Tank Model Tests Research Articles

Experimental and Numerical Investigation on the Motion Responses of a Spar-Type Floating Structure with Aquaculture Feeding Systems

The combination of aquaculture industry with floating offshore wind turbines has the potential to generate significant economic advantages for both industries. To investigate this potential, the present study focuses on analyzing the heave, and pitch dynamic responses of a Spar-type floating offshore wind turbine that incorporates an aquaculture feeding system. A series of water tank model tests, together with numerical calculations, were conducted using a 1/56 scale model of a 2 MW, displacement 3500 tons, floating Spar-type wind turbine. The feeding system was placed inside the Spar and slightly above the waterline by adjusting the configuration of the total weight. The weight of the feeding system in the experiments is 100 tons, capable of sustaining 300 tons of fish for an entire week, and the realistic applications have been expanded using the numerical calculation. For this reason, the present study serves a good case study for general understanding, because the integration of the feeding system inevitably raises the center of gravity of the structure and potentially affects its overall stability. The experiments revealed no discernible increase in the heave motion. Moreover, the pitch motion theoretically increased, but occasionally decreased in the experiments with the overall inclination angles being less than 1.2 degrees during the experiments. As a result, the present study supports the practice of integrating a Spar-type wind turbine with feeding systems. Future research should continue to comprehensively examine, both experimentally and numerically, the motion responses of the wind turbine and aquaculture facilities with varying configurations.

Numerical analysis of influencing factors on wave load for an amphibious aircraft

Numerical method of wave load for an amphibious aircraft is carried out in this paper, and its effectiveness is verified by comparing with towing tank model test. It shows that at the same wavelength and speed, the aircraft’s wave load is positively correlated with the change of wave height, but with the increase of wavelength, the difference shows a gradually decrease. And wave load is positively correlated with the speed, the greater the speed, the greater the wave load is. The wave load decreases with the increase of the wavelength. The peak load generally occurs in the short wave state of 1.2 times the length of the fuselage. With the increase of the wavelength, the aircraft load gradually decreases.

Numerical and experimental study of stern flaps impact on resistance and propulsion of high–speed displacement ships

This study investigates hydrodynamic interactions between a high-speed displacement ship and various stern flap configurations. It combines towing tank model tests and advanced Computational Fluid Dynamics (CFD) simulations to explore hydrodynamics and energy-saving potential. Sixteen flap combinations were tested across Froude numbers (Fn) from 0.198 to 0.452 to understand post-installation hydrodynamics and energy-saving potential. The alignment between model tests and CFD simulations reinforces the potential of stern flaps to enhance efficiency and environmental friendliness in high-speed displacement vessels with transom sterns. CFD enhanced visualisation of flow, pressure, and other hydrodynamic parameters. The study reveals that the stern flaps reduce resistance and effective power, saving energy across all the combinations. However, the effectiveness of the flaps is limited at lower speeds (Fn < 0.198), where increasing flap angles incur higher resistance penalties. The greatest decrease in resistance is noted when the Froude number (Fn) is at 0.367, with a subsequent reduction after that. Stern flaps influence trim, sinkage, and hydrodynamic length, reducing wave-making resistance without increasing friction. Increased wake fraction and reduced thrust deduction enhance propulsion efficiency, while stern flaps suppress waves, lowering overall resistance. A reduction of effective power by 6% was observed in the present study. This research provides valuable insights into stern flap hydrodynamics and energy-saving potential, guiding ship design and operation.

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.

Multi wave absorber platform design, modelling and testing

The subject of this paper is the development of physical and numerical models and a tank test programme to investigate the performance of a multi wave energy absorber platform (MWAP). The platform is inspired by the proposed designs for large scale platforms to be used for floating offshore wind (FOW). The modular design of the physical model enables a variable number of absorbers to be mounted to the platform, with up to 9 absorbers tested simultaneously. The absorbers used are a simplified version of a submerged pressure differential device, with each absorber incorporating a set of mechanical springs to approximate the response of the real internal air spring. Physical model tank tests will be undertaken during 2023, utilizing a range of environmental conditions representative of those at an exposed site on the west coast of Scotland, leased through the ScotWind programme and which has an appropriate water depth and wave resource for large scale wave energy exploitation. Measurements taken during physical model testing will be used to validate numerical models of the MWAP and will allow subsequent investigation of key drivers of annual energy performance, exploring platform configuration options not tested in the wave tank. The motivation for this project, design considerations and balance between tank scale &amp; full-scale design requirements will be given. Discussion will be provided on the implications of the limitations and assumptions made during the physical and numerical modelling work, as well as next steps for utilisation of the tools beyond the scope of this project.

Numerical analysis of influencing factors on wave load for an amphibious aircraft

Numerical method of wave load for an amphibious aircraft is carried out in this paper, and its effectiveness is verified by comparing with towing tank model test. It shows that at the same wavelength and speed, the aircraft’s wave load is positively correlated with the change of wave height, but with the increase of wavelength, the difference shows a gradually decrease. And wave load is positively correlated with the speed, the greater the speed, the greater the wave load is. The wave load decreases with the increase of the wavelength. The peak load generally occurs in the short wave state of 1.2 times the length of the fuselage. With the increase of the wavelength, the aircraft load gradually decreases.

Experimental study on the towing stability of a towed underwater object

The towing stability of a towed underwater object was investigated through towing tank model tests. Three types of towing cables were employed, and the attitude of a towed object was measured by an inertial measurement unit. The towed object's geometry and the position of the towing point were fixed. The lower center of gravity enabled the positive pitch moment due to the increased moment arm and reduced the fluctuation of pitch motion. Three types of appendages, which were vanes, a streamlined bracket, and a spoiler, were employed. The magnitude of the damping force by the vanes and the resulting towing stability depended on the vanes' exposed area to the inflow. The damping force by the streamlined bracket enhanced the pitch stability. On the other hand, the spoiler deteriorated the towing stability as the tilted spoiler resulted in a stall and thereby nonlinear and unfavorable damping force.

Towards Data-Driven Models in the Prediction of Ship Performance (Speed—Power) in Actual Seas: A Comparative Study between Modern Approaches

In the extremely competitive environment of shipping, minimizing shipping cost is the key factor for the survival and growth of shipping companies. However, stricter rules and regulations that aim at the reduction of greenhouse gas emissions published by the International Maritime Organization, force shipping companies to increase the operational efficiency of their fleet. The prediction of a ship speed in actual seas with a given power by its engine is the most important performance indicator and thus makes it the “holy grail” in pursuing better efficiency. Traditionally, tank model tests and semi-empirical formulas were the preferred solution for the aforementioned prediction and are still widely applied. However, currently, with the increased computational power that is widely available, novel and more sophisticated methods taking into consideration computational fluid dynamics (CFD) and machine learning (ML) algorithms are emerging. In this paper, we briefly present the different approaches in the prediction of a ship’s speed but focus on ML methods comparing a representative number of the latest data-driven models used in papers, to provide guidelines, discover trends and identify the challenges to be faced by researchers. From this comparison, we can distinguish that artificial neural networks (ANN), being used in 73.3% of the reviewed papers, dominate as the algorithm of choice. Researchers mostly rely on physical laws governing the phenomena in the crucial part of data preprocessing tasks. Lastly, most researchers rely on data acquisition systems installed at ships in order to achieve usable results.

Power output estimation of WEC with HF radar measured complex representative sea states

Wave tank model testing has been widely used to assess the performance of Wave Energy Converters (WEC) in different technology readiness levels (TRL). At early stage the use of simple wave conditions such as regular waves and parametric wave spectrum JONSWAP or Pierson-Moskowitz spectrum is acceptable. However at later stages there is a need to use site specific complex wave conditions representative of potential prototype deployment sites. In previous research, 10 different regrouping methods on HF radar measured wave spectrum were tested to find out the most representative sea states for tank testing. It has been shown that by using the K-means clustering technique, the characteristics of wave conditions can be well preserved. In order to assess the power capture performance of a typical WEC in these representative sea states, the RM3 point absorber has been simulated. By analysing how well the average power output predicted from different representative sea-state selection methods compares with the total power output prediction, it is shown that the non-directional wave spectrum K-means clustering method provides the most representative sea states and, for a point absorber, with a very accurate estimation of the total power output, which is not the case by using a traditional binning method. The importance of using the complex site-specific sea states rather than simplified parametric JONSWAP sea states to obtain the accurate total power estimation has also been shown.

The water impact load study for seaplane during get-off and alighting process on rough water

The scaled model tank test on rough water of a seaplane is conducted, and then we study the influence rules of wave length, wave height and test velocity on water load systematically, the results turn out to the that: the water load decreases as the wave length goes up, it decreases rapidly when the model moves at relatively high speed and slowly when model moves at low speed. as the test velocity goes up, the water load increases much more rapidly at short wave length than that at long wave length. when the model remains navigation status, the water load change slightly but rapidly in a linear fashion as to wave height when model remains planning status. in conclusion, the water load gets relatively high value at the status of higher speed and shorter wave length, and relatively low value at the status of lower speed and longer wave length.

Study on the performance of a 300W counter-rotating type horizontal axis tidal turbine

Tidal current energy shows great attractiveness as it stores an enormous amount of predictable sustainable resources that can be extracted and used for commercial power generation. The present study aims at investigating the performance of a 300 W counter-rotating type horizontal axis tidal turbine (HATT) by computational fluid dynamic (CFD) and experiments. And this study provides a novel method to test the performance of a tidal current turbine. In the present work, a bi-directional counter-rotating type HATT, the power and blade diameter are 300 W and 1 m respectively, was designed according to blade element momentum theory (BEMT). The CFD simulations, flume experiment tests, and sea trial were carried out to evaluate its performance. The experiment tests include 1/4 prototype blades towing tank model test and prototype large radius rotating arm tank test. The power coefficients of the blades under different blade tip speed ratios were obtained. Results shown that a good agreement has been obtained between the CFD predictions and the experiment data, moreover, the counter-rotating type HATT has a great power output performance. Such results provide valuable data for validating the hydrodynamic design and numerical simulations of counter-rotating type HATT. What's more, this work provides a novel method to test the performance of a tidal current turbine, which is a large-radius rotating arm tank test.

Experimental and Numerical Study on the Characteristics of Motion and Load for a Floating Solar Power Farm under Regular Waves

Recently, the demand for floating solar power farms in lakes and coasts (rather than on land) has been increasing rapidly. It is important to develop a numerical analysis technique that considers environmental conditions to predict structural stability and accurate motion response while designing a floating solar power farm. In this study, we performed a comparison under conditions similar to those of the Inha University towing tank (IUTT) model test to verify the numerical analysis method. The results revealed that heave and pitch movements were dominant under head sea conditions. Relative behavior occurred because of the hinge connection of each unit, and complex motion characteristics appeared depending on the wave conditions. The numerical method was verified based on the motion response and load of the floating solar farm. The validity of the results was also confirmed.

Effects of wave loads on the strength of semisubmersible drilling platform

In order to reduce the failure risk of the structures of semisubmersible drilling platform during its service life, this research studies the effects of ocean wave loads on the strength of the platform’s structures. The response spectra of the platform obtained from model test in wave tank were used to verify the accuracy of the numerical model employed in this research. Eight wave load cases, which may affect the strength of the platform but not involved in the classification societies such as ABS and DNV, were newly considered in this research. The results of the research indicate that a) four of the eight newly added wave load cases are found to be greatly affecting the strength of the platform and need to be considered in designing the structures; b) torsional moment and shearing force caused by the ocean wave would cause the stress of the structures of platform at a high level and need to be carefully evaluated.

Development and validation of a method to predict the soil thermal conductivity using thermal piezocone penetration testing (T-CPTU)

A new in situ thermal piezocone penetration test (T-CPTU) system is developed to determine the thermal properties of soil. It is expected to overcome most of the shortcomings observed in existing in situ test techniques. Based on Fourier's heat conduction equation and pore pressure dissipation theoretical equation, a method for calculating the thermal conductivity, namely the predicted temperature method, was proposed. The accuracy of the T-CPTU probe testing process and thermal conductivity calculation results were verified by numerical simulation, laboratory large-scale model tank tests, and thermal needle tests. Finally, the field data of T-CPTUs at three sites in Nanjing, China, were collected and compared with the laboratory thermal needle tests. The results indicated that the thermal conductivities obtained using T-CPTU were accurate and closer to those of laboratory thermal needle tests for most soils. The thermal conductivities of the undisturbed soil samples measured in the laboratory were lower than those obtained by T-CPTU.

Numerical and experimental investigation for extreme storm-safe drilling riser

ABSTRACT Extreme storm-safe drilling riser, a solution to overcome high time cost of riser emergency retrieval under the situation of the imminent typhoon arrival, is to modify the existing drilling riser to make it disconnectable and leave the long riser string below in a freestanding mode to survive. The buoyancy can maintains neutral during the normal drilling operation. However, locally the buoyancy can will have some effect on the riser system nearby. Numerical analysis and a hybrid scaled truncated model test in the water tank are conducted for the two critical configuration modes: connected mode and freestanding mode. A series of load cases under various current and wave, buoyancy upthrust are conducted in the experimental test to evaluate the hydrodynamic and strength performance of the riser near buoyancy can. The numerical analysis, experimental model design, data post-process method and result discussion can be a valuable reference for deepwater drilling engineering.

Model testing of a floating wave energy converter with an internal U-shaped oscillating water column

The development of wave energy converters is centred on the combination of two factors: cost-effectiveness of energy extraction and system survivability on extreme sea conditions. Despite advances in numerical modelling, wave tank model testing still presents the most reliable option to evaluate these two factors. This paper presents an experimental study on the hydrodynamic responses of the UGEN, a wave energy converter consisting of an asymmetric floater with an internal U-shaped tank partially filled with water. The device absorbs energy through the oscillating-water-column (OWC) motion inside the U-shaped tank, induced by the wave action on the floater. The experimental testing of a bottom-moored 1:24th-scale model was performed at the COAST Laboratory, University of Plymouth, UK, considering regular and irregular wave conditions. The wave tank test measurements report six-degree-of-freedom rigid-body motions, mean drift forces, OWC motion, structural stresses and mooring loads. Results present the characterization of the energy absorption at the internal OWC induced by the floater’s sway, heave and roll. The occurrence of low-cycle auto-parametric resonance under certain wave conditions was detected and induced large roll motions, which affected power extraction and increased mooring line loads, particularly for large wave amplitudes.

부분 침수 조건에서 작동하는 프로펠러의 공기유입과 축계 기진력에 대한 실험적 연구

Through a series of bollard pull tests of a propeller in partially submerged condition, thrust, torque, and shaft excitation force of a conventional propeller model were measured using a six-component load cell. By variation of the Weber number and Reynolds number, a consistent towing tank model test condition was derived. The effects of propeller immersion depth on the ventilation behavior and change of force and moment acting onto the propeller shaft were investigated. The decrease in thrust owing to the inception of ventilation was confirmed, and a large degree of dispersion of the thrust and torque coefficients were also observed in the transition region where the blade tip was under the water surface. The shaft excitation force was derived from the force and moment onto the propeller shaft.

Validation of Real-Time Nonlinear Model Predictive Control on Point Absorber Type Wave Energy Converter by Tank Test

Real-time implementation of a nonlinear model predictive control (NMPC) for a point absorber type wave energy converter (PAWEC) with a tubular air cored permanent magnet generator is experimentally validated through tank model tests. The control inputs of the NMPC were updated by the differential equation to trace the solution of an associated two-point boundary-value problem. Two conventional control strategies, the resistive load control and the approximate complex-conjugate control with considering the copper loss (ACL), and the NMPC were implemented to the PAWEC model. The floater heave motion, control force of the generator, and power generation characteristics were compared in these control strategies. The power generation performance of the NNPC was the same level of that of the ACL in regular and irregular waves. The sensitivities to the linear viscous damping estimation error and to the wave excitation force estimation error in the NMPC were experimentally evaluated by the tank model tests.

Application of Monte Carlo simulations to uncertainty assessment of ship powering prediction by the 1978 ITTC method

Abstract The present study concerns uncertainty assessment of powering prediction from towing tank model tests, suggested by the International Towing Tank Conference (ITTC). The systematic uncertainty of towing tank tests was estimated by allowance of test setup and measurement accuracy of ITTC. The random uncertainty was varied from 0 to 8% of the measurement. Randomly generated inputs of test conditions and measurement data sets under systematic and random uncertainty are used to statistically analyze resistance and propulsive performance parameters at the full scale. The error propagation through an extrapolation procedure is investigated in terms of the sensitivity and coefficient of determination. By the uncertainty assessment, it is found that the uncertainty of resultant powering prediction was smaller than the test uncertainty.

Numerical Study on Wave-Ice Interaction in the Marginal Ice Zone

The effect of waves on ice sheet is critical in the marginal ice zone (MIZ). Waves break large sea ice into small pieces and cause them to collide with each other. Simultaneously, the interaction between sea ice and waves attenuates these waves. In this study, a numerical research is conducted based on a computational fluid dynamics (CFD) method to investigate the response of single ice floe to wave action. The obtained results demonstrate that the sea ice has a violent six degree of freedom (6DoF) motion in waves. Ice floes with different sizes, thicknesses, and shapes exhibit different 6DoF motions under the action of waves. The heave and surge response amplitude operator (RAO) of the sea ice are related to wavelength. Furthermore, the overwash phenomenon can be observed in the simulation. The obtained results are compared with the model test in the towing tank based on artificial ice, and they agree well with test results.