Towing Tank Tests Research Articles

Experimental dataset of a model-scale ship in calm water and waves.

This article presents data derived from a series of experiments conducted on a scaled model ship, examining its performance in both calm water and regular waves. The acquisition of high-quality experimental data is essential for refining Computational Fluid Dynamics (CFD) simulations and modifying analytical methods to evaluate the powering performance of ships. Despite notable advancements in numerical models, there exists a corresponding imperative to elevate the precision of measurements and insights obtained from towing tank tests. Accordingly, a self-propelled model-scale of the KRISO Container Ship (KCS) hull is used to assess hydrodynamic performance of ships and investigate the interaction between the hull, propeller, and rudder. A set of captive model tests is carried out on the single-screw KCS model in the University of Southampton's Boldrewood towing tank. The model-scale experiments are conducted in an offloaded propeller condition at ship's design speed, which is characterised by a specific Froude number of 0.26. Various test configurations are explored, encompassing four rudder angles, five leeway angles, two wave conditions, and two propeller speeds. Throughout the experiments, multiple parameters were recorded, including the wave environment, ship motions, hull forces and moments, propeller thrust and torque, as well as rudder forces and moments. Initial analysis of the data involved comparing the calm water resistance results with previously published experimental data, revealing a favourable agreement. Additionally, video footage captured from two different angles during various runs serves as illustrative samples of the experimental procedures. This comprehensive series of experiments offers a benchmark for future research endeavours, providing a foundation for refining subsequent experiments, validating numerical methods, and enhancing mathematical models.

Experimental investigation on the longitudinal stability of the aerodynamically alleviated marine vehicle with multi-steps

To investigate the hydrodynamic performance and motion characteristics of the ultra-high-speed aerodynamically alleviated marine vehicle (AAMV) with multi-steps, a towing tank test scheme was designed and carried out at the China Special Vehicle Research Institute. The study analyzed the effects of canard angle, flap angle, longitudinal center of gravity, and displacement tonnage on the motion stability of multi-stepped AAMV at different speeds. The results indicate that the canard generates an overturning moment that reduces the resistance but brings forward the speed at which porpoising behavior occurs. Additionally, the backward shift of the longitudinal center of gravity causes motion oscillation during the high-speed planing phase, which negatively affects longitudinal stability. On the other hand, the flaps provide aerodynamic lift and restoring moments, improving the lift-drag ratio and enhancing longitudinal stability. Furthermore, while increased mass may result in higher total resistance, it can actually improve resistance performance per unit mass and improve the lift-drag ratio at cruising speed. The computational fluid dynamics (CFD) method was used to analyze the destabilization mechanism of AAMV under extreme conditions in the test. Numerical results indicate that the longitudinal stability of AAMV is directly affected by the relative positions of the center of gravity and the center of pressure. These results demonstrate the changing rules of resistance performance and longitudinal stability of AAMV under different design parameters, thus providing a powerful tool for optimizing AAMV.

The Blockage Effect on Resistance Coefficients Estimation for AUVs with Different Configurations in the Towing Tank

When a resistance test of an underwater vehicle model is conducted in a towing tank, the blockage effect will inevitably occur, particularly since the experimental model is relatively large. This paper investigates the estimation of resistance coefficients for an Axisymmetrical Rotary Body Underwater Vehicle (ARBUV) and a Blended Wing Body Underwater Vehicle (BWBUV). The Computational Fluid Dynamics (CFD) method is employed to predict the resistance of Autonomous Underwater Vehicles (AUVs). In order to quantify the blockage effect on the resistance coefficients of AUVs with different configurations, the resistance coefficients of AUVs are calculated in the infinite domain and finite domain under various blockage ratios. Through analysis of the resistance results, velocity distribution, and pressure distribution, the action law of the blockage effect is provided. It indicates that blockage effects have a greater influence on the pressure resistance for ARBUV. Surprisingly, the resistance coefficients of BWBUV are less affected, though it is closer to the sidewalls. It suggests that the blockage ratio of ARBUV and BWBUV should be separately smaller than 0.375% and 2.5% in the towing tank test. The towing tank experiments satisfy the blocking ratio with a Reynolds number greater than 107, which saturates the blocking effect and further reduces the effect on the drag coefficient.

Towards a reliable method for extrapolation of propulsion performance for vessels with twin-crp-pod system

The study presents power performance prediction of an Ultra Large Container Ship (ULCS) with hybrid twin-crp-pod propulsion system. Twin crp-pod propulsion system is a combination of three concepts: twin screw, contra-rotating propellers (crp) and conventional shaft propellers with pod propulsors behind. The presented study shows the current extrapolation method for crp propulsion systems and tries to point out its weaknesses. As a case study, a 400 m ULCS has been investigated in full-scale and in model scales of 24 and 37.416. The analyses were carried out for all scales with use of CFD numerical methods and for the scale of 37.416 based on towing tank tests. All the results have been extrapolated with the same method and results have been compared. The investigations clearly show differences in delivered power prediction extrapolated from towing tank results giving the maximum value and from CFD made to scale of 24 the minimum value. Finally, conclusions on possible sources of differences, including the numerical and analytical methods are presented.

MMG 3DOF model identification with uncertainty of observation and hydrodynamic maneuvering coefficients using MCMC method

The trajectory prediction using ship maneuverability mathematical models is one of the essential technologies implemented in autonomous surface ship. Several ship maneuverability mathematical models and each one with a particular hydrodynamic coefficient approximation using towing tank tests are existed. However, it is presented difficult to directly inverse estimate the hydrodynamic maneuvering coefficients of a ship maneuverability mathematical model from operational data consisting of ship trajectory and maneuvering operation records. This paper proposed a method for estimating the hydrodynamic maneuvering coefficients of the MMG 3DOF model using three types of time-series ship motions (surge, sway, and yaw velocity) as observed data. In the assumption of this paper, there is uncertainty in observations and the hydrodynamic maneuvering coefficients of the MMG 3DOF model. The proposed method outputs samples of the simultaneous posterior probability distribution of the hydrodynamic maneuvering coefficients by the MCMC method using the observed data and stochastic model. A robust trajectory with a wide range can be presented by conducting ship maneuvering simulations using these samples. To verify the feasibility of the proposed method, this paper conducted observation system simulation experiments (OSSE) using the KVLCC2 L7 model and applied the proposed method to several free-running model ship tests. Results showed that on the assumption that MMG 3DOF model can explain the ship's state and trajectory in real world, the proposed method can estimate the ship hydrodynamic maneuvering coefficients of the MMG 3DOF model corresponding to the observed ship trajectory and control data including the error of observed data.

Dynamic motion analysis of stepless and stepped planing hulls in random waves: A CFD model perspective

Predicting the dynamic responses of planing hulls in real sea conditions is important for identifying how basic design factors influence their seakeeping performance. Hence, there is a pressing need to provide high-fidelity models for predicting the motions of these hulls in random waves, representing actual seas. In this article, a computational-based model for solving viscous fluid flow around the vessel is built to address this problem. Three different planing hulls, denoted as C, C1, and C2, each distinguished by the number of steps incorporated on their bottom surfaces (1 and 2 indicating the respective step count, with case C being the stepless hull), are modeled in a Computational Fluid Dynamics (CFD) tank, allowing for analysis of the effects of steps on dynamic responses of a planing surface operating in random waves. CFD data is compared against those collected in towing tank tests, revealing a satisfactory level of accuracy. Extreme value and gamma distributions are shown to give probabilities of maxima/minima of displacements and vertical acceleration at the center of gravity (CG) for all three hulls. It is shown that the stepless boat may be exposed to lower vertical acceleration at an early planing speed, but at higher planing speeds, a double-stepped design mitigates the vertical acceleration. Nevertheless, the double-stepped hull would experience more significant extreme heave responses across all speeds and may be exposed to less significant extreme pitch responses during the ride at the highest speed compared to the stepless and one-stepped hulls. The skewness of heave and pitch is evaluated, and it is found that the heave response tends to skew toward positive values (upward). This skewness becomes more noticeable with increasing speed but remains insensitive to wave steepness. Additionally, the pitch response at lower planing speeds shows a partial skew towards negative values (bow-down), but eventually, they may also be partially skewed towards positive values at higher speeds. Moreover, a correlation is observed between the kurtosis of responses of different hulls and the occurrence of the 1/100 highest responses, indicating that a kurtosis greater than 3.0 would result in more extreme responses. Overall, this analysis offers practical insights into planing hull behavior in actual sea conditions from a CFD model perspective, highlighting the potential of CFD in simulating this complex problem.

Experimental Investigation of Paint Roughness on the Resistance of a Flat Plate

In this work, an experimental investigation of the hydrodynamic resistance of a flat plate painted with newly developed marine antifouling paints of polyurethane (PU) and silicone (Si) formulations was performed. In total, six different paint systems of Si, PU, and acrylic formulations were applied, both experimental and commercial. The total resistance of each painted condition of the plate was measured through towing tank tests for the range of 0.75–2.5m/sec, with a step of 0.25m/sec. The Si and PU formulations exhibited similar hydrodynamic behavior, fluctuating around the smooth condition, whereas the acrylic system exhibited the highest resistance increase of all. The roughness function calculation was based on Ra and the correlation with the Colebrook roughness function was generally limited for most systems. Extrapolation to ship scale revealed that no significant drag differences are expected in the as-painted condition among the different paint system types.

Assessment of Numerical Captive Model Tests for Underwater Vehicles: The DARPA SUB-OFF Test Case

During the early design stage of an underwater vehicle, the correct assessment of its manoeuvrability is a crucial task. Conducting experimental tests still has high costs, especially when dealing with small vehicles characterized by low available budget. In the current investigation, virtual towing tank tests are simulated using the open-source OpenFOAM library in order to assess the reliability of CFD methods for the prediction of hydrodynamic forces and moments. A well-known case study, the Defence Advanced Research Projects Agency (DARPA) SUB-OFF model, is used, and the outcomes are compared to the experimental results available in the literature. Five different configurations are investigated for pure drift tests, rudder tests and pure rotation in both vertical and horizontal plane. The results show an overall good agreement with the experimental data with a quite low demanding mesh arrangement of 3M cells, a favourable balance between accuracy and computational time. In more detail, the expected error in the most significant forces during manoeuvres is less than 2% for the fully appended configuration (the submarine real operative condition), whereas the accuracy is moderately reduced for the barehull configuration (a case not representative of a real hull) with an expected error of 15%. A possible reason for the differences observed could be attributed to the description of the two streamwise vortices generated when manoeuvring. Apart from the lateral force and yaw moment, the results of the longitudinal force are also presented, having a greater disparity when compared to the experimental data. Nevertheless, the longitudinal force has no important role for the purpose of making stability and control predictions. The study contributes to the validation and consolidation of CFD methods, offering insights into their accuracy and limitations for practical applications in underwater vehicles.

Experimental analysis of a planing monohull model during forward acceleration: part II – evaluation of an indirect method for applying thrust angle in the experiments

ABSTRACT Most towing tank model tests conducted on planing hulls are not performed under self-propulsion conditions, and it is often not feasible to directly apply towing force at the corresponding point of action and along the thrust of the full-scale vessel. Therefore, it is essential to establish a well-defined method for accurately applying the thrust line in bare hull model tests using alternative loading solutions, such as CG shift, and understand how any deviation affects the model’s running attitude and performance. This article presents an analysis of the dynamic equilibrium equations of motion for the model, considering various variables that can be used to adjust the thrust line in towing tank tests. The proposed formalism can aid in determining the external loading requirements in resistance tests. Finally, the article discusses the challenges and provides an error estimation for a simplified method of applying a constant thrust angle in the accelerated tests.

Four-dimensional particle tracking velocimetry measurements of unsteady three-dimensional vortex onset and progression for 5415 straight ahead, static drift, and pure sway

Large-scale towed system four-dimensional particle tracking velocimetry (4DPTV) implementation and measurements are presented for towing tank tests for a naval combatant 5415 ship model for straight ahead, static drift β = 10°, and pure sway βmax = 10° conditions. The results, for the first time, provide instantaneous volumetric flow field data around the ship model including near the hull surface, and a complete description of the sonar dome 3D unsteady vortex separation onset and progression due to the 4DPTV larger measurement volume and higher data rates in comparison with previous results using tomographic particle image velocimetry (TPIV); thereby, providing the essential data required for the assessment of current hybrid Reynolds-averaged Navier–Stokes/large eddy simulation turbulence modeling capabilities and guidance for the necessary modeling improvements. The 4DPTV system is summarized and compared with the previous TPIV, including the camera calibration procedures, trigger systems, and synchronization with the sway motion. Analysis procedures, including data reduction procedures and the 3D vortex core detection and voxel labeling techniques, are described. The identification of the complex vortex separations and breakdown is aided using complementary detached eddy simulations. The vortex–vortex interaction process is visualized from instantaneous volumetric datasets. The pros and cons of the 4DPTV vs TPIV, the comparison between the second- and third-generation vortex visualization technique, and the statistical convergence error analysis of sonar dome port vortex for β = 10° are discussed. Plans for increased spatial resolution of the 4DPTV system and additional data reduction techniques for detailed turbulence analysis are also discussed.

Accuracy of BEMT and CFD on the power and trust prediction of tidal turbines

We compute the loads on a model-scale tidal turbine with Blade Element Momentum (BEM) theory and Computational Fluid Dynamics (CFD) simulations, and we compare the results with towing tank tests. CFD simulations are wall-resolved, steady, Reynolds-averaged Navier-Stokes simulations with a k − ω SST turbulence model, where only a 120◦ wedge domain with a single blade is resolved in a non-inertial frame of reference. We undertake a detailed uncertainty analysis to identify the sources of error. BEM uncertainty is computed with a Monte-Carlo approach based on the differences in the predictions of CFD and Xfoil for the sectional lift and drag coefficients,while CFD uncertainty is based on the errors due to the finite number of iterations and spatial resolution. The maximum error of CFD (8.0%) with respect to the experimental data is about half of that of BEM (15.5%) for the power (CP) and the thrust (CT) coefficients and both errors are within 4.1% for CFD and within 7.2% for BEM around the optimal tip-speed ratio (λ = 6.03). The BEM error is within the uncertainty associated with the imprecise knowledge of the sectional lift and drag coefficients. The sectional forces from CFD and BEM disagree at both the tip and the root, resulting in a substantial BEM underprediction of CP at high λ values (up to 15.5%), yet CT is well predicted (within 2.3%) at every λ. The CFD uncertainty is markedly smaller than the error, which is thus mostly due to a modelling error such as the turbulence model, the neglected effect of the support structure, the free surface, and the imprecise knowledge of the input conditions. Overall these results suggest that CFD provides both a maximum error and uncertainty that are substantially smaller than that of BEM, but both methods suffer from modelling errors that require further investigation.

Preliminary performance assessment from towing tank testing of a horizontal-axis turbine

Following the Norwegian government’s goal to be a ‘low emission society’ by 2050, there is a significant push to develop offshore renewable energy; principally offshore wind, but also wave and tidal stream. The MarinLab towing tank at the Western Norway University of Applied Sciences, Norway is 50 m long with a 3.0×2.2 m section and was inaugurated in 2016 as an educational and research facility, supporting local industry to achieve a low-carbon transition.
 To advance knowledge of aero- or hydrodynamic interaction of future turbines for both wind and tidal stream energy, a model scale test-bed horizontal axis turbine has been developed. This turbine will enable testing of rotor diameters typically in the range of 500-600 mm. The turbine is instrumented with a torque-thrust sensor of 5 Nm/100 N capacity, custom-manufactured by Marin in the Netherlands. The turbine is speed regulated via a 4096 counts angular encoder connected to a 200 W Maxon EC-i brushless motor.
 Before testing new rotor geometries, a benchmarking study is being undertaken with an existing known geometry. The benchmark rotor has diameter, D=700 mm and employs the same NACA 63418 airfoil as Mycek et al. (2014), allowing comparison. Unlike Mycek et al. (2014), the nacelle has a nominal diameter of 90 mm and length 760 mm. The size of the rotor risks exceeding the capacity of the torque sensor, such that maximum tow-speed is limited to 0.8 m/s. The benchmark blades are machined from solid aluminium in a four-axis CNC milling machine, following a method similar to Payne et al. (2017). Due to machining limitations, the minimum trailing edge thickness is specified as 0.2 mm. The final surface finish is achieved by manual polishing, and the final dimensions, quantified using a Hexagon ROMER Absolute laser scanner, are found to be within ±0.2 mm accuracy. Future blade sets will typically have a smaller diameter, allowing for 3D printing and consistency of surface finish.
 A blade-element momentum model has been run with Prandtl tip and hub losses and 0° pitch (Fig. I). Lift and drag coefficients were calculated for a range of chord Reynolds numbers using XFOIL, for angles of attack between -5 to 16° and extrapolated to ±180° with Viterna’s method. Due to difficulties in estimating laminar-turbulent transition around critical Reynolds numbers, there is uncertainty in the XFOIL coefficients. At peak TSR, the chord-based Reynolds number is approximately 280k at 3/4 span. Curves for both Rec =250k (solid) and 500k (dashed) with Ncrit = 9 are presented, showing a significant drop in performance for lower Reynolds numbers, due to a collapse in Cl/Cd. Initial tests were conducted in near- zero ambient turbulence, though passive turbulence grids are available for future testing. Reasonable agreement on CT is observed when corrected for blockage according to Bahaj (2007), and further assessment will provide results on CP, tower loads and wake recovery.

PIV wake survey of a drone propeller for amphibious applications

Aerial and underwater drones are one of the most attractive technologies to a large number of applications, extending from surveillance of natural reserves to the monitoring of structures. For these reasons, innovative and uncommon applications are constantly appearing. Within this context, drones capable to operate continuously and efficiently in air and water can extend the standard aerial capabilities allowing underwater inspections of harbour structures, pipelines or marine reserves. For this reason, an attractive characteristic for drones is the capability to manoeuvre in different fluids as air and water. This article presents an experimental campaign, carried out both in a towing tank and in a cavitation tunnel, aimed at study the fluid-dynamics of an aeronautic drone-propeller in off-design conditions. Dynamometric, PIV and Stereo-PIV tests are carried out to evaluate the aeronautic propeller functioning in water and optimize it for amphibious missions. In particular, the forces are measured for different advance ratios J provided by varying both rotational regime and free stream velocity, in open water conditions (Towing tank tests) and in confined water (Cavitation tunnel tests). PIV and Stereo-PIV fields, acquired in the Cavitation tunnel, allow us to investigate the behaviour of the propeller in the water in a number of selected, operative conditions.

Development of rapid and effective oil-spill response system integrated with oil collection, recovery and storage devices for small oil spills at initial stage: From lab-scale study to field-scale test

In the present study, through the laboratory-to-field scale experiments and trials, we report the development and evaluation of an integrated oil-spill response system capable of oil collection, recovery (separation), and storage, for a timely and effective response to the initial stage of oil-spill accidents. With the laboratory-scale experiments, first, we evaluate that the water-surface waves tend to abate the oil recovery rate below 80% (it is above 95% for the optimized configuration without the waves), which is overcome by installing the hydrophilic (and oleophobic) porous structures at the inlet and/or near the water outlet of the separator. In the follow-up meso-scale towing tank tests with a scaled-up prototype, (i) we optimize the maneuverability of the assembled system depending on the speed and existence of waves, and (ii) evaluate the oil recovery performance (more than 80% recovery for the olive oil and Bunker A fuel oil). Although more thorough investigations and improvements are needed, a recovery rate of over 50% can be achieved for the newly enforced marine fuel oil (low sulfur fuel oil, LSFO) that was not targeted at the time of development. Finally, we perform a series of field tests with a full-scale system, to evaluate the rapid deployment and operational stability in the real marine environment. The overall floating balance and coordination of each functional part are sustained to be stable during the straight and rotary maneuvers up to the speed of 5 knots. Also, the collection of the floating debris (mimicking the spilled oil) is demonstrated in the field test. The present system is now being tested by the Korea Coast Guard and we believe that it will be very powerful to prevent the environmental damage due to the oil spills.

Ship motions and unsteady pressures on ship hull in oblique waves estimated by potential-based solvers

The seakeeping performances in oblique wave conditions, such as ship motions and unsteady pressures on a ship hull, are getting more important, recently. These physical quantities are used for estimating loads induced by waves and evaluating the safety of a ship. Thanks to the evaluation of various incident wave angles, a rational ship design with sufficient safety and less construction cost can be realized. Therefore, the estimation by numerical schemes in those conditions is demanded for the ship design. However, schemes were usually validated through the comparison with experimental data in only heading wave conditions because few towing tanks can carry out the experiment for a ship advancing in oblique waves. The computed results in oblique waves should be validated well before the industrial usage of schemes. Although Computational Fluid Dynamics is useful to know the seakeeping performance in oblique waves thanks to the development of computer performance in these years, it takes much longer time than the schemes based on a potential theory. For this reason, three solvers based on the potential theory, the Salvesen-Tuck-Faltinsen method, the Green function method, and the Rankine panel method, are validated by comparing ship motions and unsteady pressure on the ship hull obtained from towing tank tests in oblique wave conditions.

An experimental investigation of the effect of ride control systems on the motions response of high-speed catamarans in irregular waves

To ensure high-quality passenger comfort and enhance the operability and performance of high-speed catamarans, reducing the severity of motions and structural loads using Ride Control Systems (RCS) is beneficial. To optimize ride control algorithms, it is essential to have a thorough understanding of the RCS in actual ship sailing conditions. In this paper, a set of towing tank tests was undertaken to study the effectiveness of different control algorithms, including linear and nonlinear versions of the heave control, pitch control, and local control, on motion responses of a 2.5 m scaled model of a 112 m INCAT Tasmania high-speed catamaran in irregular waves. The RCS included a centre bow-fitted T- Foil and two transom-mounted stern tabs. Obtained results were also compared with the scale model responses with passive RCS and with no RCS fitted. Heave and pitch motion responses as well as vertical accelerations of the catamaran were calculated in head seas at a model speed of 2.89 m/s (37 knot full scale), a modal period of 1.5 s (10 s full scale) and two significant wave heights of 60 mm and 90 mm, simulating full scale wave heights of 2.7 m and 4 m, respectively. It was demonstrated that deploying a passive RCS led to modest reductions in the peak motion responses. The most significant reductions in ship motions took place in the nonlinear modes of the heave and pitch control algorithms at a significant wave height of 60 mm (full-scale 2.7 m). In this condition, the nonlinear pitch control mode was demonstrated to be the most effective algorithm since this control mode mitigated the peak pitch RAO by 41% and vertical accelerations by 46%. This was a substantial reduction in ship motions with the RCS at an equivalent full-scale speed of 37 knot at 2.7 m wave height in the random sea condition.

Comparative study of experimental and CFD results for stepped planing hulls

In recent years, research has been conducted on reducing resistance by adding steps on the bottom of high-speed craft. The most significant issue in the design of multi-stepped planing craft is the selection of an appropriate step configuration, i.e., step geometry, location, and height. This requires a general knowledge of the hydrodynamic behavior of each step configuration. Although the towing tank test is an effective method to predict accurately the hydrodynamic behavior of stepped planing boats, there are restrictions in studying some details. In this study, a Computational Fluid Dynamic (CFD) method is used to investigate the hydrodynamic behavior of a stepped planing hull with eight different step configurations in detail. Comparison of the results of trim angle, resistance, sinkage, wetted surface, and ventilation length of swept-stepped planing hulls for different step configurations at various Froude numbers shows that a maximum average resistance reduction occurs at 1.9 <FrB < 4.0 with the step height of 2.73% BTC located at 48.46% L from the transom. There is also a lower resistance associated with a step height of 0.91% BTC at 48.35% L distance from the transom at FrB > 4. These results can be used to improve high-speed planing hull performances by utilizing an appropriate step configuration.

Scaled model testing for the helical strakes in reducing the vortex-induced vibrations

The accuracy of the prediction of the suppression efficiency of the triplex helical strakes for vortex-induced vibrations (VIV) is important in the offshore industry for the risers. Towing tank tests of the 1:1 section model have been used in the study of one degree of freedom; however, this method requires a long time for both the preparation and the testing. In this study, a scaled model testing method based on the flume and the oscillating frame is proposed, which measured the oscillating amplitude and the forces for both the bare pipe and the triplex helical strakes. The scaled tests were carried out in the TU Delft, with the range of Reynolds number between 6000 and 20000. The results were compared with the real model test applied in the towing tank to evaluate the accuracy. The measured strake efficiency of the scale model test agrees with the full-scale model test, providing support for the scaled model test in reducing the vortex-induced vibrations.

Pool-Based Tow System for Testing Tethered Hydrokinetic Devices Being Developed to Harvest Energy From Ocean Currents

Abstract The immense potential for ocean current energy harvesting is being actively explored as the push for renewable energy becomes more urgent. This paper demonstrates a tow testing platform built to examine and validate mathematical models related to the performance of tethered, underwater, hydrokinetic devices in development to harvest energy from ocean currents, and presents experimental results illustrating how such a system can be used. The platform has been modularly designed to allow for the testing of various tethered, underwater energy-generation systems, including kite-based systems, coaxial turbines, and duct sails. Previous research on tethered energy-generating systems has primarily been focused on airborne systems. Additionally, the limited experimental research on tethered, underwater energy-generation systems has relied on a rigid rod for mechanical and electrical connections between the test articles and instrumentation. The tow testing platform presented in this paper accomplishes the mechanical and electrical connection through a dual-function tether, featuring internal conductors and an external sheath to support towing loads. The goal of this platform was to enable the emulation of ocean currents, which are largely unidirectional, and to retrofit a regular pool into a cost-effective, adaptable, small-scale tow tank test bed. The capabilities of the system include two-way communication with tethered devices, multiple towing profiles in order to emulate different flow regimes, real-time control, and differential velocities via dual winch operation.

To study the effectiveness of stern appendages (Cruciform & X Shaped configurations) for maneuverability of autonomous underwater vessel using computational fluid dynamics

Maneuverability is one of the main aspects to be considered during the early design stage of Autonomous Underwater Vehicles. Several captive tests such as Planar Motion Mechanism (PMM), Oblique towing test, and Rotating Arm tests were conducted to obtain the hydrodynamic derivatives of the Autonomous Underwater Vehicle (AUV). In this research, the effectiveness of control surfaces with Cruciform and X configurations has been predicted for the maneuverability of the DARPA SUBOFF model. Computational Fluid Dynamics (CFD) technique was applied and the k- ω turbulence model was used to estimate the flow characteristics in the boundary layer region. The Straight-Line Towing Tank test has been used to calculate the hydrodynamic derivatives due to linear velocity, while the Rotating Arm test with a moving reference frame has been used to estimate the hydrodynamic derivatives. All the tests were conducted at a speed of 6.5 knots and three angles of incidence (10,30,50) for Straight-Line motion and three radii (13m,18m,24m) for Rotating Arm test were adopted. The simulation results of hydrodynamic coefficients have been compared with experimental results for the Cruciform configuration and the error was below 15%. So, the same procedure was adopted for the X-form configuration, and the stability index was calculated for both configurations.