Bayesian Estimation of Directional Wave Spectra Based on Ship Motions

Iseki, Toshio; Ohtsu, Kohei; Fujino, Masataka

doi:10.2534/jjasnaoe1968.1992.172_17

Cited by 39 publications

(52 citation statements)

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“…For example, the ship's roll motion is more likely to be affected by waves approaching from the side than if the ship would face them with the bow first. Iseki and Terada (2001), Tannuri et al (2003), Nielsen (2007Nielsen ( , 2008, and Iseki (2010, 2011) study the problem of estimating the directional wave spectrum from ship motion. The wave spectrum can then be used to simulate a ship's response over time, to apply control or to suggest appropriate actions.…”

Section: Research Motivationmentioning

confidence: 99%

Graybox Modelling of Ships Using Indirect Input Measurements

Linder¹

2014

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A ship's roll dynamics is very sensitive to changes in the loading conditions and a worst-case scenario is that the ship will capsize. Actually, the mass and center of mass are two of the most influential parameters in most mechanical systems. However, it is difficult to uniquely estimate these parameters for a ship under normal operational conditions without special experiments or equipment.Instead of focusing on a sensor-rich environment where all possible signals on a ship can be measured and a complete model of the ship can be estimated, this thesis presents an approach where a model of a subsystem of the ship's dynamics is estimated using only a limited set of sensors. More specifically, the roll dynamics is studied and it is assumed that only motion measurements from an inertial measurement unit (IMU) together with measurements of the rudder angle are available. Hence, direct measurements of the true inputs to the subsystem are not available, but the measurements indirectly contain information about the inputs and these indirect input measurements can be used as a substitute.To understand the properties of the proposed method, it is applied to an approximate model of the ship's roll dynamics. The analyses show that only a subset of the unknown parameters can be estimated simultaneously and that the estimation problem is similar to closed-loop system identification.A multi-stage method that uses several datasets is introduced to circumvent the restrictions shown in the identifiability analysis. An iterative closed-loop instrumental variable approach is used to estimate subsets of the parameters in each step. The approach is verified on experimental data with good results.It is shown that a well-established and more complete ship model can be used to derive a generalization of the approximate model, with more input measurements and a few extra parameters. The generalized model has the same basic properties as the approximate model. The added complexity is due to the ship's interaction with water. Because of this extra complexity, an iterative joint closed-loop instrumental variable approach based on a graybox formulation and using multiple datasets simultaneously is introduced to estimate the parameters.Finally, experiments with a scale ship model are described. The joint identification method is applied to the collected data and gives promising results.v Populärvetenskaplig sammanfattningEtt skepps beteende är väldigt känsligt för hur det är lastat och om det är fellastat kan det i värsta fall kapsejsa. Skeppets lastförhållande kan beskrivas med hjälp av dess massa och tyngdpunkt, vilka är två av de fysikaliska storheter som har störst inverkan på många mekaniska systems beteende. Tyvärr är det under normala förhållanden svårt att bestämma dessa storheter entydigt för ett skepp utan att göra speciella experiment eller att använda speciell utrustning.Istället för att fokusera på fall där man kan mäta alla signaler som behövs och skatta en komplett dynamisk modell från dessa så presenteras här ett til...

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Section: Research Motivationmentioning

confidence: 99%

Graybox Modelling of Ships Using Indirect Input Measurements

Linder¹

2014

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“…The use of satellite data is not yet a feasible approach for onboard wave measurements, although in the future this could change. The present work relies on the wave buoy analogy [12,20,21,24,27,26,29] where the fundamental input is a set of response measurements (motions, accelerations, strains, etc.). In this way, the way buoy analogy utilises onboard response measurements that are often carried out irrespectively on many of today's naval and commercial vessels.…”

Section: Sea State Estimationmentioning

confidence: 99%

Towards fault-tolerant decision support systems for ship operator guidance

Nielsen

Lajic

Jensen

2012

Reliability Engineering & System Safety

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Abstract. Fault detection and isolation are very important elements in the design of faulttolerant decision support systems for ship operator guidance. This study outlines remedies that can be applied for fault diagnosis, when the ship responses are assumed to be linear in the wave excitation. A novel numerical procedure is described for the calculation of residuals using the ship's transfer functions which correlate the wave excitation and the ship responses. As tests, multiplicative faults have artificially been imposed to full-scale motion measurements and it is shown that the developed model is able to detect and isolate all faults.

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“…Iseki and Terada (2001) study the problem of estimating the directional wave spectrum from ship motion. The wave spectrum can then be used to simulate a ship's response over time, to apply control or to suggest appropriate actions.…”

Section: Introductionmentioning

confidence: 99%

Online Estimation of Ship's Mass and Center of Mass Using Inertial Measurements

Linder¹,

Enqvist²,

Fossen³

et al. 2015

IFAC-PapersOnLine

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A ship's roll dynamics is sensitive to the mass and mass distribution. Changes in these physical properties might introduce unpredictable behavior of the ship and a worst-case scenario is that the ship will capsize. In this paper, a recently proposed approach for online estimation of mass and center of mass is validated using experimental data. The experiments were performed using a scale model of a ship in a wave basin. The data was collected in free run experiments where the rudder angle was recorded and the ship's motion was measured using an inertial measurement unit. The motion measurements are used in conjunction with a model of the roll dynamics to estimate the desired properties. The estimator uses the rudder angle measurements together with an instrumental variable method to mitigate the influence of disturbances. The experimental study shows that the properties can be estimated with quite good accuracy but that variance and robustness properties can be improved further.

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Bayesian Estimation of Directional Wave Spectra Based on Ship Motions

Cited by 39 publications

References 0 publications

Graybox Modelling of Ships Using Indirect Input Measurements

Graybox Modelling of Ships Using Indirect Input Measurements

Towards fault-tolerant decision support systems for ship operator guidance

Online Estimation of Ship's Mass and Center of Mass Using Inertial Measurements

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