Search

This research study delves into the hydrodynamic frictional characteristics of fouled panels coated with different types of coatings, investigating how fouling coverage and surface roughness influence drag. The investigation incorporates data on the overall percentage coverage of fouling, as well as roughness measurements obtained through a 3D profilometer. Drag data collected from a flowcell simulation of real-world flow conditions complements these measurements. Notably, the determination of the level of fouling leverages the capabilities of CIE L*a*b as an image analysis method, focusing on the overall coverage rather than individual fouling species. The objective is to illustrate how fouled panels perform under varying flow and coating conditions compared to their clean counterparts. Furthermore, the paper proposes a roughness scaling approach that considers both the percentage coverage and measured areal roughness for each coating type, encompassing both fouled and unfouled areas. This approach provides valuable insights into the combined effects of fouling and surface roughness on hydrodynamic performance, enhancing our understanding of the intricate interplay between these factors. [ABSTRACT FROM AUTHOR]

The thermocapillary migration of a concentric compound drop in an arbitrary viscous flow under the consideration of negligible Reynolds number is investigated. The thermocapillary effect refers to the migration of a drop under the influence of a temperature gradient. The thermal and hydrodynamic problems are examined. The thermal field is governed by the heat conduction equation whereas the hydrodynamic fluid velocities are governed by the linearized Navier–Stokes equations. Presence of temperature gradient results in variation of the interfacial tension which is assumed to depend on temperature linearly. Variation of interfacial gradient leads to the coupling of the hydrodynamic problem with the thermal problem through the boundary condition. A complete general solution of Stokes equations is utilized to obtain closed-form expressions for the velocity vector and pressure. The hydrodynamic forces acting on the compound drop are obtained and expressed in terms of Fax́en's law. Some important asymptotic limiting cases of hydrodynamic drag are also derived. The hydrodynamic drag for cases of uniform flow, shear flow, and heat source with the known ambient flow are derived and it is found that in the case of shear flow, the hydrodynamic drag is contributed only by the thermal component and the shear flow has no effect on it. The obtained results for drag and torque in the limiting cases are in agreement with the existing results in the literature. Furthermore, the migration velocity of the compound drop is obtained by equating the hydrodynamic drag force to zero. The results obtained for migration velocity are explained with the aid of graphs. The migration velocity is found to be a monotonic function of the Marangoni number and the radius of the innermost drop. [ABSTRACT FROM AUTHOR]

Relevance. The use of anti-turbulent additives for transporting hydrocarbon liquids through main pipelines allows reducing significantly the energy consumption of pumping power stations. Aim. Comparative analysis of the anti-turbulent efficiency of high-molecular polymers and compositions of surfactants. Methods. Laboratory-scale experimentation aimed to study the flow of dilute polymer solutions and dispersed surfactant systems through a cylindrical channel of a turbulent rheometer. Results. The author has carried out the comparative experimental studies of the anti-turbulent efficiency of extremely dilute solutions of polymers and colloidal systems. The results were obtained that suggest a higher anti-turbulent efficiency of high-molecular-weight polymers compared to micellar surfactant systems. Solutions of high molecular weight polybutadiene and aluminum polyhydroxydicarboxylates in gasoline were used as samples for the experimental comparison of hydrodynamic efficiency. The paper describes the laboratory setup, on which the studies were carried out, and introduces the formulas used for quantitative calculations. The structure of polymer solutions and colloidal systems is considered and a theoretical explanation is given for the preferential use in industrial practice of high-molecular polymers in extremely low concentrations in real pipelines. It was found out that the mechanisms of degradation of antiturbulent properties of polymer solutions and dispersed surfactant systems are different. This is due to the difference in the structure of macromolar coils of polymer with an immobilized solvent and that of micelles from low molecular amphiphilic compounds. The paper introduces the arguments that explain the degradation of the antiturbulent properties of polymers not by the destruction of carbon-chain macromolecules, but by decomposition in a turbulent flow of the original large associates, consisting of a large number of chains, into individual and smaller macromolecular coils with an immobilized solvent.

Surface patterning is a recent promising approach to promote performance of pressure‐driven membranes in water treatment and desalination. Nevertheless, knowledge about foulant deposition mechanisms, especially at early stage of filtration, is still lacking. The applicability of particle imaging velocimetry to study fluid characteristics atop surface patterned thin‐film composite membranes was investigated at different operating conditions. This work is an important first step toward reliable understanding of the impacts of topographical membrane surface modification on hydrodynamic conditions and foulant deposition mechanisms. [ABSTRACT FROM AUTHOR]

The major goal of this work is to analyze the magnetic effect on the creeping viscous flow past a porous spheroidal particle, a particle of slightly deformed spherical shape. Brinkman's model is proposed to govern the flow in the porous media. Boundary value problem considers the conditions of continuity of velocity components, continuity of normal stresses, and stress jump boundary condition for tangential stress. A transverse magnetic field of uniform nature is applied to the flow. An expression for the drag force acting on the spheroidal particle is derived analytically. The effects of the physical parameters involved in the flow like permeability, deformation, Hartmann number's, viscosity ratio, and stress jump coefficient parameters are visualized through graphs and tables. The applied magnetic field seems to suppress the flow of fluid that leads to the increase in the drag experienced on the porous spheroid. It is also observed that the increase in the deformation, stress jump, and permeability decreases the drag coefficient. Our results without magnetic effect match with the results reported earlier in the literature. [ABSTRACT FROM AUTHOR]

This paper describes the design of an enhanced, plane channel, flowcell and its use for testing large-scale coated plates (0.6 m × 0.22 m) in fully developed flow, over a wide range of Reynolds numbers, with low uncertainty. Two identical, hydraulically smooth plates were experimentally tested. Uniform biofilms were grown on clean surfaces to test skin friction changes resulting from different biofilm thickness and densities. A velocity survey of the flowcell measurement section, using laser Doppler anemometry, showed a consistent velocity profile and low turbulence intensity in the central flow channel. The skin friction coefficient was experimentally determined using a pressure drop method. Results correlate closely to previously published regression data, particularly at higher speeds. Repeated measurements indicated very low uncertainty. This study demonstrates this flowcell's applicability for representing consistent frictional drag of ship hull surfaces, enabling comparability of hydrodynamic drag caused by surface roughness to the reference surface measurements. [ABSTRACT FROM AUTHOR]

In recent years, importance has been recognized increasingly for the reduction of fuel consumption of ships in a seaway to reduce green-house gas emissions from shipping. From a ship design viewpoint, it is of crucial importance to establish reliable prediction methods for ship's resistance and propulsive power. The required power for the propulsion unit depends on the ship resistance and speed. There are three solutions for the prediction of ship resistance as follow analytical methods, model tests in tanks and Computational Fluid Dynamics (CFD). The rapid developments in computers and computational methods increased the opportunities of the CFD simulation to be used in the ship design process. The present paper aims at simulating ship resistance using CFD simulations method which is conducted using ANSYS-CFX software package. As a case study, Container ship scale model is investigated. The results show the ship resistance which calculated at various ship speeds and Froude number. Predicted results for resistance components at various Froude numbers were compared against Resistance results computed by using Holtop method. It is shown that the simulation results agree fairly well with the results computed from Holtrop method, and that ANSYS-CFX code can predict ship resistance. [ABSTRACT FROM AUTHOR]

Featured Application: Our study focuses on inhibiting hydrodynamic drag in many applications of mirco-/nano-fluidic channels, including micro-/nano-electromechanical systems (MEMS/NEMS), micro-/nano-fluidic systems, confined biological system, etc. Boundary conditions of the liquid–solid interface of micro/nano fluid flow are of great interest, as slippage is linked with decreased drag. However, previous studies have seldom included a systematic analysis of the effect of roughness on the measurement and quantification of slip length. For the measurement of slip length using atomic force microscopy (AFM), which is believed to be the most accurate method, a theoretical description of the drainage of thin liquid films between sphere and surface, with realistic roughness, is yet to be published. This study focuses on the measurement and quantification of slip length on rough surfaces immersed in liquids, based on AFM and laser confocal scanning microscopy. A reformulation of the boundary condition is presented, taking into account the effect of surface roughness. The correction to the effective slip length is analyzed, then surfaces with various degrees of spacing roughness Rsm were fabricated. Quantitative analysis of the effective slip length is presented. Results show that the corrected effective slip length remains constant with increased spacing roughness Rsm of surfaces. The results are discussed for the coagulation process of colloids and measurement of slip lengths on roughness-induced surfaces with AFM. [ABSTRACT FROM AUTHOR]

Energy saving mechanisms in nature allow following organisms to expend less energy than leaders. Queues, or ordered rows of individuals, may form when organisms exploit the available energy saving mechanism while travelling at near-maximal sustainable metabolic capacities; compact clusters form when group members travel well below maximal sustainable metabolic capacities. The group size range, given here as the ratio of the difference between the size of the largest and smallest group members, and the size of the largest member (as a percentage), has been hypothesized to correspond proportionately to the energy saving quantity because weaker, smaller, individuals sustain the speeds of stronger, larger, individuals by exploiting the energy saving mechanism (as a percentage). During migration, small individuals outside this range may perish, or form sub-groups, or simply not participate in migratory behaviour. We approximate drag forces for leading and following individuals in queues of the late Devonian ( c. 370 Ma) trilobite Trimerocephalus chopini. Applying data from literature on Rectisura herculea, a living crustacean, we approximate the hypothetical walking speed and maximal sustainable speeds for T. chopini. Our findings reasonably support the hypothesis that among the population of fossilized queues of T. chopini reported in the literature, trilobite size range was 75%, while the size range within queues was 63%; this corresponds reasonably with drag reductions in following positions that permit c. 61.5% energy saving for trilobites following others in optimal low-drag positions. We model collective trilobite behaviour associated with hydrodynamic drafting. [ABSTRACT FROM AUTHOR]

Boundary conditions of the liquid–solid interface of micro/nano fluid flow are of great interest, as slippage is linked with decreased drag. However, previous studies have seldom included a systematic analysis of the effect of roughness on the measurement and quantification of slip length. For the measurement of slip length using atomic force microscopy (AFM), which is believed to be the most accurate method, a theoretical description of the drainage of thin liquid films between sphere and surface, with realistic roughness, is yet to be published. This study focuses on the measurement and quantification of slip length on rough surfaces immersed in liquids, based on AFM and laser confocal scanning microscopy. A reformulation of the boundary condition is presented, taking into account the effect of surface roughness. The correction to the effective slip length is analyzed, then surfaces with various degrees of spacing roughness Rsm were fabricated. Quantitative analysis of the effective slip length is presented. Results show that the corrected effective slip length remains constant with increased spacing roughness Rsm of surfaces. The results are discussed for the coagulation process of colloids and measurement of slip lengths on roughness-induced surfaces with AFM.

We investigate the drag load on low-aspect ratio circular cylinders, submerged as in infinite fluid and subjected to steady current. A series of experiments are carried out in a circulating water tunnel with three different types of models; open and closed cylinders, and open with a splitter plate inside the middle of the cylinders. The length-to-draft ratio of the models, L / D , varies from 0.15 to 0.6. The Reynolds number, based on the cylinder diameter, varies from 40 000 to 105 000. The experiments show small Reynolds number dependency. The drag coefficient, C D , varies substantially for the open cylinder case; being around 2 for the lowest aspect ratios L / D ≤ 0. 2 , while 0.65-0.8 for L / D > 0. 25. There is an abrupt change of flow pattern for L / D = 0. 25 : for L / D ≤ 0. 2 the flow which is separated from the front half of the cylinder goes through the cylinder, producing a wide von Karman type vortex street, while for L / D ≥ 0. 25 the flow does not go through the models and, as a consequence, produces a significantly more narrow wake. The wide wake regime is suppressed when the splitter plate is added, with drag coefficients C D = 0. 6 − 0. 8. The drag coefficients for the closed cylinders are lower than the ones with splitter plate, and also consistent with published data on low-aspect ratio closed cylinders. A rational drag load model is proposed for the high-drag regime, with reasonable results. Tests where the cylinder with splitter plate is sectioned into a front and a rear half are presented, revealing a very small contribution of the drag from the rear half. This is discussed in view of existing studies on two-dimensional flat plates in tandem. [ABSTRACT FROM AUTHOR]

The hydrodynamic drag of towed fishing gears leads to direct impacts on the benthic environment, and can play a major role in the overall economic efficiency of the fishing operation and emissions of nitrogen oxides, sulphur oxides and greenhouse gases such as CO 2 . Here we investigate some of the underpinning processes which govern these issues and make direct hydrodynamic drag measurements and calculate the hydrodynamic drag coefficients for a range of well-defined gear components that, when fished, are in contact with the seabed. We measure the concentration and particle size distribution of the sediment mobilised into the water column in the wake of these gear elements, at a range of towing speeds, and demonstrate that as the hydrodynamic drag increases the amount of sediment mobilised also increases. We also vary the weight of the elements and show that this does not influence the amount of sediment put into the water column. These results provide a better understanding of the physical and mechanical processes that take place when a towed fishing gear interacts with the seabed. They will permit the development of more fuel efficient gears and gears of reduced benthic impact and will improve the empirical modelling of the sediment mobilised into the turbulent wake behind towed fishing gears which will lead to better assessments of the environmental and ecological impact of fishing gears. [ABSTRACT FROM AUTHOR]

Buoyancy battery underwater energy storage is an emerging area of research relating to the storage of energy generated by renewable resources such as offshore wind and solar. This study presents an experimental analysis of a basic buoyancy system. Tests were performed on a container with minimal ambient fluid volume, as well as in a large offshore testing tank. Development and integration of fundamental system components is discussed in terms of experimental apparatus and larger application. Discharge cycling was performed with variables relating to discharge voltage, power, and discharge velocity obtained. Energy losses to kinetic energy and hydrodynamic drag are estimated for completed trails. The effect of pulley friction is evaluated for no‐load discharge testing. Conclusions are drawn as to the observed operation of the system as designed, primary areas for performance improvements, and next steps for system development. [ABSTRACT FROM AUTHOR]

The variables applied in microflotação may present different degrees of influence on the results obtained with the experiments. In order to increase understanding about his influence statistical studies can lead to more accurate data. In this way, the objectives of this study related to (i) understand the significance of the variables pH, gas flow and time of flotation have on the microflotation (with experiments conducted in duplicates); (ii) assess whether there is a strong correlation between these variables and (iii) study on particle size tracks, within the applied in the study, particles suffer greater hydrodynamic drag (for the experimental conditions). The experimental parameters, whose definition included data from literature review of published studies, were: mineral - pure quartz; surfactant (collector) - dodecilamine; equipment - Hallimond tube with medium extender - 10 cm (250 mL volume); mass of essays - 3.00 (± 0.05) g; reagent concentration - 10-3 mol.L-1; conditioning time - 20 s; volume of conditioning - 250 mL; particle size range - 53 µm to 212 µm. The analyses of Yates method and reverse Yates method have been applied to the study of the data obtained. As a result it was obtained that the variable pH and pH variable interactions with the variable gas flow are the most significant (≥ 95.0 % of reliability). It was noted also that the hydrodynamic drag was greater for the grain sizes close to 74 µm [ABSTRACT FROM AUTHOR]

Gravity installed anchors (GIAs) are released from a height of 30–150 m above the seabed, achieving velocities up to 19–35 m/s at the seabed, and embed to depths of 1.0–2.4 times the anchor length. Challenges associated with GIAs include the prediction of anchor initial embedment depth, which determines the holding capacity of the anchor. Based on the coupled Eulerian–Lagrangian approach, a numerical framework is proposed in this paper to predict the embedment depth of GIAs, considering the effects of soil strain rate, soil strain-softening and hydrodynamic drag (modeled using a concentrated force), with the anchor-soil friction described appropriately. GIAs are influenced by the hydrodynamic drag before penetrating into the soil completely, hence the anchor accelerates less than the previous investigations in shallow penetration, even decelerates directly at the terminal impact velocity. The hydrodynamic drag has more influence on OMNI-Max anchors (with an error of ∼4.5%) than torpedo anchors, and the effect becomes more significant with increasing impact velocity. An extensive parametric study is carried out by varying the impact velocity, strain rate and strain-softening parameters, frictional coefficient, and soil undrained shear strength. It is concluded that the dominant factor affecting the penetration is the soil undrained shear strength, then are the impact velocity, strain rate dependency and frictional coefficient, and the minimal is the strain-softening of soil. In addition, although the strain rate dependency is partly compensated by the softening, the anchor embedment depth accounting for the effects of strain rate and strain-softening is lower than that for ideal Tresca soil. Strain rate dependency dominates the combined effects of strain rate and strain-softening in the dynamic installation of GIAs, on which should pay more attention, especially for the calibration of the related parameters and the measured solutions. In the end, the theoretical model based on the bearing resistance method is extended by accounting for the hydrodynamic drag effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • A visualization platform was designed to study the bubble-particle interaction. • Four types of interaction behaviors between bubbles and particles were observed. • Hydrophobicity has a significant effect on the particle trajectory and velocity. • Highly hydrophobic particle can jump in instantaneously after a short sliding time. • The individual forces of particle provide a valuable insight into the interaction. The collisional interaction process between bubbles and particles is considered to play an important role in flotation. This paper aims to investigate the effect of particle hydrophobicity on the bubble-particle collision and subsequent interaction process. Four types of bubble-particle interaction behaviors were observed, namely the non-collision, the collision but without attachment, the attachment with jump-in after collision, and the attachment without jump-in after collision. The 'jump-in' event was interpreted as the rupture of the water film, providing the formation and growth of a 'three-phase contact line' (TPCL). The mildly hydrophobic particle could attach to the bubble surface without the rupture of the water film, whereas the highly hydrophobic particle had the higher collision and attachment probability. The significant effect of particle hydrophobicity was found in the observed particle trajectories and velocities. The distance between the bubble and the particle of weakly hydrophobicity and mildly hydrophobicity remained almost constant in the particle sliding process on the bubble surface. However, the highly hydrophobic particle was observed to jump in instantaneously after a short interaction time. Influenced by hydrodynamic drag, the maximum sliding velocity of any particles near the bubble's equatorial plane was higher than the particle terminal velocity, and highly hydrophobic particle had a higher difference. The analysis of the individual force components of particle provides valuable insights into the kinematic properties of particle as it slides. The hydrodynamic drag coefficient decreased with an increase in the particle contact angle, implying the highly hydrophobic particle had a smaller hydrodynamic drag. Additionally, the reaction force was introduced for the first time to satisfy the radial force balance relationship, and explanations were proposed in terms of its source. [ABSTRACT FROM AUTHOR]

A modular and integrated optimisation model for the design of underwater vehicles is presented. In the proposed optimisation model two modules (i.e. low fidelity and high fidelity) are incorporated and the basic geometric definition of computer aided design (CAD) is integrated with computational fluid dynamic (CFD) analysis. The hydrodynamic drag is considered as single objective with constraints on the geometric parameters of dimension, space and volume. The CAD model is implemented in MATLAB*™ and CFD model is implemented in Shipflow**™. A real-world design example of an existing underwater vehicle is presented. The applicability of proposed optimisation model is shown. The presented results show that within given set or sets of constraints the application of optimisation model in design results into an efficient hull form. [ABSTRACT FROM AUTHOR]

Reducing otter-board angle of attack (AOA) has been proposed as a way to limit the habitat impacts of demersal trawls, but there are few quantitative assessments. This study tested the hypothesis that a novel otter-board design, termed the "batwing" (comprising a 0.1-m wide sled with an offset sail at 208 AOA) would have relatively fewer bottom impacts than a conventional flat-rectangular otter board (358 AOA, with a similar hydrodynamic spreading force). Pairs of each otter board were suspended beneath a purpose-built rig comprising a beam and posterior semi-pelagic collection net and repeatedly deployed across established trawl grounds in an Australian estuary. Compared with the conventional otter boards, the batwings displaced significantly fewer empty shells (Anadara trapezia and Spisula trigonella) by 89% and school prawns (Metapenaeus macleayi) by up to 78%. These rates were similar to the difference in base-plate bottom contact (87%). Further, the batwing damaged proportionally fewer damaged shells, attributed to their displacement away from the board's surface area. Other debris (lighter pieces of wood) and benthic fish (bridled gobies, Arenigobius bifrenatus) were not as greatly mobilised (i.e. reduced by 50 and 25%, respectively); possibly due to their position on or slightly off the bottom, and a similar influence of hydrodynamic displacement by the hydro-vane surface areas. Although the consequences of reducing otter-board bottom contact largely remain unknown, low AOA designs like the batwing may represent a practical option for fisheries where trawling is perceived to be hazardous to sensitive habitats. [ABSTRACT FROM AUTHOR]

Nonisothermal flow past a circular cylinder of the fluid with spherical gas inclusions is studied. It has been established that as the volume concentration of the dispersed phase increases, the drag force of the cylinder reduces and its heat transfer with the medium decreases. [ABSTRACT FROM AUTHOR]

In the present paper, the effects of the increase in surfaces backward sweep angle of horizontal tail and the hydrofoil of a typical submarine on its hydrodynamic drag are investigated with Computational Fluid Dynamics (CFD). Results show that with the increase in the horizontal tail backward sweep angle about 50° in constant surface area, hydrodynamic drag can reduce 6% than zero backward sweep angle condition. This value is equal to 44 N reductions in hydrodynamic drag force and 180 watt of consumption power in 4 m/s speeds of this submarine. Also, with increasing 60° of this submarine hydrofoil backward sweep angle, the constant hydrofoil volume can reduce 14% from hydrodynamic drag rather than zero hydrofoil backward sweep angle. This hydrodynamic drag reduction of this typical submarine in cruising speed (4 m/s) is equal to 97 N force, saving 388 watt of the consumption power. In general, the 50° of horizontal tail backward sweep angle and 60° of hydrofoil backward sweep angle can reduce 19% of hydrodynamic drag rather than zero tail and hydrofoil backward sweep angles. These amounts of drag reduction and power saving in this typical submarine can increase the range and the endurance. [ABSTRACT FROM AUTHOR]

Despite the importance of maintaining good alignment to minimize resistive drag in swimming there is a paucity of literature relating to the effect of technique asymmetries on rotations of the body about a vertical axis (yaw). The purpose of this paper was to present an approach to analyzing the effect of technique asymmetries on rotations in swimming, exemplifying the process with a case study of a breaststroke swimmer. The kinematics and angular kinetics of an elite female international breaststroke swimmer performing a 'fatigue set' of four 100m swims were derived from digitized three-dimensional video data using a 13 segment body model. Personalised anthropometric data required to quantify accurately segment and whole body centres of mass and segmental angular momentum were obtained by the elliptical zone method. Five episodes of torques producing yaw occurred in the stroke cycle sampled for each 100m swim of this swimmer. These torques were linked to bilateral differences in upper limb kinematics during 1) out-sweep; 2) in-sweep; 3) upper limb recovery; and lower limb kinematics during 4) Lower limb recovery and 5) the kick. It has been shown that by quantifying whole body torques, in conjunction with the kinematic movement patterns, the effect of technique asymmetries on body alignment can be assessed. Assessment of individual swimmers in this manner provides a solid foundation for planning interventions in strength, flexibility, and technique to improve alignment and performance. [ABSTRACT FROM AUTHOR]

The present study investigated the drag increase on aquaculture nets due to biofouling of the colonial hydroid Ectopleura larynx. It had two main parts: firstly the growth characteristics of E. larynx were investigated by use of field tests at a Norwegian aquaculture site; secondly the hydrodynamic drag on the fouled twines was studied in a towing tank by using fabricated models of net twines with artificial hydroid fouling. In the field tests, the growth of the hydroids was first measured after three weeks of immersion and then again after six weeks. During this interval, the density of hydroids and the thickness of the hydroid stem were almost constant (1.4 hydroids/mm and 0.29 mm, respectively), while the average length of the hydroids increased from 6.4 to 11.2 mm. The hydroid length followed a Rayleigh distribution, while the thickness was normal (Gaussian) distributed. Replicas of twines with three different levels of hydroid growth were made (1.5 hydroids/mm twine, hydroid length 9 mm, 16 mm and 20 mm), and the drag on these twines was measured at different towing velocities (0.1 to 1.4 m/s) and with different twine configurations. For the twine with the shortest hydroids (9 mm), the drag was from 1.5 times ( Re=4000) to 2.2 times ( Re=1000) the drag on a clean twine. For the longest hydroids (21 mm), the drag was 2 times and 3.8 times, respectively. [ABSTRACT FROM AUTHOR]

To improve the heat-transfer calculation in dense beds of metallurgical aggregates, the heat-transfer coefficient between the gas flux and pellets on heating is refined experimentally. Steady channel flow with Re = 100-1400 is observed in the bed. The heat-transfer coefficient is calculated, and the pellet temperature on heating is determined to within ±11.4°C. [ABSTRACT FROM AUTHOR]

This paper investigates the response of full-scale submerged riparian vegetation to hydrodynamic loading, using data from towing tank experiments of high resolution and accuracy. Drag force and physical property data are presented for 21 foliated and defoliated trees, including specimens ofAlnus glutinosa, Populus nigraandSalix alba. The force–velocity data and contribution of foliage to the total drag are first discussed, highlighting the non-classical drag force behaviour of flexible vegetation. A theoretical model, based on the vegetative Cauchy number, is proposed from dimensional consideration to account for the bending and reconfiguration of the trees under flow action. The model links measurable vegetation properties, such as volume, height and flexural rigidity, to the force–velocity response. This allows the otherwise complex drag force of flexible vegetation to be predicted with greater accuracy than compared with a rigid cylinder approximation. [ABSTRACT FROM PUBLISHER]

Abstract: Diversity of dissolved, colloidal and solid materials present in papermaking process waters influences the rise of microbubbles by increasing their drag. This effect is known to reduce the gas separation efficiency but its importance thus far has not been quantified by experimental studies. In this paper the terminal velocities and drag coefficients of bubbles as a function of the bubble Reynolds number are studied experimentally in papermaking process waters with a high-speed CMOS camera and a submersed back-light illumination in a pressurised bubble column. Bubbles are tracked in time to provide time series data for every bubble that passes the focal plane of the imaging system. Image sequences are analysed with automatic image processing algorithms that measure the velocity and size of bubbles, and also the velocity of the fluid surrounding the bubbles revealing the instantaneous slip velocity of each bubble. Results show how suspension viscosity, surface tension and solids content affect the kinetics of microbubbles. Changes in microbubble formation during a pressure drop and differences of bubble size distributions in a variety of process waters and model solutions are also shown. Finally, an empirical correlation between the bubble drag coefficient and the bubble Reynolds number is generated for the investigated process waters. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM)-based dynamic force spectroscopy of single molecular interactions involves characterizing unbinding/unfolding force distributions over a range of pulling speeds. Owing to their size and stiffness, AFM cantilevers are adversely affected by hydrodynamic forces, especially at pulling speeds >10 μm/s, when the viscous drag becomes comparable to the unbinding/unfolding forces. To circumvent these adverse effects, we have fabricated polymer-based membranes capable of actuating commercial AFM cantilevers at speeds ≥100 μm/s with minimal viscous drag effects. We have used FLUENT®, a computational fluid dynamics (CFD) software, to simulate high-speed pulling and fast actuation of AFM cantilevers and membranes in different experimental configurations. The simulation results support the experimental findings on a variety of commercial AFM cantilevers and predict significant reduction in drag forces when membrane actuators are used. Unbinding force experiments involving human antibodies using these membranes demonstrate that it is possible to achieve bond loading rates ≥106 pN/s, an order of magnitude greater than that reported with commercial AFM cantilevers and systems. [ABSTRACT FROM AUTHOR]

Abstract: Capillary electrophoretic separation of 60 mer single-stranded DNA (ssDNA) and a single-base-substituted ssDNA was demonstrated using a size- and composition-controlled poly(ethylene glycol)-oligodeoxyribonucleotide block copolymer (PEG-b-ODN) as an affinity ligand. Under appropriate conditions, PEG-b-ODN and ssDNA with a complementary sequence formed a reversible complex via hybridization during the electrophoresis, while the copolymer did not interact with the single-base-substituted ssDNA. The copolymer''s PEG length determined the electrophoretic mobility of the ssDNA; upon formation of the complex, the electrically neutral PEG added hydrodynamic friction to ssDNA. Simultaneously using two types of PEG-b-ODN copolymers whose PEG segments were of different lengths, we achieved the complete separation of the 60 mer ssDNA, its single-base-substituted ssDNA, and impurities. This method was sensitive enough to quantify a slight amount (approximately 1%) of the single-base-substituted ssDNA. The present results suggest that our approach is applicable to quantitative detection of minor genotypes. [Copyright &y& Elsevier]

Abstract: We consider the unsteady motion of a sedimenting rigid spherical particle in order to examine the relative strength of the hydrodynamical forces acting on particles in fluid flows. The relative strength of the forces on all stages of the particle motion is a major concern for closing constitutive equations describing the more complex motion of particulate flows such as fluidised beds. The formulation results in a first order nonlinear integro-differential equation in terms of the instantaneous velocity of the sphere. This equation is made dimensionless and the particle Reynolds number and the fluid–particle density ratio are identified as the relevant physical parameters describing the particle motion. We obtain analytical solutions for the limits of small density ratios and small Reynolds number. In addition, a numerical solution is used for arbitrary values of the density ratio. The results show that the motion of spherical particles is significantly affected by the unsteady drag dominated by the memory Basset force on the early stages of the motion and on the approach to the steady state (terminal velocity). The present calculations indicate that the unsteady hydrodynamic drags might become of the same order of magnitude of the dominant viscous drag for flows with moderate particle–fluid density ratio. Therefore, unsteady drags should be taken into account on modelling multiphase particulate flows with moderate density ratio. [Copyright &y& Elsevier]

Abstract: Studying dynamic stability of a vertically suspended, fully submerged pipe conveying fluid upwards, researchers have found a contradiction between theoretical predictions and experiments. Experiments did not show any instability, while theory predicts instability at infinitesimally low fluid velocities for a pipe without dissipation mechanisms. To explain this contradiction, in 2005 Païdoussis and co-workers postulated a new description of the boundary condition at the free end of the pipe. Subject to this boundary condition the pipe is predicted to become unstable by divergence (stable node to saddle bifurcation) at a velocity higher than yet achieved in experiments. In this paper, it is shown that a realistic description of hydrodynamic drag in combination with conventional boundary conditions might result in even higher critical velocity, and hence, this could also be an explanation of the contradiction. The description of the hydrodynamic drag is based on experimental data available in literature. This data has been obtained by experimenting with submerged rigid cylinders. To make it applicable to flexible pipes, a key step is undertaken in this paper to translate the data from the frequency domain to the time domain. Using the time-domain description of the hydrodynamic drag in combination with the conventional boundary conditions at the free end, it is shown that the pipe becomes unstable by flutter (stable focus to unstable focus bifurcation) at a critical velocity, which is much higher than that attainable in small-scale experiments. For fluid velocities exceeding the critical one, the pipe motion reaches a steady oscillation of finite amplitude, i.e. a stable limit cycle. [Copyright &y& Elsevier]

Abstract: A significant component of foraging energetics is the cost of locomotion, which for marine animals, is the cost of swimming. Increases in the cost of swimming may have significant impacts on foraging efficiency. Minimizing the cost of swimming can contribute to the optimization of foraging strategies by reducing the energetic cost of foraging. Results of several field studies suggest that an increase in the cost of locomotion may have comparable effects on foraging behavior and efficiency to a decrease in prey availability. We tested the hypothesis that an increased cost of swimming, brought on by increased hydrodynamic drag, has the same effect on dive behavior and efficiency as reduced prey availability under standard locomotion. Experiments were performed using two adult female Steller sea lions at the Alaska SeaLife Center in Seward, AK, using the same animals and general experimental design previously used to test the effects of reduced prey encounter rate on dive behavior and efficiency. Animals were fitted with a drag-inducing harness for half of the 500 simulated foraging dives in order to increase the cost of swimming. Individual dive duration and foraging time were significantly reduced in all cost-increased dives, comparable to the effects of reduced prey encounter rate. However, on a bout-by-bout basis, dive and foraging efficiency were only slightly reduced, which is likely due to an average 50% reduction in post-dive surface recovery duration during cost-increased dives. Increased heat flux across the body surface measured in a parallel study confirmed a significant increase in work during drag-increased dives. These results suggest that sea lions are able to compensate for changes in the cost of foraging and maintain their foraging efficiency by altering their dive strategy over an entire bout of dives when operating well within their aerobic scope. [Copyright &y& Elsevier]

We present a numerical model applied to the simulation of granular flow in a fluid. The description of particle flow is discrete. Particle trajectories are calculated by Newton's law and collisions are described by a soft-sphere approach. The fluid flow is modelled using the Navier-Stokes equation. The momentum transfer is directly calculated from the stress tensor around particles. This model is validated through the calculation of the drag coefficient, making it possible to discern the limitations on the Reynolds number according to the mesh size and the computational time. The accuracy of the Navier-Stokes solver is estimated by the calculation of the hydrodynamic drag of a fluid flowing through a porous media at low Reynolds numbers. The analysis shows that dense media require a smaller mesh size than diluted media. This model is then used to describe the sedimentation of two particles to reproduce the ''Draft, Kiss and Tumbled'' effect. This shows the capacity of the model to reproduce hydrodynamic interactions acting on the scale of the particle. The terminal velocity of particles is in good agreement with experiments. Simulations of the sedimentation of a system of particles makes it possible to recover the Richardson and Zaki law in an acceptable CPU time. [ABSTRACT FROM AUTHOR]

Similar morphologies between species may be due to shared ancestry or convergent evolution . Understanding instances of morphological and ecological convergence is central to evolutionary ecology because they help us understand the fit between organism and environment. Two species of stream-dwelling natricine snakes, Thamnophis rufipunctatus and Nerodia harteri present a model system for studying ecological and morphological convergence and adaptation. The species are allopatric and both live in shallow riffles in streams and forage visually for fish. We studied morphological similarity, trait evolution and functional significance of ecologically relevant traits in these and related species, and used mitochondrial DNA sequences for the ND4 gene to estimate their phylogenetic relationships. Character mapping of head length and head width supported the hypothesis of independent evolution of head shape in T. rufipunctatus and N. harteri. The elongate snout is a derived trait in these two taxa that is associated with reduced hydrodynamic drag on the snakes’ heads when in a swift current, compared to other species with the ancestral blunt snout. We hypothesize that lower hydrodynamic drag facilitates prey capture success in these species that are known to forage by holding their position in currents and striking at fish prey. The elongate snout morphology has also resulted in a diminished binocular vision field in these snakes, contrary to the hypothesis that visually orientated snakes should exhibit relatively greater binocular vision. Convergent evolution of the long snout and reduced hydrodynamic drag in T. rufipunctatus and N. harteri are consistent with the hypothesis that the long snout is an adaptation to foraging in a swift current. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 363–371. [ABSTRACT FROM AUTHOR]

Abstract: Experiments were conducted to compare deposition fluxes of 1.1 and 5.7μm carboxylate-modified polystyrene latex microspheres in packed porous media and simple shear systems. A range of flow conditions were examined in the packed columns (2, 4, and 8mday−1 average pore water velocities), and impinging jet cells (0.01, 0.03, and 0.05mlmin−1 jet discharge rates), and were scaled to yield equivalent near-surface velocities in the two systems. Two ionic strengths (0.006 and 0.02M NaCl) were examined under electrostatically unfavorable attachment conditions, whereas electrostatically favorable conditions were examined at a single ionic strength (0.02M). Deposition fluxes onto quartz and glass substrata were examined. Initial attachment fluxes were sometimes higher, sometimes lower, in the porous media relative to the simple shear systems under equivalent conditions. Deposition efficiencies (deposition flux normalized to deposition flux under favorable conditions) were consistently higher in the porous media relative to the impinging jet when the angular substrate (quartz) was examined, whereas deposition efficiency was lower in the glass bead porous media relative to the glass substratum in the impinging jet under the one condition examined. These results corroborate the hypothesis that deposition in quartz media is enhanced by the presence of rear stagnation points, whereas this phenomenon was not manifested in the smooth spherical porous media. Hydrodynamic drag was implicated as an important governor of the initial attachment flux on the basis of lack of deposition of 5.7μm microspheres despite theoretical predictions, as well as an observed lack of increase in 1.1μm microsphere attachment flux with increased flow rate under favorable conditions, and an observed decrease in 1.1μm microsphere attachment flux with increased flow rate under unfavorable conditions. Experiments run with a mixture of the 1.1 and 5.7mm microspheres indicated association of the different sized microspheres on the surface. Results from the packed porous media suggested indirect association (via the hydrodynamic field) at the grain surface, whereas observations in the impinging jet indicated direct association of the 1.1 and 5.7mm microspheres. [Copyright &y& Elsevier]

Particle deposition and fouling are critical factors governing the performance of microfiltration and ultrafiltration systems. Particle trajectories were evaluated by numerical integration of the Langevin equation, accounting for the combined effects of electrostatic repulsion, enhanced hydrodynamic drag, and Brownian diffusion. In the absence of Brownian forces, particles are unable to enter the membrane pores unless the drag associated with the filtration velocity can overcome the electrostatic repulsion. Brownian forces significantly alter this behavior, allowing some particles to enter the pore even at low filtration velocities. The average particle transmission, evaluated from the probability of having a particle enter the pore, increases with increasing filtration velocity due to the greater hydrodynamic drag force on the particle. These results provide important insights into particle behavior in membrane systems. [Copyright &y& Elsevier]