Range Of Excitation Frequencies Research Articles

Effect of Multi-Material Substitutions on Static and Dynamic Properties of Electric Vehicles

Automotive weight reduction is a challenging task due to many performance targets that must be satisfied simultaneously, in particular in terms of static and dynamic properties direct relating to strength, stiffness and NVH characteristics of vehicles. Compared to all-steel vehicle frame, multi-material substitutions are adopted in each structural component for higher product performance and a lightweight electric vehicle frame in this paper. The SHELL63 element is selected to construct finite element (FE) model of vehicle frame based on the FEA software ANSYS. Under full bending loading and torsional loading respectively, static analysis of frame is performed, and the strength and stiffness are evaluated as well. The Block Lanczos is adopted for dynamic analysis of vehicle frame. Their first eight modal properties are obtained and far away exciting frequency range of rough road. The multi-material vehicle frame has been designed to be made of mild steel, aluminum and magnesium alloys. Its static and dynamic properties show that the strength, stiffness and NVH characteristics are better than ones from all-steel vehicle frame with weight reduction of 31.7%. These procedures will help to design a lightweight and thus to provide technical support for reducing fuel consumption and greenhouse gas emissions.

Phase diagram of magnetic vortex dynamics

The dynamics of a magnetic vortex are influenced profoundly by nonlinear effects at large and small amplitudes. For example, a strongly driven magnetic vortex is unstable with respect to internal deformation, leading to reversal of its core magnetization. At small amplitudes, a nonlinear response is associated with pinning of the vortex core. Given these phenomena, there is an acute need for a global picture of vortex dynamics over a wide range of excitation amplitudes and frequencies. We have constructed a phase diagram of vortex dynamics in permalloy (Ni${}_{80}$Fe${}_{20}$) disks by probing the response spectrum over four orders of magnitude in excitation power. We identify the boundary separating pinned and unpinned dynamics in a phase space of amplitude and frequency. Our approach allows for a highly quantitative analysis of the pinning potential for localized defects and can be used to trace the dynamics of a single vortex from deep in the pinning regime to the onset of core reversal.

On the performance of a dual-mode non-linear vibration energy harvesting device

The research trend for harvesting energy from the ambient vibration sources has moved from using a linear resonant generator to a non-linear generator in order to improve on the performance of a linear generator; for example, the relatively small bandwidth, intolerance to mistune and the suitability of the device for low-frequency applications. This article presents experimental results to illustrate the dynamic behaviour of a dual-mode non-linear energy-harvesting device operating in hardening and bi-stable modes under harmonic excitation. The device is able to change from one mode to another by altering the negative magnetic stiffness by adjusting the separation gap between the magnets and the iron core. Results for the device operating in both modes are presented. They show that there is a larger bandwidth for the device operating in the hardening mode compared to the equivalent linear device. However, the maximum power transfer theory is less applicable for the hardening mode due to occurrence of the maximum power at different frequencies, which depends on the non-linearity and the damping in the system. The results for the bi-stable mode show that the device is insensitive to a range of excitation frequencies depending upon the input level, damping and non-linearity.

NDT sensor design optimization for accurate crack reconstruction

Purpose – The inverse problem related to eddy current testing (ECT) is often formulated as a shape optimization problem. The purpose of this paper is to propose a methodology for determining the optimal parameters of a sensor system for more accurate reconstruction of the crack shape.Design/methodology/approach – In this paper, an objective function is formulated using the shape sensitivity information computed from the ECT data. The design of a non‐destructive testing (NDT) sensor is carried out through optimizing the sensor parameters under such a criterion.Findings – The methodology proposed results in modifications to the original sensor geometry which makes it more sensitive to the depth changes in a crack. A square wave form of excitation is used in order to provide more information on the size of the crack at different depths, essentially through the superposition of a range of excitation frequencies, each of which has a different depth of penetration. The newly designed ECT sensor system is suitab...

BIFURCATION CONTROL OF A PARAMETRIC PENDULUM

In this paper, we apply chaos control methods to modify bifurcations in a parametric pendulum-shaker system. Specifically, the extended time-delayed feedback control method is employed to maintain stable rotational solutions of the system avoiding period doubling bifurcation and bifurcation to chaos. First, the classical chaos control is realized, where some unstable periodic orbits embedded in chaotic attractor are stabilized. Then period doubling bifurcation is prevented in order to extend the frequency range where a period-1 rotating orbit is observed. Finally, bifurcation to chaos is avoided and a stable rotating solution is obtained. In all cases, the continuous method is used for successive control. The bifurcation control method proposed here allows the system to maintain the desired rotational solutions over an extended range of excitation frequency and amplitude.

Nonlinear liquid sloshing in a square tank subjected to obliquely horizontal excitation

AbstractNonlinear responses of surface waves in rigid square and nearly square tanks partially filled with liquid subjected to obliquely horizontal, sinusoidal excitation are investigated theoretically and experimentally. Two predominant modes of sloshing are significantly coupled nonlinearly because their natural frequencies are nearly identical resulting in 1:1 internal resonance. Therefore, if only one of these modes is directly excited, the other mode is indirectly excited due to the nonlinear coupling. In the nonlinear theoretical analysis, the modal equations of motion are derived for the two predominant sloshing modes as well as five higher sloshing modes. The linear viscous terms are incorporated in order to consider the damping effect of sloshing. The expressions for the frequency response curves are determined using van der Pol’s method. The influences of the excitation direction and the aspect ratio of the tank cross-section on the frequency response curves are numerically examined. Planar and swirl motions of sloshing, and Hopf bifurcations followed by amplitude modulated motions including chaotic motions, are predicted when the excitation frequency is close to one of the natural frequencies of the two predominant sloshing modes. Lyapunov exponents are calculated and reveal the excitation frequency range over which liquid chaotic motions occur. In addition, bifurcation sets are shown to clarify the influences of the parameters on the change in the structural stability. The theoretically predicted results are in good agreement with the measured data, thus the theoretical analysis was experimentally validated.

An innovative multi dof TMD system for motorcycle handlebars designed to reduce structural vibrations and human exposure

Motor vehicle ride comfort is mainly affected by reciprocating engine inertia unbalances. These forces are transmitted to the driver through the main frame, the engine mounts, and the auxiliary sub systems—all components with which he physically comes into contact.On-road traction vehicle engines are mainly characterized by transient exercise. Thus, an excitation frequency range from 800 RPM (≈15Hz for stationary vehicles) up to 15,000 RPM (≈250Hz as a cut off condition) occurs. Several structural resonances are induced by the unbalancing forces spectrum, thus exposing the driver to amplified vibrations.The aim of this research is to reduce driver vibration exposure, by acting on the modal response of structures with which the driver comes into contact.An experimental methodology, capable of identifying local vibration modes was developed. The application of this methodology on a reference vehicle allows us to detect if/when/how the above mentioned resonances are excited.Numerical models were used to study structural modifications. In this article, a handlebar equipped with an innovative multi reciprocating tuned mass damper was optimized.All structural modifications were designed, developed and installed on a vehicle. Modal investigations were then performed in order to predict modification efficiency.Furthermore, functional solution efficiency was verified during sweep tests performed on a target vehicle, by means of a roller bench capable of replicating on-road loads. Three main investigation zones of the vehicle were detected and monitored using accelerometers: (1) engine mounts, to characterize vibration emissions; (2) bindings connecting the engine to the frame, in order to detect vibration transfer paths, with particular attention being paid to local dynamic amplifications due to compliances and (3) the terminal components with which the driver comes into contact.

Electronic coherence lineshapes reveal hidden excitonic correlations in photosynthetic light harvesting

The effective absorption cross-section of a molecule (acceptor) can be greatly increased by associating it with a cluster of molecules that absorb light and transfer the excitation energy to the acceptor molecule. The basic mechanism of such light harvesting by Förster resonance energy transfer (FRET) is well established, but recent experiments have revealed a new feature whereby excitation is coherently shared among donor and acceptor molecules during FRET. In the present study, two-dimensional electronic spectroscopy was used to examine energy transfer at ambient temperature in a naturally occurring light-harvesting protein (PE545 of the marine cryptophyte alga Rhodomonas sp. strain CS24). Quantum beating was observed across a range of excitation frequencies. The shapes of those features in the two-dimensional spectra were examined. Through simulations, we show that two-dimensional electronic spectroscopy provides a probe of the adiabaticity of the free energy landscape underlying light harvesting.

Bipolar pulsed excitation of erbium-doped nanosilicon light emitting diodes

High quantum efficiency erbium doped silicon nanocluster (Si-NC:Er) light emitting diodes (LEDs) were grown by low-pressure chemical vapor deposition (LPCVD) in a complementary metal-oxide-semiconductor (CMOS) line. Erbium (Er) excitation mechanisms under direct current (DC) and bipolar pulsed electrical injection were studied in a broad range of excitation voltages and frequencies. Under DC excitation, Fowler-Nordheim tunneling of electrons is mediated by Er-related trap states and electroluminescence originates from impact excitation of Er ions. When the bipolar pulsed electrical injection is used, the electron transport and Er excitation mechanism change. Sequential injection of electrons and holes into silicon nanoclusters takes place and nonradiative energy transfer to Er ions is observed. This mechanism occurs in a range of lower driving voltages than those observed in DC and injection frequencies higher than the Er emission rate.

Axis-switching and breakup of low-speed elliptic liquid jets

Theoretical and experimental investigations are conducted to analyze the instability of a low-speed liquid jet emerging from an elliptic nozzle. The complexity of viscous free surface flow analysis for an asymmetric geometry is simplified using an approach based on the Cosserat theory (also called director theory) which reduces the exact three-dimensional equations to a system depending only on time and on a single spatial variable. This work is mainly focused on the spatial instability analysis to examine the key characteristics of an elliptic jet such as jet profile, axis-switching and breakup length. In the experimental part, both natural (free) and excited (forced) breakup behaviors are studied. In the natural breakup, the effects of nozzle’s ellipticity and length to diameter ratio are examined. In the forced breakup case, disturbances are applied to the jet, by modulating the jet exit velocity using a piezoelectric actuator with given sinusoidal perturbations. The spatial evolution of the jet shape is captured with a high speed camera. Liquid jet instability is studied for various nozzle geometries over a specific range of jet velocities and excitation frequencies. Results are compared with conventional circular nozzles which can be considered as a special case of an elliptic jet.

Innovative Wavy Bolts and their Supporting Mechanism for Burst Prone Rock Masses

A new type of bolt with wavy body has been designed for the supporting of burst prone rock masses and turned out to be a great success. To reveal its working mechanism, static and dynamic analyses have been carried out. Firstly, static pull-out investigations show that wavy body of the bolt has largely improved its deformation capability. Then, vibration modes and corresponding frequencies of wavy bolts and traditional point anchored bolts are obtained respectively by mode analyses. It is revealed that, at the same exciting frequency range, more vibration modes, especially the axial vibrations, can be excited for wavy bolts than for traditional bolts. Furthermore, Analyses on wave interaction between bolt and rock masses show that the energy catcher function of wavy bolt cluster is vital for its excellent supporting effect in burst prone rock masses.

Dynamic Modeling and Analysis of Mechanical Snubbing

This paper presents four alternate models of varying complexity to examine mechanical snubbing in elastomeric isolators. Although the modeling, analysis, and experimentation presented is limited to snubbing of elastomeric isolators, the models are generic and can be adapted to other snubbing mechanisms as well, such as friction snubbing. Two of the four models presented in this paper use the Bouc–Wen model in order to capture hysteresis and gradual stiffening behavior, which is generally exhibited by elastomeric snubbing systems. The other two models are relatively simplistic and do not account for a time-varying parameter to model significant hysteresis. However, these two models can still be useful for applications with a small range of excitation frequencies and for applications where the snubbing design needs to incorporate an abrupt transition in stiffness. A parameter identification technique is used to determine the variables associated with each model. The parameter identification technique is based on the use of an optimization algorithm associated with the force–displacement characterization. All four models presented in this paper capture the coupled dynamics of the isolation system and the snubbing system and are, therefore, a significant improvement upon the currently used models. The models presented are expected to facilitate the design and analysis of a passive isolation system in conjunction with the design of the snubbing system and the base frame supporting the snubbing system.

Design of 'road friendly' suspensions for quarter and half heavy goods vehicle models by using genetic algorithm and a multi-objective performance index

The main objective of present study is to design a road friendly suspension (which minimises road damage) for a heavy goods vehicle (HGV). Quarter HGV model and half HGV model are used to represent vehicle dynamics. Genetic algorithm has been used for optimisation. It is shown that, for less road damage, soft suspension spring and hard damper are required. For half HGV, the tyre station that has more road damaging potential has been optimised more. Even though the suspension is optimised for a uniform vehicle speed on a given random road profile, the optimised suspension is shown to perform well over a wide frequency range for a sinusoidal road excitation. It is also shown that the optimised passive suspension performs well for hump road input. A comparative study between multi-objective performance index and road damage performance index alone is also presented.

Magnetic Properties Measurement of Soft Magnetic Composite Materials Over Wide Range of Excitation Frequency

Accurate measurements of magnetic properties of soft magnetic composite (SMC) material are performed on an improved 3-D tester by means of novel precision B-H sensing coils attached to the surface of a cubic SMC specimen. By controlling the adjustable excitation topologies, magnetic properties over wide excitation frequency range from 2 Hz to 1000 Hz are acquired and analyzed. In this paper, the relationship between the magnetic flux density vector B and magnetic field strength vector H has been systematically measured under alternating and 3-D conditions, and the core loss features have been analyzed. Compared with the conventional magnetic properties only at 50 Hz, wide-range-frequency magnetic properties contribute to extending application area of the new SMC electrical machines.

An experimental study on a generalized Maxwell model for nonlinear viscoelastic dampers used in seismic isolation

Long-stroke fluid dampers may be installed under seismic isolation systems to provide supplementary damping. Due to the larger vibration amplitude and velocity, highly nonlinear viscoelastic behavior may exist in a long-stroke fluid damper. In order to accurately simulate the hysteretic behavior of such a damper, this paper presents and experimentally verifies a mathematical model called the generalized Maxwell model (GMM). Similar to the classic Maxwell model, the GMM is composed of a stiffness and a viscous elements connected in series. However, nonlinearity is incorporated into both elements of the GMM by assuming that their resistant forces are exponential functions of the relative velocity and deformation of the damper. By adjusting the two exponential coefficients, the GMM is able to simulate the more complicated viscoelastic behavior of fluid dampers. The GMM is reduced to the Maxwell model when both exponential coefficients are set to one. To verify the GMM, both an element test with harmonic excitations and a shaking table test with seismic excitations were conducted for a long-stroke fluid damper with highly nonlinear viscoelastic behavior. The result of the element test confirms that the GMM model is very accurate in simulating the hysteretic property of the fluid damper under a wide range of excitation frequencies, while the classic Maxwell and the viscous models may only be accurate under a certain excitation frequency. Moreover, the shaking table test, in which the fluid damper is used to provide supplementary damping for a sliding isolation system, demonstrates that the GMM is able to more accurately predict the amount of energy dissipation by the damper and also the peak isolator drift of the isolation system, especially for an earthquake with a long-period pulse.

Field Testing and Investigation of the Dynamic Performance and Comfort of Timber Floors

Field tests were conducted on timber floors in three wood-framed buildings in order to obtain their dynamic characteristics and evaluate the vibration comfort. The measured fundamental vibration frequency, damping ratio and root-mean-square acceleration, were used to evaluate human comfort caused by timber floor vibration. The results show that the fundamental vibration period of the thirteen tested timber floors was between 9.96Hz and 18.70Hz, which is sufficiently outside the frequency range of human activities excitation to preclude the resonance of timber floors. The thirteen timber floors in the test program satisfied the vibration control standards when the vibration environments and duration were taken into consideration. The damping ratios of the timber floors show a strong amplitude dependence, with high damping ratios correlated with large vibration amplitude. The average value of the damping ratio obtained from the impulse load tests was 5.05%, which was suitable for timber floors under normal human activities. In practice, vibration should be considered during the design of large-span timber floors.

State transitions in the Duffing resonator excited by narrow band random noise

The Dufffing hardening spring resonator has the status of a canonical model for nonlinear vibrations. Over a limited range of excitation frequencies and depending on the degree of nonlinearity, it has three states of response to sinusoidal excitation, one of which is unstable. The system will remain stably in either of the other two states depending on the history of excitation: in a higher energy state for the frequency ascending and in the lower energy state for the frequency descending. When the sinusoidal excitation is replaced by narrow band random excitation, the author showed in a 1961 paper experimentally that the system could make transitions between these two states and argued that the fluctuating phase of the excitation would allow the source to inject or draw energy from the resonator allowing a transition from one state to the other. This presentation develops a dynamic model for the system that allows energy transmission between the source and resonator and an indicator of the state of response based on instantaneous impedance.

Dynamic response of a nuclear fuel rod impacting on elastoplastic gapped supports

The paper concerns the study of the vibrational behavior of a fuel rod supported by elastoplastic supports. Nuclear fuel rods in reactor conditions are always exposed to turbulent flow, which in turn creates random vibrations. Shock vibration can also occur as a result of unwanted conditions, such as seismic and LOCA accidents. Excessive external forces can induce plastic deformation in the nuclear fuel rod. Therefore, a bilinear elastoplastic contact force model is utilized to simulate nonlinear behavior, and the plastic deformation of the supports is computed based on a predictor–corrector scheme. Once the contact force exceeds the yielding point, it can be shown that the supports behave nonlinearly, and that the gap becomes larger due to the plastic deformation. Three categories of vibration – harmonic, random, and shock vibration – are dealt with in this work. The elastoplastic response of supports subjected to such vibrations is reviewed, and the stress levels developed in the fuel cladding is evaluated. It has been found that the minimum required force to cause plastic deformation is dependent on excitation frequency as well as gap size, but it can be seen that the excitation frequency range is more sensitive for random vibrations. For all simulation cases, the stress level of the fuel cladding is below the yield limit, and results show that the most severe conditions are induced by random vibrations in terms of the stress intensity.

Design of a solenoid valve based active engine mount

This paper describes the design of a versatile and fully controllable active engine mount. The proposed active mount is capable of addressing vibration isolation requirements at various driving conditions. This design addresses a better ride quality that has always been demanded by the automotive industry, as well as satisfying sophisticated vibration isolation requirements for the unconventional engines, i.e. variable displacement, and hybrids. The proposed engine mount replaces the decoupler of the original design with a solenoid actuator. The mathematical model of the active mount is obtained. The dynamic characteristics of the mount are shown to be highly controllable over the operating frequency range of excitation in engines. The effectiveness of the developed active engine mount for various working conditions of engine is also evaluated. Several driving conditions are investigated and proper control strategies are utilized to demonstrate the mount's capability to fulfill the isolation requirements for each condition. The promising results, in addition to compactness, low cost, fail safety, and durability are the main advantages of the proposed active engine mount, which makes it viable for automotive applications.

Optimum Design of Engine Test Bench Based on Finite Element Analysis

A test bench of vehicle engine is designed and the three-dimensional solid model is established in UG software. Then the model is imported into ANSYS software to conduct static stress analysis, the stress and deformation distribution of test bench are obtained, referenced the results and the bracket are optimized to improve support ability, the maximum stress and the maximum displacement of test bench decreased 66.9% and 76.9%, respectively. Lastly modal analysis of test bench is performed, the chassis base is strengthen design according to the first-order mode shape, then the first natural vibration frequency is heightened 91.0%, it is far away from the engine excitation frequency range, the stability of test bench is enhanced.