Hydrodynamic Interference Research Articles

Fabrication of meso- and nano-scale structures on surfaces of chalcogenide semiconductors by surface hydrodynamic interference patterning

We observe the change of surface relief on amorphous Ge-As-Se thin films after irradiation with an electron beam. The beam softens the glass and induces various topological surface changes in the irradiated area. The film relief change depends on the film thickness, deposited charge, and film composition. Various structures are formed: Gausian-like cones, extremely sharp Taylor cones, deep craters, and craters with large spires grown on the side. Our investigation shows that these effects can be at least partially a result of electro-hydrodynamic material flow, but the observed phenomena are likely more complex. When we irradiated structural patterns formed by the electron beam with a red laser beam, we could not only fully relax the produced patterns, but also form very complex and intricate superstructures. These organized meso- and nano-scale structures are formed by a combination of photo-induced structural relaxation, light interference on structures fabricated by the e-beam, and photo-induced material flow.

Investigating the Characteristics of the Solitary Wave-Induced Forces on Coastal Twin Bridge Decks

AbstractA computational fluid dynamics–based numerical parametric study for the characteristics of the solitary wave–induced forces on typical coastal twin bridge decks is conducted in this study. At first, the second-order solitary-wave model is developed followed by a verification process with the analytical one and a related experimental study. The laminar flow model and shear stress transport (SST) k-ω model are adopted and the comparisons of their results demonstrate that they can make close predictions for the bridge deck forces. Then, the general characteristics of the wave forces for a fixed deck gap and variable deck gaps with different still water levels (SWLs) and various submersion coefficients are observed. In addition, the characteristics of the wave forces on the landward bridge deck are presented by normalized factors based on the wave forces on the seaward deck. Finally, the hydrodynamic interference effects between the twin bridge decks are investigated and the effects of the deck vibrat...

Assessment of the tidal current energy resource in São Marcos Bay, Brazil

At the present time, the role of renewable energy in Brazil is significant as hydropower and other renewable energies, principally biomass, contribute 76.9 and 6.0 %, respectively, towards the total offer of electricity, as compared to the corresponding values of 15.8 and 2.8 % worldwide. Nevertheless, there is already an increasing role which is played by wind energy, and a promising potential for the exploitation of tidal current energy. This paper is concerned with the assessment of the tidal current resource in Sao Marcos Bay, which is located at the northeastern coast of Brazil, and which possesses a highly promising potential for the generation of electricity through the conversion of tidal current energy. Three potential zones for tidal power exploitation have been identified employing a two-dimensional (2DH) hydrodynamic model. Power densities for these regions are in the range of 9.2–11.2 MWh/m $$^{2}$$ -year. Three array densities for two thrust coefficient values have been studied in each zone to evaluate hydrodynamic interferences, revealing positive as well as negative impacts regarding power density.

Predicting the Probability of Riser Collision Under Stochastic Excitation and Multiple Uncertainties

As the offshore industry moves to deeper waters, riser collision becomes a more crucial concern. Riser interference assessments need to rely on time domain simulations due to nonlinearities such as hydrodynamic interferences, however, one difficulty is that riser collision is an extreme event. In a recent work, the authors proposed an efficient procedure for predicting the probability of riser collision, based on extrapolating the dynamic response characteristics; thus obviating the need to capture actual collisions during simulation. However, the prior work considers randomness only from the irregular waves. This paper extends the prior work by developing a method to account for multiple uncertainties. The random variables considered herein are the current, drag coefficient, vessel motions, and riser mass. The proposed method is computationally efficient; the additional simulations necessary to incorporate four random variables are only slightly more than the original simulation case. Using a top-tensioned riser system as a case study, the likelihood of collision predicted by the proposed method is found to compare well with the Monte Carlo simulation. Moreover, it is shown that the random variables can increase the probability by an order of magnitude and all of the considered variables meaningfully contribute to this increase.

Research on Control Scheme of Submarine Hydraulic Rudder

According to the composition of the submarine hydraulic rudder system, the paper analyzed the different advantages and disadvantages of the rudder type, steering agencies and the hydraulic rudder control system as well as the scope of application. System steering bodies of pump control servo, variable pump displacement control system, steering control system and rudder hydrodynamic interference model were modeled. Fuzzy logic hydraulic servo parameter adjustment method is presented, and simulation analysis of the variable pump displacement control system and steering system. As the system parameter uncertainties and load disturbance, the performance impact of parameter variation and load disturbance simulation analysis.

Design and analysis of a new AUV’s sliding control system based on dynamic boundary layer

The new AUV driven by multi-vectored thrusters not only has unique kinematic characteristics during the actual cruise but also exists uncertain factors such as hydrodynamic coefficients perturbation and unknown interference of tail fluid, which bring difficult to the stability of the AUV’s control system. In order to solve the nonlinear term and unmodeled dynamics existing in the new AUV’s attitude control and the disturbances caused by the external marine environment, a second-order sliding mode controller with double-loop structure that considering the dynamic characteristics of the rudder actuators is designed, which improves the robustness of the system and avoids the control failure caused by the problem that the design theory of the sliding mode controller does not match with the actual application conditions. In order to avoid the loss of the sliding mode caused by the amplitude and rate constraints of the rudder actuator in the new AUV’s attitude control, the dynamic boundary layer method is used to adjust the sliding boundary layer thickness so as to obtain the best anti-chattering effects. Then the impacts of system parameters, rudder actuator’s constraints and boundary layer on the sliding mode controller are computed and analyzed to verify the effectiveness and robustness of the sliding mode controller based on dynamic boundary layer. The computational results show that the original divergent second-order sliding mode controller can still effectively implement the AUV’s attitude control through dynamically adjusting the sliding boundary layer thickness. The dynamic boundary layer method ensures the stability of the system and does not exceed the amplitude constraint of the rudder actuator, which provides a theoretical guidance and technical support for the control system design of the new AUV in real complex sea conditions.

Numerical Calculation of Hydrodynamic Interference Coefficients between Hull, Rudder and Propeller

CFD developed rapidly in capability and practicality during past years. A lot of research works on numerical simulation of viscous flow field around ship were widely carried out in past decades. But the research of interference effect among the hull, rudder and propeller was rarely concerned. In this paper, based on an unsteady Reynolds Averaged Navier–Stokes method, the dynamic mesh methods(6DOF) are adopted to simulate straight line and oblique towing test of ship with twin propellers and twin rudders. And based on the simulation results, the interference coefficients, such as effective weak coefficient ωp, rudder’s effective longitudinal velocity uR, effective attack angle αR, rudder force’s modificatory factor αH for shiphandling derivational transverse force and its dimensionless distance to ship’s gravity point, are calculated. The computed results of this paper agree well with the experimental results carried out in the tower tank of ITTC. It shows that the methods on numerical calculation of Interference Coefficients between hull, rudder and propeller is successful.

A Novel Fuzzy Logic PID Algorithm for Submarine Hydraulic Rudder Control

According to the composition of the submarine hydraulic rudder system, the paper analyzed the different advantages and disadvantages of the rudder type, steering agencies and the hydraulic rudder control system as well as the scope of application. System steering bodies of pump control servo, variable pump displacement control system, steering control system and rudder hydrodynamic interference model were modeled. Fuzzy logic hydraulic servo parameter adjustment method is presented, and simulation analysis of the variable pump displacement control system and steering system. As the system parameter uncertainties and load disturbance, the performance impact of parameter variation and load disturbance simulation analysis.

Aeroacoustic power generated by multiple compact axisymmetric cavities: Effect of hydrodynamic interference on the sound production

Aeroacoustic sound generation due to self-sustained oscillations by a series of compact axisymmetric cavities exposed to a grazing flow is studied both experimentally and numerically. The driving feedback is produced by the velocity fluctuations resulting from a coupling of vortex sheddings at the upstream cavity edges with acoustic standing waves in the coaxial pipe. When the cavities are separated sufficiently from each other, the whistling behavior of the complete system can be determined from the individual contribution of each cavity. When the cavities are placed close to each other there is a strong hydrodynamic interference between the cavities which affects both the peak amplitude attained during whistling and the corresponding Strouhal number. This hydrodynamic interference is captured successfully by the proposed numerical method.

Comparative investigation of the stagger variation influence on the hydrodynamic interference of high speed trimaran

Abstract This paper numerically investigates the influence of stagger variation of the outriggers on the hydrodynamic interference of high speed trimaran (HST). The slender body method (SBM) embedded in the Hullspeed© [1] module of the Maxsurf© [2] package is used for calculating the resistance of three symmetric trimaran series moving in a calm free surface of deep water. Each individual trimaran series comprises of 4681 configurations generated by considering 151 staggers covering the interval (−50% ⩽ α ⩽ +100%), and 31 separations covering the interval (100% ⩽ β ⩽ 400%) for 81 Froude numbers covering the interval (0.20 ⩽ Fn ⩽ 1.0). In developing the three trimaran series, Wigley©-st [3] , AMECRC©-09 [4] , [5] , and NPL©-4a [6] , [7] models are used separately for both the main and side hulls of each individual series models. Seeking automation, a computer macro-named Tri-PL© is developed from scratch based on the Visual Basic for Applications© [8] programming language. To generate each model of the individual series together with its detailed hydrostatic particulars, Tri-PL© automatically interferes the Maxsurf© [2] module. To calculate the resistance components together with the associating wave pattern for each model of the individual series, Tri-PL© automatically interferes the Hullspeed© [1] module. To benchmark Tri-PL© macro-together with the mathematical procedures embedded therein, and to rely on the analysis outcomes, the numerical results of both Wigley©-st [3] and AMECRC©-09 [4] , [5] models are validated. To visualize the significant data of the analysis properly, a graph template of the SigmaPlot© [9] is created to read the numerical results of the Tri-PL©, and then automatically prepares all the necessary analysis graphs.

Bifurcation Analysis for Sailing Stability of Autonomous Underwater Vehicle

There are several nonlinear elements in the equations of Autonomous Underwater Vehicle(AUV) movements. It is difficult to deal nonlinear problem with traditional methods. A hydrodynamic parameter interference is chosen as bifurcation parameter at first. Then the sailing stability of AUV with proportional-derivative controller is analysed by bifurcation theory. The center manifold theory is used to get the expression of system state parameters. And the Hopf bifurcation of system is analysed. The result is verified by numerical simulations. It shows that the hydrodynamic parameter’s changing will bring Hopf bifurcation for depthkeeping saiiling. And the range of hydrodynamic parameter value that insures AUV sailing stability is given.

Methodology for evaluating DP crane-barge operation in close proximity of a FPSO

This paper presents an analysis methodology for evaluating the operation of a DP crane-barge in close proximity to a FPSO. Offshore crane operations are critical, since the barge is kept in close proximity with other vessel or platform, and large loads are transported in a pendulum configuration. A precise positioning of the crane-barge is required, in order to avoid unsafe relative motions, as well as keep the load being transported on a stable position. The operation analyzed in the present paper, as an example, is the replacement of a process equipment from the plant of a turret moored FPSO. Several aspects are previously assessed by means of numerical simulation in order to guarantee a safe operation, such as: relative motions between both vessels, relative motion of the FPSO and the equipment in pendulum configuration, tension in the lifting cables, barge DP performance and station keeping capacity. A full nonlinear time domain simulator (Numerical Offshore Tank – TPN) is used to perform the coupled analysis of the system subjected to several environmental conditions, considering also the dynamics of the suspended load. The hydrodynamic interference between the FPSO and the barge are considered by means of potential calculation of wave effects. CFD model is used to a preliminary assessment of the current shadow zone induced by the FPSO and the effects on the barge DP power requirement. The simulator also considers the DP follow-target mode that is used during the operation, in which the barge follows the FPSO guaranteeing a safe distance between them.

Interference and diffraction of pressure shocks in flow around bodies of revolution located near a surface

This paper presents the results of experimental and computational investigations of a supersonic (M∞ = 4.03, Re1 = 55⋅10 6 m −1 ) flow around two bodies of revolution with conical noses with an opening θ = 40 o and cylindrical cases with an extension λ = 5 located near a flat surface at zero angles of attack at a relative distance from each other Z = 1.4. We have made a comparison between the structure of the shock waves formed in the zone of hydrodynamic interference of the bodies of revolution in free flight and in flight over the surface at a distance Y = 0.96. We have demonstrated the possibility of satisfactory prediction of the hy- drodynamic structure of the realized flows and aerodynamic characteristics of the bodies under investigation on the basis of the numerical solution of Euler equations. Introduction. The investigation of the supersonic flows realized in the flight of a group of vehicles near a surface is an urgent problem of modern aerogas dynamics. A detailed analysis of their gas-dynamic structure is neces- sary for explaining the effects of aerodynamic interference and predicting the appearance therewith of forces and mo- ments. Since experimental studies of such complex flows are very difficult and require considerable expenses, an important role in solving problems of the considered class is played by the methods of computational aerodynamics. As is known, more complete modeling of the real properties of flows connected with viscous effects is only possible with the use of the methods of solving Navier-Stokes equations with different turbulence models (RANS) or direct nu- merical simulation (LES). These methods require huge computational resources and a considerable time expenditure. Therefore, in many cases, for practical purposes simpler and cheaper methods of obtaining necessary information on the basis of solving Euler equations are used. This was demonstrated, for example, in (1-9) in which a comparison between the results of numerical calculations of a nonviscous flow and the experimental data was made. The above- mentioned works showed a satisfactory agreement between the calculated and experimental aerodynamic characteristics of the investigated bodies, although in a number of cases considerable discrepancies in local pressure distributions were observed. Such differences are most often explained by the boundary-layer separations that take place in the real flow and are formed under the action of pressure shocks (8, 9). The present work is a sequel of the investigations presented in (1-4, 6-8, 10-12). The aim of the work is to consider in detail the wave structures formed in the process of interference-diffraction phenomena in the space between the bodies and the plate, as well as to check further the possibilities of using numerical calculations within the frame- work of Euler equations for investigating such complex flows. Experimental. Experiments were carried out in a T-313 supersonic wind tunnel of the S. A. Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences at a Mach number M ∞ = 4.03 and a Reynolds number Re 1 55⋅10 6 m −1 . The model consisting of a flat plate FP and two iden- tical bodies of revolution (B 1 and B 2 ) with an opening of their noses θ = 40 o located over it parallel to the flow is

Interfacing Microchip Electrophoresis to a Growth Tube Particle Collector for Semicontinuous Monitoring of Aerosol Composition

Semicontinuous monitoring of aerosol chemical composition has continually increased in demand because of the high spatial and temporal variability of atmospheric particles and the effects these aerosols have on human health and the environment. To address this demand, we describe the preliminary development of a semicontinuous aerosol composition analyzer consisting of a growth tube particle collector coupled to a microfluidic device for chemical analysis. The growth tube enlarges particles through water condensation in a laminar flow, permitting inertial collection into the microchip sample reservoir. Analysis is done by electrophoresis with conductivity detection. To avoid hydrodynamic interference from the sampling pressure, the microchip was operated isobarically by sealing the buffer reservoirs from the atmosphere and interconnecting all the reservoirs with air ducts. The collector samples at 1 L min(-1) and deposits particles into 30 microL of solution. Sample accumulates with time, and sequential injections are performed as aerosol concentration increases. For extended analyses, a sample rinsing system flushes the sample collection reservoir periodically. For inorganic anions, temporal resolution of 1 min and estimated detection limits of 70-140 ng m(-3) min were obtained. The system was used to measure sulfate and nitrate, and results were compared to a particle-into-liquid-sampler running in parallel. Results indicate that the prototype growth tube-microchip system (termed aerosol chip electrophoresis, ACE) could provide a useful complement to existing aerosol monitoring technologies, especially when less expensive and/or rapid analyses are desired.

Dynamics of arrays of floating point-absorber wave energy converters with inter-body and bottom slack-mooring connections

If point absorbers are employed in the extensive exploitation of the offshore wave energy resource, they should be deployed in arrays, the distance between the elements in the array being possibly tens of meters. In such cases, it may be more convenient that the array is spread moored to the sea bottom through only some of its elements, located in the periphery, while the other array elements are prevented from drifting and colliding with each other by connections to adjacent elements. An array of identical floating point absorbers located at the grid points of an equilateral triangular grid is considered in the paper. A spread set of slack-mooring lines connect the peripheric floaters to the bottom. A weight is located at the centre of each triangle whose function is to pull the three floaters towards each other and keep the inter-body mooring lines under tension. The power take-off system (PTO) is a linear damper activated by the buoy heaving motion. The whole system–buoys, moorings and power take-off systems–is assumed linear, so that a frequency domain analysis may be employed. Hydrodynamic interference between the oscillating buoys in array is accounted for. Equations are presented for a set of three identical point absorbers. This is then extended to more complex equilateral triangular grid arrays. Results from numerical simulations, with regular and irregular waves, are presented for the motions and power absorption of hemispherical converters in arrays of three and seven elements and for different mooring parameters and wave incidence angles. Comparisons are given with the unmoored and independently-moored buoy situations.

Energetics of swimming by the ferret: Consequences of forelimb paddling

The domestic ferret (Mustela putorius furo) swims by alternate strokes of the forelimbs. This pectoral paddling is rare among semi-aquatic mammals. The energetic implications of swimming by pectoral paddling were examined by kinematic analysis and measurement of oxygen consumption. Ferrets maintained a constant stroke frequency, but increased swimming speed by increasing stroke amplitude. The ratio of swimming velocity to foot stroke velocity was low, indicating a low propulsive efficiency. Metabolic rate increased linearly with increasing speed. The cost of transport decreased with increasing swimming speed to a minimum of 3.59+/-0.28 J N(-1) m(-1) at U=0.44 m s(-1). The minimum cost of transport for the ferret was greater than values for semi-aquatic mammals using hind limb paddling, but lower than the minimum cost of transport for the closely related quadrupedally paddling mink. Differences in energetic performance may be due to the amount of muscle recruited for propulsion and the interrelationship hydrodynamic drag and interference between flow over the body surface and flow induced by propulsive appendages.

A Neutrally Buoyant, Upper Ocean Sediment Trap

Abstract The authors have designed and deployed a neutrally buoyant sediment trap (NBST) intended for use in the upper ocean. The aim was to minimize hydrodynamic flow interference by making a sediment trap that drifted freely with the ambient current. The principal design problem was to make the NBST descend to and stay near a prescribed depth. For a variety of reasons, the most success has been with NBSTs that were autoballasted by means of a microprocessor-controlled volume changer. Autoballasting NBSTs has demonstrated an ability to hold a prescribed depth to within 10 m. There have been two successful, concurrent deployments of NBSTs and conventional surface-tethered sediment traps (STSTs) at the Bermuda Atlantic Times Series site. During both periods the observed flow past the STSTs was low, about 0.05 m s−1, so that hydrodynamic effects on the STSTs would have been minimized. Comparisons of the trap results (described in a companion paper by Buesseler et al.) indicate that the total mass of collect...

Water surface wave radiation generated by multiple cylinders oscillating with identical frequency

The water surface wave radiation problem caused by multiple cylinders oscillating with identical frequency was solved in frequency domain by the boundary element method using simple Green' s function in the inner water region combined with the eigenfunction expansions in the outer water region. The numerical method is suitable to the situation of constant depth of outer regions and complicated boundary conditions of inner region, while the oscillating modes, motion amplitudes and phases of the cylinders may be different from one another. The second order potential and hydrodynamic forces acting on each cylinder were evaluated completely by perturbation method. Compared with the case of single oscillating cylinder, hydrodynamic interference phenomena, such as weve resonance and negative added mass, of the radiation problem due to the oscillatory motions of multiple cylinders are identified which is of engineering importance to the design of moorings and other facilities involving multiple structures.

Power Absorption by Arrays of Interacting Vertical Axisymmetric Wave-Energy Devices

The paper deals with the evaluation of the optimum wave-power absorption characteristics of arrays of interacting wave-energy devices. The hydrodynamic interference effects among the devices are exactly accounted for using a method that can solve the problem to any desired accuracy. The method is based on single-body hydrodynamic characteristics that are properly combined through the physical idea of multiple scattering to account for interaction effects. Extensive numerical results for a variety of different array arrangements and individual device geometries are presented and comparisons are made to predictions based on approximate theories, the accuracy of which is critically assessed.

Hydromechanical mechanisms of colony organization and cost of hefense in an encrusting bryozoan, Membranipora membranacea

In bryozoans, hydrodynamic interactions among colony members can substantially affect filtering rates and access to food‐rich water for zooids within a colony and for the colony as a whole. Hydrodynamic theory suggests that highly integrated (area‐filling) colony architectures lead to strong interference between neighboring zooids, whereas less integrated architectures do not. The highly integrated bryozoan Membranipora membranacea displays two morphological specializations that modify hydrodynamic interactions: internal excurrent zones (chimneys) and inducible defensive spines. In this study, possible hydrodynamic mechanisms underlying the cost of inducible defense and chimney organization were tested experimentally by culturing spined and unspined colonies under controlled flow conditions.Spines reduced colony growth rate when growth was limited by clearance rates, but not when transport of particles from upstream limited growth. This supports the hypothesis that the cost of inducible defense is primarily a reduction in clearance rate (i.e. spines cause hydrodynamic interference with feeding currents) rather than metabolic investment in spine construction. Chimneys were more closely spaced in spined than unspined colonies, consistent with a mechanism for organizing chimney formation based on responses by zooids to local hydromechanical cues rather than a rigid, colony‐level control of zooid growth form (astogeny). Direct manipulation of hydrodynamic cues resulted in substantial changes in chimney morphology, again supporting the hydromechanical organization mechanism. More generally, these experimental results support the theoretical assessment that the highly integrated architecture is hydrodynamically unfavorable. The success of Membranipora in some habitats suggests that its architecture confers compensating advantages, such as improved ability to compete for space. This tradeoff in growth habit may explain shifts in relative prevalence of bryozoan architectures with depth and across other environmental gradients.