scholarly journals Determination of non-linear damping coefficients of bottom-hinged oscillating wave surge converters using numerical free decay tests

2015 ◽  
pp. 507-513 ◽  
Author(s):  
H Asmuth ◽  
P Schmitt ◽  
B Elsaesser ◽  
A Henry
Keyword(s):  
Damping Coefficients ◽  
Free Decay ◽  
Non Linear ◽  
Linear Damping ◽  
Decay Tests

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.

Study of the Wave Drift Damping for a Very Large Crude Carrier

2007 ◽  
Author(s):  
Joel S. Sales ◽  
Vinicius L. F. Matos ◽  
Andre R. da Silva ◽  
Ge´rson B. Matter ◽  
Sergio H. Sphaier
Keyword(s):  
Linear Part ◽  
Regular Waves ◽  
Damping Coefficients ◽  
Pull Out ◽  
Wave Drift ◽  
Decay Test ◽  
Wave Drift Damping ◽  
Linear Damping ◽  
The Mean ◽  
Decay Tests

Pull-out test and decay tests in still water and in waves for the surge motion of a VLCC in ballast condition are carried out at LabOceano. The pull-out test associated with the mean drift displacement in regular waves is used to determine mean drift force. From the decay tests the damping coefficients are adjusted using the Froude energy method and the procedure based on the logarithm decrement. For the decay test in waves, the response is subdivided in the mean drift contribution, the regular wave response and the transient response. The wave drift damping is considered as an increase on the linear damping in still water. So, we introduce an additional damping to the linear part of the damping coefficient in still water and simulate the decay test in waves. Comparing the results from the simulation with the experiments the wave drift damping contribution is adjusted. Finally, the mean drift results are compared with the results obtained with the potential theory. The wave drift damping coefficients obtained from the experiments are compared with coefficients obtained with a formulation proposed in the literature.

scholarly journals A Numerical Method to Model Non-linear Damping Behaviour of Martensitic Shape Memory Alloys

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2178 ◽  
Author(s):  
Pouya Haghdoust ◽  
Antonietta Lo Conte ◽  
Simone Cinquemani ◽  
Nora Lecis
Keyword(s):  
Finite Element ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Hysteresis Loops ◽  
Element Model ◽  
Thin Layers ◽  
Hybridization Technique ◽  
Free Decay ◽  
Non Linear ◽  
Linear Damping

This article investigates the efficiency of hybridizing composites with thin layers of martensitic shape memory alloys for improvement of damping. The non-linear damping behaviour of martensitic shape memory alloys is simulated using a modified version of Masing’s rules. The model was implemented in a user subroutine of a finite element code, and validated by a numerical simulation of experimental hysteresis loops at different maximum strain amplitudes. The experimental free decay of hybridized glass fiber reinforced polymer beams was simulated using the finite element model, including the validated model of the investigated materials. The amplitude-dependent damping of the hybrid beams in free decay was reproduced successfully in the numerical analysis and it was proven that the hybridization technique is efficient for improvement of damping.

scholarly journals Estimation of the Motion Performance of a Light Buoy Adopting Ecofriendly and Lightweight Materials in Waves

2020 ◽  
Vol 8 (2) ◽  
pp. 139 ◽  
Author(s):  
Se-Min Jeong ◽  
Bo-Hun Son ◽  
Chang-Yull Lee
Keyword(s):  
Fluid Dynamics ◽  
Wave Motion ◽  
Viscous Damping ◽  
Motion Simulation ◽  
Incoming Wave ◽  
Damping Coefficients ◽  
Free Decay ◽  
Computational Fluid Dynamics Cfd ◽  
Motion Performance ◽  
Decay Tests

In this study, the methods and results of numerical simulations to estimate the motion performance of a newly developed lightweight light buoy in waves and to check the effect of conceptually developed appendages on that performance were introduced. The results from a potential-based motion analysis with viscous damping coefficients obtained from free decay tests using computational fluid dynamics (CFD) and those obtained from wave motion simulation using CFD were compared. From these results, it was confirmed that viscous damping should be considered when the frequency of an incoming wave is close to the natural frequency of the buoy. It was estimated that the pitch and heave motions of the light buoy became smaller when the developed appendages were adopted. Although the quantitative superiority of the appendages was different, the qualitative superiority was similar between both results.

Assessment of Nonlinear Heave Damping Model for Spar With Heave Plate Using Free Decay Tests

2016 ◽  
Author(s):  
Mahesh J. Rao ◽  
S. Nallayarasu ◽  
S. K. Bhattacharyya
Keyword(s):  
Cfd Simulation ◽  
Linear Quadratic ◽  
Cfd Simulations ◽  
Free Decay ◽  
Linear Damping ◽  
Heave Plate ◽  
Decay Tests ◽  
Heave Motion ◽  
Damping Model ◽  
Quadratic Damping

Linear damping models have been used in the past for solving floating body dynamics, especially for simple geometries such as spar. However, due to the addition of heave damping elements to spar such as heave plate, complex flow around these elements may change the relationship between damping and velocity of the body to nonlinear. The damping plays a major role in accurate determination of motion response of spars, especially the heave. Free decay tests have been carried out for spar with and without heave plate in calm water condition. The Computational Fluid Dynamics (CFD) simulation of heave decay is carried out using ANSYS FLUENT and validated by free decay test results using scale models. Mesh convergence study has been conducted to determine the optimum mesh size. The heave motion obtained from CFD are used to derive the damping terms by matching the heave motion obtained using equation of motion by changing the damping term with linear, quadratic and the combination of linear and quadratic. The heave motion obtained from linear damping model matches well with that obtained from measured motion and CFD simulation for spar without heave plate. However, the linear / quadratic damping models alone are not suitable for spar with heave plate. Hence a combination of linear and quadratic damping model is proposed for spar with heave plate. The heave motion computed using a combination of linear and quadratic damping model matches well with that obtained from experimental studies and CFD simulations thus indicating the complexity of flow around heave plate in comparison to the spar alone. Further, the vortices around the spar models obtained from CFD simulations are also presented and discussed with regard to the higher order damping.

scholarly journals A Decrement Method for Quantifying Nonlinear and Linear Damping in Multi-Degree of Freedom Systems

2006 ◽  
Author(s):  
Craig Meskell
Keyword(s):  
Natural Frequencies ◽  
Degree Of Freedom ◽  
Pass Band ◽  
Response Measurement ◽  
Free Decay ◽  
Decay Test ◽  
Non Linear ◽  
Linear Damping ◽  
The Time Domain ◽  
Single Response

A method is presented which can estimate the linear and non-linear damping parameters in a lightly damped multi-degree of freedom system. This in effect allows the system to be decomposed into a set of single degree of freedom nonlinear systems. Only a single response measurement from a free decay test is required as input. This ensures that the magnitude of the damping parameters is not compromised by phase distortion between measurements. The response is band-pass filtered in the time domain, with the pass band centered on each of the natural frequencies. This provides a set of free response measurements, one for each mode. However, it does introduce a restriction in that the natural frequencies must be distinct and separated somewhat. The instantaneous energy of each trace is used to describe the long-term evolution of the mode. Practically this is achieved by using only the peak amplitudes in each period. In this way the stiffness and inertial forces are effectively ignored, and only the damping forces are considered. For this reason, the method is not unlike the familiar decrement method, which can be used to estimate the viscous damping in linear systems. The method is developed in the context of a weakly non-linear, lightly damping two degree-of-freedom system, with both linear and Coulomb damping. Simulated response data is used to demonstrate the accuracy of the technique.

scholarly journals Continuum model of wave propagation in fragmented media: linear damping approximation

2017 ◽  
Vol 24 (3) ◽  
pp. 461-466 ◽  
Author(s):  
Maxim Khudyakov ◽  
Arcady V. Dyskin ◽  
Elena Pasternak
Keyword(s):  
Wave Propagation ◽  
Energy Loss ◽  
Wave Scattering ◽  
Continuum Model ◽  
Low Frequencies ◽  
Damping Coefficients ◽  
Linear Damping ◽  
Voigt Model ◽  
Attenuation And Dispersion

Abstract. Energy dissipation during wave propagation in fragmented geomaterials can be caused by independent movement of fragments leading to energy loss on their impact. By considering a pair of impacting fragments at times much greater than the period of their oscillations, we show that at a large timescale, the dynamics of the pair can be described by a linear viscous model with damping coefficients expressed through the restitution coefficient representing energy loss on impact. Wave propagation in fragmented geomaterials is also considered at the large timescale assuming that the wavelengths are much larger than the fragment sizes such that the attenuation associated with wave scattering on the fragment interfaces can be neglected. These assumptions lead to the Kelvin–Voigt model of damping during wave propagation, which allows the determination of a dispersion relationship. As the attenuation and dispersion are not related to the rate dependence of rock deformation, but rather to the interaction of fragments, the increased energy dispersion at low frequencies can be seen as an indication of the fragmented nature of the geomaterial and the capacity of the fragments for independent movement.

A Decrement Method for Quantifying Non-Linear and Linear Damping

2005 ◽  
Author(s):  
Craig Meskell
Keyword(s):  
Total Force ◽  
Response Measurement ◽  
Response Data ◽  
Damped System ◽  
Free Decay ◽  
Decay Test ◽  
Damping Parameter ◽  
Non Linear ◽  
Linear Damping ◽  
Single Response

A method is presented which can estimate the linear and non-linear damping parameters in a lightly damped system. Only a single response measurement from a free decay test is required as input. This ensures that the magnitude of the damping parameters is not compromised by phase distortion between measurements. The method uses the instantaneous energy to describe the long-term evolution of the system. Practically this is achieved by using only the peak amplitudes in each period. In this way the stiffness is effectively ignored, and only the damping forces are considered. For this reason, the method is not unlike the familiar decrement method, which can be used to estimate the linear damping in linear systems. The method is developed in the context of a weakly non-linear, lightly damping system, with both linear and cubic damping. Simulated response data is used to demonstrate the accuracy of the technique. The non-linear damping parameter is extracted from the response data to within 5% of the exact value, even though the non-linear term contributes less than 1% to the total force in the system.

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