Tank Experiments Research Articles

Uncertainty estimation in wave energy systems with applications in robust energy maximising control

Under control action, wave energy devices typically display nonlinear hydrodynamic behaviour, making the design of energy maximising control somewhat onerous. One solution to approach the optimal performance for nonlinear control problem under model mismatches is to employ a linear control strategy, which can be robust to linear model mismatches. However, accurate characterisation of the uncertainty in the linear model is vital, if the controller is to adequately capture the full extent of the uncertainty, while not being overly conservative due to overestimation of the uncertainty. This paper describes a procedure, employing CFD-based numerical tank experiments, to accurately produce a nominal linear empirical transfer function model, along with an accurate estimate of the uncertainty bounds in that linear model, due to hydrodynamic uncertainty. A robust control case study is provided, illustrating the nominal model estimation process, and its corresponding uncertainty set, including the complete procedure, required to generate the robust controller. Robust control results, on the fully nonlinear CFD model, are provided to demonstrate the efficacy of the modelling and control philosophy.

Experiments on Pilot-Scale Constructed Floating Wetlands Efficiency in Removing Agrochemicals.

The efficiency of constructed floating wetlands (CFWs) in their ability to remove agrochemicals (nutrients and pesticides) is here investigated in a series of pilot-scale systems. Four experimental CFWs were designed and constructed; three of them were planted with the aquatic plant species Lemna minor, Azolla pinnata and Eichhornia crassipes. The fourth did not contain any plants and was used as the control. The aim of the study was to evaluate the efficiency of CFW containing aquatic macrophytes in the reduction of pesticides and nutrients, under field conditions. The CFWs operated continuously from May 2021 to September 2021, and their removal efficiencies of nitrogen and phosphorus ions, and five commonly used pesticides were examined. The CFW systems were fed daily with agricultural wastewater which was prepared by mixing a fertilizer and predetermined doses of pesticides. The hydraulic residence time was kept at 14 days. Samples were collected on a weekly basis from both the influent and the effluent of each experimental tank, and were subsequently analyzed in the laboratory. HPLC-DAD and Ion Chromatography were implemented for sample analysis following a very simple sample preparation. Reductions for nutrient ranged from no reduction to 100% removal, whereas for pesticides these varied from no reduction to 98.8% removal, indicating that these systems can be used as efficient and low-cost pollution control technologies for agrochemical wastewater treatment. Significant reduction for certain pesticides was also observed in the algae control tank, thus, proving the efficiency of algae in organic pollution reduction, and recognizing the limitations of aquatic plant use in decontamination.

Design and experiment of a double-wing wave energy converter

Considering the prospect to use marine energy to power ocean platforms, a double-wing wave energy converter suitable for power supply for them is proposed. Based on the mechanical structure and hydrodynamic parameters of the system, the frequency-domain dynamic model is established. According to the Cummins equation and the state space identification of the convolution term of the radiation force, the time-domain simulation of the system excited by wave is built. In addition, a 1:10 scaled prototype is manufactured and a tank experiment is carried out to study its performance. The accuracy of the simulation model is verified with the comparison between experimental and simulation results. The experimental results show that the power output of the prototype reaches 0.74 W under the regular wave with a period of 2.0 s and a wave height of 16 cm. Finally, adopting the similarity theory, the power output of the full-size system is calculated to be 2340.09 W. This study provides new ideas for solving the energy supply problem of ocean platforms.

Fast absolute 3D CGO-based electrical impedance tomography on experimental tank data

Objective. To present the first 3D CGO-based absolute EIT reconstructions from experimental tank data. Approach. CGO-based methods for absolute EIT imaging are compared to traditional TV regularized non-linear least squares reconstruction methods. Additional robustness testing is performed by considering incorrect modeling of domain shape. Main Results. The CGO-based methods are fast, and show strong robustness to incorrect domain modeling comparable to classic difference EIT imaging and fewer boundary artefacts than the TV regularized non-linear least squares reference reconstructions. Significance. This work is the first to demonstrate fully 3D CGO-based absolute EIT reconstruction on experimental data and also compares to TV-regularized absolute reconstruction. The speed (1–5 s) and quality of the reconstructions is encouraging for future work in absolute EIT.

Full-Duplex UAC Receiver With Two-Sensor Transducer

In this brief we present a design of a full-duplex (FD) underwater acoustic communication (UAC) receiver with a two-sensor transducer. The transducer consists of two piezo-ceramic cylinders cast together in polyurethane resin; one acts as a hydrophone and the other a projector. As the distance between the projector and hydrophone is extremely short, a high level of self-interference (SI) from the projector is received at the hydrophone. This SI must be eliminated to enable far-end data demodulation. In this brief, we adopt a digital SI cancellation scheme based on adaptive filtering. We investigate the SI cancellation and far-end data demodulation performance with the two-sensor transducer in tank and lake experiments. The Rake receiver is used for the far-end data demodulation. As demonstrated by the experimental results, the far-end SNR loss in the FD experiment is less than 3 dB compared to the half-duplex experiment when there is only far-end transmission.

Biomimetic Robotic Sea Lion Foreflippers: Design, Modeling, and Experimentation

Otariidae are excellent swimmers and the only ones among the marine mammals that use foreflippers for propulsion. Taking California sea lion as the bionic prototype, this article proposed and developed a biomimetic robotic sea lion foreflipper device (robotic flipper for short), which is composed of a pair of bionic flippers and a serial mechanism consisting of a wobbling coin mechanism and a RSSR spatial crank-rocker mechanism. The attitude and motion characteristics of the bionic flipper were obtained based on the kinematic analysis of the robotic flipper. Kinematic analysis and tank experiments show that the robotic flipper can effectively imitate the motion characteristics of the sea lion foreflipper. In addition, it can also obtain different flipper tip trajectories by adjusting the length of the connecting rod of the RSSR mechanism, and the generated thrust from the trajectory like sea lion foreflipper is larger than that from other flipper tip trajectories. A higher clapping frequency can generate a higher thrust, and the bionic flexible flipper has higher thrust and thrust efficiency than the rigid one. A larger pitch angle of the robotic flipper can result in a larger peak thrust but not always a larger average thrust. The present robotic flipper shows a better thrust performance at the pitch angle of 15°.

Изменение конструкции малого опытового бассейна для комплексных испытаний подвесных лодочных моторов

When studying the characteristics of the outboard motors with capacity of more than 10 kW weighing over 100 kg at full equipment, the Department of Water Transport Operation of Astrakhan State Technical University needed to change the design of a small experimental tank. Previously, the small experimental tank was adapted for testing outboard motors with capacity not exceeding 8 l/s - 6 kW and weight up to 25 kg having such technical indicators as the screw stop, the developed power of the outboard motor, tank water temperature, exhaust gas temperature, fuel consumption, rate of heating the aquatic environment during the engine operation, the number of revolutions 
 of the engine crankshaft, the number of revolutions of the screw, with possibility of environmental studies of noise levels, vibration levels, as well as harmful discharges and exhaust emissions of outboard motors by sampling water and gases. In addition to sensors and devices designed to measure technical and environmental indicators, the small experimental tank was previously equipped with an auxiliary equipment: supply and exhaust ventilation, a water level gauge in a basin tank, a steam compressor refrigeration unit, a water supply and drainage system with sampling fittings, a gas sampling probe, a rotary rod for installing a noise meter, a platform with steps, general and local lighting fixtures. There has been illustrated a layout of an experimental tank covered with heat-insulating paint from the outside. In the course of changing the structure there was installed a lifting boom and an external transom. The tank bowl was upgraded by installing a bypass pipe. The described technical solutions have expanded the possibilities of the small experimental tank in conducting the research on outboard motors.

Multiple‐input multiple‐output sonar adaptive beamforming using transmission diversity smoothing and backward processing

AbstractBenefit from the transmission diversity smoothing (TDS) effect upon coherent targets decorrelation, the kind of adaptive beamformers can be directly applied for multiple‐input multiple‐output (MIMO) sonar applications. Increasing the number of transmitted signals helps improve the TDS‐based decorrelation performance. However, a large number of transmitters is not feasible for those sonar systems mounted on small platforms with limited space. To address the lack of TDS‐based degrees of freedom for smoothing, an improved TDS decorrelation method is proposed for MIMO sonar in this study. With the conjugated MIMO data covariance matrix being left‐multiplied and right‐multiplied, respectively, by the exchange matrix, the authors obtain a backward‐smoothed data covariance matrix. Afterwards, the authors average it with the original MIMO receiving data covariance matrix to reconstruct a new data covariance matrix. Compared with TDS, the improved TDS strengthens the decorrelation performance by increasing the number of covariance matrix for smoothing and thus enables the new rank restored signal covariance matrix to have better non‐singularity. Without increasing any aperture loss and system complexity, a lower correlation between echoes is obtained, and the performance of the minimum variance distortionless response beamformer is hence improved in the presence of coherent targets. The effectiveness of the proposed decorrelation method is verified by numerical simulations and real data from a water tank experiment.

Numerical and Experimental Analysis of the Velocity Field Inside an Artificial Reef. Application to the Ares-Betanzos Estuary

The placement of artificial reef (AR) units on the seabed modifies the velocity field of the water, making the nutrients circulate properly and creating the necessary habitat for the settlement of the desired species. This paper proposes a methodology for determining the circulation in the vicinity of one specific AR unit module previously defined in the existing literature. This has been based on both the application of three-dimensional hydrodynamic criteria and computational fluid dynamics (CFD) together with their validation using towing tank tests. In order to achieve the goals, the starting points are both the initial design of the AR units and the 3D hydrodynamic circulation model in the estuary. The latter predicts the nutrient supply to each module by taking into account the variation of speeds with height. From the vertical profile of circulation velocities, developed for each implantation site, a CFD tool is used to determine the circulation of nutrients in the vicinity of the AR unit, around 5 times the AR size. Then, the results are validated by carrying out towing tank experiments. The main contribution is to combine a circulation model of the estuary together with a CFD model validated with towing tank tests. Although this work was applied to the Ares-Betanzos estuary, it can be extrapolated to other zones worldwide.

Free vibration and stability of a fully submerged pipe aspirating water: An experiment and new physical insights

Dynamic stability due to internal axial flow is a considerable problem for a pipe conveying fluid such as deep seawater intaking for an Ocean Thermal Energy Conversion (OTEC) plant. However, there has been much ambiguity about its dynamics, and this raises a question about whether such an aspirating pipe submerged in water flutters or not. Therefore, the objective of this paper is to provide an experiment to take a new look at the dynamics of pipe aspirating fluid (water). The experimental apparatus is constructed to eliminate expected disturbances, and we measure free damped vibrations of a submerged 4 m length pipe with internal flow. As a result, we observe the nonlinear and non-planar behavior, however, the pipe converges to the zero point and remains stable at a maximum velocity of 1.66 m/s. Subsequently, we review existing theoretical models, and present a comparison with the results from the tank experiment. In addition, we provide a new model of the inlet flow field, which plays an important role on stability, considering the flow separation and jet formed inside of the pipe entrance. This equation is solved by FEM for time integration and eigenvalue analysis, and the results seem to reproduce the experimental natural period and amplitude of the free vibration with internal flow. The model also suggests that an aspirating pipe submerged in water does not flutter up to the maximum flow velocity attainable in the experiment.

Modeling and evaluation of NAPL-impacted soil vapor intrusion facilitated by vadose zone breathing

The water table fluctuations can cause a reciprocating advection of soil gas in the vertical direction, known as vadose zone breathing. In this study, we developed a vadose zone breathing-facilitated vapor intrusion (VI) model and applied it to evaluate the influence of NAPL (non-aqueous phase liquid)-impacted soils. The developed model was first validated with data from previously conducted sand tank experiments and then used to simulate VI scenarios involving different fluctuation amplitudes and periods of the water table, soil types, building structures, and source depths. Our results suggest that within one month of vadose zone breathing (amplitude of 0.5 m and period of 4 d), the indoor pollutant concentration varies by approximately seven orders of magnitude, and the averaged concentration is nearly nine times larger than the steady-state concentration. The results also show that with the increase of mean soil particle size, the indoor pollutant concentration tends to increase and becomes more sensitive to vadose zone breathing; compared to the basement foundation, buildings with a slab-on-grade foundation are less susceptible; when the source depth exceeds 10 m, the source depth plays an insignificant influence. Our findings highlight that vadose zone breathing can promote the VI risks of buildings with a basement foundation at sites with shallow water tables, significant groundwater fluctuations, and coarse-textural soils.

Underwater variable frequency vibrating dipole detection of artificial lateral line based on the joint time-frequency analysis

Inspired by the lateral line system (LLS) of fish, an underwater pressure sensor array, aka, artificial lateral line system (ALLS) was proposed for underwater perception. The Fourier transform (FT) was the most widely used method to extract features from the ALLS signals. However, the FT lost efficacy when the vibrating condition of the dipole such as frequency varied over time. To overcome this problem, four joint time-frequency analysis (JTFA) methods were employed to transform the original pressure signal into the frequency domain and time domain. The short-time Fourier transform (STFT) and wavelet transform (WT) showed better performance in the dipole vibrating frequency evaluation. Later, the results of JTFA were input into a convolutional neural network (CNN) model to identify the motion pattern and position of the dipole. In this paper, different frequency rise/drop duration represented different motion patterns of variable frequency dipole. The position of the dipole indicated the coordinate of the dipole relative to the ALLS. The experiment result showed that the identification result of dipole motion pattern and position could reach 99.93 % and 2.134 mm respectively. Lastly, the ALLS pressure signals were discussed under the external flow and multiple dipole targets based on the tank experiment and computational fluid dynamics (CFD) simulation. The pressure drifting generated by the external flow was affected by both the flow velocity and the water depth variation. The distinction between JTFA results of different ALLS sensors exhibited correspondence with the state of multiple dipoles. The underwater feature extraction method of ALLS signal based on the JTFA proposed in this paper showed a promising way in the perception of the target in more challenging motion states.

Growth assessment of pure bred Clarias gariepinus (Burchell, 1822), Heterobranchus longiflis (Valenciennes, 1840), Heterobranchus bidorsalis (Geoffrey Saint Hillarie, 1809) and their Hybrids

This study examined the growth performance of pure bred Clarias gariepinus, Heterobrachus spp and their hybrids. The broodstocks of the species were selected and used for breeding in the Hatchery. The crosses (treatments) were pure C. gariepinus (T1), Heterobranchus longifilis (T2), Heterobranchus bidorsalis (T3), C. gariepinus x H. longifilis (T4), C. gariepinus x H. bidorsalis (T5). 900 fingerlings of 32 days old were randomly selected from each of the five crosses and stocked separately in triplicate using experimental tanks. T1 recorded the lowest significant (p0.05) in FW, WG, DGR and DGR among T2, T3, T4 and T5 but T5 had the highest values. The combination of female C. gariepinus x male H. bidorsalis (T5) will be more suitable for fish farming business.

Impact of Garlic (Allium sativum) on Glycogen Level of Fresh Water Fish Channa Striatus (Bloch, 1793)

The present work was conducted to study the effect of garlic (Allium sativum) on glycogen content of fresh water fish Channa striatus. Live specimens of Channa striatus were collected from local market of Amravati city. The controlled fishes were fed with normal diet and experimental fishes were fed with garlic pellets. Fishes were randomly selected from each control and experimental tanks, anesthetized, sacrificed after day 7, 14 and 21days and muscle tissue were taken for glycogen estimation. The glycogen levels in the muscle of the controlled and experimental fishes were estimated by Nelson-somogy’s method. The glycogen level of controlled and experimental was compared. The present investigation indicated that the glycogen contents in muscle of experimental fish decreased 29.07±0.833, 26.18±0.904, 23.78±1.784 as compared to control 30.45± 1.18, 28.73±0.591 and 30.33±0.498. Thus, Allium sativum fed to Channa striatus showed significant decreased in the glycogen level of muscle tissue.

An RF Amplifier Circuit for Enhancement of Echo Signal Detection in Bathymetric LiDAR

The echo signal from the water bottom in bathymetric light detection and ranging (LiDAR) onboard unmanned boat is very weak. As a result, the signal’s amplitude cannot be resampled using an analog-to-digital (AD) sampling module after being detected by the photomultiplier tube (PMT). In addition, the traditional methods, which adopt the trans-impedance circuit, cannot provide sufficient gain and bandwidth, resulting in incorrect detection of echo signals. For the reasons above, this article presents an radio frequency (RF) amplifier circuit for signal amplification, in which a dc paranoid network associated with a matching circuit is used to ensure the stable operation of the circuit; the ac-coupled and low-noise voltage stabilizers are adopted to ensure a low-noise signal output; the shielding is adopted to suppress the interference of electromagnetic fields and static electricity. The validations are conducted in indoor and outdoor laboratories, including a simulated amplitude and bandwidth using a signal generator in the indoor laboratory, the water tank, the test well, the pond, and the pool. The experimental results show that the proposed RF amplifier circuit can amply the gain of 25.31 dB when using a signal generator in the bandwidth range of 500 MHz, 650 MHz, and 800 MHz; 1 GHz; and 34.63, 31.62, and 25.78 dB under the experiments in the water tank, in the test well, and in the pond when the PMT control voltages are 0.4, 0.5, and 0.7 V, respectively, and amplify the echo signals to 451–568 mV under the bandwidth of 500 MHz.

Analysis of the rigid-body fluid–structure interaction on a log boom

Log booms are modular and floating structures that partially cross the hydroelectric power plant reservoir to retain and deflect floating objects in the river that can damage and clog the turbine and reduce energy availability. In rivers with a high volume of logs or vegetation, the correct design of these structures is essential to ensure the operability of the hydroelectric power plant. In order to aid in the design of log booms, this paper proposes a method to predict the hydrodynamics forces and movement of log boom lines using CFD tools. Due to the high computational cost of simulating the entire line, simulations are conducted only on a single log boom module using boundary conditions that simulate the interference effects from its adjacent ones, considering different velocity magnitudes and direction combinations. The individual module results are composed to obtain the expected forces on the log boom line. A towing tank experiment with a model-scale model of a segment of the log boom line is conducted to verify the reliability of the numerical model results, comparing the module movement (heave and pitch) and line extremity tension forces. The agreement between numerical and experimental approaches shows that the proposed method can be used to predict the tension in the log boom line and evaluate other conditions, log boom geometries, or line shapes.

CFD-FEM Simulation of Slamming Loads on Wedge Structure with Stiffeners Considering Hydroelasticity Effects

In this paper, both numerical and experimental methods are adopted to study the fluid–structure interaction (FSI) problem of a wedge structure with stiffeners impacted with water during the free-falling water entry process. In the numerical model, a partitioned two-way couple of CFD and FEM solvers is applied to deal with the FSI problem, where the external fluid pressure exported from the CFD simulation is used to derive the structural responses in the FEM solver, and the structural deformations are fed back into the CFD solver to deform the mesh. Moreover, a tank experiment using a steel wedge model that has the same structural properties is also conducted to compare with the numerical results. Verification and validation of the numerical results indicate that the CFD-FEM coupled method is feasible and reliable. The slamming response results by numerical simulation and experiments, including displacement, velocity, acceleration, slamming pressure, deformation, structural stresses and total forces on the wedge, accounting for hydroelasticity effects in different free falling height conditions are comprehensively analyzed and discussed.

Broken Ice Photogrammetry in Model-Scale Experiments with Sloped Structure

Testing a physical model of an ice-resistant marine structure in an ice tank is one of the methods used for design validation. For a stationary structure design, not only is the possible global ice load of interest but also the processes of creation and evolution of ice rubble in front of the contacting surface. While the load registering technique in model-scale experiments is very well-developed, the photogrammetric analysis of broken ice morphometry and locomotion is not. The photographs taken to illustrate the breaking process do not usually accompany the information necessary for the photogrammetric reconstruction of the scene. This paper outlines a systematic approach to the photogrammetric analysis of the scenes in model-scale conditions. Using this approach, the broken ice dimensions were measured in seven model-scale experiments for which the model of a sloped marine structure was reconstructed. In these experiments, a 700 mm wide slope with an inclination angle of 53° caused an upward flexural failure of the model’s granular ice. Reference global load histories for these experiments are provided. For the first contact episodes, the successful reconstruction of the broken ice mosaic in the polynya showed the insignificant contribution of compressive failure. In continual ice–structure interaction, the morphometry of the ice blocks visible on the slope of the rubble pile and on the surface of the surrounding ice sheet was retrieved from orthorectified video frames. The results were compared with the after-test nadir drone view of the polynya. The error in estimating the top-side area and the maximum linear dimension of the ice block fell into the interval of 0–10%. The morphometric information of the broken ice floes obtained in ice tank experiments with physical models can be used for the improvement of the mechanical models of ice fracture and failure against inclined offshore ice-resistant structures.

Extreme wave excitation from localized phase-shift perturbations.

The modulation instability is a focusing mechanism responsible for the formation of strong wave localizations not only on the water surface, but also in a variety of nonlinear dispersive media. Such dynamics is initiated from the injection of sidebands, which translate into an amplitude modulation of the wave field. The nonlinear stage of unstable wave evolution can be described by exact solutions of the nonlinear Schrödinger equation(NLSE). In that case, the amplitude modulation of such coherent extreme wave structures is connected to a particular phase-shift seed in the carrier wave. In this Letter, we show that phase-shift localization applied to the background, excluding any amplitude modulation excitation, can indeed trigger extreme events. Such rogue waves can be for instance generated by considering the parametrization of fundamental breathers, and thus by seeding only the local phase-shift information to the regular carrier wave. Our wave tank experiments show an excellent agreement with the expected NLSE hydrodynamics and confirm that even though delayed in their evolution, breather-type extreme waves can be generated from a purely regular wave train. Such a focusing mechanism awaits experimental confirmation in other nonlinear media, such optics, plasma, and Bose-Einstein condensates.

Study on the Relationship Between Ship Resistance and Trim, Supported by Experimental and Software-Based Analysis

In this study, towing tank experiments have been carried out for a container ship under different trim-draft conditions. Experimental results have been interpreted together with the results of the Holtrop method used in both Maxsurf and Orca to identify reactions to changing trim conditions. The study has shown that towing tank experiment findings differ from other relevant findings. The ship shows different resistance characteristics under different trim conditions, but generally the least resistance without trim. In addition, the total resistance change at ship design speed was found to be up to 18% higher in the trim by aft condition. We believe that study findings will help better understand the constantly changing resistance variable depending on draft, speed, and trim conditions.