The Italian experience in the field of `stand alone' monitoring systems for viaducts shows that the design of said systems, as well as that of the single components utilized, must satisfy complex and often unusual...
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(纸本)0819414883
The Italian experience in the field of `stand alone' monitoring systems for viaducts shows that the design of said systems, as well as that of the single components utilized, must satisfy complex and often unusual operating conditions and, at times, yield to compromises of various types. This is necessitated by the fact that the electronic devices used are expensive and the characteristics of high resistance to the elements and long term reliability they must satisfy. Therefore, it is often preferable to limit the system performance envelope in the interest of ease of maintenance characteristics, intrinsic safety, simplicity of installation, resistance to the most aggressive atmospheric agents, imperviousness to outside disturbances, etc. One of the most onerous aspects the design engineers must take into account comprises the interaction, between those work site activities specifically connected with the installation of the monitoring system and those that merely relate to the construction of the structure. The difference in tradition in terms of the scope of monitoring strategies between the designer of measuring and telecontrol systems and the design engineers of the structure in question must not be forgotten.
In recent years, new smart composites have been introduced in the market that open up new possibilities in controlling or sensing flexible structures. The internal properties of these smart or intelligent material can...
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In recent years, new smart composites have been introduced in the market that open up new possibilities in controlling or sensing flexible structures. The internal properties of these smart or intelligent material can be changed by application of magnetic field (in magneto-strictive material), voltage (in piezoelectric material), or heat (in shape memory alloys). In this paper, we design a feedback control law to damp vibrations in simple mechanical systems by manipulating the internal parameters of the system.
The efficiency of conventional passive coatings for the reduction of the reflection coefficients of surfaces in underwater acoustics is limited, especially at low frequencies. Recent progress in active control makes u...
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The efficiency of conventional passive coatings for the reduction of the reflection coefficients of surfaces in underwater acoustics is limited, especially at low frequencies. Recent progress in active control makes us consider the possibility of using piezoelectric transducers to control the reflection coefficients of surfaces. The latter depends on the frequency, the physical characteristics of the transducer, the radiation impedance and the control impedance. By considering an analog circuit of the system, expressions of the reflection coefficient, and of the optimal control impedance to reduce it, are given. Numerical examples and the influence of some parameters are also studied.
This paper investigates the feasibility of using embedded magnetostrictive mini actuators (MMA) for smart structure applications, such as vibration suppression of beams. A cantilever beam, embedded with MMA and subjec...
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Proposed here is a method of vibration control based on limiting the maximum axial forces in the active members of an adaptive truss. The actuators simulate linear elastic-perfectly plastic-linear elastic behavior and...
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Proposed here is a method of vibration control based on limiting the maximum axial forces in the active members of an adaptive truss. The actuators simulate linear elastic-perfectly plastic-linear elastic behavior and consume the vibrational energy as work. The method is applicable to both statically determinate as well as indeterminate truss structures. However, for energy efficient control of statically indeterminate trusses, extra actuators may be needed on the redundant bars. An energy formulation relating the various control parameters is derived to get an estimate of the control time. Since the simulation of linear elastic-perfectly plastic-linear elastic behavior requires a piecewise linear control law, a general analytical solution is not possible. Numerical simulation by step-by-step integration is performed to simulate the control of an example truss structure. The problems of application to statically indeterminate trusses and optimal actuator placement are identified for future work.
The vibration control of flexible structures with variable disturbances in different frequencies becomes more and more important because of the demand for higher positional accuracy and more stable manipulation. This ...
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The vibration control of flexible structures with variable disturbances in different frequencies becomes more and more important because of the demand for higher positional accuracy and more stable manipulation. This paper reports on a proof-of-concept experimental investigation focused on evaluating the elastodynamic characteristics of hollow cantilever beams filed with a hydrous-based ER fluid consisting of cornstarch and silicone oil. The beams are considered to be uniform viscoelastic materials and modeled as a viscously damped harmonic oscillator. Electric field dependent natural frequencies, loss factors, and complex moduli are evaluated and compared among three different beams: two types of different volume fraction of the ER fluid and one type of different particle concentration of the ER fluid by weight.
This paper presents a finite-element analysis of vibration control in planar mechanisms consisting of flexible links provided with nearly collocated piezoceramic sensors and actuators. Euler-Bernoulli-theory-based bea...
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This paper presents a finite-element analysis of vibration control in planar mechanisms consisting of flexible links provided with nearly collocated piezoceramic sensors and actuators. Euler-Bernoulli-theory-based beam finite elements with p-convergence capabilities have been cast into a total Lagrangian formulation in order to represent large rotations of the links. A simple control strategy based on the placement of closed-loop poles has been applied. Numerical predictions of active vibration control in links undergoing geometrically non-linear deflections of the von Karman class are presented.
Active control of flexible multi-body systems and structures through utilization of smartmaterials is considered in this paper. Specifically, utilization of piezoceramics for sensing and actuation is investigated. Ex...
Active control of flexible multi-body systems and structures through utilization of smartmaterials is considered in this paper. Specifically, utilization of piezoceramics for sensing and actuation is investigated. Experimental setups have been developed at CRRL to study modeling issues and control design approaches for flexible structures with embedded (or surface-mounted) piezoceramics. In this paper, experimental results on vibration suppression for a flexible manipulator with surface mounted piezoceramics are presented. It will be shown that piezoceramics substantially improve the performance of the systems under consideration. The advocated approaches for control designs are decentralized frequency shaping and self-tuning adaptive controllers. The self-tuning controller is based on identification of the system dynamics in frequency domain utilizing Fast Fourier Transform (FFT). Addition of a self-tuning regulator enhances the performance and the robustness of the controlled system to parameter variations.
This work studies geometry control in prestressed adaptive space trusses. Geometry control is required in space structures to satisfy the precision requirements of the measurement equipment supported by them. The join...
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This work studies geometry control in prestressed adaptive space trusses. Geometry control is required in space structures to satisfy the precision requirements of the measurement equipment supported by them. The joints of space trusses are stabilized by global prestressing in order to make the `response-geometry control' relations linear. In adaptive space trusses global prestressing is achieved by induced element elongations. It is not possible to prestress a statically determinate truss structure by induced elongations. Therefore adaptive space trusses have to be statically indeterminate, implying that the length-adjusting actuators have to work against the existing prestressing forces, and also against the stresses caused by the actuation. These type of difficulties do not exist in statically determinate adaptive trusses where, except for overcoming the friction, the actuators operate under zero axial force, and require almost no energy. The actuator-placement problem in statically indeterminate trusses is therefore governed by energy and strength requirements. This paper includes a discussion of the various strategies of static geometry control and provides new methodologies for the solution of the actuator-placement problem in prestressed adaptive space trusses.
An approximate method for modal analysis of a piezostructure testbed is used to generate a dynamic model for closed-loop, multiple-input-multiple-output (MIMO) feedback controller design. An innovative pole-residue sy...
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An approximate method for modal analysis of a piezostructure testbed is used to generate a dynamic model for closed-loop, multiple-input-multiple-output (MIMO) feedback controller design. An innovative pole-residue system model for structures instrumented with piezoelectric sensor and actuators is developed which is compatible with existing modal curve-fitting algorithms. This paper examines the use of the new pole-residue model in the absence of truly collocated response information. It is shown that nearly-collocated measurements may be used to estimate a structure's modal parameters;high-precision signal conditioning electronics required for exact drive-point response measurements are thereby avoided. A simply-supported plate is used to demonstrate the approximate piezostructure modal test approach. The test model is then used to design up to a four input, sixteen channel output MIMO feedback control experiment. Closed-loop results are presented which show that more than 10 dB of suppression is achieved near structural resonances within the control bandwidth (10-250 Hz).
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