. Mongolian women has high rate of hip line and calf length. 4) As a result comparison using the body index of Mongolian and Korean women (bust thickness/ bust width, waist thickness / waist width, hip thickness / hip width, when regarding the height as 100 ), it was found that Mongolian women are flatter than korean women.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.68-72
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• 1999

In an effort to construct a structure under the design principle of minimal use of materials for maximum performances, a discrete gradient structure has been introduced in laminate composite systems. Using a sequential linear programming method, the gradient structure of composites to maximize the buckling load was optimized in terms of fiber volume fraction and thickness of each layer. Theoretical optimization results were then verified with experimental ones. The buckling load of laminate composite showed maximum value with the outmost [$0^{\circ}$] layer concentrated by almost all the fibers when the ratio of length to width(aspect ratio) was less than 1.0. But when the aspect ratio was 2.0, the optimum was determined in a structure where the thickness and fiber volume fraction were well balanced in each layer. From the optimization of gradient structure, the optimal fiber volume fraction and thickness of each layer were proposed. Experimental results agreed well with the theoretical ones. Gradient structures have also shown an advantage in the weight reduction of composites compared with the conventional homogeneous structures.

• 대한기계학회논문집B
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• 제25권6호
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• pp.751-757
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• 2001

An experimental study of impinging jet-flow structure has been carried out for a fully developed single circular jet impingement cooling on a flat plate, and the effect of the wall thickness at nozzle exit edge is investigated. Impinging jet flow structures have been measured by Laser-Doppler Velocimeter to interpret the heat transfer results presented previously by Yoon et al.(sup)(10) The peaks of heat transfer rate are observed near the nozzle edge owing to the radial acceleration of jet flow when the nozzle locates close to the impingement plate. The growth of the velocity fluctuations in the wall jet flow is induced by the vortices which originate in the jet shear layer, and consequently the radial distribution of local Nusselt numbers has a secondary peak at the certain radial position. As a wall of circular pipe nozzle becomes thicker for small nozzle-to-target distance, the entrainment can be inhibited, consequently, the acceleration of wall jet flow is reduced and the heat transfer rate decreases.

• 한국기계가공학회지
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• 제19권4호
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• pp.79-84
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• 2020

Induction bending via high-frequency heating is widely used for manufacturing pipe and section steel bends. It allows productivity improvement, unit cost reduction, delivery time compliance, and good mechanical properties. The recent increase in high-end vessels and offshore plants has raised the demand for high-frequency bending, which should improve the product quality and reduce the costs by simplifying the fabrication process; therefore, the characteristics and performance of this technique must be studied and proper design technology is required. During hot pipe bending via induction heating, the outward wall thickness of the pipe is thinned due to tensile stress and this thickness reduction cannot exceed 12.5%. This study focused on pipe bends with a bending curvature of 5D and their optimization design; in particular, the conditions that can both improve the productivity of the high-frequency bending process and keep the maximum thickness reduction below 12.5% were determined.

• 한국가스학회지
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• 제19권1호
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• pp.18-22
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• 2015

본 연구는 LPG 강재용기에서 상단반구와 하단반구의 코너반경이 응력강도 안전성에 미치는 영향을 FEM으로 해석한 것이다. FEM 해석결과에 의하면, 응력강도 안전성에 큰 영향을 미치는 요소는 용기의 두께보다 상단반구 및 하단반구의 코너반경이다. 그러나 강재용기의 두께는 경량화에 직결되기 때문에 간과해서는 안 되는 중요한 설계요소이다. LPG 강재용기의 강도안전성 검사에서 최고시험압력이 3.04MPa임을 감안할 때, 20kg용 LPG 강재용기의 두께는 2.3~2.6mm, 상단반구와 하단반구의 코너반경은 157mm 이상으로 최적화 설계하는 것이 바람직함을 알 수 있다.

• Advances in Automotive Engineering
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• 제1권1호
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• pp.41-59
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• 2018

In the study, investigation of fiber- reinforced composite materials that can be an alternative to conventional steel was performed by finite element analysis with the help of software. Steel and composite materials have been studied on a four axle truck chassis model. Three-dimensional finite element model was created with software, and then analyzes were performed. The analyses were performed for static and dynamic/fatigue cases. Fatigue cases are formed with the help of design spectra model and fatigue analyses were performed as static analyses with this design spectra. First, analyses were performed for steel and after that optimization analyses were made for the AS4-PEEK carbon fiber composite and Eglass-Epoxy fiber composite materials. Optimization of composite material analyzes include determining the total laminate thickness, thickness of each ply, orientation of each ply and ply stacking sequence. Analyzes were made according to macro mechanical properties of composite, micromechanics case has not been considered. Improvements in weight reduction up to %50 provided at the end of the composite optimization analyzes with satisfying stiffness performance of chassis. Fatigue strength of the composite structure depends on various factors such as, fiber orientation, ply thickness, ply stack sequence, fiber ductility, ductility of the matrix, loading angle. Therefore, the accuracy of theoretical calculations and analyzes should be correlated by testing.

• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.45-54
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• 2004

In order to meet the requirement for higher thickness accuracy in cold rolling processes, it is strongly desired to have high performance in control units. To meet this requirement, we have considered an output regulating control system with a roll-eccentricity estimator for each rolling stand of tandem cold mills. Considering entry thickness variation as well as roll eccentricity as the major disturbances, a synthesis of multivariable control systems is presented based on H$\sub$$\infty$/ control theory, which can reflect the knowledge of input direction and spectrum of disturbance signals on the design. Then, to reject roll eccentricity effectively, a weight function having some poles on the imaginary axis is introduced. This leads to a non-standard H_ control problem, and the design procedures for solving this problem are analytically presented. The effectiveness of the proposed control method is evaluated through computer simulations and compared to that of the conventional LQ control and feedforward control methods for roll eccentricity.

• 한국소음진동공학회논문집
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• 제15권5호
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• pp.604-611
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• 2005

The relationship between floor impact sound and vibration has been studied by field measurements, and the vibration modal characteristics have been analyzed. Vibration levels impacted by a standard heavy-weight impact source have been predicted according to the main design parameters using finite element method. Experimental results show that the dominant frequencies of the heavy impact sounds range below 100 Hz and that they are coincident with natural frequencies of the concrete slab. In addition, simple 2-dimensional finite element models are proposed to substitute 2 types of 3-dimensional models of complicated floor structural slabs those by The analytical result shows that the natural frequencies from first to fifth mode well correspond to those by experiments with an error of less than $12\%$, and acceleration peak value iscoincident with an error of less than $2\%$. Using the finite element model. vibration levels areestimated according to the design Parameters, slab thickness, compressive strength, and as a result, the thickness is revealed as effective to increase natural frequencies by $20\~30\%$ and to reduce the vibration level by 3$\~$4 dB per 30 mm of extra thickness.