Tank Experiments Research Articles

Simulation and experimental research on hydrodynamic performance of fully attached submarine in the surface and near the surface modes

The switch between the surface and near-surface modes is critical to the hydrodynamic performance of the submarines. In this study, based on tank experiments, an improved delayed detached-eddy simulation (IDDES) method based on the shear stress transport (SST) K-Omega was tested for its ability to predict the hydrodynamic coefficients of submarines with satisfactory results. By expanding the simulation range, the changes in the hydrodynamic performance of the submarine on and near the water surface were analyzed with respect to force coefficient, flow field, maximum wave height, and maximum ray angle. The change in the drag coefficient of the hull has a water surface mode and near-water surface mode, which leads to a peak value of the drag coefficient at different submerged depths. When a "hump" phenomenon occurs at high Froude number(Fr = 0.5), the flow separation at the stern shoulder of the hull weakens, resulting in an increase in wake velocity and ray angle. The numerical simulation results showed that the Rabaud and Moisy model has better applicability, but when Fr > 0.8 and Hd > 1.5, the theory underestimates the maximum ray angle.

Experimental study on the motion reduction performance of a small suspension catamaran exploiting an active skyhook control strategy

A nine degrees of freedom suspension catamaran has been developed. The ship is so designed that the heave, pitch, and roll motions of the cabin are separable from those of the twin-hull. One brushed DC motor/generator (M/G) is employed at each of the four suspending locations to produce control force. An active skyhook control strategy utilizing proportional-only control is proposed to calculate the desired control input to reduce the cabin’s local vertical velocity and thus improve ride comfort. The mechanical responses of the suspension unit and the performance of the control system are verified through a group of bench tests. The ship motion responses in regular waves are investigated through a series of towing tank experiments. It is found that the proposed control strategy had significant effectiveness on motion reduction of heave and pitch of the cabin in head waves, but a small contribution to the roll motion reduction in beam waves except in the vicinity of the cabin’s natural roll frequency. In head waves, the average motion reduction ratios of the heave and pitch of the cabin both exceeded 50% at zero forward speed, which at 1.5m/s were 39% and 71%, respectively. In beam waves, the average motion reduction ratios of the heave and roll of the cabin were 62% and −57%, respectively.

Experimental assessment of a nonlinear, deterministic sea wave prediction method using instantaneous velocity profiles

This paper presents the experimental proof-of-concept of a nonlinear, deterministic wave prediction method. The method is based on the adapted version of the HOS-NWT wave model and uses wave-induced velocity profiles as input information on the sea state. Unlike most HOS approaches, it does not need any optimization procedure or data assimilation step to initialize the simulation. Wave tank experiments were conducted to validate the method for irregular, long-crested waves with a low significant steepness. Data was collected using wave probes, an ADV and the fifth beams of two ADCP sensors set-up with a High-Resolution mode. Despite challenging experimental conditions for the ADCPs, the method proved able to reconstruct reliable instantaneous horizontal velocity profiles from the acoustic sensor measurements. These profiles were used as boundary conditions in the wave prediction model. The sea surface elevation predicted was compared to wave probe measurements and showed good agreement all over the theoretical prediction area.

The influence of dihedral bulbous bows on the resistance of small fishing vessels: A numerical study

Environmental aspects in the shipping industry are nowadays taking more relevance. Independently of the type of fuel used, good drawing lines in ships might help with the emission mitigation and also with the ship efficiency. In the fishing industry, ships lines in non-developed countries and in small traditional ships are normally not optimized what leads to a no optimal use of the resources and operation. In this work this topic is treated. The lines of two fishing vessels are studied numerically and compared with towing tank experiments. Those lines from a displacement and a semi-displacement hull, are optimized by adding a new type of bow named as dihedral bulbous bow. This bow produces a reduction over 10% of the ship’s resistance. This work focuses on explaining numerically why that difference occurs. The bulbous bow reduces the pressure resistance by softening the flow that reaches the bow.

Research on Wake Field Characteristics and Support Structure Interference of Horizontal Axis Tidal Stream Turbine

The harnessing and utilization of tidal current energy have emerged as prominent topics in scientific inquiry, due to their vast untapped resource potential, leading to numerous investigations into the efficacy of hydrokinetic turbines under various operational conditions. This paper delineates the wake field characteristics and performance of horizontal axis tidal stream turbines under the influence of support structures, using a comprehensively blade-resolved computational fluid dynamics (CFDs) model that employs Reynolds-averaged Navier–Stokes (RANS) equations in combination with the RNG k-ε turbulence model. To achieve this, the study utilized experimental tank tests and numerical simulations to investigate the distribution characteristics and recuperative principles of the turbine’s wake field. The velocity distribution and energy augmentation coefficient of the wake field showed strong agreement with the experimental results. To further assess the effect of support structures on the flow field downstream of the unit and its performance, the hydrodynamic attributes of the turbine wake field were analyzed with and without support structures. The interference elicited by the support structure modified the velocity distribution of the near-wake flow field, resulting in a 4.41% decrease in the turbine’s power coefficient (Cp), significantly impacting the turbine’s instantaneous performance.

A Scaled Tank Experiment for the Stochastic Rough Interface Scattering

Bottom reverberation is an important limitation that affects the detection performance of active sonar in shallow water. The stochastic rough seafloor surface scattering is one of the main scattering sources of the bottom reverberation. Since there are much uncertainties, such as propagation fluctuation, unstable station of transmit and receive equipment, it is difficult to investigate the quantitative relationship between the random rough interface parameters and the statistical property by processing the experimental reverberation data collected in the ocean In this paper, the statistical characteristics of the irregular 3D printed interface scattering field are studied by a scaled tank experiment, and the detailed results are presented by the comparison between the COMSOL simulations and the recorded data, the feasibility of the random rough interfaces experiment is verified well. Because the relationship between parameters is precisely controllable, it lays a foundation for the subsequent experimental research of target extraction under the background of interface scattering.

Thermo-hydraulic characteristics of thermal interface induced by natural convection in water tank with internal heat source

Large-scale water tank or pool with internal heat source is common structures in solar energy and nuclear power. In this paper, a visible thermal interface is captured in the experiments in a square water tank with a horizontal heating rod, which is an interesting phenomenon hardly reported before. The direct shadowgraphy method is employed to record gray graphs of the forming process and flow regimes of the thermal interface. Corresponding transient numerical simulations with the large eddy simulation (LES) method are conducted to display detailed thermo-hydraulic characteristics of the thermal interface. Based on the temperature distribution and flow field, a natural convection circulation driven by buoyancy is formed above a stagnant zone, which is regarded as a two-layer stratified shear flow. The horizontal shear flow above the stagnant zone induces the visible thermal interface. Because the heat transfer mode switches from convection to conduction when crossing the interface, the sharp temperature gradient and density variation occur at the interface. The effect of the heat flux of the heating rod is investigated, and three different flow regimes of the thermal interface are observed under different heat loads. The stability of the flow regimes is analyzed by the gradient Richardson number, which is the ratio of the buoyancy to the turbulent shear. At low heat load, the thermal interface is destabilized because the turbulent shear overcomes the density barrier. As the heat loading increases, the buoyancy increasing rate exceeds the shear increasing rate, and the stronger potential barrier dominates the flow structure, which is beneficial to the interface stability.

High-resolution geologic modeling and CO2 flow simulation of a realistic clastic deltaic 3D model derived from a laboratory flume tank experiment

Carbon sequestration in geologic reservoirs is a proven method for reducing carbon dioxide (CO2) emissions from industrial point sources. Subsurface deltaic deposits are attractive candidates for CO2 storage projects due to their common occurrence as host to significant hydrocarbon and hydrologic resources, and are highly prospective for subsurface storage of large volumes of CO2. This research informs subsurface passive margin deltaic reservoir characterization and fluid flow performance for geologic carbon storage. The objective of this research is to create a high-resolution geocellular digital model that honors both the large-scale stratigraphic architecture and local vertical and lateral facies heterogeneity represented in deltaic environments of deposition. We present a novel approach to reservoir model generation by utilizing a previously generated meter-scale physical flume sand tank analog experiment to represent realistic deltaic stratigraphic architectures and facies distributions. The result is an extremely high-resolution geologic model that can be used for a variety of applications, including single and multiphase fluid flow simulation. An application is presented using the example model to simulate buoyant fluid (CO2) migration and resulting saturation distribution. Results emphasize the importance of recognizing sequence stratigraphic architectures in deltaic depositional settings for predicting CO2 migration and retention (storage capacity).

Susceptibility of whiteleg shrimp (Litopenaeus vannamei) to Vibrio parahaemolyticus strain VP36 at different salinities

ABSTRACT This study aimed to evaluate the susceptibility of whiteleg shrimp (Litopenaeus vannamei) to Vibrio parahaemolyticus, a causative agent of acute hepatopancreatic necrosis disease at different salinities. Experimental shrimp were stocked at 40 individuals/tank containing 40 L of 15 ppt seawater. Salinities in the experimental tanks were adjusted to 10, 20, 25, 30, and 35 ppt, and remaining tanks (15 ppt) used as controls. The water temperature was maintained at 28°C. Three days after acclimatization to different salinities, shrimp were challenged with V. parahaemolyticus. Ten days after challenge, shrimp growing in 35 ppt salinity showed higher cumulative mortality than shrimp growing in 10 ppt. No significant difference occurred among the groups exposed to 15, 20, 25, and 30 ppt salinity. The median lethal time of challenged shrimp was 25.31 ± 4.06 hours at 35 ppt and significantly shorter than at 10 ppt (161.19 ± 4.60 hours) and at 15 ppt (91.30 ± 4.25 hours). The results suggest that whiteleg shrimp juveniles are more susceptible to V. parahaemolyticus when reared at 35 ppt salinity than at lower salinities.

Comparative study on gamma-ray detectors for in-situ ocean radiation monitoring system

Large-sized crystals and state-of-the-art photosensors are desirable to cope with low environmental radioactivity (e.g., 1–2 Bq∙m−3137Cs in surface seawater) for homeland security purposes. We compared the performances of two different gamma-ray detector assemblies, GAGG crystal + silicon photomultiplier (SiPM) and NaI(Tl) crystal + photomultiplier tube, for our mobile in-situ ocean radiation monitoring system. We performed energy calibration, followed by water tank experiments with varying the depth of a137Cs point source. Experimental energy spectra were compared with MCNP-simulated spectra with identical setup and the consistency was validated. We finally assessed the detection efficiency and minimum detectable activity (MDA) of the detectors. Both GAGG and NaI detectors exhibited favorable energy resolutions (7.98 ± 0.13% and 7.01 ± 0.58% at 662 keV, respectively) and MDAs (33.1 ± 0.0645 and 13.5 ± 0.0327 Bq∙m−3 for 24-h 137Cs measurement, respectively). Matching the geometry of the GAGG crystal with that of the NaI crystal, the GAGG detector outperformed the NaI detector. The results demonstrated that the GAGG detector is potentially advantageous over the NaI detector in detection efficiency and compactness.

Modeling of a hinged-raft wave energy converter via deep operator learning and wave tank experiments

Model identification for a hinged-raft wave energy converter (WEC) is investigated in this paper, based on wave tank experiments and deep operator learning. Different from previous works which all formulated this issue as a function approximation task, this work, for the first time, formulates it as an operator approximation task (which learns the mapping from a function space to another function space). As such, a continuous-time WEC model is identified from data, greatly expanding the horizon of data-based WEC modeling because previous works were limited to discrete-time model identification. The error accumulation for multi-step predictions in the discrete-time formulation is thus also addressed. The model is developed by first carrying out a set of wave tank experiments to generate the training data, and then the deep operator learning model, i.e. the DeepONet, is constructed and trained based on the experimental data. The validation study shows that the model captures the WEC dynamics accurately. A new set of experimental runs are further carried out and the results show that after training, the model can be used as a digital wave tank, an alternative to the expensive numerical and physical wave tanks, for accurate and real-time simulations of the WEC dynamics.

Tide-induced infiltration and resuspension of microplastics in shorelines: Insights from tidal tank experiments

In the present study, the infiltration and resuspension of microplastics (MPs) in a slope substrate under the influence of repeated tidal forces were investigated using a tidal tank. In the scenario in which MPs were placed on the top of the slope, increasing numbers of particles were observed on the water surface with the increase in tidal cycles. More particles of smaller equivalent particle diameter (dMP) and low density floated to the water surface. The horizontal positions (positive toward the lower tide zone) of MPs showed significant positive correlation with the shortest length c of MPs, MP density, MP weight, dMP, and Corey shape factor, whereas they showed significant negative correlation with the rate of tidal level change and the longest length a of MPs. The vertical positions (positive in the downward direction) of MPs showed significant positive correlation with the shortest length c of MPs, MP density, MP weight, dMP, and Corey shape factor, while they demonstrated significant negative correlation with the largest cross-section area and surface tension of MPs. In the scenario in which MPs were placed at the bottom of the tank, the smaller and low-density particles had a higher possibility of moving upward to the water surface under repeated tidal forces. High-density particles also migrated to the water surface due to the surface tension force. Further, a lower rate of tidal level change contributed to more floating of particles. The horizontal positions of MPs showed significant positive correlation with MP density, while they demonstrated significant negative correlation with the largest cross-section area and surface tension of MPs. The vertical positions of MPs showed significant positive correlation with the longest length a of MPs, MP density, MP weight, and dMP. These results imply that large, high-density, and less flatty particles tend to be distributed in the lower tidal zone and deeper substrate layers. These findings can help understand the redistribution of MPs and assess their risk in the shoreline environment.

Insights from sloshing experiments in a rectangular hydrophobic tank

The wave impingement on the side walls due to the oscillation of a rectangular tank under harmonic sway motion is analysed experimentally with hydrophobic coated and uncoated tank surfaces. Impact pressures and free surface deformations are compared in three water filling levels over an excitation frequency range encompassing the first natural frequency. The reduced hydrodynamic loads acting on the tank walls are observed under hydrophobic effects and discussed in detail. Experimental observations clearly indicate that there is a strong effect of the solid surface properties on the free surface elevation, wave generation and pressure distribution. In particular, major changes have been traced around the resonance frequency due to more dominant tangential flow and altered wave form, which results in lower peak pressure values with increased water movement within the tank under the hydrophobic effects.

Effects of surface tension reduction on wind-wave growth and air–water scalar transfer

Effects of surface tension reduction on wind-wave growth are investigated using direct numerical simulations of air–water two-phase turbulent flows. The incompressible Navier–Stokes equations for air and water sides are solved using an arbitrary Lagrangian–Eulerian method with boundary-fitted moving grids. The wave growth of finite-amplitude and non-breaking gravity–capillary waves, whose wavelength is less than 0.07 m, is simulated for two cases of different surface tensions under a low-wind-speed condition of several metres per second. The results show that significant wave height for the smaller surface tension case increases faster than that for the larger surface tension case. Energy fluxes for gravity and capillary wave scales reveal that when the surface tension is reduced, the energy transfer from the significant gravity waves to capillary waves decreases, and the significant waves accumulate more energy supplied by wind. This results in faster wave growth for the smaller surface tension case. The effect on the scalar transfer across the air–water interface is also investigated. The results show that the scalar transfer coefficient on the water side decreases due to the surface tension reduction. The decrease is caused by suppression of turbulence in the water side. In order to support the conjecture, the surface tension effect is compared with laboratory experiments in a small wind-wave tank.

Experiment and Simulation of the Shape and Stored Gas Characteristics of the Flexible Spherical Airbag for Underwater Compressed Air Energy Storage

Underwater compressed air energy storage (UCAES) is an advanced technology used in marine energy systems. Most components, such as turbines, compressors, and thermal energy storage (TES), can be deployed on offshore platforms or on land. However, underwater gas-storage devices, which are deployed in deep water, have specific characteristics. Flexible inflatables have become a viable alternative for underwater compressed air energy storage (UCAES) as air storage devices. Few studies have been conducted on the characteristics of partially inflated structures during the inflating and deflating processes. A tank experiment of a 1 m model of an underwater spherical airbag was performed to investigate the characteristics of the deformed shape, pressure, and volume of the stored compressed air. A finite element (FE) simulation of an airbag model with the same dimensions was established in Abaqus/Explicit. The simulation under shallow testing conditions was in good agreement with the experimental results. Furthermore, studies on the performance of a 4 m airbag prototype with different water depths are presented. The results indicated that the shape variation was only related to the volume (inflation ratio). The pressure varied approximately linearly with the inflation ratio during the quasi-static process from an empty shape to a zero-pressure shape. The operating depth had a slight effect on the deformation. Because the scaling factor influences the pressure difference of the surface at the same height proportion, the larger the dimensions of the airbag, the higher the pressure difference will be.

Stability and Migration Characteristics of SDS and SiO2 Colloidal Gas Aphron and Its Removal Efficiency for Nitrobenzene-Contaminated Aquifers

The instability of colloidal gas aphrons (CGAs) in aquifers is one of the major obstacles influencing the remediation efficiency of CGAs-flushing. In this study, hydrophobic nano-SiO2 (HN-SiO2) was utilized to enhance the stability of CGAs. The batch experiments were carried out to investigate the effect of hydrogeochemical conditions on the stability of HN-SiO2 stabilized CGAs in aquifers, such as ions, pH, and nitrobenzene (NB); 2-D tank experiments designed with various injection velocities and medium particle sizes were conducted to determine the factors influencing the migration of CGAs in the aquifer; and 1-D column experiments were established to evaluate the remediation efficiency of HN-SiO2 stabilized CGAs flushing for NB removal. The results indicated that HN-SiO2 had a favorable effect on the stability of CGAs, which enhanced the half-life of CGAs from 328 to 1,050 s. HN-SiO2 particles formed a shell film on the gas-liquid interface of CGAs to slow down the gas escape and drainage velocity. The stability of CGAs decreased while pH<6 or pH>8, whereas this was enhanced with the addition of 0.1 wt.% NaCl. The 2-D tank experiments demonstrated that the HN-SiO2 stabilized CGAs had better stability when they flowed in aquifers compared to sodium dodecyl sulfate (SDS) CGAs. The fine medium and high injection velocity facilitated CGAs forming the larger radius remediation area. The injection pressure was inversely proportional to the medium grain sizes, whereas directly proportional to the injection velocities. In addition, column experiments demonstrated the remediation efficiency of HN-SiO2 stabilized CGAs (81.7%) flushing for NB removal was higher than that of SDS CGAs (61.4%) flushing. Therefore, in comparison with SDS CGAs, HN-SiO2 stabilized CGAs were more efficient reagents for NB removal. CGAs-flushing technique using HN-SiO2 stabilized CGAs is feasible to remedy the contaminated aquifers.

Digestibility, Blood Profile and Enzyme Activity of Clarias gariepinus (Burchell, 1822) Fed Diets Containing Sweet Potato Peel

This study evaluated digestibility, haematological indices and enzymes activities of Clarias gariepinus fed sweet potato peel as a replacement for maize. Five experimental diets were formulated at a crude protein of 35% using Pearson’s square method; maize was replaced by sweet potato peel in the diets at 0%, 25%, 50%, 75% and 100%. Fifteen plastic tanks of 200-litres each were used. 10 juveniles of C. gariepinus were introduced into the experimental tanks. The fish were fed at 5% biomass twice per day. The experiment lasted for 12 weeks. The fish fed 100% sweet potato peel gave the best digestibility coefficients contents of 43.17%, 65.44% and 95.12% for apparent ash, fat and protein digestibility, respectively. The fish fed 100% sweet potato peel recorded the highest packed cell volume of 27.75% in the blood while the least percentage of 23.21 was recorded in the fish fed 25% sweet potato peel. The lipase activity was highest (0.79U/mg) in the fish fed 100% sweet potato peel while the fish fed 25% sweet potato peel had the least (0.47U/mg). This research revealed that the enzymes activities were the main factors that activated the experimental fish to assimilate the sweet potato peel more efficiently.

Underwater Acoustic Positioning for Close Sources Using Time Division and Code Division Multiplexing

Underwater acoustic positioning system (UAPS) is used to know the positions of underwater robots and underwater structures. In ultra-short baseline (USBL) acoustic positioning systems, the three-dimensional position is determined by measuring the time difference of arrival (TDOA). In this paper, we investigate the acoustic positioning system targeting multiple sound sources and propose a simultaneous multi-point measurement method using time division and code division multiplexing (TD-CDM). TD-CDM provides higher position accuracy than code division multiplexing (CDM) and has a much shorter positioning time than time division and multiplexing (TDM). The effectiveness of TD-CDM has been proven by the results of the water tank experiment and simulation.

High‐angular‐ and range‐resolution imaging using MIMO sonar with two‐dimensional deconvolution

AbstractA real‐aperture high‐resolution imaging method utilising a multiple‐input multiple‐output (MIMO) sonar with two‐dimensional (2‐D) deconvolution processing is proposed. Via derivation, the authors show that the conventional beamformer (CBF) output of the MIMO sonar can be approximately expressed as the 2‐D convolution between the original angular and range distributions of scatterers and a 2‐D point spread function (PSF). Hence, to improve the imaging performance degraded by the convolution effect, the 2‐D Richardson‐Lucy (R‐L) algorithm is used to deconvolve the CBF output of the MIMO sonar. Specifically, the authors give the iteration formula of the 2‐D R‐L algorithm attached to the MIMO sonar, and take the absolute values of the CBF outputs of the virtual array as the deconvolution inputs. The analytical expression of the 2‐D PSF is also given, which is designed as the angular‐ and range‐domain (amplitude) responses of a far‐field ideal scatterer located in the normal direction of the virtual array. Meanwhile, the authors point out that the mismatch made by the approximation may degrade the imaging performance, and suggest that a small number of iterations in the 2‐D R‐L algorithm can be used to alleviate the mismatch problem. Via numerical simulations and a tank experiment, the authors show that the proposed method can simultaneously increase the angular and range resolutions and suppress the sidelobes, when compared to the existing MIMO sonar imaging method.

Dietary supplementation with soybean oil has not favored the tilapia growth in BFT tanks submitted to feeding restriction

The present work aimed at assessing the possibility of compensating the notorious deficiencies of bioflocs in lipids by supplementing the tilapia commercial diet with soybean oil. In the positive control, there was no feeding restriction nor dietary supplementation with soybean oil. In the experimental treatments, the commercial diet was restricted by 25% over the positive control level. In the negative control tanks, there was feeding restriction and the artificial diet had no oil supplementation. In the experimental tanks, soybean oil was mixed daily with the commercial diet at the levels of 0.6%, 1.2 and 2.4%. Additionally, there were fed-restricted tanks that received a daily supplementation of 1.2% soybean oil mixed with dry molasses, and not with the commercial diet. In general, only the restriction of the commercial diet affected the water quality. The supplementation of the artificial diet with soybean oil up to 2.4% has not improved the proximate composition of bioflocs, nor the fish growth performance. It was concluded that the strategy of supplementing the Nile tilapia juveniles’ commercial diet with increasing levels of soybean meal, in BFT tanks submitted to 25%-feeding restriction, was not capable of avoiding the fish growth performance deterioration.