우리나라 해역별 해양환경에 최적화된 확률모형 개발

조용준 한국해안,해양공학회 2024 한국해안해양공학회 논문집 Vol.36 No.1

본 연구에서는 먼저 우리나라 해역별 해양환경 특성이 담긴 장기 파랑 관측자료로부터 Goda 모형을활용하여 파력과 양력 시계열자료를 생성하였다. 이어 이렇게 생성된 시계열자료부터 Three-parameter Weibull distribution에 기반한 파력과 양력 확률모형을 개발하였다. 해역별로 다른 우리나라 해양환경은 파력과 양력 확률모형 모수에서도 그 차이를 확연하게 드러내었다. 충분히 발달한 풍성 파가 우월한 남해안의 경우 큰 Scale Coefficient, 작은 Location Coefficient, 1.3 전후의 Shape Coefficient로 특정되는 것을 확인하였다. 이에 비해 파랑의성장이 취송거리에 의해 제한되는 서해를 마주하고 있는 군산의 경우 작은 Scale Coefficient, 큰 Location Coefficient, 2.0 전후의 Shape Coefficient로 특정되었다. 서해와 남해가 만나는 해역을 마주하고 있는 목포의 경우 작은 Scale Coefficient, 큰 Location Coefficient, 제일 작은 Shape Coefficient를 지녀 남해와 서해의 해양환경이 혼재한다는 사실도 확인할 수 있었다. In this study, probabilistic models for the wave- and lifting forces were derived directly from long term in-situ wave data embedding the Korean marine environment characteristics varying from sea to sea based on the Three-Parameter Weibull distribution. Korean marine environment characteristics varying from sea to sea carved out their presence on the probability coefficients of probabilistic models for wave- and lifting forces. Energetic wave conditions along the southern coast of Korea distinguish themselves from the others with a relatively large scale coefficient, small location coefficient, and shape coefficient around 1.3. On the other hand, mild marine environment along the western coast has a small variability, leading to small scale-coefficient, large location coefficient and shape coefficient around 2.0. In the sea off Mokpo, near the boundary between the South and West Seas, marine environment was characterized by small scale-coefficient, large location coefficient, and shape coefficient around 1.2, implying that marine environments characteristics of the South-and West Sea coexist in the sea off Mokpo.

Steady Aerodynamic Characteristics of Two-Dimensional NACA0012 Airfoil for One Revolution Angle of Attack

Park, Byung Ho,Han, Yong Oun The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2

Steady variations in aerodynamic forces and flow behaviors of two-dimensional NACA0012 airfoil were investigated using a numerical method for One Revolution Angle of Attack (AOA) at Reynolds number of $10^5$. The profiles of lift coefficients, drag coefficients, and pressure coefficients were compared with those of the experimental data. The AERODAS model was used to analyze the profiles of lift and drag coefficients. Wake characteristics were given along with the deficit profiles of incoming velocity components. Both the characteristics of normal and reverse airfoil models were compared with the basic aerodynamic data for the same range of AOA. The results show that two peaks of the lift coefficients appeared at $11.5^{\circ}$ and $42^{\circ}$ and are in good agreement with the pre-stall and post-stall models, respectively. Counter-rotating vortex flows originated from the leading and trailing edges at a high AOA, which formed an impermeable zone over the suction surface and made reattachments in the wake. Moreover, the acceleration of inflow along the boundary of the vortex wrap appeared in the profile of the wake velocity. The drag profile was found to be independent of the airfoil mode, but the lift profile was quite sensitive to the airfoil mode.

Friction Coefficient for the Quantification of Needle Grasp in the Lifting-Thrusting Method

Son, Young-Nam,Kim, Jung,Lee, Hyo-Sang,Shin, Kyung-Min,Han, Ye-Ji,Lee, Seung-Deok Korean Society for Precision Engineering 2014 International Journal of Precision Engineering and Vol.15 No.7

We propose a coefficient of friction for quantifying the needle grasp sensation of acupuncture needles applied using the lifting-thrusting method. To measure the force exerted on an acupuncture needle, six tissue specimens of varying hardness were selected and the lifting-thrusting method was applied to the samples using a needle insertion measurement system. The measured values of the force can be expressed as friction coefficients through analysis with a modified Karnopp friction model. Needle grasp was measured using the visual analog scale (VAS). By comparing the coefficients of friction and the VAS values, we determined that the subjective phenomenon of needle grasp can be quantified with Cp (the positive coefficient of the kinetic friction). Objective measurements of changes in sensation can thus be obtained by determining Cp.

경비행기의 최대양력계수 추정에 대한 연구

이정훈(Jung-Hoon Lee),류시융(Si-Yoong Yoo) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

Estimated values for maximum lift coefficients of a light airplane, ChanGong-91, derived from an analytical method using a test database, a computational fluid dynamic method, a wind tunnel test, and a flight test are compared. The DATCOM method and VSAERO code are applied as the analytical method and the computational fluid dynamic method, respectively, in order to estimate the maximum lift coefficients of a light airplane. The wind tunnel test is conducted using a 1/14.5 scaled model installed in a closed circuit type wind tunnel. For the flight test approach, the wings-level power-off stall tests are performed to obtain the maximum lift coefficients. As a point of reference for the flight test results of the maximum lift coefficients, the differences of both estimates derived from the DATCOM method and the wind tunnel test data are smaller than those derived from VSAERO.

Friction Coefficient for the Quantification of Needle Grasp in the Lifting-Thrusting Method

손영남,이승덕,김정,이효상,신경민,한예지 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.

We propose a coefficient of friction for quantifying the needle grasp sensation of acupuncture needles applied using the liftingthrustingmethod. To measure the force exerted on an acupuncture needle, six tissue specimens of varying hardness were selected andthe lifting-thrusting method was applied to the samples using a needle insertion measurement system. The measured values of the forcecan be expressed as friction coefficients through analysis with a modified Karnopp friction model. Needle grasp was measured usingthe visual analog scale (VAS). By comparing the coefficients of friction and the VAS values, we determined that the subjectivephenomenon of needle grasp can be quantified with Cp (the positive coefficient of the kinetic friction). Objective measurements ofchanges in sensation can thus be obtained by determining Cp.

에어댐의 높이가 차체 표면의 압력변화에 미치는 영향

박종수,김성준 江原大學校 産業技術硏究所 2002 産業技術硏究 Vol.22 No.B

3-D numerical studies are performed to investigate the effect of the air dam height and approaching air velocities on the pressure distribution of notchback road vehicle. For this purpose, the models of test vehicle with four different air dam heights are introduced and PHOENICS, a commercial CFD code, is used to simulate the flow phenomena and to estimate the values of pressure coefficients along the surface of vehicle. The standard k-ε model is adopted for the simulation of turbulence. The numerical results show that the height variation of air dam makes almost no influence on the distribution of the value of pressure coefficient along upper and rear surface but makes strong effects on the bottom surface. That is, the value of pressure coefficient becomes smaller as the height is increased along the bottom surface. Approaching air velocity makes no differences on pressure coefficients. Through the analysis of pressure coefficient on the vehicle surface, one tries to assess aerodynamic drag and lift of vehicle. The pressure distribution on the bottom surface affects more on lift than the pressure distribution on the upper surface of the vehicle does. The increase of air dam height makes positive effects on the lift decrease but no effects on drag reduction.

하단배출형 연직 가동보의 방류량 산정

최용환,이지행,최흥식 한국방재학회 2016 한국방재학회논문집 Vol.16 No.5

The equations of discharge coefficient for under flow through the openness of vertical lift weir were developed for the calculation of free and submerged flows. In hydraulic characteristic analyses, the variation of upstream depth and the depth difference between up and down stream of gate depend on the gate openness and discharge. For free and submerged flows, the equations of discharge coefficient were developed by the definition of submergence ratio and the ratio of gate openness height to depth difference of up and down stream at gate in addition to the submergence ratio as well. Correlation analyses were carried out between flows of the experimental and the calculated by the developed equation of discharge coefficient. For free flow, the root mean square error (RMSE) and mean absolute percentage error (MAPE) were 0.0008 m 3 /s and 4.87%, respectively. There were 67% and 92% calculation discharges within the 68% and 95% confidence intervals (CI), respectively. For submerged flow, the RMSE and MAPE were 0.0006 m 3 /s and 4.18%, respectively. There were 75% and 94% calculation discharges within the 68% and 95% confidence intervals (CI), respectively, indicating a high degree of correlation between the experimental and calculate discharges results in the applicability. 연직가동 수문의 개도에 따른 자유월류와 잠수월류 형태에 따른 방류량의 산정을 위한 유량계수 관계식을 개발하였다. 수문의 상류수심의 변화와 수문의 상류와 하류의 수위차는 유량과 수문의 개도높이와 상관이 있음을 확인하였다. 자유월류와 잠수월류에 따른 잠수도를 정의하고, 이를 이용한 유량계수 관계식을 개발하였다. 잠수도와 더불어 수문의 개도높이와 수문의 상류와 하류의 수심차와의 비를 이용한 유량계수 관계식을 제시하였다. 개발한 유량계수 관계식을 이용한 방류량과 실험유량간의 상관분석을 수행하였다. 그 결과 자유월류에서는 RMSE는 0.0008 m 3 /s, MAPE는 4.87%, 68%와 95% 신뢰도 구간에는 각각 67%, 92%가 포함됨을 확인하였다. 잠수월류에서는 RMSE는 0.0006 m 3 /s, MAPE는 4.18%, 68%와 95% 신뢰도 구간에는 각각 75%, 94%가 포함됨을 확인하였다. 따라서 개발한 유량계수 관계식에 의해 산정한 방류량과 실험유량은 높은 상관이 있어 사용성이 있는 것으로 판단된다.

익형 뒷전 형상이 날개 공력 특성에 미치는 영향

김왕현(W. H. Kim),류기명(G. M. Ryu),김병수(B. S. Kim) 한국전산유체공학회 2014 한국전산유체공학회지 Vol.19 No.4

In the paper, a study on the analysis of the effects of trailing edge thickness on the aerodynamic characteristics of an airfoil is described. In this research, modification of the formula representing NACA symmetric airfoil is studied to change the airfoil shape with different trailing edge thickness of user’s choice. According to the result of aerodynamic characteristics, as the trailing edge thickness increases the maximum lift coefficient increases while the lift-to-drag ratio decreases. In this paper flow calculation results are demonstrated and the analysis on those results and findings on the effects of non-zero thickness of trailing edge are suggested.

글라이딩 하는 잠자리 날개 주름의 영향에 대한 수치해석적 연구

김원갑(Won-Kap Kim),변도영(Do-Young Byun),박훈철(HoonCheol Park) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

We investigate the aerodynamic performance of the dragonfly wing which has the cross-sectional corrugation by using the static 2-dimensional unsteady simulation. Computational condition is at Re=150, 1400 and 10,000 with the angles of attack from 0 to 40 degrees. As computational results, lift coefficients are increased by the wing corrugation at all Reynolds number. But corrugation have little influence on the drag coefficients. The flow such as vortex in the valley of corrugation and near the edge of corrugation are locally different from the elliptic wing. But such local flow have little influence on the time averaged wing performance. From the numerical experiment in this study, suction side corrugation of the wing have very little influence on increase of the lift coefficient at the positive angle of attack.

궤적변화 향상을 위한 위플볼 디자인 설계

최수현(Soo-hyoun Choi),허진규(Jin-kyu Heo),김병준(Byoung-jun Kim),박수인(Su-in Park),김도균(Do-kyun Kim) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

A wiffle ball is a ball that can create a change trajectory that bends at a large angle. However, for someone, it can be difficult to throw a ball while creating a change trajectory. Even if we want to compensate for these shortcomings, there are not many previous studies on wiffle ball so far. Through the Ansys Fluent program, we investigated the ambient air flow when throwing a wiffle ball, its separation point, ambient air flow and lift coefficient. In addition, we created a new wiffle ball design by changing the surface and length of the hole of the ball to improve the change trajectory, and this also verified the lift and lateral force through Fluent.