Experimental Investigation of Roll and Heave Motion of Triswach Ships

2015 ◽  
Author(s):  
I. Stojanovic ◽  
E. Muk-Pavic ◽  
R. Bucknall ◽  
J. Falls ◽  
A. Onas ◽  
...  
Keyword(s):  
Experimental Data ◽  
Linear Method ◽  
Empirical Method ◽  
Naval Research ◽  
Naval Academy ◽  
Roll Damping ◽  
Damping Coefficients ◽  
Decay Tests ◽  
Heave Motion ◽  
The U.S

Trimaran Small Waterplane Area Centre Hull (TriSWACH) is a concept hybrid hull form between SWATH ships (centre hull) and Trimarans (side hulls). The resistance and seakeeping characteristics of this hullform are currently investigated by the Atlantic Centre for Innovative Design and Control of Small Ships (ACCeSS) consortium, supported by the U.S. Office of Naval Research. The main design advantages of this novel hull are (1) small wave resistance at high speeds; (2) large usable deck area; and (3) superior seakeeping characteristics, compared to monohull ships. Roll damping and response, as key design features for the safety and operational efficiency of the vessel, are currently under investigation. The ultimate goal is to propose an improved method for prediction of roll motions and also investigate how it affects the heaving response of the TriSWACH. This paper presents the findings from roll and heave decay tests, conducted at the U.S. Naval Academy (Annapolis, MD), focusing on the roll damping and the effect of side hull geometry on roll and heave motion coupling. Roll and heave decay tests were conducted for two scale models with different side hull shapes (conventional with haunches and prismatic with no haunches). Significant coupling between roll and heave was observed for the model with conventional side hulls. A quasi-linear method is used to obtain the roll damping coefficients using the experimental data and ITTC recommended semi-empirical method was used to approximate the roll damping coefficients. Both methods have shown good correlation with experimental data.

scholarly journals Bilge Keel Induced Roll Damping of an FPSO With Sponsons

2016 ◽  
Author(s):  
Babak Ommani ◽  
Nuno Fonseca ◽  
Trygve Kristiansen ◽  
Christopher Hutchison ◽  
Hanne Bakksjø
Keyword(s):  
Free Surface ◽  
Two Dimensions ◽  
The Body ◽  
Proximity Effects ◽  
Roll Damping ◽  
Damping Coefficients ◽  
Free Decay ◽  
Strip Theory ◽  
Decay Tests ◽  
Bilge Keel

The bilge keel induced roll damping of an FPSO with sponsons is investigated numerically and experimentally. The influence of the bilge keel size, on the roll damping is studied. Free decay tests of a three-dimensional ship model, for three different bilge keel sizes are used to determine roll damping coefficients. The dependency of the quadratic roll damping coefficient to the bilge keel height and the vertical location of the rotation center is studied using CFD. A Navier-Stokes solver based on the Finite Volume Method is adopted for solving the laminar flow of incompressible water around a section of the FPSO undergoing forced roll oscillations in two-dimensions. The free-surface condition is linearized by neglecting the nonlinear free-surface terms and the influence of viscous stresses in the free surface zone, while the body-boundary condition is exact. An averaged center of rotation is estimated by comparing the results of the numerical calculations and the free decay tests. The obtained two-dimensional damping coefficients are extrapolated to 3D by use of strip theory argumentations and compared with the experimental results. It is shown that this simplified approach can be used for evaluating the bilge keel induced roll damping with efficiency, considering unconventional ship shapes and free-surface proximity effects.

scholarly journals Experimental Determination of Non-Linear Roll Damping of an FPSO Pure Roll Coupled with Liquid Sloshing in Two-Row Tanks

2020 ◽  
Vol 8 (8) ◽  
pp. 582 ◽  
Author(s):  
Jane-Frances Igbadumhe ◽  
Omar Sallam ◽  
Mirjam Fürth ◽  
Rihui Feng
Keyword(s):  
Linear Method ◽  
Computational Effort ◽  
Liquid Sloshing ◽  
Linear Quadratic ◽  
Roll Damping ◽  
Decay Test ◽  
Increased Risk ◽  
Decay Tests ◽  
Bad Weather ◽  
Vessel Motion

Wave excited roll motion poses danger for moored offshore vessels such as Floating Production Storage and Offloading (FPSO) because they cannot divert to avoid bad weather. Furthermore, slack cargo tanks are almost always present in FPSOs by design. These pose an increased risk of roll instability due to the presence of free surfaces. The most common method of determining roll damping is roll decay tests, yet very few test have been performed with liquid cargo, and most liquid cargo experiments use tanks that span the entire width of the vessel; which is seldom the case for full scale FPSO vessels during normal operations. This paper presents a series of roll decay test carried out on a FPSO model with two two-row-prismatic tanks with different filling levels. To directly investigate the coupling between the liquid sloshing and the vessel motion, without modifying the damping, tests were performed at a constant draft. The equivalent linear roll damping coefficients consisting of linear, quadratic and cubic damping terms are analyzed for each loading condition using four established methods, the Quasi-linear method, Froude Energy method, Averaging method and the Perturbation method. The results show that the cubic damping term is paramount for FPSOs and at low filling levels, were the FPSO is more damped. Recommendations regarding the applicability of the methods, their accuracy and computational effort is given and the effect of the liquid motion on the vessel motion is discussed.

Estimation of Roll Damping Coefficients Based on Model Tests Responses of a FPSO in Waves

2019 ◽  
Author(s):  
Claudio A. Rodríguez ◽  
Paulo T. T. Esperança ◽  
Mauro C. Oliveira
Keyword(s):  
Model Tests ◽  
Viscous Effects ◽  
Roll Damping ◽  
Damping Coefficients ◽  
Numerical Predictions ◽  
Intact Stability ◽  
Calm Water ◽  
Wave Conditions ◽  
Decay Tests ◽  
Damping Estimation

Abstract Roll damping estimation is of great concern for the prediction of motions in waves of ship and offshore platforms, especially when viscous effects are relevant. Although this problem dates back to the times of William Froude, it has regained much attention in the context of the development of the second-generation intact stability criteria of ships, especially because there are still not accurate and efficient tools for roll damping prediction. For offshore applications, a common approach for roll damping estimation is to perform roll decay tests with scale models in calm water and then use the resultant values in the roll equation to predict motions in waves. However, for some wave conditions, the damping coefficients obtained from those tests may not be representative of the actual damping in waves. To assess the influence of wave conditions in the roll damping coefficients, the present work proposes a simplified hybrid approach that combines experimental results from model tests with numerical predictions of roll motion in waves. The numerical tool adopted here is based on a frequency domain single-degree-of-freedom model with linearized external damping that includes viscous effects. A series of experimental model tests with a typical FPSO hull in regular and irregular has been analyzed to obtain the roll damping coefficients in waves. These results are compared with those from decay tests in calm-water as well as from semi-empirical predictions based on Ikeda’s method. Despite the linearized assumption, it is expected that the damping coefficients from wave tests provide a more realistic representation of the roll dynamics than those from typical decay tests.

Prospective Study of Respiratory Infections at the U.S. Naval Academy

2001 ◽  
Author(s):  
Gregory C. Gray ◽  
Robert G. Schultz ◽  
Gary D. Gackstetter ◽  
Jamie A. McKeehan ◽  
Kathleen V. Aldridge
Keyword(s):  
Prospective Study ◽  
Respiratory Infections ◽  
Naval Academy ◽  
The U.S

History of Respiratory Illness at the U.S. Naval Academy

2001 ◽  
Author(s):  
Tammy L. Blankenship ◽  
Gary Gackstetter ◽  
Gregory C. Gray
Keyword(s):  
Respiratory Illness ◽  
Naval Academy ◽  
History Of ◽  
The U.S

Effects of Over Fire Air on the Combustion and NOx Emission Characteristics of a 600 MW Opposed Swirling Fired Boiler

2012 ◽  
Vol 512-515 ◽  
pp. 2135-2142 ◽  
Author(s):  
Yu Peng Wu ◽  
Zhi Yong Wen ◽  
Yue Liang Shen ◽  
Qing Yan Fang ◽  
Cheng Zhang ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Empirical Method ◽  
Nox Emission ◽  
Emission Characteristics ◽  
Cfd Model ◽  
Nitrogen Release ◽  
Computational Fluid Dynamics Cfd ◽  
Low Nox Emission

A computational fluid dynamics (CFD) model of a 600 MW opposed swirling coal-fired utility boiler has been established. The chemical percolation devolatilization (CPD) model, instead of an empirical method, has been adapted to predict the nitrogen release during the devolatilization. The current CFD model has been validated by comparing the simulated results with the experimental data obtained from the boiler for case study. The validated CFD model is then applied to study the effects of ratio of over fire air (OFA) on the combustion and nitrogen oxides (NOx) emission characteristics. It is found that, with increasing the ratio of OFA, the carbon content in fly ash increases linearly, and the NOx emission reduces largely. The OFA ratio of 30% is optimal for both high burnout of pulverized coal and low NOx emission. The present study provides helpful information for understanding and optimizing the combustion of the studied boiler

Calculation and Measurement of the Stiffness and Damping Coefficients for a Low Impedance Hydrodynamic Bearing

1997 ◽  
Vol 119 (1) ◽  
pp. 57-63 ◽  
Author(s):  
M. J. Goodwin ◽  
P. J. Ogrodnik ◽  
M. P. Roach ◽  
Y. Fang
Keyword(s):  
Experimental Data ◽  
Dynamic Stiffness ◽  
Perturbation Technique ◽  
The Novel ◽  
Oil Film ◽  
Hydrodynamic Bearing ◽  
Damping Coefficients ◽  
Stiffness And Damping ◽  
Film Stiffness ◽  
Novel Design

This paper describes a combined theoretical and experimental investigation of the eight oil film stiffness and damping coefficients for a novel low impedance hydrodynamic bearing. The novel design incorporates a recess in the bearing surface which is connected to a standard commercial gas bag accumulator; this arrangement reduces the oil film dynamic stiffness and leads to improved machine response and stability. A finite difference method was used to solve Reynolds equation and yield the pressure distribution in the bearing oil film. Integration of the pressure profile then enabled the fluid film forces to be evaluated. A perturbation technique was used to determine the dynamic pressure components, and hence to determine the eight oil film stiffness and damping coefficients. Experimental data was obtained from a laboratory test rig in which a test bearing, floating on a rotating shaft, was excited by a multi-frequency force signal. Measurements of the resulting relative movement between bearing and journal enabled the oil film coefficients to be measured. The results of the work show good agreement between theoretical and experimental data, and indicate that the oil film impedance of the novel design is considerably lower than that of a conventional bearing.

Development and Verification of Modeling Practice for CFD Decay Calculations to Obtain Roll Damping of FPSO

2021 ◽  
Author(s):  
Arjen Koop ◽  
Pierre Crepier ◽  
Sebastien Loubeyre ◽  
Corentin Dobral ◽  
Kai Yu ◽  
...  
Keyword(s):  
Model Test ◽  
Test Results ◽  
Cfd Modelling ◽  
Roll Damping ◽  
Natural Period ◽  
Computational Mesh ◽  
Safety Studies ◽  
Offshore Industry ◽  
Decay Tests ◽  
Set Up

Abstract Estimates for roll damping are important input parameters for simulation studies on vessels operating at sea, e.g. FPSO mooring in waves, wind and current, workability and operability investigations, Dynamic Position studies, ship-to-ship operations and safety studies of vessels. To accurately predict the motions of vessels this quantity should be determined with confidence in the values. Traditionally, model experiments in water basins using so-called decay tests are carried out to determine the roll damping. With recent advancements in CFD modelling, the offshore industry has started using CFD as an alternative tool to compute the roll damping of FPSO’s. In order to help adopt CFD as a widely accepted tool, there is a need to develop confidence in CFD predictions. Therefore, a practical CFD modelling practice is developed within the Reproducible CFD JIP for roll decay CFD simulations. The Modelling Practice describes the geometry modelling, computational mesh, model set-up and post-processing for these type of CFD calculations. This modelling practice is verified and validated by three independent verifiers against available model test data. This paper provides an overview of the developed modelling practice and the calculated CFD results from the verifiers. The CFD modelling practice is benchmarked against available model test results for a tanker-shaped FPSO. By following this modelling practice, the CFD predictions for the equivalent linear damping coefficient and natural period of the roll motions are within 10% for all verifiers and within 10% from the model test results. Therefore, we conclude that when following the developed modelling practice for roll decay simulations, reliable, accurate and reproducible results can be obtained for the roll damping of tanker-shaped FPSOs.

scholarly journals Revisiting Theoretical Limits for One-Degree-of-Freedom Wave Energy Converters

2020 ◽  
pp. 1-11
Author(s):  
Nathan Tom
Keyword(s):  
Power Generation ◽  
Wave Energy ◽  
Degree Of Freedom ◽  
Upper And Lower Bounds ◽  
Complex Conjugate ◽  
Hydrodynamic Coefficients ◽  
Damping Coefficients ◽  
Wave Energy Converters ◽  
Heave Motion ◽  
Energy Converters

Abstract This work revisits the theoretical limits of one-degree-of-freedom wave energy converters (WECs). This paper considers the floating sphere used in the OES Task 10 WEC modeling and verification effort for analysis. Analytical equations are derived to determine bounds on displacement amplitude, time-averaged power (TAP), and power-take-off (PTO) force. A unique result found shows that the TAP absorbed by a WEC can be defined solely by the inertial properties and radiation hydrodynamic coefficients. In addition, a unique expression for the PTO force was derived that provides upper and lower bounds when resistive control is used to maximize power generation. For complex conjugate control, this same expression only provides a lower bound, as there is theoretically no upper bound. These bounds assist in comparing the performance of the floating sphere if it were to extract energy using surge or heave motion. The analysis shows because of differences in hydrodynamic coefficients for each oscillating mode, there are different frequency ranges that provide better power capture efficiency. The influence of a motion constraint on TAP while utilizing a nonideal power take-off is examined and found to reduce the losses associated with bidirectional energy flow. The expression to calculate TAP with a nonideal PTO is modified by the mechanical-to-electrical efficiency and the ratio of the PTO spring and damping coefficients. The PTO spring and damping coefficients were separated in the expression, allowing for limits to be set on the PTO coefficients to ensure net power generation.

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