Vibration Isolation From Harmonic Disturbances Through Use of Internally Rotating Masses

This paper considers the use of a chain of translating carts or housings having internally rotating eccentric masses in order to accomplish vibration isolation. First a single degree-of-freedom system is harmonically excited to uncover the qualitative behavior of each rotating mass. The simple model is then expanded into a chain of housings, containing rotating eccentric masses, which are interconnected with springs. The internal rotating eccentric masses are damped along their circular pathway by means of linear viscous damping. Due to the lack of elastic or gravitational constraint on the rotating eccentric masses, they provide a nonlinear inertial coupling to their housings. Previous research has shown that such systems are capable of reducing shock or impulsive loading by converting some of the translational kinetic energy into rotational kinetic energy of the internal masses. This paper examines the potential for vibration isolation of a chain of such systems subjected to persistent, harmonic excitation. It is seen that the dynamics of these systems is very complicated, but that trends are observed which have implications for practical isolation systems. Using simulation studies, tradeoffs are examined between displacement and transmitted force for a range of physical parameter values.

Research on the Piezoelectric Ultrasonic Actuator Applied to SFSS

This paper presents an investigation of a novel linear-type piezoelectric ultrasonic actuator for application in a Smart Fuze Safety System (SFSS). Based on the requirements of SFSS, the structural parameters of the proposed piezoelectric ultrasonic actuator are determined by fuze arming mode. Moreover, sensitivity analysis of the structural parameters to the frequency consistency is conducted using FEM software, after which the optimal dimensions are obtained with two close natural vibration frequencies. To validate the results of FEM, the frequency sweep tests of the piezoelectric ultrasonic actuator are performed to determine the motor’s actual working mode frequencies with PSV-300-B Doppler laser vibrometer system. Furthermore, the results of frequency sweep test are compared with that of the finite element analysis, and further verified by impedance analyzer. To investigate the overall performance of the piezoelectric ultrasonic actuator, vibration modes of actuator’s stator, output speed and force of the piezoelectric ultrasonic actuator are tested. The experimental results show that the output speed and force of the actuator can reach 88.2 mm/s and 2.3N respectively, which means that piezoelectric ultrasonic actuator designed in this paper can meet the demands of the SFSS.

An Electrochemical Model Based Optimal Charging Algorithm for Lithium-Ion Batteries

In recent years, Lithium-Ion battery has gathered lot of importance in many forms of energy storage applications due to its overwhelming benefits. Any battery pack alone cannot achieve its optimal performance unless there is a robust and efficient energy management system, commonly known as battery management system or BMS. The Lithium-Ion charger is a voltage-limiting device that is similar to the lead acid system. The difference lies in a higher cell voltage; tighter voltage tolerance and the absence of trickle or float charge at full charge. In this work, we propose the design of a novel optimal strategy for charging the battery that better suits the battery performance. A performance index is defined that aims at minimizing the effort of regeneration along with a minimum deviation from the rated maximum thresholds for cell temperature and charging current. A more realistic model based on battery electrochemistry is used for the optimal algorithm design as opposed to equivalent circuit models. To solve the optimization problem, Pontryagin’s principle is used which is very effective for constrained optimization problems with both state and input constraints. Simulation results show that the proposed optimal charging algorithm is capable of shortening the charging time of a Lithium Ion cell while maintaining the temperature constraint when compared with the standard constant current charging.

On Primary Resonance of Electrostatically Actuated Double Walled Carbon Nanotube Cantilever Biosensors

This paper investigates electrostatically actuated Double Walled Carbon Nanotubes (DWCNT) cantilever biosensors using the Method of Multiple Scales (MMS) and the Harmonic Balance Method (HBM). Forces acting on the outer tube of the DWCNT are electrostatic, damping, and van der Waals, while only van der Waals acts on the inner tube. The electrostatic actuation is provided by a soft AC voltage. Van der Waals forces are present between the carbon nanotubes, coupling the deflections of the tubes; herein, for modal coordinate transformation, only the linear term of the van der Waals force will be considered. The nonlinearity of the motion is produced by the electrostatic and van der Waals forces. The DWCNT undergoes nonlinear parametric dynamics. MMS is employed to investigate the system under soft excitations and/or weak nonlinearities. The frequency-amplitude response is found in the case of primary resonance. DWCNTs are modelled after the Euler-Bernoulli cantilever beam. The expected nonlinear dynamic behavior is important to improve DWCNT resonator sensitivity in the application of mass sensing.

On Controlling Non-Autonomous Time-Delay Feedback Systems

Time-delay feedback oscillators of non-autonomous type are considered in the paper. These oscillators have been studied extensively for many decades in a broad set of fields such as sensor design, manufacturing, and machine dynamics. A time-delay model system having one time-delay constant and several nonlinear feedback terms in the governing differential equation is first studied. Many researches have demonstrated that a time-delay feedback even in the form of a small perturbation is able to perturb the oscillator to exhibit complex dynamical responses including bifurcation and route-to-chaos. These motions are harmful as they have a very negative impact on the stability, and thus output quality, of the system. For example, manufacturing processes that are characterized by time-delay feedback all have an operation limit on speed because the chaotic behaviors which are unpredictable and extremely unstable are difficult to control. With a viable control solution, the performance, quality, and capacity of manufacturing can be improved enormously. A novel concept capable of simultaneous control of vibration amplitude in the time-domain and spectral response in the frequency-domain has been demonstrated to be feasible for the control of dynamic instability including bifurcation and route-to-chaos in many nonlinear systems. The concept is followed to create a control configuration that is feasible for the mitigation of non-autonomous time-delay feedback oscillators. Featuring wavelet adaptive filters for simultaneous time-frequency resolution and filtered-x least mean square algorithm for online identification, the controller design is shown to successfully moderate the dynamic instability of the time-delay feedback oscillator and unconditionally warrant a limit cycle. The controller design that integrates all these features is able to mitigate dynamical deterioration in both the time and frequency domains and properly regulate the responses with the desired reference signal. Specifically the qualitative behavior of the controlled oscillator output follows a definitive fractal topology before settling into a stable manifold. The controlled response is categorically quasi-periodic and of the prescribed vibration amplitude and frequency spectrum. The control scheme is novel and requires no linearization. By applying wavelet domain analysis approach to the nonlinear control of instability, the true dynamics of the time-delay feedback system as delineated by both the time and frequency information are faithfully retained without being distorted or misinterpreted. Through employing adaptive technique, the high sensitivity of the time-delay feedback system to external disturbances is also properly addressed.

Application of Scaling to Multibody Dynamics Simulations

This paper will examine the importance of applying scaling to the equations of motion for multibody dynamic systems when applied to industrial applications. If a Cartesian formulation is used to formulate the equations of motion of a multibody dynamic system the resulting equations are a set of differential algebraic equations (DAEs). The algebraic components of the DAEs arise from appending the joint equations used to model revolute, cylindrical, translational and other joints to the Newton-Euler dynamic equations of motion. Stability issues can arise in an ill-conditioned Jacobian matrix of the integration method this will result in poor convergence of the implicit integrator’s Newton method. The repeated failures of the Newton’s method will require a small step size and therefore simulations that require long run times to complete. Recent advances in rescaling the equations of motion have been proposed to address this problem. This paper will see if these methods or a variant addresses not only stability concerns, but also efficiency. The scaling techniques are applied to the Gear-Gupta-Leimkuhler (GGL) formulation for multibody problems by embedding them into the commercial multibody code (MBS) Virtual. Lab Motion and then use them to solve an industrial sized automotive example to see if performance is improved.

Damage Detection in Laminated Composite Plates and Shells Using Second Derivatives of Mode Shape Data Through Dynamic Analysis of These Structures

The main objective of this study is to evaluate the dynamics-based techniques for damage detection in laminated composite cantilevered rectangular plates and cylindrical shells with damages in the form of surface macro-level cracks using finite element analysis (FEA). However, the quantitative change in global vibration characteristics is not sufficiently sensitive to local structural damages especially to small size damages. Hence certain parameters called damage indicators based on mode shape curvature, which are the second derivatives of the vibration characteristics (mode shapes), are used in this study to detect the location and size of even small damages accurately in laminated composite structures. The commercial FEA package ANSYS is used for the theoretical modal analysis to generate the natural frequencies and normalized mode shapes of the intact and damaged structures. Experimental investigations are carried out on the laminated plate and shell structural elements to provide a validation of the analysis. Experimental investigations are carried out on the laminated composite (E-glass unidirectional fibers reinforced epoxy resin) cantilevered plate and shell structural elements to provide a validation of the analysis. The effectiveness of these methods is clearly demonstrated by the results obtained.

Dynamic Modelling of an Off-Road Vehicle for the Design of a Semi-Active, Hydropneumatic Spring-Damper System

In this paper a tool integrating a multibody full car model of a tractor and the hydraulic model of the suspension system is presented as a virtual tool able to help the designer and also the control tuning of the system. The full car approach is chosen in order to be able to describe all the vehicles movements (roll, yaw, pitch) while the detailed lumped parameters model of the hydraulic suspensions allows to consider the role of the electrohydraulic valves, accumulator, hydraulic actuator on the vehicle dynamic behaviour. The hydraulic model and the multibody model exchange forces and displacements at the joint points: one between actuator and sprung mass (chassis) and the other one between actuator and unsprung mass (front axle and wheels). Experimental test have been performed (suspension leveling maneuvers, tests on ISO 50008 track, bump tests) and the results of the numerical model have been compared with the experimental data, allowing the understanding of the influence of the numerous design and control parameters involved in the determination of the vehicle dynamic behaviour. The influence of mechanical and geometrical parameters on the damping force hysteresis measured during levelling test are shown and described. Finally, the dynamic behavior of the suspension is analyzed making reference to a dynamic test over a bump.

On Boundary Damping for Semi-Infinite Strings and Beams

In this paper, initial boundary value problems for a linear string and beam equation are considered. The main aim is to study the reflection of an incident wave at the boundary and the damping properties for different types of boundary conditions such as a mass-spring-dashpot for semi-infinite strings, and pinned, sliding, clamped and damping boundary conditions for semi-infinite beams. The system of transverse vibrations are divided into model 1 and model 2 which are described as a string problem and beam problem, respectively. In order to construct explicit solutions of the boundary value problem for the first model the D’Alembert method will be used to the one dimensional wave equation on the semi-infinite domain, and for the second model the method of Laplace transforms will be applied to a beam equation on a semi-infinite domain. It will be shown how waves are damped and reflected for different types of boundaries and how much energy is dissipated at the boundary.

Structural Damage Detection Using Slopes of Longitudinal Vibration Shapes

While structural damage detection based on flexural vibration shapes, such as mode shapes and steady-state response shapes under harmonic excitation, has been well developed, little attention is paid to that based on longitudinal vibration shapes that also contain damage information. This study originally formulates a slope vibration shape for damage detection in bars using longitudinal vibration shapes. To enhance noise robustness of the method, a slope vibration shape is transformed to a multiscale slope vibration shape in a multiscale domain using wavelet transform, which has explicit physical implication, high damage sensitivity, and noise robustness. These advantages are demonstrated in numerical cases of damaged bars, and results show that multiscale slope vibration shapes can be used for identifying and locating damage in a noisy environment. A three-dimensional (3D) scanning laser vibrometer is used to measure the longitudinal steady-state response shape of an aluminum bar with damage due to reduced cross-sectional dimensions under harmonic excitation, and results show that the method can successfully identify and locate the damage. Slopes of longitudinal vibration shapes are shown to be suitable for damage detection in bars and have potential for applications in noisy environments.