• 대한기계학회논문집
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• 제15권5호
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• pp.1563-1571
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• 1991

본 연구에서는 가상일 원리로 부터 유한 요소 수식화를 updated-Lagrangian 형태로 유도하였으며, 유도된 수식화를 연속체 유한 요소로 유한 근사화 하였다. 이 때 초소성 재료의 거동은 비압축성, 비선형 점성 유ㄷ옹으로 묘사하였다. 유한 요소 프로그램은 성형 기구 해석과 하중 압력을 제어하는 기법으로 구성되어 있으며 하중 압력의 제어는 성형 시간이 최소가 되게 하기 위하여 변형률 속도 민감 계수가 최대가 되고, 국부 변형에 의한 두께 감소를 방지하며 변형률 속도는 일정하게 유지되면서 성 형이 될 수 있도록 하였다. 즉 하중 압력 제어는 상당 변형률 속도가 최대가 되게하 여 성형 시간을 최소화하게 구성하였다.개발된 유한 요소 프로그램은 정수압 벌징 가공에 적용하였으며 최적 압력 시간 선도, 성형 형상, 두께 및 두께 변형률 분포, 상 당 변형률 분포 등을 구하였다.

• Mycobiology
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• 제38권2호
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• pp.149-152
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• 2010

This study describes a new record of a thelotremoid lichen (Leucodecton desquamescens) from South Korea. The taxon is characterized by thick, bulging thallus with many calcium oxalate crystal inclusions; an immersed, round to irregular ascomata with free exciple, ellipsoid to $\pm$ roundish submuriform, brown ascospores, and lack of secondary metabolites. A detailed taxonomic description and comments are presented for this taxon. The lichen genus Leucodecton is reported for the first time in South Korea.

• Archives of Plastic Surgery
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• 제34권2호
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• pp.229-236
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• 2007

Purpose: Breast reconstruction with deep inferior epigastric perforator(DIEP) free flap is known to be the most advanced method of utilizing autologous tissue. The DIEP free flap method saves most of the rectus abdominis muscle as well as anterior rectus sheath. Therefore, the morbidity of the donor site is minimized and the risk of hernia is markedly decreased. Methods: We chose the internal mammary artery and its venae comitantes as recipient vessels, and deep inferior epigastric vessels as donor vessels. The number and location of the perforators derived from medial or lateral branch of deep inferior epigastric artery(DIEA) in 23 DIEP flaps were identified. Ten patients underwent evaluation of their abdominal wall function preoperatively and 6 months postoperatively by using Lacote's muscle grading system. Results: Of the 23 patients, a patient with one perforator from lateral branch of DIEA experienced partial necrosis of flap. Total flap loss occurred in one patient. Mild abdominal bulging was reported in one patient 4 months postoperatively probably because of early vigorous rehabilitational therapy for her frozen shoulder. Postoperative abdominal wall function tests in 10 patients showed almost complete recovery of muscle function upto their preoperative level of upper and lower rectus abdominis and external oblique muscle function at 6 months postoperatively. All patients have been able to resume their daily activities. Conclusion: The breast reconstruction with DIEP free flap is reliable and valuable method which provide ample soft tissue from abdomen without compromising the integrity of abdominal wall. Selection of reliable perforators is important and including more than two perforators may decrease fat necrosis and partial necrosis of flap.

• 대한기계학회논문집
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• 제13권3호
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• pp.337-344
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• 1989

본 연구에서는 플래쉬(flash)를 가진 축대칭 리브-웨브형(rib-web type) 제품의 형단조가공을 해석하기 위한 UBET 프로그램을 개발하고 변형중의 경계 조건처리를 다르게 한 세 가지 유동모델에 대하여 소재의 유동상태와 단조하중을 계산하여 효과적인 유동모델을 제시하였다. 또한 체적은 같으나 반지름과 높이의 비가 다른 몇 가지 초기소재 형상에 대하여 변형에 따른 소재의 다이충만도 및 하중을 비교하여 적절한 초기소재의 형상을 찾고자 하였다. 본 연구에서 제시한 유동모델의 효율성을 검증하기 위하여 플라스씬(plasticine) 소재를 사용한 실험과 그 결과를 비교, 분석하였다.

• 소성∙가공
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• 제23권5호
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• pp.317-322
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• 2014

Bursting during tube hydroforming is preceded by localized necking. The retardation of the initiation of necking is a means to enhance hydroformability. Since high strain gradients occur at the necking sites, a decrease in local strain gradients is an effective way to retard the initiation of necking. In the current study, the expansion at potential necking sites was intentionally restricted in order to reduce the strain gradient at potential necking sites. From the strain distribution obtained from FEM, it is possible to determine strain concentrated zones, which are the potential necking sites. Prior to the hydroforming of a trailing arm, an incompressible material(such as lead) is attached to the tube where the strain-concentrated zone would contact the die. Due to the incompressibility of lead, the tube expansion is locally restricted, and the resultant strain extends to adjacent regions of the tube during hydroforming. After the first stage of hydroforming, the lead is removed from the tube, and the hydroforming continues to the final targeted shape without any local restriction. This method was successfully used to fabricate a complex shaped automotive trailing arm that had previously failed during traditional hydroforming fabrication.

• 소성∙가공
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• 제27권6호
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• pp.331-338
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• 2018

Electrohydraulic forming (EHF) process is a high speed forming process that utilizes the electric energy discharge in fluid-filled chamber to deform a sheet material. This process is completed in a very short time of less than 1ms. Therefore, finite element analysis is essential to observe the deformation mechanism of the material in detail. In addition, to perform the numerical simulation of EHF, the material properties obtained from the high-speed status, not quasi static conditions, should be applied. In this study, to obtain the parameters in the constitutive equation of Al 6061-T6 at high strain rate condition, a surrogate model using an artificial neural network (ANN) technique was employed. Using the results of the numerical simulation with free-bulging die in LS-DYNA, the surrogate model was constructed by ANN technique. By comparing the z-displacement with respect to the x-axis position in the experiment with the z-displacement in the ANN model, the parameters for the smallest error are obtained. Finally, the acquired parameters were validated by comparing the results of the finite element analysis, the ANN model and the experiment.

• Archives of Plastic Surgery
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• 제35권5호
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• pp.581-588
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• 2008

Purpose: It is generally accepted that anatomical structures of the soft tissue in Asian faces are quite different from those in Caucasian. It is presumed that these differences are due to collagen rich thick dermis and durable superficial musculo-apponeurotic system (SMAS) in Asian. We classified the aging lower eyelids and reviewed the operative procedures according to the types of aging lower eyelids in Asian. Methods: We compared preoperative and postoperative photos of 117 patients over 30 years of age, who underwent lower blepharoplasty at the Kyunghee Medical Center from January 2001 to April 2006. We classified the patients based on the degree of skin laxity, presence of nasojugal groove and malar bag, the extent of aging process. We also reviewed the operative procedures according to each type of classification. Results: We classified our patients into four types as following. Type I patients showed minimal skin-muscle excess confined to lower eyelids regardless of the facial line. For these patients, we performed only transcutaneous or transconjunctival blepharoplasty. In type II patients, nasojugal grooves were shown and skin- muscle laxity was limited to the medial side of imaginary vertical line at lateral margin of pupil. In these cases, we performed free fat graft or fat repositioning on nasojugal groove or fat removal and septal duplication confined to medial side. Type III patients displayed more advanced medial bulging and remarkable laxity over the lateral side, the same operation methods as those of type II were applied at the lateral side of the line. Type IV patients demonstrated extensive midfacial aging changes including malar bags and underwent superficial subciliary cheek lift. Conclusion: The lower eyelid aging of Asian is different from those of Caucasian. We think that our classification is useful in selection of appropriate operative procedure to address specific problems for Asian patients.

• Archives of Reconstructive Microsurgery
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• 제19권1호
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• pp.56-60
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• 2010

Purpose: Breast reconstruction with abdominal flap has many advantages. However, it might cause abdominal complications such as bulging or hernia. SIEA (Superficial inferior epigastric artery) flap is the most advanced form of abdominal flap which has no adverse effect on abdominal fascia. We report 2 cases of breast reconstruction with SIEA flap with reference review. Methods: From Jun 2006 to Jan 2009, 110 patients underwent breast reconstruction with free abdominal flap. We tried to find the SIEA in every cases and adopted SIEP flap if the diameter was larger than 1mm and it had visible pulsation. 2 patients underwent breast reconstruction with SIEA flap. After design of abdominal flap SIEA was investigated with portable Doppler. SIEA was usually found 4-5 cm lateral to the midline. Flap was elevated with SIEA and SIEV to their maximal length at hiatus. Results: There were no complications, such as infection, hematoma, and necrosis of flap. In both cases, flaps survived completely with excellent vascularity and breast reconstruction was successful. In one case, there was skin necrosis of mastectomy flap, and it was healed by conservative management. Conclusion: With the SIEA flap, donor site morbidity can be minimized along with reduction of operation time. If there is reliable SIEA, SIEA flap would be the preferred skills. However, the limitation of the SIEA flap is difficulty in identifying the SIEA. The reason for less availability of the flap in Korea might include high prevalence of the Caesarian section scar and relatively higher level of the lower margin of the flap.

• 대한정형외과학회지
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• 제54권3호
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• pp.211-218
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• 2019

추간판 탈출증이란 추간판이 정상적으로 위치해야 할 자리에서부터 추간판 내부의 수핵이나 섬유륜이 탈출하는 질환을 지칭하며, 대부분 양호한 자연 경과를 거친다. 하지만 심각한 신경학적 증상이 있거나, 악화되는 신경 증상, 마미 증후군이 동반된 경우, 보존적 치료에 반응하지 않는 경우 등에 대해서는 수술적 치료가 권고된다. 수술 방법에는 고식적인 관혈적 방법, 현미경을 이용한 방법, 통형 견인기(tubular retractor)를 이용한 방법, 그리고 내시경을 이용한 방법에 이르기까지 다양한 방법들이 소개되었는데, 그 중 현미경적 추간판 제거술이 현재 표준 치료로 간주되고 있다. 내시경을 이용한 방법 중에서 두 개의 입구를 통한 내시경 척추 수술(biportal endoscopic spinal surgery, BESS)의 경우, 다른 방법에 비해 수술 기구들의 독자적인 움직임이 가능하여 자유로운 조작이 가능하며, 재발된 추간판 탈출증에 대해서도 추간판 제거가 비교적 수월하게 시행되고, 작은 피부 절개로 넓은 시야 확보가 가능하며, 지속적인 생리식염수의 세척으로써 습기나 안개를 지속적으로 제거해야 되는 번거로움을 덜 수 있고 술 후 감염률을 낮추는 효과도 있다. 기존의 관절경 및 척추 수술 기구들을 그대로 쓸 수 있다는 장점도 있으며, 약 2,700-6,700 lux의 밝은 조도 하에 최대 28-35배로 확대된 영상으로 수술하기 때문에 섬세한 조작이 가능하다. 따라서 이러한 장점을 지닌 두 개의 입구를 통한 BESS는 요추부 추간판 탈출증에 대한 이상적인 수술 방법으로 생각된다.