Vibration Control of Offshore Platforms Using a Wideband METMD System

2006 ◽  
Author(s):  
Dong Zhao ◽  
Rujian Ma ◽  
Dongmei Cai
Keyword(s):  
Vibration Control ◽  
Natural Frequency ◽  
Fem Simulation ◽  
Average Frequency ◽  
Offshore Platforms ◽  
Frequency Bandwidth ◽  
Wave Load ◽  
Control Effect ◽  
Exciting Frequency ◽  
Specific Frequency

A wideband multiple extended tuned mass dampers (METMD) system has been developed for reducing the multiple resonant responses of the platforms to all kinds of loads, such as earthquake, typhoon, tsunami and big ice load. This system is composed of several subsystems, each of which consists of one set of extended tuned mass damper (ETMD) unit covering a specific frequency bandwidth, and its average frequency is tuned to one of the first resonant frequencies of the platform. The offshore platform is simplified to a single degree-of-freedom (DOF) system to which a METMD subsystem (composed of m ETMDs) is attached and constitutes m+1 DOFs system. The total mass ratio of the METMD subsystem to the platform is 14% and the frequency ratio of the exciting frequency to the platform’s natural frequency varies in [0.5, 1.5]. The theory analysis shows that: 1) the platform has the better vibration control effect when the non-dimensional frequency bandwidth Ω, which is defined as the ratio of the frequency range to the controlled (target) platforms natural frequency, is in [0.35, 0.6]; 2) the damping coefficient ξ of ETMD systems is in [0.05, 0.15] and 3) the number of the ETMDs is 5 when Ω = 0.45 and ξ = 0.1. The FEM simulation shows that the METMD has a better vibration control effect on the mega-platforms’ vibration control under the random ocean wave load.

The Vibration Control of a Combined Anti-Vibration Platform Under the Rare Seismic Wave Forces

2007 ◽  
Author(s):  
Dong Zhao ◽  
Dongmei Cai ◽  
Rujian Ma ◽  
Zhaofu Qu ◽  
Zhonghe Chen ◽  
...  
Keyword(s):  
Vibration Control ◽  
Natural Frequency ◽  
Seismic Wave ◽  
Seismic Waves ◽  
Average Frequency ◽  
Wave Forces ◽  
Seismic Loads ◽  
Control Effect ◽  
Average Decrease ◽  
Exciting Frequency

The combined anti-vibration platform, which was composed of the mega-frame platform (MFP) and the multiple extended tuned mass damper (METMD) system, was simplified as a multiple-degree-of-freedom system for the study of the resonant responses’ decrease of the platforms under the rare seismic wave forces. The METMD system was made up of several ETMD units that had a specific frequencies’ bandwidth. The average frequency was tuned to the platform’s first natural frequency, which was the target frequency to be controlled. So, the offshore platform and the METMD system were simplified to an m+1 DOFs system to be analyzed theoretically. The ratio of the METMD system mass to the platform residual mass was 14% and the ratio of the exciting frequency to the platform’s natural frequency varied between 0.5 and 1.5 The theoretical analysis shows that the platform has the best vibration control effect when the frequencies’ bandwidth is 0.45; the damping coefficient is 0.1 and the number of the ETMDs is 5. In order to analyze the dynamic response of the combined anti-vibration platform under the random seismic loads, the El-Centro, Taft and Qian’an seismic waves were chosen as typical loads and their maximal acceleration values had been adjusted according to 8 level fortification under rarely occurred earthquake. The FEM simulations shows that: 1) the average vibration displacements decrease ratios of the entire platform in the X, Y, Z directions are 80.48%, 61.93% and 64.31% respectively under the El-Centro seismic wave; 2) the X, Y, Z directions average decrease ratios for the entire platform are 84.21%, 49.95% and 56.6% respectively under the Taft seismic wave; 3) the X, Y, Z directions average decrease ratios of the entire platform are 50.09%, 32.645% and 23.34% respectively under the Qian’an seismic wave; and 4) the average displacement decrease ratios of the whole platform in X, Y and Z-direction are 71.59%, 48.18% and 48.08% respectively considering all seismic waves above. So the combined anti-vibration platform has the better ability on the vibration control under the random seismic loads.

scholarly journals Optimal Design and Application of a Multiple Tuned Mass Damper System for an In-Service Footbridge

2019 ◽  
Vol 11 (10) ◽  
pp. 2801 ◽  
Author(s):  
Chao Wang ◽  
Weixing Shi
Keyword(s):  
Optimal Design ◽  
Vibration Control ◽  
Damping Ratio ◽  
Element Model ◽  
Frequency Bandwidth ◽  
Dynamic Amplification Factor ◽  
Control Effect ◽  
In Situ Test ◽  
Dynamic Amplification

Slender steel footbridges suffer excessive human-induced vibrations due to their low damping nature and their frequency being located in the range of human-induced excitations. Tuned mass dampers (TMDs) are usually used to solve the serviceability problem of footbridges. A multiple TMD (MTMD) system, which consists of several TMDs with different frequencies, has a wide application in the vibration control of footbridges. An MTMD system with well-designed parameters will have a satisfactory effect for vibration control. This study firstly discusses the relationship between the acceleration dynamic amplification factor and important parameters of an MTMD system, i.e., the frequency bandwidth, TMD damping ratio, central frequency ratio, mass ratio and the number of TMDs. Then, the frequency bandwidth and damping ratio optimal formulas are proposed according to the parametric study. At last, an in-service slender footbridge is proposed as a case study. The footbridge is analyzed through a finite element model and an in situ test, and then, an MTMD system is designed based on the proposed optimal design formulas. The vibration control effect of the MTMD system is verified through a series of in situ comparison tests. Results show that under walking, running and jumping excitations with different frequency, the MTMD system always has an excellent vibration control effect. Under a crowd-induced excitation with the resonance frequency, the footbridge with an MTMD system can meet the acceleration limit requirement. It is also found that the analysis result agrees well with the in situ test.

Simulation of Vibration Control of Offshore Platforms Under Earthquake Loadings

2008 ◽  
Author(s):  
Rujian Ma ◽  
Jungang Wang ◽  
Dong Zhao
Keyword(s):  
Vibration Control ◽  
Natural Frequency ◽  
Natural Frequencies ◽  
Offshore Platforms ◽  
Ansys Software ◽  
Important Conclusion ◽  
First Order

The simulation of vibration control of offshore platforms under earthquake loadings is performed in this paper by using the ANSYS software, in which the first three order natural frequencies of the platform are controlled by the ETMD system where the parameters of the system are taken in the optimal regions. The results show that the ETMD system can reduce the vibration of the platform effectively under earthquake loadings. Another important conclusion is that reasonable control effects can be obtained by control the first order natural frequency. There are 10% and 20% increase in y and z directions when the first two and three order natural frequencies are controlled simultaneously.

Vibration Control of Jacket Platforms by DTMD System

2005 ◽  
Author(s):  
Dong Zhao ◽  
Rujian Ma ◽  
Weiqiang Wang ◽  
Dongmei Cai
Keyword(s):  
Control System ◽  
Vibration Control ◽  
Frequency Ratio ◽  
Excitation Frequency ◽  
Fem Simulation ◽  
Mass Ratio ◽  
Control Effect ◽  
Theory Analysis ◽  
Additional Mass ◽  
Mass Damper

The turned mass damper (TMD) system has found extensive applications in vibration control nowadays. The main disadvantage of the system is to add additional mass to the structures. In order to make use of its merits and overcome its disadvantage, the developed turned mass damper (DTMD) vibration control system is studied in this paper. It uses the equipment set on the structure instead of additional mass to control the vibration of structures. The theory analysis shows that the frequency range is enlarged and the resonant band is reduced with the mass ratio increasing. The FEM simulation shows that the DTMD vibration control system could absorb more vibration energy when the frequency of the DTMD is near the excitation frequency. The platform has better vibration control effect when the mass ratio between 3.75 and 5 and when the frequency ratio is in the range of (0.3,0.35) and (0.35,0.5). The whole system, including the platform and the DTMD, has the smaller vibration response when the frequency ratio is between 0.5 and 2. The results of the simulation also showed that the DTMD is more effective in the vibration control for the jacket platforms.

Control of Vibration Using Compliant Actuators

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Sannia Mareta ◽  
Dunant Halim ◽  
Atanas A. Popov
Keyword(s):  
Vibration Control ◽  
Active Control ◽  
Passive Control ◽  
Performance Comparison ◽  
Control Performance ◽  
Frequency Bandwidth ◽  
Series Configuration ◽  
Compliant Actuators ◽  
Stiffness And Damping ◽  
Compliant Actuator

This work proposes a method for controlling vibration using compliant-based actuators. The compliant actuator combines a conventional actuator with elastic elements in a series configuration. The benefits of compliant actuators for vibration control applications, demonstrated in this work, are twofold: (i) vibration reduction over a wide frequency bandwidth by passive control means and (ii) improvement of vibration control performance when active control is applied using the compliant actuator. The vibration control performance is compared with the control performance achieved using the well-known vibration absorber and conventional rigid actuator systems. The performance comparison showed that the compliant actuator provided a better flexibility in achieving vibration control over a certain frequency bandwidth. The passive and active control characteristics of the compliant actuator are investigated, which shows that the control performance is highly dependent on the compliant stiffness parameter. The active control characteristics are analyzed by using the proportional-derivative (PD) control strategy which demonstrated the capability of effectively changing the respective effective stiffness and damping of the system. These attractive dual passive–active control characteristics are therefore advantageous for achieving an effective vibration control system, particularly for controlling the vibration over a specific wide frequency bandwidth.

Quantitative measurement of vertigo frequency: Preliminary results

2003 ◽  
Vol 13 (1) ◽  
pp. 53-56
Author(s):  
Robert Aureo Zalewski-Zaragoza ◽  
Erik Scott Viirre
Keyword(s):  
Quantitative Measurement ◽  
Average Frequency ◽  
Repeated Measurements ◽  
Virtual Image ◽  
Subjective Ratings ◽  
Image System ◽  
Head Mounted Display ◽  
Tinnitus Treatment ◽  
Specific Frequency ◽  
Rehabilitation Exercises

Persons who experience vertigo often describe their symptoms as a sensation of oscillations. Based on such a description, a pilot study was performed to determine if the frequency of the vertigo sensation could be quantified in a manner analogous to tone matching in tinnitus treatment. Fifteen subjects were tested using a virtual image system that consisted of a head mounted display showing a scene that oscillated horizontally or vertically at an adjustable frequency. Subjects were asked to adjust the direction and frequency to match their typical vertigo sensation. Results show that most persons with chronic vertigo had symptoms that could be realistically simulated by vection induced by the oscillating scene and that matched to a consistent specific frequency. They reported an average frequency of 1.09 Hz (range 0.27 to 3.3 Hz, SD 0.25). The large majority (13 out of 15) matched to a horizontal stimulus. Subjects that gave particularly high subjective ratings of the similarity of the motion sensation (7–8 out of 10) from the vection to their vertigo had lower frequency matches (average 0.61 +/- 0.25). Repeated measurements in 4 subjects 8 to 27 days later showed consistent results. This vertigo measurement technique may be used in the future to assess the ability of vestibular rehabilitation to reduce chronic vertigo. Identification of a specific frequency of chronic vertigo may be important in the specification of rehabilitation exercises.

Optimal Placement of Piezoelectric Sensors and Actuators for Controlled Flexible Linkage Mechanisms

2005 ◽  
Vol 128 (2) ◽  
pp. 256-260 ◽  
Author(s):  
Xianmin Zhang ◽  
Arthur G. Erdman
Keyword(s):  
Vibration Control ◽  
Simulation Analysis ◽  
Active Vibration Control ◽  
Optimal Placement ◽  
Control Effect ◽  
Sensors And Actuators ◽  
Piezoelectric Sensors And Actuators ◽  
Active Vibration ◽  
Flexible Mechanism ◽  
Flexible Linkage

The optimal placement of sensors and actuators in active vibration control of flexible linkage mechanisms is studied. First, the vibration control model of the flexible mechanism is introduced. Second, based on the concept of the controllability and the observability of the controlled subsystem and the residual subsystem, the optimal model is developed aiming at the maximization of the controllability and the observability of the controlled modes and minimization of those of the residual modes. Finally, a numerical example is presented, which shows that the proposed method is feasible. Simulation analysis shows that to achieve the same control effect, the control system is easier to realize if the sensors and actuators are located in the optimal positions.

Frequency manipulation of a light-activated shape-memory polymer-laminated cylindrical shell

2021 ◽  
pp. 095440892110632
Author(s):  
Tao He ◽  
Pengpeng Zhu ◽  
Xiangmin Zhang
Keyword(s):  
Cylindrical Shell ◽  
Shape Memory ◽  
Natural Frequency ◽  
Frequency Control ◽  
Shape Memory Polymer ◽  
Control Effect ◽  
Optimal Scheme ◽  
Simply Supported ◽  
Control Capability ◽  
Laminated Cylindrical Shell

A light-activated shape-memory polymer is a novel smart material that exhibits a dynamic Young's modulus when exposed to light. The non-contact actuation feature facilitates the lamination of a light-activated shape-memory polymer on host structures for realising frequency control. In this study, we investigated the natural frequency of a simply supported cylindrical shell coupled with light-activated shape-memory polymer patches located arbitrarily on the shell. Initially, we compared the natural frequency of a completely laminated cylindrical shell using two different approaches. Further, we analysed the effect of changes in the length and location of the light-activated shape-memory polymer patch pair on the natural frequency of the cylindrical shell. Based on the experimental results, we propose an optimal scheme, wherein several light-activated shape-memory polymer patch pairs are distributed on the surface of the shell, and the frequency control capability of the proposed scheme is evaluated comprehensively. The results verify that the optimal scheme has an adequate control effect on the natural frequency of the cylindrical shell.

Sign in / Sign up

Export Citation Format

Share Document