Sinusoidal Wave Excitation Research Articles

A wave energy harvester based on an ultra-low frequency synergistic PTO for intelligent fisheries

This paper proposes a nodding-duck wave energy harvester with coaxial contra-rotating power take-off based on the ultra-low frequency synergistic principle to solve the self-powered problems in intelligent fisheries. The design and working principle of nodding-duck wave energy harvester are described in detail, and the coaxial contra-rotating disengagement-engagement coupling model of nodding-duck wave energy harvester is established based on the ultra-low frequency synergistic principle. A dry bench test, charging test and water flume test were performed to evaluate the performance of the nodding-duck wave energy harvester. Dry bench experimental results show that the integrated disengagement ratio of the device can be increased by increasing the excitation frequency and amplitude and can achieve a maximum voltage output of 24.1 V and average power of 210.5 mW by sinusoidal wave excitation of 1 Hz and swing angle of 5π/12. The water flume experiment is used as supportive evidence to demonstrate the power supply performance of the device. Different analyses proved that the device had the potential to supply energy effectively for intelligent fishery sensors.

Optimal operation of dielectric elastomer wave energy converters under harmonic and stochastic excitation

AbstractDielectric elastomers are a promising technology for wave energy harvesting. An optimal system operation can allow maximizing the extracted energy and, simultaneously, reducing wear that would lead to a reduction in the wave harvester lifetime. We pursue a model‐based optimization approach to identify optimal controls for wave energy harvesters based on dielectric elastomers. First, a direct method is used for time‐discretization of the dielectric elastomer wave energy harvester in the optimal control problem. The two conflicting objectives are considered in a multiobjective optimization framework. Considering a periodic, sinusoidal wave excitation, the optimal solution shows turnpike properties for the optimal periodic mode of operation. However, since real wave motion is neither monochromatic nor predictable on longer time horizons, further extensions are pursued. First, we introduce a stochastic wave excitation. Second, an iterative model‐predictive control scheme is designed. Due to multiple objectives, the control scheme has to include an automated adaption of the corresponding priorities. Here, we propose and evaluate a heuristic rule‐based adaption in order to maintain the damage below target levels. The approach presented here might be used in the future to guarantee for autonomous operation of farms of wave energy harvesters.

Multiferroic Cantilevers Containing a Magnetoactive Elastomer: Magnetoelectric Response to Low-Frequency Magnetic Fields of Triangular and Sinusoidal Waveform.

In this work, multiferroic cantilevers comprise a layer of a magnetoactive elastomer (MAE) and a commercially available piezoelectric polymer-based vibration sensor. The structures are fixed at one end in the horizontal plane and the magnetic field is applied vertically. First, the magnetoelectric (ME) response to uniform, triangle-wave magnetic fields with five different slew rates is investigated experimentally. Time and field dependences of the generated voltage, electric charge, and observed mechanical deflection are obtained and compared for four different thicknesses of the MAE layer. The ME responses to triangular and sinusoidal wave excitations are examined in contrast. Second, the ME response at low frequencies (≤3 Hz) is studied by the standard method of harmonic magnetic field modulation. The highest ME coupling coefficient is observed in the bias magnetic field strength of ≈73 kA/m and it is estimated to be about 3.3 ns/m (ME voltage coefficient ≈ 25 V/A) at theoretically vanishing modulation frequency ( Hz). Presented results demonstrate that the investigated heterostructures are promising for applications as magnetic-field sensors and energy harvesting devices.

Prediction of the driver’s head acceleration and vibration isolation performance of the seating suspension system using the time and frequency domain modeling

Long-time exposure to low-frequency vibration will negatively impact human health.A rapid biodynamic system modeling method has been proposed to study the human body’s response to the low-frequency vibration excitation in the whole vehicle environment. The sensitivity of design parameters of the seating suspension system to the vibration isolation performance will be studied. The dynamic model consists of a lumped parameter mass-spring-dashpot model of seven degrees of freedom (7DOF) and used for the prediction of the head acceleration in the time domain and peak transmissibility ratio in the frequency domain under a sinusoidal wave excitation and random road profile excitations of different road classes and vehicle speeds. A calculation formula has been established to predict the seat effective amplitude transmissibility (SEAT) from the transmissibility ratios and frequency weighting function of the ISO 8606, while the transmissibility ratios can be calculated from the frequency response analysis of the seven degrees of freedom system dynamic equations. The simulation results in the frequency domain have been verified by those in the time domain for the linear system assumption. The change trends of the driver’s head acceleration, SEAT value, and peak transmissibility ratio from the driver’s head to the seat base with respect to the stiffness and damping coefficients of the seat and cushion have been compared with and verified by one another.It is proved that in the vehicle system, individually, reducing the individual stiffness and damping coefficients of the seat structure, reducing the individual seat cushion stiffness, and increasing the individual seat cushion damping coefficient one by one will be able to reduce the driver’s head acceleration, peak transmissibility ratio, and SEAT value from the head to seat base, and improve the ride comfort. Simultaneously reducing the stiffness and damping coefficients of the seat and cushion will be able to reduce the driver’s head acceleration, peak transmissibility ratio, and SEAT value from the head to seat base and improve the ride comfort. The reduction effect of the driver’s head acceleration is more substantial under the Class E road profile of a large profile roughness than that under the other road classes.

Study on a new electromagnetic flowmeter based on three-value trapezoidal wave excitation

Excitation technology plays an important part in the field of electromagnetic flowmeter (EMF). The form of the magnetic field directly determines the characteristics of the flow signal. No breakthrough has been made on the excitation technology since the invention of sinusoidal wave excitation, rectangular wave excitation, and double-frequency excitation. In this paper, firstly a new three-value trapezoidal wave excitation with transient responses is proposed. Then the signal model is established, and the verification experiments are carried out. Finally, flow calibration experiments and comparative experiments on the trapezoidal wave excitation are conducted on the experimental platform. The experiment results show that the electromotive force output by the EMF based on three-value trapezoidal wave excitation is linearly related to the flow velocity. When the flow velocity is 0.257 m/s, the relative error is only 1.635%. When the flow velocity reaches 2.133 m/s, the relative error is reduced to 0.432%. The three-value trapezoidal wave excitation with the transient analysis satisfies the requirements of the EMF with high accuracy. The research also shows that the excitation frequency has a great influence on the measurement accuracy of the EMF based on three-value trapezoidal wave excitation.

A General and Accurate Iron Loss Calculation Method Considering Harmonics Based on Loss Surface Hysteresis Model and Finite-Element Method

In order to predict the performance of designed electric machines, and also based on which the high efficiency of the drive systems can be obtained, the accurate calculation of the iron loss is necessary. Taking modeling accuracy versus modeling complexity into account, this article proposes a general and accurate iron loss calculation method considering harmonics based on the loss surface (LS) hysteresis model and finite-element method (FEM). Compared with the previous triangular wave excitation, this article uses the data under sinusoidal wave excitation to establish the LS model, which is more convenient for engineering application. A specimen is tested for different flux densities with harmonics, the extensive results verify the modeling method. Due to a powerful hysteresis model, the iron loss calculation can be realized by the direct integration of hysteresis loops. A separated iron loss calculation package is developed, and it is combined with the commercial finite-element software to compute the iron loss distribution. The method that combines the LS model and FEM is proved feasible by comparing the calculated iron loss with the measured one for the Epstein frame.

Automatic Extraction of Measurement-Based Large-Signal FET Models by Nonlinear Function Sampling

A new method is proposed for the accurate experimental characterization and fully automated extraction of compact nonlinear models for field-effect transistors (FETs). The approach, which leads to a charge-conservative description, is based on a single large-signal measurement under a two-tone sinusoidal wave excitation. A suitable choice of tone frequencies, amplitudes, and bias allows to adequately characterize the transistor over the whole safe operating region. The voltage-controlled nonlinear functions describing the two-port FET model can be computed over an arbitrarily dense voltage domain by solving an overdetermined system of linear equations. These equations are expressed in terms of a new nonlinear function sampling operator based on a biperiodic Fourier series description of the acquired frequency spectra. The experimental validation is carried out on a 0.25- $\mu \text{m}$ gallium nitride (GaN) on silicon carbide (SiC) high-electron-mobility transistor (HEMT) under continuous-wave (CW) and two-tone excitation (intermodulation distortion test).

The Effects of Phase-Modulated Excitation on the Focused Acoustic Field.

Various modulation approaches, such as amplitude and frequency modulations, have been applied widely to modify the acoustic field and improve the performance of ultrasound imaging and therapy. However, phase modulation (PM) has not been investigated extensively in the ultrasound applications, especially at a long-pulse duration. In this study, the effects of PM on the acoustic field were investigated. The radiated acoustic pressure waveforms produced using different PM strategies (i.e., sequential phase inversion every cycle, every two cycles, and random phase inversion) were explored, and the distributions of acoustic pressure and average acoustic intensity along and transverse to the transducer axis were compared with those of a sinusoidal wave excitation in both measurement and simulation. It is found that the phase inversion between the modulated signals is not clearly seen in the radiated waveform because of the limited fractional bandwidth of the therapeutic ultrasound transducer. As a result, the radiated waveform has a higher oscillating frequency, and the pressure at the focus and the -6-dB beam size are decreased. Both simulation and measurement show similar trends. Furthermore, produced acoustic fields of the phased array using these PM strategies were also simulated at the varied lateral and axial focus shifting distances. The magnitude and beam size of both the main lobe and grating lobe are found between them, especially at the large focus shifting. In summary, the acoustic field is dependent on the PM, and the appropriate excitation scheme could improve the ultrasound application.

Dynamic response characteristics of steel portal frames having semi-rigid joints under sinusoidal wave excitation

To demonstrate the characteristics of the nonlinear response of steel frames, an elastic dynamic response analysis of the semi-rigid frame is performed under the harmonic wave. The semi-rigid contact is represented by the alternating spring which is given stiffness by a three-parameter energy model which approaches the hysterical curve by hardening model. The properties of spectra and hysteric curves are presented. This study shows that (1) the greater the acceleration input capacitance the smaller the instant connection capability and the smaller is the response. (2) However, by allowing an extreme increase in capacitance input acceleration, response spectra can be increased as the contact stiffness results near zero.

S-wave impedance measurements of the uppermost material in surface ground layers: Vertical load excitation on a circular disk

S-wave impedance is one of the most effective parameters used to study the ground motion amplification of soil deposits. We propose a new approach to measure the S-wave impedance of the uppermost material in surface ground layers. First, a circular disk is set on the ground surface, and it is vertically loaded by sinusoidal wave excitation. When the time series of the loading velocity is synchronized with the reaction force, the ratio of the reaction force to the loading velocity is proportional to the S-wave impedance. We then estimate the proportionality coefficient from numerical experiments and check its accuracy. The measurement error is estimated to be within 1% for the homogeneous half-space case. We also discuss the applicability of this new approach and its limitations on the basis of numerical experiments for inhomogeneous media: a two-layered medium and a one-dimensional (1-D) random medium. The proposed approach is effective for both cases if we select the appropriate circular disk size.

Citizen sensors for SHM: use of accelerometer data from smartphones.

Ubiquitous smartphones have created a significant opportunity to form a low-cost wireless Citizen Sensor network and produce big data for monitoring structural integrity and safety under operational and extreme loads. Such data are particularly useful for rapid assessment of structural damage in a large urban setting after a major event such as an earthquake. This study explores the utilization of smartphone accelerometers for measuring structural vibration, from which structural health and post-event damage can be diagnosed. Widely available smartphones are tested under sinusoidal wave excitations with frequencies in the range relevant to civil engineering structures. Large-scale seismic shaking table tests, observing input ground motion and response of a structural model, are carried out to evaluate the accuracy of smartphone accelerometers under operational, white-noise and earthquake excitations of different intensity. Finally, the smartphone accelerometers are tested on a dynamically loaded bridge. The extensive experiments show satisfactory agreements between the reference and smartphone sensor measurements in both time and frequency domains, demonstrating the capability of the smartphone sensors to measure structural responses ranging from low-amplitude ambient vibration to high-amplitude seismic response. Encouraged by the results of this study, the authors are developing a citizen-engaging and data-analytics crowdsourcing platform towards a smartphone-based Citizen Sensor network for structural health monitoring and post-event damage assessment applications.

Semi-analytical numerical approach for the structural dynamic response analysis of spar floating substructure for offshore wind turbine

A semi-analytical numerical approach for the effective structural dynamic response analysis of spar floating substructure for offshore wind turbine subject to wave-induced excitation is introduced in this paper. The wave-induced rigid body motions at the center of mass are analytically solved using the dynamic equations of rigid ship motion. After that, the flexible structural dynamic responses of spar floating substructure for offshore wind turbine are numerically analyzed by letting the analytically derived rigid body motions be the external dynamic loading. Restricted to one-dimensional sinusoidal wave excitation at sea state 3, pitch and heave motions are considered. Through the numerical experiments, the time responses of heave and pitch motions are solved and the wave-induced dynamic displacement and effective stress of flexible floating substructure are investigated. The hydrodynamic interaction between wave and structure is modeled by means of added mass and wave damping, and its modeling accuracy is verified from the comparison of natural frequencies obtained by experiment with a 1/100 scale model.

Study of Moving Sinusoidal Wave Load Across Simple Supported Beam for Sensor Structural Configuration

A continuous structure has several response characteristics that make it a good candidate for a sensor to be used in locating an acoustic source. In this paper, based on a beam structure with simple supports on both ends, the response of the structure to transient sinusoidal wave excitations is examined analytically and also verified by a finite element method (FEM). For sensor configuration on this structure, various interesting parameters such as the aperture of the structure, material properties, and thickness are examined by evaluating their effects on structure displacement responses. Results will be used for acoustic wave identification in the future.

118203 構造物振動を利用した発電手法に関する研究 : 複数の種類の添加剤を含む圧電素子の発電特性(一般02 機械力学・制御工学2)

An electrical power generating device using piezoelectric element (PZT) has been developed to convert structural vibration energy into electrical energy. This paper describes the electrical generation characteristics of PZT and PZT including several kinds of additives under vibration load. Vibration tests are performed by using an experimental equipment composed of PZT, weights and a support frame structure. Sinusoidal wave excitation tests are carried out under the condition of the constant initial compressive load acting on PZT. Effects of several kinds of additives, vibration frequency and vibration load on generated voltage and electric power of PZT are evaluated from the vibration test results.

J0404-7-3 構造物振動を利用した発電手法に関する研究 : 圧電素子の振動耐久性([J0404-7]知的材料・構造システム(7):圧電関連)

An electrical power generating device using piezoelectric element (PZT) has been developed to convert structural vibration energy into electrical energy. This paper describes the electrical generation characteristics of PZT and PZT including Nb under vibration load. Vibration tests are performed by using an experimental equipment composed of PZT, weights and a support frame structure. Sinusoidal wave excitation tests are carried out under the condition of the constant initial compressive load acting on PZT. Effects of the concentration of Nb, vibration frequency and vibration load on generated voltage and electric power are evaluated by the vibration test.

Development of Quakeproof Reinforcement Methods for Masonry Walls

Railway lines in Japan are sometimes fl anked by earthretaining structures consisting of piled-up stones, known as masonry walls (see Fig. 1). Although railway operators are aware that these walls can collapse and damage trains in the event of an earthquake, the behavior of such structures when subjected to seismic motion has not yet been clarifi ed. Against this background, the Railway Technical Research Institute (RTRI) investigated the deformation mechanism of masonry walls in earthquake conditions. Based on the results of this research, a technique called the pin-up method was developed to effectively reinforce masonry walls against earthquakes. A model collapse test on a masonry wall revealed that its backfi ll cobblestones slid outward due to the relative movement between the ashlars on the front and the ground behind, thereby generating residual displacement in the wall. In view of these deformation-causing factors, the earthquake resistance of masonry walls is expected to improve if the movement of backfi ll cobblestones can be suppressed. It is therefore thought that measures to fi x these cobblestones using grouting materials will provide an effective means of helping masonry walls to resist earthquakes. However, these cobblestones play a role in draining water that penetrates the ground, thereby preventing it from applying pressure to the backside of ashlars. If grouting material is injected into the backfi ll cobblestone layer at random, this drainage function may be lost. The RTRI therefore designed the pin-up method (types I and II) to enable the suppression of backfi ll cobblestone movement while maintaining its drainage function (see Fig. 2). Type I of the pin-up method combines four adjacent ashlars and the backfi ll cobblestones in the wall behind them to create stiffening blocks, thereby achieving the goal of improving the earthquake resistance of the masonry wall while maintaining the drainage function of the backfi ll cobblestones and suppressing their movement. Type II, on the other hand, also anchors the combined stiffening blocks to the ground using deformed bars, and is applied when the level of earthquake resistance required is higher than that offered by type I. Pin-up method types I and II are so named because they can be likened to fi xing masonry walls to the ground with pushpins. Figure 3 shows the results of shaking table tests to verify the effect of earthquake reinforcement work applied to model masonry walls using pin-up method types I and II. When the models were subjected to sinusoidal wave excitation at a maximum acceleration of 7 m/s2, deformation was suppressed to one-third or less that of a non-reinforced wall with the model reinforced using pin-up method type I. On the other hand, the model reinforced using type II showed virtually no deformation at all. As these test results demonstrated that masonry walls reinforced using the pin-up method have a high level of earthquake resistance, the RTRI discussed concrete methods of reinforcement in consideration of actual conditions, clarified the quality of applicable grouting materials and decided on suitable methods of injection. Based on the results of model tests, the Institute also determined methods to evaluate the degree of deformation in masonry walls in earthquake conditions, evaluate their stability and design reinforcement work using the pin-up method. By summarizing these study results, the RTRI was able to create a manual for design and reinforcement work related to masonry walls. In January 2009, the pin-up method was applied in actual masonry wall reinforcement work for the fi rst time (see Fig. 4). The RTRI will strive to promote the adoption of this method over wide areas in order to contribute to the improvement of disaster prevention for railway wayside slopes.

COMBUSTION ENHANCEMENT OF A GAS FLARE USING ACOUSTICAL EXCITATION

ABSTRACT The effect of acoustical excitation on flame stability, trajectory, exhaust emissions, and gas temperatures from a gas flare stack in a crossflow was experimentally investigated. Circular, elliptical, and cup nozzle configurations were examined and compared with a sinusoidal wave excitation. It was found that increasing the pulsation amplitude enhances the combusting efficiency up to the quenching limit. Increasing the Strouhal number enhances the mixing with an optimum value at 0.25. With acoustical excitation, there was a reduction in the CO, unburned hydrocarbon (UHC), and NOx concentrations. It was found that the elliptical burner exhibits the widest stability range with respect to the pulsation strength, with the highest average CO concentration. The cup nozzle produced the least amounts of CO and UHC. Both nozzles revealed higher flame temperatures than those of the circular nozzle. There was an increase in flame temperatures with excitation, with the subsequent widening and reduction in flame length.

Development and characterization of surface micromachined, out-of-plane hot-wire anemometer

In this paper, we report the development of a new type of hot-wire anemometer (HWA) realized by using a microfabrication process that combines surface micromachining and an efficient three-dimensional assembly technique. The HWA uses a thermal element (hot wire) that is made of Pt/Ni/Pt film with a measured temperature coefficient of resistance (TCR) of 2400 ppm//spl deg/C. The thermal element is elevated out of plane by using support beams made of polyimide. In our current design, the support beam is 2.7 /spl mu/m thick and up to 1 mm tall, and the length of the thermal element varies from 50 /spl mu/m to 200 /spl mu/m. Steady-state response to air velocity has been experimentally obtained up to 20 m/s under both constant current (CC) and constant temperature (CT) modes. The transient-state response has been examined using square wave and sinusoidal wave excitation signals in CT modes with the maximum cutoff frequency found to be approximately 10 kHz. This new HWA offers a number of unique materials and performance characteristics. The sensor does not require the use of silicon as either substrate or sensing materials. Using this process, it is possible to form large arrays of HWA on a variety of substrate materials.

Dynamic Buckling Experiments on Liquid Containing Cantilever Cylindrical Shells under Horizontal Excitation.

Dynamic buckling experiments on thin cylindrical shells placed inside a rigid liquid container were carried out by using a shaking table. The shells represent the thermal baffles and the container represents the reactor vessel of a fast breeder reactor. The fluid pressure caused by the horizontal excitation distributes nonuniformly around the cylinders and causes external pressure buckling deformation on them. The buckling pressure on various types of test cylinders and seismic waves was measured, and it was confirmed to be higher than that predicted by static buckling analysis. It was also found that sub harmonic vibration occurs under a certain sinusoidal-wave excitation, and the response displacement increases suddenly at a lower pressure than the buckling pressure measured by seismic-wave-excitation tests. The test results indicated that in seismic design to prevent buckling of the thermal baffles, the static bucklimg analysis can be used as ling as sub-harmonic vibration does not occur.

Studies on the Seismic Buckling Design Guideline of FBR Primary Coolant Systems. 2nd Report. Analytical Studies on Subharmonic Vibration of Clamped-free Thin Cylindrical Shells Immersed in Fluid under Horizontal Excitation.

When a thin cylindrical shell immersed in fluid is subjected to sinusoidal wave excitations in the horizontal direction, subharmonic vibration accompanying shell mode vibration may occur depending on the excitation condition. This phenomenon was investigated by dynamic stability analysis and was proved to be dependent both on frequency and acceleration amplitude of excitation. Calculation results under sinusoidal wave excitation and comparison of dynamic pressure when subharmonic vibration occurs with elastic buckling pressure provide a criterion for assessing stability of subharmonic vibration under seismic wave excitation.