Suppression Of Mechanical Vibrations Research Articles

Mechanical vibration absorber for flexural wave attenuation in multi-materials metastructure

Vibration isolation is a promise to suppress mechanical vibration from a host structure, similarly, a mechanical vibration absorber, a simple but effective device to attenuate flexural wave propagation, which has been implemented in civil and mechanical engineering. This paper presents a type of composite sandwich phononic crystal to attenuate the flexural wave propagation in a beam structure, which can effectively suppress mechanical vibration in a broad band gap by repetitively arranging phononic crystal. First, the elastic wave dispersion characteristic in a composite sandwich beam structure is derived, and a triangular shape phononic crystal for flexural wave attenuation by taking advantage of destructive interference is presented. Then two dimensional phononic crystals are designed by assembling four different unit-cells of metabeam. Finally, numerical experiments are conducted to verify the effectiveness of the proposed mechanical metamaterial absorbers to attenuate flexural wave propagation, the numerical results indicate that the proposed metamaterial is of good performance in mechanical vibration suppression, which can effectively mitigate structure vibration in low-frequency domain than the structure without phononic crystal and single layer metamaterial beam structure. It is the first attempt to design a mechanical metamaterial absorber with the mechanism of destructive interference with composite sandwich phononic crystal.

Variational optimality condition in control of hyperbolic systems with boundary delay parameters

An optimal control problem of a first-order hyperbolic system is studied, in which a boundary condition at one of the ends is determined from a controlled system of ordinary differential equations with constant state lag. Control functions are bounded and measurable functions. The system of ordinary differential equations at the boundary is linear in state. However the matrix of coefficients depends on control functions. Therefore, the optimality condition of Pontryagin’s maximum principle type in this problem is a necessary, but not a sufficient optimality condition. In this paper, the problem is reduced to an optimal control problem of a special system of ordinary differential equations. The proposed approach is based on the use of an exact formula of the cost functional increment. The reduced problem can be solved using a wide range of effective methods used for optimization problems in systems of ordinary differential equations. Problems of this kind arise when modeling thermal separation processes, suppression of mechanical vibrations in drilling, wave processes and population dynamics.

A comprehensive performance comparison of linear quadratic regulator (LQR) controller, model predictive controller (MPC), $$H_{\infty }$$ loop shaping and $$\mu $$-synthesis on spatial compliant link-manipulators

Position control and mechanical vibration suppression are still open problems in compliant link mechanisms. Operation and accuracy improvements of manipulators can be made by finding solutions for these problems. This paper presents a comprehensive performance comparison between controllers (two of them robust controllers) to control position and reduce mechanical vibration over a compliant link-manipulator in a three-dimensional environment: (i) linear quadratic regulator, (ii) model predictive controller, (iii) $$H_{\infty }$$ loop shaping, and (iv) $$\mu $$ -synthesis. The comparisons of controllers are made based on position tracking, vibration damping and control effort in the simulation environment by taking the gravity effect into account. Finally, the paper makes a conclusion by providing some information about main purpose, advantages and disadvantages of each controller in compliant link-manipulator applications.

Direct measurement of high-frequency viscoelastic properties of pre-deformed rubber

Rubber is an effective and low-cost material for mechanical vibration suppression because in the glass-transition zone it exhibits high damping abilities. However, analytical predictions of the viscoelasticity of rubber are inaccurate because viscoelasticity depends on the frequency, amplitude and pre-deformation; this inaccuracy impedes the mechanical design of rubber parts. Previously, viscoelasticity measurements under uniaxial deformation have been performed. However, the dominant parameters cannot be clarified in these tests because the strain distribution is not uniform, and the shear strain and hydrostatic pressure are cross-coupled. In this research, a new test method was studied that enabled the direct measurement of the high-frequency viscoelasticity of rubber by independently applying simple shear pre-strain and hydrostatic pressure. The viscoelasticity of nitrile rubber was measured using this method at frequencies from 200 Hz to 2000 Hz under shear pre-strain and pre-compression. The results showed that hydrostatic pressure had a much larger influence than shear pre-strain. The hydrostatic pressure should be considered as a more essential parameter than the stretch or strain in this material.

Prediction-based control of linear input-delay system subject to state-dependent state delay - Application to suppression of mechanical vibrations in drilling

In this paper, we consider linear dynamics subject to a distributed state-dependent delay and a pointwise input-delay. We propose a prediction-based controller which exponentially stabilizes the plant. The controller design is based on a backstepping approach where delays are reformulated as hyperbolic transport PDEs. Infinity-norm stability analysis of the corresponding closed-loop system is addressed. We show that this result is of interest to suppress mechanical vibrations arising in drilling facilities, which have been attributed recently to a coupling between torsional and vertical displacement involving an implicit state delay equation. Numerical simulations illustrate the merits of our controller in this context.

Piezo-electromechanical smart materials with distributed arrays of piezoelectric transducers: Current and upcoming applications

This review paper intends to gather and organize a series of works which discuss the possibility of exploiting the mechanical properties of distributed arrays of piezoelectric transducers. The concept can be described as follows: on every structural member one can uniformly distribute an array of p iezoelectric transducers whose electric terminals are to be connected to a suitably optimized electric waveguide. If the aim of such a modification is identified to be the suppression of mechanical vibrations then the optimal electric waveguide is identified to be the `electric analog' of the considered structural member. The obtained electromechanical systems were called PEM (PiezoElectroMechanical) structures. The authors especially focus on the role played by Lagrange methods in the design of these analog circuits and in the study of PEM structures and we suggest some possible research developments in the conception of new devices, in their study and in their technological application. Other potential uses of PEMs, such as Structural Health Monitoring and Energy Harvesting, are described as well. PEM structures can be regarded as a particular kind of smart materials, i.e. materials especially designed and engineered to show a specific and well-defined response to external excitations: for this reason, the authors try to find connection between PEM beams and plates and some micromorphic materials whose properties as carriers of waves have been studied recently. Finally, this paper aims to establish some links among some concepts which are used in different cultural groups, as smart structure, metamaterial and functional structural modifications, showing how appropriate would be to avoid the use of different names for similar concepts.

Micromechanical theoretical and computational modeling of energy dissipation due to nonlinear vibration of hard ceramic coatings with microstructural recursive faults

Engine failures due to high-cycle fatigue during severe dynamic vibration have cost the US Air Force an estimated $400 million dollars per year over the past two decades. Therefore, structural materials that exhibit high damping capacities are desirable for mechanical vibration suppression and acoustic noise attenuation. Few experimental studies suggested that hard ceramic coatings, which are commonly used as thermal barrier coatings (TBCs) to protect engine components from high temperatures and corrosion, can also serve as passive dampers due to their unique microstructure which consists of several layers of splats with inter- and intra-microstructural recursive faults (micro-cracks). Therefore, the focus of this study is on the development of a fundamental understanding of the unique microstructural features and mechanisms responsible for this observed energy dissipation in ceramic coatings under nonlinear vibration through the development of a micromechanical computational framework. Inter- and intra-fatigue damage and internal friction is simulated through the development of thermodynamic-based nonlinear cohesive laws that consider interfacial degradation, debonding, plastic sliding, and Coulomb/contact friction between the interfaces of microstructural faults. Representative volume element-based micromechanical simulations are conducted in order to assess the main micromechanical mechanisms responsible for the experimentally observed nonlinear (amplitude- and frequency-dependent) damping in plasma sprayed hard ceramic coatings. It is concluded that the major part of energy dissipation is achieved through contact friction which results from sliding of the splat interfaces along the microstructural recursive faults. Energy dissipation due to progressive decohesion and evolution of new micro-cracks is not that significant as compared to energy dissipated due to increased friction from existing and new created faults. Therefore, internal friction is the main mechanism that makes TBCs effective dampers.

Equivalent Mechanical and Electrical Models of the Vibration Suppression System Using Piezoelectric Elements

This paper describes the equivalent mechanical and electrical models for systems of the vibration suppression in flexible structures using piezoelectric elements. There are two main methods to suppress vibration of flexible structures. One is active vibration control and the other is passive vibration suppression. Because they include both mechanical and electrical systems, the mechanism of the vibration suppression is complicated and can not be understood easily. To make matters worse, the knowledge of the mechanical vibration suppression device and the electrical circuit are not utilized in those systems with piezoelectric elements. Hence, this paper describes the way to derive the equivalent mechanical and electrical models. Using those equivalent models, the mechanism of the vibration suppression can be easily comprehended and the knowledge of mechanical and electrical systems can be applied effectively.

The Leipzig high-energy ion nanoprobe: A report on first results

The high-energy ion nanoprobe LIPSION at the University of Leipzig has been operational since October 1998. Its magnetic quadrupole lens system, arranged as a separated Russian quadruplet, has been developed by the Microanalytical Research Centre (MARC), Melbourne. The ultrastable single-ended 3.5 MV SINGLETRON™ accelerator (High Voltage Engineering Europa) supplies H + and He + ion beams with a beam brightness in the range of 10–20 A rad −2 m −2 eV −1 [D.J.W. Mous, R.G. Haitsma, T. Butz, R.-H. Flagmeyer, D. Lehmann, J. Vogt, Nucl. Instr. and Meth. B 130 (1997) 31]. Due to this high brightness, the excellent optical properties of the focusing system of the nanoprobe and the suppression of mechanical vibrations, lateral resolutions of 100 nm for the low current mode (STIM) and 340 nm at a current of 10 pA (PIXE, RBS, SEI modes) were achieved. Further improvements are expected.

Modeling the time-dependent growth of single-crystal fibers

A model is developed to simulate time-dependent behavior in laser-heated miniature pedestal growth (LHPG) of single-crystal fibers. This process is meniscus controlled since the diameter of the growing fiber changes in response to variations between the equilibrium and the instantaneous contact angle at the melt/solidifying-solid interface. One of the operational problems associated with the LHPG technique is controlling diameter fluctuations in the growing fiber due to process perturbations. Smooth source feed and fiber pull rates, steady laser-heat input, and suppression of mechanical vibrations are necessary to achieve a constant fiber diameter. We derive a system of time-dependent, one-dimensional equations of motion and heat transfer as the leading order equations in an asymptotic expansion based upon the melt slenderness ratio (fiber radius/melt height). This system is solved numerically to predict the thermal profiles, mean positions of the melting and solidifying fronts, melt/gas interface, melt volume, and fiber diameter. System response to perturbations in the pull rates, thermal environment, and gravitational field is investigated.

Analysis and compensation of speed drive systems with torsional loads

This paper proposes a fast and robust speed controller for motor drive systems having torsional loads and containing a gear backlash. The controller is designed using the state feedback technique combined with state variable observers and is implemented on a digital signal processor. Analysis, simulation and experimental results of a prototype speed drive system are presented and discussed. It is shown that the proposed speed controller yields a robust system with respect to system uncertainties and modeling errors and is very effective for the suppression of mechanical vibrations. >