Ship Righting Arm Model Determination in Adverse Weather
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Solution Overview
Problem
Existing methods for determining a ship's righting arm model are limited to calm conditions, failing to account for environmental disturbances like strong winds and waves, which are critical for assessing stability.
Innovation Solution
A method using ship sensors to obtain excitation signals and motion data, which are then processed in a dynamic model to minimize residuals and determine the righting arm model, even in non-calm conditions, by accounting for process disturbances and parameterizing the model with key parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional inclining test methods are used to determine the righting arm model, then measurement precision is improved under calm conditions, but the method cannot be applied in adverse weather conditions with strong winds and waves
Solution Approach 1:
The patent converts the harmful effect of environmental disturbances (waves, winds, currents) into a beneficial signal source. Instead of treating wave-induced ship motions as noise to be eliminated, the method uses these natural excitations as the input signal for system identification. The wave spectrum provides sufficient excitation energy across a range of frequencies, enabling righting arm model determination without requiring calm weather conditions or active ship maneuvering.
Solution Approach 2:
The ship's natural interaction with the marine environment serves the purpose of stability assessment. The ship's own response to wave excitation is utilized as the measurement data, and the environmental conditions that would normally prevent testing actually provide the necessary excitation signals. This eliminates the need for separate testing procedures in calm waters and allows continuous stability monitoring during normal operations.
2Ease of operation
If natural roll motion is used to estimate metacentric height, then the estimation can be performed without external excitation, but the method requires calm weather and still water conditions
Solution Approach 1:
The patent transforms environmental disturbances from obstacles into the excitation source. Natural wave motions provide sufficient energy to excite the ship's roll response, eliminating the need for artificial excitation devices while also removing the requirement for calm weather. The method uses spectral analysis to extract the righting arm characteristics from the ship's response to these natural excitations.
Solution Approach 2:
The method utilizes vibrational analysis and spectral techniques to extract system characteristics from the ship's roll motion. By analyzing the frequency domain characteristics of the roll response and comparing it with the wave excitation spectrum, the righting arm model can be identified through system identification methods, enabling operation in various sea states.
3Adaptability or versatility
If ship sensors are used to obtain motion data in adverse weather, then the righting arm model can be determined in non-calm conditions, but environmental disturbances and process noise affect measurement precision
Solution Approach 1:
The method employs iterative system identification with feedback mechanisms. The initial righting arm model is used to predict ship response, the predicted response is compared with actual sensor measurements, and the model parameters are updated based on the residuals. This iterative refinement process continues until convergence, effectively filtering out the influence of environmental disturbances and process noise to achieve accurate model determination even in adverse weather conditions.
Solution Approach 2:
The patent introduces a dynamic model of ship motion as an intermediary between the raw sensor measurements and the righting arm model determination. This model acts as a filter that separates the ship's inherent stability characteristics from the environmental disturbances. By using the model-based approach, the method extracts the righting arm information from the noisy measurements while accounting for wave effects, current, and other external forces.
Data Source
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AI summary
The invention concerns a method, ship stability determining arrangement and computer program product for determining a model of the righting arm of a ship. The arrangement comprises a righting arm model determining unit that obtains (38) a ship excitation signal applied in the control of the ship, ship motion data (40) from ship sensors when the ship is under influence of the ship excitation signal, uses (42) the ship motion data and the excitation signal in a dynamic model of the ship comprising a process disturbance and a parameter set comprising at least one parameter defining the righting arm model, determines (44) one or more residuals, and obtains (46) the righting arm model through minimizing a function of the residuals.