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.

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.

Earthquake-Induced Instability of a Rotor Supported by Oil Film Bearings

1990 ◽  
Vol 112 (2) ◽  
pp. 160-165 ◽  
Author(s):  
Y. Hori ◽  
T. Kato
Keyword(s):  
Natural Frequency ◽  
Seismic Wave ◽  
Critical Speed ◽  
Seismic Waves ◽  
Strong Shock ◽  
Linear Analysis ◽  
Oil Film ◽  
Jeffcott Rotor ◽  
The Stability ◽  
Bearing System

The effect of seismic waves on the stability of a Jeffcott rotor supported by oil film bearings is investigated by calculating loci of the centers of the journal and the disk using the Runge-Kutta-Gill method. It will be shown that a linearly stable rotor can become unstable under a strong artificial shock and a real seismic wave, if it is running at speeds above twice the first critical speed, which is close to the natural frequency of the rotor. Thus, it will be pointed out that the linear analysis is insufficient to examine the stability of a rotor-bearing system if the rotor is operated above twice the critical speed and a strong shock such as due to an earthquake is expected.

scholarly journals Rapid estimation of tsunami earthquake magnitudes at local distance

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Akio Katsumata ◽  
Masayuki Tanaka ◽  
Takahito Nishimiya
Keyword(s):  
Magnitude Estimation ◽  
Seismic Wave ◽  
Seismic Waves ◽  
Wave Amplitude ◽  
Amplitude Distribution ◽  
Distribution Method ◽  
Finite Fault ◽  
Tsunami Earthquakes ◽  
Tsunami Earthquake ◽  
The Moment

AbstractA tsunami earthquake is an earthquake event that generates abnormally high tsunami waves considering the amplitude of the seismic waves. These abnormally high waves relative to the seismic wave amplitude are related to the longer rupture duration of such earthquakes compared with typical events. Rapid magnitude estimation is essential for the timely issuance of effective tsunami warnings for tsunami earthquakes. For local events, event magnitude estimated from the observed displacement amplitudes of the seismic waves, which can be obtained before estimation of the seismic moment, is often used for the first tsunami warning. However, because the observed displacement amplitude is approximately proportional to the moment rate, conventional magnitudes of tsunami earthquakes estimated based on the seismic wave amplitude tend to underestimate the event size. To overcome this problem, we investigated several methods of magnitude estimation, including magnitudes based on long-period displacement, integrated displacement, and multiband amplitude distribution. We tested the methods using synthetic waveforms calculated from finite fault models of tsunami earthquakes. We found that methods based on observed amplitudes could not estimate magnitude properly, but the method based on the multiband amplitude distribution gave values close to the moment magnitude for many tsunami earthquakes. In this method, peak amplitudes of bandpass filtered waveforms are compared with those of synthetic records for an assumed source duration and fault mechanism. We applied the multiband amplitude distribution method to the records of events that occurred around the Japanese Islands and to those of tsunami earthquakes, and confirmed that this method could be used to estimate event magnitudes close to the moment magnitudes.

scholarly journals Viscoelastic Boundary Conditions for Multiple Excitation Sources in the Time Domain

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
Chen Xia ◽  
Chengzhi Qi ◽  
Xiaozhao Li
Keyword(s):  
Finite Element ◽  
Seismic Response ◽  
Time Domain ◽  
Seismic Waves ◽  
Three Dimensional ◽  
Seismic Loads ◽  
Element Analysis ◽  
Artificial Boundaries ◽  
The Time Domain ◽  
Transmitting Boundaries

Transmitting boundaries are important for modeling the wave propagation in the finite element analysis of dynamic foundation problems. In this study, viscoelastic boundaries for multiple seismic waves or excitations sources were derived for two-dimensional and three-dimensional conditions in the time domain, which were proved to be solid by finite element models. Then, the method for equivalent forces’ input of seismic waves was also described when the proposed artificial boundaries were applied. Comparisons between numerical calculations and analytical results validate this seismic excitation input method. The seismic response of subway station under different seismic loads input methods indicates that asymmetric input seismic loads would cause different deformations from the symmetric input seismic loads, and whether it would increase or decrease the seismic response depends on the parameters of the specific structure and surrounding soil.

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.

Seismic wave attenuation due to fluid pressure diffusion at the mesoscopic scale: an experimental and numerical study

2021 ◽  
Author(s):  
Samuel Chapman ◽  
Jan V. M. Borgomano ◽  
Beatriz Quintal ◽  
Sally M. Benson ◽  
Jerome Fortin
Keyword(s):  
Seismic Wave ◽  
Seismic Waves ◽  
Wave Attenuation ◽  
Fluid Pressure ◽  
Fluid Distribution ◽  
Mesoscopic Scale ◽  
Seismic Wave Attenuation ◽  
X Ray ◽  
Pressure Diffusion ◽  
Attenuation And Dispersion

<p>Monitoring of the subsurface with seismic methods can be improved by better understanding the attenuation of seismic waves due to fluid pressure diffusion (FPD). In porous rocks saturated with multiple fluid phases the attenuation of seismic waves by FPD is sensitive to the mesoscopic scale distribution of the respective fluids. The relationship between fluid distribution and seismic wave attenuation could be used, for example, to assess the effectiveness of residual trapping of carbon dioxide (CO2) in the subsurface. Determining such relationships requires validating models of FPD with accurate laboratory measurements of seismic wave attenuation and modulus dispersion over a broad frequency range, and, in addition, characterising the fluid distribution during experiments. To address this challenge, experiments were performed on a Berea sandstone sample in which the exsolution of CO2 from water in the pore space of the sample was induced by a reduction in pore pressure. The fluid distribution was determined with X-ray computed tomography (CT) in a first set of experiments. The CO2 exosolved predominantly near the outlet, resulting in a heterogeneous fluid distribution along the sample length. In a second set of experiments, at similar pressure and temperature conditions, the forced oscillation method was used to measure the attenuation and modulus dispersion in the partially saturated sample over a broad frequency range (0.1 - 1000 Hz). Significant P-wave attenuation and dispersion was observed, while S-wave attenuation and dispersion were negligible. These observations suggest that the dominant mechanism of attenuation and dispersion was FPD. The attenuation and dispersion by FPD was subsequently modelled by solving Biot’s quasi-static equations of poroelasticity with the finite element method. The fluid saturation distribution determined from the X-ray CT was used in combination with a Reuss average to define a single phase effective fluid bulk modulus. The numerical solutions agree well with the attenuation and modulus dispersion measured in the laboratory, supporting the interpretation that attenuation and dispersion was due to FPD occurring in the heterogenous distribution of the coexisting fluids. The numerical simulations have the advantage that the models can easily be improved by including sub-core scale porosity and permeability distributions, which can also be determined using X-ray CT. In the future this could allow for conducting experiments on heterogenous samples.</p>

scholarly journals Near-Field Measurement of Six Degrees of Freedom Mining-Induced Tremors in Lower Silesian Copper Basin

Sensors ◽  
2020 ◽  
Vol 20 (23) ◽  
pp. 6801
Author(s):  
Krzysztof Fuławka ◽  
Witold Pytel ◽  
Bogumiła Pałac-Walko
Keyword(s):  
Seismic Wave ◽  
Degrees Of Freedom ◽  
Seismic Waves ◽  
Near Field ◽  
High Energy ◽  
Rotational Component ◽  
Empirical Formulas ◽  
Six Degrees Of Freedom ◽  
The Impact

The impact of seismicity on structures is one of the key problems of civil engineering. According to recent knowledge, the reliable analysis should be based on both rotational and translational components of the seismic wave. To determine the six degrees of freedom (6-DoF) characteristic of mining-induced seismicity, two sets of seismic posts were installed in the Lower Silesian Copper Basin, Poland. Long-term continuous 6-DoF measurements were conducted with the use of the R-1 rotational seismometer and EP-300 translational seismometer. In result data collection, the waveforms generated by 39 high-energy seismic events were recorded. The characteristic of the rotational component of the seismic waves were described in terms of their amplitude and frequency characteristics and were compared with translational measurements. The analysis indicated that the characteristic of the rotational component of the seismic wave differs significantly in comparison to translational ones, both in terms of their amplitude and frequency distribution. Also, attenuation of rotational and translational components was qualitatively compared. Finally, the empirical formulas for seismic rotation prediction in the Lower Silesian Copper Basin were developed and validated.

Vibration Control of Space Truss Structure with Viscoelastic Laminated Composite Damper

2014 ◽  
Vol 971-973 ◽  
pp. 860-863 ◽  
Author(s):  
Bao Xian Jia ◽  
Feng Gao ◽  
Wen Feng Bian
Keyword(s):  
Vibration Control ◽  
Resonance Region ◽  
Truss Structure ◽  
Pulse Excitation ◽  
Control Effect ◽  
Modal Strain Energy ◽  
Viscoelastic Composite ◽  
Optimal Position ◽  
Space Truss ◽  
Space Truss Structure

This paper works on the vibration control of the space truss structure. The damper made of viscoelastic composite was designed according to the configuration parameters of the truss structure. The parameters of damper were obtained by using the method of modal strain energy. The optimal position configuration of the damper was determined. The truss in the time domain and frequency domain was analyzed. The dynamic characteristics of three structures which are without damper, with damper in the random position configuration and with damper in the optimal position configuration were compared in the sweep excitation and pulse excitation. The result shows that the structure with damper in the optimal position configuration has a great improvement in the amplitude of vibration in the first resonance region and the amplitude attenuation of the truss. The space truss structure with viscoelastic composite damper has excellent vibration control effect.

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