scholarly journals A Bufferable Tuned-Mass Damper of an Offshore Platform against Stroke and Response Delay Problems under Earthquake Loads

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Qiong Wu ◽  
Xilu Zhao ◽  
Shuai He ◽  
Wenxian Tang ◽  
Rencheng Zheng
Keyword(s):  
Seismic Waves ◽  
Large Earthquake ◽  
Tuned Mass Damper ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Response Delay ◽  
Earthquake Loads ◽  
Response Characteristics ◽  
Mass Damper ◽  
Dynamic Performances

A tuned-mass damper (TMD) is applied to ensure the safety and stability of an offshore platform in practice; however, damper stroke and response delay problems always result in intractable performances of vibration control while exposed to large earthquake loads. Therefore, this paper proposes a bufferable TMD, a passive TMD with buffers on both sides, to improve the performance of offshore platforms subjected to large seismic waves. A comprehensive simulation and experimental study was executed to investigate the dynamic performances of the bufferable TMD, by application of a 1 : 200-scale offshore platform prototype. It is verified that the bufferable TMD can be effective in absorbing the stroke energy, while the damper exceeds limitations of motion. Meanwhile, the bufferable TMD can maintain high-response characteristics. In conclusion, the experimental results indicate that the displacement, acceleration, and frequency performances of an offshore platform can be significantly decreased, and the evaluation indices show that the method is effective in reducing overall vibration levels and maximum peak values, with the application of the bufferable damper system.

scholarly journals High Response Performance of a Tuned-Mass Damper for Vibration Suppression of Offshore Platform under Earthquake Loads

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Qiong Wu ◽  
Xilu Zhao ◽  
Rencheng Zheng ◽  
Keisuke Minagawa
Keyword(s):  
Vibration Suppression ◽  
Initial Period ◽  
Offshore Platform ◽  
High Response ◽  
Experimental Investigations ◽  
Offshore Platforms ◽  
Earthquake Loads ◽  
Response Characteristics ◽  
Response Performance ◽  
The Stability

Currently, tuned-mass dampers (TMDs) are widely applied to maintain the stability of offshore platforms in hostile environments; however, the stability system of offshore platforms faces considerable challenges under critical earthquake loads of the initial period. Therefore, this study concentrated on the high response performance of a simple passive TMD system, and numerical and experimental investigations were performed using a 1 : 200-scale prototype. The obtained results indicated that the displacement, acceleration, and their power spectral density all decreased significantly for the offshore platform with the TMD system. By further analyses of its high response characteristics, it was validated that the TMD reactions can commence within the first 3 s of earthquake excitation, while the fundamental natural frequency was consistently tuned for the TMD system dependent on the dynamic magnification factor. The evaluation indices also confirmed that this method is effective in reducing the overall vibration level and the maximum peak values of the offshore platform exposed to earthquake excitations, mainly because of its high response characteristics.

scholarly journals A Tuned Mass Damper with Nonlinear Magnetic Force for Vibration Suppression with Wide Frequency Range of Offshore Platform under Earthquake Loads

2018 ◽  
Vol 2018 ◽  
pp. 1-18 ◽  
Author(s):  
Qiong Wu ◽  
Wei Zhao ◽  
Weiguo Zhu ◽  
Rencheng Zheng ◽  
Xilu Zhao
Keyword(s):  
High Speed ◽  
Permanent Magnets ◽  
Vibration Suppression ◽  
Wide Frequency Range ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Frequency Range ◽  
Response Characteristics ◽  
Narrow Frequency Band ◽  
Dynamic Performances

Tuned mass dampers (TMDs) are applied to ensure the safety and stability of offshore platforms; however, linear dampers are effective for a single resonance frequency, providing vibration suppression only within a narrow frequency band. Therefore, this paper proposed a magnetic TMD with two pairs of permanent magnets on both sides of the structures, which can generate a nonlinearly repulsive force, making the magnetic TMD reliable and robust in damping the oscillations of structures with wide frequency range under seismic excitations. A comprehensively numerical and experimental study was processed to investigate the dynamic performances of the proposed magnetic TMD, by application of a 1 : 200-scale prototype of the offshore platform. The results verified that the performance of the magnetic TMD can be significantly improved than that of the linear TMD, meanwhile maintaining high-speed response characteristics. The experimental results indicated that the displacement, acceleration, and frequency responses of the offshore platform can be significantly reduced; furthermore, the evaluation indices showed that the magnetic TMD system is credible in reducing the overall vibration levels and maximum peak values.

Study on Seismic Performance of Offshore Platform with Rocking Wall - TMD System

2014 ◽  
Vol 610 ◽  
pp. 78-83
Author(s):  
Ji Gang Zhang ◽  
Zhi Wei Jiang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Seismic Performance ◽  
Tuned Mass Damper ◽  
Offshore Platform ◽  
Element Analysis ◽  
Mass Damper ◽  
Jacket Offshore Platform ◽  
Rocking Wall ◽  
Wall System

Offshore platform rocking wall system and tuned mass damper are briefly introduced, and the paper integrates the advantages of these two kinds of seismic method, and the TMD is attached to the jacket offshore platform - rocking wall system, using the ANSYS for finite element analysis, and the analysis results are optimized. The results show that compared with the offshore platform - rocking wall system, additional TMD can give full play to the performances of the two kinds of seismic methods, which is remarkable.

Study on the Stability of Non-Structural Element Using Active Tuned Mass Damper

2020 ◽  
Vol 17 (7) ◽  
pp. 3224-3230
Author(s):  
Hong-Won Kim ◽  
Dong-Gi Kwag
Keyword(s):  
High Frequency ◽  
Seismic Waves ◽  
Passive Control ◽  
Control Method ◽  
Amplitude Ratio ◽  
Vibration Reduction ◽  
Tuned Mass Damper ◽  
Structural Element ◽  
High Frequency Region ◽  
Mass Damper

Currently, the frequency of earthquakes is increasing in Korea, but due to the lack of appropriate seismic equipment, significant damage is expected. In order to solve this problem, active tuned mass damper will be developed to reduce earthquake damage in response to seismic waves, which are combined from low frequency to high frequency. In this paper, various control methods are introduced to reduce the amplitude ratio occurring at the 1st and 2nd natural frequencies for 3 DOF nonstructural elements. Through mathematical modeling, we confirm how each control method is applied and present the problems of the existing passive tuned mass damper and suggest the active tuned mass damper. To induce an active copper reducer, the response according to the control method can be predicted with a focus on the energy change rate. The active controller receives feedback from the relative displacement and relative velocity of the structure and uses it as a variable to set the control method. The passive control method and the active control method are compared through the simulation, and excellent control performance can be confirmed in the high frequency region as well as the second natural frequency. Vibration reduction performance was confirmed by each control method and the most ideal control method was selected. The optimum vibration reduction performance can be confirmed by using the signal function to always generate 180° of phase difference with respect to the speed of the structure. Not only earthquake but also mechanical vibration, wind load, etc., it can be used in all fields where damage is caused by excitation force inherent in various complex frequencies.

scholarly journals A Hybrid Tuned Mass Damper for Response Mitigation of Offshore Platforms

2022 ◽  
Author(s):  
Quoc Huong Cao
Keyword(s):  
Vibration Control ◽  
Tuned Mass Damper ◽  
Offshore Platforms ◽  
Structural Stiffness ◽  
Mass Ratio ◽  
Structural Vibrations ◽  
Numerical Computations ◽  
Tuned Liquid Column Damper ◽  
Parametric Investigation ◽  
Mass Damper

Abstract A new hybrid type of the Tuned Mass Damper (HTMD), which consists of a Tuned Liquid Column Damper (TLCD) fixed on the top of a traditional Tuned Mass Damper (TMD), is developed for vibration control of an offshore platform. The results obtained from the parametric investigation show that the mass ratio between TLCD and TMD significantly affects the HTMD's performance. To assess the effectiveness and robustness of HTMD, extensive comparisons are made between an optimized HTMD and an optimum TMD with the same weight as the HTMD. The numerical computations indicate that the proposed HTMD offers a higher level of effectiveness in suppressing structural vibrations compared with a traditional TMD. However, the optimum HTMD is not robust in resisting the variation of the structural stiffness.

scholarly journals Motion Control of Pentapod Offshore Wind Turbines under Earthquakes by Tuned Mass Damper

2019 ◽  
Vol 7 (7) ◽  
pp. 224 ◽  
Author(s):  
Wenhua Wang ◽  
Xin Li ◽  
Zuxing Pan ◽  
Zhixin Zhao
Keyword(s):  
Seismic Waves ◽  
Passive Control ◽  
Control Method ◽  
Tuned Mass Damper ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Integrated Analysis ◽  
Analysis Model ◽  
Mass Damper ◽  
Structural Responses

The dynamic characteristics of a bottom-fixed offshore wind turbine (OWT) under earthquakes are analyzed by developing an integrated analysis model of the OWT. Further, the influence of the interactions between the rotor and support system on the structural responses of the OWT subjected to an earthquake is discussed. Moreover, a passive control method using a tuned mass damper (TMD) is applied to the OWT to control the responses under earthquakes. The effects of the mass ratio, location and tuned frequency of the TMD on controlling structural responses of the OWT under different recorded seismic waves are studied.

scholarly journals Passive Control of a Pentapod Offshore Wind Turbine Under Earthquakes by Using Tuned Mass Damper

2017 ◽  
Author(s):  
Wenhua Wang ◽  
Zhen Gao ◽  
Xin Li ◽  
Torgeir Moan ◽  
Bin Wang
Keyword(s):  
Wind Turbine ◽  
Seismic Waves ◽  
Passive Control ◽  
Element Model ◽  
Tuned Mass Damper ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mass Damper ◽  
And Control

The finite element model (FEM) of a pentapod offshore wind turbine (OWT) is established in the newly compiled FAST. The dynamic responses of the OWT are analyzed in detail. Further, a tuned mass damper as a passive control strategy is applied in order to reduce the OWT responses under seismic loads. The influence of the tuned mass damper (TMD) locations, mass and control frequencies on the reduction of OWT responses are investigated. A general configuration of TMD can effectively reduce the local and global responses to some degree, but due to the complexity of characteristics of the OWT structure and seismic waves, the single TMD can not obtain consistent controlling effects.

Response Control of TLP Using Tuned Mass Dampers

2014 ◽  
Author(s):  
Srinivasan Chandrasekaran ◽  
Deepak Kumar ◽  
Ranjani Ramanathan
Keyword(s):  
Large Amplitude ◽  
Experimental Studies ◽  
Tuned Mass Damper ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Scaled Model ◽  
Response Control ◽  
Extreme Loads ◽  
Mass Damper

Offshore tension leg platform (TLP) is a compliant type offshore structure where the tendons are deployed under initial pretension to counteract the excessive buoyancy. TLPs show large amplitude response under environmental loads due to their compliancy, which poses threat under extreme loads. Use of passive dampers like Tuned Mass Damper (TMD) is common to control such large amplitude motion, however their deployment in offshore structures is relatively new. Response control of a scaled model of TLP is attempted using tuned mass damper of pendulum type under regular waves. Based on the experimental studies carried out, it is seen that there is a significant reduction in the surge response under the folded pendulum type damper. Results also show that there is a reduction in the heave response due to the control envisaged in the surge motion. The discussed method of response control is one of the effective methods of retrofitting offshore platforms whose operability at rough sea states is a serious concern.

Tuned Mass Damper for Vibration Control in Steel Jacket Platforms

2008 ◽  
Author(s):  
A. A. Golafshani ◽  
A. Gholizad
Keyword(s):  
Vibration Control ◽  
Fatigue Damage ◽  
Safety Margin ◽  
Tuned Mass Damper ◽  
Offshore Platforms ◽  
Control Mechanisms ◽  
Sea State ◽  
Steel Jacket ◽  
Mass Damper ◽  
Environmental Events

Considering the stress cycles in joints and members due to wave induced forces on offshore platforms, fatigue analysis is therefore one of the most important analyses in offshore platforms design. Most of steel jacket type platforms located in areas with relatively high ratios of operational sea-states to maximum design environmental events; fall in acceptable safety margin in inplace and seismic analyses. But in fatigue analyses they will face critical condition. Therefore it seems that utilizing control mechanisms with the aim of increasing fatigue life in such platforms will be more preferable to merely deck displacement control. Investigation of tuned mass dampers adjustable parameters optimality for vibration control of wave excited structures implies that optimum tuning and damping ratios are strongly dependent to sea-state in addition to system parameters. The efficiency of optimally designed tuned mass damper for fatigue damage mitigation in realistic steel jacket platforms has been evaluated in this study. Full stochastic spectral analysis method has been employed to estimate the maximum fatigue damage as objective function to be minimized. This leads to a min-max problem which has been solved with Micro Genetic Algorithm. Furthermore the efficiency of a variable TMD with different optimum mass for each sea-state has been evaluated in comparison with a TMD with constant parameters.

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