Laboratory Tank Research Articles

Dynamic response analysis of the vessel under the action of motion compensation equipment

The importance of motion compensation equipment in mitigating wave-induced vessel motion has attracted widespread attention, and many scholars have researched and developed multi-degree-of-freedom motion compensation equipment for marine engineering. However, while compensating for wave-induced motions, motion compensation equipment also has unknown effects on the vessel's motions. To investigate the dynamic response of the vessel under the action of motion compensation equipment, a co-simulation system considering hydrodynamics, multi-body dynamics and control strategy is developed to analyze the dynamic behavior of the motion compensation equipment and the installed vessel. The simulation results show that as the load on the motion compensation equipment increases, the vessel becomes more unstable during the compensation process. A scaled-down shipboard Stewart platform prototype was fabricated and the reliability of the simulation was experimentally investigated in a laboratory tank. The numerical simulation and experimental results show good agreement, the findings of this study can guide the design and operation of the motion compensation equipment.

Assessment of unidirectional internal solitary wave models in a two-layer fluid system through an improved experimental method

The suitability of unidirectional internal solitary wave (ISW) models in a two-layer fluid system is evaluated using an improved experimental method. A new method for generating internal solitary waves in the laboratory tank is proposed, utilizing a piston-type wave maker in a density stratified two-layer fluid. The prescribed velocities of the pistons are determined by the mean velocities derived from the adjusted High-order Unidirectional (aHOU) model for the upper and lower layers. Experimental conditions encompass a range of wave Reynolds numbers between 1.8×105 and 2.3×105. The repeatability and amplitude control of the proposed wave-making method are verified. The unidirectional models considered in this study encompass the Korteweg–de Vries (KdV), Gardner and aHOU model. Laboratory experiments and theoretical computations have been systematically compared in this study to examine the wave characteristics inherent in typical unidirectional internal solitary wave models. It is found that Reynolds number (Re) and nonlinear parameter (α=|a|/h) serve as suitable criteria for delineating the range of applicability of unidirectional models. According to these criteria, the KdV theory is suitable for ISWs with amplitudes α<0.02 across all Reynolds number cases, while the Gardner model is valid for cases where α<0.02 and Reω>2.2×105, with α<LimG, where LimG represents the non-dimensional limiting amplitude. The aHOU model exhibits the capability to capture fully nonlinear ISWs across all Reynolds numbers considered in this study.

Modeling and field demonstration of water-to-ice wireless optical communication system based on highly-sensitive detectors.

In this paper, the first water-to-ice (W2I) wireless optical communication (WOC) system model is proposed and verified by laboratory and field experiments. The Monte Carlo (MC) approach is used to simulate the optical characteristics of ice and water, resulting in the channel impulse response and received optical power (ROP) distribution. The simulation results demonstrate that the substantial absorption and scattering of the ice and ice-water interface significantly affect the cross-medium communication. A comparative study in the laboratory validated the channel characteristics obtained from the simulation. Following this, a W2I WOC system based on photomultiplier tubes (PMTs) was established. Using the maximum ratio combining (MRC) technique, a net data rate of 400 Mbps was achieved in a 1-m laboratory tank, and a net data rate of 320 Mbps was achieved across a 1-m transmission distance in the reservoir. To reduce the computational complexity and realize practical system deployment, the orthogonal matching pursuit (OMP) approach is employed to compress the equalizer. The number of kernels in the Volterra equalizer is reduced by 36% in the laboratory experiment and 36.9% in the field experiment, respectively. The results of this study can serve as a reference for future deployment of W2I WOC systems.

Robust security‐based model predictive control for nonlinear cyber‐physical system under random occurring deception attacks and actuator saturation

AbstractThis article presents a robust security‐based model predictive control (MPC) framework for a class of discrete‐time nonlinear cyber‐physical systems (CPSs) suffering random deception attacks and persistent actuator saturation. In CPSs, the attacks can significantly degrade the control performance. Naturally, a larger degree of control is required, prompting the consideration of actuator saturation in CPS's structure. In our work, the cyberattacks on the controller‐actuator (C‐A) channel are described as a stochastic process with specific probability and bounded energy. The security‐related constraint is introduced to improve the resistance and robustness against attacks. Mean‐square quadratic boundedness is derived to estimate the robustly invariant set. By placing the saturated input into a convex hull, a robust security‐based MPC optimization problem is addressed less conservatively with linear matrix inequality technique. Furthermore, the feasibility of the proposed method is proved recursively, and the stability and security of the closed‐loop system are established in mean‐square sense. In the end, the laboratory tank and reactor‐separator process are applied to validate the effectiveness of the proposed algorithm.

Testing transfer learning for source ranging in a laboratory tank

One difficulty in applying deep learning techniques to ocean acoustics is the spatially and temporally varying environmental properties. Another challenge is the lack of labeled data for training large networks. The overall goal of this work is to develop deep learning approaches that can be adaptable to different conditions. For example, a trained neural network will fail to generalize when the appropriate environmental variability is not included in the training data. To improve network performance, transfer learning can modify a pre-trained network to make predictions on data that was recorded under different conditions than the original dataset. In this work, a convolutional neural network was trained on acoustic data measured in a water tank, while the water was at room temperature, to predict source-receiver range. Transfer learning was used to update the pre-trained model with a smaller set of data measured at different water temperatures. The resulting model better generalizes to measurements at different temperatures. This approach illustrates how transfer learning can be used in ocean acoustics to improve generalizability in a specific area with less labeled data and lower computational cost. [Work supported by the Office of Naval Research, Grant N00014-22-12402.]

Flocculation characteristics of suspended Mississippi River mud under variable turbulence, water and salt sources, and salinity: a laboratory study

Muddy sediment constitutes a major fraction of the suspended sediment mass carried by the Mississippi River. Thus, adequate knowledge of the transport dynamics of suspended mud in this region is critical in devising efficient management plans for coastal Louisiana. We conducted laboratory tank experiments on the sediment suspended in the lower reaches of the Mississippi River to provide insight into the flocculation behavior of the mud. In particular, we measure how the floc size distribution responds to changing environmental factors of turbulent energy, sediment concentration, and changes in base water composition and salinity during summer and winter. We also compare observations from the tank experiments to in situ observations. Turbulence shear rate, a measure of river hydrodynamic energy, was found to be the most influential factor in determining mud floc size. All flocs produced at a given shear rate could be kept in suspension down to shear rates of approximately 20 s−1. At this shear rate, flocs on the order of 150–200 μm and larger can settle out. Equilibrium floc size was not found to depend on sediment concentration; flocs larger than 100 μm formed in sediment concentrations as low as 20 mgL−1. An increase in salinity generated by adding salts to river water suspensions did not increase the flocculation rate or equilibrium size. However, the addition of water collected from the Gulf of Mexico to river-water suspensions did enhance the flocculation rate and the equilibrium sizes. We speculate that the effects of Gulf of Mexico water originate from its biomatter content rather than its ion composition. Floc sizes in the mixing tanks were comparable to those from the field for similar estimated turbulent energy. Flocs were found to break within minutes under increased turbulence but can take hours to grow under conditions of reduced shear in freshwater settings. Growth was faster with the addition of Gulf of Mexico water. Overall, the experiments provide information on how suspended mud in the lower reaches of the Mississippi might respond to changes in turbulence and salinity moving from the fluvial to marine setting through natural distributary channels or man-made diversions.

Analysis of vortex merging from a rotating tank laboratory experiment

Oceanic vortex merging is an important physical process for the vortex evolution and its impact on marine environment. However, limitation of the in-situ oceanic observational data of vortex merging inhabits its better understanding. This study investigates the interactions between non-ideal vortices in a four-vortex flow field in a rotating tank. We examine the merging stages of anticyclonic vortices, influenced by two other cyclonic vortices and their respective dynamical behaviors and quantify the effects of merging on vortex characteristics. The results indicate a strong shear flow between two counter-rotating vortices, which accelerates the motion of the anticyclonic vortex, while cyclonic ones exhibit greater stability. Subsequently, different stages of non-ideal vortex merging in a co-rotating framework are defined, primarily the encircling stage, rapid approaching stage, and merging vortex stage. In addition, we quantify and compare variations in morphological parameters and anti-symmetric vorticity distribution of non-ideal vortices across these stages. The stretching of vortices primarily occurs along the line connecting their centers due to the strain field exerted by neighboring vortices, resulting in an asymmetric stretching pattern in the interactions among non-ideal vortices. Furthermore, during the merging process, non-ideal vortices disperse vorticity outward and accumulate vortex filaments in the surrounding environment, leading to distinctive variations in anti-symmetric vorticity distribution, affecting their respective merging efficiency.

Improved ERT imaging with 3-D surface-to-horizontal borehole configurations: relevance to dense non-aqueous phase liquids

SUMMARY Accurate characterization and monitoring strategies are essential for designing and implementing remedial programs for sites polluted with dense non-aqueous phase liquids (DNAPLs). Electrical resistivity tomography (ERT) is a widely used geophysical technique for mapping subsurface features and processes of interest, and exhibits desirable characteristics for DNAPL sites due to its ability to gather large volumes of continuous subsurface information in a non-invasive, cost-effective and time-efficient manner. However, ERT measured only from the surface suffers from poor imaging quality with depth. Enhanced ERT imaging can be obtained via electrodes deployed on the surface and within horizontal boreholes, but so far it has only been investigated for 2-D imaging. This study evaluates the potential of 3-D surface-to-horizontal borehole (S2HB) ERT configurations for imaging 3-D DNAPL source zones. Laboratory tank experiments were first conducted with a 3-D S2HB ERT configuration, which consisted of a surface grid and a single borehole line of electrodes, being used to monitor DNAPL migration within porous media. Results demonstrate that 3-D S2HB ERT with a single borehole provides improved sensitivity at depth, and therefore enhanced imaging compared to conventional 3-D surface ERT. Further tank experiments were performed to assess the performance of single borehole S2HB ERT when (i) the distance between surface and borehole is increased, and (ii) additional horizontal boreholes are included. The S2HB ERT with a single borehole significantly outperforms surface ERT at larger depths, and performs comparably to S2HB ERT using multiple boreholes. This study suggests that 3-D S2HB ERT with a single borehole can provide the enhanced imaging ability needed to map DNAPLs, while also being relatively practical for implementation at field sites.

Development of a Mobile Buoy with Controllable Wings: Design, Dynamics Analysis and Experiments

Marine monitoring equipment such as Argo profiling buoys and underwater gliders are important devices for oceanographic research and marine resource exploration. In this study, a novel mobile buoy capable of vertical profiling motion like Argo profiling buoys and sawtooth gliding motion like underwater gliders is proposed. The proposed mobile buoy can switch between the two motion modes with controllable wings. To verify the feasibility of the proposed mobile buoy, a fluid–multibody coupling model considering multibody dynamics and hydrodynamics was developed to investigate the dynamic response. A scaled-down buoy prototype was fabricated and the feasibility of the two motion modes was experimentally investigated in a laboratory tank. The experimental results agree well with the results of numerical simulation. This work can be helpful for the design and analysis of this kind of mobile buoy.

Simple and Low-Model-Dependent Strategy for the Economic and Safe Control of Direct-Drive Wave Energy Converters

For engineering application and commercialization, a wave energy converter (WEC) should harness as much wave energy as possible to improve its economy and maintain each component works within their physical constraints for safe operation. Model predictive control (MPC) can maximize wave energy extraction under constraints for the direct-drive WEC. MPC requires accurate modelling parameters, wave prediction and complex computation, while these can hardly be guaranteed in real application. Besides, researchers generally take position and force constraints into consideration, while power constraint is neglected. In this work, we analyze the power extraction characteristics under constraints and propose a strategy to realize economic and safe control of WECs by decoupling it into different control modes of a permanent magnet synchronous generator (PMSG). In this way, the control is simple and low-model-dependent and power constraint can be also maintained. The strategy is put through comprehensive simulation tests with MPC as the benchmark, and it is proven to be effective under various wave conditions and constraint settings. Furthermore, experimental tests are carried out for a prototype device in a wave tank laboratory and these tests validate the applicability, effectiveness, and robustness of our strategy.

Deep learning and beamforming comparison of source ranging in a laboratory tank

Deep learning has been shown to be useful for ocean acoustics applications, such as source ranging. The variable nature of the ocean causes difficulty when attempting to apply trained models to new datasets. To explore ways to train supervised deep learning models that are robust to environmental variability, laboratory tank measurements can be used. A laboratory tank presents a system where uncertainty in the acoustic environment can be adjusted in a more controlled manner. In this work, recordings of ultrasonic chirps (50–200 kHz) are obtained at different source-receiver positions. Time-averaged spectral density levels are used to train one-dimensional convolutional neural networks that predict source-receiver range. The trained networks are tested on data obtained under different conditions. Data augmentation techniques are applied to increase the models’ robustness in the presence of limited uncertainty. Metrics such as root mean-squared error and mean absolute percent error are used to quantify the model’s performance. The results from deep learning with single channel recordings and multi-channel recordings are compared with traditional beamforming methods on the multi-channel data. [Work supported by the Office of Naval Research.]

3D simulations and laboratory experiments to evaluate a dynamic airbag valve

Airbag pressure determines the restraint effect during a vehicle crash. The pressure required to restrain the occupant depends on pre-crash detection, collision parameters and the occupant’s mass and position. This work modulated airbag pressure for optimum safety using a novel airbag control valve for cold-gas inflators. This paper evaluates the valve’s stationary and dynamic performances for Helium by 3D flow simulations using a pressure-based solver in ANSYS Fluent® and SAE J2238 laboratory tank tests. The predicted and measured tank pressures for the fully open (stationary) valve were agreed by an average 93.73% with an excellent correlation (correlation coefficient, R = 0.9995). For the first dynamic operation with 10 ms switching time, the results agreed by 92.78% with R = 0.9975. In the second test with 30 ms switching, 83.67% agreement was observed with R = 0.9893. The research concluded that the valve modulates the bag pressure and is implementable in vehicles.

Fetch effects on air-sea momentum transfer at very high wind speeds

ABSTRACT Accurate estimates of momentum flux through the air-sea interface at very high wind speeds are important for predicting tropical cyclone intensities. To estimate the air-sea momentum flux under the long-fetch condition (20 m fetch) at very high wind speeds using a laboratory tank, a simple momentum flux measurement method using only four water-level gauges is conducted based on the momentum budget method. The air-water momentum flux under long-fetch conditions at very high wind speeds was measured in a typhoon simulation tank at the Research Institute of Applied Mechanics, Kyushu University. The verification was performed using previous values estimated by the eddy correlation method in a typhoon simulation tank at Kyoto University, Japan. The results showed good correlation between the values of momentum flux measured by the present momentum budget method and the other methods. The drag coefficient at very high wind speeds (41 m/s) under long-fetch conditions leveled off, as well as under the short-fetch condition (4.5 m and 6.5 m fetch). Moreover, a very weak relationship was found between the drag coefficient and the fetch. Since the maximum fetch in the present laboratory experiments is 20 m, the future field observation with the longer fetch condition will be needed for applying the results to oceans.

On the role of organic matter composition in fresh-water kaolinite flocculation

Organic matter has long been understood to affect fine sediment flocculation, yet the specific effects of different types of organic matter remain only partially understood. To address this knowledge gap, laboratory tank experiments were conducted in fresh water to investigate the sensitivity of kaolinite flocculation to varying organic matter species and contents. Three species of organic matter (xanthan gum, guar gum and humic acid) were investigated at varying concentrations. Results revealed a significant enhancement in kaolinite flocculation when organic polymers (xanthan gum and guar gum) were introduced. In contrast, the addition of humic acid had minimal influence on aggregation and floc structure. Notably, the nonionic polymer guar gum demonstrated greater efficacy in promoting the development of floc size compared to the anionic polymer, xanthan gum. We observed non-linear trends in the evolution of mean floc size (Dm) and boundary fractal dimension (Np) with increasing ratios of organic polymer concentration to kaolinite concentration. Initially, increasing polymer content facilitated the formation of larger and more fractal flocs. However, beyond a certain threshold, further increases in polymer content hindered flocculation and even led to the break-up of macro-flocs, resulting in the formation of more spherical and compact flocs. We further quantified the co-relationships between floc Np and Dm and found that larger Np values corresponded to larger Dm. These findings highlight the significant impact of organic matter species and concentrations on floc size, shape and structure, and shed light on the complex dynamics of fine sediment and associated nutrients and contaminants in fluvial systems.

A CO2 and H2O Gas Analyzer with Reduced Error due to Platform Motion

Abstract One long-standing technical problem affecting the accuracy of eddy correlation air–sea CO2 flux estimates has been motion contamination of the CO2 mixing-ratio measurement. This sensor-related problem is well known but its source remains unresolved. This report details an attempt to identify and reduce motion-induced error and to improve the infrared gas analyzer (IRGA) design. The key finding is that a large fraction of the motion sensitivity is associated with the detection approach common to most closed- and open-path IRGA employed today for CO2 and H2O measurements. A new prototype sensor was developed to both investigate and remedy the issue. Results in laboratory and deep-water tank tests show marked improvement. The prototype shows a factor of 4–10 reduction in CO2 error under typical at-sea buoy pitch and roll tilts in comparison with an off-the-shelf IRGA system. A similar noise reduction factor of 2–8 is observed in water vapor measurements. The range of platform tilt motion testing also helps to document motion-induced error characteristics of standard analyzers. Study implications are discussed including findings relevant to past field measurements and the promise for improved future flux measurements using similarly modified IRGA on moving ocean observing and aircraft platforms.

An experimental study of stabilizing ordinary fishing nets (SOFNets) on a stationary SWATH ship seakeeping behavior under irregular waves

The present research aims to experimentally demonstrate the effectiveness of an innovative method for reducing the ship motions using Stabilizing Ordinary Fishing Nets that we call it SOFNets from now on. To this end, the influence of a range of SOFNets on the seakeeping behavior of a Small-Waterplane-Area Twin Hull (SWATH) ship in irregular waves is investigated physically in a towing tank laboratory. Understanding, controlling, and improving the seakeeping behavior of ships has always been a major concern of ship designers. As a result, various techniques have been utilized to stabilize ships, including the use of anti-rolling tanks, gyrostabilizers, and stabilizer fins, all three of which are bulky, heavy, and costly. These disadvantages have prevented many ships from using conventional rolling reduction methods. In contrast, the present idea, SOFNets, does not suffer from these shortcomings and can be used in any type of ship with any tonnage. The prepared model is tested in the towing tank of the National Iranian Marine Laboratory (NIMALA) using three different net samples in order to compare the behavior of those nets. This research has introduced for the first time the concept of using a SOFNets to reduce motion amplitude in waves. The length of the SWATH model was 2.1 m, and the tests were carried out according to the International Towing Tank Conference (ITTC) guidelines. The research findings for the SWATH ship indicate that the heave and pitch amplitudes in the head sea state were reduced by up to 21%, and the roll amplitude in the beam sea state was reduced by up to 36%.

Analysis of affecting factors for laser underwater transmission echo signals based on semi-analytic Monte Carlo

ABSTRACT In order to design an economical and reliable LiDAR, it is necessary to quantify the influence of different factors on the attenuation of laser propagation in water. Although these factors have been widely investigated, a complete understanding is still few. In addition, a comparative analysis between the measured data and the simulation results of LiDAR to build the design of LiDAR is still lacking. For these reasons, a semi-analytical Monte Carlo method was applied to establish a simulation model of the underwater laser echo signal propagation. The control variable method was quantified with the three major types of influencing factors: 1) LiDAR system parameters, 2) water optical characteristics and 3) external conditions. The effects of these different influencing factors on laser underwater echo signal transmission were investigated. With the experimental results, the attenuation rate of laser transmission in turbid harbour was 7.1 and 19.2 times higher than that in coastal water and clean ocean. Compared with other influencing factors, the optical characteristics of water have the most significant influence on underwater laser transmission. The laser echo signals in water with different concentrations of suspended solids were investigated in a laboratory tank using a LiDAR prototype developed by our research group. The results were compared with that from the semi-analytical Monte Carlo simulation to further explore the influence of the inherent optical characteristics of water on laser energy attenuation. The experimental results showed that with increasing water turbidity, the light beam diverged by strong scattering, the size of the light spot increased, the energy of the echo signal decreased as a whole and the backscattering signal of the water changed significantly. The determination coefficients and relative errors of the measured echo signals and the normalized simulation results were 0.99 and 0.01, respectively, which demonstrate the reliability of LiDAR prototype.

Acoustics of Periodic and Multiple Drop Impacts on a Water Surface

High-speed video filming of surface currents and synchronized acoustic measurements of the underwater sound signals of falling drops were performed in a laboratory tank. During successive falling, the main structural elements of collision of a single drop with the surface are preserved in distorted form in the flow pattern: cavity, splashes, crown, and splash; shock pulses accompanying each contact are stably repeated in the phonogram. In addition, rare resonance packets are observed. For multiple falling drops, the flow pattern changes dramatically: the main structural elements of the drop impact flow disappear, and the surface is covered with floating bubbles. The phonogram assumes the form of a noise signal, in the spectrum of which separate linear sections stand out.

Hydrogen sorption properties of Li–N–F–H pellets in laboratory and small tank scales

We propose the improvement of de/rehydrogenation kinetics and reversibility of LiNH2–LiH system via F substitution for H in LiNH2. Slight content of LiF–TiH2 composite is milled with LiNH2–3LiH and the obtained mixture is compacted into the pellet. By compositing LiNH2 with excess LiH and compaction, NH3 emission poisoning fuel cell catalysts and degrading hydrogen capacity can be prevented. The formation of LiNH(2-x)Fx achieved from F substitution in LiNH2 significantly enhances kinetic properties, for example, the 1st dehydrogenation at 280 °C completes within 5 min with the capacity of 3.6 wt % H2. Although LiNH(2-x)Fx cannot be recovered, good kinetics and reversibility upon five de/absorption cycles of LiNH2–LiH (up to 3.0 wt % H2 within 20 min) are preserved due to catalytic effects of LiF. Phase compositions and hydrogen capacities in laboratory and tank scales are comparable. This suggests the maintained de/rehydrogenation performance of Li–N–F–H pellets even after upscaling.

Processes governing treatment of contaminants in low permeability zones

Herein we embrace the premise that aquifers are commonly composed of transmissive and low k (permeability) zones. Contaminants stored and subsequently released from low k zones sustain aqueous phase plumes for problematic periods. Processes governing the occurrence and treatment of contaminants in low k zones are advanced via conceptual models and a laboratory tank study. A two-dimensional sand tank with interbedded low k clay layers is flushed for 92 days with water spiked with 100 mg/L fluorescein, a proxy for chlorinated solvent contamination, and 67 mg/L bromide, a conservative tracer. Given active sources, fluorescein and bromide diffuses into the clay layers. Subsequently, the tank is flushed with water for 38 days. Water only flushing illustrates how the release of contaminants stored in low k zones sustains downgradient plumes. Next, an alkaline persulfate solution (40,000 mg/L persulfate at pH 11) is delivered to the tank for eight days. A fiber optic cable, placed on the glass wall of the sand tank, and a spectrometer with an ultraviolet light source are used to track depletion of fluorescein in transmissive sand and low k clay zones through time. Lastly, the tank is flushed with water only for 69 days to evaluate the efficacy of treatment with respect to mitigating releases from low k zones. Results indicate that flushing the tank with an alkaline persulfate solution, at a laboratory-scale, was effective in depleting fluorescein in both the transmissive and low k zones. Novelly, results capture concurrent transport of reactants and contaminants in domains governed by advection in transmissive zones and diffusion in low k zones.