Anti-rolling Tank Research Articles

Control System Design of Anti-rolling Tank Swing Bench Using BP Neural Network PID Based on LabVIEW

The anti-rolling tank swing bench is a typical hydraulic position servo system. Its function is to simulate the ship roll motion and to verify the performance of the anti-rolling tank. Generally, the PID control method can achieve an ideal control effect. But the uncertainties, such as the couplings and the nonlinearty of the swing bench, make it difficult to establish the precise mathematical model of system. During experiments, the different disturbance torques are generated according to the different dimension scales of the anti-rolling tanks. Changes of the natural characteristics of the system are caused by changes of load, and the fixed parameters of PID controller are difficult to continue to ensure a good control effect. In order to reduce the influences caused by the factors mentioned above, a BP neural network PID control system based on virtual instrument LabVIEW is designed. By simulating the responses of the system in real time control, the verification tests using actual system are avoided. Finally, the experiments of swing bench are carried out. The results show that the controller can ensure the control accuracy and stability. The parameters tuning process efficiency is improved. The operation is convenient. The data acquisition process is simple and practical.

CFD aided modelling of anti-rolling tanks towards more accurate ship dynamics

Passive anti-roll tanks (ART) have been studied extensively to optimize their various design parameters. However, not much attention has been given to the accurate estimation of their damping. Here, we have developed the motion equation of water inside ART and proposed a CFD-based methodology to find the ART damping coefficient. Since our aim is to improve the modelling of flow inside ART, our analysis focuses on ART (without ship) to remove ship related complexities. Key findings regarding the damping are: (a) It is quadratic in the velocity and the damping coefficient can be expressed using a non-dimensional number, (b) one main part of the dissipation is bend losses, computed here using steady-state turbulent CFD, and (c) a second part of the dissipation is due to turbulence near the free surface, estimated here using a simple formula. We have calculated damping coefficients for five different designs of ARTs, and validated our results through both transient CFD simulations and experiments. The effect of these designs on ship motion has been discussed. The proposed model will help in better prediction of ship dynamics as far as inaccuracies due to ART modelling are concerned.

Experimental and numerical study of the sloshing motion in a rectangular tank with a perforated screen

Rectangular tanks partially filled with water and fitted with vertical perforated screens have been proposed as Tuned Liquid Dampers to mitigate the vibratory response of land buildings, under wind or earthquake excitation. Similar devices are used as anti-rolling tanks aboard ships. Experiments are performed on a rectangular tank with one screen at mid length. The tank is subjected to forced horizontal and rolling motions, harmonic and irregular. The open-area ratio of the screen is kept constant while the motion amplitudes and frequencies are varied. The frequency range covers the first three natural sloshing modes of the clean tank (without screen). Force measurements are converted into matrices of added mass/inertia and damping coefficients. A simple numerical model is proposed, based on linearized potential flow theory and quadratic discharge equation at the screen, following earlier works by the first author. Good agreement is reported between experimental and numerical hydrodynamic coefficients.

The Design of the Anti-Rolling Tank Control System Based on CAN-Bus

As the anti-rolling tank controller based on PLC is unable to fulfill the high strength of calculation of the automatic real-time control algorithm, which leads to the limitation of anti-rolling effect, this paper proposes a distributed embedded controller based on CAN bus communication. The controller uses a high-performance ARM chip as the main chip to meet the complex algorithm calculation requirements. For CAN bus communication between the distributed modules, the system is simple and reliable. Distributed embedded controller consists of the center controller, the IO controller and the communication adapter whose hardware design and software design are proposed in this paper, and achieves the acquisition of real-time data of ships status information and intelligent control algorithm. Through simulation and bench simulation experiments, the controller can achieves the excellent anti-rolling effect. The distributed controller architecture is simple and easy to expand and spread to various tonnages of real ships.

콴다효과를 적용한 고정식 핀 안정기의 성능개선에 관한 연구

A ship operating in rough sea may suffer from an undesirable motion which may severely degrade the performance of equipment onboard and give a person an uncomfortable feeling. Hence, roll stabilization received a considerable attention and various devices including bilge keels, stabilizing fins, gyroscopic, anti-rolling tanks, rudders and flaps have been conceived and utilized for the purpose. The Coanda effect is evident when a jet stream is applied tangential to a curved surface of a hydrofoil since then the jet increases the circulation around the foil and consequently the lift. Model tests and numerical simulation have been conducted to examine the practicality of a fixed type fin stabilizer augmented by the Coanda jet. The results show that the lift coefficient of the modified Coanda fin at the zero angle of attack identically coincides with that of the original fin at ${\alpha}

Preliminary assessments of the anti-roll tank as a wave energy converter

Wave energy is the largest renewable energy resource. To explore the approximate quantities of energy extraction, an anti-roll tank developed for reducing the excessive ship rolling was introduced into a type of wave energy converter (WEC). From a view of energy interaction, the interior liquid of tank absorbs part wave energy and converts to fluid kinetic energy, and this energy may exploit to generate electricity. Based on anti-roll tank technology, this study assessed the production of a particular amount of exploitable energy. A passive U-tube tank was chosen and a ship-form carrier was selected from a small craft. The liquid equation in the tank is coupled with the 5DOF equations of carrier's motion. A subroutine for integrating the tank equation is added to the non-linear strip synthesis, and all of the equations are integrated simultaneously and interactively within the time domain. Transformation efficiency is introduced to measure the percentage of power transformation. The result of the regular wave tests shows that the optimal transformation percentage occurs near the tank's natural frequency. If operating at sea, the average transformation efficiency of the proposed device is approximately 4.83%. It can be regarded as a potential device and needs further investigation.

Estimated electricity production for an anti-roll tank deployed offshore for use as a wave energy converter

Wave energy is the largest renewable energy resource; the total prospective annual wave energy resource offshore of Taiwan is approximately 16.9 TWh. To develop this energy potential, this study examines the anti-roll tank, which is used to reduce the excessive rolling of a ship, as a type of wave energy converter (WEC). From the perspective of energy interaction, the liquid in the tank absorbs part of the wave energy and converts it to a different type of kinetic energy during a ship's motion in the waves. Thus, for this study, a passive U-tube tank is chosen with a tank-carried buoy selected from a small craft. The liquid motion is coupled with the 5DOF equations of a ship's motion to calculate the frequency response functions (FRFs) of the tank's water height in regular waves, and then using the third-order Volterra model to construct the time histories of response at given seaway. The wave climate around Taiwan's coastal area is simulated using the Taiwan Coastal Ocean Modeling System (TaiCOMs) and the Longdong (25°05′43′′N, 121°55′21′′E), which is located in the northeastern coastal area of Taiwan, as a target testing area. Results show that the entire available electricity of 2009 was estimated to be approximately 7.2 × 104 kWh per deployed buoy.

A 3D fully coupled analysis of nonlinear sloshing and ship motion

This study investigates the coupling effects of six degrees of freedom in ship motion with fluid oscillation inside a three-dimensional rectangular container using a novel time domain simulation scheme. During the time marching, the tank-sloshing algorithm is coupled with the vessel-motion algorithm so that the influence of tank sloshing on vessel motions and vice versa can be assessed. Several factors influencing the dynamic behavior of tank–liquid system due to moving ship are also investigated. These factors include container parameters, environmental settings such as the significant wave height, current velocity as well as the direction of wind, wave and flow current acting on the ship. The nonlinear sloshing is studied using a finite element model whereas nonlinear ship motion is simulated using a hybrid marine control system. Computed roll response is compared with the existing results, showing fair agreement. Although the two hull forms and the sea states are not identical, the numerical result shows the same trend of the roll motion when the anti-rolling tanks are considered. Thus, the numerical approach presented in this paper is expected to be very useful and realistic in evaluating the coupling effects of nonlinear sloshing and 6-DOF ship motion.

A Lagrangian approach to nonlinear modeling of anti-roll tanks

This paper presents two novel nonlinear models of u-shaped anti-roll tanks for ships, and their linearizations. In addition, a third simplified nonlinear model is presented. The models are derived using Lagrangian mechanics. This formulation not only simplifies the modeling process, but also allows one to obtain models that satisfy energy-related physical properties. The proposed nonlinear models and their linearizations are validated using model-scale experimental data. Unlike other models in the literature, the nonlinear models in this paper are valid for large roll amplitudes. Even at moderate roll angles, the nonlinear models have three orders of magnitude lower mean square error relative to experimental data than the linear models.

250 TEU급 모바일하버를 위한 횡동요 저감 장치의 개념 설계 연구

A Mobile Harbor is a new transportation platform which can load and unload has containers to and from very large container ships on the sea. Currently designed Mobile Harbor a catamaran type which is equipped with precisely controlled gantry crane on the deck, and can transport 250 TEUs at a time. Loading and unloading works by crane require very small motion of Mobile Harbor in waves, because it may be operated outside of harbors. In this project, applicability of both tuned-type anti-rolling tank and maglev-type active mass driver is studied as anti-rolling systems.

Coupled Motion Simulation of the Mobile Harbor and Anti-Rolling Devices in Waves

The Mobile Harbor(MH) is a new transportation platform that can load and unload containers to and from very large container ships in the sea. This loading and unloading by crane can be performed with only very small movements of the MH in waves because MH is operated outside of the harbor. For this reason, an anti-rolling tank(ART) and an active mass driving system(AMD) were designed to reduce MH's roll motion, especially at the natural frequency of MH. In the conceptual design stage, it is difficult to confirm the design result of theses anti-rolling devices without modeling and simulation tools. Therefore, the coupled MH and anti-rolling devices' dynamic equations in waves were derived and a simulation program that can analyze the roll reduction performance in various conditions, such as sea state, wave direction, and so on, was developed. The coupled equations are constructed as an eight degrees of freedom (DOF) motion that consists of MH's six DOF dynamics and the ART's and AMD's control variables. In order to conveniently include the ART's and AMD's control dynamics in the time domain, MH's radiated wave force was described by an impulse response function derived by the damping coefficient obtained in the frequency domain, and wave exciting forces such as Froude-Krylov force and diffraction force and nonlinear buoyancy were calculated at every simulation time interval. Finally, the roll reduction performances of the designed anti-rolling devices were successfully assessed in the various loading and wave conditions by using a developed simulation program.

A nonlinear model of parametric rolling stabilization by anti-roll tanks

The present paper describes a mathematical model in which the fluid motion inside a U-tank is nonlinearly coupled to the heave, roll and pitch motions of the ship. The main purpose of the investigation is centred on the control of roll motion in the case of parametric resonance in longitudinal waves. A transom stern small vessel, known to be quite prone to parametric amplification, is employed in the study. Four tank designs are employed in order to study the influence of tank mass, tank natural frequency and tank internal damping on the control of parametric rolling at different head seas conditions. Additionally, the influence of the vertical position of the tank is also investigated. The main results are presented in the form of limits of stability, with encounter frequency and wave amplitudes as parameters. Distinct dynamical characteristics are discussed and conclusions are drawn on the relevant parameters for the efficient control of the roll amplifications in head seas.

Experimental and Numerical Studies on Ship Motion Responses Coupled with Sloshing in Waves

This study considers the motion responses of floating bodies in waves coupled with sloshing-induced internal forces and their effects on sloshing-induced impact loads. The linear ship motion is solved using an impulse-response-function (IRF) method, while the nonlinear sloshing flow is simulated using a finite difference method. The considered models are a liquid natural gas floating production, storage, and offloading unit (LNG FPSO) with two partially filled tanks and a modified S175 hull with an antirolling tank. In the case of the LNG FPSO model, both numerical and experimental studies are carried out. Three degree-of-freedom motion responses are allowed in the presence of regular waves, and the measured response amplitude operators (RAOs) are compared with computational results. For the modified S175 hull, the computational results are compared with other existing computational results. It is observed that the present method provides a fair agreement with experimental and other numerical results, showing significant coupling effects on both motion responses and sloshing flows. The numerical study extends to the observation of pressure field inside the tanks, and a significant difference in internal pressure is also shown.

Control of ship roll using passive and active anti-roll tanks

We numerically studied the full (six degrees of freedom) motion of a cargo ship without roll stabilizers in rough (sea state 5) conditions for multiple heading angles ranging from 0° (follower seas) to 180° (head seas). We found that the ship exhibits excessive roll motion in quartering (45° off the stern), beam, and head seas. Therefore, roll damping is critical in these conditions. We then investigated the performance of passive and active anti-roll tank (ART) systems and compared their performance in each of the three sea conditions. Each ART consists of three identical tanks, distributed along the centerline of the ship, each of which consists of two vertical ducts connected at the bottom with a horizontal duct. A pump is located at the middle of the horizontal duct of each tank. The pumps are switched on for active ARTs but switched off for passive ones. The loads (forces and moments) exerted on the ship by the ARTs are added to the hydrodynamic loads (e.g., due to pressure and viscous effects) and the thrust in the governing equations of motion of the ship. Whereas both passive and active ARTs are able to reduce the excessive roll motion, active ARTs outperform the passive ones from three perspectives. First, they are more effective in reducing the roll motion. Second, they require much less working liquid. Third, their performance is insensitive to their natural frequencies and, hence, to their geometric design. In addition, we found that head seas are most responsive to ARTs, which suggests that they are effective in mitigating parametric roll.

Research on roll stabilization for ships at anchor

With the increasing importance of ocean exploitation, providing anti-rolling stability for ships at anchor has become more and more important. The lift-generation theory of traditional fin stabilizers is based on incoming flow velocity, which is not suitable for explaining lift generated at anchor. We analyzed non-steady flows, with forces on fin stabilizers generated by non-incoming flow velocity conditions, and gave a new lift-generation model. The correctness of the model was proven by comparing experimental results of fin stabilizer motion under non-incoming velocity conditions from the fluid computation software with that from the emulator of the lift-generation model. Finally, the model was used in an anti-rolling system on a ship and the reduction of roll was much better than what could be achieved by passive anti-rolling tanks.

An investigation of different methods for the prevention of parametric rolling

The parametric rolling of modern containerships is emerging as a serious problem, to the extent that its effects warrant a study into its prevention. In light of this, two methods for reduction of parametric rolling are proposed and examined by physical model experiments. The first is a sponson attached to the side of a ship, the purpose being to decrease the rate of change of the rollrestoring moment. The second is an antirolling tank to increase roll damping. By conducting free-running model experiments for a 6600-TEU post-Panamax container ship with sponsons under typical parametric rolling conditions, it was found that the sponsons could decrease the magnitude of parametric rolling. The antirolling tank could prevent parametric rolling completely in certain conditions, even in severe head seas. Using the damping coefficients from experimentally derived data of a model ship with an antiroll tank, a numerical simulation was established. The numerical model was then compared with the free-running model experiments. The results indicated that the numerical model could qualitatively verify the experimental results. Finally, an attempt to optimise the size of an antirolling tank for preventing parametric rolling for the subject post-Panamax container ship in the North Pacific Ocean is presented.

Study on coupling effects of ship motion and sloshing

This study considers the coupling effects of ship motion and sloshing. The linear ship motion is solved using an impulse-response-function (IRF) method, while the nonlinear sloshing flow is simulated using a finite-difference method. The IRF method requires the frequency-domain solution prior to conversion to time domain, but the computational effort is much less than that of direct time-domain approaches. The developed scheme is verified by comparing the motion RAOs between the frequency-domain solution and the solution obtained by the IRF method. Furthermore, a soft-spring concept and linear roll damping are implemented to predict more realistic motions of surge, sway, yaw, and roll. For the simulation of sloshing flow in liquid tanks, a physics-based numerical approach adopted by Kim [2001. Numerical simulation of sloshing flows with impact load. Applied Ocean Research 23, 53–62] and Kim et al. [2004. Numerical study on slosh-induced impact pressures on three-dimensional prismatic tanks. Applied Ocean Research 26, 213–226] is applied. In particular, the present method focuses on the simulation of the global motion of sloshing flow, ignoring some local phenomena. The sloshing-induced forces and moments are added to wave-excitation forces and moments, and then the corresponding body motion is obtained. The developed schemes are applied for two problems: the sway motion of a box-type barge with rectangular tanks and the roll motion of a modified S175 hull with rectangular anti-rolling tank. Motion RAOs are compared with existing results, showing fair agreement. It is found that the nonlinearity of sloshing flow is very important in coupling analysis. Due to the nonlinearity of sloshing flow, ship motion shows a strong sensitivity to wave slope.

Research on the influence of action between fin and anti-rolling tank on the integrated stabilization effect

Through analyzing the roll model of the integrated system of fin and anti-rolling tank, this paper uses binomial equation to simplify the module and check how the approximate parameters simulate the original function. Based on the simplified module, the influence of fin and anti-rolling tank on the coefficient items of the roll module is discussed, and the influencing factors between fin and anti-rolling tank are analysed. And through simulation, the influence of action between fin and anti-rolling tank on the static characteristics, and the integrated stabilization effect, are analyzed.

パラメトリック横揺れ防止装置としてのアンチローリングタンクの性能推定

Recently, many incidents of parametric roll of container carriers and pure car carriers have been reported. For the prevention of parametric roll, installing an Anti-Rolling Tank (ART) is one of the most effective risk control options. To estimate the performance of ART, however, a damping coefficient of ART is required in a numerical simulation of parametric roll. For this purpose, a scaled model test of ART is normally executed while other coefficients related to the tank or coupling coefficients between the ART and the ship roll motion can be obtained from its dimensions. To overcome this drawback, we attempted to estimate the damping coefficient of ART by applying a MPS method (Moving-Particle-Semi-implicit method) and examined its applicability by comparing with the model experiment. As a result, the MPS method can estimate not only damping coefficient but also natural period of ART. By utilizing the obtained damping coefficient by the MPS method, numerical simulations of parametric rolling for a post-Panamax containership in regular head seas were conducted. Calculated results with help of the MPS method well reproduce parametric rolling observed in the model experiment. These comparisons show us the possibility of the design of an ART as a parametric rolling prevention device without any model experiments

On the development of ship anti-roll tanks

This paper reviews the development of ship anti-roll tanks from the 1880s to the present day including their modelling and control strategies. Mention is also made of other ship roll stabilization systems and the application of the technology to stabilization of other structures. The potential for the use of roll stabilization tanks on modern, high speed multi-hull craft which also have a low speed operational requirement is also discussed.