RESUMEN

To deal with the sideslip angle caused by the current disturbances or transverse motion for path following of under-actuated ships, a nonlinear observer established by an exponential function is introduced in the backstepping approach which converts the path following into heading control. Then, the model predictive control (MPC) method is used as a heading controller, addressing the rudder optimization. A linear extended state observer technology was exploited to estimate yaw rate, external disturbances, and internal uncertainties, which could avoid measuring the high-order state used in the MPC controller and promote the accuracy of the MPC internal model. Moreover, an inverse tangent function is applied to develop a new method for switching the reference heading angle to reduce rudder amplitude when the ship is choosing the next waypoint. Finally, the validity and reliability of the design method were verified through comparative computer simulation experiments.

RESUMEN

In the process of ship motion control system design, it is necessary to take into account the impact of environmental disturbances such as winds, waves and sea currents. The commonly used representatives of wave influences in this area are the unidirectional wave power spectral density functions describing sea waves of different form: long-crested, fully developed waves, developing wind waves or multi-modal waves (e.g., with swell). The existing standard PSD models describe the surge of open sea or ocean. However, they are inadequate in the case of control system testing of scale ship models for sailing in open water areas such as lakes or test pools. This paper presents a study of wind-generated wave PSD estimations for a small lake used as a test area for free-running scale ships. The publication provides a brief overview of the wave spectral density functions commonly used for control system design. A measurement instrument using the idea of a water-induced variable capacitance that works synchronously with the wind sensors is also described. The process of collected data analysis is presented. As a result of the study, a series of empirical spectral density functions of lake waves for different wind speeds are obtained. They correspond to the rescaled, two-parametric ITTC model.

RESUMEN

In view of the low accuracy of the motion parameters generated by the typical ship trajectory generator, and the fact that the problem of wind, current and wave interference is not considered, this paper establishes a new ship trajectory generator by analyzing the changes in the ship's attitude and speed under different motion states. Through simulation, the accuracy of the main motion parameters is significantly improved compared with the typical trajectory generator; the time-varying non-uniform wind, current and wave fields are constructed, and the interference effect of wind, current and waves on ship motion is analyzed by combining the empirical formulas of force and moment; an adaptive neuro fuzzy inference system (ANFIS) based on wind, current and wave interference is designed, and the fuzzy rules of the fuzzy system are determined by training and testing the measured data; the motion parameters of superimposed wind, current and wave interference are compared with the measured data, and the accuracy is further improved after superimposing wind, current and wave interference.

Asunto(s)

Navíos , Viento , Movimiento (Física) , Simulación por Computador

RESUMEN

The forces and moments acting on a marine vessel caused by the wind are most often modeled based on its speed measured at a standard 10 m above the sea level. There exist numerous well-known methods for modeling wind speed in such conditions. These models, by nature, are inadequate for simulating wind disturbances for free-running scale ship models sailing on lakes. Such scale models are being used increasingly for design and testing modern ship motion control systems. The paper describes the hardware and methodology used in measuring wind speed at low altitudes above the lake level. The system consists of two ultrasonic anemometers supplemented with wave sensor acting as a capacitor immersed partially in the water. Obtained measurement results show clear similarity to the values gathered during full-scale experiments. Analysis of the power spectral density functions of turbulence measured for different mean wind speeds over the lake, indicates that, at the present stage of research, the best model of wind turbulence at low altitude above the lake level can be obtained by assembling four of the known, standard turbulence models.

RESUMEN

The concept of the Marine Autonomous Surface Ship (MASS) requires new solutions in many areas: from law, through economics, social sciences, environmental issues to the technology and even ethics. It also plays a central role in the work of numerous research teams dealing with the ship motion control systems. This article presents the results of the experiments with application of the selected control methods in automatic steering of the movement of an autonomous ship in the two regimes: during the maneuvers at low speed (in a harbor confined waters) and during the lake trials in open water conditions. In the first case, multidimensional state controller synthesized with Linear Matrix Inequalities (LMI) algorithms was used, while, in the second case, Model Predictive Control (MPC) control was adopted. The object for which the experiments were carried out was 1:24 scale model of the Liquefied Natural Gas (LNG) carrier. The paper presents also the design of the measurement and control system and the user interface. The experiments were conducted in the natural conditions on the lake. The results of the experiments indicate the fundamental role of the measurement system in the process of controlling an autonomous ship.

RESUMEN

Profile of cybersickness and balance disturbance induced by virtual ship motion alone and in combination with galvanic vestibular stimulation (GVS) remained unclear. Subjects were exposed to a ship deck vision scene under simulated Degree 5 or 3 sea condition using a head-mounted virtual reality display with or without GVS. Virtual ship motion at Degree 5 induced significant cybersickness with symptom profile: nausea syndrome > central (headache and dizziness) > peripheral (cold sweating) > increased salivation. During a single session of virtual ship motion exposure, GVS aggravated balance disturbance but did not affect most cybersickness symptoms except cold sweating. Repeated exposure induced cybersickness habituation which was delayed by GVS, while the temporal change of balance disturbance was unaffected. These results suggested that vestibular inputs play different roles in cybersickness and balance disturbance during virtual reality exposure. GVS might not serve as a potential countermeasure against cybersickness induced by virtual ship motion.

Asunto(s)

Mareo por Movimiento , Navíos , Estimulación Eléctrica , Humanos , Inmersión , Movimiento (Física) , Sensación

RESUMEN

Transporting livestock at high stocking density by ship presents significant risks to their welfare, especially if it is over long distances. Previous research has investigated small variations in density for long periods or a moderate variation for short periods. The objective of this study was to assess the effects of a doubling of space allowance during two types of simulated ship movement, regular and irregular floor motion, on the welfare of sheep for a short one-hour period. Six 25 kg sheep were restrained in pairs in a crate on a programmable platform that generated roll and pitch motion typical of that experienced on board ship. Sheep were subjected to regular or irregular movement or a control treatment at high and low stocking densities (0.26 and 0.52 m2/sheep) in a multilevel changeover design. Irregular movement was programmed as a sequence of 30 different amplitude and duration values for pitch and roll movements, which were randomly selected by computer software controlling the movement. Regular movement was the mean of these values, which represented approximately 33% of the recommended maximum tolerance for livestock carriers. Behaviour was recorded by six cameras positioned around the crate. The low space allowance increased sheep pushing each other (Low: 4.51 events/h, High: 1.37 events/h, p < 0.001), affiliative behaviour, with their heads one on top of the other (Low 8.64, High 3.75 s/h, p = 0.02) and standing supported by the crate (Low 96, High 3.2 s/h, p < 0.001). Sheep stepped more frequently when more space was provided, particularly in the forward (Low 6.4, High 8.4 steps/h, p = 0.02) and left (Low 4.0, High 4.7 steps/h, p = 0.03) directions. The low space allowance group also had i heart rates, providing evidence of physiological stress. Irregular movement reduced rumination (Irregular 288, Control 592, Regular 403 s/h, p = 0.02), which was evidence of reduced welfare, but balance corrections by stepping were more common if the motion was regular. Thus, there was evidence that the low space allowance increased interactions between sheep and was stressful, and that irregular floor motion in simulated ship transport limited balance control and reduced welfare.