Concept Of Mechanical Impedance Research Articles

Vibration impact of rock excavation on nearby sensitive buildings: An assessment framework

As a common construction activity, rock excavation using hydraulic breakers often generates high-level ground- and structure-borne vibrations, which may adversely affect nearby buildings in terms of structural safety, occupant comfort, and ultraprecision equipment functionality. However, building vibrations induced by rock excavation have not been well investigated and understood in the literature. For example, the coupling attenuation at column bases and the floor-to-floor vibration attenuation inside a building have rarely been quantitatively studied. Moreover, traditional dynamic analysis methods in earthquake engineering may not apply to simulations of rock excavation-induced building vibrations. This paper proposed a novel assessment framework based on the mechanical impedance concept, which can quantify the coupling attenuation at column bases and the floor-to-floor vibration attenuation inside a building in a computationally efficient manner. Systematic finite element simulations of rock excavation were performed to characterize vibration propagation in the ground and buildings. The finite element simulations and field measurements successfully verified the accuracy of the proposed prediction formulas, which offers a convenient vibration impact assessment framework to construction practitioners.

Impedance Model of the Interaction Between Environment and Human Body and Its Modification Design.

This paper presents a model of environment-human body interaction, which is critical for us to perform balanced motions such as locomotion and activities of daily living while standing. Specifically, movement smoothness and stiffness are quantitatively represented by an impedance between environment and body (ENV-BODY impedance) based on the concept of mechanical impedance, which is commonly used in robotics. The ENV-BODY impedance model considers a spring and a damper to represent the behavior of the center of pressure with respect to the ground reaction force. The model parameters are obtained from experimentally measured motion data. In addition, real-time feedback is applied for intervening the ENV-BODY impedance model by either attenuating (in-phase mode) or amplifying (anti-phase mode) the displacement of the center of pressure. Experimental results show that the proposed ENV-BODY impedance model suitably reflects the relationship between ground reaction force and center of pressure during static standing, and reconstructs the center-of-pressure acceleration with average error of 4.1E-0l mm/s2 Furthermore, the stiffness is smaller at the in-phase than at the anti-phase mode, thus being consistent with the expected mechanical stability. This model could be applied to training programs for evaluating movement smoothness and roughness using real-time motion measurement/analysis and environment control technology.

Mechanical Impedance and Its Relations to Motor Control, Limb Dynamics, and Motion Biomechanics.

The concept of mechanical impedance represents the interactive relationship between deformation kinematics and the resulting dynamics in human joints or limbs. A major component of impedance, stiffness, is defined as the ratio between the force change to the displacement change and is strongly related to muscle activation. The set of impedance components, including effective mass, inertia, damping, and stiffness, is important in determining the performance of the many tasks assigned to the limbs and in counteracting undesired effects of applied loads and disturbances. Specifically for the upper limb, impedance enables controlling manual tasks and reaching motions. In the lower limb, impedance is responsible for the transmission and attenuation of impact forces in tasks of repulsive loadings. This review presents an updated account of the works on mechanical impedance and its relations with motor control, limb dynamics, and motion biomechanics. Basic questions related to the linearity and nonlinearity of impedance and to the factors that affect mechanical impedance are treated with relevance to upper and lower limb functions, joint performance, trunk stability, and seating under dynamic conditions. Methods for the derivation of mechanical impedance, both those for within the system and material–structural approaches, are reviewed. For system approaches, special attention is given to methods aimed at revealing the correct and sufficient degree of nonlinearity of impedance. This is particularly relevant in the design of spring-based artificial legs and robotic arms. Finally, due to the intricate relation between impedance and muscle activity, methods for the explicit expression of impedance of contractile tissue are reviewed.

Transverse (lateral) instantaneous force of an acoustical first-order Bessel vortex beam centered on a rigid sphere

In a recent report [F.G. Mitri, Z.E.A. Fellah, Ultrasonics 51 (2011) 719–724], it has been found that the instantaneous axial force (i.e. acting along the axis of wave propagation) of a Bessel acoustic beam centered on a sphere is only determined for the fundamental order (i.e. m = 0) but vanishes when the beam is of vortex type (i.e. m > 0, where m is the order (or helicity) of the beam). It has also been recognized that for circularly symmetric beams (such as Bessel beams of integer order), the transverse (lateral) instantaneous force should vanish as required by symmetry. Nevertheless, in this commentary, the present analysis unexpectedly reveals the existence of a transverse instantaneous force on a rigid sphere centered on the axis of a Bessel vortex beam of unit magnitude order (i.e. | m| = 1) not reported in [F.G. Mitri, Z.E.A. Fellah, Ultrasonics 51 (2011) 719–724]. The presence of the transverse instantaneous force components of a first-order Bessel vortex beam results from mathematical anti-symmetry in the surface integrals, but vanishes for the fundamental ( m = 0) and higher-order Bessel (vortex) beams (i.e. | m| > 1). Here, closed-form solutions for the instantaneous force components are obtained and examples for the transverse components for progressive waves are computed for a fixed and a movable rigid sphere. The results show that only the dipole ( n = 1) mode in the scattering contributes to the instantaneous force components, as well as how the transverse instantaneous force per unit cross-sectional surface varies versus the dimensionless frequency ka ( k is the wave number in the fluid medium and a is the sphere’s radius), and the half-cone angle β of the beam. Moreover, the velocity of the movable sphere is evaluated based on the concept of mechanical impedance. The proposed analysis may be of interest in the analysis of transverse instantaneous forces on spherical particles for particle manipulation and rotation in drug delivery and other biomedical or industrial applications.

A General Analytical Tool for the Design of Vibration Energy Harvesters (VEHs) Based on the Mechanical Impedance Concept

This paper reports on a new approach for the analysis and design of vibration-to-electricity converters [vibration energy harvesters (VEHs)] operating in the mode of strong electromechanical coupling. The underlying concept is that the mechanical impedance is defined for a nonlinear electromechanical transducer on the basis of an equivalence between electrical and mechanical systems. This paper demonstrates how the mechanical impedance of the transducer depends not only on the geometry and the nature of the electromechanical transducer itself but also on the topology and on the operation mode of the conditioning circuit. The analysis is developed for resonant harvesters and is based on the first-harmonic method. It is applied to three electrostatic harvesters using an identical conditioning circuit but employing transducers with different geometries. For each of the three configurations, the mechanical impedance of the transducer is calculated and then used to determine the optimal electrical operation mode of the conditioning circuit, allowing a desired amplitude of the mobile-mass vibration to be obtained. This paper highlights how the parameters of the conditioning circuit and of the transducer impact the transducer's mechanical impedance, directly affecting the impedance matching between the energy source (resonator) and the transducer. This technique permits the design of highly efficient VEHs whatever the means of transduction.

Oscillation Mechanics of the Respiratory System: Applications to Lung Disease

Since its introduction in the 1950s, the forced oscillation technique (FOT) and the measurement of respiratory impedance have evolved into powerful tools for the assessment of various mechanical phenomena in the mammalian lung during health and disease. In this review, we highlight the most recent developments in instrumentation, signal processing, and modeling relevant to FOT measurements. We demonstrate how FOT provides unparalleled information on the mechanical status of the respiratory system compared to more widely used pulmonary function tests. The concept of mechanical impedance is reviewed, as well as the various measurement techniques used to acquire such data. Emphasis is placed on the analysis of lower, physiologic frequency ranges (typically less than 10 Hz) that are most sensitive to normal physical processes as well as pathologic structural alterations. Various inverse modeling approaches used to interpret alterations in impedance are also discussed, specifically in the context of three common respiratory diseases: asthma, chronic obstructive pulmonary disease, and acute lung injury. Finally, we speculate on the potential role for FOT in the clinical arena.

Optimum design of a golf club head.

This paper proposes to clarify the mechanism of the impact phenomena of golf clubs and golf balls by both time series analysis and the concept of mechanical impedance in the frequency domain and to investigate the maximum restitution. By using a lumped mass system, the restitution coefficient and the impact transfer efficiency are investigated for the golf clubs and golf balls. Secondly, the optimum combination of golf club and golf ball which gives the maximum restitution coefficient and the maximum impact transfer efficiency is related to the concept of mechanical impedance. That is, the relation between time series analysis and frequency domain analysis is clarified in the problems to obtain the maximum restitution coefficient and the maximum impact transfer efficiency of two bodies. Furthermore, a few experiments on hitting the golf balls with golf clubs are performed, and the results of the experiments are compared with those of the numerical analysis.

Transfer characteristics in the collision of two elastic bars. Consideration from time domain and frequency domain.

This paper clarifies the mechanism of the impact phenomena of elastic bars by both wave propagation theory and the concept of mechanical impedance in the frequency domain, and investigates the optimum combination of elastic bars to obtain the maximum restitution. The method of the Laplace transformation is used for these analyses. The relation between the contact time of the col llsion and the mechanical impedance is clarified to obtain the maximum restitution coefficient.

The mechanics of multi-joint posture and movement control.

The dependence of muscle force on muscle length gives rise to a "spring-like" behavior which has been shown to play a role in the execution of single-joint posture and movement. This paper extends this concept and considers the influence of the apparent mechanical behavior of the neural, muscular and skeletal system on the control and coordination of multiple degree of freedom posture and movement. A rigorous definition of "spring-like" behavior is presented. From it a numerically quantifiable, experimental test of spring-like behavior is formulated. It is shown that if the steady-state force-displacement behavior of a limb is not spring-like, this can only be due to the action of inter-muscular feedback, and can not be due to intrinsic muscle properties. The directional character of the spring-like behavior of a multiple degree of freedom system is described. The unique way in which synergistic coactivation of polyarticular muscles may modulate the directional properties of the spring-like behavior of a multiple degree of freedom system is explained. Dynamic aspects of postural behavior are also considered. The concept of mechanical impedance is presented as a rigorous dynamic generalisation of the postural stiffness of the limb. The inertial behavior of the system is characterised by its mobility. As with the stiffness or impedance, in the multiple degree of freedom case it has a directional property. The way in which the apparent kinematic redundancy of the musculo-skeletal system may be used to modify its dynamic behavior is explained. Whereas the inertial behavior of a single limb segment is not modifiable, it is shown that the apparent inertial behavior of a multiple degree of freedom system may be modulated by repositioning the joints. A unified description of the posture and movement of a multi-joint system is presented by defining a "virtual trajectory" of equilibrium positions for the limb which may be specified by the neuro-muscular system. The way in which this approach may lead to a simplification of some the apparent computational difficulties associated with the control of multi-joint motion is discussed.

Noise Rating Method for Fluorescent Lamp Ballast Transformers

The noise radiated from a composite fluorescent lamp system (ballasts, lamps, fixtures, and supporting structure) is dependent to some degree upon the physical and geometrical characteristics of all components. Analytical representation of the composite continuum is inhibited by many difficulties, not the least of which is the wide variation in the various composite systems that can occur. However, the mechanical impedance concept presents a powerful tool for systems of this type where selected measurements can be performed to greatly reduce the analytical effort. Theory is presented to analytically represent the composite system in terms of mechanical impedance. Measurements utilizing a force sensor were made for a number of ballasts which yield information useful in the general theory. A rating method was devised for the ballasts, independent of the rest of the system, which compares their noise-generating capabilities. The method is based upon the measured results of over-all force levels increasing monotonically with input electrical power. (This research was sponsored by Sola Electric Company.)

Analysis of Dynamic Systems Using the Mechanical Impedance Concept

The mechanical impedance concept is a powerful tool for the analysis of dynamical structural systems consisting of a single degree-of-freedom unit coupled to an infinite degree-of-freedom unit. Actual systems of interest that approximate this are (1) instrument components coupled through isolators to the vibrating shell of aircraft or missiles with the inherent problem of predetermining the dynamic forces acting upon the component, and (2) vibrating machinery coupled through isolators to the hulls of marine vessels with the inherent problem of minimizing the sound radiating into the sea. Formulas are presented for each case with damping included by rheological models. The quantities of the formulas can be measured if the continuous supporting unit is undefined. Simpler theoretical analyses result for defined continuous units than for the usual classical approaches. No approximations are made beyond those of classical linear continuum mechanics. (This research was supported by Armour Research Foundation.)

Application of Mechanical Impedance Concept to Shock and Vibration Testing

Application of Mechanical Impedance Concept to Shock and Vibration Testing

Application of the Mechanical Impedance Concept to Shock and Vibration Testing

Until recently, the mechanical impedance concept has been ignored in connection with shock and vibration. There is no question of the importance of the concept, especially in respect to correcting vibration data for loading effects. In testing, the applications must be carefully planned so as to avoid demands for excessive amounts of data or data of a type that is difficult to obtain, excessive complexity of test equipment, and excessive complexity in the test procedures. One compromise is to operate the shaker as an approximation to an infinite-impedance or a zero-impedance source according to the relationship of the tested item of equipment to the structure to which it is attached while in use. If a zero-impedance source is favored, it is desirable to make a transition to infinite impedance at the lowest frequencies, partly because the impedance of the qeuipment is usually lower than that of the structure at such frequencies and partly because a zero-impedance shaker might have too much chance of bottoming. Impedance is controlled simply by equalization. Another compromise is to adjust the spectrum of motion prior to mounting the equipment to be tested and require that the impedance of the shaker correspond to an upper envelope of the impedance of the structure on which the item is to be used. This involves a complicated servomechanism problem which must be solved for each test fixture. Simulating the exact impedance of the structure rather than an envelope is not feasible.

Note on Propeller-Excited Hull Vibrations

This note presents a summary of the information and techniques which are available to the designer for predicting the levels of service vibration of a ship in the design stage. This involves the two phases of estimating the exciting forces and the vibratory response of a hull to given forces. It is emphasized that at present the reliability of such predictions depends on the availability of data on the levels of service vibration or the exciting forces for ships actually in operation as a standard of comparison. It is pointed out that the concept of mechanical impedance at the stern of a ship is useful in predicting forced vibration.

The Mechanical Impedance of Damped Vibrating Systems

The concept of “mechanical impedance,” a quantity equivalent to Biot's Dynamic Modulus (reference i), has been utilised since 1939 by the de Havilland Aircraft Company as a standard method of treatment of vibration problems inengine airscrew systems, the method being applied principally to torsionalvibrations. In this work the effect of damping forces was neglected, on theassumption that the resonant frequencies of a system are not affected appreciablyby such forces so long as they remain of small magnitude.The desire to justify this assumption by theoretical reasoning, and to evolve a method of attack for problems in which the damping forces are too large to be neglected, led to the application of the concept of mechanical impedance to damped systems.