A comparative assessment of approximate methods to simulate second order roll motion of FPSOs

2017 ◽  
Vol 7 (1) ◽  
pp. 53-74 ◽  
Author(s):  
Abhilash Somayajula ◽  
Jeffrey Falzarano
Keyword(s):  
Comparative Assessment ◽  
Second Order ◽  
Roll Motion ◽  
Approximate Methods

Radiant Heat Transfer From Isothermal Dispersions With Isotropic Scattering

1967 ◽  
Vol 89 (4) ◽  
pp. 300-308 ◽  
Author(s):  
R. H. Edwards ◽  
R. P. Bobco
Keyword(s):  
Heat Transfer ◽  
Approximate Solutions ◽  
Radiant Heat ◽  
Second Order ◽  
Isotropic Scattering ◽  
Radiant Heat Transfer ◽  
Approximate Methods ◽  
First Order ◽  
Order Solution ◽  
Radiant Transfer

Two approximate methods are presented for making radiant heat-transfer computations from gray, isothermal dispersions which absorb, emit, and scatter isotropically. The integrodifferential equation of radiant transfer is solved using moment techniques to obtain a first-order solution. A second-order solution is found by iteration. The approximate solutions are compared to exact solutions found in the literature of astrophysics for the case of a plane-parallel geometry. The exact and approximate solutions are both expressed in terms of directional and hemispherical emissivities at a boundary. The comparison for a slab, which is neither optically thin nor thick (τ = 1), indicates that the second-order solution is accurate to within 10 percent for both directional and hemispherical properties. These results suggest that relatively simple techniques may be used to make design computations for more complex geometries and boundary conditions.

Comparison of Real-Time Hybrid Model Testing of a Braceless Semi-Submersible Wind Turbine and Numerical Simulations

2017 ◽  
Author(s):  
Madjid Karimirad ◽  
Erin E. Bachynski ◽  
Petter Andreas Berthelsen ◽  
Harald Ormberg
Keyword(s):  
Wind Turbine ◽  
Real Time ◽  
Hybrid Model ◽  
Low Frequency ◽  
Ocean Basin ◽  
Model Testing ◽  
Second Order ◽  
Experimental Results ◽  
Scaled Model ◽  
Approximate Methods

In this paper, integrated analyses performed in SIMA are compared against experimental results obtained using real-time hybrid model testing (ReaTHM®) carried out in the ocean basin facilities of MARINTEK in October 2015. The experimental data is from a 1:30 scaled model of a semi-submersible wind turbine. Coupled aero-hydro-servo-elastic simulations are performed in MARINTEK’s SIMA software. The present work extends previous results from Berthelsen et al. [1] by including a blade element/momentum (BEM) model for the rotor forces in SIMA and comparing the coupled responses of the system to the experimental results. The previously presented hydrodynamic model is also further developed, and the importance of second order loads (and applicability of approximate methods for their calculations) is examined. Low-frequency hydrodynamic excitation and damping are seen to be important, but these loads include a combination of viscous and potential forces. For the selected concept, the second order potential flow forces have limited effects on the responses.

scholarly journals Approach for Input Uncertainty Propagation and Robust Design in CFD Using Sensitivity Derivatives1

2001 ◽  
Vol 124 (1) ◽  
pp. 60-69 ◽  
Author(s):  
Michele M. Putko ◽  
Arthur C. Taylor , ◽  
Perry A. Newman ◽  
Lawrence L. Green
Keyword(s):  
Robust Optimization ◽  
Input Parameter ◽  
Uncertainty Propagation ◽  
Statistical Moment ◽  
Second Order ◽  
Statistical Moments ◽  
Approximate Methods ◽  
Mean Values ◽  
Sensitivity Derivatives ◽  
Input Variables

An implementation of the approximate statistical moment method for uncertainty propagation and robust optimization for quasi 1-D Euler CFD code is presented. Given uncertainties in statistically independent, random, normally distributed input variables, first-and second-order statistical moment procedures are performed to approximate the uncertainty in the CFD output. Efficient calculation of both first- and second-order sensitivity derivatives is required. In order to assess the validity of the approximations, these moments are compared with statistical moments generated through Monte Carlo simulations. The uncertainties in the CFD input variables are also incorporated into a robust optimization procedure. For this optimization, statistical moments involving first-order sensitivity derivatives appear in the objective function and system constraints. Second-order sensitivity derivatives are used in a gradient-based search to successfully execute a robust optimization. The approximate methods used throughout the analyses are found to be valid when considering robustness about input parameter mean values.

scholarly journals Design of slender reinforced concrete rectangular columns subjected to eccentric loads by approximate methods

2012 ◽  
Vol 5 (4) ◽  
pp. 548-554 ◽  
Author(s):  
J. M. Calixto ◽  
T. H. Souza ◽  
E. V. Maia
Keyword(s):  
Reinforced Concrete ◽  
Second Order ◽  
Order Effects ◽  
Test Results ◽  
Approximate Methods ◽  
Design Procedures ◽  
Load Combination ◽  
Second Order Effects ◽  
The Stability ◽  
Slender Columns

Reinforced concrete codes worldwide establish that the design of slender columns must ensure that under the most unfavorable load combination, there is neither instability nor material failures. Thus, it is mandatory to consider material as well as geometrical nonlinearities. The consideration of second order effects can be done using simplified methods or the general method. This work analyses second order effects based on the approximate methods shown in NBR 6118 [1]: approximate curvature method and approximate stiffness procedure. Due to the importance of the columns in the stability of buildings is essential that these simplified design methods provide safe solutions for the design of columns. In this scenario, the objective of this study is to evaluate these simplified design procedures in terms of safety, precision and economy with respect to test results of RC slender columns subjected to eccentric loads found in the literature. The comparative analysis reveals that the approximate stiffness procedure provides better results.

Ship Rolling Prediction Based on Gray RBF Neural Network

2011 ◽  
Vol 48-49 ◽  
pp. 1044-1048 ◽  
Author(s):  
Li Sang Liu ◽  
Xia Fu Peng ◽  
Jie Hua Zhou
Keyword(s):  
Neural Network ◽  
Prediction Error ◽  
Rbf Neural Network ◽  
Second Order ◽  
Prediction Algorithm ◽  
Roll Motion ◽  
Gray Model ◽  
Rbf Network ◽  
Ship Roll ◽  
Simulation Results

To enhance the ship’s seaworthiness and seakeeping capacity, a new prediction algorithm based on Gray RBF neural network is presented to forecast roll motion accurately. The second-order gray model GM(2,1) and RBF network are introduced firstly, then using AGO (accumulated generating operation) to weaken randomness and volatility of raw data, which would affect the accuracy of RBF network. On the other hand, the algorithm flow of GMRBF(2,1) is given. Further more, GMRBF(2,1) is applied in a sample of ship roll sequence and effectively improves large prediction error of second-order gray model. The simulation results prove that the new model is more accurate and stabilizer than traditional models.

On Second-Order Roll Motions of Ships

2003 ◽  
Author(s):  
Yonghui Liu
Keyword(s):  
Second Order ◽  
Roll Motion ◽  
Frequency Domain Method ◽  
Test Results ◽  
Order Difference ◽  
Numerical Predictions ◽  
Offshore Engineering ◽  
Random Seas ◽  
Ship Roll ◽  
Good Agreement

More and more vessels for offshore engineering applications have a roll period beyond 20 seconds in order to avoid the wave frequency excitations on the roll motion. That is particularly true for the latest drilling vessels. However, this will lead to an unexpected second-order roll motion of the ships. This paper will present a new methodology to evaluate the second-order roll motions of the ships in random seas. The higher-order boundary element method (HOBEM) has been utilized to generate the second order difference-frequency roll excitations on the ships and the second-order ship roll motions were predicted by a frequency-domain method. A series of model tests have been conducted and the test results have a good agreement with the numerical predictions. Therefore, this new method has been verified and validated.

Small perturbation expansions in unsteady aerofoil theory

1977 ◽  
Vol 83 (2) ◽  
pp. 209-224 ◽  
Author(s):  
J. M. R. Graham ◽  
I. Kullar
Keyword(s):  
Turbulent Flow ◽  
Small Perturbation ◽  
Second Order ◽  
Perturbation Expansions ◽  
Approximate Methods ◽  
Unsteady Forces ◽  
Unsteady Lift

Perturbation expansions are derived to second order in a wavenumber parameter for the unsteady lift induced on an aerofoil by disturbances convected past it at subsonic speeds. The results are used to discuss other approximate methods which have been used to predict the unsteady forces and noise generated by an aerofoil in turbulent flow.

Disappearance Voltage Determinations Using a Convergent Beam

1971 ◽  
Vol 29 ◽  
pp. 184-185
Author(s):  
W. L. Bell
Keyword(s):  
Second Order ◽  
Objective Method ◽  
Uniform Thickness ◽  
Rocking Curve ◽  
Crystal Perfection ◽  
Kikuchi Line ◽  
Central Maximum ◽  
Diffraction Patterns ◽  
Convergent Beam ◽  
Beam Technique

Disappearance voltages for second order reflections can be determined experimentally in a variety of ways. The more subjective methods, such as Kikuchi line disappearance and bend contour imaging, involve comparing a series of diffraction patterns or micrographs taken at intervals throughout the disappearance range and selecting that voltage which gives the strongest disappearance effect. The estimated accuracies of these methods are both to within 10 kV, or about 2-4%, of the true disappearance voltage, which is quite sufficient for using these voltages in further calculations. However, it is the necessity of determining this information by comparisons of exposed plates rather than while operating the microscope that detracts from the immediate usefulness of these methods if there is reason to perform experiments at an unknown disappearance voltage.The convergent beam technique for determining the disappearance voltage has been found to be a highly objective method when it is applicable, i.e. when reasonable crystal perfection exists and an area of uniform thickness can be found. The criterion for determining this voltage is that the central maximum disappear from the rocking curve for the second order spot.

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