Estimation of roll related hydrodynamic coefficients through the free running model tests

Free-running model tests have been carried out based on a scaled chemical tanker ship model, having a guidance, control and navigation system developed and implemented in LabVIEW. In order to make the modelling more flexible and physically more realistic, a modified version of Abkowitz model was introduced. During the identification process, the model’s structure is fixed and its parameters have been obtained using system identification. A global optimization algorithm has been used to search the optimum values and minimize the loss functions. In order to reduce the effect of noise in the variables, different loss functions considering the empirical errors and generalization performance have been defined and implemented in the system identification program. The hydrodynamic coefficients have been identified based on the manoeuvring test data of free-running ship model. Validations of the system identification algorithm were also carried out and the comparisons with experiments demonstrated the effectiveness of the proposed system identification method.

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ESTIMATION OF HYDRODYNAMIC COEFFICIENTS OF A NONLINEAR MANOEUVRING MATHEMATICAL MODEL WITH FREE-RUNNING SHIP MODEL TESTS

The International Journal of Maritime Engineering ◽

10.5750/ijme.v160ia3.1059 ◽

2021 ◽

Vol 160 (A3) ◽

Author(s):

Haitong Xu ◽

M A Hinostroza ◽

C Guedes Soares

Keyword(s):

Mathematical Model ◽

System Identification ◽

Model Tests ◽

Loss Functions ◽

Identification Algorithm ◽

Hydrodynamic Coefficients ◽

Global Optimization Algorithm ◽

Identification Process ◽

Ship Model ◽

Free Running

Free-running model tests have been carried out based on a scaled chemical tanker ship model, having a guidance, control and navigation system developed and implemented in LabVIEW. In order to make the modelling more flexible and physically more realistic, a modified version of Abkowitz model was introduced. During the identification process, the model’s structure is fixed and its parameters have been obtained using system identification. A global optimization algorithm has been used to search the optimum values and minimize the loss functions. In order to reduce the effect of noise in the variables, different loss functions considering the empirical errors and generalization performance have been defined and implemented in the system identification program. The hydrodynamic coefficients have been identified based on the manoeuvring test data of free-running ship model. Validations of the system identification algorithm were also carried out and the comparisons with experiments demonstrated the effectiveness of the proposed system identification method.

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Evaluation of a Small and Fast Planing Boat’s Seakeeping Performance at the Design Stage

10.5957/fast-2015-060 ◽

2015 ◽

Author(s):

Dong Jin Kim ◽

Sun Young Kim

Keyword(s):

Model Tests ◽

Full Scale ◽

Scale Model ◽

Design Stage ◽

Small Scale ◽

Irregular Wave ◽

Seakeeping Performance ◽

Head Waves ◽

Scale Ratio ◽

Free Running

Seakeeping performance of a planing boat should be sufficiently considered and evaluated at the design stage for its safe running in rough seas. Model tests in seakeeping model basins are often performed to predict the performance of full-scale planing boats. But, there are many limitations of tank size and wave maker capacity, in particular, for fast small planing boats due to small scale ratio and high Froude numbers of their scale models. In this research, scale model tests are tried in various test conditions, and results are summarized and analyzed to predict a 3 ton-class fast small planing boats designed. In a long and narrow tank, towing tests for a bare hull model are performed with regular head waves and long crested irregular head waves. Motion RAOs are derived from irregular wave tests, and they are in good agreements with RAOs in regular waves. Next, model ships with one water-jet propulsion system are built, and free running model tests are performed in ocean basins. Wave conditions such as significant heights, modal periods, and directions are varied for the free running tests. Motion RMS values, and RAOs are obtained through statistical approaches. They are compared with the results in captive tests for the bare hull model, and are used to predict the full-scale boat performances.

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Forced Oscillation Model Tests for Determination of Hydrodynamic Coefficients of Large Subsea Blowout Preventers

Volume 1: Offshore Technology; Offshore Geotechnics ◽

10.1115/omae2015-41866 ◽

2015 ◽

Cited By ~ 1

Author(s):

Xavier Arino ◽

Jaap de Wilde ◽

Massimiliano Russo ◽

Guttorm Grytøyr ◽

Michael Tognarelli

Keyword(s):

Large Scale ◽

Forced Oscillation ◽

Model Tests ◽

Scale Model ◽

Hydrodynamic Coefficients ◽

Lumped Mass ◽

Towing Tank ◽

Steady Current ◽

Large Scale Model

Large scale model tests have been conducted in a towing tank facility for the determination of the hydrodynamic coefficients of subsea blowout preventers. A subsea blowout preventer (BOP) is a large, complex device 10–15 [m] tall, weighing 200–450 [ton]. The BOP stack consists of two assemblies, the ‘lower marine riser package’ (LMRP) connected to the riser string and the BOP itself, connected to the wellhead. Together they represent a large lumped mass, which directly influences the natural frequencies and vibration modes of the riser system, particularly those of the BOP-wellhead-casing assembly. Large uncertainties in the estimates of the hydrodynamic coefficients (added mass, lift and drag or damping) result in large uncertainties in the fatigue damage predictions of the riser and wellhead system. The trend toward larger and heavier BOPs, which could place BOP-wellhead-casing oscillation frequencies in the range of wave frequencies, has motivated Statoil and BP to start a new research project on this subject. The project involves a large scale model test for experimental determination of hydrodynamic coefficients. Two different BOP designs were tested in a towing tank at model scale 1:12. The models weighed about 50 [kg] in air and were about 1.2–1.5 [m] tall. A six-degree-of-freedom oscillator was mounted under the carriage of the towing tank for oscillation of the models in different directions. Static tow tests and forced oscillation tests with and in the absence of steady current were carried out. Keulegan-Carpenter (KC) numbers ranged between 0.2 and 2.0, while the Sarpkaya frequency parameter β was in the range from 4,000 to 50,000. The Reynolds numbers of the static tow tests ranged between 50,000 and 150,000. This paper focuses particularly on tests in the surge direction with and in the absence of a steady current. Results indicate that the hydrodynamic coefficients for BOP stacks are quite different from those of simpler geometries like a circular cylinder. In addition, they provide new insight for analytical modeling of global hydrodynamic forces on BOPs in many configurations and scenarios.

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Paper 26. Stability and Control in Waves: A Survey of the Problem

Journal of Mechanical Engineering Science ◽

10.1243/jmes_jour_1972_014_081_02 ◽

1972 ◽

Vol 14 (7) ◽

pp. 186-193 ◽

Cited By ~ 4

Author(s):

J. E. Conolly

Keyword(s):

Mathematical Models ◽

Orbital Motion ◽

Model Tests ◽

Point Of View ◽

Stability And Control ◽

Free Running ◽

And Control

Manoeuvrability in waves is discussed from the point of view of the dangers of broaching-to when a ship is running before the sea. Conditions are assessed under which this may occur, illustrated by documented cases, including the Wahine disaster in 1968. Because of the problems involved in investigating broaching-to by means of free-running model tests, there is an urgent need for reliable mathematical models: however, theories published so far, based on two different simplifications, are shown to have limitations. It is argued that the theory must take account of pitching, surging, rolling and orbital motion of the water particles.

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Numerical Estimation of Hull Hydrodynamic Derivatives in Ship Maneuvering Prediction

Polish Maritime Research ◽

10.2478/pomr-2021-0020 ◽

2021 ◽

Vol 28 (2) ◽

pp. 46-53

Author(s):

Radosław Kołodziej ◽

Paweł Hoffmann

Keyword(s):

Model Tests ◽

Circular Motion ◽

Computational Method ◽

Design Stage ◽

Hydrodynamic Characteristics ◽

Ship Maneuvering ◽

Hydrodynamic Derivatives ◽

Captive Model Tests ◽

Ship Maneuverability ◽

Free Running

Abstract Prediction of the maneuvering characteristics of a ship at the design stage can be done by means of model tests, computational simulations or a combination of both. The model tests can be realized as a direct simulation of the standard maneuvers with the free running model, which gives the most accurate results but is also the least affordable, as it requires a very large tank or natural lake, as well as the complex equipment of the model. Alternatively, a captive model test can be used to identify the hydrodynamic characteristics of the hull, which can be used to simulate the standard maneuvers with the use of dedicated software. Two types of captive model tests are distinguished: circular motion tests (CMT) and planar motion mechanism tests (PMM). The paper presents an attempt to develop a computational method for ship maneuverability prediction in which the hydrodynamic characteristics of the hull are identified by means of computational fluid dynamics (CFD). The CFD analyses presented here directly simulate the circular motion test. The resulting hull characteristics are verified against the available literature data, and the results of the simulations are verified against the results of free running model tests. Reasonable agreement shows the large potential of the proposed method.

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Submarine Autopilot Performance Optimization with System Identification

10.24868/issn.2631-8741.2018.014 ◽

2018 ◽

Cited By ~ 1

Author(s):

F Belanger ◽

D Millan ◽

X Cyril

Keyword(s):

System Identification ◽

Simulation Model ◽

Performance Optimization ◽

Full Scale ◽

Hydrodynamic Coefficients ◽

Scaled Model ◽

Towing Tank ◽

Ship Manoeuvring ◽

Free Running ◽

Motion Dynamics

Computer simulation models play a vital role in the assessment of a ship’s autopilot design. A well-tuned autopilot will contribute to reducing rudder activity, thereby minimizing wear on the actuation plant and also generally reducing fuel consumption. The equations that describe the ship motion dynamics contain a large number of hydrodynamic coefficients that must be calculated as accurately as possible to justify the use of a simulation model and its relevance to predicting the ship manoeuvring characteristics. Proper prediction of the ship performance is an essential pre-requisite in the process of tuning the autopilot. The hydrodynamic coefficients can be calculated by using theoretical methods or by carrying out experiments on the actual ship or on a scaled model of the ship. System Identification (SI) is an experiment-based approach and in this paper the authors present an algorithm that can estimate the coefficients with great accuracy. These coefficients can classically be obtained in a towing tank using a captive model, and with a planar motion mechanism and a rotating arm. Generally, these systems are costly and entail expensive trials programs, and SI methods have been developed in an effort to obviate some of those problems and limitations. They typically process ship manoeuvring data obtained from a free-running scaled model or full-scale trials. While similar to a surface ship, the motion dynamics of a submarine introduce additional challenges for SI methods. This is because the submarine manoeuvres in “three dimensions”, which adds complexity and more hydrodynamic coefficients to the equations. The standard submarine simulation model, also referred to as the Gertler and Hagen equations, incorporates over 120 coefficients. To calculated these coefficients, the SI algorithm uses a Square-Root Unscented Kalman filter (SR-UKF). One of its appealing features is that it calculates all the coefficients by processing data from a single submarine manoeuvre that has a repeating sinusoidal pattern in both depth and course. The manoeuvre can be performed in a towing tank by a free-running scaled model of the submarine, or it can be performed at sea on the full-scale submarine as part of the sea trials schedule.

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Calculated Dynamic Response of an Articulated Tower in Waves—Comparison With Model Tests

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.3256989 ◽

1987 ◽

Vol 109 (1) ◽

pp. 43-51 ◽

Cited By ~ 1

Author(s):

T. E. Schellin ◽

T. Koch

Keyword(s):

Dynamic Response ◽

Axial Flow ◽

Wave Theory ◽

Diffraction Theory ◽

Model Tests ◽

Linear Wave ◽

Vertical Force ◽

Hydrodynamic Coefficients ◽

Test Results ◽

Statistical Measures

Calculated dynamic response of an articulated tower in waves is compared with model tests. The theory used is based on Morison’s equation and linear wave theory and requires specified hydrodynamic force coefficients. Calculations are done with three different sets of coefficients. Firstly, coefficients are assumed not to vary with wave period. Secondly, they are selected from experimental data of oscillating flow past stationary cylinders. Thirdly, they are based on calculations using diffraction theory. Added mass and inertia coefficients have a predominant effect on calculated response, drag coefficients have almost no effect. Calculated tower top motion and horizontal force at the universal joint correlate well for all three sets of coefficients, indicating that hydrodynamic coefficients for normal flow are reasonably well selected and need not be specified with undue precision. In contrast, hydrodynamic coefficients for axial flow need to be chosen carefully. Calculated vertical force at the joint, using initially specified axial flow coefficients, correlates poorly with measurements. Correlation is greatly improved using reduced coefficients for axial flow. Calculated response is reasonably linear with wave height. Spectral analysis techniques are used to determine statistical measures for three irregular seastates. Agreement with corresponding model test results is satisfactory.

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Numerical Investigation for Vortex-Induced Vibrations of Steel-Lazy-Wave-Risers: Part I — CFD Validation Against Forced Oscillation Model Test

Volume 1: Offshore Technology; Offshore Geotechnics ◽

10.1115/omae2019-96401 ◽

2019 ◽

Author(s):

Hyunchul Jang ◽

Jang Whan Kim

Keyword(s):

Test Data ◽

Model Test ◽

Cfd Simulation ◽

Assessment Tool ◽

Forced Oscillation ◽

Model Tests ◽

Hydrodynamic Coefficients ◽

Cfd Validation ◽

Oscillation Model ◽

Water Developments

Abstract Vortex-Induced Vibration (VIV) is one of the main sources of fatigue damage for long slender risers. Typical VIV assessment of risers is conducted using semi-empirical software tools with the sectional hydrodynamic coefficients derived from forced-oscillation model tests on short rigid riser sections. The Steel Lazy Wave Riser (SLWR) with buoyancy sections is an attractive concept for improving fatigue performance in deep water developments, but there is limited model test data available for the hydrodynamic coefficients on SLWR’s. CFD simulation is an alternative VIV assessment tool, once it is validated for an existing model test. It can provide accurate estimates of VIV response and help to design configurations of SLWR’s without additional model tests. The present CFD simulations are performed to validate hydrodynamic coefficients of a SLWR section. The predicted drag and excitation (lift) coefficients on both bare riser and buoyancy sections are compared to the test data with respect to oscillation frequency and amplitude.

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SEAKEEPING AND MANOEUVRING FOR WIND ASSISTED SHIPS

10.3940/rina.win.2019.09 ◽

2019 ◽

Author(s):

R Eggers ◽

A. S. Kisjes

Keyword(s):

Wind Tunnel ◽

Model Tests ◽

Scale Model ◽

Ship Propulsion ◽

Free Running ◽

Set Up

Research on Wind Assisted Ship Propulsion (WASP) has until now focussed on performance in steady conditions whereas unsteady behaviour is an important part of ship behaviour. For “conventional” manoeuvring and seakeeping, performing direct “free running” scale model tests has been successful to gain understanding and to improve ship designs. In the “WindLab” project the opportunity was taken to extend that approach to aerodynamics: modelling real wind with a simplified wind tunnel in the basin. A unique set-up was tested for its suitability and first data was collected on the performance of wind assisted ships in unsteady scenarios.

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