• 대한토목학회논문집
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• 제30권6A호
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• pp.543-560
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• 2010

원자력발전소의 안전 관련 콘크리트 구조물은 비행체의 충격에 대해 안전하게 설계하는데, 충격하중에 의한 스캐빙과 관통을 방지하기 위한 벽체 두께는 경험적 공식에 의해서 결정한다. 이 연구는 관입 및 스캐빙 깊이와 관통두께를 결정하는 기존에 제안된 국부손상 효과 산정식을 기존 실험결과와 비교 검증하는데 목적이 있다. 충격체의 충돌속도가 95~215m/s인 범위에서 충돌실험을 수행한 Kojima의 충돌실험체에 대한 충돌해석을 수행한 후, 실험 및 해석결과의 비교를 통해서 해석모델 및 해석방법의 적정성을 확인하였다. 국부손상 산정식 비교분석에서 실험결과와 잘 맞는 Degen식을 통해 산정된 관통두께가 반영된 RC 슬래브에 대한 충돌해석을 수행한 후, 국부손상 산정식과 해석결과를 비교분석하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.174-179
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• 2001

In order to investigate the fracture behaviors(perforation modes) and resistance to perforation during ballistic impact of aluminum alloy plate, ballistic tests were conducted. Depth of penetration experiments with 5.56mm-diameter ball projectile launched into 25mm-thickness Al 5052-H34 targets were conducted. A powder gun launched the 3.55g projectiles at striking velocities between 0.6 and 1.0 km/s. radiography of the damaged targets showed different penetration modes as striking velocities increased. Resistance to perforation is determined by the protection ballistic limit($V_{50}$), a statistical velocity with 50% probability for complete perforation. Fracture behaviors and ballistic tolerance, described by perforation modes, are respectfully observed at and above ballistic limit velocities, as a result of $V_{50}$ test and Projectile Through Plates (PTP) test methods. PTP tests were conducted with $0^{\circ}$ obliquity at room temperature using 5.56mm ball projectile. $V_{50}$ tests with $0^{\circ}$ obliquity at room temperature were conducted with projectiles that were able to achieve near or complete perforation during PTP tests. The effect of various impact velocity are studied with depth of penetration.

• Steel and Composite Structures
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• 제49권6호
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• pp.667-684
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• 2023

In the context of finite element method, a computational simulation is presented to study and analyze the dynamic behavior of regularly perforated functionally graded rotating beam for the first time. To investigate the effect of perforation configurations, both regular circular and squared perforation patterns are studied. To explore impacts of graded material distributions, both axial and transverse gradation profiles are considered. The material characteristics of graded materials are assumed to be smoothly and continuously varied through the axial or the thickness direction according the nonlinear power gradation law. A computational finite elements procedure is presented. The accuracy of the numerical procedure is verified and compared. Resonant frequencies, axial displacements as well as internal stress distributions throughout the perforated graded rotating cantilever beam are studied. Effects of material distributions, perforation patterns, as well as the rotating beam speed are investigated. Obtained results proved that the graded material distribution has remarkable effects on the dynamic performance. Additionally, circular perforation pattern produces more softening effect compared with squared perforation configuration thus larger values of axial displacements and maximum principal stresses are detected. Moreover, squared perforation provides smaller values of nondimensional frequency parameters at most of vibration modes compared with circular pattern.

• 한국통신학회논문지
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• 제39A권6호
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• pp.310-321
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• 2014

정사각형 천공이 $2{\times}2$ 배열된 정사각형 패치 안테나에 근접 결합 급전을 이용하여 기판 두께와 천공의 위치 및 크기가 안테나의 대역폭과 방사특성에 미치는 영향에 대하여 연구하였다. 안테나 기판과 급전 기판의 두께가 두꺼워질수록 방사특성의 저하 없이 대역폭이 증가 되었다. 천공 중심의 위치를 패치 길이 방향 가장자리로 이동시키는 경우 방사특성의 큰 저하 없이 대역폭을 증가시킬 수 있었다. 천공 중심의 위치를 패치 폭 방향으로 이동시키는 경우 중심 위치가 대역폭과 방사특성에 미치는 영향이 매우 작았다. 천공의 크기가 작아질수록 대역폭은 증가되고 방사특성은 향상되었다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.111-118
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• 2004

For the precise analysis of high velocity impact problem though FEM with element erosive method, the adequate mesh size and critical equivalent plastic strain(EQPS) is chosen prior to the simulation. In this research, it is strongly required from a standpoint that critical EQPS is used to decide whether perforation occurs or not. The optimization of dual armor plate consisting of 4340 steel and 2024 aluminium against a die steel sphere with high-velocity has been suggested using Lagrangian explicit time-integration code, NET2D. The response surface method based on the design of experiment is utilized for the size optimization. The optimized thickness of each layer, in which perforation does not occur, the strength of multi-layer is maximized and total weight is minimized, is obtained at a constant velocity of a pellet with a designated total thickness.

• Journal of Gastric Cancer
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• 제20권3호
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• pp.245-255
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• 2020

Purpose: Recently, non-exposure simple suturing endoscopic full-thickness resection (NESS-EFTR) was developed to prevent tumor exposure to the peritoneal cavity. This study aimed to evaluate the feasibility of NESS-EFTR with sentinel basin dissection for early gastric cancer (EGC). Materials and Methods: This was the prospective SENORITA 3 pilot. From July 2017 to January 2018, 20 patients with EGC smaller than 3 cm without an absolute indication for endoscopic submucosal dissection were enrolled. The sentinel basin was detected using Tc^99m-phytate and indocyanine green, and the NESS-EFTR procedure was performed when all sentinel basin nodes were tumor-free on frozen pathologic examination. We evaluated the complete resection and intraoperative perforation rates as well as the incidence of postoperative complications. Results: Among the 20 enrolled patients, one dropped out due to large tumor size, while another underwent conventional laparoscopic gastrectomy due to metastatic sentinel lymph nodes. All NESS-EFTR procedures were performed in 17 of the 18 other patients (94.4%) without conversion, and the complete resection rate was 83.3% (15/18). The intraoperative perforation rate was 27.8% (5/18), and endoscopic clipping or laparoscopic suturing or stapling was performed at the perforation site. There was one case of postoperative complications treated with endoscopic clipping; the others were discharged without any event. Conclusions: NESS-EFTR with sentinel basin dissection is a technically challenging procedure that obtains safe margins, prevents intraoperative perforation, and may be a treatment option for EGC after additional experience.

• 한국군사과학기술학회지
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• 제11권6호
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• pp.164-171
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• 2008

A modified generalized particle algorithm, MGPA, was suggested to improve the computational efficiency of standard SPH method in numerical analysis of high speed impact behavior. This method uses a numerical failure mechanism than material failure models to describe the target penetration. MGPA algorithm was more effective to describe the impact phenomena and new boundaries produced during the calculation process were well recognized and treated in the target penetration problem of a bullet. When bullet perforation problems were analyzed by this method, MGPA algorithm calculation gives the stable numerical solution and stress oscillation or particle penetration phenomena were not shown. The error range in ballistic velocity limit is less than $2{\sim}13%$ for various target thickness.

• Advances in aircraft and spacecraft science
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• 제10권3호
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• pp.223-243
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• 2023

There is a burgeoning demand for minimizing the mass of satellites because of its direct impact on reducing launch-to-orbit cost. This must be done without compromising the structure's efficiency. The present paper introduces a relatively low-cost and easily implementable approach for optimizing structural mass to a maximum natural frequency. The natural frequencies of the satellite are of utmost pertinence to the application requirements, as the sensitive electronic instrumentation and onboard computers should not be affected by the vibrations of the satellite structure. This methodology is applied to a realistic model of Al-Azhar University micro-satellite in partnership with the Egyptian Space Agency. The procedure used in structural design can be summarized in two steps. The first step is to select the most favorable primary structural configuration among several different candidate variants. The nominated variant is selected as the one scoring maximum relative dynamic stiffness. The second step is to use perforation patterns reduce the overall mass of structural elements in the selected variant without changing the weight. The results of the presented procedure demonstrate that the mass reduction percentage was found to be 39% when compared to the unperforated configuration that had the same plate thickness. The findings of this study challenge the commonly accepted notion that isogrid perforations are the most effective means of achieving the goal of reducing mass while maintaining stiffness. Rather, the study highlights the potential benefits of exploring a wider range of perforation unit cells during the design process. The study revealed that rectangular perforation patterns had the lowest efficiency in terms of modal stiffness, while triangular patterns resulted in the highest efficiency. These results suggest that there may be significant gains to be made by considering a broader range of perforation shapes and configurations in the design of lightweight structures.

• 한국식품과학회지
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• 제46권6호
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• pp.739-742
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• 2014

이 연구에서는 식품포장분야에 사용되는 유연포장재들의 두께에 따른 방충효과를 규명하여 각각의 포장재에서 일정 수준의 방충효과를 나타내기 위한 필름의 최적의 조건을 연구하고자 하였다. 식품용 유연포장재들 중에서도 가장 널리 이용되고 있는 PE, PP, PS, AF, PET를 채택하여 실험을 진행한 결과, 각 포장재들의 두께에 따른 화랑곡나방 유충에 의한 침투율은 전반적으로 필름의 종류에 관계없이 두께가 얇을수록 포장재 내부로 빠르게 침투하는 경향을 보였다. 특히 PP와 PS의 경우 다른 필름들과는 다르게 각각 $20{\mu}m$와 $30{\mu}m$에서 72시간 이내에 100% 침투되는 결과값을 보여 방충포장소재로서의 상대적인 취약함을 보였다. 결과적으로 필름의 종류에 상관없이 두께가 증가할 수록 화랑곡 나방 유충의 침투율이 낮아진다는 것을 보여 주었다. 따라서 식품 내 해충과 같은 동물성 이물의 혼입을 방지하기 위해서는 포장 소재의 종류에 따라 특정 두께 이상을 확보해야 한다고 판단된다.

• Steel and Composite Structures
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• 제16권3호
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• pp.269-288
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• 2014

Experiments were carried out to investigate the ballistic performance of fiber reinforced plastic(FRP)-steel plates completely penetrated by hemispherical-nosed projectiles at sub-ordnance velocities greater than their ballistic limits. The FRP-steel plate consists of a front FRP laminate and a steel backing plate. Failure mechanisms and impact energy absorptions of FRP-steel plates were analyzed and compared with FRP laminates and single steel plates. The effects of relative thickness, manufacturing method and fabric type of front composite armors as well as the joining style between front composite armors and steel backing plates on the total perforation resistance of FRP-steel plates were explored. It is found that in the case of FRP-steel plates completely penetrated by hemispherical-nosed projectiles at low velocities, the failure modes of front composite armors are slightly changed while for steel backing plates, the dominate failure modes are greatly changed due to the influence of front composite armors. The relative thickness and fabric type of front composite armors as well as the joining style of FRP-steel plates have large effects whereas the manufacturing method of front composite armors has slight effect on the total perforation resistance of FRP-steel plates.