Overlapping finite element analysis for structures under thermal loads with spatially varying gradients

학위논문(박사) -- 서울대학교대학원 : 공과대학 기계항공공학부, 2022.2. 김도년.열응력 해석의 정확도는 격자 구성 및 온도 분포에 따라 달라지며, 이는 정확도 를 저하 시키는 주요 원인이 된다. 본 논문에서는 다양한 구배를 가지는 열 하중에 대해 덜 민감하게 정확성을 유지하며, 열응력 해석에 널리 사용되는 재격자 구성 과정 등 에 필요한 노력을 줄이기 위하여 적응형 형상 함수를 반영한 중첩 유한요소를 제시 한다. 구조에 작용하는 온도 분포 를 적응형 형상 함수에 반영하기 위하여 온도 정보를 보간 과정 의 가중치를 조정하기 위한 변수로 사용하며, 그에 대한 수치적 공식 을 제시하였다. 또한, 스케일링 계수를 적용하여 중첩 유한 요소의 효과를 확대한다. 적응형 형상 함수를 반영한 중첩 유한요소 의 효과를 확인하기 위하여 1D 및 2D의 열응력 해석을 수행하였다. 열응력 해석은 공간적으로 다양한 구배를 갖는 열 하중 상황에서 수행되었으며, 다른 유한요소 해석 결과와 비교를 통해 정확도 향상 효과를 확인하였다. 그리고 균등한 격자를 활용한 자유도 증가를 통하여 적응형 형상 함수를 반영한 중첩 유한요소 의 수렴성을 확인하였다. 왜곡된 격자, 그레이딩 격자 및 불균일 격자를 통한 해석 및 결과 비교를 통하여 적응형 형상 함수를 반영한 중첩 유한요소 의 정확성 개선 효과 및 특성을 확인하였다. 적응형 형상 함수를 반영한 중첩 유한요소 의 다양한 기하학적 구조물 에 대한 폭넓은 적용 성 을 확인하기 위해 클램프된 브래킷과 터보기계의 2D 축대칭 예제 모델에 대한 열응력 해석 을 수행하였으며수행하였으며, 다양한 구배의 열 하중에 대해 정확성 측면에서 민감성이 개선된 것을 확인하였으며, 타 유한요소 와 대비 하여 정확도 의 향상 효과를 확인 할 수 있었다.The accuracy of thermal stress analysis is dependent on the mesh pattern and temperature distribution, which is a significant reason for the decrease in accuracy. In this paper, the overlapping finite element with the adaptive shape function is presented for insensitivity to thermal loads with varying gradient and reducing the effort required for the remeshing process that is widely used in thermal stress analysis. Temperature distribution field is used as the variable to adjust the weight in the interpolation process for the reflection of temperature distribution field to the shape function, and its numerical formulation is given. In addition, the scaling factor is applied for expanding the effect of the overlapping finite element with the adaptive shape function. Thermal stress analyses in 1D and 2D were performed to investigate the effect of the overlapping finite element with the adaptive shape function. The effect of accuracy enhancement was studied under thermal loads with spatially varying gradients and compared with other finite elements. The convergence was also investigated for the overlapping finite element with the adaptive shape function. In addition, a mesh distortion study, a grading mesh comparison and a random mesh comparison were performed for study the characteristics of it. For a broad application to various geometries of structures, clamped bracket and 2D axisymmetric example model of turbomachinery are analyzed by the overlapping finite element with the adaptive shape function. From the results, insensitivity to thermal loads with varying gradient and the accuracy improvement effect was discerned.Abstract 1 Contents 2 List of Figures 4 List of Tables 11 1. Introduction 12 1.1. Thermal stress analysis 12 1.2. Literature review 14 1.3. Objectives and outline 17 2. The overlapping finite element in thermal stress analysis 19 2.1. Governing equations in thermal stress analysis 19 2.2. Interpolation used for the overlapping finite element 25 2.2.1. Local interpolation 25 2.2.2. Weight function 30 2.2.3. Global interpolation 34 3. The overlapping finite element with the adaptive shape function 36 3.1. The concept of the adaptive shape function 36 3.1.1. The principle of weight adjustment based on temperature field 36 3.1.2. The temperature distribution variable and its application 39 3.2. Application of the scaling parameter 41 3.2.1. The scaling parameter 41 3.2.2. Exemplary selection of the scaling parameter 42 4. Illustrative solution of problems in 1D 61 4.1. Effect of temperature distribution 61 4.2. Solution convergence with uniform mesh refinement 66 4.3. Solution accuracy with non-uniform meshes 72 4.4. Grading mesh comparison 74 5. Illustrative solution of problems in 2D 77 5.1. Clamped plate 77 5.1.1. Effect of temperature distribution 77 5.1.2. Temperature gradient around boundary condition 83 5.1.3. Solution convergence with uniform mesh refinement 87 5.1.4. Solution accuracy with distorted meshes 92 5.1.5. Grading mesh comparison 98 5.1.6. Random mesh study 101 5.2. Clamped Bracket with a hole 104 5.2.1. Effect of temperature distribution 104 5.2.2. Solution convergence with mesh refinement 108 5.3. Dynamic analysis problem 110 5.3.1. Finite element analysis of dynamic problem 110 5.3.2. Solution comparison of dynamic analyses 111 5.4. 2D axisymmetric problem 115 5.4.1. Thermal stress analysis formulation in 2D axisymmetric 115 5.4.2. The comparison under thermal loads 118 6. Conclusion 121 Nomenclature 122 Bibliography 123 Abstract (In Korean) 126박

Surgical Treatment of Rectal Prolapse: A 10-Year Experience at a Single Institution

Purpose Despite the plethora of surgical options, there is no consensus regarding the best treatment for rectal prolapse. This study is aimed at evaluating our experience with its treatment and outcomes. Methods We retrospectively reviewed rectal prolapse patients’ characteristics, clinical presentation, surgical procedure, average length of hospital stay, morbidity, mortality, and recurrence over a 10 year period at our institution. Results A total of 46 patients underwent rectal prolapse repair at our institution over a 10 year period. Of the 39 patients with primary rectal prolapse, 18 patients had an abdominal procedure, while 21 patients underwent a perineal approach. Operative duration was significantly longer in abdominal procedures, of which 16 cases were performed laparoscopically. Length of hospital stay and recurrence were not statistically significant between the 2 groups. In patients with recurrent rectal prolapse, more than 80% of the initial surgeries were done using the perineal approach. An abdominal approach was utilized in the management of 75% of recurrences. Conclusion An abdominal repair may be preferable in the treatment of recurrent rectal prolapse. Minimally invasive techniques may be feasible and can provide a safe alternative to perineal procedures in elderly patients.ope

Cost analysis of single-incision versus conventional laparoscopic surgery for colon cancer: A propensity score-matching analysis

BACKGROUND/OBJECTIVE: Although many studies have demonstrated similar perioperative outcomes for single-incision laparoscopic surgery (SILS) and conventional laparoscopic surgery (CLS) for colon cancer, few have directly compared the costs of them. We aimed to compare costs between SILS and CLS for colon cancer. METHODS: We analyzed the clinical outcomes and overall hospital costs of patients who underwent laparoscopic surgery for colon cancer from July 2009 to September 2014 at our institution; 288 were used for analysis after propensity score matching. The total hospital charge, including fees for the operation, anesthesia, preoperative diagnosis, and postoperative management was analyzed. RESULTS: The total hospital charges were similar in both groups ($8770.40 vs.$8352.80, P = 0.099). However, the patients' total hospital bill was higher in the SILS group than in the CLS group ($4184.82 vs.$3735.00, P < 0.001) mainly due to the difference of the cost of access devices. There was no difference in the additional costs associated with readmission due to late complications between the two groups ($2383.08 vs.$2288.33, P = 0.662). Incremental cost-effectiveness ratio for total incision length in 'total hospital charge' and patient's bill and government's bill in 'cost of instruments and supplies' were -$107.08/1 cm, -$109.70/1 cm, and $80.64/1 cm, respectively. CONCLUSION: SILS for colon cancer yielded similar costs as well as perioperative and long-term outcomes compared with CLS. Therefore, SILS can be considered a reasonable treatment option for colon cancer for selective patients.ope

Malignant Melanoma of Anorectum: Two Case Reports

Malignant melanoma of the anorectum is a rare disorder. Patients often present with local symptoms similar to benign diseases. The prognosis is very poor, and almost all patients die because of metastases. We report 2 female patients with unremarkable histories. Both of them received previous operations before visiting our center after they were diagnosed with anorectal malignant melanoma. One case underwent abdominoperineal resection and postoperative chemotherapy. The other had been treated with ultralow anterior resection followed by immunotherapy.ope

Optimal Complete Rectum Mobilization Focused on the Anatomy of the Pelvic Fascia and Autonomic Nerves: 30 Years of Experience at Severance Hospital

The primary goal of surgery for rectal cancer is to achieve an oncologically safe resection, i.e., a radical resection with a sufficient safe margin. Total mesorectal excision has been introduced for radical surgery of rectal cancer and has yielded greatly improved oncologic outcomes in terms of local recurrence and cancer-specific survival. Along with oncologic outcomes, functional outcomes, such as voiding and sexual function, have also been emphasized in patients undergoing rectal cancer surgery to improve quality of life. Intraoperative nerve damage or combined excision is the primary reason for sexual and urinary dysfunction. In the past, these forms of damage could be attributed to the lack of anatomical knowledge and poor visualization of the pelvic autonomic nerve. With the adoption of minimally invasive surgery, visualization of nerve structure and meticulous dissection for the mesorectum are now possible. As the leading hospital employing this technique, we have adopted minimally invasive platforms (laparoscopy, robot-assisted surgery) in the field of rectal cancer surgery and standardized this technique globally. Here, we review a standardized technique for rectal cancer surgery based on our experience at Severance Hospital, suggest some practical technical tips, and discuss a couple of debatable issues in this field.ope

Comparison of Early Clinical Outcomes Between ALTA (Aluminum Potassium Sulfate and Tannic Acid, Ziohn®) Injection Therapy and a Submucosal Hemorrhoidectomy in Patients with Internal Hemorrhoids

Purpose: The purpose of this study was to evaluate early outcomes of ALTA (aluminum potassium sulfate and tannic acid, Ziohn®) injection compared with those of a submucosal hemorrhoidectomy for the treatment of internal hemorrhoids. Methods: From September 2008 to April 2009, a total of 50 patients who had internal hemorrhoids (Golliger grade II to IV) were treated by using either ALTA injection (n=25) or a submucosal hemorrhoidectomy (n=25). Outcomes with respect to pain scores, analgesics use, and satisfaction levels of the patients, and complications were compared. Results: The mean number of hemorrhoidal piles was 3.52 in the ALTA injection group and 3.56 in the operation group. The average amount of ALTA injection was 27.34 cc. Pain scores measured at one day and 7 days after the treatment, and the number of analgesics used in the injection group were significantly lower than those in the operation group (P<0.001). However, there was no significant difference in the satisfaction level between two groups. One case of treatment failure was found in the ALTA injection group. There was no difference in complications between the injection group (n=4) and the operation group (n=5) (P=0.725). Conclusion: When compared with a submucosal hemorrhoidectomy, ALTA injection showed less post-treatment pain and less analgesics use. Overall complication rates were not different between the two groups. We found the early outcomes of ALTA injection for the treatment of internal hemorrhoids to be comparable to those of surgery. Thus, large-scale and long-term follow-up studies are needed to clarify the proper indications for ALTA injection.ope

Neorectal Mucosal Prolapse After Intersphincteric Resection for Low-Lying Rectal Cancer: A Case Report

Radical resection for low rectal cancer is the mainstay among the treatment modalities. Intersphincteric resection (ISR) is considered a relatively new but effective surgical treatment for low-lying rectal tumor. As the sphincter preserving techniques get popularized, we notice uncommon complication associated with it in the form of rectal mucosal prolapse. We presented 2 rare cases that developed neorectal mucosa prolapse after ISR a complication following low rectal cancer surgery. Although ISR is a safe and effective surgical technique for low rectal cancer, it should be considered to correct modifiable possible risk factors. Also, Delorme procedure is good option for management of neorectal mucosal prolapse.ope

Clostridium difficile Infection After Ileostomy Reversal

Clostridium difficile infection (CDI) after ileostomy reversal is rare, with few reports available in the available literature describing this condition. The diagnosis of CDI after ileostomy reversal is challenging because symptoms such as diarrhea observed in these patients can occur frequently after surgery. However, CDI can be fatal, so early diagnosis and prompt treatment are important. We discuss 2 patients with positive C. difficile toxin assay results on stool cultures performed after ileostomy reversal. Clinical progression differed between these patients: one patient who presented with severe CDI and shock was successfully treated following a prolonged intensive care unit stay for the management of vital signs and underwent hemodialysis, while another patient showed symptoms of mild colitis but we could not confirm whether diarrhea was associated with CDI or with the usual postoperative state. To our knowledge, these represent 2 of just a few cases reported in the literature describing CDI after ileostomy reversal.ope

Triple synchronous primary neoplasms in the gastrointestinal tract

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Double-layered hand-sewn anastomosis: a valuable resource for the colorectal surgeon

Hand-sewn anastomosis is an essential and fundamental skill for surgeons dealing with any gastrointestinal anastomosis. Despite the advances in minimally invasive surgery and stapling devices, there are still complex surgical circumstances when the surgeon's surgical know-how are necessary. Therefore, a safe hand-sewn technique for bowel anastomosis is required to establish a tension-free, well-perfused, and sealed anastomosis that allows gastrointestinal continuity with no unexpected complications. We describe a step-by-step procedure for hand-sewn double-layered anastomosis that reflects these principles and is practical for small and large bowel anastomosis.ope