• 한국추진공학회지
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• 제13권3호
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• pp.41-49
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• 2009

본 논문은 공기흡입식 추진기관의 고체 로켓 부스터 분리에 관한 수학적 모델링과 시뮬레이션 기법을 기술하였다. 비행체 및 부스터는 하나의 다물체(multi-body)로 고려하였고 부스터는 단지 비행체의 축 방향으로 움직이는 것으로 가정하였다. 비행체 및 부스터의 동적 운동은 Kane 방법에 의해 모델링 되었다. 다양한 부스터 위치에 따라 전체 시스템에 작용하는 공력은 DATCOM 소프트웨어를 사용하여 산출되었으며 부스터 분리 유효 작용면에 작용하는 내부 분리 압력은 일반적인 기체역학 및 Taylor-MacColl 관계식에 의해 산출되었다. 수치적 해석은 Mathworks사의 Matlab이 사용되었다. 해석 결과에 의하면 부스터 분리 동안 마하수 및 받음각 변화 등은 크지 않는 것으로 나타났으며, 실제 시험 장치를 이용한 부스터 분리 시험이 진행될 경우 자세 각 변화, 흡입 유동 특성 등은 무시할 만한 수치임을 확인할 수 있었다.

• 한국해양환경ㆍ에너지학회지
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• 제14권4호
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• pp.273-279
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• 2011

최근 관심이 높아지고 있는 해상풍력 터빈의 성능평가를 위해 풍력터빈 날개에 대한 점성유동장 해석을 수행하였다. Fluent package를 사용하여 회전하는 비관성 좌표계에서 Reynolds-averaged Navier-Stokes 방정식의 해를 구하였다. 난 류 모형은 realizable k-$\varepsilon$ 모델을 사용하였으며, 격자계는 구조 격자계와 비구조 격자계를 혼합하여 사용하였다. 먼저 실험값이 공개되어 있는 2차원 날개에 대한 유동해석을 통해 수치계산 결과를 검증하였다. 다음으로 NACA 4-series 단면을 가지는 세 개의 날개가 2 MW의 정격출력을 내도록 설계된 풍력터빈 날개를 대상으로 회전수와 피치각을 고정시킨 상태에서 입사류의 속도를 변화하여 주속비 별로 성능해석을 수행하였다. 그리고 풍력터빈의 성능향상을 위해 날개의 끝에 세 가지 형태의 날개 끝판을 붙여 성능 변화를 추정하였다. 그 중에서 날개의 흡입면에 날개 끝판을 붙인 경우가 가장 우수한 성능을 보였다. 또한 풍력터빈 날개가 경사각과 레이크를 가진 경우에 대하여 출력계수를 각각 비교하였다.

• 대한조선학회논문집
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• 제49권1호
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• pp.79-86
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• 2012

It is very important to investigate and understand the motion of a FPSO on waves because green water phenomenon occurs owing to the relative motions between incident waves and a ship on them. In this research, both experimental and some numerical approaches have been performed in head sea conditions with regular waves. As an object model of this research, a FPSO model is set free to heave and pitch during the experiments. Also, the motions of the FPSO model which are the results of the experiments are used for the corresponding numerical computations. The purpose of this study is to clarify the effect of bow flare on green water load. In this research, it is found that the amount of green water entered from the side of bow is decreased by the increase of bow flare angle. Moreover, the relation between the green water on the bow upper deck and the impact load on the vertical wall located at turrethead is investigated. The results of this research could be used as one of the fundamental data to design bow flares. Also, an optimized bow flare angle is proposed in this study.

• 대한치과보철학회지
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• 제45권4호
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• pp.482-491
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• 2007

Statement of problem: The screws of dental implant, having various thread types, can be categorized into different classes by their geometrical form, and each type transmits dissimilar amount and form of stress to alveolar bone. Purpose: The purpose of this study was to find an inclination angle of the screw thread that is favorable in distributing the stresses to alveolar bone. Material and methods: In this study, We used three dimensional finite element analysis with modeling having three types of thread inclination angles and fixed pitch-0.8 mm (single thread type with $3.8^{\circ}$ inclination, double thread type with $7.7^{\circ}$ inclination, triple thread type with $11.5^{\circ}$ inclination). Results: The results obtained from this study were as follows; 1. When the number of thread increased, the amount of Von-Mises stress was reduced since the generated stress was effectively distributed. 2. Since the maximum principal stress affects on the alveolar bone can influence deeply on the longevity of the implants when comparing the magnitude of the maximum principal stress double thread had least amount of stress. This shows that the double thread screw gave best result. Conclusion: In conclusion, double, and triple thread screws were found to be more effective on distribution of the stress than the single thread screws. But, increasing in the thread inclination angle such as triple thread screw relate on the magnitude of the maximum principal stress affecting on the alveolar bone can become problematic. Thus, effective combination of thread number and thread inclination angle can help prolonging the longevity of implant.

• 대한족부족관절학회지
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• 제17권2호
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• pp.115-120
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• 2013

Purpose: Calcaneal lengthening osteotomy is one option for the treatment of symptomatic flexible flatfoot in adults. The aim of the study was to evaluate the short term clinical and radiologic results and analyze its complications. Materials and Methods: Twelve feet who had undergone calcaneal lengthening osteotomy without flexor digitorum longus transfer between December 2009 and July 2011 were included. The mean age was 40.6 years (23~75 years). The mean followup was 17.3 months (13~25 months). Clinical outcome were assessed using American Orthopadics Foot ans Ankle Society (AOFAS) score and visual analogue scale (VAS) for pain. Four radiologic parameters were measured from weightbearing radiographs to evaluate the difference between preoperatively and postoperatively measures. To analyze the complications, calcaneocuboid joint subluxation and degenerative change were measured postoperatively. Results: The mean AOFAS score improved from 55.3 points preoperatively to 82.2 points at lastest follow-up (p=0.000). The mean VAS improved from 6.3 points preoperatively to 3.2 points postoperatively (p=0.002).All radiologic parameters, the mean talonavicular coverage angle on AP view, the mean talo-1st metatarsal angle on AP and lateral view and the mean calcaneal pitch angle, significantly improved after calcaneal lengthening osteotomy. Nine feets (75%) were shown the degenerative change in the calcaneocuboid joint at latest follow-up radiographs. Conclusion: Calcaneal lengthening osteotomy for the symptomatic flexible flatfoot in adults produced significant improvement in clinical and radiologic parameters, but calcaneocuboid joint osteoarthritis occurred postoperatively remained a major problem.

• 대한전자공학회논문지SD
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• 제44권2호
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• pp.55-60
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• 2007

본 논문에서는 1차원 CMOS 포토다이오드 픽셀 어레이를 이용한 광학 각도 센서에서, 해상도를 2배 향상시키는 인터폴레이션 방법을 제안한다. 제안된 구조는 인터폴레이션을 위하여 모든 픽셀을 짝수 픽셀 그룹과 홀수 픽셀 그룹으로 나누어, 각 그룹에서 가장 밝은 빛이 들어오는 픽셀(winner)을 winner take all 회로를 이용하여 찾아 이로부터 인터폴레이션을 수행하여 각도 센서의 해상도를 2배 향상시킨다. 제안된 인터폴레이션 방법은 픽셀이나 WTA 회로의 추가없이 간단히 하나의 XOR 게이트와 전압 비교기 회로를 이용하여 구현할 수 있다. $5.6{\mu}m$의 픽셀 피치를 가진 336개의 포토다이오드 픽셀 어레이를 $0.35{\mu}m$ CMOS 공정으로 구현한 후, 그 위에 $50{\mu}m$ 폭의 슬릿을 붙여서 광학 센서를 구성하여 실험하였다. 측정된 각도 해상도는 $0.1{\circ}$이며 35mW의 전력을 소모하고 최대 초당 8000번 각도를 측정할 수 있다.

• 대한조선학회논문집
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• 제52권6호
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• pp.485-493
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• 2015

Planing hull form is widely used as a high speed vessel hull. There is a problem of the planing hull not solved yet. The problem is that the planing hull has very large vertical acceleration and large heave and pitch motions. As one method for overcoming this problem, there is "wave-piercing hull". Before the motion in waves is investigated, the resistance and running attitude must be investigated. In this paper, the running attitude and resistance of two wave-piercing hulls are investigated by model tests. Model test results show that the wave-piercing hulls have large trim angle and sinkage at the high speed, so additional model tests are conducted by using the hull appended by stern interceptor that is very thin plate to increase the hydrodynamic pressure at the attached location. The results are compared with other planing hulls and the resistance components and the hydrodynamic force are discussed. From the model test results, it can be known that the stern interceptor is the effective appendage for the reduction of the resistance and trim angle of wave-piercing hull.

• 대한족부족관절학회지
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• 제20권1호
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• pp.27-31
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• 2016

Purpose: Several techniques have been introduced for correction of pes cavo-varus deformity. We retrospectively reviewed and compared the data of patients who underwent 1st metatarsal osteotomy alone, Dwyer's osteotomy alone, and 1st metatarsal osteotomy combined with Dwyer's osteotomy to determine the effect on radiographic parameters. Materials and Methods: Data on 28 cases in 27 consecutive patients recruited from 2006 to 2014 who underwent 1st metatarsal osteotomy alone (group F), Dwyer's osteotomy alone (group H), or 1st metatarsal osteotomy followed by Dwyer's osteotomy (group HF) with a minimum 1-year follow-up were reviewed retrospectively. Results: Calcaneal pitch angle on the standing foot lateral radiographs was significantly decreased after the operation in groups H and HF whereas Meary angle was decreased in groups F and HF. Hindfoot alignment angle and ratio on the hindfoot alignment view were improved in groups H and HF. Maximal medial cuneiform height reduction was observed in group HF. 1st ray was significantly shortened in groups F and HF. Conclusion: Combined forefoot and hindfoot operation took the largest correction power of all radiologic parameters.

• 한국태양에너지학회 논문집
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• 제35권4호
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• pp.43-55
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• 2015

This paper presents the thermal hydraulic performance of a three dimensional rib-roughened solar air heater (SAH) duct with the one principal wall subjected to uniform heat flux. The SAH duct has aspect ratio of 12.0 and the Reynolds number ranges from 2000 to 12000. The roughness has relative rib height of 0.045, ratio of dimple depth to print diameter of 0.5 and rib pitch ratio of 8.0. The flow attack angle is varied from $35^{\circ}$ to $70^{\circ}$. Various turbulent flow models are used for the heat transfer and fluid flow analysis and their results are compared with the experimental results for smooth surfaces. The computational fluid dynamics (CFD) results based on the renormalization k-epsilon model are in better outcomes compared with the experimental data. This model is used to calculate heat transfer and fluid flow in SAH duct with the compound roughness of V-shaped ribs and dimples. The overall thermal performance based on equal pumping power is found to be the highest (2.18) for flow attack angle of $55^{\circ}$. The thermo-hydraulic performance for V-pattern shaped ribs combined with dimple ribs is higher than that for dimple rib shape and V-pattern rib shape air duct.

• 대한조선학회논문집
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• 제53권5호
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• pp.343-352
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• 2016

In this study, a pre-swirl duct for the 180,000 DWT bulk carrier has been designed from a propulsion standpoint using CFD. The stern duct - designed by NMRI - was selected as the initial duct. The objective function is to minimize the value of delivered power in model scale. Design variables of the duct include duct angle, diameter, chord length, and vertical and horizontal displacements from the center. Design variables of the stators are blade number, arrangement angle, chord length, and pitch angle. A parametric design was carried out with the objective function obtained using CFD. Reynolds averaged Navier-Stokes equations have been solved; and the Reynolds stress model applied for the turbulent closure. A double body model is used for the treatment of free-surface. MRF and sliding mesh models have been applied to simulate the actuating propeller. A self-propulsion point has been obtained from the results of towing and self-propelled computations, i.e., form factor obtained from towing computation and towing forces obtained from self-propelled computations of two propeller rotating speeds. The reduction rate of the delivered power of the improved stern duct is 2.9%, whereas that of the initial stern duct is 1.3%. The pre-swirl duct with one inner stator in upper starboard and three outer stators in portside has been designed. The delivered power due to the designed pre-swirl duct is reduced by 5.8%.