New Concept of Numerical Ship Motion Modelling for Total Ship Operability Analysis by Integrating Ship and Environment Under One Overall System

This paper represents the first stage of research into a multi-objective method of planning safe trajectories for marine autonomous surface ships (MASSs) involved in encounter situations. Our method applies an evolutionary multi-objective optimisation (EMO) approach to pursue three objectives: minimisation of the risk of collision, minimisation of fuel consumption due to collision avoidance manoeuvres, and minimisation of the extra time spent on collision avoidance manoeuvres. Until now, a fully multi-objective optimisation has not been applied to the real-time problem of planning safe trajectories; instead, this optimisation problem has usually been reduced to a single aggregated cost function covering all objectives. The aim is to develop a method of planning safe trajectories for MASSs that is able to simultaneously pursue the three abovementioned objectives, make decisions in real time and without interaction with a human operator, handle basic types of encounters (in open or restricted waters, and in good or restricted visibility) and guarantee compliance with the International Regulations for Preventing Collisions at Sea. It should also be mentioned that optimisation of the system based on each criterion may occur at the cost of the others, so a reasonable balance is applied here by means of a configurable trade-off. This is done throughout the EMO process by means of modified Pareto dominance rules and by using a multi-criteria decision-making phase to filter the output Pareto set and choose the final solution

Section: Model Of the Ship's Hull And Propellermentioning

confidence: 99%

Framework of an Evolutionary Multi-Objective Optimisation Method for Planning a Safe Trajectory for a Marine Autonomous Surface Ship

Szlapczynski

Ghaemi

2019

“…These issues are especially important for severe sea conditions during operations in open sea. Some may focus on dynamic positioning issues and the influence of ship propulsion systems, such as bow tunnel thrusters on ship motions [1], while others may focus on operability based on the assessment of ship motions as a response to wave excitations [2]. In the last decade, a large number of computational analyses concerning ship motions in waves have been published [3,4,5,6,7,8].…”

Section: Introductionmentioning

confidence: 99%

“…However, experiments at the model scale along with full-scale trials [9] are still the most accurate approaches for checking operability criteria, but the cost of model tests sometimes limits the number of considered cases. This study focuses on an experimental approach to roll motion prediction as it plays a very important role in the assessment of ship operability [2], as well as having a significant influence on ship safety during operations in severe seas [10]. These motions are mostly important for station keeping vessels in the offshore industry during operations in the vicinity of platforms in open seas.…”

Section: Introductionmentioning

confidence: 99%

Prediction of Ship Motions in Irregular Waves Based on Response Amplitude Operators Evaluated Experimentally in Noise Waves

Bielicki¹

2021

The most common methods for predicting ship roll motions in a specified sea state are direct measurements of motions in a representative irregular wave realisation (time domain) or calculations of motions from response amplitude operators (RAOs) in the frequency domain. The result of the first method is valid only for the tested sea state, whilst the second method is more flexible but less accurate. RAO-based predictions are calculated assuming a linear model of ship motions in waves. RAO functions are usually evaluated by means of tests in regular waves for a limited number of frequencies and a constant wave amplitude. This approach is time-consuming and the discrete form of the RAO functions obtained for a limited number of frequencies may lead to discrepancies in the prediction of seakeeping and often does not allow the actual amplitude of the response in resonant frequency to be determined. Another challenge is the appropriate selection of wave amplitude for tests due to the considerable influence of viscous damping on roll response in irregular sea waves. There are alternative methods for the experimental determination of RAO functions and one of them is presented in this study. The presented approach allows RAO functions to be evaluated in one run by the generation of irregular waves characterised by a white or coloured noise spectrum. This method reduces the experiment duration, with almost continuous RAO characteristics obtained. The flat (white noise) and linear (coloured noise) wave spectral energy characteristics are considered in the experiment and the obtained predictions are compared with the results of accurate measurements in irregular waves.

“…The effect of radical hull shape changes can be analysed using computer simulations (strip or panel methods, CFD) [45]. The obtained research data can be used to increase the ship propulsion efficiency, and improve the safety and comfort of ship operation [26], [52], [53], [54], [55], [56]. However, bearing in mind enormous cost of shipbuilding, the predicted seakeeping characteristics obtained from numerical analyses for the ship to be built should be finally verified using experimental methods (in the towing tank, for instance).…”

Section: Introductionmentioning

confidence: 99%

Determination of Seakeeping Performance for a Case Study Vessel by the Strip Theory Method

Niklas

Karczewski

2020

The increase of seakeeping performance is of particular importance for car and passenger ferries, service ships in the gas and oil extraction industry and offshore wind power farm industry, as well as for special purpose ships (including military applications). In the water areas of the Baltic Sea, North Sea, and Mediterranean Sea, which are characterised by a short and steep wave, the hull shape has a substantial impact on the operational capacity and propulsion efficiency of the ship, as well as on comfort and safety of navigation. The article analyses selected aspects of seakeeping for four variants of a selected case study vessel, indicating practical limitations of the strip method. The analysed aspects included hull heaving and pitching, added resistance, Motion Thickness Indicator (MSI), and Subjective Magnitude (SM). Experimental tests were also performed in the towing tank. Their comparison with the numerical results has indicated high inaccuracy of the strip method. What is more, the simplified representation of hull shape used in the strip method makes it impossible to analyse the effect of hull shape changes on the predicted seakeeping characteristics. Especially for the case of head wave, neglecting highly non-linear phenomena, such as slamming or head wave breaking, in strip method-based computer simulations will significantly decrease the reliability of the obtained results. When using the strip method, the seakeeping analysis should be complemented with model tests in a towing tank, or by another more complex numerical analysis, such as CFD for instance.