Determination of Viscous Damping for Low Frequency Motions of Floating Structures

2011 ◽  
Author(s):  
Z. J. Huang ◽  
B. J. O’Donnell ◽  
T. W. Yung ◽  
S. T. Slocum
Keyword(s):  
Forced Oscillation ◽  
Low Frequency ◽  
Test Method ◽  
Irregular Waves ◽  
Viscous Damping ◽  
Damping Force ◽  
Near Resonance ◽  
Research Company ◽  
Decay Tests ◽  
Scale Motion

ExxonMobil Upstream Research Company developed an advanced model test method to determine reliable damping values for predicting low frequency motions of an FLNG barge and an LNG carrier [1]. An inertial compensation system was introduced in the test to confidently isolate the relatively very small viscous damping force from the total measured forces in the forced oscillation tests. In the system, the spring stiffness in the restoring mechanism was tuned such that the test was done near resonance. This method has been successfully applied to ExxonMobil forced oscillation tests to measure damping of deeply submerged, double body models. Three types of motions were generated in the tests: sinusoidal motions, decay motions and motions with multiple frequencies. In this paper, the authors attempt to correlate the damping obtained from decay tests and from tests with motions of multiple frequency components. Findings from this work help determine damping for predictions of full scale motion in irregular waves.

An Advanced Test Method to Determine Viscous Damping of Floating Structures

2010 ◽  
Author(s):  
Z. J. Huang ◽  
B. J. O’Donnell ◽  
T. W. Yung ◽  
S. T. Slocum
Keyword(s):  
Low Frequency ◽  
Test Method ◽  
Total Force ◽  
Viscous Damping ◽  
Damping Force ◽  
Restoring Force ◽  
Viscous Forces ◽  
Motion Time ◽  
Research Company ◽  
Time Histories

ExxonMobil Upstream Research Company developed an advanced model test method to determine reliable damping values for predicting low frequency motions of an FLNG barge and an LNG carrier. Since viscous damping forces are a very small portion of the total force on the model, how to separate the viscous forces from the total forces is the key technical challenge. To better isolate viscous damping forces, an inertial compensation system consisting of springs was employed in the test. The spring stiffness was designed such that the restoring force cancelled the large inertial loads at the oscillation frequency. Furthermore, double-body models were built and were deeply submerged to minimize surface wave damping. With such an experimental setup, the total force measured was mainly the viscous damping force. Viscous damping was derived from the measured force and motion time histories.

Reliable Estimation of Low-Frequency Viscous Damping for a Turret-Moored FLNG in Current

2018 ◽  
Author(s):  
Z. Huang ◽  
S. Ryu ◽  
D. Lee ◽  
C. S. Hughes
Keyword(s):  
Low Frequency ◽  
Test Method ◽  
Inertia Force ◽  
Total Force ◽  
Viscous Damping ◽  
Damping Force ◽  
Damping Coefficients ◽  
Calm Water ◽  
Oscillation Test ◽  
Measured Force

For a turret-moored Floating Liquefied Natural Gas Plant (FLNG), it is important to use confidently derived low frequency viscous damping coefficients in the prediction of its motions and mooring loads in wind, wave and current conditions. In this paper we present our recent experimental work on the low frequency sway and yaw viscous damping in calm water and in current. In general, damping force is a relatively small portion of the total hydrodynamic force on an oscillatory model. In a previous ExxonMobil damping test in calm water (Huang et al., 2010), i.e. without current and wave, a deeply submerged double-body model was forced to oscillate to avoid surface wave contamination. An inertia compensation system was also designed to cancel the inertia force and the restoring force during oscillations, then the measured force was mainly damping force. Because of the schedule constraints of the present study, it was not possible to perform the submerged oscillation test. Instead, a forced oscillation test in water surface was performed based on KC-number and β-number. In order to obtain reliable damping coefficients, we had to carefully design the test conditions, i.e. current speeds, oscillation amplitudes and frequencies so that an adequate portion of damping force within the total force could be achieved with no significant surface waves that could contaminate the damping results being generated by the oscillating model. Good damping results were obtained. To check the acceptance of the test method based on Froude scaling, a limited number of tests were performed in which the oscillation amplitudes and frequencies were scaled down based on the Froude scaling. Magnitudes of the measured force and moment are significantly low. The time series of the measurements have drifting and significant noise. We could not confidently determine viscous damping results from the measurements.

scholarly journals Real-Time Hybrid Model Testing of a Braceless Semi-Submersible Wind Turbine: Part II — Experimental Results

2016 ◽  
Author(s):  
Erin E. Bachynski ◽  
Maxime Thys ◽  
Thomas Sauder ◽  
Valentin Chabaud ◽  
Lars Ove Sæther
Keyword(s):  
Wind Turbine ◽  
Real Time ◽  
Hybrid Model ◽  
Low Frequency ◽  
Physical Structure ◽  
Ocean Basin ◽  
Test Method ◽  
Experimental Results ◽  
Irregular Waves ◽  
Aerodynamic Loads

Real-Time Hybrid Model (ReaTHM) tests of a braceless semi-submersible wind turbine were carried out at MARINTEK’s Ocean Basin in 2015. The tests sought to evaluate the performance of the floating wind turbine (FWT) structure in environmental conditions representative of the Northern North Sea. In order to do so, the tests employed a new hybrid testing method, wherein simulated aerodynamic loads were applied to the physical structure in the laboratory. The test method was found to work well, and is documented in [1]. The present work describes some of the experimental results. The test results showed a high level of repeatability, and permitted accurate investigation of the coupled responses of a FWT, including unique conditions such as blade pitch faults. For example, the influence of the wind turbine controller can be seen in decay tests in pitch and surge. In regular waves, aerodynamic loads due to constant wind had little influence on the structure motions (except for the mean offsets). Tests in irregular waves with and without turbulent wind are compared directly, and the influence of the wave-frequency motions on the aerodynamic damping of wind-induced low-frequency motions can be observed.

scholarly journals Modeling and Analysis of a SiC Microstructure-Based Capacitive Micro-Accelerometer

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6222
Author(s):  
Xiang Tian ◽  
Wei Sheng ◽  
Zhanshe Guo ◽  
Weiwei Xing ◽  
Runze Tang
Keyword(s):  
Low Frequency ◽  
Superior Performance ◽  
Viscous Damping ◽  
Damping Force ◽  
Modeling And Analysis ◽  
Time Frequency ◽  
Capacitive Accelerometer ◽  
Silicon Devices ◽  
Main Components ◽  
Inertial Measurements

In this study, a comb-type capacitive accelerometer based on a silicon carbide (SiC) microstructure is presented and investigated by the finite element method (FEM). It has the advantages of low weight, small volume, and low cross-coupling. Compared with silicon(111) accelerometers with the same structure, it has a higher natural frequency. When the accelerometer vibrates, its resistive force consists of two main components: a viscous damping and an elastic damping force. It was found that viscous damping dominates at low frequency, and elastic damping dominates at high frequency. The second-order linear system of the accelerometer was analyzed in the time-frequency domain, and its dynamic characteristics were best when the gap between the capacitive plates was 1.23 μm. The range of this accelerometer was 0–100 g, which is 1.64 times that of a silicon(111) accelerometer with the same structure. In addition, the accelerometer could work normally at temperatures of up to 1200 °C, which is much higher than the working temperatures of silicon devices. Therefore, the proposed accelerometer showed superior performance compared to conventional silicon-based sensors for inertial measurements.

scholarly journals Unifying causal model of rate-independent linear damping for effectively reducing seismic response in low-frequency structures

2020 ◽  
Author(s):  
Hao LUO ◽  
Kohju Ikago
Keyword(s):  
Seismic Response ◽  
Fractional Order ◽  
Causal Model ◽  
Low Frequency ◽  
Viscous Damping ◽  
Damping Force ◽  
Practical Applications ◽  
Proposed Model ◽  
P Rate ◽  
Linear Damping

Rate-independent linear damping (RILD) demonstrates similar performance to that of linear viscous damping for the same loss factor when incorporated in a structure to control seismic response displacement. Nevertheless, the damping force generated by the RILD is relatively low in frequency ranges higher than the natural frequency of the primary structure. This leads to efficient displacement control with low damping force and floor response acceleration when RILD is integrated with low-frequency structures. However, the noncausality of RILD hinders its practical applications, and thus, causal models are widely studied to mimic the RILD behavior.This paper proposes a causal model of RILD using Maxwell elements whose damping force is generated according to the fractional-order derivative of displacement. The proposed model, further represented by a fractional-order damping function, is found to be a unifying model that includes existing causal RILD models from literature, thereby providing further insights to better understand the nature of RILD.Furthermore, several methods were examined to physically realize the proposed model.

Damping characteristics of a magneto-rheological damper with dual independent controllable ducts

2021 ◽  
pp. 1045389X2110188
Author(s):  
Jianqiang Yu ◽  
Xiaomin Dong ◽  
Tao Wang ◽  
Zhengmu Zhou ◽  
Yaqin Zhou
Keyword(s):  
Dynamic Range ◽  
Fluid Flows ◽  
Mr Damper ◽  
Viscous Damping ◽  
The Novel ◽  
The Finite Element Method ◽  
Damping Force ◽  
Damping Characteristics ◽  
Magneto Rheological ◽  
The Mathematical Model

This paper presents the damping characteristics of a linear magneto-rheological (MR) damper with dual controllable ducts based on numerical and experimental analysis. The novel MR damper consisting of a dual-rod cylinder system and a MR valve is used to reduce the influences of viscous damping force and improve dynamic range. Driven by the dual-rod cylinder system, MR fluid flows in the MR valve. The pressure drop of the MR valve with dual independent controllable ducts can be controlled by tuning the current of two independent coils. Based on the mathematical model and the finite element method, the damping characteristics of the MR damper is simulated. A prototype is designed and tested on MTS machine to evaluate its damping characteristics. The results show that the working states and damping force of the MR damper can be controlled by the two independent coils.

Collective oscillations in bubble clouds

2011 ◽  
Vol 680 ◽  
pp. 114-149 ◽  
Author(s):  
ZORANA ZERAVCIC ◽  
DETLEF LOHSE ◽  
WIM VAN SAARLOOS
Keyword(s):  
Frequency Response ◽  
Acoustic Field ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Viscous Damping ◽  
Edge States ◽  
Bubble Cloud ◽  
Collective Oscillations ◽  
The Individual ◽  
Bubble Oscillations

In this paper the collective oscillations of a bubble cloud in an acoustic field are theoretically analysed with concepts and techniques of condensed matter physics. More specifically, we will calculate the eigenmodes and their excitabilities, eigenfrequencies, densities of states, responses, absorption and participation ratios to better understand the collective dynamics of coupled bubbles and address the question of possible localization of acoustic energy in the bubble cloud. The radial oscillations of the individual bubbles in the acoustic field are described by coupled linearized Rayleigh–Plesset equations. We explore the effects of viscous damping, distance between bubbles, polydispersity, geometric disorder, size of the bubbles and size of the cloud. For large enough clusters, the collective response is often very different from that of a typical mode, as the frequency response of each mode is sufficiently wide that many modes are excited when the cloud is driven by ultrasound. The reason is the strong effect of viscosity on the collective mode response, which is surprising, as viscous damping effects are small for single-bubble oscillations in water. Localization of acoustic energy is only found in the case of substantial bubble size polydispersity or geometric disorder. The lack of localization for a weak disorder is traced back to the long-range 1/r interaction potential between the individual bubbles. The results of the present paper are connected to recent experimental observations of collective bubble oscillations in a two-dimensional bubble cloud, where pronounced edge states and a pronounced low-frequency response had been observed, both consistent with the present theoretical findings. Finally, an outlook to future possible experiments is given.

High Efficient Viscoelastic Damper for Heavy Trucks

2012 ◽  
Vol 215-216 ◽  
pp. 318-321 ◽  
Author(s):  
Sai Fei Zhang ◽  
Xiao Ling Liu ◽  
Yong Liu
Keyword(s):  
Flow Rate ◽  
Viscous Damping ◽  
Calculation Formula ◽  
Performance Curve ◽  
Test Results ◽  
Viscoelastic Damper ◽  
Damping Force ◽  
Heavy Trucks ◽  
High Efficient ◽  
Damper Design

In this paper, a new viscoelastic damper design for heavy trucks is presented and a calculation formula of viscous damping force considering the effect of Viscoelastic Fluids (VF) flow rate is carried out. By numerically simulating this equation, curves of the viscoelastic damper performance curve is obtained, and the results show that theoretical calculation result and the test results are well consistent, with the exception at the start point. Theoretical curves are more plumpness in compared with test curves.

Numerical Study on Hydrodynamic Responses of a Two-Body System in Side-by-Side Operation

2016 ◽  
Author(s):  
Shaowu Ou ◽  
Shixiao Fu ◽  
Wei Wei ◽  
Tao Peng ◽  
Xuefeng Wang
Keyword(s):  
Numerical Study ◽  
Low Frequency ◽  
Optimal Operation ◽  
Hydrodynamic Interactions ◽  
Irregular Waves ◽  
Mooring System ◽  
Time Varying ◽  
Body System ◽  
The Time Domain ◽  
Two Bodies

Typically, in some side-by-side offshore operations, the speed of vessels is very low or even 0 and the headings are manually maneuvered. In this paper, the hydrodynamic responses of a two-body system in such operations under irregular seas are investigated. The numerical model includes two identical PSVs (Platform Supply Vessel) as well as the fenders and connection lines between them. A horizontal mooring system constraining the low frequency motions is set on one of the ships to simulate maneuver system. Accounting for the hydrodynamic interactions between two bodies, 3D potential theory is applied for the analysis of their hydrodynamic coefficients. With wind and current effects included, these coefficients are further applied in the time domain simulations in irregular waves. The relevant coefficients are estimated by experiential formulas. Time-varying loads on fenders and connection lines are analyzed. Meanwhile, the relative motions as well as the effects of the hydrodynamic interactions between ships are further discussed, and finally an optimal operation scheme in which operation can be safely performed is summarized.

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