• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.5
• /
• pp.1563-1571
• /
• 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
• /
• v.38 no.2
• /
• pp.149-152
• /
• 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
• /
• v.34 no.2
• /
• pp.229-236
• /
• 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.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.3
• /
• pp.337-344
• /
• 1989

The upper bound elemental technique (UBET) is used to simulate the bulk flow characteristics in axisymmetric closed die forging process. Internal flow inside the cavity is predicted using a kinematically admissible velocity field that minimizes the rate of energy consumption. Application of the technique includes an assessment of the formation of flash and of degree of filling in rib-web type cavity using billets with various aspect rations. The technique considering bulging effect is performed in an incremental manner. The results of simulation show how it can be used for the prediction of forging load, metal flow, and free surface profile. The experiments are carried out with plasticine. There are good agreements in forging load and material flow in cavity between the simulation and experiment. The developed program using UBET can be effectively applied to the various forging problems.

• Transactions of Materials Processing
• /
• v.23 no.5
• /
• pp.317-322
• /
• 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.

• Transactions of Materials Processing
• /
• v.27 no.6
• /
• pp.331-338
• /
• 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
• /
• v.35 no.5
• /
• pp.581-588
• /
• 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
• /
• v.19 no.1
• /
• pp.56-60
• /
• 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.

• Journal of the Korean Orthopaedic Association
• /
• v.54 no.3
• /
• pp.211-218
• /
• 2019

Herniation of the intervertebral disc is a medical disease manifesting as a bulging out of the nucleus pulposus or annulus fibrosis beyond the normal position. Most lumbar disc herniation cases have a favorable natural course. On the other hand, surgical intervention is reserved for patients with severe neurological symptoms or signs, progressive neurological symptoms, cauda equina syndrome, and those who are non-responsive to conservative treatment. Numerous surgical methods have been introduced, ranging from conventional open, microscope assisted, tubular retractor assisted, and endoscopic surgery. Among them, microscopic discectomy is currently the standard method. Biportal endoscopic spinal surgery (BESS) has several merits over other surgical techniques, including separate and free handling of endoscopy and surgical instruments, wide view of the surgical field with small skin incisions, absence of the procedure of removing fog from the endoscope, and lower infection rate by continuous saline irrigation. In addition, existing arthroscopic instruments for the extremities and conventional spinal instruments can be used for this technique and surgery for recurred disc herniation is applicable because delicate surgical procedures are performed under a brightness of 2,700 to 6,700 lux and a magnification of 28 to 35 times. Therefore, due to such advantages, BESS is a novel technique for the surgical treatment of lumbar disc herniation.