Application of Monte Carlo method in rudder control precision

After the trajectory simulation model of rudder control rocket with six degrees of freedom is established by Matlab/ Simulink, the simulated targeting of rudder control rocket with rudder angle error and starting control moment error is carried out respectively by means of Monte Carlo method and the distribution of impact points of rudder control rocket is counted from all the successful subsamples. In the case of adding interference errors associated with rudder angle error and starting time error, the simulation analysis of impact point dispersion is done and its lateral and longitudinal correction abilities at different targeting angles are simulated to identify the effects of these factors on characteristics and control precision of the rudder control rocket, which provides the relevant reference for high-precision design of rudder control system.

Hydrodynamic Performance Analysis of Propeller-rudder System with the Rudder Parameters Changing

In order to study the effects of geometric parameters of the rudder on the hydrodynamic performance of the propeller-rudder system,the surface panel method is used to build the numerical model of the steady interaction between the propeller and rudder to analyze the relevant factors.The interaction between the propeller and rudder is considered through the induced velocities,which are circumferentially averaged,so the unsteady problem is translated to steady state.An iterative calculation method is used until the hydrodynamic performance converges.Firstly,the hydrodynamic performance of the chosen propeller-rudder system is calculated,and the comparison between the calculated results and the experimental data indicates that the calculation program is reliable.Then,the variable parameters of rudder are investigated,and the calculation results show that the propeller-rudder spacing has a negative relationship with the efficiency of the propeller-rudder system,and the rudder span has an optimal match range with the propeller diameter.Futhermore,the rudder chord and thickness both have a positive correlation with the hydrodynamic performance of the propeller-rudder system.

CFD simulation of propeller and rudder performance when using additional thrust fins

To analyse a possible way to improve the propulsion performance of ships,the unstructured grid and the Reynolds Average Navier-Stokes equations were used to calculate the performance of a propeller and rudder fitted with additional thrust fins in the viscous flow field.The computational fluid dynamics software FLUENT was used to simulate the thrust and torque coefficient as a function of the advance coefficient of propeller and the thrust efficiency of additional thrust fins. The pressure and velocity flow behind the propeller was calculated. The geometrical nodes of the propeller were constituted by FORTRAN program and the NUMBS method was used to create a configuration of the propeller,which was then used by GAMMBIT to generate the calculation model. The thrust efficiency of fins was calculated as a function of the number of additional fins and the attack angles. The results of the calculations agree fairly well with experimental data,which shows that the viscous flow solution we present is useful in simulating the performance of propellers and rudders with additional fins.

Energy Optimization of the Fin/Rudder Roll Stabilization System Based on the Multi-objective Genetic Algorithm （MOGA）

Energy optimization is one of the key problems for ship roll reduction systems in the last decade. According to the nonlinear characteristics of ship motion, the four degrees of freedom nonlinear model of Fin/Rudder roll stabilization can be established. This paper analyzes energy consumption caused by overcoming the resistance and the yaw, which is added to the fin/rudder roll stabilization system as new performance index. In order to achieve the purpose of the roll reduction, ship course keeping and energy optimization, the self-tuning PID controller based on the multi-objective genetic algorithm （MOGA） method is used to optimize performance index. In addition, random weight coefficient is adopted to build a multi-objective genetic algorithm optimization model. The objective function is improved so that the objective function can be normalized to a constant level. Simulation results showed that the control method based on MOGA, compared with the traditional control method, not only improves the efficiency of roll stabilization and yaw control precision, but also optimizes the energy of the system. The proposed methodology can get a better performance at different sea states.

Design and Comparison of H∞/H2 Controllers for Frigate Rudder Roll Stabilization

Roll motion of ships can be distinguished in two parts:an unavoidable part due to their natural movement while turning and an unwanted and avoidable part that is due to encounter with waves and rough seas in general.For the attenuation of the unwanted part of roll motion,ways have been developed such as addition of controllable fins and changes in shape.This paper investigates the effectiveness of augmenting the rudder used for rejecting part of the unwanted roll,while maintaining steering and course changing ability.For this purpose,a controller is designed,which acts through intentional superposition of fast,compared with course change,movements of rudder,in order to attenuate the high-frequency roll effects from encountering rough seas.The results obtained by simulation to exogenous disturbance support the conclusion that the roll stabilization for displacement can be effective at least when displacement hull vessels are considered.Moreover,robust stability and performance is verified for the proposed control scheme over the entire operating range of interest.

Using RANS to Simulate the Interaction and overall Performance of Propellers and Rudders with Thrust Fins

The Reynolds-averaged Navier-Stokes (RANS) method, along with the Fluent software package, was used to study the steady and unsteady interaction of propellers and rudders with additional thrust fins.The sliding mesh model was employed to simulate unsteady interactions between the blades, the rudder and the thrust fins.Based on the numerical results, the pressure distribution on the propeller and the efficiency of the fins were calculated as a function of the attack angle.The RANS results were compared with results calculated by the potential method.It was found that the results for the potential method and the RANS method have good consistency, but they yield maximum efficiencies for the fins, and thus corresponding attack angles, that are not identical.

Synchro-control of Twin-rudder with Cloud Model

In ships having two rudders, an angle error exists if there is a difference in structural and electrical parameters in two steering gear systems. Such an error also results in reduced efficiency of ship maneuverability during navigation. For the sake of reducing the angle error, a synchro-ballistic control approach based on cloud model is proposed in this paper. First, the mechanism model of steering gear system is introduced. Second, the structure of synchro-control system of twin-rudder is proposed based on the master-slave control strategy. Third, synchro-ballistic controller based on cloud model is designed to solve the nonlinearity and uncertainty of system. Finally, the designed controller is tested via simulation under two different situations. The simulated results demonstrate that this method is simple and has stronger robustness against the variation of states and parameters of plants. Hence, the validity and reliability of the method is proved for synchro-control of two rudders, which is a significant engineering application.

Application of H~∞ control in rudder/flap vector robust control of a ship's course

Given the uncertainty of parameters and the random nature of disturbances that effect a ships course, a robust course controller should be designed on the basis of rudder/flap vector control. This paper analyzes system uncertainty, and the choice of weighting functions is also discussed. When sea waves operate on a ship, the energy-concentrating frequency varies with the angle of encounter. For different angles of encounter, different weighting functions are designed. For the pole of a nominal model existing in an imaginary axis, the bilinear-transform method is used. The "2-Riccati" equation is adopted to solve the H∞ controller. A system simulation is given, and the results show that, compared with a PID controller, this system has higher course precision and more robust performance. This research has significant engineering value.

Numerical Evaluation of Rudder Performance Behind a Propeller in Bollard Pull Condition

Correct evaluation of rudder performance is a key issue in assessing ship maneuverability.This paper presents a simplified approach based on a viscous flow solver to address propeller and rudder interactions.Viscous flow solvers have been applied to this type of problems,but the large computational requests limit(or even prevent)their application at a preliminary ship design stage.Based on this idea,a simplified approach to include the propeller effect in front of the rudder is considered to speed up the solution.Based on the concept of body forces,this approach enables sufficiently fast computation for a preliminary ship design stage,therebymaintaining its reliability.To define the limitations of the proposed procedure,an extensive analysis of the simplified method is performed and the results are compared with experimental data presented in the literature.Initially,the reported results show the capability of the body-force approach to represent the inflow field to the rudder without the full description of the propeller,also with regard to the complex bollard pull condition.Consequently,the rudder forces are satisfactorily predicted at least with regard to the lift force.However,the drag force evaluation ismore problematic and causes higher discrepancies.Nevertheless,these discrepancies may be accepted due to their lower influence on the overall ship maneuverability performance.

Numerical Simulation of Transverse Jet Interaction with Rudders in Supersonic Free Stream for Simplified Missile

Numerical simulation is carried out for jets arranged at 7 different positions for the same model and compared with non-jet flows.The total and rudder force and moment amplification is calculated and analyzed by the pressure distribution on the surface and rudders of the simplified missile.Numerical results show that interactions take great effect on the configuration of the flow field around rudders and the pressure distribution on the missile surface.

Rudder Roll Damping Autopilot Using Dual Extended Kalman Filter–Trained Neural Networks for Ships in Waves

The roll motions of ships advancing in heavy seas have severe impacts on the safety of crews,vessels,and cargoes;thus,it must be damped.This study presents the design of a rudder roll damping autopilot by utilizing the dual extended Kalman filter(DEKF)trained radial basis function neural networks(RBFNN)for the surface vessels.The autopilot system constitutes the roll reduction controller and the yaw motion controller implemented in parallel.After analyzing the advantages of the DEKF-trained RBFNN control method theoretically,the ship’s nonlinear model with environmental disturbances was employed to verify the performance of the proposed stabilization system.Different sailing scenarios were conducted to investigate the motion responses of the ship in waves.The results demonstrate that the DEKF RBFNN based control system is efficient and practical in reducing roll motions and following the path for the ship sailing in waves only through rudder actions.

Studies on the Seizure of Rudder on the Flight Safety of an Aircraft

The demands of aircraft quality design criterion on main control system failure and subsequently instantaneous response were analyzed.According to the simulation,the flight characteristics of an aircraft were studied in different angle of rudder seizure.It demonstrated that when rudder seizure with high angle and pilot could not take action immediately,the flight parameters would change sharply.The yaw angle increased 50 degrees in 5 minutes,side velocity could attain 40 meters per-second,the angle of attack and sideslip would surpass 30 degrees,roll rate would reach -20 degrees per second,side load would arrive 0.6g.Simultaneity the angle of attack exceeded the limited angle,the aircraft would stall.If control wasn't working,the disaster would happen.These phenomena supply the sufficient information of the rudder malfunction. The validity of correcting yaw moment by asymmetry thrust was testified,the simulation results showed that even rudder seizure in most serious conditions,adopting asymmetry thrust can correct yaw moment caused by the rudder seizure.The judgment standards of flight safety level for the state of malfunction were given.The safety level was assessed caused by the rudder seizure.For an aircraft with two engines on one side,the pilots need to adjust the 4 engines to balance the asymmetric moment,the work load is increased enormously.According the flight safety standards,the safety level is level Ⅲ.

Numerical Study on Flow Around Modern Ship Hulls with Rudder-Propeller Interactions

Reducing the fuel consumption of ships presents both economic and environmental gains. Although in the past decades,extensive studies were carried out on the flow around ship hull, it is still difficult to calculate the flow around the hull while considering propeller interaction. In this paper, the viscous flow around modern ship hulls is computed considering propeller action. In this analysis, the numerical investigation of flow around the ship is combined with propeller theory to simulate the hull-propeller interaction. Various longitudinal positions of the rudder are also analyzed to determine the effect of rudder position on propeller efficiency. First, a numerical study was performed around a bare hull using Shipflow computational fluid dynamics(CFD) code to determine free-surface wave elevation and resistance components.A zonal approach was applied to successively incorporate Bpotential flow solver^ in the region outside the boundary layer and wake, Bboundary layer solver^ in the thin boundary layer region near the ship hull, and BNavier-Stokes solver^in the wake region. Propeller open water characteristics were determined using an open-source MATLAB code Open Prop, which is based on the lifting line theory, for the moderately loaded propeller. The obtained open water test results were specified in the flow module of Shipflow for self-propulsion tests. The velocity field behind the ship was recalculated into an effective wake and given to the propeller code that calculates the propeller load. Once the load was known, it was transferred to the Reynolds-averaged Navier-Stokes(RANS) solver to simulate the propeller action. The interaction between the hull and propeller with different rudder positions was then predicted to improve the propulsive efficiency.

Effective model based fault detection scheme for rudder servo system

The inherent nonlinearities of the rudder servo system(RSS) and the unknown external disturbances bring great challenges to the practical application of fault detection technology. Modeling of whole rudder system is a challenging and difficult task. Quite often, models are too inaccurate, especially in transient stages. In model based fault detection, these inaccuracies might cause wrong actions. An effective approach, which combines nonlinear unknown input observer(NUIO) with an adaptive threshold, is proposed. NUIO can estimate the states of RSS asymptotically without any knowledge of external disturbance. An adaptive threshold is used for decision making which helps to reduce the influence of model uncertainty. Actuator and sensor faults that occur in RSS are considered both by simulation and experimental tests. The observer performance, robustness and fault detection capability are verified. Simulation and experimental results show that the proposed fault detection scheme is efficient and can be used for on-line fault detection.

Thrust Allocation Optimization in Dynamic Positioning Vessels with Main PropellerRudders

In order to deal with the chattering of rudder angle and the problem of non-convex attainable thrust regions,introduce the concept of dynamic attainable region for each thruster and rudder to limit the thruster rotational speed and the rudder angle,and decompose the thrust allocation optimization problem into several optimization sub-problems.The optimization sub-problems were solved by particle swarm optimization(PSO) algorithm.Simulation studies with comparisons on a model ship were carried out to illustrate the effectiveness of the proposed thrust allocation optimization method.

Experimental investigation on aero-heating of rudder shaft within laminar/turbulent hypersonic boundary layers

The aero-heating of the rudder shaft region of a hypersonic vehicle is very harsh, as the peak heat flux in this region can be even higher than that at the stagnation point. Therefore, studying the aero-heating of the rudder shaft is of great significance for designing the thermal protection system of the hypersonic vehicle. In the wind tunnel test of the aero-heating effect, we find that with the increase of the angle of attack of the lifting body model, the increasement of the heat flux of the rudder shaft is larger under laminar flow conditions than that under turbulent flow conditions. To understand this, we design a wind tunnel experiment to study the effect of laminar/turbulent hypersonic boundary layers on the heat flux of the rudder shaft under the same wind tunnel freestream conditions. The experiment is carried out in the ?2 m shock tunnel(FD-14 A) affiliated to the China Aerodynamics Research and Development Center(CARDC). The laminar boundary layer on the model is triggered to a turbulent one by using vortex generators, which are 2 mm-high diamonds. The aero-heating of the rudder shaft(with the rudder) and the protuberance(without the rudder) are studied in both hypersonic laminar and turbulent boundary layers under the same freestream condition. The nominal Mach numbers are 10 and 12, and the unit Reynolds numbers are2.4 × 10~6 m^(-1) and 2.1 × 10~6 m-1. The angle of attack of the model is 20°, and the deflection angle of the rudder and the protuberance is 10°. The heat flux on the model surface is measured by thin film heat flux sensors, and the heat flux distribution along the center line of the lifting body model suggests that forced transition is achieved in the upstream of the rudder. The test results of the rudder shaft and the protuberance show that the heat flux of the rudder shaft is lower in the turbulent flow than that in the laminar flow, but the heat flux of the protuberance is the other way around,i.e., lower in the laminar flow than in the turbulent flow. The wind tunnel test results is also validated by numerical simulations. Our analysis suggests that this phenomenon is due to the difference of boundary layer velocities caused by different thickness of boundary layer between laminar and turbulent flows, as well as the restricted flow within the rudder gap. When the turbulent boundary layer is more than three times thicker than that of the laminar boundary layer, the heat flux of the rudder shaft under the laminar flow condition is higher than that under the turbulent flow condition. Discovery of this phenomenon has great importance for guiding the design of the thermal protection system for the rudder shaft of hypersonic vehicles.

Hydrodynamic interaction among hull,rudder and bank for a ship sailing along a bank in restricted waters

By applying a CFD tool to solve the RANS equations, the viscous flow around a model of hull-rudder system towed along a bank in shallow water is numerically simulated. Hydrodynamic forces and moments acting on the ship are calculated for different ship-bank distances and rudder angles. A container ship, KCS, is taken as an example for the numerical study. Under the assumption of low ship speed, the influences of free surface elevation and ship squat are assumed to be negligible. Based on the calculation results, the hydrodynamic interaction among the hull, rudder and bank is analyzed.

Shafting Alignment Based on Hydrodynamics Simulation Under Larger Rudder Corner Conditions

With the rudder angles getting larger and larger,the moment and force on propeller shafts,which are caused by complex flowing field,become more and more.They influence the shafting alignment greatly.Stress analysis of propeller shafts has been done under increasing rudder corner conditions with complex hydrodynamics simulation for a great domestic liquified natural gas(LNG) vessel,which is with dual propulsion systems.The improved three-moment equation is adopted in the process of dual propulsive shafting alignment.The calculated results show that the propeller hydrodynamic characteristics,which affect dual propulsive shafting alignment greatly,must be considered under large rudder angle conditions.Shafting accidents of Korean LNG vessels are interpreted reasonably.At the same time,salutary lessons and references are afforded to the marine multi-propulsion shafting alignment in the future.

超空泡航行体尾舵展开过程水动力载荷数值研究

超空泡航行体全沾湿航行阶段尾舵展开过程的流体动力载荷对于航行体稳定性分析以及尾舵机性能设计具有重要影响。建立了基于重叠网格技术和网格域间相对运动思想的尾舵展开过程数值计算方法;结合超空泡航行体设计需求,研究了尾舵不同展开速率、不同攻角状态展开以及尾舵展开前后的水动力载荷变化规律;通过对尾舵附近速度矢量场、压力场以及尾舵表面压力系数分析,揭示了尾舵不同状态的流体动力载荷变化原因。研究成果对超空泡航行体尾舵展开过程流场特性研究具有重要参考价值,同时为尾舵机性能设计提供了重要设计依据。

变形翼舵技术在导弹领域的应用需求及技术发展路线

采用变形翼舵技术可解决导弹对发射平台尺寸强约束问题,改善导弹升阻比及弹道末段机动性能,实现飞行全程气动外形最优,适应多任务作战需求。对国内外变形翼舵技术发展进行了概述,介绍了变形翼舵方案组成,分析了导弹对变形翼舵技术的需求,提出了单次阶跃变形、往复伸缩变形、柔性连续变形三阶段技术发展路线以及各阶段的关键技术,为变形翼舵技术在导弹武器领域的深入研究及应用提供了参考。