Shallow Tank Research Articles

Detection of free-swimming fish passing through a narrow passage using MHz-band ultrasonic reflected and transmitted waves

In this study, we evaluated the validity of detecting free-swimming fish using echoes from the fish, transmitted waves, and backwall echoes propagated through the fish, using a pair of transducers with MHz-band ultrasound in a small, shallow water tank. The increases in the amplitudes and the numbers of peaks in the echoes, the decreases in amplitudes and time-of-flight in the backwall echoes and the transmitted waves were observed for each event in which the fish either stayed or passed between two transducers. We found that the point at which the fish were irradiated with ultrasound had a major effect on the properties of the measured ultrasound. We demonstrated that free-swimming fish passing or staying between two transducers could be detected via the MHz-band ultrasonic echoes from the fish and from the backwall and from the waves transmitted through the fish.

Data-Driven Parameter Estimation of Nonlinear Ship Manoeuvring Model in Shallow Water Using Truncated Least Squares Support Vector Machines

A data-driven method, the truncated LS-SVM, is proposed for estimating the nondimensional hydrodynamic coefficients of a nonlinear manoeuvring model. Experimental data collected in a shallow water towing tank are utilized in this study. To assess the accuracy and robustness of the truncated LS-SVM method, different test data sizes are selected as the training set. The identified nondimensional hydrodynamic coefficients are presented, as well as the corresponding parameter uncertainty and confidence intervals. The validation is carried out using the reference data, and statistical measures, such as the correlation coefficient, centred RMS difference, and standard deviation are employed to quantify the similarity. The results demonstrate that the truncated LS-SVM method effectively models the hydrodynamic force prediction problems with a large training set, reducing parameter uncertainty and yielding more convincing results.

Experimental investigation and simulation of water cooling by natural evaporation

A setup of water cooling by natural evaporation is investigated. It includes a shallow water tank, insulated and covered with a thin aluminum plate in complete contact with the water. A dark-color fabric was fixed stretched on the plate, which was continuously wetted to cause natural evaporation by solar radiation. The setup was placed on a building rooftop of the University of Patras, Greece. Measurements during a warm period showed significant decrease in water temperature maintained lower than ambient air temperature by 2–16°C, with differences greater than 5°C with 57% probability. Moreover, a computational model was developed and implemented. It is based on energy balance of the water in the tank using local climate recordings (air temperature, relative humidity, wind speed, and solar radiation). The water temperature predictions agree very well with the measurements (3.5% normalized rms deviation). Since the water temperature was always lower than the ambient air temperature, and the operating performance of the setup was high enough, this methodology could be developed for sustainable house cooling during the warmer seasons of the year. This system is environmentally friendly, economically feasible, and sustainable, as it uses water, wind, and solar energy, without emitting greenhouse gases. Statement of Industrial Relevance The proposed technology improves the process of passive water cooling through evaporation of a continuously wetted fabric without losing the cooled water. In parallel, a software was developed that simulated satisfactorily the process. We aim to further improve this technology to make it more easily applicable for mild house cooling, as a renewable and sustainable energy source that saves cooling water and uses wind and solar energy, without emitting greenhouse gases. Moreover, it is environmentally friendly, economically feasible, and operates with high performance. This adds value to the Environmental Engineering Laboratory, the Department of Civil Engineering, and the University of Patras. Novelty or Significance This technology improves the water-cooling process through wet fabric evaporation and is suitable for sustainable house cooling. This is achieved by interposing a thin aluminum plate between fabric and cooling water, in complete contact with them. The evaporating water may be potable or not. The environmentally friendly fabric color allows installations on roofs or in gardens. The structure is simple with common materials, economically feasible with high operating efficiency. The cooling water temperature is maintained from 2 to 16°C lower than ambient air (>5°C with 57% probability). The software developed may be used for designing or assessing such systems.

HYDRODYNAMIC INTERACTION BETWEEN SHIPS AND RESTRICTED WATERWAYS

In open and unrestricted waters the water displaced by a forward sailing vessel can travel without major obstruction underneath and along the ship. In restricted and shallow sailing conditions, the displaced water is squeezed between the hull and the bottom and/or the bank. This results in higher flow velocities and as a consequence a pressure drop around the same hull. In the vicinity of a bank this pressure drop generates a combination of forces and moments on the vessel, known as bank effects. The major achievement of the presented research is the development of a realistic and robust formulation for these bank effects. This knowledge is acquired with an extensive literature study on one hand and with dedicated model tests carried out in different towing tanks on the other. The majority of the utilised model tests were carried out in the shallow water towing tank at Flanders Hydraulics Research in Antwerp, Belgium. The data set on bank effects consists of more than 8 000 unique model test setups (which is by far the most elaborate research ever carried out on this subject). These model tests provide the input for the analysis of bank effects and the creation of the mathematical model.

Mathematical modeling of zebrafish social behavior in response to acute caffeine administration.

Zebrafish is a model organism that is receiving considerable attention in preclinical research. Particularly important is the use of zebrafish in behavioral pharmacology, where a number of high-throughput experimental paradigms have been proposed to quantify the effect of psychoactive substances consequences on individual and social behavior. In an effort to assist experimental research and improve animal welfare, we propose a mathematical model for the social behavior of groups of zebrafish swimming in a shallow water tank in response to the administration of psychoactive compounds to select individuals. We specialize the mathematical model to caffeine, a popular anxiogenic compound. Each fish is assigned to a Markov chain that describes transitions between freezing and swimming. When swimming, zebrafish locomotion is modeled as a pair of coupled stochastic differential equations, describing the time evolution of the turn-rate and speed in response to caffeine administration. Comparison with experimental results demonstrates the accuracy of the model and its potential use in the design of in-silico experiments.

Hydrodynamic ship–ship and ship–bank interaction: A comparative numerical study

The hydrodynamic interaction between ships or between the ship and the bank was studied by numerical methods. A number of new numerical results were obtained, for both ship–ship interaction and ship–bank interaction cases, by applying the double-body potential flow code HYDINTER earlier developed at Instituto Superior Técnico (University of Lisbon, Portugal). A comparative numerical study was made between these results and those obtained earlier for the same ship forms at Ghent University (Belgium) with a different potential code (ROPES), with a Computational Fluid Dynamics (CFD) code (ISIS-CFD) and with Experimental Fluid Dynamics (EFD) data obtained in the shallow water towing tank at Flanders Hydraulics Research, Belgium.A panel method is – in comparison with CFD – relatively fast and can often be used in real-time simulations. Because of this substantial benefit, the research focuses on identifying the limitations of applicability of this alternative computation method which neglects viscous effects and free-surface deformation. In this research, on the one hand good predictions are obtained for ship–ship interaction between encountering ships. On the other hand, the results for ship–bank interactions fail to predict the experimental trends. The errors increase at very close distances to the bank or another ship. The same holds true for the cases characterised by very large drift angles e.g. a tug crabbing near a large vessel.

Numerical study of a Whitham equation exhibiting both breaking waves and continuous solutions

We consider a Whitham equation as an alternative for the Korteweg–de Vries (KdV) equation in which the third derivative is replaced by the integral of a kernel, i.e., ηxxx in the KdV equation is replaced by ∫−∞∞Kν(x−ξ)ηξ(ξ,t)dξ. The kernel Kν(x) satisfies the conditions limν→∞Kν(x) = δ″(x), where δ(x) is the Dirac delta function and limν→0Kν(x) = 0. The questions studied here, by means of numerical examples, are whether adjustment of the parameter ν produces both continuous solutions and shocks of the kernel equation and how well they represent KdV solutions and solutions of the underlying hyperbolic system. A typical example is for resonant forced oscillations in a closed shallow water tank governed by the kernel equation, which are compared with those governed by a partial differential equation. The continuous solutions of the kernel equation associated with frequency dispersion in the KdV equations limit to the shocks of the shallow water equations as ν → 0. Two experimental problems are solved in a single equation. As another example, suitable adjustment of ν in the kernel equation produces solutions reminiscent of a hydraulic and undular bore.

Adaptation of a Deep Liquid-Containing Tank into an Effective Structural Vibration Control Device by a Submerged Cylindrical Pendulum Appendage

Due to a high proportion of impulsive liquid mass and low inherent damping, liquid-containing deep tanks, such as conventional overhead water tanks, are generally not considered for design as tuned liquid dampers (TLDs) for passive vibration control of structures under lateral excitation. This paper presents a novel concept to convert deep tanks into effective vibration control systems through the incorporation of a submerged cylindrical pendulum appendage (CPA). The CPA is placed in the impulsive liquid zone of the tank and its oscillating frequency is tuned to the dominant frequency of the primary structure. When laterally excited, the primary structure transfers vibrational energy to the CPA, thereby setting it into oscillation. The motion of the CPA is opposed by the drag exerted by the surrounding liquid on it, which leads to dissipation of the vibrational energy. This particular design utilizes impulsive liquid mass in the energy dissipation mechanism, while allowing fluctuation in the liquid level in the upper region of the tank, thereby fulfilling the functional requirements of the tank. In this paper, the mathematical model and working principle of the deep tank with CPA (DT-CPA) damper are developed. The equations of motion of a two degree-of-freedom (2-DOF) structure-damper system are derived. The design of the DT-CPA damper is illustrated considering an example structure and the performance of the damper is examined by subjecting the structure-damper system to pre-recorded seismic base excitations. The sensitivity of the performance of the proposed damper to tuning ratio is further studied. Results indicate that the DT-CPA damper is effective in controlling structural vibrations and its performance is comparable to that of a conventional tuned mass damper (TMD) and even slightly superior to that of a conventional TLD system of the shallow tank configuration. The proposed concept thus holds potential for the utilization of deep tanks as energy dissipation devices with minimal interference to their usual functionality.

ORTHOGONAL WAVE CURRENT INTERACTION OVER A FIXED RIPPLED BED: PRELIMINARY RESULTS OF AN EXPERIMENTAL CAMPAIGN

This paper reports some results obtained in the framework of the TA WINGS, funded by the EU through the Hydralab+ program. The project was aimed at investigating the hydrodynamic effects of an orthogonal wave onto a current in order to understand the nature of the velocity distribution along the water column over fixed ripples. Velocity profiles were acquired within the DHI shallow water tank by means of several Vectrinos in order to investigate the effects of wave-current interaction. A comparison between wave only case and wave plus current case showed that, when the current overlaps to waves, the recirculating cells formed near the bed are flatter than those formed in wave only. Moreover, the vorticity increases outside the boundary layer and decreases inside it when the current superposes to the wave.

Comparative Analysis between Experimental and Numerical Model resultsof a Jetin a Shallow Water Tank

In this work a comparative analysis of a turbulent jet experiment produced by the injection of dyed water into a shallow tank filled with water of the same density and the results of a numerical modelare presented. Dye was injected with the source fluid as a tracer. The concentration of the dye in the shallow turbulent flow was determined using a video imaging technique.The present laboratory experiments were conducted in a tank of small depth, and it is significantly wide to avoid the effect of the side walls. The space between the parallel walls of the tank can be varied during the experiments. The large-scale turbulent flow in the water sheet between the walls of the tank is confined to essentially two-dimensional motion. The shear on the bottom of the tank is a momentum sink to be considered.A comparison of the numerical resultswith the experimental data showed a very good agreement in terms of the position reached by the jet at different times after injection is initialized. These findings are useful for turbulent modeling of the shallow shear flow and for application to the large scale heat and mass exchange processes in lagoons, lakes, the ocean and the atmosphere

Numerical Analysis of Non Contact Transportation System for Wafer Warping

In this work a comparative analysis of a turbulent jet experiment produced by the injection of dyed water into a shallow tank filled with water of the same density and the results of a numerical modelare presented. Dye was injected with the source fluid as a tracer. The concentration of the dye in the shallow turbulent flow was determined using a video imaging technique.The present laboratory experiments were conducted in a tank of small depth, and it is significantly wide to avoid the effect of the side walls. The space between the parallel walls of the tank can be varied during the experiments. The large-scale turbulent flow in the water sheet between the walls of the tank is confined to essentially two-dimensional motion. The shear on the bottom of the tank is a momentum sink to be considered.A comparison of the numerical resultswith the experimental data showed a very good agreement in terms of the position reached by the jet at different times after injection is initialized. These findings are useful for turbulent modeling of the shallow shear flow and for application to the large scale heat and mass exchange processes in lagoons, lakes, the ocean and the atmosphere.

Wave-Current Flow and Vorticity Close to a Fixed Rippled Bed

An experimental study of wave and current interaction over ripples is presented in this paper. The campaign was carried out at the shallow water tank at the Danish Hydraulic Institute (DHI, Denmark), in the framework of the TA WINGS (Waves plus currents INteracting at a right anGle over rough bedS), funded by the European Union (EU) through the Hydralab+ program. Mean velocity profiles, measured with acoustic Doppler velocimeters for different flow conditions including current only, wave only and wave plus current were recorded and allowed to recover flow and vorticity fields. Recirculating cells in both wave only and wave plus current conditions form but they flatten when the current superposes over the wave. It was found that the superposition of current reduces the undertow present in the case of only waves and leads to an increase of vorticity outside the boundary layer. Instead, inside the boundary layer, the vorticity is dumped by the effect of current.

SPH model for interaction of sloshing wave with obstacle in shallow water tank

The violent fluid motion in a partially filled vessel is called sloshing. Resonance occurs when the natural frequency of the fluid oscillation approaches that of its container. This result may lead to structural failure. In this study, a Smoothed Particle Hydrodynamics (SPH) model is established to investigate the sloshing motion in a shallow water reservoir. Sloshing in a submerged obstacle, cylinder array, rectangular and wall-inclined topography is considered. In terms of results, the cylinder array is more effective than the other models to reduce the impact force due to the sloshing wave in a rectangular tank. The results prove that the proposed SPH model is capable of simulating sloshing in the shallow water tank.

The influence of confined water on blast response of reinforced concrete slabs: Experimental investigation

In this paper, the main objective is to investigate the influence of confined water on the dynamic response of reinforced concrete (RC) slabs under a near-field air explosion. The confined water is stored in a relatively shallow tank that is placed either above or below the RC-slab. The depth of the water tank is selected to be approximately 40% of the thickness of the slab. The study is conducted experimentally with the aid of field blast tests. Experimental observations indicate that confined water can significantly intensify the energy of the explosion and the level of damages (i.e., concrete spalling and perforations) introduced in a RC-slab. The damages are found to be more severe when the confined water is located above the slab and encounters the blast shock waves prior to the slab. The capability of confined water in amplifying the energy of explosion may be viewed as a potential technique for engineering demolition of deteriorated structures in urban areas with the aid of minor detonations.

Analysis of the flow conditions between the bottoms of the ship and of the waterway

A physical model test was performed, to which a scaled model (1:40) was designed and constructed to carry two Laser Doppler Velocimetry sensors and provide optical access at different locations along the hull to detect the stream close to bottom of the hull and resolving the boundary layer flow at the hull. The measurement campaign was conducted in a shallow water towing tank and included a range of water depths and ship speeds such that the influence of each became analysable. The purpose of the experiment is to provide validation data to further corroborate a numerical approach and to gain deeper insight in the flow conditions in the gap flow underneath the vessel in very shallow water. In addition the extension of the effect of propulsion on the dynamic sinkage and trim in very shallow water was checked. Even though for one particular ship design and restricted to model scale 1:40, the results are regarded a valuable basis for further investigations on this phenomenon.

A deep neural network approach to acoustic source localization in a shallow water tank experiment.

In this paper, an acoustic source localization method using the emerging technology of the deep neural network (DNN) is proposed. After the construction and training of the DNN, the capability of the DNN for source localization through a set of numerical simulations is verified. Next, experimental studies and demonstrations in a very shallow water tank with acoustic reflective walls are prepared, which enable the quick acquisition of a huge amount of experimental data for the training of a one-dimensional DNN-based source localization model. The development of the DNN-based source localization method and the corresponding numerical and experimental demonstration constitute the main contribution of this work. The associated performance is then evaluated at various frequencies. In particular, the localization results of the DNN are compared with readily available model-based localization methods, such as the conventional matched field processing method and the normal-mode based multiple signal classification method. The comparison shows that the proposed DNN approach is able to produce satisfactory accuracy in this reflective shallow water tank environment, for which a forward acoustic propagating model is not required. Last but not least, the generality of the proposed DNN approach from one-dimensional localization to progressively more complicated two-dimensional tasks is also considered.

CFD-based numerical simulation of pure sway tests in shallow water towing tank

The pure sway tests in shallow water towing tank are numerically simulated for the DTC container ship model by using an unsteady RANS solver. The verification study in terms of mesh and time-step convergence for the assessment of numerical error and uncertainty is conducted. The hydrodynamic forces, the hydrodynamic derivatives and the reconstructed hydrodynamic forces from the resultant hydrodynamic derivatives are validated against experimental data in very shallow water, and a satisfactory agreement is obtained. Using the validated numerical method, systematic simulations are carried out considering the influences of water depth, ship speed and dynamic sinkage and trim on the hydrodynamic quantities during the pure sway tests. The effects of depth restrictions on the hydrodynamic forces are expressed by polynomial regression equations with the corresponding ratios of hydrodynamic derivatives in shallow water to those in deep water. Besides, the side wall effects of tank in very shallow water that affect significantly the results of model tests for ship speed close to the Schijf's limiting speed are analyzed. From the present study, the ability of CFD method in evaluating the shallow water effect and side wall effect on the pure sway test results in shallow water towing tank is demonstrated.

Analysis of moving model experiments in a towing tank for aerodynamic drag measurement of high-speed trains

The present study assesses the applicability of towing tank experiments using a moving model for the investigation of the aerodynamics of long land-borne heavy vehicles such as buses, trucks, and trains. Based on experiments with a 1:22 scaled model of a high-speed train, the influence of various conditions relevant for the transferability of the results obtained in water to air is analysed exemplarily. These conditions include surface waves, cavitation and submergence depth. The experiments were carried out in the shallow water towing tank of the Technische Universitat Berlin. It is shown that outside a critical Froude number range of about 0.2 < Fr < 1.2 the impact of the surface waves can be neglected and no cavitation appears in the velocity range investigated. Furthermore, a correction method is proposed taking into account the bias through surface waves at small submergence and thus allowing for a wider Froude number range. The data obtained in the towing tank are found to be in excellent agreement to other investigation methods.

Target strength measurements of spherical and wobbly bubbles

Methane gas bubbles released from the seafloor transport gas upwards through the water column and in some cases even to the atmosphere. Researchers exploit the large acoustic impedance contrast between the gas within the bubble and the surrounding water to acoustically estimate the flux of methane in the ocean. Flux estimation employs the use of analytical acoustic scattering models to convert acoustic backscatter measurements of gas bubbles to size estimates. However, these models assume that bubbles are both spherical and that their radius is much smaller than the acoustic wavelength (ka « 1). Typically, bubbles in the ocean range from 1 to 5 mm in radius are non-spherical in shape and are observed for ka values that are greater than 0.1. A controlled shallow water tank (<6 m) experiment was conducted to assess the uncertainty associated with using analytical models that assume bubbles are spherical and that ka values are much smaller than one. Small, spherical and large, wobbly gas bubbles (radii ranging from 0.7 to 4.5 mm) were ensonified over a broad range of frequencies (10–250 kHz) in order to observe ka values from 0.1 to 5.

Pilot-scale demonstration of efficient ammonia removal from a high-strength municipal wastewater treatment sidestream by algal-bacterial biofilms affixed to rotating contactors

This report details our investigation of a novel, fixed-biofilm algal and bacterial system for the treatment of high-strength municipal anaerobic digester filtrate. Each reactor in the pilot-scale system comprises multiple Algaewheel™ rotating algal contactors (RACs) that help efficiently oxygenate the anaerobic digester filtrate being treated in a shallow tank. Total ammonia nitrogen (TAN) removal by microbial oxidation and anabolic uptake varied between 45 and 60% at hydraulic retention times (HRTs) of 0.5–2 days. Of the TAN removed during treatment, >95% was oxidized to nitrite with 27–36% subsequently evolved as N2 and only 3–11% oxidized to nitrate. The low extent of nitrate formation makes biological nutrient removal less costly, since nitrite reduction demands less oxygen, by 25%, and organic carbon, by 40%, than nitrate reduction. In addition, due to the efficient aeration by RACs, it should be possible to design systems for sidestream treatment of digester filtrate that require up to 80% less electricity than are typical for aerobic ammonia oxidation.