Search Results (16)

The integrated development of offshore wind power and marine aquaculture represents a promising approach to the sustainable utilization of ocean resources. The present study investigated the hydrodynamic response of an innovative combination of a wind farm monopile and pontoon raft aquaculture facilities (PRAFs). Physical water tank experiments were conducted on PRAFs deployed around a wind farm monopile using the following configurations: single- and three-row arrangements of PRAFs with and without a monopile. The interaction between the aquaculture structure and the wind farm monopile was examined, with a particular focus on the mooring line tensions and bridle line tensions under different wave conditions. Utilizing the wind farm monopile foundation as an anchor, the mooring line tension was reduced significantly by 16–66% in the single-row PRAF. The multi-row PRAF arrangement experienced lower mooring line tension in comparison with the single-row PRAF arrangement, with the highest reduction of 73%. However, for the bridle line tension, the upstream component was enhanced, while the downstream one was weakened with a monopile, and they both decreased in the multi-row arrangement. Finally, we developed numerical models based on flume tank tests that examined the interactions between the monopile and PRAFs, including configurations of a single monopile, along with single- and three-row arrangements of PRAFs. The numerical simulation results confirmed that the monopile had a dampening effect on the wave propagation of 5% to 20%, and the impact of the pontoons on the monopile was negligible, implying that the integration of aquaculture facilities around wind farm infrastructure may not significantly alter the hydrodynamic loads experienced by the monopile. Full article

Deep-sea fisheries depend on various fishing methods, including trawling, purse seining, and longline fishing, among others. Studying the dynamic characteristics of trawling operations is essential for the trawl mechanism. Because of the solid truss support, the beam trawl system may be employed in extreme sea conditions, the high-speed driving of tugs, and maneuvering situations. This study systematically investigates the dynamic responses and structural safety of a midwater beam trawl during towing via the lumped mass method and OrcaFlex 9.7e simulations. Firstly, a trawl model with four towlines was developed and validated against flume tank experiments. Secondly, multiple operational scenarios were analyzed: towing speeds, angular velocity variations under a fixed turning radius, and radius effects under constant angular velocity. The results show that line tension increases with the speed increment and that the rigid frame destabilizes at angular velocities exceeding 20°/s due to centrifugal overload. Furthermore, line fracture scenarios during startup and straight-line towing were emphasized. Single-line failure leads to edge constraint loss, redistributing stress to the remaining lines, and asymmetric dual-line fracture triggers net torsion, reducing fishing efficiency. This study provides theoretical guidance for optimizing the safe operational parameters of midwater beam trawls. Full article

The over-arching goal of the WATERLINE project is the creation of a European Digital Water Higher Education Institution (HEI) Alliance, with a core part of this goal being the development and delivery of meaningful water engineering education through extended reality technology, allowing students to engage with virtualised water engineering models, such as flume tanks and water distribution networks in a manner that will promote engaged deep learning. To realise this goal, researchers need to engage with pedagogic, creative, and technical considerations to ensure that water engineering students are presented with engaging applications that provide the “right” knowledge and provide experiences where deep and memorable learning can take place. Full article

Netting is an important component of fishing gear design, and its ability to sink determines the effectiveness of fishing gears such as purse seines, falling nets, and stick-held nets. Therefore, it is crucial to thoroughly investigate the sinking parameters (sinking depth and sinking speed) of the netting panel as a function of the leadline weights using various twine materials, knot types, and solidity ratios. In this study, a generalized additive model (GAM) was utilized to analyze the impact of each factor on the sinking performances of the netting. The results revealed that the sinking depth of the netting was positively correlated with sinking time and leadline weight. However, the netting featured a maximum sinking depth limit, indicating that the sinking depth would not increase beyond a leadline weight of 69.5 g. During the initial phase of the sinking process, the sinking velocity of each netting panel initially increased but gradually decreased over time. The incorporation of a leadline weight reduced sinking time. Thereby, polyester netting exhibited the shortest average sinking time. A comparison of netting types with similar solidity ratios showed that the maximum sinking depth of the nylon netting was 13.20% and 10.11% greater than that of polyethylene and polyester nettings, respectively. In addition, nylon nets’ time average sinking speed was 64.58% and 4.62% greater than that of polyethylene and polyester nettings, respectively. The analysis of the GAM model clearly showed that the leadline weight has a significant effect on the netting sinking speed and depth. To ensure that the netting can reach its maximum sinking speed, it is strongly recommended to use nylon and polyester nettings with a low solidity ratio, i.e., a lower twine diameter and greater mesh size with a higher leadline weight, when constructing fishing gear such as purse seines with higher net leadline weights. Full article

The grid is a crucial component in constructing grid-type bycatch reduction devices. The grid’s structural characteristics and orientation significantly impact the hydrodynamic characteristics and efficacy of the separation device. Therefore, it is essential to thoroughly understand the grid device’s hydrodynamic characteristics and flow field to optimize its structure. Thus, this study used CFD numerical simulation and flume tank experiments to investigate the effects of inclination grid angles and grid bar spacing on hydrodynamic forces and flow fields around a circular grid. The results indicated that the hydrodynamic forces acting on the circular grid increased with higher flow velocity and inclination grid angle, decreasing with smaller grid bar spacing. Flow velocity acceleration zones were observed at the upper and lower ends of the grid and between the grid bars. Additionally, upwelling and vortices were present at the back of the grid. It was found that an increase in the inclination grid angle accelerated the vortex and wake effects. Full article

Debris flow is a devastating phenomenon that happens in hilly and mountainous regions and has a serious impact on affected areas. It causes casualties and serious damage to the environment and society. Therefore, a susceptible assessment is necessary to prevent, mitigate, and raise awareness of the impact of debris flows. This paper focuses on evaluating the deposition area along the deposition board. The methodology involved an experiment on a physical model by demonstrating the debris flow based on the steepness of the flume slope at 15°, 20°, and 25° angles. The limestone particles with a total volume of 2.5 × 10⁶ mm³ acted as debris and were released with water from the tank to the deposition board with an area of 10 × 10⁵ mm². The volume, area, and length of particle distribution carried from the flume to the deposition board were then determined. Based on the experimental results, the deposition board is covered with particles of about 696.19 × 10³ mm³, 748.29 × 10³ mm³, and 505.19 × 10³ mm³ volume for each 15°, 20°, and 25° angle, respectively. In actual situations, debris flow is capable of causing significant risk to the affected area. This study can be deemed useful for a risk assessment approach, to help develop guidelines, and to mitigate the regions where debris flows are most probable to occur. Full article

This study is concerned with the generation and propagation of strongly nonlinear waves in shallow water. A numerical wave flume is developed where nonlinear waves of solitary and cnoidal types are generated by use of the Level I Green-Naghdi (GN) equations by a piston-type wavemaker. Waves generated by the GN theory enter the domain where the fluid motion is governed by the Navier–Stokes equations to achieve the highest accuracy for wave propagation. The computations are performed in two dimensions, and by an open source computational fluid dynamics package, namely OpenFoam. Comparisons are made between the characteristics of the waves generated in this wave tank and by use of the GN equations and the waves generated by Boussinesq equations, Laitone’s 1st and 2nd order equations, and KdV equations. We also consider a numerical wave tank where waves generated by the GN equations enter a domain in which the fluid motion is governed by the GN equations. Discussion is provided on the limitations and applicability of the GN equations in generating accurate, nonlinear, shallow-water waves. The results, including surface elevation, velocity field, and wave celerity, are compared with laboratory experiments and other theories. It is found that the nonlinear waves generated by the GN equations are highly stable and in close agreement with laboratory measurements. Full article

This paper presents experimental studies of the force generated on the rotating cylinder implemented as a bow rudder on a large-scale ship model. The research focused on the maneuverability of the unit equipped with a rotating cylinder (RC) in the front part of the model and its future use as a steering device on small draft river barges. The study presented in this paper is a continuation of the research carried out using the small physical model of a river push train in 1:20 geometric scale equipped with two bow RCs and open water tests of separated rotating cylinders carried out in a flume tank. The experimental test setup with RC installed on the model in 1:24 geometric scale allowed to compare the parameters of standard maneuvers performed with the use of RC and without it. The proposed method based on the measurement of the ship model trajectory during maneuvers allowed to compare the hydrodynamic steering force generated by RC with the steering force generated by the conventional stern spade rudder. The results of the experiments compared with empirical models show a similar trend. RC dynamics was tested for rotational speeds up to 570 RPM (revolutions per minute) and ship model velocity up to 1 m/s. The rotating cylinder generated velocity field is presented and phenomena influencing the generated hydrodynamic force are discussed. Full article

The otter board, which is designed to maintain the horizontal opening of trawl nets, is a vital component of a trawl system. It requires a high lift-to-drag ratio, which is directly related to the trawling efficiency and economic effectiveness of the single trawler. To improve the hydrodynamic efficiency of a symmetrical elliptic otter board, four model otter boards, i.e., aspect ratio (AR) = 0.507, 0.640, 0.766, and 0.895, were designed in the present work and the effects of aspect ratios on the hydrodynamic performance of the otter board were investigated by flume tank experiments. Further, the k-ε EARSM turbulence model was adopted to analyze the hydrodynamic coefficients and the flow distribution around the otter board using the computational fluid dynamics (CFD) method. The optimal aspect ratio was obtained based on the analysis of experimental data, wherein the lift coefficient, the drag coefficient, and the lift-to-drag ratio at different angles of attack (AOA) were measured. The results show that the symmetrical elliptic otter board model is within the critical Reynolds number region when the Reynolds number is larger than 1.682 × 10⁵, and its hydrodynamic coefficient is consistent with the real otter board. When the AR was 0.766, the elliptic otter board had the best hydrodynamic performance, of which the lift coefficient and the lift-to-drag ratio were 1.05 and 1.14 fold that of the initial otter board (AR = 0.640), and the volume of the wing-tip vortex reaches a maximum. The results show the hydrodynamic performance of the symmetrical elliptic otter board, and parameter optimization of the otter board has also been provided for reference. Full article

Open water flume tanks with closed-loop circulation driven by centrifugal pumps are essential for hydro experimentation in academic settings as well as research centers. The device is also attractive due to its versatility and easy-to-maintain characteristics. Nevertheless, commercial open flume systems can be expensive and become less prioritized in engineering schools. This paper describes the design and fabrication of an affordable, medium-size water flume tank, suitable for education purposes. The central piece of the system is a transparent observation chamber where fluid experiments are typically conducted and observed. The expected maximum average water speed in the observation chamber of about 60 cm per second was achieved by the inclusion of a 3 hp centrifugal pump. The size and capacity of the current design were constrained by space limitation and available funds. The educational facility was assigned as a two-semester multi-disciplinary capstone senior design project incorporating students and faculty of mechanical, electrical, and computer engineering programs in our campus. The design process provides a training platform for skills in the area of Computer Aided Designs (CAD), Finite Element Analysis (FEA), Computational Fluid Dynamics (CFD), manufacturing, and experimentation. The multi-disciplinary project has contributed to the improvement of soft skills, such as time management, team working, and professional presentation, of the team members. The total material cost of the facility was less than USD 6000, which includes the pump and its variable frequency driver. The project was made possible due to the generous sponsor of the Vibration Institute. Full article

In this work we consider the problem of finding the simplest arrangement of resonant deep-water gravity waves in one-dimensional propagation, from three perspectives: Theoretical, numerical and experimental. Theoretically this requires using a normal-form Hamiltonian that focuses on 5-wave resonances. The simplest arrangement is based on a triad of wavevectors $K_1+K_2=K_3$ (satisfying specific ratios) along with their negatives, corresponding to a scenario of encountering wavepackets, amenable to experiments and numerical simulations. The normal-form equations for these encountering waves in resonance are shown to be non-integrable, but they admit an integrable reduction in a symmetric configuration. Numerical simulations of the governing equations in natural variables using pseudospectral methods require the inclusion of up to 6-wave interactions, which imposes a strong dealiasing cut-off in order to properly resolve the evolving waves. We study the resonance numerically by looking at a target mode in the base triad and showing that the energy transfer to this mode is more efficient when the system is close to satisfying the resonant conditions. We first look at encountering plane waves with base frequencies in the range 1.32–2.35 Hz and steepnesses below $0.1$, and show that the time evolution of the target mode’s energy is dramatically changed at the resonance. We then look at a scenario that is closer to experiments: Encountering wavepackets in a 400-m long numerical tank, where the interaction time is reduced with respect to the plane-wave case but the resonance is still observed; by mimicking a probe measurement of surface elevation we obtain efficiencies of up to $10\%$ in frequency space after including near-resonant contributions. Finally, we perform preliminary experiments of encountering wavepackets in a 35-m long tank, which seem to show that the resonance exists physically. The measured efficiencies via probe measurements of surface elevation are relatively small, indicating that a finer search is needed along with longer wave flumes with much larger amplitudes and lower frequency waves. A further analysis of phases generated from probe data via the analytic signal approach (using the Hilbert transform) shows a strong triad phase synchronisation at the resonance, thus providing independent experimental evidence of the resonance. Full article

The paper presents the experimental test setup and measurement method of hydrodynamic force generated on the rotating cylinder (rotor) under uniform flow including the free surface effect. The experimental test setup was a unique construction installed in the flume tank equipped with advanced flow generating and measuring systems. The test setup consisted of a bearing mounted platform with rotor drive and sensors measuring the hydrodynamic force. The low length to diameter ratio cylinders were selected as models of bow rotor rudders of a shallow draft river barge. The rotor dynamics was tested for the rotational speeds up to 550 rpm and water current velocity up to 0.85 m/s. The low aspect ratio of the cylinder and free surface effect had significant impacts on the phenomena influencing the generated hydrodynamic force. The effects of the rotor length to diameter ratio, rotational velocity to flow velocity ratio, and the Reynolds number on the lift force were analyzed. The validation of the computational model against experimental results is presented. The results show a similar trend of results for the simulation and experiment. Full article

Tidal stream turbines fixed on the seabed can harness the power of tides at locations where the bathymetry and/or coastal geography result in high kinetic energy levels of the flood and/or neap currents. In large turbine arrays, however, avoiding interactions between upstream turbine wakes and downstream turbine rotors may be hard or impossible, and, therefore, tidal array layouts have to be designed to minimize the power losses caused by these interactions. For the first time, using Navier-Stokes computational fluid dynamics simulations which model the turbines with generalized actuator disks, two sets of flume tank experiments of an isolated turbine and arrays of up to four turbines are analyzed in a thorough and comprehensive fashion to investigate these interactions and the power losses they induce. Very good agreement of simulations and experiments is found in most cases. The key novel finding of this study is the evidence that the flow acceleration between the wakes of two adjacent turbines can be exploited not only to increase the kinetic energy available to a turbine working further downstream in the accelerated flow corridor, but also to reduce the power losses of said turbine due to its rotor interaction with the wake produced by a fourth turbine further upstream. By making use of periodic array simulations, it is also found that there exists an optimal lateral spacing of the two adjacent turbines, which maximizes the power of the downstream turbine with respect to when the two adjacent turbines are absent or further apart. This is accomplished by trading off the amount of flow acceleration between the wakes of the lateral turbines, and the losses due to shear and mixing of the front turbine wake and the wakes of the two lateral turbines. Full article

This article deals with the possibility of using a biosorbent in the form of a mixture of cones from coniferous trees to remove the residual concentration of hazardous metals contained in hazardous waste, which is disposed of in a neutralization station. The efficiency of the tested biosorbent in removing Ni, Zn, Cu, and Fe was monitored here. Laboratory research was carried out before the actual testing of the biosorbent directly in the operation of the neutralization station. With regard to the planned use of the biosorbent in the operational test, the laboratory experiments were performed in a batch mode and for the most problematic metals (Ni and Zn). The laboratory tests with real wastewater have shown that the biosorbent can be used to remove hazardous metals. Under the given conditions, 96% of Ni and 19% of Zn were removed after 20 min when using NaOH activated biosorbent with the concentration of 0.1 mol L⁻¹. The inactivated biosorbent removed 93% of Ni and 31% of Zn. The tested biosorbent was also successful during the operational tests. The inactivated biosorbent was applied due to the financial costs. It was used for the pre-treatment of hazardous waste in a preparation tank, where a significant reduction in the concentration of hazardous metals occurred, but the values of Ni, Cu, and Zn still failed to meet the emission limits. After 72 h, we measured 10 mg L⁻¹ from the original 4,056 mg L⁻¹ of Ni, 1 mg L⁻¹ from the original 2,252 mg L⁻¹ of Cu, 1 mg L⁻¹ from the original 4,020 mg L^–1 of Zn, and 7 mg L⁻¹ from the original 1,853 mg L⁻¹ of Fe. However, even after neutralization, the treated water did not meet the emission limits for discharging into the sewer system. The biosorbent was, therefore, used in the filtration unit as well, which was placed in front of the Parshall flume. After passing through the filtration unit, the concentrations of all the monitored parameters were reduced to a minimum, and the values met the prescribed emission limits. The biosorbent was further used to thicken the residual sludge in the waste pre-treatment tank, which contributed to a significant reduction in the overall cost of disposing of residual hazardous waste. This waste was converted from liquid to solid-state. Full article

Geological disasters of seabed instability are widely distributed in the Yellow River Delta, posing a serious threat to the safety of offshore oil platforms and submarine pipelines. Waves act as one of the main factors causing the frequent occurrence of instabilities in the region. In order to explore the soil failure mode and the law for pore pressure response of the subaqueous Yellow River Delta under wave actions, in-lab flume tank experiments were conducted in this paper. In the experiments, wave loads were applied with a duration of 1 hour each day for 7 consecutive days; pore water pressure data of the soil under wave action were acquired, and penetration strength data of the sediments were determined after wave action. The results showed that the fine-grained seabed presented an arc-shaped oscillation failure form under wave action. In addition, the sliding surface firstly became deeper and then shallower with the wave action. Interestingly, the distribution of pores substantially coincided with that of sliding surfaces. For the first time, gas holes were identified along with their positioning and angle with respect to the sediments. The presence of gas may serve as a primer for submarine slope failures. The wave process can lead to an increase in the excess pore pressure, while the anti-liquefaction capacity of the sediments was improved, causing a decrease in the excess pore pressure resulting from the next wave process. Without new depositional sediments, the existing surface sediments can form high-strength formation under wave actions. The test results may provide a reference for numerical simulations and engineering practice. Full article