Excitation Force Research Articles

Response and reliability analysis of a nonlinear VEH systems with FOPID controller by improved stochastic averaging method and LBFNN algorithm

In engineering, it is an important issue to guarantee the normal working of a vibration energy harvesting (VEH) device to harvest electricity. However, the determination of the system dynamics is a huge challenge due to random excitation, nonlinear structure, and control force. This paper aims to study the response and reliability of a kind of nonlinear and coupled VEH system with an FOPID controller. The stationary response is analyzed by an improved stochastic averaging method, in which an amplitude-dependent frequency is taken into account during the averaging procedure in the case of the strongly nonlinear system. Time-varying reliability in the VEH system is analyzed by using a new LBFNN algorithm, and weight coefficients at each time in this algorithm is obtained through an iteration procedure. Numerical results show that there are essential differences between the weakly nonlinear system and the strongly nonlinear one in terms of averaging procedure and response probability. The fractional orders in the FOPID controller are critical parameters to bring stochastic bifurcations. In addition, strongly nonlinear structure together with lower-order fractional derivative and higher-order fractional integration in FOPID controller are helpful to enhance the reliability performance of the VEH system.

Optical coherence elastography under homolateral parallel acoustic radiation force excitation for ocular elasticity quantification.

Alteration in the elastic properties of biological tissues may indicate changes in the structure and components. Acoustic radiation force optical coherence elastography (ARF-OCE) can assess the elastic properties of the ocular tissues non-invasively. However, coupling the ultrasound beam and the optical beam remains challenging. In this Letter, we proposed an OCE method incorporating homolateral parallel ARF excitation for measuring the elasticity of the ocular tissues. An acoustic-optic coupling unit was established to reflect the ultrasound beam while transmitting the light beam. The ARF excited the ocular tissue in the direction parallel to the light beam from the same side of the light beam. We demonstrated the method on the agar phantoms, the porcine cornea, and the porcine retina. The results show that the ARF-OCE method can measure the elasticity of the cornea and the retina, resulting in higher detection sensitivity and a more extensive scanning range.

Vibrational dynamics of a subjected system to external torque and excitation force

This work focuses on the dynamical response of a novel auto-parametric two-degrees-of-freedom (DOF) dynamical system when it is subjected to external torque and force. It consists of a forced oscillator with nonlinear stiffness that is connected to a linear spring. In accordance with the system’s DOF, an organizing system of equations of motion (EOM) is produced using Euler–Lagrange’s equations. To obtain the analytical approximate solutions (ASs) of the equations of this system, the multiple scales technique (MST) is employed. The provided solutions are being juxtaposed with the numerical solutions (NSs) for comparison to show how closely they agree, as well as the precision of the MST. In view of removing secular terms, the system’s solvability criteria are obtained. All arising resonance cases are classified, and two of them are then examined at once. The relevant system of modulation equations is solved numerically to illustrate the advantageous influence of diverse factors on the behavior of the modified phases and amplitudes. Based on the values of these parameters, the frequency response curves (FRCs) are drawn to explore different zones of stability and instability. A wide variety of values for the system’s parameters shows that its behavior is steady. The achieved outcomes are deemed novel, as the MST has been applied on a new dynamical model. The results have broad relevance and can be implemented in various engineering contexts, including the analysis of ship movements, in which nonlinear coupling between rolling and pitching motions can be found.

Vibration Characteristic Research of 100 m New Polar Exploration Cruise Based on Finite Element Modeling

Luxury cruise ships are high-end passenger ships with facilities on board for the leisure and entertainment of passengers, so the comfort of luxury cruise ships is a matter of great concern. In this paper, a finite element model of a new polar exploration cruise ship is established, and the wet modes of the whole ship are calculated using the virtual mass method and compared with the principal frequencies of the excitation forces to initially verify the rationality of the design of the structural vibration characteristics of the whole ship. The admittance matrix of the vibration velocity to excitation force was calculated by a frequency response analysis, and the vibration velocities at the stern plate and main engine foundations were tested during sailing. Then, the obtained propeller and main engine excitation forces were loaded into the finite element model; the vibration velocities of each compartment were calculated and compared with the compartment vibration velocity test values. The errors were within the engineering allowable range, verifying the accuracy of the excitation forces. The propeller and main engine excitation forces were loaded separately on the finite element model to calculate the vibration velocity of each cabin, and the contribution of the two excitation sources to the vibration velocity of each cabin was analyzed. It was found that the contribution of the excitation source to the cabin response was related to the relative position between the cabin and the excitation source. When the cabin was located in the cabin adjacent to or directly above a certain excitation source, the contribution of the excitation source to the cabin response was greater. When the cabin was farther away from both excitation sources, the contribution of the propeller excitation was greater. This provides a targeted reference for the preliminary vibration assessment and later vibration control of the new polar expedition cruise ship.

Computational prediction of impact sound insulation of a full-scale timber floor applying a FEM simulation procedure

During the recent decades, simulation procedures involving the finite element method (FEM) have been developed to enable prediction of impact sound insulation of timber slabs and floors. FEM simulations have previously been applied for timber floors mainly in low frequencies despite their evident ability to operate over a wide frequency range. Additionally, the validation processes have involved calibrations and experimental modal analyses which can seldom be performed in product development tasks concerning full structures. The purpose of this research was to study the applicability of a FEM simulation procedure to predict normalised impact sound pressure levels Ln of a full-scale timber floor if material data provided by the product manufacturers is used. The floor was studied at three construction stages where the FEM simulations were performed for the bare floor and the rib slab, and the floor covering was considered in the post-processing stage in case of the full floor. The impact force excitation generated by the ISO standard tapping machine was described with the recently published procedure involving explicit dynamics analysis. To serve the purposes of this study, the FEM models were fully constructed before the measurements were carried out. According to the results, the 1/3-octave Ln of the full floor and the floor without covering was predicted with a 0 to 9 dB accuracy depending on the frequency band and the single-number quantities with a 0 to 4 dB accuracy. The single-number quantities of the bare rib slab were underestimated with the simulations by 4 to 5 dB. Probable causes for the discrepancies between the simulation and measurement results pointed mainly to the uncertain material properties but possibilities for modelling inaccuracies could not be excluded.

An experimental approach to multi-input multi-output nonlinear active vibration control of a clamped sandwich beam

Large amplitude vibrations are often associated with geometric nonlinearity. These nonlinear systems are usually controlled using linear controllers, such as positive position feedback (PPF). Nonlinear control has also often been limited to single-input single-output (SISO) architectures. The present study develops a nonlinear PPF controller implemented with both a SISO and a multiple-input multiple-output (MIMO) architecture on a real experimental set-up, consisting of a clamped composite sandwich beam. The controller aimed to reduce the vibration amplitude observed when the structure was subject to a stepped-sine excitation in the frequency neighborhood of the first natural frequency for different force excitation levels. The developed nonlinear controller is based on a linear PPF controller to which a cubic term was added since the system under study is of hardening type. The control parameters were selected by optimization of the reduction of the vibration at low excitation amplitude. The nonlinear MIMO and SISO versions of the controller were compared to linear MIMO and SISO versions, which omitted the cubic term but maintained the other parameters. The nonlinear controllers were found to outperform the linear ones, and the MIMO versions of each controller also outperformed the SISO ones. Overall, the experimental evidence shows that a nonlinear MIMO PPF controller should be preferred for the application under study.

LSTM RNN-based excitation force prediction for the real-time control of wave energy converters

Wave energy is a type of abundant and dense renewable energy. Wave force prediction is a critical technology that influences power absorption efficiency in the real-time control of wave energy converter (WEC). Could wave elevation be used to predict wave excitation force directly by training artificial neural network? This method results in rapid and suitable prediction for real-time control. A long short-term memory recurrent neural network (LSTM RNN) algorithm is introduced to identify characteristics of wave excitation forces based on wave elevations. In this method, the wave elevations in front of the structure are measured to obtain sufficient time to actuate the control manipulation. A total of 180 regular wave and 12 irregular wave tests are conducted, and the LSTM RNN model is trained based on the experimental results. The performance of the LSTM algorithm is verified. According to the regular cases in the study, the LSTM prediction can identify high-order harmonic loads, and the anti-noise capability of the LSTM algorithm can filter random noises from the measure signals. In the irregular cases, the LSTM RNN algorithm performs effectively to predict the wave force excited on the structure using wave elevations measured by wave probes. The best combinations of the test setting parameters are determined to guide experimental tests and WEC prototypes.

Investigating the influence of excitation force on compaction behavior of gravel in granular blends through DEM simulation

During the construction of subgrades, the compaction of granular blends is typically achieved through vibrational techniques at varying the frequencies and excitation forces. This study investigates the impact of excitation forces, within the range of 300-600 kPa, on subgrade compaction by employing the discrete element method (DEM). Calibration tests were conducted to establish the contact parameters for the DEM models, and their reliability was verified via vibration compaction tests. The research further explores the evolution of settlement, particle motion, and contact interactions at both macroscopic and mesoscopic levels as influenced by the excitation forces. Furthermore, the influence of excitation force on the stability of skeleton frameworks was analyzed. The results indicated that the number of contacts in the final state increased consistently with the excitation force, leading to a more uniform distribution. This change contributes to a time-dependent stability within the skeleton framework, which effectively limits the movement of fine particles in the final stages and diminishes the sliding between the coarse particles. Conversely, in the initial phases, a rise in excitation force increases the stress concentration between the contacts, which increases the sliding damage to the skeleton frameworks and leads to greater compaction deformation.

Research on structural resonance of large axial fan in power plant

According to the structural characteristics of the axial fan, the causes of equipment resonance are analyzed. Four reference methods are proposed, including strengthen the structural stiffness, change the exciting frequency, weaken the exciting force, and strengthen the damping. The characteristics of the response treatment measures are discussed. Take the two-stage axial-induced draft fan of a 600 MW unit as an example, the axial resonance problem has been dealt with well by improving the support stiffness and reducing the excitation force. The research results and treatment can provide an experience reference for the analysis and treatment of the resonance problem of large axial fans.

Research on axial nonlinear vibration characteristics of ball screw feed system considering segmented restoring force

Taking the ball screw feed system as the research object, the two degree of freedom axial dynamic model of the system is constructed firstly. Based on Hertz contact theory, when the ball screw pair adopts variable lead self-preloading to eliminate the assembly clearance between the ball and raceway, considering the nonlinear segmented axial elastic recovery force generated by the uneven contact deformation between the ball and raceway under the action of external excitation force, further derive the nonlinear dynamic equation group of the system. Next, the fourth-order Runge-Kutta method was used to numerically solve the equation system, obtaining the system’s two and three-dimensional phase diagrams, Poincaré sections, time-domain waveform diagrams, frequency spectra, and bifurcation diagrams. Then, the effects of damping constant, initial contact angle between ball and raceway in ball screw pairs, and number of balls on the system’s response characteristics were analyzed, and the influence of external excitation forces on system stability was further studied. Finally, it was verified through experiments that the axial vibration of the system is indeed nonlinear vibration, providing a theoretical basis for the study of the dynamic characteristics of the ball screw feed system.

Research on Simulation Technology of Excitation Response of Aircraft Structural Based on Finite Element Model in Flutter Flight Test

To simulate excitation response of the aircraft structural of flutter test aircraft under different excitation methods. A simulation method for excitation response of flutter flight tests based on finite element models has been proposed. This method is based on the finite element model of the aircraft structure. Establish aerodynamic and excitation force models for flutter flight tests. Obtain a simulation model for the excitation response of aircraft flutter flight tests. Solve the model and simulate various excitation methods for flutter flight tests. Firstly, a detailed introduction was given to the excitation modeling method for aircraft flutter flight tests, including two excitation models: external excitation and control surface excitation. Then, the finite element model of the structural dynamics of a single wing with ailerons is taken as the research object. Establish a single wing flutter flight test excitation response model. Implemented simulation of control surface sweep excitation, control surface pulse excitation, and small rocket excitation. The feasibility of this method has been verified. Finally, based on the finite element model of the entire aircraft, a flutter flight test excitation response simulation model was established. We have conducted analysis and research on sensor position optimization, excitation method optimization, excitation response amplitude prediction, and flutter boundary prediction. And the simulation optimization analysis results were compared with the flight test results. Analyzed the promoting effect of flutter flight test excitation response simulation on flight tests.

Bidirectional Multi-Spectral Vibration Control: Insights from Automotive Engine Mounting Systems in Two-Dimensional Structures with a Damaged Vertical Active Element

Active mounting systems have become more prevalent in recent years to effectively mitigate structure-induced vibration across the automobile chassis. This trend is particularly evident in engine mounts. Considerable research has been dedicated to this approach owing to its potential to enhance the quietness and travel comfort of automobiles. However, prior research has concentrated on a limited spectrum of specific vibrations and noise control or has been restricted to vertical vibration control. This article describes the modeling, analysis, and control of a source structure employing a multidirectional active mounting system designed to closely simulate the position and direction of an actual automobile engine mount. A piezoelectric stack actuator is connected in series to an elastic (rubber) mount to form an active mount. The calculation of the secondary force required for each active mount is achieved through the application of harmonic excitation forces. The control signal can also reduce vibrations caused by destructive interference with the input signal. Furthermore, horizontal oscillations can be mitigated by manipulating the parameters via dynamic interconnections of the source structure. We specifically examined the level of vibration reduction performance in the absence of a vertical active element operation and determined whether the control is feasible. Simulation outcomes demonstrate that this active mount, which operates in both the vertical and horizontal directions, effectively mitigates excitation vibrations. Furthermore, a simulation was conducted to mitigate the vibrations caused by complex signals (AM and FM signals) and noise. This was achieved by monitoring the system response using an adaptive filter NLMS algorithm. Adaptive filter simulations demonstrate that the control efficacy degrades in response to complex signals and noise, although the overall relaxation trend remains unchanged.

Multiple scales method for analyzing a forced damped rotational pendulum oscillator with gallows

This study reports the analytical solution for a generalized rotational pendulum system with gallows and periodic excited forces. The multiple scales method (MSM) is applied to solve the proposed problem. Several types of rotational pendulum oscillators are studied and talked about in detail. These include the forced damped rotating pendulum oscillator with gallows, the damped standard simple pendulum oscillator, and the damped rotating pendulum oscillator without gallows. The MSM first-order approximations for all the cases mentioned are derived in detail. The obtained results are illustrated with concrete numerical examples. The first-order MSM approximations are compared to the fourth-order Runge–Kutta (RK4) numerical approximations. Additionally, the maximum error is estimated for the first-order approximations obtained through the MSM, compared to the numerical approximations obtained by the RK4 method. Furthermore, we conducted a comparative analysis of the outcomes obtained by the used method (MSM) and He-MSM to ascertain their respective levels of precision. The proposed method can be applied to analyze many strong nonlinear oscillatory equations.

The study of input power of an underwater free-damping ribbed plate in statistical energy analysis

To study the vibration characteristics of the free-damping ribbed plate with fluid load under point force excitation in statistical energy analysis (SEA), the theoretical model of input power calculation was established in this research. The simulational results from SEA commercial software validated the correctness of the proposed theoretical model. As inferred from the theoretical model, the added damping layer and ribs significantly affect the effective bending stiffness and area density, and the added fluid load only affects the effective area density. These effective parameters will affect the input power of the fluid-loaded free-damping ribbed plate, resulting in increased input power as a function frequency. The research in this paper could provide theoretical guidance on the vibroacoustic analysis of underwater complex ship structures.

RESEARCH ON THE RESPONSE MECHANISM OF CLAMPING POINT POSITION TO THE VIBRATION PROPAGATION CHARACTERISTICS OF WOODEN MATERIALS

Vibratory harvesting is to dislodge fruits by applying excitation force to fruit trees, so the vibration response characteristics of fruit trees are of great significance for vibratory forest and fruit harvesting machinery to realize efficient harvesting. The effects of different clamping points and vibration frequencies on vibration responsiveness and energy transfer in Broussonetia papyrifera branches are investigated in this study. The results show that the effects of different clamping point positions and vibration frequencies on the branch vibration response are mutual. The ideal distance between the clamping point position and the base of the main branch should be between 48% and 73% of the branch length, and the distance between the clamping point position and the base of the main branch increased with the increase of vibration frequency. This is because, when the clamping point is close to the base of the main branch, a higher excitation frequency increases the energy consumption at the base of the main branch, and the amount of ineffective vibration energy transferred to the base of the main branch also increases. Therefore, when the location of the clamping point is close to the base of the main branch, the suppression of high-frequency vibration at the base of the main branch is stronger than the suppression of low-frequency vibration. When the clamping point is located in the center of the branch, the overall response of the branch to vibration is better.

Utilizing data-driven algorithms for blind modal parameter identification of structures from output-only video measurements

In structural dynamics and vibration analysis, modal identification plays a pivotal role in understanding and characterizing the dynamic behavior of complex systems. Traditional modal analysis techniques heavily rely on accurate sensor placement and knowledge of the excitation forces, which may not always be feasible or practical in real-world scenarios. Recently, non-contact video-based modal analysis methods for structures with arbitrary complexity using computer vision techniques have gained much importance. But these methods need to know ahead of time where the structure's natural frequency ranges are, and they use steerable pyramids, which are complicated multi-scale image decomposition filters. To address these issues, a blind modal identification technique is suggested to extract the modal parameters (modal frequency and mode shapes) from the recorded structural vibration video signal. The proposed algorithm for unsupervised machine learning is the Non-Negative Matrix Factorization (NNMF) method, which is combined with the Generalized Complexity Pursuit (GCP) method for blind source separation. The NNMF algorithm is directly applied to the raw pixel-time series made from the video data to get the temporal components, which are then separated using GCP to find the individual modal frequencies and mode shapes. The above algorithm is first validated on a numerical model and then implemented on laboratory scale models (cantilever, single-degree, and multi-degree frame models). Finally, the proposed methodology is implemented on real-world recorded structural vibration videos to determine its noise sensitivity, such as the Tacoma Narrows bridge and the London Millennium footbridge. The modal parameters extracted are compared with those from the available literature for validation. The estimation errors obtained from all the validations are well below 1%, which makes the technique quite suitable and reliable for structural vibration monitoring by identifying and reproducing complex vibration modes.

Vibration Characteristics Analysis of Twin-Screw Compressor Shell Based on the Fluid-Solid Coupling Method

Under the action of the flow field force and the constraint reaction force of the negative rotor and the positive rotor, the twin screw compressor shell will produce vibration, which will affect the life of the parts and produce noise. The rotors restraint reaction force are calculated by fluid-structure coupling method. The shell inherent frequency is solved by modal analysis, and the shell resonance is analyzed during the rotors meshing process. On this basis, the flow field force and rotor constraint reaction force are used as the compressor shell vibration excitation sources, and the vibration response of the compressor shell under the action of excitation force is studied. The research results can provide some reference for the optimized design of compressor shell structure.

Wave excitation force prediction for arrays of wave energy converters in directional waves

The implementation of advanced control strategies is an effective means of maximizing the energy production of wave energy converters (WECs), and most of them require future wave excitation forces to determine the optimal control sequence. The WECs deployed in arrays can enable a significant reduction in the cost of wave energy and improve prediction performance by incorporating excitation forces from the array. In this paper, a critical comparison of the excitation prediction methods, including the time series, machine learning, and neural network, for a two-body heaving point absorber WEC is presented. Considering the symmetry of the WEC and arrays, the directional spectrum is utilized to determine the reference measurement of wave excitation. The prediction methods are applied to isolated WEC and different array layouts. Moreover, additional sensitivity analyses are performed to evaluate the performance. The results show that the autoregressive with extra input (ARX) model has the best performance in short-term wave excitation force prediction. In most cases, the ARX model is weakly influenced by the sampling period and can adapt well to changes in the directional distribution and sea states of irregular waves, and the ARX model requires the least amount of computational time in the simulations.

Wave blocking performance of the symmetrical double-wing floating breakwater

In this paper, a double-wing floating breakwater (DWFB) is proposed, that is, the wing with a curved upper surface and flat lower surface is installed on both sides of the box-type floating breakwater (FB). The analytical model of the DWFB under wave action is established to solve the wave diffraction problem. The modified mild slope equation (MMSE) is used to deal with the unsteady water depth problem above the wing, and the reflection coefficient, transmission coefficient, and the wave excitation force in the surge, heave, and pitch are obtained. After the analytical model is verified, the effect of the wing shape and wing size (height and length) on the wave blocking performance of the DWFB is analyzed, and then the single-wing FB and DWFB are compared. The results show that the increase in wing length is obvious to reduce the transmission coefficient. The single-wing floating breakwater (SWFB) with a longer wing length but similar cross-sectional area to the DWFB has a smaller transmission coefficient when the wave number is between 0.45 and 0.85. However, as the wave number continues to increase, the wave blocking performance of the DWFB is relatively better.

Identification of system parameters of a large‐scale dynamic multiaxial testing facility

AbstractLarge‐scale multiaxial testing facilities mainly serve to experimentally examine the horizontal behavior of full‐scale critical structural members, such as columns and seismic isolation bearings, on which a large vertical compression load is exerted as they simultaneously undergo horizontal deformation. The system friction and inertia force play an important role in obtaining sufficiently reliable test results, and it is not easy to comprehensively grasp all the issues involved. To understand the system friction and inertia force of the Bi‐Axial Dynamic Testing System (BATS) at the National Center for Research on Earthquake Engineering Tainan laboratory and to avoid complexity caused by specimens as much as possible, a lubricated flat sliding bearing is chosen as the specimen to be tested under horizontal triangular and sinusoidal reversed loading together with a constant vertical compression load. When no specimens are installed, that is, without vertical compression loading, the system friction of BATS generated by the various sliding surfaces can be identified and mathematically characterized using the horizontal triangular reversed loading test results; then, the effective mass of BATS can be estimated using the horizontal sinusoidal reversal loading test results to solve the inertia force problem. When applying a vertical compression load, it is assumed that the system friction of BATS and the shear force of the specimen are simply related to the applied total normal force (or vertical compression load) and horizontal excitation rate. An iteration methodology is proposed to identify and mathematically describe the dependency of the friction performance of BATS and the specimen on total normal forces (or vertical compression loads) and horizontal excitation rates by iterating the horizontal triangular and sinusoidal reversed loading test results. Finally, a lead‐rubber bearing and a direct force measurement system are connected in series such that the measurement system precludes the system friction and inertia force and a series of tests are conducted. The reliability of the proposed mathematical model for BATS and the feasibility of the proposed direct force measurement strategy are further demonstrated by comparing the calibrated force response with the directly measured response.