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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.

Questions of energy dissipation or friction appear immediately when addressing the problem of a body moving in a fluid. For the most simple problems, involving a constant steady propulsive force on the body, a straightforward relation can be established balancing this driving force with a skin friction or form drag, depending on the Reynolds number and body geometry. This elementary relation closes the full dynamical problem and sets, for instance, average cruising velocity or energy cost. In the case of finite-sized and time-deformable bodies though, such as flapping flyers or undulatory swimmers, the comprehension of driving/dissipation interactions is not straightforward. The intrinsic unsteadiness of the flapping and deforming animal bodies complicates the usual application of classical fluid dynamic forces balance. One of the complications is because the shape of the body is indeed changing in time, accelerating and decelerating perpetually, but also because the role of drag (more specifically the role of the local drag) has two different facets, contributing at the same time to global dissipation and to driving forces. This causes situations where a strong drag is not necessarily equivalent to inefficient systems. A lot of living systems are precisely using strong sources of drag to optimize their performance. In addition to revisiting classical results under the light of recent research on these questions, we discuss in this review the crucial role of drag from another point of view that concerns the fluid-structure interaction problem of animal locomotion. We consider, in particular, the dynamic subtleties brought by the quadratic drag that resists transverse motions of a flexible body or appendage performing complex kinematics, such as the phase dynamics of a flexible flapping wing, the propagative nature of the bending wave in undulatory swimmers, or the surprising relevance of drag-based resistive thrust in inertial swimmers., (© 2018 The Author(s).)

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]

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]

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]

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]

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]

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]