Effect of Negative Damping on Offshore Structures

2018 ◽  
Author(s):  
Gizat Derebe Amare ◽  
Yonas Zewdu Ayele
Keyword(s):  
Dynamic Response ◽  
Structural Design ◽  
Offshore Structures ◽  
Response Amplitude ◽  
Time Varying ◽  
Flow Induced Vibrations ◽  
Negative Damping ◽  
Wave Conditions ◽  
Short Time ◽  
Damping Model

Offshore structures are inevitably exposed to flow induced loads and flow-induced vibrations. The effect of these loads will affect the responses of structures, and the combined of two together on the response can lead the structures to induce different phenomena. The effect of damping is to counteract any dynamic response; however, “negative damping” increases the response amplitude. For example, the response amplitude may increase and can lead to structure instabilities, and it might cause damage in the short time. In order to achieve the best possible structural design, it is then relevant to study conditions under which structure instabilities occur. The purpose of this paper is to discuss the conditions under which offshore structures could induce “negative damping” and different structural phenomena that have been caused by “negative damping”. The discussion suggests a damping model with linear and time-varying terms, and shows theoretically that the model is negative under certain wave conditions.

Simulated Field Measurements Based Response Amplitude Operators Estimation via the TVAR Model

2012 ◽  
Author(s):  
Edwar Yazid ◽  
Mohd. Shahir Liew ◽  
Setyamartana Parman
Keyword(s):  
Field Measurements ◽  
Offshore Structures ◽  
Response Amplitude ◽  
Time Varying ◽  
New Approach ◽  
Offshore Engineering ◽  
Motion Responses ◽  
Practical Algorithm ◽  
Simulated Field ◽  
Response Amplitude Operators

The purpose of this paper is to propose and investigate a new approach for estimating field measurements based response amplitude operators (RAOs) for offshore structures. The approach is based on applying time-varying autoregressive (TVAR) model. This work is virtually unexplored in offshore engineering field. In the literatures, a number of works have shown that RAO are discrete Fourier transform (DFT). Here, we outline a practical algorithm for TVAR model which uses expectation-maximization (EM) algorithm based Kalman smoother to generate RAOs of surge, heave and pitch motions. The method is then applied to sampled discrete wave as excitation input and motion responses of offshore structures as outputs, generated from simulated field measurements. The proposed approach outlined here has shown tremendous potential in the application of RAO estimation. The results indicate that TVAR model bring enhanced accuracy, less noisy in obtaining RAOs estimates over other Fourier based methods. TVAR model also allows for the creation of time-varying RAOs.

Vibration-based fault diagnosis of helical gear pair with tooth surface wear considering time-varying friction coefficient under mixed EHL condition

2021 ◽  
pp. 1-16
Author(s):  
Siyu Wang ◽  
Rupeng Zhu
Keyword(s):  
Dynamic Response ◽  
Hydrodynamic Lubrication ◽  
Helical Gear ◽  
Calculation Model ◽  
Tooth Surface ◽  
Time Varying ◽  
Gear Pair ◽  
Surface Wear ◽  
Mesh Stiffness ◽  
Helical Gear Pair

Abstract Based on “slice method”, the improved time-varying mesh stiffness (TVMS) calculation model of helical gear pair with tooth surface wear is proposed, in which the effect of friction force that obtained under mixed elasto-hydrodynamic lubrication (EHL) is considered in the model. Based on the improved TVMS calculation model, the dynamic model of helical gear system is established, then the influence of tooth wear parameters on the dynamic response is studied. The results illustrate that the varying reduction extents of mesh stiffness along tooth profile under tooth surface wear, in addition, the dynamic response in time-domain and frequency-domain present significant decline in amplitude under deteriorating wear condition.

Experimental Investigation on the Dynamic Response of a Three Legged Articulated Type Offshore Wind Tower

2016 ◽  
Author(s):  
Chinsu Mereena Joy ◽  
Anitha Joseph ◽  
Lalu Mangal
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Renewable Energy Sources ◽  
Offshore Structures ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Experimental Investigations ◽  
Offshore Wind Turbine ◽  
Ocean Engineering ◽  
Study Results

Demand for renewable energy sources is rapidly increasing since they are able to replace depleting fossil fuels and their capacity to act as a carbon neutral energy source. A substantial amount of such clean, renewable and reliable energy potential exists in offshore winds. The major engineering challenge in establishing an offshore wind energy facility is the design of a reliable and financially viable offshore support for the wind turbine tower. An economically feasible support for an offshore wind turbine is a compliant platform since it moves with wave forces and offer less resistance to them. Amongst the several compliant type offshore structures, articulated type is an innovative one. It is flexibly linked to the seafloor and can move along with the waves and restoring is achieved by large buoyancy force. This study focuses on the experimental investigations on the dynamic response of a three-legged articulated structure supporting a 5MW wind turbine. The experimental investigations are done on a 1: 60 scaled model in a 4m wide wave flume at the Department of Ocean Engineering, Indian Institute of Technology, Madras. The tests were conducted for regular waves of various wave periods and wave heights and for various orientations of the platform. The dynamic responses are presented in the form of Response Amplitude Operators (RAO). The study results revealed that the proposed articulated structure is technically feasible in supporting an offshore wind turbine because the natural frequencies are away from ocean wave frequencies and the RAOs obtained are relatively small.

Experiment Study on Dynamic Response of Rough AC Surface under Vehicle

2011 ◽  
Vol 243-249 ◽  
pp. 4366-4372
Author(s):  
Guang Hai Zhang ◽  
Hai Gui Kang ◽  
Yuan Xun Zheng
Keyword(s):  
Service Life ◽  
Dynamic Response ◽  
Structural Design ◽  
Asphalt Pavement ◽  
Road Surface ◽  
Dynamic Responses ◽  
Experiment Study ◽  
Asphalt Road

In order to study dynamic response of rough road surface resulting from different speeds and loads under a certain roughness for purpose of effective enhancement pertinence for structural design of an asphalt pavement and extension of its service life, displacement meters, stress meters and strain meters are embedded at different structural layers on the rough road surface to monitor the dynamic responses of AC pavement. The result shows that roughness can dramatically increase response on an asphalt road surface resulting from load and speed.

scholarly journals Dynamic Analysis of Suction Stabilized Floating Platforms

2020 ◽  
Vol 8 (8) ◽  
pp. 587
Author(s):  
Susheelkumar C. Subramanian ◽  
Michaela Dye ◽  
Sangram Redkar
Keyword(s):  
Floquet Theory ◽  
Normal Forms ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Harsh Environment ◽  
Time Varying ◽  
Floating Platform ◽  
Dynamical Characteristics ◽  
Floating Platforms ◽  
Generic Design

The occurrence of parametric resonance due to the time varying behavior of ocean waves could lead to catastrophic damages to offshore structures. A stable structure that could withstand the wave perturbations is quintessential to operate in such a harsh environment. In this work, the authors detail the relevance of a Suction Stabilized Float (SSF) or a Suction Stabilized Floating platform towards such an application. A generic design of a symmetrically shaped float structure along with its inherent stabilization behavior is discussed. Furthermore, the authors extend their prior research on this topic towards modelling the dynamics of SSF and perform stability analysis. The authors demonstrate the dynamical characteristics of SSF analytically using Floquet theory and Normal Forms technique, in this work. Additionally, the simulation results are verified and validated with the numerical methods.

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