Towards a Realistic Estimation of the Powering Performance of a Ship with a Gate Rudder System

This paper presents an investigation on the scale effects associated with the powering performance of a Gate Rudder System (GRS) which was recently introduced as a novel energy-saving propulsion and maneuvring device. This new system was applied for the first time on a 2400 GT domestic container ship, and full-scale sea trials were conducted successfully in Japan, in 2017. The trials confirmed the superior powering and maneuvring performance of this novel system. However, a significant discrepancy was also noticed between the model test-based performance predictions and the full-scale measurements. The discrepancy was in the power-speed data and also in the maneuvring test data when these data were compared with the data of her sister container ship which was equipped with a conventional flap rudder. Twelve months after the delivery of the vessel with the gate rudder system, the voyage data revealed a surprisingly more significant difference in the powering performance based on the voyage data. The aim of this paper, therefore, is to take a further step towards an improved estimation of the powering performance of ships with a GRS with a specific emphasis on the scale effect issues associated with a GRS. More specifically, this study investigated the scale effects on the powering performance of a gate rudder system based on the analyses of the data from two tank tests and full-scale trials with the above-mentioned sister ships. The study focused on the corrections for the scale effects, which were believed to be associated with the drag and lift characteristics of the gate rudder blades due to the low Reynolds number experienced in model tests combined with the unique arrangement of this rudder and propulsion system. Based on the appropriate semi-empirical approaches that support model test and full-scale data, this study verified the scale effect phenomenon and presented the associated correction procedure. Also, this study presented an enhanced methodology for the powering performance prediction of a ship driven by a GRS implementing the proposed scale effect correction. The predicted powering performance of the subject container vessel with the GRS presented an excellent agreement with the full-scale trials data justifying the claimed scale effect and associated correction procedure, as well as the proposed enhanced methodology for the practical way of predicting the powering performance of a ship with the GRS.

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Benchmark Case Study of Scale Effect in Self-Propelled Container Ship Squat

Volume 8: CFD and FSI ◽

10.1115/omae2020-18619 ◽

2020 ◽

Author(s):

Zhen Kok ◽

Jonathan Duffy ◽

Shuhong Chai ◽

Yuting Jin

Keyword(s):

Scale Effect ◽

Body Force ◽

Full Scale ◽

The Body ◽

Water Model ◽

Container Ship ◽

Confined Water ◽

Cfd Model ◽

Empirical Prediction ◽

Model Scale

Abstract A URANS CFD-based study has been undertaken to investigate scale effect in container ship squat. Initially, CFD studies were carried out for the model scale benchmarking squat cases of a self-propelled DTC container ship. In this study, a quasi-static modelling approach was adopted where the hull was fixed from sinking and trimming which is computationally more efficient than dynamic mesh methods that models actual motion directly. Instead, the quasi-static approach allows estimation of the squat base on the recorded hydrodynamic forces and moments. Propulsion of the vessel was modelled by the body-force actuator disc method. Upon successful verification and validation of the model scale self-propelled CFD model against benchmark data, full scale investigations were then undertaken. Validation of the full scale set-up was demonstrated by computing the full scale bare hull resistance in deep, laterally unrestricted water and comparing against the extrapolated resistance of model scale benchmark resistance data. Upon validating the setup, it was used to predict full scale ship squat in confined waters. The credibility of the full scale confined water model was checked by comparing vessel resistance in confined water against the Landweber empirical prediction. To quantify scale effect in ship squat predicitons, the benchmarking squat cases were computed by adopting the validated full scale CFD model with body-force propulsion. Comparison between the full scale CFD, model scale CFD and model scale benchmark EFD squat results demonstrates that scale effect is negligible.

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Investigation on Reasons for Possible Difference Between VIM Response in the Field and in Model Tests

Volume 2: CFD and VIV ◽

10.1115/omae2016-54746 ◽

2016 ◽

Cited By ~ 2

Author(s):

Arjen Koop ◽

Jaap de Wilde ◽

André Luís Condino Fujarra ◽

Oriol Rijken ◽

Samuel Linder ◽

...

Keyword(s):

Reynolds Number ◽

Fatigue Damage ◽

Model Test ◽

Scale Effects ◽

Model Tests ◽

Full Scale ◽

Strong Impact ◽

Numerical Verification ◽

Field Observations ◽

Test Results

Floating offshore structures, such as production semi-submersibles and spars, can exhibit significant in-line and transverse oscillatory motions under current conditions. When caused by vortex shedding from the floater, such motions are generally called Vortex-Induced Motions (VIM). For semi-submersibles these motions could have a strong impact on the fatigue life of mooring and riser systems. Some field development studies indicate that the VIM induced fatigue damage for larger diameter Steel Catenary Risers (SCRs) can have a magnitude equal to or larger than the wave-induced fatigue damage. The VIM phenomenon for multi-column floaters is characterized by complex interactions between the flow and the motions of the floater. Presently, model tests are the preferred method to predict the VIM response of a multi-column floater. However, several studies indicate that the observed VIM response in the field is less than what is observed in model test campaigns: typical model test results are very conservative. Using such test results in the development of mooring and riser design can easily result in very conservative designs which can have a significant impact on mooring and riser cost, or even affect SCR selection and/or feasibility. The primary objective of the VIM JIP was to increase the physical insight into the VIM phenomenon. This knowledge is then used to address possible areas that could explain the differences between the results from model tests and field observations. To address these objectives, the JIP focused on model testing and CFD studies. A key segment of the JIP was the use of identical semi-submersible hull geometries for the numerical and experimental studies thereby facilitating the interpretation of the various response comparisons. The JIP identified that a CFD model, at model-scale Reynolds number, can reasonably well reproduce the VIM response observed in model tests. However, to have confidence in the CFD results extensive numerical verification studies have to be carried out. The effect of external damping was investigated in model tests and in CFD calculations. Both the numerical and experimental results show that external damping significantly reduces the VIM response. Comparisons between CFD results at model- and full-scale Reynolds number indicate that Froude scaling is applicable, with minor scale effects identified on the amplitudes of the VIM motions. Changing the mass ratio of the floater has a small influence on the VIM response. Experimentally it was found that VIM response under inline or transverse waves is slightly smaller than without the presence of waves and is wave heading and wave height dependent. The presence of waves does not explain the observed differences between model test results and field observations. The effect of unsteady current on the VIM response is minimal. Based on the results from the JIP it is concluded that increased external damping reduces the VIM response. The questions that remain are if the increased external damping is actually present in full-scale conditions and if the mooring and riser systems provide the required damping to reduce the VIM amplitudes.

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Model Test and Full Scale Measurements of Whipping on Container Vessels in the North Atlantic

Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B ◽

10.1115/omae2009-79127 ◽

2009 ◽

Cited By ~ 2

Author(s):

Gaute Storhaug ◽

Jan Mathisen ◽

Svein Erling Heggelund

Keyword(s):

Model Test ◽

North Atlantic ◽

Ship Design ◽

Full Scale ◽

Elastic Model ◽

Container Ship ◽

Hull Girder ◽

The North ◽

The North Atlantic ◽

Wave Induced

Ships vibrate due to waves, and these wave induced vibrations can not easily be avoided by moderate changes to the hull lines. The waves may cause the whole hull girder to vibrate due to springing (resonance) and whipping (transient response), which increase the fatigue and extreme loading. Recently this has also become an industry concern. Modern hull monitoring systems in combination with model tests are the best tools to answer the key questions: How important is the wave induced vibrations, and does it have to be included in design? This paper addresses the effect of whipping on the extreme loading. Measurements have been carried out on two container vessels operating in the North Atlantic. An elastic model of the larger vessel has also been tested. Results are obtained at quarter lengths and amidships. From the measurements the increase due to whipping is considerable, even though the wave conditions are not extreme. The full scale measurements and model test show that IACS URS11 rule loads may be exceeded in less than extreme sea states, in particularly amidships and in the aft ship. The IACS UR S11 may need revision for container ship design. MAIB’s report based on the investigation of the MSC Napoli incident (vessel broke in two) also recommends increased requirements for container ship design and further research into the effect of whipping.

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A Comparison of Four Adolescent Language Tests

Language Speech and Hearing Services in Schools ◽

10.1044/0161-1461.1803.250 ◽

1987 ◽

Vol 18 (3) ◽

pp. 250-266 ◽

Cited By ~ 4

Author(s):

R. Jane Lieberman ◽

Ann Marie C. Heffron ◽

Stephanie J. West ◽

Edward C. Hutchinson ◽

Thomas W. Swem

Keyword(s):

Test Performance ◽

Sixth Grade ◽

Significant Discrepancy ◽

Language Impaired ◽

Language Functions ◽

Language Tests ◽

Significant Difference ◽

Sixth Grade Students ◽

Overall Performance ◽

Selection Of

Four recently developed adolescent language tests, the Fullerton Test for Adolescents (FLTA), the Test of Adolescent Language (TOAL), the Clinical Evaluation of Language Functions (CELF), and the Screening Test of Adolescent Language (STAL), were compared to determine: (a) whether they measured the same language skills (content) in the same way (procedures); and (b) whether students performed similarly on each of the tests. First, respective manuals were reviewed to compare selection of subtest content areas and subtest procedures. Then, each of the tests was administered according to standardized procedures to 30 unselected sixth-grade students. Despite apparent differences in test content and procedures, there was no significant difference in students' performance on three of the four tests, and correlations among test performance were moderate to high. A comparison of the pass/fail rates for overall performance on the tests, however, revealed a significant discrepancy between the proportions of students identified in need of further evaluation on the STAL (20%) and the proportion diagnosed as language impaired on the three diagnostic tests (60-73%). Clinical implications are discussed.

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Effect of mesh on CFD aerodynamic performances of a container ship

Tạp chí Khoa học và Công nghệ Biển ◽

10.15625/1859-3097/20/3/15249 ◽

2020 ◽

Vol 20 (3) ◽

pp. 343-353

Author(s):

Ngo Van He ◽

Le Thi Thai

Keyword(s):

Water Surface ◽

Reference Model ◽

Full Scale ◽

Scale Model ◽

Container Ship ◽

Ansys Fluent ◽

Remarkable Effect ◽

Aerodynamic Performances ◽

Mesh Convergence

In this paper, a commercial CFD code, ANSYS-Fluent has been used to investigate the effect of mesh number generated in the computed domain on the CFD aerodynamic performances of a container ship. A full-scale model of the 1200TEU container ship has been chosen as a reference model in the computation. Five different mesh numbers for the same dimension domain have been used and the CFD aerodynamic performances of the above water surface hull of the ship have been shown. The obtained CFD results show a remarkable effect of mesh number on aerodynamic performances of the ship and the mesh convergence has been found. The study is an evidence to prove that the mesh number has affected the CFD results in general and the accuracy of the CFD aerodynamic performances in particular.

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Semi-Empirical Crest Distributions of Long-Crest Nonlinear Waves of Three-Hour Duration

Volume 1: Offshore Technology ◽

10.1115/omae2017-61226 ◽

2017 ◽

Author(s):

Zhenjia (Jerry) Huang ◽

Qiuchen Guo

Keyword(s):

Nonlinear Wave ◽

Wave Height ◽

Model Test ◽

Significant Wave Height ◽

Spectral Peak ◽

Wave Crest ◽

Empirical Formulas ◽

Peak Period ◽

Significant Wave ◽

Semi Empirical

In wave basin model test of an offshore structure, waves that represent the given sea states have to be generated, qualified and accepted for the model test. For seakeeping and stationkeeping model tests, we normally accept waves in wave calibration tests if the significant wave height, spectral peak period and spectrum match the specified target values. However, for model tests where the responses depend highly on the local wave motions (wave elevation and kinematics) such as wave impact, green water impact on deck and air gap tests, additional qualification checks may be required. For instance, we may need to check wave crest probability distributions to avoid unrealistic wave crest in the test. To date, acceptance criteria of wave crest distribution calibration tests of large and steep waves of three-hour duration (full scale) have not been established. The purpose of the work presented in the paper is to provide a semi-empirical nonlinear wave crest distribution of three-hour duration for practical use, i.e. as an acceptance criterion for wave calibration tests. The semi-empirical formulas proposed in this paper were developed through regression analysis of a large number of fully nonlinear wave crest distributions. Wave time series from potential flow simulations, computational fluid dynamics (CFD) simulations and model test results were used to establish the probability distribution. The wave simulations were performed for three-hour duration assuming that they were long-crested. The sea states are assumed to be represented by JONSWAP spectrum, where a wide range of significant wave height, peak period, spectral peak parameter, and water depth were considered. Coefficients of the proposed semi-empirical formulas, comparisons among crest distributions from wave calibration tests, numerical simulations and the semi-empirical formulas are presented in this paper.

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Guidelines for CFD Simulations of Spar VIM

Volume 7: CFD and VIV ◽

10.1115/omae2013-10333 ◽

2013 ◽

Cited By ~ 8

Author(s):

Charles Lefevre ◽

Yiannis Constantinides ◽

Jang Whan Kim ◽

Mike Henneke ◽

Robert Gordon ◽

...

Keyword(s):

Reynolds Number ◽

Test Data ◽

Model Test ◽

Model Tests ◽

Full Scale ◽

Mooring System ◽

Time Step ◽

Cfd Simulations ◽

Scaled Model ◽

Sway Motion

Vortex-Induced Motion (VIM), which occurs as a consequence of exposure to strong current such as Loop Current eddies in the Gulf of Mexico, is one of the critical factors in the design of the mooring and riser systems for deepwater offshore structures such as Spars and multi-column Deep Draft Floaters (DDFs). The VIM response can have a significant impact on the fatigue life of mooring and riser components. In particular, Steel Catenary Risers (SCRs) suspended from the floater can be sensitive to VIM-induced fatigue at their mudline touchdown points. Industry currently relies on scaled model testing to determine VIM for design. However, scaled model tests are limited in their ability to represent VIM for the full scale structure since they are generally not able to represent the full scale Reynolds number and also cannot fully represent waves effects, nonlinear mooring system behavior or sheared and unsteady currents. The use of Computational Fluid Dynamics (CFD) to simulate VIM can more realistically represent the full scale Reynolds number, waves effects, mooring system, and ocean currents than scaled physical model tests. This paper describes a set of VIM CFD simulations for a Spar hard tank with appurtenances and their comparison against a high quality scaled model test. The test data showed considerable sensitivity to heading angle relative to the incident flow as well as to reduced velocity. The simulated VIM-induced sway motion was compared against the model test data for different reduced velocities (Vm) and Spar headings. Agreement between CFD and model test VIM-induced sway motion was within 9% over the full range of Vm and headings. Use of the Improved Delayed Detached Eddy Simulation (IDDES, Shur et al 2008) turbulence model gives the best agreement with the model test measurements. Guidelines are provided for meshing and time step/solver setting selection.

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FROUDE’S LAW OF SIMILITUDE – CONTEMPORARY AND FUTURE SEAKEEPING TESTING

The International Journal of Maritime Engineering ◽

10.5750/ijme.v153ia2.849 ◽

2021 ◽

Vol 153 (A2) ◽

Author(s):

R P Dallinga ◽

R H M Huijsmans

Keyword(s):

Model Test ◽

Scale Effects ◽

Higher Order ◽

Air Pressure ◽

Test Results ◽

Viscous Effects ◽

Two Phase ◽

Scale Models ◽

Non Linear

Historically “scale effects” in the interpretation of tests with scale models in waves using Froude’s Law of Similitude are mostly associated with viscous effects. Nowadays, with a much more complete modelling of reality and a focus on higher order non-linear phenomena, scaling of model test results implies a wider range of assumptions than the validity of Froude’s Law. Our contribution to the conference is a visionary review of contemporary and future problems in the interpretation of these tests. In this context we will discuss the developments in test techniques, including the development of a new Two-Phase Laboratory facilitating seakeeping and sloshing tests at reduced air pressure.

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A COMPARISON BETWEEN MODEL AND PROTOTYPE WAVES IN HARBOURS

Coastal Engineering Proceedings ◽

10.9753/icce.v16.38 ◽

1978 ◽

Vol 1 (16) ◽

pp. 38

Author(s):

Sverre Bjordal ◽

Alf Torum

Keyword(s):

Physical Model ◽

Model Test ◽

Field Measurements ◽

Full Scale ◽

Common Method ◽

Test Results ◽

Open Coast ◽

The World ◽

Mooring Forces ◽

Absolute Basis

A common method of estimating the sheltering effects of different breakwater locations and layouts is to carry out physical model wave disturbance tests. Such tests have been carried out in different laboratories throughout the world for many years. But to our knowledge no reports are available in the literature showing comparison between model measurements and field measurements. The trend is that we know more and more on the wave cl imate along our coasts. Hence we have a better basis to make our economical calculations on breakwaters. We therefore also want to operate our models on a more absolute basis rather than on a comparative basis. The trend in recent years has also been to study breakwater locations and layouts in order to minimize mooring forces and ship movements. On this background VHL found a comparison between model test results and field measurements necessary. Full scale measurements of waves were carried out in two harbours by VHL during the winter 1976/77. This paper will present the results of the comparison of the model and the full scale measurements in Berlevag and Vard0 fishing harbours on the open coast of Finnmark in the northern part of Norway (Fig. I) . The model tests, as well as the full scale measurements, have been sponsored by the Norwegian State Harbour Authorities.

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