Resonance Frequency Of Structure Research Articles

Assessment of sound insulation of naturally ventilated double skin facades

The sound insulation spectrum is analysed of 18 double glazing arrangements facades, of which 9 double skin facades were measured in situ and 9 in a laboratory setting. The influence of the cavity thickness, the parallelism of the two glass panels, the absorptivity of the cavity and the effect of the size of ventilation slots are investigated. The results are compared with double layer wall insulation prediction models. Also a new, simple model is proposed that predicts the sound insulation of naturally ventilated double skin facades, based on the coincidence frequency, the structural resonance frequencies, the cavity resonance frequencies, the façade construction, the dimensions the and material properties. The model predictions are validated by measurement data.

Differential cubature and quadrature-Bolotin methods for dynamic stability of embedded piezoelectric nanoplates based on visco-nonlocal-piezoelasticity theories

This paper is concerned with the dynamic stability response of an embedded piezoelectric nanoplate made of polyvinylidene fluoride (PVDF). In order to present a realistic model, the material properties of nanoplate are assumed viscoelastic using Kelvin–Voigt model. The visco-nanoplate is surrounded by viscoelastic medium which is simulated by orthotropic visco-Pasternak foundation. The PVDF visco-nanoplate is subjected to an applied voltage in the thickness direction. In order to satisfy the Maxwell equation, electric potential distribution is assumed as a combination of a half-cosine and linear variation. Adopting the nonlocal Mindlin plate theory, the governing equations are derived based on the energy method and Hamilton’s principle. A novel numerical method namely as differential cubature method (DCM) in conjunction with the Bolotin’s method is applied to obtain the dynamic instability region (DIR) and parametric resonance responses of the visco-nanoplate. The effects of different parameters such as nonlocal parameter, external electric voltage, structural damping, boundary condition, dimension of nanoplate and viscoelastic medium are shown on DIR and parametric resonance frequency of structure. The accuracy of the proposed method is verified by comparing its numerical prediction with other theoretical and experimental published works as well as solution of system with differential quadrature method (DQM). Results indicate that the external electric voltage increases the frequency of the system especially in thick nanoplates.

Comparative studies of global and targeted control of walkway bridge resonant frequencies

In this paper, three controllers are investigated for active vibration control of a pedestrian walkway structure. They comprise direct velocity feedback, observer-based and independent modal space controllers that are implemented in single-input single-output (SISO), multi-SISO and multiple-input multiple-output (MIMO) configurations. The objective of the SISO controller schemes is to compare vibration mitigation performances arising from global control versus selective control of structural resonant frequencies in a given frequency bandwidth. The objectives set out for the multi-SISO and MIMO controllers are to realize global control within the same frequency bandwidth considered in the SISO studies. A novel aspect of these latter studies is the independent control of selected resonant frequencies at different locations on the structure with the aim of imposing global control. Vibration mitigation performances are evaluated using frequency response function measurements and uncontrolled and controlled responses to a synthesized walking excitation force. In the SISO studies, selective control of specific resonant frequencies has a slight degradation in the global vibration mitigation performance, although it reflects better performance around the target frequencies. For the multi-SISO and MIMO controller studies, the selective control of the two lowest and dominant frequencies of the structure at two different locations still offers comparative vibration mitigation performances with the controllers considered as global in the sense that they target both structural frequencies at both locations. Attenuations of between 10 and 35 dB are achieved.

Nonlinear dynamics induced in a structure by seismic and environmental loading.

In this study, it is shown that under very weak dynamic and quasi-static deformation that is orders of magnitude below the yield deformation of the equivalent stress-strain curve (around 10(-3)), the elastic parameters of a civil engineering structure (resonance frequency and damping) exhibit nonlinear softening and recovery. These observations bridge the gap between laboratory and seismic scales where elastic nonlinear behavior has been previously observed. Under weak seismic or atmospheric loading, modal frequencies are modified by around 1% and damping by more than 100% for strain levels between 10(-7) and 10(-4). These observations support the concept of universal behavior of nonlinear elastic behavior in diverse systems, including granular materials and damaged solids that scale from millimeter dimensions to the scale of structures to fault dimensions in the Earth.

Performance of pre-deformed flexible piezoelectric cantilever in energy harvesting

This paper proposes a novel structure for pre-rolled flexible piezoelectric cantilevers that use wind energy to power a submunition electrical device. Owing to the particular installation position and working environment, the submunition piezoelectric cantilever should be rolled when not working, but this pre-rolled state can alter the energy harvesting performance. Herein, a working principle and installation method for piezoelectric cantilevers used in submunitions are introduced. To study the influence of the pre-rolled state, pre-rolled piezoelectric cantilevers of different sizes were fabricated and their performances were studied using finite element analysis simulations and experiments. The simulation results show that the resonance frequency and stiffness of the pre-rolled structure is higher than that of a flat structure. Results show that, (1) for both the pre-rolled and flat cantilever, the peak voltage will increase with the wind speed. (2) The pre-rolled cantilever has a higher critical wind speed than the flat cantilever. (3) For identical wind speeds and cantilever sizes, the peak voltage of the flat cantilever (45 V) is less than that of the pre-rolled cantilever (56 V). (4) Using a full-bridge rectifier, the output of the pre-rolled cantilever can sufficiently supply a 10 μF capacitor, whose output voltage may be up to 23 V after 10 s. These results demonstrate that the pre-rolled piezoelectric cantilever and its installation position used in this work are more suitable for submunition, and its output sufficiently meets submunition requirements.

Effects of occupant weight and sitting posture on vehicle seat structural dynamics

The characterisation of the occupied vehicle seat structural dynamics is still challenging owing to the complex and nonlinear dynamic behaviour of the human body. The human body has significant influences on the occupied vehicle seat structural dynamics. In this paper, the structural dynamics of the unoccupied seat, occupied seat in lean-on posture, and occupied seat in lean-off posture are investigated. The results of this investigation show that, in lean-on condition when the occupant weight increases, the lateral resonant frequencies of the seat decrease whereas both fore-aft resonant frequency and twisting resonant frequency increase. The structural resonant frequencies of the occupied seat in lean-off condition are considerably different from those in the corresponding lean-on condition. This indicates that the coupling of the occupant body and the seatback plays a major role on occupied seat structural dynamics and transmission of the vibration to the occupant body in frequencies where the seat has structural vibration modes.

Acceleration Sensor-based First Resonance Vibration Suppression of a Double-clamped Piezoelectric Beam

This paper investigates resonance vibration suppression under persistent excitation near the first structural resonant frequency of a clamped-clamped (doubly-clamped) piezoelectric flexible beam. In this study, an acceleration sensor is used to measure the resonant vibration. Firstly, the finite element method (FEM) is utilized to derive the dynamics model of the system, and modal analysis is carried out. Secondly, an acceleration feedback-based proportional-integral control algorithm and variable structure control algorithms are designed, and a numerical simulation is performed. Finally, a doubly-clamped piezoelectric flexible beam experimental setup is constructed. Experiments are conducted on resonant vibration suppression using the designed control algorithms. The numerical simulation and experimental results demonstrate that the resonant vibration can be suppressed by using the designed control methods, and the improved variable structure control method shows better control performance in suppressing the resonant vibration.

Micromachined magnetoflexoelastic resonator based magnetometer

In this paper, we demonstrate the performance of a magnetoflexoelastic magnetometer consisting of a micromachined ultra-thin (7.5 μm) quartz bulk acoustic resonator on which 500 nm thick magnetostrictive Metglas® (Fe85B5Si10) film is deposited. The resonance frequency of the unimorph resonator structure is sensitively affected by the magnetostrictively induced flexoelastic effect in quartz and is exploited to detect low frequency (<100 Hz) and nanoTesla magnetic fields. The resonance frequency shift is measured by tracking the at-resonance admittance of the resonator as a function of the applied magnetic field. The frequency shifts are linearly correlated to the magnetic field strength. A minimum detectable magnetic flux density of ∼79 nT has been measured for 10 Hz modulated magnetic field input signals which corresponds to a frequency sensitivity of 0.883 Hz/μT.

Thermal expansion mismatch resonant infrared sensor and array

A resonant infrared thermal sensor with high sensitivity, whose sensing element is a bimaterial structure with thermal expansion mismatch effect, is presented. The sensor detects infrared radiation by means of tracking the change in resonance frequency of the bimaterial structure with temperature attributed to the infrared radiation from targets. The bimaterial structure is able to amplify the change in resonance frequency compared with a single material structure for a certain mode of vibration. In accordance with the vibration theory and the design principle of an infrared thermal detector, the resonant sensor, which can be arranged in an array, is designed. The simulation results, by using finite element analysis, demonstrate that the dependence of resonance frequency on temperature of the designed structure achieves 1 Hz/10 mK . An array of 6×6 resonant thermal sensors is fabricated by using microelectronics processes that are compatible with integrated circuit fabrication technology. The frequency variation corresponding to the temperature shift is obtained by electrical measurement.

Elastic metamaterial-based impedance-varying phononic bandgap structures for bandpass filters

In this study, we propose a novel impedance-variation scheme in a half-quarter-wave stack (HQWS) structure to achieve desired bandpass filtering performances such as quasi-flat tops, steep bandedges and wide surrounding bandgaps. Specifically, only the characteristic impedances of constituent half-wave layers are varied without altering the phase shift of π at the center frequency of the target passband that is the Fabry–Perot resonance frequency of the unperturbed original HQWS structure. Because the simultaneous control of characteristic impedance and phase shift in each of the constituent half-wave layers is not achievable only by layer-sizing, the varied layers must be realized by metamaterials. So, specially-configured aluminum-based metamaterials having a double-slit void inhomogeneity are engineered and the actual wave transmission performance of the metamaterial-realized HQWS structure is examined numerically and experimentally.

A frequency-shifted bispectrum for rolling element bearing diagnosis

This paper is in the field of vibration based fault diagnosis for rolling element bearings, where one major issue is the ability to detect faults as early as possible. Bispectrum analysis has been applied in bearing diagnosis. In this paper, a frequency-shifted bispectrum is studied for bearing diagnosis.It is found that the frequency-shifted bispectrum is more suitable for analyzing amplitude modulated and frequency modulated signals than the bispectrum, when choosing the carrier frequency as the specific frequency shift value. For bearing vibration signals with amplitude modulation characteristics, in which the carrier frequencies are structural resonant frequencies, one of the structural resonances can be chosen as the specific frequency shift value for the frequency-shifted bispectrum analysis.To increase diagnostic ability of the frequency-shifted bispectrum for bearing faults, firstly, the frequency resolution is increased in the frequency-shifted bispectrum analysis through band pass filtering and frequency zooming; secondly, integration of the frequency-shifted bispectrum along one frequency variable is used to produce a one-dimensional spectral representation. Numerical simulation and experimental results show the feasibility of the proposed method for qualitatively and quantitatively diagnosing bearing faults.

Wideband transmission line model for Archimedean spiral slot structures

Spiral slot structures appear in a variety of microwave applications such as circuit elements, transmission lines and broadband antennas. However, design methodologies for these structures that are accurate above the first resonance involve multi-line transmission line models – requiring difficult to compute multi-line characteristics. This study presents the methodology for a transmission line model for an Archimedean spiral slot structure that uses singly-coupled line characteristics, which can be found analytically, to approximate the multi-line transmission line. With this model, the first resonance and many higher-order resonant frequencies of the spiral structure are well predicted, enabling multi-frequency use of the spiral slot. The results of the model compare well with full-wave simulations and are validated with measurements.

A fractional order controller for seismic mitigation of structures equipped with viscoelastic mass dampers

In this paper a fractional order (FO) controller is proposed for solving the vibration suppression problem in civil structures. A laboratory scaled steel structure, with one floor, modeled as a single degree-of-freedom system is used as a case study. Two passive control solutions are proposed: a tuned mass damper (TMD) and a viscoelastic damper (VED), the latter being modeled using fractional derivatives. The simulation results show that the VED is able to further reduce the vibrations induced as forced oscillations or due to seismic excitation inputs, as compared to the passive TMD. The FO controller is then tuned using a new approach based on imposing a magnitude condition for the closed-loop system at the structural resonance frequency. The resulting FO active control strategy, together with the VED, ensures an increased seismic mitigation. Structural modeling errors are also considered, with the proposed active FO control strategy behaving robustly in terms of vibration suppression. The novelty of the paper resides in the tuning approach, as well as in the proposed active control strategy that is based upon combing VEDs, described using an FO model, and an FO controller.

Robust Resonant Frequency-Based Contact Detection With Applications in Robotic Reaching and Grasping

This paper presents a method for detecting contact by tracking a compliant structure's resonant frequency, which increases with external contact. The approach uses an inexpensive accelerometer mounted on or embedded inside the structure, and a phase locked loop circuit and actuator to oscillate the structure at its resonant frequency. This approach is applied to a robotic finger, and two contact detection metrics are compared. The first and best-performing metric detects changes in the frequency of oscillation. The second metric measures changes in the amplitude of the oscillation and detects contact based on amplitude attenuation. The frequency-based method was shown to be approximately three times as sensitive as the amplitude metric, capable of detecting contacts at between 0.03 and 1.65 N, depending on the contact location, approach velocity, and finger stiffness, while the amplitude-based metric detected contacts at between 0.1 and 8 N. The resonant frequency-based approach to contact detection resulted in reliable contact detection anywhere on the finger, including the finger pads, back of the finger, and even out of plane on the side of the finger.

The dynamics of an offshore wind turbine in parked conditions: a comparison between simulations and measurements

AbstractOffshore wind turbines are complex structures, and their dynamics can vary significantly because of changes in operating conditions, e.g., rotor‐speed, pitch angle or changes in the ambient conditions, e.g., wind speed, wave height or wave period. Especially in parked conditions, with reduced aerodynamic damping forces, the response due to wave actions with wave frequencies close to the first structural resonance frequencies can be high. Therefore, this paper will present numerical simulations using the HAWC2 code to study an offshore wind turbine in parked conditions. The model has been created according to best practice and current standards based on the design of an existing Vestas V90 offshore wind turbine on a monopile foundation in the Belgian North Sea. The damping value of the model's first fore‐aft mode has been tuned on the basis of measurements obtained from a long‐term ambient monitoring campaign on the same wind turbine. Using the updated model of the offshore wind turbine, the paper will present some of the effects of the different design parameters and the different ambient conditions on the dynamics of an offshore wind turbine. The results from the simulations will be compared with the processed data obtained from the real measurements. The accuracy of the model will be discussed in terms of resonance frequencies, mode shapes, damping value and acceleration levels, and the limitations of the simulations in modeling of an offshore wind turbine will be addressed. Copyright © 2014 John Wiley & Sons, Ltd.

Dual electric and magnetic frequency tuning of coupled oscillations in a composite magnetodielectric resonator

The possibility of dual magnetic and electric tuning of resonance frequencies of the electrodynamic structure consisting of dielectric resonator and the epitaxial film of Yittrium-Iron Garnet (YIG)- lead zirconate titanate (LZT) heterostructure has been shown. The coupled electromagnetic-andspin oscillations of dielectric resonator and epitaxial YIG film were theoretically and experimentally investigated. The experiments revealed the possibility of implementing the electric frequency tuning of coupled oscillations of a composite magnetodielectric resonator. This possibility is determined by induced elastic stresses in the epitaxial YIG film. A theoretical model is proposed for calculating the frequency shift of coupled oscillations caused by the electric field applied to the piezodielectric layer. It is shown that the basic Q-factor of composite resonator and the range of electric frequency tuning of hybrid oscillations increase with the reduction of the magnetic bias field.

Design and fabrication of a multimode ring vector hydrophone

Typical underwater acoustic sensors can measure the magnitude of an incoming sound wave but cannot identify the direction. In this paper, a new simple method for detecting the direction of a sound wave with a piezoelectric ring hydrophone is proposed. This method divides the piezoceramic ring of the hydrophone into eight elements and distinguishes the direction of the sound wave by combining the output voltages of the elements in a particular manner. The validity of the design method was confirmed through the fabrication of an experimental prototype of the ring hydrophone with the proposed structure and a comparison of its performance with the design results. The method allows the ring vector hydrophone to operate over a very wide frequency range without being restricted to its structural resonant frequencies.

In vivo application of an optical segment tracking approach for bone loading regimes recording in humans: A reliability study

This paper demonstrates an optical segment tracking (OST) approach for assessing the in vivo bone loading regimes in humans. The relative movement between retro-reflective marker clusters affixed to the tibia cortex by bone screws was tracked and expressed as tibia loading regimes in terms of segment deformation. Stable in vivo fixation of bone screws was tested by assessing the resonance frequency of the screw-marker structure and the relative marker position changes after hopping and jumping. Tibia deformation was recorded during squatting exercises to demonstrate the reliability of the OST approach. Results indicated that the resonance frequencies remain unchanged prior to and after all exercises. The changes of Cardan angle between marker clusters induced by the exercises were rather minor, maximally 0.06°. The reproducibility of the deformation angles during squatting remained small (0.04°/m–0.65°/m). Most importantly, all surgical and testing procedures were well tolerated. The OST method promises to bring more insights of the mechanical loading acting on bone than in the past.

Fluid–structure interaction in compliant insect wings

Insect wings deform significantly during flight. As a result, wings act as aeroelastic structures wherein both the driving motion of the structure and the aerodynamic loading of the surrounding fluid potentially interact to modify wing shape. We explore two key issues associated with the design of compliant wings: over a range of driving frequencies and phases of pitch-heave actuation, how does wing stiffness influence (1) the lift and thrust generated and (2) the relative importance of fluid loading on the shape of the wing? In order to examine a wide range of parameters relevant to insect flight, we develop a computationally efficient, two-dimensional model that couples point vortex methods for fluid force computations with structural finite element methods to model the fluid–structure interaction of a wing in air. We vary the actuation frequency, phase of actuation, and flexural stiffness over a range that encompasses values measured for a number of insect taxa (10–90 Hz; 0-π rad; 10−7–10−5 N m2). We show that the coefficients of lift and thrust are maximized at the first and second structural resonant frequencies of the system. We also show that even in regions of structural resonance, fluid loading never contributes more than 20% to the development of flight forces.

Application of the Smart Integrator in the Ship-Borne Radar Servo System

Along with improvement of capability of the precision measurement radar, the servo system with more high capability is needed. A large antenna reduces rigidity and structural resonance frequency of antenna system, and it is even possible to make radar lose the target. Based on analyzing Ship-borne servo system, the model of servo system has been set up and intelligent integral has been applied in the Position Control Loop. The result of simulation shows that this method can decrease overshoot of the servo system and improve the quickness of the servo system.