Component Of Lift Force Research Articles

Variation of the lift force components of a settling particle caused by structural evolution of flowing foam

Wet foam fluid with a settling particle, as a special gas-liquid-solid three-phase flow, is increasingly found in related engineering fields. However, the detailed microscopic evolution of foam structure, which influences migration of the settling particle, has not been fully understood. In this study, the forces, exerted on the particle by foam film and bubble pressure in the flow direction, are defined as the lift force components Fnx and Fpx, respectively. The flow of the wet foam with a circular settling particle is studied by numerical method, and the distribution characteristics of the bubble-bubble and bubble-particle separations in the flowing foam are shown. More importantly, the influences of the microscopic structural evolution of foam film, such as the bubble-particle contact, the bubble-bubble and the bubble-particle separations, on the lift force components are in detail discussed. It is found that both the bubble-bubble and the bubble-particle separations can cause decreasing lift force and relaxing film stress, and the instantaneous bubble-particle contact can significantly change the lift force components. At the film scale, this study reveals the correlation between the particle movement and the microscopic structural evolution of foam fluid.

Experimental investigation into the kinetics of Falcon UF concentration: Implications for fluid dynamic-based modelling

Centrifugal gravity separators, such as the Falcon UltraFine (UF) concentrator, are the most common gravity concentration techniques used for fine particles processing. Hence, understanding the kinetics and separation mechanisms at play within these separators is of paramount interest. Recent research yielded a predictive physical model for the Falcon UF which however does not explain some results obtained with industrial ores. The Falcon UF kinetics have been investigated through the processing of fine-grained ores from the Altenberg tin deposit (Germany), the Tabuaço tungsten deposit (Portugal), a synthetic iron ore as well as results from previous studies on kaolin residues. Results have shown an evolution of Falcon UF performance with time/feed mass in contradiction with the stationary separation hypothesis on which the physical model was based. In terms of Falcon UF separation timing, four phases can be distinguished. First, upon initial feeding of the bowl, particles are trapped or rejected depending on their settling velocity. It yields a relatively ineffective selection according to density so that only ultrafine particles are ejected from the bowl, resulting in the quick growth of the concentrate bed. When the bed reaches a critical size, recovery and enrichment continue to increase through selective resuspension phenomenon that favours the concentration of dense particles and the ejection of larger particles. This way, the bed builds up while the content of concentrate bed surface evolves until resuspension balances the stream of dense material reaching the bed and recovery drops. The evolution of partition curves over time confirmed the low recovery of ultrafine particles during the whole operation but also showed a decrease of coarse particles recovery with time. It suggests that the second separation mechanism is less sensible to particle size compared to the first one and that size even has a negative impact on recovery. Furthermore, erosion figures in furrows are observed in the concentrate bed which may play locally an active role in the separation. These observations suggest that two separation mechanisms are at play. Firstly, differential particles settling within the flowing film which is already accounted for in the existing physical model. Secondly, resuspension of particles from the concentrate bed by the action of a lift force acting preferentially on coarse particles deposited at the surface of the bed and resulting in the rejection of coarser and lower-density particles. The addition of a lift force component to the existing model is discussed and a resuspension criterion is proposed as a guidance of the physics involved in this second separation mechanism. Future developments will require a dynamic model which would need to integrate the evolution of the concentrate bed content over time.

Comparison of the aerodynamics of bridge cables with helical fillets and a pattern-indented surface

In this paper, the aerodynamics of bridge cables with helical fillets and a pattern-indented surface are examined. To this end, an extensive wind-tunnel test campaign was undertaken to measure the static force coefficients about the critical Reynolds number region, with varying relative cable-wind angles. The tests confirmed that the pattern-indented tubing exhibits the lowest drag coefficient, reaching its supercritical flow state for Reynolds numbers lower than the other cables tested. For this cable, vortex-shedding was found to be present throughout the supercritical range. The asymmetry of the surface pattern introduce a wind-angle of attack dependency that leads to a prediction of Den Hartog galloping instability. For yawed positions, flow transition was found to be independent of the relative cable-wind angle and therefore only governed by the along-wind flow velocity. The helically filleted cable was found to have a much slower flow transition for near normal flow and relatively large lift force components for the yawed positions. Flow visualizations confirmed the existence of specific flow structures which are often associated with the presence of lower drag or large lift forces. The visualization tests confirmed the presence of an axial flow that was greatly hindered by the presence of the helical fillets.

대각도 받음각을 갖는 무인잠수정에 작용하는 동유체력 특성에 관한 실험적 연구

회류수조에서의 대각도 정적(static) 모형실험을 통해 Manta형 무인잠수체에 작용하는 동유체력을 측정하였으며, 동유체력에 미치는 Reynolds수의 영향을 고찰하였다. 이를 위해 동유체력을 cross-flow drag과 양력(lift force)으로 성분 분석을 하였으며, 양력 성분에는 Reynolds수의 영향을 무시하고, cross-flow drag 성분에만 Reynolds수의 영향을 고려하였다. 그 후 이들 두 성분을 다시 합성함으로써 실물 무인잠수정에 작용하는 동유체력의 추정 기법을 제시하였다. The authors adopt the Unmanned Undersea Vehicle(UUV), the shape of which is like a manta. They call here it Manta UUV. Manta UUV has been designed from the similar concept of the UUV called Manta Test Vehicle(MTV), which was originally built by the Naval Undersea Warfare Center of USA(Lisiewicz and French, 2000; Simalis et al., 2001; U.S. Navy, 2004). The present study deals with the effect of Reynolds numbers on hydrodynamic forces acting on Manta UUV at large angles of attack. The large angles of attack cover the whole range of 0 to <TEX>${\pm}$</TEX> 180 degrees in horizontal plane and in vertical plane respectively. Static test at large attack angles has been carried out with two Manta UUV models in circulating water channel. The authors assume that the experimental results of hydrodynamic forces (lateral force, yaw moment, vertical force and pitch moment) are analyzed into two components, which are lift force component and cross-flow drag component. First of all, Based on two dimensional cross-flow drag coefficient at 90 degrees of attack angle, the cross-flow drag component at whole range of attack angles is calculated. Then the remainder is assumed to be the lift force component. The only cross-flow drag component is assumed to be subject to Reynolds number.entstly the authors suggest the methodology to predict hydrodynamic derivertives acting on the full-scale Manta UUV.

Effect of acoustic resonance on the dynamic lift forces acting on two tandem cylinders in cross-flow

Abstract Direct measurements of the dynamic lift force acting on two tandem cylinders in cross-flow are performed in the presence and absence of acoustic resonance. The dynamic lift force is measured because it represents the integrated effect of the unsteady wake and therefore it is directly related to the dipole sound source generated by vortex shedding from the cylinder. Three spacing ratios inside the proximity interference region, L/D=1.75, 2.5 and 3 are considered. During the tests, the first transverse acoustic mode of the duct housing the cylinders is self-excited. In the absence of acoustic resonance, the measured dynamic lift coefficients agree with those reported in the literature. When the acoustic resonance is initiated, a drastic increase in the dynamic lift coefficient is observed, especially for the downstream cylinder. This can be associated with abrupt changes in the phase between the lift forces and the acoustic pressure. The dynamic lift forces on both cylinders are also decomposed into in-phase and out-of-phase components, with respect to the resonant sound pressure. The lift force components for the downstream cylinder are found to be dominant. Moreover, the out-of-phase component of the lift force on the downstream cylinder is found to become negative over two different ranges of flow velocity and to virtually vanish between these two ranges. Acoustic resonance of the first mode is therefore excited over two ranges of flow velocity separated by a non-resonant range near the velocity of frequency coincidence. It is therefore concluded that the occurrence of acoustic resonance is controlled by the out-of-phase lift component of the downstream cylinder, whereas the effect of the in-phase lift component is confined to causing small changes in the acoustic resonance frequency.

The lift force on an arbitrarily shaped body in a steady incompressible inviscid linear shear flow with weak strain

This paper presents a mathematical derivation using the classical theory of fluid dynamics for the force on an arbitrarily shaped body in a linear shear flow. To make the analysis tractable, the problem is linearized by assuming that the strain rate is weak and neglecting terms of the order of the strain rate squared. The argument generalizes previous established analytical results due to Darwin regarding the drift-volume and Lighthill for the asymptotic form of the rotational velocity field induced by the body. The final expression for the force is determined by generalizing an analytical argument due to Auton for the sphere. The results identify for the first time a rotational lift force component that occurs only when the body shape is truly asymmetric.

Prediction of hydrodynamic forces on submarine pipelines using an improved Wake II Model

The hydrodynamic force model for prediction of forces on submarine pipelines as described includes flow history effect (wake effects) and time dependence in the force coefficients. The wake velocity correction is derived by using a closed-form solution to the linearized Navier–Stokes equations for oscillatory flow. This is achieved by assuming that the eddy viscosity in the wake is only time dependent and of a harmonic sinusoidal form. The forces predicted by the new Wake (Wake II) Model have been compared to Exxon Production Research Company Wake Model in terms of time histories (force shape) and magnitudes of peak forces. Overall, the model predictions by the Wake II Model are satisfactory and represent a substantial improvement over the predictions of the conventional models. The conventional force models representing adaptations of Morison's equation with ambient velocity and constant coefficients give predictions that are in poor agreement with the measurements especially for the lift force component. The Wake II Force Model can be used for submarine pipeline on-bottom stability design calculations for regular waves with various pipe diameters.

Particles in a shear flow near a solid wall: Effect of nonsphericity on forces and velocities

Hydrodynamic forces and velocities of spheroidal particles in a simple shear flow near a solid wall are calculated by a variant of the boundary integral equation method, combined with the use of the reciprocal theorem for Stokes flow equations. It is shown that the effect of the wall decreases with increasing particle nonsphericity (decreasing aspect ratio). For long slender particles the effective distance where the wall effect is significant is measured by several particle shorter axes. In the vicinity of the wall spheroids experience several interactions, which do not exist for spheres. These are the lift force component perpendicular to the wall and the corresponding rotational-translational coupling component of the resistance tensor. The data on particle hydrodynamic interactions are used to calculate the velocities of the inertialess spheroidal particles in a shear flow near a wall. The calculations reveal that the effect of the wall is to create a nonzero velocity component in the direction of the normal to the wall surface. This velocity is zero for spheroids in a free shear flow; near the wall it vanishes for spherical and, seemingly, for oblong particles. Therefore a spheroid moving in a shear flow near the wall will perform an oscillatory motion towards and away from the wall. The wall will retard the particle motion parallel to its surface, albeit in a lesser extent than for spheres. In addition, spheroidal particles will perform periodic rotational motion, as they do in an unbounded shear flow, however, with larger periods. For force components which act on spheres, as well as on nonspherical particles the wall effect is most pronounced for particles whose shape is close to spherical. Several correlation formulae are proposed for the forces and torques acting on spheroids, as well as for their friction tensor coefficients.

Response of a cylinder in oscillatory flow

The two-dimensional response of a flexibly mounted rigid cylinder in oscillatory flow is studied in this paper. Both measurements of cylinder response obtained in a U-tube and mathematical modelling of this problem are considered. Trajectories of the cylinder response are obtained experimentally for ranges of Keulegan-Carpenter numbers from 2 to 60 and the ratio of the natural frequency of the cylinder in water to the frequency of oscillation of the U-tube from 1 to 9. It is found that the cylinder responds in a strongly two-dimensional fashion for particular combinations of these parameters. Regions of repeatable two-dimensional response are identified. These are separated by transition regions characterized by poor synchronization between the vortex shedding and the motion of the cylinder, with resulting three-dimensional response. The ability of the cylinder to respond both in-line and transverse to the flow has a significant influence on the resulting response. In order to analyse this fluid-structure interaction problem, three simple mathematical models are formulated which attempt to predict this two-dimensional response. The first two models use the relative velocity formulation of the Morison equation for the force in-line with the flow, but with different expressions for the transverse force. The equations of motion for these models are uncoupled. In contrast, the third model considers drag and lift force components in directions parallel and perpendicular to the direction of instantaneous relative velocity between the cylinder and the flow, which results in coupled equations of motion. The usefulness and limitations of each of the models are assessed by comparison with the experimental observations. In general, the simple models used here are able to predict the cylinder response in a satisfactory fashion, even though the interaction between the response of the cylinder and the flow is very complicated.

Dynamic response of structures loaded by a transverse wind force component

AbstractThe paper first presents an analytical solution for the dynamic analysis of slender structures due to wind actions. The transverse lift force component of wind is assumed as external loading. The structure is then treated as a lumped parameter system. The normal mode method of analysis is used by means of Laplace transforms.