Steady Force Research Articles

Effects of steady wave forces on course-keeping manoeuvres of full- and model-scale ships moving obliquely in short waves

ABSTRACT We investigated the effects of the steady wave force variations generated by oblique motions upon ship manoeuvre estimations, using a numerical simulation that incorporated only steady wave forces into a three-degrees-of-freedom conventional modular mathematical model in calm water. The investigation was conducted for a very large crude carrier undergoing course-keeping manoeuvres in regular short waves. The steady wave forces in the simulation were provided via two methods, depending on the experimental data and the presence or absence of a ship drift angle. The simulation was validated via a free-running model test; this involved various rudder effectiveness conditions for the ship model and full-scale ships, both with and without engine limits. Through this validation, we showed that the steady wave force variations generated by oblique motions are non-negligible when accurately estimating the manoeuvres of full-scale ships in short waves, although they are negligible for ship models.

Mechanical behavior analysis of high power commercial lithium-ion batteries

In application, lithium-ion cells undergo expansion during cycling. The mechanical behavior and the impact of external stress on lithium-ion battery are important in vehicle application. In this work, 18 Ah high power commercial cell with LiNi0.5Co0.2Mn0.3O2/graphite electrode were adopted. A commercial compress machine was applied to monitor the mechanical characteristics under different stage of charge (SOC), lifetime and initial external force. The dynamic and steady force was obtained and the results show that the dynamic force increases as the SOC increasing, obviously. During the lifetime with high power driving mode, different external force is shown to have a great impact on the long-term cell performance, with higher stresses result in higher capacity decay rates and faster impedance increases. A proper initial external force (900 N) provides lower impedance increasing. Postmortem analysis of the cells with 2000 N initial force suggests a close correlation between electrochemistry and mechanics in which higher initial force leads to higher direct current internal resistance (DCIR) increase rate. In addition, for the cell with higher external force, deformation of the cathode and thicker solid electrolyte interface (SEI) film on the surface of anode and separator are observed. Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring. The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis. In addition, for the cell with higher external force, deformation of the cathode and thicker SEI film on the surface of anode and separator are observed. Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring. The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis.

Intra-muscle Synergies Stabilizing Reflex-mediated Force Changes

We used the framework of the uncontrolled manifold hypothesis to explore force-stabilizing synergies and motor equivalence in the spaces of individual motor unit (MU) firing frequencies. Healthy subjects performed steady force production tasks by pressing with one finger or three fingers of a hand. Surface EMG was used to identify individual MU action potentials. MUs formed stable groups (MU-modes) with parallel scaling of the firing frequency in both flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC) that allowed identifying them with the reciprocal and coactivation commands. Smooth lifting of the fingers by an “inverse piano” device led to an unintentional, reflex-based force increase. There was significantly larger motion in the space of MU-modes that kept the force unchanged (motor equivalent) compared to motion that changed force (non-motor equivalent). The force change was stabilized by co-varying contributions of the MU-modes defined separately for FDS and EDC. In contrast, analysis of the three-finger task in the space of individual finger forces showed no synergies stabilizing total force change. Effects of hand dominance were seen on multi-finger synergies but not intra-muscle synergies. We conclude that spinal mechanisms, such as recurrent inhibition and reflex loops from proprioceptors, contribute significantly to intra-muscle synergies, while multi-finger synergies reflect supra-spinal processes. These results provide methods to explore the contributions of spinal vs supraspinal circuitry to changed motor synergies in populations with a variety of neurological disorders.

Study on the splitting and expansion–splitting modes of thin-walled circular tubes under axial compression

In this paper, the deformation and energy absorption of thin-walled circular tubes in splitting and expansion–splitting modes are investigated by experiments and theory modeling. First, axial compression experiments of both steel and aluminum alloy tubes were conducted. The results show that the initial peak force in splitting mode could be reduced by increasing the number of initial cracks, and the steady force and the stroke efficiency of tubes could be greatly improved by introducing splitting deformation to the expansion mode in series. Afterwards, theoretical models for these two modes are developed by considering the stress coupling and stress equilibrium, which can well predict the experimental results. Based on the theoretical models, it is found that the initial peak force increases with the decrease of the number and the length of the initial cracks. However, when these two parameters are smaller enough, the initial peak force will not increase. In expansion–splitting mode, the splitting effect can weak the force induced by the expansion deformation, and there is a critical expansion die angle to make the steady force minimum. Moreover, the plastic dissipation is always larger than the tearing dissipation, while the friction dissipation can account for the largest proportion when the expansion die angle is small.

Numerical investigation on hopf bifurcation problem for nonlinear dynamics of a towed vessel in calm water and waves

In this study, the Hopf bifurcation problem with regard to the nonlinear dynamics of a towed vessel was numerically investigated. A time-domain simulation method based on three degrees-of-freedom maneuvering equations of motion was applied to study the nonlinear dynamic responses of a towed vessel in calm water, wind and waves. In the towing operation, it is assumed that a vessel is passively towed by a tug via a towline with a constant towing speed following a straight line. In the case of wind or wave conditions, the steady wind or wave drift forces are considered as additional external force components. The hydrodynamic forces acting on the towed vessel are modeled as a modular-type hull force model, and the towline force is simply modeled as a linear spring. First, for the validation, the motion trajectories of the towed vessel were compared between the experimental data and numerical simulation results under the calm water condition. Discussions are provided on the effect of skegs on the dynamics of the towed vessel and related Hopf bifurcation according to the skeg size. Next, the wind speed was changed, and the resulting limit cycles were studied. It can be observed that the Hopf bifurcation can be delayed according to the wind speed and direction. Finally, the dynamic characteristics of the towed vessel in regular waves were investigated via numerical simulations. The stability of the towed vessel with no skegs increases owing to the mean wave drift forces for both the model test and numerical simulation. The effects of the wave height and period on the Hopf bifurcation were studied based on numerical simulations. It was found that the occurrence of Hopf bifurcation for nonlinear dynamics of a towed vessel is sensitive to the conditions of wave height and period.

Estuarine water quality: One-dimensional model theory and its application to a riverine subtropical estuary in Florida

In this study, analytical solutions were found for nutrients and phytoplankton in an idealized one-dimensional estuary with tidally averaged conditions. Steady forcing conditions and first order kinetics were assumed for freshwater inflow, nutrients, and algal loading input. These analytical solutions consist of two parts, a steady state solution and a non-steady state solution. The steady state solution was determined for a typical advection-dispersion-reaction equation for a nonconservative constituent. For phytoplankton, the non-steady solution has exponential growth or decay depending on the difference between the net growth rate (μnet) and the flushing rate (f). When μnet is greater than f, exponential growth or algal bloom could occur; otherwise, it would be an exponential decay over the time scale of 1/(f- μnet). The steady state solution for phytoplankton predicted the chlorophyll maximum and its location, which would move downstream with increasing freshwater inflows, a phenomenon observed in field studies (Doering et al., 2006; Valdes-Weaver et al., 2006). When applied to the Caloosahatchee River Estuary, a shallow riverine estuary in southwest Florida, the steady state solution for phytoplankton was able to reasonably reproduce the general shape of observed longitudinal phytoplankton distribution. Consistent with the findings of a recent box model study (Sun et al., submitted), this one-dimensional model suggests that there may be important contributions from external loading of phytoplankton to downstream phytoplankton biomass. This finding can inform future improvement of more complex numerical models of estuarine eutrophication as well as practical water management strategies.

Two identical tandem square prisms with rounded edges and hard marine fouling at incidence in cross-flow: Effect of spacing and Reynolds number on unsteady fluid dynamics

Because of their long submerged columns, deep-draft semi-submersible floating structures are particularly susceptible to vortex-induced motions. This paper focuses on the steady and unsteady forces that act on such a column pair, as well as on the frequency and strength of the shed vortices behind the downstream column. Wind tunnel experiments were performed on two rounded and lightly rough square-section prisms in cross-flow for Reynolds numbers from 100,000 up to 7 million. They are arranged inline at centre-to-centre distances of S/D = 2.8, 4, and 5.6 and at 0° or 45° incidence angle. The trend of the drag curve for the upstream prism deviates at S/D = 2.8 and 4 sharply from that for a single prism. The drag force on the downstream prism strongly depends on both S/D and α. At S/D = 2.8, a thrust force occurs either in certain (α = 0°) or in all (α = 45°) flow states. Larger spacing values lead to an overall higher drag and a flattening of the Cd2 (ReD) curve. The highest fluctuating lift forces on the downstream prism are obtained at α = 45°. Regarding the vortex shedding frequency, differences between both incidence angles occur at S/D = 5.6 only.

Study on energy absorption characteristics of expansion tube with light magnesium alloy

This paper proposed a lightweight magnesium alloy expansion energy-absorbing structure. The structure adopts lightweight materials, which can greatly reduce its own weight on the basis of ensuring energy absorption performance. Firstly, the geometric model of structure is designed and the corresponding physical prototype is processed. The theoretical model of magnesium alloy expansion tube is studied, and the main mechanical response is analyzed. Then the structural mechanical properties are studied by quasi-static compression test. Combined with the theoretical model, several typical deformation stages in expanding are analyzed. The effects of geometric parameters on the energy absorption performance are studied. The results show that with the increase of die angle, die expansion size and tube thickness, the maximum peak force, average force, energy absorption and specific energy absorption increase. Then the test results are compared with the corresponding theoretical steady force to verify the applicability of the theoretical model. The theoretical values are basically in good agreement with the experimental values. The error of all results is within 10%. Finally, comparing the characteristics of magnesium alloy, aluminum alloy and steel energy absorbing tube with the same quality, it is concluded that the specific energy absorption of magnesium alloy structure is 31.6% and 4.1% higher than that of steel and aluminum respectively, and magnesium alloy tube has higher specific energy absorption.

Temporally stable beta sensorimotor oscillations and corticomuscular coupling underlie force steadiness

As humans, we seamlessly hold objects in our hands, and may even lose consciousness of these objects. This phenomenon raises the unsettled question of the involvement of the cerebral cortex, the core area for voluntary motor control, in dynamically maintaining steady muscle force. To address this issue, we measured magnetoencephalographic brain activity from healthy adults who maintained a steady pinch grip. Using a novel analysis approach, we uncovered fine-grained temporal modulations in the beta sensorimotor brain rhythm and its coupling with muscle activity, with respect to several aspects of muscle force (rate of increase/decrease or plateauing high/low). These modulations preceded changes in force features by ∼40 ms and possessed behavioral relevance, as less salient or absent modulation predicted a more stable force output. These findings have consequences for the existing theories regarding the functional role of cortico-muscular coupling, and suggest that steady muscle contractions are characterized by a stable rather than fluttering involvement of the sensorimotor cortex.

Classification characteristics of fine motor experts based on electroencephalographic and force tracking data

The application of machine learning techniques provides a data-driven approach for a deeper understanding of the development and expressions of expertise. In extension to the common procedure of comparing experts' and novices' performances in expertise-domain-related tasks we applied conventional classification algorithms. We distinguished between tasks for each participant and between groups, i.e., experts or novices, based on electroencephalographic (EEG) activity patterns and force output variables during four different force modulation tasks. The tasks under investigation involved sinusoidal and steady force tracking tasks, which were performed with the left and right hand. Classification of tasks based on EEG patterns as well as force output was possible with high accuracy in novices and experts, whereas classification of group membership, i.e., experts or novices, was at chance level. In follow-up analyses, we found a high degree of individuality in the EEG patterns of the experts, implying the long-term development of specialized central processing during fine motor tasks in fine motor experts. Taken together, the results suggest that continuous practice in the work context leads to the development of a highly individual and task-specific central control pattern.

Scale effect of applying Tauti's law in model experiment: CFD models for flow across planar netting

Tauti's similarity criterion is the core problem in physical experiments and is associated with the accuracy of the final estimation of physical system results. In this study, a computational fluid dynamics (CFD) simulation study related to the steady fluid hydrodynamic forces acting on netting was performed by solving Reynolds-averaged Navier–Stokes equations. First, the prediction accuracy of the netting hydrodynamic forces in a flume tank was investigated. Subsequently, the basic characteristics of CFD simulations to reproduce the flow field and the hydrodynamics of a prototype net were studied. The flow field around the netting was analysed using five different schemes. When a same scale ratio was adopted (λ = λ′ = λ″, where λ is the large-scale ratio, and λ′ and λ″, are the small-scale ratios of the mesh length and twine diameter, respectively), the results demonstrate that as the scale ratio increases, the drag coefficient of the netting increases, and the relative error between the drag restored by the Tauti criterion and the original netting drag force also increases. When adopting a double different scale ratio (λ,λ′=λ″) in the schemes of the prototype netting, the drag coefficient of the netting decreased with an increase in the scale ratio, and the drag value gradually deviated from the standard value. When thress different scale ratios (λ,λ′,λ″) were adopted under various mesh sizes and twine diameters, the flow velocity reduction trend downstream of the netting was opposite to that upstream, verifying that the same small-scale ratio is accurate for the reduction result. Finally, we confirmed the improvement in the selection of the scale ratio of the Tauti criterion and the correction suggestions after adopting the scale ratio. The aforementioned findings can provide a theoretical guidance for the physical testing and design of fishing gear.

Wake transitions and steady -instability of an Ahmed body in varying flow conditions

The paper investigates experimentally the flow past a flat-back, taller than wide Ahmed body having rectangular base aspect ratio $H/W=1.11$ in the context of ground vehicle aerodynamics. Parametric studies at Reynolds number $2.1\times 10^5$ explore the sensitivity of the aerodynamic force and body pressure distribution with respect to varying flow conditions defined from variable ground clearance $C$ (taken at mid-distance from the front and rear axles of the body), pitch angle $\alpha$ , and yaw angle $\beta$ (equivalent to a crosswind). Two-dimensional parametric maps in the parametric spaces $(\beta,C)$ and $(\beta,\alpha )$ are obtained for parameter ranges covering real road vehicle driving conditions. The study of the base pressure gradient reveals non-trivial and sharp transitions identified as significant changes of near wake orientation in both parametric spaces. All unsteady transitions correspond to fluctuation crises of the vertical gradient component only. These transitions are summarized in phase diagram representations. Both phase diagrams in $(\beta,C)$ and $(\beta,\alpha )$ parametric spaces can be unified at large yaw in the $(\beta,C_r)$ space, where the rear clearance $C_r$ separating the lower edge of the base from the ground is a simple function of the pitch $\alpha$ and the clearance $C$ . The impacts of the wake transitions are clearly identified in the base drag, drag, lift and side force coefficients. The contribution of the steady near wake $z$ -instability (Grandemange et al., Phys. Fluids, vol. 25, 2013a, pp. 95–103) is assessed by repeating the sensitivity analysis with a rear cavity. As reported previously, the rear cavity suppresses the steady instability by symmetrizing the wake. A domain for the existence of the instability is finally proposed in the attitudes map $(\beta,\alpha )$ defined from regions where the mean lateral force coefficients are significantly decreased by the presence of the rear cavity. In addition, it is found that the steady instability forces the wake to be less unsteady for all attitudes that do not correspond to unsteady transitions.

A Thermodynamically Consistent, Microscopically-Based, Model of the Rheology of Aggregating Particles Suspensions.

In this work, we outline the development of a thermodynamically consistent microscopic model for a suspension of aggregating particles under arbitrary, inertia-less deformation. As a proof-of-concept, we show how the combination of a simplified population-balance-based description of the aggregating particle microstructure along with the use of the single-generator bracket description of nonequilibrium thermodynamics, which leads naturally to the formulation of the model equations. Notable elements of the model are a lognormal distribution for the aggregate size population, a population balance-based model of the aggregation and breakup processes and a conformation tensor-based viscoelastic description of the elastic network of the particle aggregates. The resulting example model is evaluated in steady and transient shear forces and elongational flows and shown to offer predictions that are consistent with observed rheological behavior of typical systems of aggregating particles. Additionally, an expression for the total entropy production is also provided that allows one to judge the thermodynamic consistency and to evaluate the importance of the various dissipative phenomena involved in given flow processes.

Influence of Fluid Viscosity and Compressibility on Nonlinearities in Generalized Aerodynamic Forces for T-Tail Flutter

The numerical assessment of T-tail flutter requires a nonlinear description of the structural deformations when the unsteady aerodynamic forces comprise terms from lifting surface roll motion. For linear flutter, a linear deformation description of the vertical tail plane (VTP) out-of-plane bending results in a spurious stiffening proportional to the steady lift forces, which is corrected by incorporating second-order deformation terms in the equations of motion. While the effect of these nonlinear deformation components on the stiffness of the VTP out-of-plane bending mode shape is known from the literature, their impact on the aerodynamic coupling terms involved in T-tail flutter has not been studied so far, especially regarding amplitude-dependent characteristics. This term affects numerical results targeting common flutter analysis, as well as the study of amplitude-dependent dynamic aeroelastic stability phenomena, e.g., Limit Cycle Oscillations (LCOs). As LCOs might occur below the linear flutter boundary, fundamental knowledge about the structural and aerodynamic nonlinearities occurring in the dynamical system is essential. This paper gives an insight into the aerodynamic nonlinearities for representative structural deformations usually encountered in T-tail flutter mechanisms using a CFD approach in the time domain. It further outlines the impact of geometrically nonlinear deformations on the aerodynamic nonlinearities. For this, the horizontal tail plane (HTP) is considered in isolated form to exclude aerodynamic interference effects from the studies and subjected to rigid body roll and yaw motion as an approximation to the structural mode shapes. The complexity of the aerodynamics is increased successively from subsonic inviscid flow to transonic viscous flow. At a subsonic Mach number, a distinct aerodynamic nonlinearity in stiffness and damping in the aerodynamic coupling term HTP roll on yaw is shown. Geometric nonlinearities result in an almost entire cancellation of the stiffness nonlinearity and an increase in damping nonlinearity. The viscous forces result in a stiffness offset with respect to the inviscid results, but do not alter the observed nonlinearities, as well as the impact of geometric nonlinearities. At a transonic Mach number, the aerodynamic stiffness nonlinearity is amplified further and the damping nonlinearity is reduced considerably. Here, the geometrically nonlinear motion description reduces the aerodynamic stiffness nonlinearity as well, but does not cancel it.

Smart handheld medical device with patient-specific force regulation mechanism

PurposeThe purpose of this paper is to design a smart handheld device with force regulating function, which demonstrates the concept of patient-specialized tools.Design/methodology/approachThis handheld device integrates an electrical bioimpedance (EBI) sensor for tissue measurement and a constant force regulation mechanism for ensuring stable tool–tissue contact. Particular focuses in this study are on the design of the constant force regulation mechanism whose design process is through genetic algorithm optimization and finite element simulation. In addition, the output force can be changed to the desired value by adjusting the cross-sectional area of the generated spring.FindingsThe following two specific applications based on ex vivo tissues are used for evaluating the designed device. One is in terms of safety of interaction with delicate tissue while the other is for compensating involuntary tissue motion. The results of both examples show that the handheld device is able to provide an output force with a small standard deviation.Originality/valueIn this paper, a handheld device with force regulation mechanism is designed for specific patients based on the genetic algorithm optimization and finite element simulation. The device can maintain a steady and safe interaction force during the EBI measurement on fragile tissues or moving tissues, to improve the sensing accuracy and to avoid tissue damage. Such functions of the proposed device are evaluated through a series of experiments and the device is demonstrated to be effective.

Design of a new passive end-effector based on constant-force mechanism for robotic polishing

Polishing is an important final machining process in manufacturing. For robotic polishing, active compliance control is the most frequently used approach to control the contact force between the end-effector and workpiece. However, it usually exhibits the problem of force overshoot at the start of contact, with poor force accuracy normally larger than 1 N. This paper proposes the concept design of a novel end-effector based on constant-force mechanism for robotic polishing. This design is the first constant-force mechanism based robotic end-effector for use in polishing experiment. An industrial robot is used to position the end-effector and the end-effector regulates the contact force passively. The constant-force motion range acts as a buffer to counteract the excessive displacement caused by inertia. As a result, there is no force overshoot, producing the consistency for the workpiece’s surface quality. Moreover, the property of the constant force ensures more accurate contact force without using a complex controller. Design, modeling, and simulation study have been performed to demonstrate the proposed idea. A prototype is fabricated for experimental testing. The end-effector is adopted to polish rusty steel, and the recorded contact force signal during polishing demonstrates the effectiveness of the constant-force mechanism in counteracting the force overshoot and improving the force accuracy. Results indicate that the polished surface is extremely uniform with steady contact force regulated by the constant-force mechanism.

Numerical Investigation on the Internal Flow Field of Electronic Expansion Valve as the Throttle Element

<div class="section abstract"><div class="htmlview paragraph">As one of the key components of the heat pump system, the electronic expansion valve mainly plays the role of throttling and reducing pressure in the heat pump system. The refrigerant flowing through the orifice will produce complex phase change. It is of great significance to study the internal flow field by means of CFD calculations. Firstly, a three-dimensional fluid model is established and the mesh is divided. Secondly, the phase change model is selected, the material is defined and the boundary conditions are determined. According to the principle of the fluid passing through thin-walled small holes, the flow characteristics of electronic expansion valve are theoretically analyzed. Then the flow characteristics of expansion valve are numerically calculated, and a bench for testing mass flow rate of the expansion valve is built. Then the theoretical value, CFD value and experimental value are compared to verify the correctness of the established three-dimensional fluid model. The flow rate changes of expansion valve are studied under the condition of changing geometric parameters such as the cone angle of the valve spool and the radius of circular arc at the end of the valve seat. According to the momentum theorem, the steady hydraulic force is theoretically deduced. Then the changes of steady hydraulic force are studied under the conditions of different inlet pressure and outlet pressure. At the same time, there also analyzes the effects of the conditions of different valve spool cone angle and valve seat arc radius on steady hydraulic force on the valve spool. Finally, transient analysis is carried out by using dynamic mesh technology. The speed of spool movement is defined by User Defined Function (UDF). Under constant pressure difference conditions, the influence of the spool movement on the hydraulic force and outlet flow of the valve is studied. And the change of the internal pressure field are shown.</div></div>

Polymer Translocation through Nanometer Pores.

In this paper the loaded polymer transport and its escape via a nanometer size aperture, virtually by nanomembrane, the polymer being moved by an exterior electrostatic field, has been studied. Assuming a linear dependency of the friction coefficient on the number of segments m and a parabolic behavior for the open-free (Gibbs) energy, in attendance of a present electrical potential across nanopore, an explicit flux formula for the polymers passed over a dimensional restricted pore, was derived. In addition, the linear polymers transport through a nanometer-sized pore under the action of a constant force is presented. The important mechanical effects of superimposed steady force and the monomers number of macromolecule chain on the polymer translocation process by nanomembranes, in a 2D diffusion model, have been demonstrated. The escape time by a three-dimensional graph as a function of the electric field intensity and monomers number of polymer was represented.

Multi-scale Crystal Viscoplasticity Approach for Estimating Anisotropic Steady-State Creep Properties of Single-Crystal SnAgCu Alloys

Creep can have a significant impact on the reliability of Sn-based solder alloys even at room temperature because of their relatively low melting temperatures. SnAgCu (SAC) solder joints used in electronic packaging typically consist of only a few highly anisotropic grains, which consist of Sn dendrites embedded in a near-eutectic Sn-Ag component. The unique grain structure of each joint leads to stochastic variations in the thermomechanical response of such joint. Therefore, grain-scale testing and modeling are recommended to better characterize the anisotropic behavior and to estimate the influence of stochastic variability of grain structure on the viscoplastic response of the joint. This work aims to investigate the anisotropic steady-state creep behavior of single-crystal SAC solder joints. The orientation-dependent viscoplastic behavior of individual SAC grains is modeled with a multi-scale crystal-viscoplasticity approach for representing the relevant dislocation mechanics. The response predicted by the crystal viscoplasticity model is then captured in an equivalent homogenized continuous-scale constitutive model (Hill-Garofalo formulation).This modeling strategy was implemented in numerical simulations, as an illustrative example, to analyze the behavior of single-grain solder joints subjected to combined steady compression (from heat-sink clamping force) and thermal cyclic loading. The cyclic ratcheting in the presence of the steady compressive force causes: (i) transverse expansion of the solder ball, potentially leading to eventual short circuits; and (ii) cyclic fatigue damage leading to eventual failure of the solder joint. The proposed grain-scale modeling approach is shown to be able to address the stochastic variability of both these damage mechanisms, as a function of grain orientation. The present methodology can be used to predict the realistic behavior of solder joints, based on their microstructure, and provide valuable insights for their reliability analysis.

On the application of current blockage model to steady drag force on fish net

This paper introduces a hydrodynamic model to characterise steady drag force on fish net. The proposed method is based on the current blockage model commonly used in offshore engineering, which is capable of accounting for fluid flow reduction due to the presence of fish net acting as an obstacle array. Based on available measurements reported in the literature, the proposed method is applied and compared against the measurements. This paper demonstrates that the proposed method is able to produce respectable agreements both in terms of drag force as well as velocity reduction factor for a wide range of Reynolds numbers (Re), solidity ratios (Sn) and inflow angles (defined as the angle between the flow direction and the normal vector of the net panel). In particular, for forces acting on a rectangular fish panel with 0∘ inflow angle, the proposed method shows that the fitted drag coefficients (Cd) are independent of Re ranging from 35 to 5000, and that Cd can be grouped into three flow regimes depending on Sn ranging from 0.12 to 0.32. The proposed method provides a different perspective in the modelling and may contribute to a more accurate prediction of hydrodynamic loads on fish net in steady flow.