Characteristics Of Lift Forces Research Articles

Experimental investigation about the lift force of a single bubble in the water at a linear shear flow

The rising motion of a single bubble in water at a linear shear flow was experimentally studied. A curved screen was used to generate a stable low-turbulence linear shear flow field. PIV was used to measure the flow field. Bubbles were generated through different sizes of needles by a syringe pump. A high-speed camera obtained two-dimensional photographs of the rising bubble to get the bubble's instantaneous positions, velocities, and forces through image processing. The lift coefficient CL was obtained by quasi-steady-state analysis. This paper analyzed the lift force characteristics of a single bubble under the present experimental conditions and got the critical size for the bubble's lateral migration direction changing. A lift force empirical correlation was proposed based on the difference of bubbles’ lift force characteristics between high-viscosity fluid and the low-viscosity fluid. The predicted results were in good agreement with the experimental results.

A new airfoil design method for wind turbine to improve maximum lift of airfoil

A new wind turbine airfoil design method is established. This method generates an airfoil by fusing different airfoils. The airfoil designed by this method could restrict the airflow separation near the trailing edge of airfoil at high angle of attack, meanwhile the turbulence also is restricted. As a result, the maximum lift force is increased about 16.4% at high angle of attack. Meanwhile, the drag force is decreased about 31.3%. By analyzing the influence of scale factor and rotation angle on the airfoil aerodynamic force characteristics, the simulated results indicate that the larger scale factor and rotation angle could increase the lift stall angle and the maximum lift force. Therefore, this method could be used for designing wind turbine airfoil with high maximum lift force characteristics.

Numerical Flow Simulation on Lift Force Characteristics of the Conventional Line Pantograph under Crosswind

Numerical Flow Simulation on Lift Force Characteristics of the Conventional Line Pantograph under Crosswind

Effects of Pantograph-Head Variation on Lift-Force Characteristics of Conventional Railway Pantograph under Cross-Wind Environment

Effects of Pantograph-Head Variation on Lift-Force Characteristics of Conventional Railway Pantograph under Cross-Wind Environment

고속선 운항 안정성을 위한 수중익 배치 및 종모멘트 특성에 관한 실험적 연구

본 연구에서는 수중익 배치와 종모멘트 특성이 전몰형 수중익선의 종방향 운동 안정성에 미치는 영향에 대하여 Tandem 수중익 모형의 시험을 통하여 고찰한다. 먼저, Canard 날개배치를 가지는 Tandem 수중익 모형을 제작하고 수중익의 양력 및 항력 계측 실험을 수행하여 양력 및 항력 특성을 평가하였다. 또한 종방향 운동의 초기 안정성과 자기 안정성을 가지는 Tandem 수중익 모형의 날개 배치를 결정하였다. Tandem 수중익 모형의 종안정성 시험에서는 선수 및 선미 수중익의 종방향 간격 변화와 종모멘트의 자기안정성 변화에 따른 Pitch 및 Heave 운동 특성, 익주 상태의 종안정성을 평가하였다. 먼저, Canard 날개배치를 가지는 Tandem 수중익 모형을 제작하고 수중익의 양력 및 항력 계측 실험을 수행하여 양력 및 항력 특성을 평가하였다. 또한 종방향 운동의 초기 안정성과 자기 안정성을 가지는 Tandem 수중익 모형의 날개 배치를 결정하였다. Tandem 수중익 모형의 종안정성 시험에서는 선수 및 선미 수중익의 종방향 간격 변화와 종모멘트의 자기안정성 변화에 따른 Pitch 및 Heave 운동 특성, 익주 상태의 종안정성을 평가하였다. 실험 수행 결과 본 연구의 주요 결론의 다음과 같다. 종 모멘트 자기 안정성이 클수록 주어진 고정 pitch 각에서 pitch운동에 대한 자기안정성이 높다. 다음 종모멘트 자기 안정성이 클수록, pitch각도 변화에 따른 pitch운동 및 heave운동의 변동 폭이 상대적으로 작으며 종방향 안정성이 우수하다. 마지막으로 종모멘트 자기안정성이 클수록, 수중익 양력이 동일한 경우, Tandem 수중익의 안정적인 익주를 위해서는 충분한 종모멘트의 자기안정성을 확보하는 것이 필수적인 것을 시험을 통하여 확인하였다. In this study, we have discussed about the effect of hydrofoil arrangement and longitudinal moment characteristic on longitudinal motion stability of fully-submerged hydrofoil by the experiment of tandem hydrofoil model. First of all, tandem hydrofoil model that has canard wing arrangement has been made and characteristics of lift force and drag force by performing the lift force and drag force measuring experiment has also been estimated. Besides, tandem hydrofoil model's wing arrangement which has the initial stability and self stability of longitudinal motion has also been determined. In longitudinal stability experiment of tandem hydrofoil model, the motion characteristic of pitch and heave and the longitudinal stability of foil borne condition by variation of self stability of longitudinal moment and longitudinal distance are estimated. The result from the experiment and it's important conclusion can be described as below; Increase the self stability for longitudinal moment, the higher self stability for pitch motions in a constant pitch angles. By increasing the self stability for longitudinal moment, the range of fluctuation of pitch motion and heave motion for pitch angle also will change relatively small and longitudinal stability is excellent. Lastly, when the lift force of hydrofoil is remain constants, we can conclude that securing the enough self stability for longitudinal moment is essential for stable foil borne condition of tandem hydrofoil.

Flow interference between a stationary cylinder and an elastically mounted cylinder arranged in proximity

The flow interference between two circular cylinders, one stationary and the other free to oscillate in the transverse direction, are studied numerically at Re=150. The incompressible Navier–Stokes equation in two space dimensions, an assumption that is expected to be valid at the considered Re, is solved by the characteristic-based-split (CBS) finite element method using the T4/C3 MINI triangular element. The center-to-center spacing between the two cylinders is fixed at 4 D, where D is the cylinder diameter. The angle of incident flow, α, with respect to the line through the two cylinder centers, varies within the range from α=0° to 90°. For the elastically mounted cylinder, the reduced mass considered is M r =2.0; the structural damping coefficient is assigned to be zero, which encourages high amplitude oscillations. For each α, the computations are conducted for a wide range of reduced velocities, U r . The flow interference is examined by scrutinizing (i) the frequency characteristics of the vortex shedding and oscillation; (ii) the dynamic response of the oscillating cylinder, including the amplitude of displacement, the drag and lift force characteristics and the phase relationship between the lift and the displacement series; and (iii) the flow response in terms of the instantaneous vorticity field. It was found that the flow interference type is significantly affected by the angle of the incident flow. As the cylinder is oscillated outside of the region of the wake behind the stationary cylinder ( α≥30°), it behaves similarly to its isolated counterpart. In contrast, if the cylinder is partially or entirely submerged within the upstream wake ( α<30°), then both the flow and body responses are substantially modified due to the vigorous interaction between the upstream wake and the oscillating cylinder; the response therefore belongs to the wake-induced regime. The U r range associated with the higher amplitude response is significantly shifted toward a higher U r . The maximum vibration amplitude builds up to a significantly higher level, even increasing the U r far beyond the resonance regime. In general, the wake flow associated with the wake-induced vibration (WIV) regime appears to be more unperiodic than does that corresponding to the vortex-induced oscillation regime. It is also revealed that both the vortex-cylinder and the shear layer-cylinder interaction mechanisms are responsible for the characteristics of the responses of oscillating cylinder. The larger momentum required for the higher oscillation amplitude is obtained from the duration of the energy transfer from the fluid to the cylinder, which is ascribed to the phase lag between the lift force and the cylinder displacement.

Numerical Analysis of Levitating Force Using Magnetic Shielding Effect of YBCO Plates

A magnetic levitation system using magnetic shielding effect of HTS bulk is studied. The system is constructed by permanent magnets, zero-field-cooled superconducting bulks and ferromagnetic rails, and lift force stability is obtained from magnetic field that is generated by the permanent magnet and is shaped by the superconducting bulks. In previous studies, we showed characteristics of lift force and stability about a basic model which had a small ferrite permanent magnet, three YBCO bulk superconductors and a short ferromagnetic bar. Now, improving the basic model, we found new models which have better characteristics of lift force by numerical analysis using 3D Integral Element Method (IEM). The new models are reported

Experimental and Numerical Analysis of Lift Force in Magnetic Levitation System

A new type of magnetic levitation system using the shielding effect of the HTS bulk is studied. The system includes a permanent magnet and three HTS bulks as a vehicle, and a ferromagnetic bar as a guide way. The simple structure of the guide way reduces large amount of construction costs. The system also provides stable lift force without any active control system. The characteristics of lift force are numerically analyzed using IEM(Integral Element Method). Experiment was performed using a small model. The two results are compared.

Dependence of Size and Position of Ferromagnetic Bars on Lift Force in Magnetic Levitation System

Basic experiment for examining characteristics of lift force using magnetic shielding effect of a superconducting bulk is performed. The new levitation system provides stable lift force without any active control system. Simple structure of guide way on the ground with only a ferromagnetic bar makes it possible to reduce great amount of cost. The characteristics of lift force for various size of ferromagnetic bar are measured and examined. We have confirmed that there is a limit in the size of ferromagnetic bar to obtain stable lift force. The ferromagnetic bar with a width of 18 mm was the most applicable size in obtaining stability and larger lift force. The results also showed that magnitude of lift force depends on the width of ferromagnetic bar (when the height is within the parameter of 2 to 10 mm), not the volume.

空中静止小型飛しょう体ロボットの基礎検討

Basic research for developing a small hovering robot is performed. Small hovering robots will be very effective for inspecting and observing the site and circumstances in a narrow or dangerous space, where human cannot access safely. In this paper, how to hover the small robot successfully in air, especially by using rotating blades mechanisms is investigated, and it is clarified that measured lift force characteristics almost agree with the theory, and main parameters governing the lift force are the wing length and the rotation speed. Using a 135 mm diameter rotor, lift of 0.3-0.4 N can be obtained. The wing size should not be reduced so much because the wing length has drastic influence on the lift. For this reason, methods to reduce the robot size without reducing the wing length are investigated When putting a part of the rotor upon another one, the lift is weakened only less than 10%, and minimizing the robot size is possible. In order to verify the present technology level, a four-rotor hovering robot with a size of 238 mm square and a mass of 121 g is manufactured, and basic performance is exhibited

Characteristics of Lift Forces on a Circular Pile in Waves

Hydraulic characteristics of lift forces on a circular pile due to regular waves are investigated experimentally. The generation of lift forces is discussed. It is found that this is based on the unsymmetry of vortices, and that the characteristics of lift forces, namely, the frequency and the magnitude, are influenced by the vortex patterns. Furthermore, the lift coefficients are calculated from the experimental resuts, and an empirical formula for estimation of the lift coefficients is proposed under some theoretical considerations. Finally, it is concluded that the total wave force for the design of ocean structures has to be considered in terms of the vectorial sum of the in-line forces and the lift forces.