Measurements Of Hydrodynamic Forces Research Articles

Parabolic transport measurement of hydrodynamic forces for flow around circular/triangular distance dependent obstructions: Finite element analysis

<abstract><p>The present effort is the low Reynolds finite element hybrid meshed solution to apprehend the flow field properties in a convergent-divergent (CD) domain having engineering standpoints applications. To be more specific, we have considered the CD domain rooted with two types of obstructions in three various arrangements namely triangular/triangular, circular/triangular, and triangular/circular in CD throat. The viscous fluid is introduced from the inlet and interacts with installed obstacles. The moving stream in the channel is modelled mathematically in terms of the two-dimensional time-independent equations. The finite element approach is used to disclose numerical solutions by means of a hybrid meshing scheme. Optimized drag and lift force values encountered by an obstruction are offered through line integration across the external obstruction surfaces. In comparison to obstruction in left vicinity, the lift force faced by the triangle obstacle on the right side of the CD throat is larger. Furthermore, as compared to the drag force faced by the triangular obstruction in the same proximity, the circular obstacle experienced greater values as a drag. The lifting force sensed by the triangular cylinder is larger than circular cylinders. The assessment of marine hydrodynamic forces and stability individualities for fully or partially submerged objects in ocean engineering will benefit from the results of this study.</p></abstract>

Effect of surface shape on the aerodynamic coefficient of volleyball

Volleyball is a sport that begins with the serve, so effective service is essential to winning matches. The trajectory of the ball changes in a complex manner under the influence of fluid forces that depend on the speed, number of revolutions, and shape of the frame. Therefore, the purpose of this study was to understand the aerodynamic characteristics of the ball and to propose an ideal serving method by measuring fluid forces, measuring flight trajectory, and analyzing particle image velocimetry. In wind tunnel experiments, the fluid forces on the ball were measured at wind speeds ranging from 4 to 28 m/s. The results showed that the fluid force on the ball strongly depends on the type of ball and the orientation of the panel. In the flight trajectory measurement, the flight trajectory of the ball was measured by a high-speed camera and its speed was controlled by an ejector. The landing position of the ball was found to be strongly influenced by the shape of the panel; PIV measurements revealed the detachment of the ball. The air hole also moved the position of the detachment backward. The influence of panel shape shown by the hydrodynamic force measurement was consistent with the results of the trajectory analysis, revealing the importance of panel shape in serving.

Direct Measurements of Hydrodynamic Forces Induced by Tidal Bores

AbstractTidal bores are sudden discontinuities in water depth, and can be classified as undular and breaking bores when tidal waves propagate upstream in a river mouth and on beaches. The impact of different types of bores on sediment transport is not clear; hence, specially designed experiments were conducted to clarify the mechanism of sediment initiation. Here, a laser Doppler anemometer, a force sensor, and ultrasonic displacement meters accompanied by video recordings were used to investigate simultaneously the incipient motion of sediment under tidal bores. No sediment motion was observed during the initial steady flows. It was observed that only a few particles changed their initial position during the undular bore; however, a group of particles were seen moving upstream during the breaking bore. The inception of sediment motion was closely related to the passage of the breaking roller, that is, the forces that caused the inception of particle motion were not only due to velocity but also to the sudden discontinuity in free water surface. According to the experimental results, the upward vertical force due to swelling in free water surface before the roller toe was the main force in destabilizing the particles. Later, a large upstream longitudinal force was found to be the dominant cause promoting upstream particle motion during the breaking roller passage. Furthermore, phases of both horizontal and vertical forces play an important role in tidal bore propagation. It is interesting to note that by using the measured force, the observed phenomenon can be well explained by the Shield threshold criterion.

Experimental study on the selected aspects of bow thruster generated flow field at ship zero-speed conditions

The paper presents the results of experimental study on the interaction between the bow thrusters understood as the flow field changes generated by bow tunnel thruster in deep water conditions operated as a single and twin units. The research was limited to zero-speed case for the ship dead in the water. The influence of the hull form and jet spread between the neighbouring thrusters for several combinations of the applied bow thruster propeller revolutions has been discussed. The results of the flow field measurements - velocity field, volume of fluid rate, mean velocity and thrust have been compared with the measurements of hydrodynamic forces generated by the bow thrusters on the hull. Both experiments were conducted at zero-speed using the same large physical man-manned model of a car–passenger ferry in 1:16 scale.

Morphing Hydrofoil Model Driven by Compliant Composite Structure and Internal Pressure

In this work, a collaborative experimental study has been conducted to assess the effect an imposed internal pressure has on the controlling the hydrodynamic performance of a compliant composite hydrofoil. It was expected that the internal pressure together with composite structures be suitable to control the hydrodynamic forces as well as cavitation inception and development. A new concept of morphing hydrofoil was developed and tested in the cavitation tunnel at the French Naval Academy Research Institute. The experiments were based on the measurements of hydrodynamic forces and hydrofoil deformations under various conditions of internal pressure. The effect on cavitation inception was studied too. In parallel to this experiment, a 2D numerical tool was developed in order to assist the design of the compliant hydrofoil shape. Numerically, the fluid-structure coupling is based on an iterative method under a small perturbation hypothesis. The flow model is based on a panel method and a boundary layer formulation and was coupled with a finite-element method for the structure. It is shown that pressure driven compliant composite structure is suitable to some extent to control the hydrodynamic forces, allowing the operational domain of the compliant hydrofoil to be extended according to the angle of attack and the internal pressure. In addition, the effect on the cavitation inception is pointed out.

2016S-GS2-17 平水中自由航走状態における操縦流体力の計測について

2016S-GS2-17 平水中自由航走状態における操縦流体力の計測について

Hydrodynamic Performance of a Modular Biolocomotion Emulator

This paper presents experimental measurements of the internal and external forces and moments generated during forced oscillation of a modular biolocomotion emulator executing four distinct gaits at three reduced frequencies and three Reynolds numbers (including zero). The purpose of the experimental program is to develop a database of hydrodynamic force measurements that can be used to validate low-order computational methods, such as the unsteady vortex lattice method, for design analysis.

Confinement effects on energy harvesting by a heaving and pitching hydrofoil

Wall confinement effects on the energy harvesting performance by a flapping hydrofoil (aspect ratio = 4.5) have been investigated in a circulating water flume at a Reynolds number of 50,000. Measurements of hydrodynamic forces are taken for three different confinement configurations (unconfined, one-wall and two-wall confinement) and a series of confinement levels for each configuration. Compared with the unconfined situation, a significant improvement of efficiency performance is obtained for strong two-wall confinement due to the enhancement of the hydrodynamic forces, while only a modest increase is observed in the one-wall confinement configuration. Results show that the heave component of efficiency is the primary contributor to the performance improvement. A parametric study, varying reduced frequency and pitching amplitude, shows that as the confinement increases, the optimal energy harvesting occurs at larger values of the reduced frequency and pitching amplitude, and can reach a Lanchester–Betz efficiency as high as 50%.

Discontinuity of lift on a hydrofoil in reversed flow for tidal turbine application

This work presents an experimental investigation of a hydrofoil in reversed flow configuration in the context of marine current turbine development. Experiments consist in hydrodynamic force measurements and PIV flow observations on a NACA 0015 hydrofoil, at 5×105 Reynolds number. The hydrofoil in reversed flow produces a higher lift than in the classical forward flow for very low angles of attack and proved to be relatively efficient for an angle of attack lower than 10°, despite a much higher drag than the same foil in direct flow. Moreover, the lift coefficient shows a discontinuity with an hysteresis effect when the angle of attack is varied up and down around zero-degree. It is shown that the sharp leading edge generates an early Leading Edge Separation Bubble on one side (suction side) even for vanishing angles of attack. This separation bubble triggers the transition to turbulence of the boundary layer on the suction side while the pressure side boundary layer remains laminar. As a consequence, separation on the rounded trailing edge occurs farther downstream on the (turbulent) suction side compared to the (laminar) pressure side. The Leading Edge Separation Bubble and the inherent up–down asymmetry in the boundary layer regime are responsible for the lift singularity.

Validation of hybrid URANS/LES methods for determination of forces and wake parameters of KVLCC2 tanker at manoeuvring conditions

In this paper, computations of integral forces, surface pressure distribution and the wake behind the KVLCC2 tanker under simple manoeuvring (drift angles 6° and 12°) and complete manoeuvring (drift angle and yaw rate of 0.2, 0.4 and 0.6) conditions were performed and their results were compared with experimental results by Kume, K., Hasegawa, J., Tsukada, Y., Fujisawa, J., Fukasawa, R. and Hinatsu, M. (2006. Measurements of hydrodynamic forces, surface pressure, and wake for obliquely towed tanker model and uncertainty analysis for CFD validation. Journal of Marine Science and Technology, 11(2), pp.65–75). Different numerical methods including URANS k-ω SST (Menter. 1993. Zonal two equation k-ω turbulence models for aerodynamic flows. AIAA Papers, 93–2906), the hybrid URANS-LES model proposed in Kornev, N., Taranov, A., Shchukin, E. and Kleinsorge, L. (2011. Development of hybrid urans-les methods for flow simulation in the ship stern area. Ocean Engineering, 38, pp.1831–1838), the hybrid Improved Delayed Detached Eddy Simulation approach (Shur, M. L., Spalart, P. R., Strelets, M. K., and Travin, A. K. 2008. A hybrid RANS-LES approach with delayed-DES and wall- modelled LES capabilities. International Journal of Heat and Fluid Flow, 29(6), pp.1638–1649) based on Spalart-Allmaras URANS model were utilised. The doubled model of the KVLCC2 tanker with the scale (1/64.4) without appendages (propeller and rudder) was calculated at Reynolds number of 3.95 × 106 and Froude number of 0.142. The free surface deformation effect was neglected. Calculations were performed using OpenFOAM toolkit.

The effects of free surface and end cell on flow around a finite circular cylinder with low aspect ratio

Vortex-induced motion is an oscillatory phenomenon which occurs to a floating body with low aspect ratio. The basic phenomenological study about the effects of free surface and end cell on flow around a finite fixed circular cylinder was investigated in this study using particle image velocimetry and hydrodynamic force measurement. It was found from the former experiment that the wake of the cylinder is influenced by the both end cell and free surface. Blowup and back flow are generated from the end cell, and their effects are suspended by free surface. The result of hydrodynamic force measurement showed the effect of Reynolds number, Froude number, and the aspect ratio of the floating body on the hydrodynamic force. Fluctuating components of hydrodynamic coefficients decrease for increasing Reynolds number, Froude number, and the aspect ratio. On the other hand, the mean drag coefficient increases as Froude number increases and decreases as the aspect ratio increases. The interpretation to these results was discussed in comparison with flow structures observed in the experiment. In addition, it was found that the effect of Reynolds number on the mean drag coefficient changes at different aspect ratios. A possible interpretation to this phenomenon was proposed.

Modeling and Error Analysis of Hydrodynamic Experimental Apparatus

A hydrodynamic experiment apparatus is constructed to accomplish the measurement of hydrodynamic force on three-dimensional. This paper firstly introduces the mechanical structure of the novel hydrodynamic experiment apparatus. Then, it introduces the mathematical modeling of the hydrodynamic experiment apparatus which is based on the relationship between measurement data and the force on experiment subject. Finally, the error source of the mechanical structure and load cells were analyzed and the error compensation model is established to improve the measurement accuracy.

Hydrodynamic force measurements under precisely controlled conditions: Correlation of slip parameters with the mean free path

A customized atomic force microscope has been utilized in dynamic mode to measure hydrodynamic forces between a sphere and a flat plate, both coated with gold. In order to study the influence of the mean free path on slippage without systematic errors due to varying surface properties, all data have been acquired at precisely the same spot on the plate. Local accommodation coefficients and slip lengths have been extracted from experimental data for He, Ne, Ar, Kr, as well as N2, CO2, and C2H6, at Knudsen numbers between 3 × 10−4 and 3. We found that slippage is effectively suppressed if the mean free path of the fluid is lower than the roughness amplitude on the surface, while we could not observe a clear correlation between the accommodation coefficient and the molecular mass.

Volumetric reconstruction of the mean flow around circular cylinders fitted with strakes

The volumetric reconstruction technique presented in this paper employs a two-camera stereoscopic particle image velocimetry (SPIV) system in order to reconstruct the mean flow behind a fixed cylinder fitted with helical strakes, which are commonly used to suppress vortex-induced vibrations (VIV). The technique is based on the measurement of velocity fields at equivalent adjacent planes that results in pseudo volumetric fields. The main advantage over proper volumetric techniques is the avoidance of additional equipment and complexity. The averaged velocity fields behind the straked cylinders and the geometrical periodicity of the three-start configuration are used to further simplify the reconstruction process. Two straked cylindrical models with the same pitch (p = 10d) and two different heights (h = 0.1 and 0.2d) are tested. The reconstructed flow shows that the strakes introduce in the wake flow a well-defined wavelength of one-third of the pitch. Measurements of hydrodynamic forces, fluctuating velocity, vortex formation length, and vortex shedding frequency show the interdependence of the wake parameters. The vortex formation length is increased by the strakes, which is an important effect for the suppression of vortex-induced vibrations. The results presented complement previous investigations concerning the effectiveness of strakes as VIV suppressors and provide a basis of comparison to numerical simulations.

Reliable Measurements of Interfacial Slip by Colloid Probe Atomic Force Microscopy. II. Hydrodynamic Force Measurements

Here we report a new study on the boundary conditions for the flow of a simple liquid in a confined geometry obtained by measuring hydrodynamic drainage forces with colloid probe atomic force microscopy (AFM). In this work, we provide experimental data obtained using a best practice experimental protocol and fitted with a new theoretical calculation (Zhu, L.; Attard, P.; Neto, C. Langmuir 2010, submitted for publication, preceding paper). We investigated the hydrodynamic forces acting on a silica colloid probe approaching a hydrophobized silicon surface in a single-component viscous Newtonian liquid (di-n-octylphthalate), a partially wetting system. The measured average slip lengths were in the range of 24-31 nm at approach velocities of between 10 and 80 μm/s. Using our experimental approach, the presence of nanoparticle contaminants in the system can be indentified, which is important because it has been shown that nanoparticles lead to a large apparent slip length. Under our stringent control of experimental conditions, the measurement of the slip length is reproducible and independent of the spring constant of the cantilever.

Flow structures and hydrodynamic force during sediment entrainment

An experimental investigation of the role of coherent structures and their effect on hydrodynamic forces responsible for inception of sediment motion has been carried out using a laboratory flume. Two types of experiments, namely, movable and fixed ball, were conducted using spherical roughness element beds with particle image velocimetry used to measure the instantaneous flow velocity field. Movable ball experiments revealed the predominance of large sweep structures at the instant of entrainment for both shielded and exposed particles. Fixed ball experiments involving simultaneous measurements of hydrodynamic forces and velocity on the particle at entrainment conditions revealed the significance of impulse in initiating sediment entrainment such that an optimum combination of force and duration is required to produce the threshold impulse. Short‐duration lift forces of magnitudes greater than the submerged weight are thought to be responsible for partial lifting of the completely shielded particle. Quadrant analysis and probability distribution function plots of the dominant hydrodynamic force reveal the higher probability of occurrence of high‐magnitude force induced by sweep (Q4) events.

Influence of the spring constant of cantilevers on hydrodynamic force measurements by the colloidal probe technique

There is a substantial disagreement in literature on the interpretation of hydrodynamic forces measured with the colloidal probe technique (CPT). While some authors find indications of slip of polar liquids on hydrophilic surfaces (including two of the authors), Honig and Ducker [Phys. Rev. Lett. 98 (2007) 028305] noticed no slip when they used relatively stiff cantilevers. Here, we tested a number of cantilevers with different shapes, dimensions, and spring constants to analyse their influence on hydrodynamic force measurements. In accordance with Honig and Ducker, we show that results obtained with the CPT do not contradict the no-slip boundary condition if the experiments are carried out with stiff cantilevers. The slip lengths inferred from the measurements can be related to the cantilever spring constant, the velocity at which the cantilever is dragged through the liquid, and the viscosity of the liquid. An empirical threshold value is suggested that could help avoiding artefacts.

Measurement of no-slip and slip boundary conditions in confined Newtonian fluids using atomic force microscopy

We report measurements of slip length at smooth and rough hydrophilic silica surfaces, using the hydrodynamic force measurement atomic force microscope (AFM). There has been some debate in the literature as to whether the boundary condition between a solid and a wetting fluid is one of no-slip or partial-slip; in particular the results of Neto et al. (C. Neto, V. S. J. Craig and D. R. M. Williams, Eur. Phys. J. E, 2003, 12, S71-S74) and of Honig and Ducker (C. D. F. Honig and W. A. Ducker, Phys. Rev. Lett., 2007, 98, 028305) are inconsistent. Unexpectedly, the AFM cantilever geometry leads to a different measurement of hydrodynamic drainage force. Rectangular cantilevers give results consistent with a no-slip boundary condition on smooth and rough surfaces, while v-shaped cantilever measurements show variability and can produce a finding of apparent partial-slip, consistent with earlier results in the literature. Possible reasons for the discrepancy are discussed. Equilibrium force measurements show no cantilever shape dependence. We conclude that the appropriate boundary condition for aqueous solutions on smooth and nanoscale-rough hydrophilic surfaces is one of no-slip.

Investigation of flow mechanism of a robotic fish swimming by using flow visualization synchronized with hydrodynamic force measurement

When swimming in water by flapping its tail, a fish can overcome the drag from uniform flow and propel its body. The involved flow mechanism concerns 3-D and unsteady effects. This paper presents the investigation of the flow mechanism on the basis of a 3-D robotic fish model which has the typical geometry of body and tail with periodic flapping 2-freedom kinematical motion testing in the case of St = 0.78, Re = 6,600 and phase delay mode (φ = −75°), in which may have a greater or maximum propulsion (without consideration of the optimal efficiency). Using a special technique of dye visualization which can clearly show vortex sheet and vortices in detail and using the inner 3-component force balance and cable supporting system with the phase-lock technique, the 3-D flow structure visualized in the wake of fish and the hydrodynamic force measurement were synchronized and obtained. Under the mentioned flapping parameters, we found the key flow structure and its evolution, a pair of complex 3-D chain-shape vortex (S–H vortex-rings, S1–H1 and S2–H2, and their legs L1 and L2) flow structures, which attach the leading edge and the trailing edge, then shed, move downstream and outwards and distribute two anti-symmetric staggering arrays along with the wake of the fish model in different phase stages during the flapping period. It is different with in the case of St = 0.25–0.35. Its typical flow structure and evolution are described and the results prove that they are different from the viewpoints based on the investigation of 2-D cases. For precision of the dynamic force measurement, in this paper it was provided with the method and techniques by subtracting the inertial forces and the forces induced by buoyancy and gravity effect in water, etc. from original data measured. The evolution of the synchronized measuring forces directly matching with the flow structure was also described in this paper.

1139 魚類の発進時推力の発生機構の分析(J04-2 生物の運動機能/バイオミメティクスとバイオメカニクス/バイオロボティクスとバイオメカトロニクス(2),J04 生物の運動機能/バイオミメティクスとバイオメカニクス/バイオロボティクスとバイオメカトロニクス)

The mechanism of propulsive force generation of fishes in quick start motion was analyzed by means of hydrodynamic force measurement and the velocity field measurement. A waving wing model was used for the experiments, and the time series velocity field was measured by PIV system. The small change of wing motion sometimes causes large difference of thrust force, and it depends on the interaction between the wing motion and the wake of the last swing motion.