• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.92.4-92
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• 2001

Estimation of the general along-track acceleration was performed in the KOMPSAT-1 orbit determination process. Several sets of the atmospheric drag and solar radiation pressure coefficients were also derived with the different spacecraft area. State vectors in the orbit determination with the different spacecraft area were compared in the time frame. The orbit prediction using the estimated coefficients was performed and compared with the orbit determination results. The orbit prediction with the different general acceleration values was also carried out for the comparison.

• 한국추진공학회지
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• 제25권4호
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• pp.78-87
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• 2021

KSLV 상단의 임무 다각화를 위해서는 저중력 환경에서 액체 추진제의 거동을 정확히 파악하고 있어야 한다. 지상에서 저중력 환경을 모사하는 방법은 자유낙하 방법이 있지만, 공기저항이 항상 동반된다. 공기 저항을 제거하기 위하여 공기 저항 차단캡슐을 이용한 낙하 시험을 진행하였다. 공기 저항 차단캡슐 내부에 시험체를 위치하고 7 m 높이에서 1.2초 동안 낙하하여 시험체의 저중력 환경을 조성하였다. 낙하하는 동안 0.01 g 이하의 중력가속도를 측정하였으며 지표면에 도달하기 전 최소 가속도는 약 0.005 g였다. 추후 낙하 높이 및 낙하 시간이 증가한다면 개선될 수 여지가 있다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.204-209
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• 2004

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 and under the limits of joint ability with respect to the tasks required to bt performed. To investigate the manipulability of underwater robotic arms, a modeling and analysis method are presented. The dynamic equation of motion of underwater manipulator is derived from the Lagrange - Euler equation considering with the hydraulic forces caused by added mass, buoyancy and hydraulic drag. The hydraulic drag term in the equation: is established as analytical form using Denavit - Hartenberg (D-H) link coordination of manipulator. Two analytical approaches based on 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 torque in joint space while the other is shifted ellipsoid which depicts total acceleration boundary of end-effector by shifting the ellipsoid in work space. An analysis example of 2-link manipulator with proposed analysis scheme is presented to validate the method.

• 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.

• Journal of Mechanical Science and Technology
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• 제16권6호
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• pp.745-756
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• 2002

The re-entry problem consists of guidance design and trajectory control. This paper summarizes the detailed relationships between the velocity, drag acceleration and altitude in determining reference trajectories. The computational issues are also addressed, and the performance of the proposed simple nonlinear control of a bank angle for the longitudinal/ lateral trajectory is demonstrated. In particular, the fixed bank angle methods that can reduce the drag acceleration errors at low-speeds are proposed. The importance of bank reversals with respect to the azimuth errors Is also elucidated.

• Journal of Astronomy and Space Sciences
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• 제15권1호
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• pp.221-228
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• 1998

유한 전력 추력 기를 사용하는 저 궤도의 우주 비행 체가 다른 저 궤도의 우주 비행 체와 랑데부할 때 공기저항의 영향을 연구하였다. 공기의 밀도는 지수 함수적으로 감소한다고 가정하였고 능동 비행 체의 주차 궤도는 6655.935km의 반경을 갖는 윈 궤도, 수동 비행 체의 궤도는 7321.529km의 윈 궤도로 가정하였다. 능동 비행 체의 궤적, 소모된 연료의 양, 추력 가속도의 크기를 비교한 결과, 저 궤도의 우주비행 체간의 랑데뷰 시 연료의 최적화 문제에 공기저항이 무시할 수 없는 영향을 미친다는 결론을 내릴 수 있었다. 그리고 능동 비행 체가 $360^{\circ}$이상의 각으로 회전하는 경우일 때 공기저항의 효과가 더 크게 나타난다는 결론을 얻었다.

• 한국전산유체공학회지
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• 제15권4호
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• pp.1-8
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• 2010

This article describes the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body. Numerical analyses for turbulent blood flow were performed with different magnitude of periodic accelerations using a modified turbulence model which was considering drag reduction of non-Newtonian fluid. The blood was considered to be a non-Newtonian fluid which was based on the power-law viscosity. In order to validate the modified $k-{\varepsilon}$ model, numerical simulations were compared with the standard $k-{\varepsilon}$ model and the Malin's low Reynolds number turbulence model for power-law fluid. As results, the modified $k-{\varepsilon}$ model represents intermediate characteristics between laminar and standard $k-{\varepsilon}$ model, and the modified $k-{\varepsilon}$ model showed good agreements with Malin's verified power law model. Moreover, the computing time and computer resource of the modified $k-{\varepsilon}$ model were reduced about one third than low Reynolds number model including Malin's model.

• Journal of Astronomy and Space Sciences
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• 제19권2호
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• pp.89-96
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• 2002

General along-track acceleration was estimated in the KOMPSAT-1 orbit determination process. Several sets of the atmospheric drag and solar radiation pressure coefficients were also derived with the different spacecraft area. State vectors in the orbit determination with the different spacecraft area were compared in the time frame. The orbit prediction using the estimated coefficients was performed and compared with the orbit determination results. The orbit prediction with the different general acceleration values was also carried out for the comparison

• Tribology and Lubricants
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• 제39권5호
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• pp.203-211
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• 2023

This study experimentally investigates the effects of angular acceleration on the friction and wear performances of a gas foil thrust bearing (GFTB) using a typical GFTB with six pads. The outer radius of the bearing is 31.5 mm, the total bearing area is 2,041 mm² , and the bump foil and incline (ramp) height are both 500 ㎛. The newly developed GFTB test rig for measuring the friction torque and coefficient measures the axial load, drag torque, lift-off speed, and touch-down speed. The experiment is conducted for angular accelerations of 78.5, 314.2, and 328.3 rad/s² at axial loads of 5, 10, and 15 N, respectively. The test shows that the start-up friction coefficient increases with increasing axial load at the same angular acceleration, and the friction coefficient decreases with increasing angular acceleration under the same axial load. As the angular acceleration increases, the lift-off speed at the motor start-up increases, and the touch-down speed at the motor stop decreases. The wear distance of the GFTB for a single on/off cycle increases with increasing axial load at the same angular acceleration and decreases nonlinearly with increasing angular acceleration under the same axial load. The test results suggest that adjusting the rotational angular acceleration helps reduce bearing friction and wear.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.380-391
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• 2014

In this study, the scale effect on the performance of the podded propeller of tractor type is investigated. Turbulent flow computations are carried out for Reynolds numbers increasing progressively from model scale to full scale using the CFD analysis. The result of the flow calculation for model scale Reynolds numbers agrees well with that of the experiment of a large cavitation tunnel. The existing numerical analysis indicates that the performance of the podded propeller blades is mainly influenced by the advance coefficient and relatively little by the Reynolds number. However, the drag of pod housing with propeller in operation is different from that of pod housing without propeller due to the acceleration and swirl of propeller slipstream which is altered by propeller loading as well as the pressure recovery and friction according to Reynolds number, which suggests that the pod housing drag under the condition of propeller in operation is the key factor of the scale effect on the performance between model and full scale podded propellers. The so called 'drag ratio', which is the ratio of pod housing drag to total thrust of podded propeller, increases as the advance coefficient increases due to accelerated flow in the slipstream of the podded propeller. However, the increasing rate of the drag ratio reduces continuously as the Reynolds number increases from model to full scale progressively. The contribution of hydrodynamic forces, which acts on the parts composed of the pod housing with propeller operating in various loading conditions, to the thrust and the torque of the total propeller unit are presented for a range of Reynolds numbers from model to full scales.