• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.62-64
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• 1995

This paper describes the characteristics of electromagnetic forces of Combined superconducting maglev system. Generation of the levitation, the propulsion and the guidance force by a single coil is proved by the phasor- analysis. It is also shown that double-layered configuration has better characteristics in efficiency, pulsation of the forces and drag ratio than single-layered configuration.

• 한국수자원학회논문집
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• 제50권6호
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• pp.419-427
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• 2017

산지하천 하상에서 흔히 발견되는 호박돌에 작용하는 항력은 하천의 거동과 반응을 예측하는 데 있어서 중요하나 이를 위한 항력계수 연구는 미흡한 실정이다. 본 연구는 호박돌의 항력 실험을 통해서 호박돌 형상과 항력계수의 관계를 분석하였다. 호박돌의 장축과 단축이 흐름방향을 따를 때 항력계수에 미치는 형상계수의 영향을 분석하였다. 항력계수는 장축보다 단축에서 더 크며 호박돌의 등가직경 Reynolds 수가 증가하면 감소하였다. 항력계수와 등가직경 Reynolds 수의 관계에서 결정계수는 단축보다 장축에서 더 크다. 이는 호박돌 형상의 불규칙성에 따른 항력이 축에 따라 변화하기 때문인 것으로 판단된다. 항력분포 변화는 호박돌의 교호진동을 초래하였다. 그 진폭은 $R_{ep}$가 약 12,000에서 급격히 증가하였으며 장축보다 단축에서 더 큰 것으로 나타났다.

• Korea-Australia Rheology Journal
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• 제19권3호
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• pp.147-156
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• 2007

The orientation and deformation of polymer chains in a confined channel flow has been investigated. The polymer chain was modeled as a Finitely Extensible Nonlinear Elastic (FENE) dumbbell. The Brownian configuration field method was extended to take the interaction between the flow and local chain dynamics into account. Drag and Brownian forces were treated as anisotropic in order to reflect the influence of the wall in the confined flow. Both Poiseuille flow and 4 : 1 contraction flow were considered. Of particular interest was molecular tumbling of polymer chains near the wall. It was strongly influenced by anisotropic drag and high shear close to the wall. We discussed the mechanism of this particular behavior in terms of the governing forces. The dumbbell configuration was determined not only by the wall interaction but also by the flow type of the geometric origin. The effect of extensional flow on dumbbell configuration was also discussed by comparing with the Poiseuille flow.

• 제어로봇시스템학회논문지
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• 제11권8호
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• pp.688-695
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• 2005

This paper describes dynamic manipulability analysis of robotic arms moving in viscous fluid. The manipulability is a functionality of manipulator system in a given configuration under the limits of joint ability with respect to the task required to be performed. To investigate the manipulability of underwater robotic arms, a modeling and analysis method is presented. The dynamic equation of motion of underwater manipulator is derived based on the Lagrange-Euler equation considering with the hydrodynamic forces caused by added mass, buoyancy and hydraulic drag. The hydrodynamic drag term in the equation is established as analytical form using Denavit-Hartenberg (D-H) link coordination of manipulator. Two analytical approaches based oil manipulability ellipsoid are presented to visualize the manipulability of robotic arm moving in viscous fluid. The one is scaled ellipsoid which transforms the boundary of joint torque to acceleration boundary of end-effector by normalizing the torques in joint space, while the other is shifted ellipsoid which depicts total acceleration boundary of end-effector by shifting the ellipsoid as much as gravity and velocity dependent forces in work space. An analysis example of 2-link manipulator with proposed analysis scheme is presented to validate the method.

• 한국터널지하공간학회 논문집
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• 제14권3호
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• pp.277-292
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• 2012

본 논문에서는 쉴드 TBM 커터비트의 절삭력 평가를 위한 기초적 연구를 실시하였다. 기존 커터비트 절삭력 분석을 위한 여러 이론식이 존재하지만 기존이론식은 실제 커터비트 절삭력과 차이를 보인다. 따라서 실제 커터비트의 절삭력을 분석하기위하여 축소모형실험을 실시하였으며, 축소모형시험에서 얻은 결과는 기존 이론식과 비교 분석하였다. 이 연구로부터 얻은 결과는 TBM 커터헤드 설계에 있어 기본적으로 매우 필수적인 자료로 활용될 것이라 판단된다.

• Journal of Mechanical Science and Technology
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• 제19권3호
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• pp.877-886
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• 2005

Two-dimensional incompressible Navier-Stokes equations are solved using SIMPLER method in the intrinsic curvilinear coordinates system to study the unsteady viscous flow physics over two-dimensional ellipses. Unsteady viscous flows over various thickness-to-chord ratios of 0.6, 0.8, 1.0, and 1.2 elliptic cylinders are simulated at different Reynolds numbers of 200, 400, and 1,000. This study is focused on the understanding the effects of Reynolds number and elliptic cylinder thickness on the drag and lift forces. The present numerical solutions are compared with available experimental and numerical results and show a good agreement. Through this study, it is observed that the Reynolds number and the cylinder thickness affect significantly the frequencies of the force oscillations as well as the mean values and the amplitudes of the drag and lift forces.

• Wind and Structures
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• 제20권6호
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• pp.811-827
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• 2015

This study presents experimental and numerical aerodynamic investigation of a prototype vehicle. Aerodynamics forces examined which exerted on a prototype. This experimental study was implemented in a wind tunnel for the Reynolds number between $10^5-3.1{\times}10^5$. Numerical aerodynamic analysis of the vehicle is conducted for different Reynolds number by using FLUENT CFD software, with the k-$\varepsilon$ realizable turbulence model. The studied model aims at verifying the aerodynamic forces between experimental and numerical results. After the Reynolds number of $2.8{\times}10^5$, the drag coefficient obtained experimentally becomes independent of Reynolds number and has a value of 0.25.

• 동력기계공학회지
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• 제14권2호
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• pp.48-54
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• 2010

An improved numerical scheme, to which the hydroelastic method is adapted, is introduced for predicting the motion and structural responses of tension leg platforms(TLPs) in regular waves. The numerical approach in this work is based on a combination of the three dimensional source distribution method and the finite element method. The hydrodynamic interactions among TLP members, such as columns and pontoons, are included in the motion and structural response analysis. The drag forces on the submerged slender members, which are proportional to the square of relative velocity, are included in order to estimate the responses of members with better accuracy. Comparisons with other results verify the works in this paper.

• 전기학회논문지
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• 제57권4호
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• pp.589-595
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• 2008

Detent force of a permanent magnet linear motor(PMLSM) consist of cogging and drag forces, and should be minimized for high precision control purpose applications. This paper shows that the cogging force can be reduced effectively by employing 9 pole 10 slot structure. The drag force is minimized by optimizing the total length and shape of the exterior teeth of armature core simultaneously by using($1+{\lambda}$) evolution strategy coupled with response surface method. After optimization, the optimized PMLSM is proven to reduce 95% and 92.6% of the cogging and total detent forces, respectively, and give 12% and 6.4% higher Back-emf and thrust force, respectively, compared with a conventional 12 pole 9 slot structure under the same condition. Additionally, Simulation results by the proposed optimum design are verified by the experiment results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.77-79
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• 1995

This paper investigates the force on a rectangular AC supercoducting coil moving above and parallel to a conducting plate of finite thickness. Expressions are developed for the levitation and drag forces on the coil a a function of speed and frequency. The levitation force are generated at all speed including stand still in a AC supercoducting coil. The levitation and drag forces on a rectangular AC supercoducting coil are compared with those on a rectangular DC supercoducting coil moving above and parallel to a conducting plate.