Dynamic Trim Research Articles

Optimal trim control of a high-speed craft by trim tabs/interceptors Part I: Pitch and surge coupled dynamic modelling using sea trial data

A pitch and surge coupled dynamic model of a high-speed craft is not available for dynamic trim control applications in the literature. The existing fluid-structure interaction models of a high-speed craft are not adequate for simulations and control applications, since they require a great deal of computation time, for example more than 20–40s depending on a vessel particulars. Hence, in this work, we aimed to obtain a dynamic model of a high-speed craft for surge and pitch motions. Then the obtained model will be utilized to design an automatic controller which adjust the command signal on a high-speed craft to increase fuel efficiency, safety and comfort of passengers in a vessel. The coupled pitch and surge motion of a high-speed craft with trim tabs/interceptors was modelled by using full scale sea trial data. The linear parametric modelling using System Identification (SI) Methods and Artificial Neural Network (ANN) modelling were carried out and the comparisons of both the training and validation results are given. High correlation coefficients and low average values of absolute errors in surge and pitch dynamics were obtained by using ANN Method. The ANN model can be improved for further control designs on a marine vessel's operations.

Evolutionary optimization of transonic airfoils for static and dynamic trim performance

The development and accelerated use of optimization frameworks in aircraft design is a testament to their ability to identify optimal and often non-intuitive shapes as a result of multi-disciplinary design objectives. Airfoil design is a continuously revised multi-disciplinary problem, and is pivotal to illustrate the performance of optimization frameworks involving numerical simulation, flexible shape parametrization, and intelligent evolutionary algorithms. An often overlooked component of this classic problem is to consider the dynamic aeroelastic behavior under trim conditions, which can generate explicit boundaries to the flight envelope. Trim introduces a significantly strong coupling with objectives governing static performance, e.g. aerodynamic and/or structural, thereby resulting in a highly nonlinear and discontinuous design space. In this paper, a multi-objective particle swarm optimization framework for multi-disciplinary performance improvement is presented, pertaining to aerodynamic, structural and aeroelastic design criteria at trim conditions. The framework is assisted by the construction of adaptive Kriging surrogates, which is cooperatively used with the numerical solver to identify optimal solutions within a computational constraint. Designer preferences are introduced to reflect the optimal compromise between the objectives. Results of the optimization process indicate a large spread in design variable influence and interaction, and a subtle yet clear distinction between all objectives is illustrated through the catalog of final airfoil candidates obtained.

An Extended Verification and Validation Study of CFD Simulations for Planing Hulls

In the context of marine application of computational fluid dynamic (CFD), it is well known that the numerical simulations of planing craft are significantly less reliable than that of displacement ships. For this reason, it is important to perform a comprehensive approach to the verification and validation (V&V) methodology and procedures for simulating CFD planing craft. In the first part of this paper, an assessment of the accuracy and effectiveness of different simulation setups and techniques for planing craft is performed. In the second part, the results of the V&V study are reported for three different hull models at four Froude numbers (Fr). The Unsteady Reynolds-Averaged Navier-Stokes code results were validated using benchmark experimental data obtained for three hull models characterized by systematic variation of the length to beam ratio. Grid independence, iteration, and time-step convergence analysis for response variables (resistance coefficients, wetted surfaces, and dynamic trim angles) were conducted using the main error and uncertainty estimation methods available in the literature. The same procedures were followed for the profiles of the wave patterns. The results showed that there was improved reliability of the numerical simulation of the planing craft in terms of the errors and uncertainties, related to the predictions of resistance, running attitude, and wave pattern. The results of the V&V study highlighted the fact that modeling of the planing craft is a critical point to improve the reliability of the numerical simulation.

An Extended Verification and Validation Study of CFD Simulations for Planing Hulls

In the context of marine application of computational fluid dynamic (CFD), it is well known that the numerical simulations of planing craft are significantly less reliable than that of displacement ships. For this reason, it is important to perform a comprehensive approach to the verification and validation (V&V) methodology and procedures for simulating CFD planing craft. In the first part of this paper, an assessment of the accuracy and effectiveness of different simulation setups and techniques for planing craft is performed. In the second part, the results of the V&V study are reported for three different hull models at four Froude numbers (Fr). The Unsteady Reynolds-Averaged Navier-Stokes code results were validated using benchmark experimental data obtained for three hull models characterized by systematic variation of the length to beam ratio. Grid independence, iteration, and time-step convergence analysis for response variables (resistance coefficients, wetted surfaces, and dynamic trim angles) were conducted using the main error and uncertainty estimation methods available in the literature. The same procedures were followed for the profiles of the wave patterns. The results showed that there was improved reliability of the numerical simulation of the planing craft in terms of the errors and uncertainties, related to the predictions of resistance, running attitude, and wave pattern. The results of the V&V study highlighted the fact that modeling of the planing

잠수함의 종동요각 한계예측 알고리즘 설계

An envelope protection system is a control system that allows a submarine to operate freely using its own operational envelope without exceeding the structural limit, dynamic limit, and control input limit. In this paper, an envelope protection system for the pitch angle of a submarine is designed using a dynamic trim algorithm. A linear quadratic regulator and artificial neural network are used for the true dynamics approximation. A submarine maneuvering simulation program developed using experimental data is used to validate the designed envelope protection system. Simulation results show the effectiveness of the designed envelope protection system.

Design of a safety operational envelope protection system for the pitch angle of a submarine

Submarines have a safety operating envelope, the boundary of which is closely related to structural limits and the safety of crew. An envelope protection system guarantees that the submarine does not exceed the boundary, which reduces the frequency of operational accidents and mission time. In this article, an envelope protection system for the pitch angle is designed for a submarine. The envelope protection system consists of limit detection and limit avoidance. Limit detection is designed using a dynamic trim algorithm, and command limiting is used for the limit avoidance. An artificial neural network is adopted for on-line learning and modeling uncertainty compensation, and a linear quadratic regulator is employed to stabilize the error dynamics. A submarine maneuvering simulation program developed from the experimental data is used to validate the designed envelope protection system. The simulation results show the effectiveness of the envelope protection system.

트림 변화에 따른 컨테이너선의 저항성분별 특성 연구

The shipping and shipbuilding industries have had business difficulties since the implementation of regulations on the CO2 emissions from ships by IMO and the occurrence of the global financial crisis in 2008. Under this global recession, most shipping firms have started to operate their fleets at slow steaming rates with the goal of improving the profit ratio per transported unit. This study analyzed the resistance performance of a 6,800 TEU container ship corresponding to its trim variation with slow steaming, compared with that at its original design speed. Two different grid systems were used for the numerical calculation, one that considered the free surface allowing the capture of the dynamic trim and one that did not. This made it possible to clearly classify each resistance component to provide useful information to hull-form designers. In addition, a form factor assumption method using CFD was used for a reasonable effective power prediction in compliance with the 1978 ITTC performance prediction method. It was found that the total resistance of a 6,800 TEU container ship was reduced by 2.6% in the case of a 1-m trim at the bow at 18 kn.

LADRC-based attitude decoupling control for helicopter and parameters tuning

To meet the ADS-33E-PRF flight quality and effectively overcome the influence of external disturbance,an attitude control strategy based on a linear active disturbance rejection control( LADRC) is proposed for helicopter. Flight dynamics model of UH-60 A and the wind model were established. UH-60 A was trimmed for verifying accuracy of dynamic model and trim algorithm. Helicopter attitude decoupling control loop based on the single input / single output second-order LADRC controller was set up with stabilization feedback loop. The controller parameter tuning problem was transformed into constrained optimization problem in time and frequency domain according to quality requirement of ADS-33E-PRF. Combining H-infinity synthesis algorithm and steepest descent algorithm,the optimization of parameters was calculated. Quality assessment of attitude control was made and the control loop was applied to the attitude hold control simulation in atmospheric disturbance. The results of simulation and quality evaluation show that the attitude control system based on LADRC has good decoupling performance and capability of anti-disturbance.

Rankine Source Method for Ship–Ship Interaction Problems

A Rankine source method is extended and applied to ship–ship interaction problems. The method covers the nonlinear steady flow and linear seakeeping in the frequency domain. The nonlinear steady flow solution accounts for the nonlinear free-surface conditions, ship wave, and dynamic trim and sinkage. Periodic flow due to waves is linearized with respect to the wave amplitude, taking into account interactions with the nonlinear steady flow following Hachmann approach, which considers the steady perturbation potential as constant in the body-fixed reference frame. This is advantageous for the prediction of ship motions at moderate to high Froude numbers. In this context, a new formulation of the boundary condition for the multibody case is derived. Two examples are considered, overtaking in calm water and replenishment at sea. For a feeder vessel overtaken by a container ship, horizontal forces and yaw moment are computed and compared with reference data. As an example of replenishment operation, interaction between a frigate and a supply vessel is studied. Ship motions are computed for two relative positions and three forward speeds and compared with model test data for the largest forward speed. The Rankine source method proves as more accurate compared with a zero-speed freesurface Green function method. [DOI: 10.1115/1.4029316]

Numerical investigation of a stepped planing hull in calm water

Stepped planing hulls enable the feasibility of running at relatively low Drag-Lift ratio by means of achieving more optimal trim angle at high speeds. Currently, there is no precise method to analyze these hulls over the full range of operating speeds. In this study, a three-dimensional computational fluid dynamics (CFD) model using volume of fluid (VOF) approach is presented for examining the characteristics of a planing hull having one transverse step. A procedure is presented to transform a series of fixed-position simulations into a free to heave and pitch simulation. Resistance, lift, running draft, dynamic trim angle, and wetted area are compared with available experimental data and those of a semi-empirical method at volumetric Froude number in the range of 2.41–7.12. Centerline wake profile and reattachment location are compared with those of empirical equations. Wetted area at forebody chines-dry mode is qualitatively compared with a typical under water photograph of a stepped hull. The quantitative and qualitative results are found in acceptable correlation with experimental data, hence they can be reliably used in the stepped hull hydrodynamic investigation.

1인승 소형 보트 설계 및 속도성능 분석

The objective of the This study is to access the speed performance employing the sea trial test and CFD with the our own designed and manufactured one-man boat. The overall design process including hull form design was explained. The sea trial was carried out with a manufactured boat in the clam sea. Brake power at the design speed of a boat through the sea trial was measured as 1680 W. The flow computation was conducted considering free surface and dynamic trim using a commercial CFD code(STAR-CCM+). The result of computation provided the information that residual resistance is bigger than fraction`s at design speed. The total efficiency were predicted based on the sea trial and CFD. The Total efficiency was divided into shaft efficiency and quasi-propulsive efficiency. By using quasi-propulsive efficiency, it becomes possible to predict speed performance of boat in future. The results can provide information regarding hull form design, performance analysis and development of a boat in future.

Forward flight of birds revisited. Part 2: short-term dynamic stability and trim.

Thrust generation by flapping is accompanied by alternating pitching moment. On the down-stroke, it pitches the bird down when the wings are above its centre of gravity and up when they are below; on the up-stroke, the directions reverse. Because the thrust depends not only on the flapping characteristics but also on the angle of attack of the bird's body, interaction between the flapping and body motions may incite a resonance that is similar to the one that causes the swinging of a swing. In fact, it is shown that the equation governing the motion of the bird's body in flapping flight resembles the equation governing the motion of a pendulum with periodically changing length. Large flapping amplitude, low flapping frequency, and excessive tilt of the flapping plane may incite the resonance; coordinated fore–aft motion, that uses the lift to cancel out the moment generated by the thrust, suppresses it. It is probably incited by the tumbler pigeon in its remarkable display of aerobatics. The fore–aft motion that cancels the pitching moment makes the wing tip draw a figure of eight relative to the bird's body when the wings are un-swept, and a ring when the wings are swept back and fold during the upstroke.

Concurrent Learning Enabled Adaptive Limit Detection for Active Pilot Cueing

Neural-network-based adaptive dynamic models are commonly used to estimate allowable control travel and the proximity to a limiting flight condition in the design of advanced envelope protection algorithms for fly-by-wire aircraft. In this paper, linear models are compensated with adaptive neural networks, which use instantaneous sensor data as well as past flight history information for concurrent learning. A law for collecting appropriate training data into the history stack is established. It is observed that using the proposed time history data for online neural network training provides more accurate dynamic trim and control limit predictions compared to using instantaneous sensor data only. Simulation results for a fixed-wing aircraft during maneuvers show comparisons between the different adaptation schemes.

Linear and Nonlinear Sectional Loads With Potential and Field Methods

A Rankine source method is applied to predict linear and weakly nonlinear sectional loads of a modern container ship. The method uses solution in the frequency domain, linearized with respect to wave amplitude about the nonlinear steady flow due to forward speed, which accounts for the nonlinear free-surface conditions, ship wave, and dynamic trim and sinkage. Weak nonlinearity of the sectional loads in waves (e.g., hogging-sagging asymmetry) is taken into account by pressure extrapolation and integration up to the estimated actual water line. The sectional forces obtained with this method are compared with the results of other methods, including (1) linear Rankine panel method, where flow due to waves is linearized about the double-body flow, (2) linear zero-speed Green function method with correction for forward speed, (3) fully nonlinear simulations based on field-based solution of Reynolds-averaged Navier–Stokes (RANS) equations, and (4) model tests. Comparison with RANS solution and model tests shows, that the proposed method can accurately predict sectional loads for small to moderate wave heights.

The Analysis of Motion Dynamics and Resistance of the Multipurpose Boat Operating in Shallow Water

Polish market of small boats has been developed very dynamically in recent years. Market competition forces the shipyards to build new more efficient hull forms and to cut the cost of production as well. This is why modern computer simulation programs are used more often by naval architects. Another trend is to design more universal ships that may be used by larger number of diversified customers. This paper presents project proposal of multipurpose boat hull form. The boat was design to fulfill the requirements imposed by public services like water police, fire brigades, and border guards. It is supposed to be operated on unexplored floodplains and other type shallow waters. The analysis of boat’s motion was based on computer simulations. The resistance curve was evaluated with two methods: comparison study of model test results of similar ships and CFD methods. The results obtained from Ansys Fluent and FINE/Marine systems were compared in this paper. It was shown that taking into consideration dynamic trim and sinkage has a significant impact on free surface capture and resistance values.

Experimental Study of a Tanker Ship Squat in Shallow Water

One of the phenomena restricting the tanker navigation in shallow waters is reduction of under keel clearance in the terms of sinkage and dynamic trim that is called squatting. According to the complexity of flow around ship hull, one of the best methods to predict the ship squat is experimental approach based on model tests in the towing tank. In this study model tests for tanker ship model had been held in the towing tank and squat of the model are measured and analyzed. Based on experimental results suitable formulae for prediction of these types of ship squat in fairways are obtained.

Experimental evaluation of ship squat in shallow waters

Enlargement of ship size in recent decades and no change in the harbors and approach channels have resulted in global attention toward navigation in shallow and confined waters. A phenomenon which restricts ship navigation in shallow waters is reduction of under-keel clearance in terms of sinkage and dynamic trim, which is called squatting. Due to the complexity of flow around the ship hull, one of the best methods for predicting the ship squat is the experimental approach based on systematic model tests in the towing tank. In this study, model tests for tanker ship model and traditional Persian Gulf and Oman Sea vessel called dhow had been performed in the towing tank and the squat of the models were measured and analyzed. Based on the experimental results, suitable formulae for the prediction of these types of ship squat in fairways are obtained.

고속선의 트림제어 장치가 항주 자세 및 저항 성능에 미치는 영향

The displacement Deep-V catamaran concept was developed in Newcastle University(UNEW) through development of the systematic Deep-V catamaran series. One of the most important Deep-V catamaran launched to date is Newcastle University's own multi-purpose research vessel, The Princess Royal. The vessel was launched in 2011 and enhanced the Deep-V catamaran concept further with the successful adoption of a novel anti-slamming bulbous bow and tunnel stern for improved efficiency. It was however identified that the vessel has substantial amount of dynamic trim that limited the visibility of the captain. The dynamic trim also increased the wave-making resistance thereby preventing the vessel from attaining its maximum speed in certain sea states. This paper therefore presents the application of devices such as Trim Tabs, Interceptors, Transom Wedges and Integrated Transom Wedges-Tabs to control the dynamic trim and improvement of fuel efficiency of the vessel. All of these energy saving devices were fitted into a model for tests in Newcastle University's Towing Tank. Model test verification confirmed that the optimum appendage was the interceptors, they produced a 5% power saving and 1.2 degree trim reduction at 15 knots, and investigations of full scale trials will be scheduled with and without application of device to compare the improvement of performance.

Experimental investigation of dynamic trim control devices in fast speed vessel

The displacement Deep-V catamaran concept was developed in Newcastle University(UNEW) through development of the systematic Deep-V catamaran series. One of the most important Deep-V catamaran launched to date is Newcastle University`s own multi-purpose research vessel, The Princess Royal. The vessel was launched in 2011 and enhanced the Deep-V catamaran concept further with the successful adoption of a novel anti-slamming bulbous bow and tunnel stern for improved efficiency. It was however identified that the vessel has substantial amount of dynamic trim that limited the visibility of the captain. The dynamic trim also increased the wave-making resistance thereby preventing the vessel from attaining its maximum speed in certain sea states. This paper therefore presents the application of devices such as Trim Tabs, Interceptors, Transom Wedges and Integrated Transom Wedges-Tabs to control the dynamic trim and improvement of fuel efficiency of the vessel. All of these energy saving devices were fitted into a model for tests in Newcastle University`s Towing Tank. Model test verification confirmed that the optimum appendage was the interceptors, they produced a 5% power saving and 1.2 degree trim reduction at 15 knots, and investigations of full scale trials will be scheduled with and without application of device to compare the improvement of performance.

선박의 트림 자세가 저항 성능에 미치는 영향

The primary objective of the current work is to obviously analyze regarding effects of trim conditions of a ship on resistance performance using model test and CFD. Model tests at a towing tank are conducted to investigate resistance for trim conditions at the given same displacement. Measured resistance shows small but distinct differences according to trim conditions. However, these differences are difficult to be clarified by measured physical quantities and wave pattern analysis from model tests. CFD is employed for the assessment of resistance performance according to trim conditions. The flow computation is conducted considering free surface and dynamic trim using a commercial CFD code (STAR-CCM+). The initiative of the present work is to systematically demonstrate pressure resistance acting on each region of divided finite zones of ship surface along the length and draught direction of surface when pressure distribution on the ship is interpreted. Also, a standard to assess the pressure resistance applied on the divided regions of a ship is established.