대형 용접구조물의 탄소성 열변형 해석을 위한 용접부의 변형률 경계조건에 관한 연구

하윤석,Ha, Yun-Sok 대한용접접합학회 2011 대한용접·접합학회지 Vol.29 No.4

A thermal distortion analysis which takes strains directly as boundary conditions removed barrier of analysis time for the evaluation of welding distortion in a large shell structure like ship block. If the FE analysis time is dramatically reduced, the structure modeling time or the input-value calculating time will become a new issue. On the contrary to this, if the calculation time of analysis input-value is dramatically reduced and its results also are more meaningful, a little longer analysis time could be affirmative. In this study, instead of using inherent strain based on elastic analysis, a thermal strain based on elasto-plastic analysis is used as the boundary condition of weldments in order to evaluate the welding distortion. Here, the thermal strain at the weldment was established by using a stress-strain curve established from the test results. It is possible to automatically recognize the modeling induced-stiffness in the shrinkage direction of welded or heated region. The validity of elasto-plastic thermal distortion analysis was verified through the experiment results with various welding sequence.

용접구조물의 변형 최소화를 위한 최적 용접순서의 해석적 방법

하윤석,Ha, Yunsok 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.3

Several methodologies analyzing welding distortions of large shell structures like ship blocks have been developed and utilized in shipyards for a long times ago. In general, one of objects of thermal distortion analysis is to find welding sequence making least-deformation without any suppliance, and it can be solved easily and rapidly by EP strain-boundary method. But after assembly construction, there are usually more than 10 weldments in each process, and the number of sequence will follow the Factorial calculation. In this research, a method has been suggested to decide the best welding sequence by minimum analysis. Using this method, welding deformation could be reduced just analyzing some cases as many as the number of weldments. Experiments and Analysis of all cases were also done, and their best results are good agreements with predictation by suggested methodology.

초대형 구조모델을 활용한 쉘구조물의 용접변형 해석

하윤석,이명수,Ha, Yunsok,Yi, Myungsu 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.3

A very large shell-structure built in shipyards like ship hulls or offshore structures are joined by welding through full process. As the welding contains a high thermal cycle at a local area, the welded structures should be distorted unavoidably. Because a distorted ship block should be revised to the designed value before the next stage, the ability to predict and to control the weld distortion is an accuracy level of the yard itself. Despite the ship block size, several present thermal distortion methodologies can deal those sizes, but it is a different story to deal full ship size model. Even a fully constructed ship hull not remaining any welding can have an accuracy issue like outfitting installation problems. Any present thermal distortion methodology cannot accept this size for its recommended element size and the number. The ordinary welding breadth at erection stage is about 20~40 mm. It can hardly be a good choice to make finite element model of these sizes considering human effort and computational environment. The finite element model for structure analysis of a ship hull is prepared at front-end engineering design stage which is the first process of the project. The element size of the model is as fine as the longitudinal space, and it is not proper to obtain a weld distortion at the erection stage. In this study, a methodology is suggested that a weldment can be shrunk at original place instead of using structural finite element model. We cut the original shell elements at erection weld-line and put truss elements between the edges of cut elements for weld shrinkage. Additional truss elements are used to facsimile transverse weld shrinkage which cannot be from the weld-line truss element shrink. They attach to weld-line truss element like twigs from barks. The capacity of developed elements is verified through an accuracy check of erection process of a container vessel at the apt. hull. It can be a useful tool for verifying a centering accuracy after renew and for block-separating planning considering accuracy.

유한요소법(FEM)기반의 외력을 반영한 운전영역에서의 축류팬의 동적 안전성 해석

하윤석,곽원일,이전국,이용복 한국유체기계학회 2019 한국유체기계학회 학술대회 논문집 Vol.2019 No.11

Phosphaturia as a Promising Predictor of Recurrent Stone Formation in Patients with Urolithiasis

하윤석,최동은,강호원,김용준,윤석중,이상철,김원재 대한비뇨의학회 2010 Investigative and Clinical Urology Vol.51 No.1

Purpose: Recent studies have suggested that renal phosphate leakage and the associated phosphaturia are significant underlying causes of calcium urolithiasis. The aims of this study were to assess whether phosphaturia relates to urinary metabolic abnormalities and recurrent stone formation. Materials and Methods: A database of patient histories and urine chemistries was analyzed for 1,068 consecutive stone formers (SFs) and 106 normal controls. Urine values for phosphaturia that were higher than 95% of the normal control values were defined as indicating hyperphosphaturia, and the effect of phosphaturia on urinary metabolites and stone recurrence was determined. Of these patients, 247 patients (23.1%) who had been followed up for more than 36 months or had a recurrence of stones during follow-up (median, 46.0 months; range, 5-151) were included in the analyses for stone recurrence. Results: Of the SFs, 19.9% (212/1,068) had increased urinary phosphate excretion. SFs with hyperphosphaturia had a greater urinary volume and higher levels of calcium, uric acid, oxalate, and citrate than did SFs with normophosphaturia. A multivariate Cox regression model, stratified by stone episodes, revealed that hyperphosphaturia was an independent predictor of recurrent stone formation in first-time SFs (hazard ratio [HR]: 2.122; 95% confidence interval [CI]: 1.100-4.097; p=0.025). No association was detected between hyperphosphaturia and recurrent stone formation in recurrent SFs. Kaplan-Meier curves showed identical results. Conclusions: This study demonstrates that hyperphosphaturia is closely associated with urinary metabolic abnormalities. Furthermore, hyperphosphaturia is a significant risk factor for stone recurrence in first-time SFs. Purpose: Recent studies have suggested that renal phosphate leakage and the associated phosphaturia are significant underlying causes of calcium urolithiasis. The aims of this study were to assess whether phosphaturia relates to urinary metabolic abnormalities and recurrent stone formation. Materials and Methods: A database of patient histories and urine chemistries was analyzed for 1,068 consecutive stone formers (SFs) and 106 normal controls. Urine values for phosphaturia that were higher than 95% of the normal control values were defined as indicating hyperphosphaturia, and the effect of phosphaturia on urinary metabolites and stone recurrence was determined. Of these patients, 247 patients (23.1%) who had been followed up for more than 36 months or had a recurrence of stones during follow-up (median, 46.0 months; range, 5-151) were included in the analyses for stone recurrence. Results: Of the SFs, 19.9% (212/1,068) had increased urinary phosphate excretion. SFs with hyperphosphaturia had a greater urinary volume and higher levels of calcium, uric acid, oxalate, and citrate than did SFs with normophosphaturia. A multivariate Cox regression model, stratified by stone episodes, revealed that hyperphosphaturia was an independent predictor of recurrent stone formation in first-time SFs (hazard ratio [HR]: 2.122; 95% confidence interval [CI]: 1.100-4.097; p=0.025). No association was detected between hyperphosphaturia and recurrent stone formation in recurrent SFs. Kaplan-Meier curves showed identical results. Conclusions: This study demonstrates that hyperphosphaturia is closely associated with urinary metabolic abnormalities. Furthermore, hyperphosphaturia is a significant risk factor for stone recurrence in first-time SFs.

500㎾급 소수력 발전용 수차 런너의 실링 유닛(Sealing Unit) 설계를 위한 CFD 기반의 유동해석 및 퇴적물로 인한 상호 연계성 연구

하윤석,김정완,이용복 한국유체기계학회 2019 한국유체기계학회 학술대회 논문집 Vol.2019 No.11

MS Point 저감 용접재에 적용한 냉각시 용접부 열변형률 분석에 관한 연구

하윤석,남성길,박세진,권창길,Ha, Yunsok,Nam, Seongkil,Park, Sejin,Kwon, Changgil 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.6

This study targets to make clear the connection between MS (Martensite start) point and welding shrinkage. We approved that a Martensite-transformed weldment may not yield state under low MS point, but also admitted the limitation of numerical calculation by inherent strain approach or thermal strain approach. Therefore, new thermal strain formulae during cooling stages were made. As a thermal strain is obtained by integrating thermal extension coefficient, a constant of integration should be decided. In our suggested formulae, the origin was based on totally remained austenite, and added strain from volume changes in Martensite transformation was based on totally transformed ferrite. Through the suggested methodology, It is verified that an MS point under a critical temperature can let weld shrinkage relax and the critical value can be obtained. For supporting this process, 15 weld-consumables were made, were tested by fillet type and were measured. As a result, a positive correlation between MS point and level of weld-distortion was obtained, but it was rather weak.

쉘 요소를 이용한 K및 X개선 용접구조물의 열변형 해석방법에 관한 연구

하윤석,최지원,Ha, Yunsok,Choi, Jiwon 대한용접접합학회 2012 대한용접·접합학회지 Vol.30 No.6

Because ships and offshore structures have very large dimensions and complicated shapes, it is difficult to determine the deformation or internal stress in the structure by simple lab tests. Thus, a rigorous analysis by using the computer simulation technology is essential for obtaining their distortions by considering the entire production process characteristics. The rapid development of computer technology made it possible to analyze the heat transfer phenomena, deformation and phase transformation in the welded joint. For large shell structures, shell elements modeling contributed primarily to this development. But if a welding is done by multi-pass, shell elements whose thickness are unchangeable can hard to describe the local situation. Recently, it was researched how to introduce the imaginary temperature for V grooved multi-layer butt welding in strain-boundary method (a kind of shrinkage methodologies). In the present study, we formulated the imaginary temperature for the double bevel and double V groove by considering the thickness change of each pass through the bead and the thickness directions simultaneously and also demonstrated the feasibility of the formula by applying it to the thermal distortion analysis of the erection process of crane pedestal.

도파민 치료와 연관된 딸꾹질 1예

하윤석,김민정 고신대학교 의과대학 2010 고신대학교 의과대학 학술지 Vol.25 No.2

Drug induced hiccups may be associated with a various agents, including corticoste-roid, antibiotics, and benzodiazepines. Rarely, levodopa or dopamine agonist therapy in Parkinson’s disease patient, can trigger hiccups. We report a case of persistent hiccup, occurring with dopaminergic medication in a patient with Parkinson’s disease 약물 유발성 딸꾹질은 코르티코스테로이드, 항생제 그리고 벤조디아제핀 등의 약물에 의하여 발생할 수 있다. 드물게 파킨슨병의 치료 목적으로 사용하는 레보도파나 도파민 효현제가 딸꾹질을 유발시킬 수 있다. 저자들은 파킨슨병의 치료 목적으로 레보도파와 도파민 효현제를 사용한 환자에서 조절되지 않는 딸꾹질을 경험하였기에 문헌 고찰과 함께 보고하는 바이다.

삼차동맥존속증을 동반한 정중엽 다리뇌경색

하윤석,김명국,유봉구 고신대학교 의과대학 2010 고신대학교 의과대학 학술지 Vol.25 No.2

Persistent trigeminal artery (PTA) is the most frequently observed fetal anastomosis between the carotid and vertebrobasilar circulations. PTA is usually associated with hypoplasia or aplasia of the vertebrobasilar artery. A 56-year-old woman presented with right hemiparesis and dysarthria. Brain MRI showed acute infarction in the right paramedian pons. CT angiogram revealed right persistent trigeminal artery and hypoplasia of the proximal basilar artery