Mechanics and Control
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ISSN 2083-6759
e-ISSN: 2300-7079
Issue Date
2013
Volume
Vol. 32
Number
No. 2
Description
Journal Volume
Mechanics and Control
Vol. 32 (2013)
Projects
Pages
Articles
Profesor Zbigniew Engel, doktor honoris causa multi 1933-2013 wspomnienia o profesorze
(2013) Batko, Wojciech
This tribute is devoted to the memory of Professor Zbigniew Engel, who passed away recently at the age of eighty. The text describes the late Professor Engel's scientific life-track and his research activities, which resulted in the creation of a new scientific discipline: vibroacoustics. An outline of his scientific activities in several research fields is presented, together with examples of his numerous innovatory technological achievements. Professor Engel was also a highly respected teacher and tutor of students and scientific staff. His very active involvement in the organization of scientific life as well as the participation in the activities of various Polish and international scientific associations of mechanical and acoustical engineers deserves special mention. This activity spread in the world the good name of the AGH University of Science and Technology, the university to which he devoted his entire scientific life.
Rejection of harmonic and transient disturbances of a smart structure with piezoelectric actuators
(2013) Duarte Vera, Franklyn Gerardo; Ballesteros, Pablo; Shu, Xinyu; Bohn, Christian
Light flexible structures are easily prone to vibrate due to external forces or due to forces generated in the inner structure. This situation is common in machinery or mechanical structures with rotational devices. The unwanted vi-bration of such structures can be compensated with the addition of piezoelectric actuators for active vibration control (AVC). The rejection of harmonic disturbances is frequently done with controllers based on the internal model principle. The goal of this research is to reduce the effect of harmonic disturbances with known (measured) time-varying fre¬quencies acting on a system as well as to increase the damping of the system for the transient response (first mode of vibration). The experimental setup is made up of a slender aluminium flexible beam, a pair of piezoelectric actuators, an accelerometer and two DC motors, as well as the data acquisition and signal conditioning equipment. The harmonic disturbance is generated by DC motors. The control design utilizes an augmented description of the plant. The plant including the disturbance is modelled as a polytopic linear parameter-varying (pLPV) system. An observer-based gain-scheduling controller is calculated based on quadratic stability and the stability is guaranteed for the specified range ofvariation of the scheduling parameters, also restriction in the performance is introduced in the sense of the H2-norm. Experimental results show very good disturbance cancellation.
Control of micro-inverters as an overvoltage prevention method under high PV penetration
(2013) Gagrica, Ognjen; Kling, Wil L; Uhl, Tadeusz
Low voltage (LV) residential grids are generally not designed for high penetration of photovoltaic (PV) distributed generation. Maximization of PV output is not only opposed by solar energy intermittency, but also by grid impacts in form of reverse power flow and overvoltage. More intelligent control of PV inverters is required to balance the voltage requirements of the grid and maximum energy yield wanted by the end user. This paper discusses how micro-inverter topology could be utilized to handle overvoltage problem and avoid power output losses by applying an innovative control method. Control is realized as partial generation shedding at PV module level which is an optimized alternative comparing to conventional, entire PV array tripping in the event of overvoltage.
LQR control of the nodal displacements in a spatial truss with active piezoelectric members
(2013) Grzybek, Dariusz
The ability to damp vibrations is important in many structures, in which trusses are one of the main elements. The increase of the damping of the truss vibrations is possible by passive means or by the use of an active vibration control system integrated with the structure of the truss. The control system can affect the truss structure by specially designed actuators, which generate active forces in appropriate nodes of the truss. Piezoelectrics can be used to build such actuators. The design of the control system encompasses the structure of the actuating active truss member, the spacing of active members inside the truss structure, the design of the control algorithm and the spacing of measurement sensors generating feedback signals. In this article, the application of the LQR algorithm to the node displacement control in a spatial truss has been presented. The spacing of active members in the truss structure on the basis of the force distribution in the truss members has been suggested.
Computer-aided prototyping of interdigital transducers for the structural health monitoring of planar structures
(2013) Mańka, Michał; Ambroziński, Łukasz; Uhl, Tadeusz
In recent years an intensive research activity into the application of guided waves (GWs) for structural health monitoring (SHM) can be observed. For instance, Lamb waves (LWs) have shown a great potential in monitoring of thin, planar structures. However, due to the dispersive and multimodal nature of the LWs, their snapshots can consist of many pulses even for an intact structure, which makes damage detection very complex. Moreover, small PZT transducers, most commonly used in SHM systems, act normally as omni-directional wave sources, therefore, dense or sparse transducers networks are required for damage localization. Some of the above-mentioned drawbacks of single PZT emitters and sensors can be overcome using interdigital transducers (IDT) designed to excite and sense a single, selected mode. The mode-tuning is performed by changing the span of finger electrodes to match the wavelength of the excited mode for the selected frequency. An IDT is a directional source, therefore, it generates a wave steered to the direction perpendicular to the electrodes. The width of the excited main lobe can be determined by the length of the electrodes. Since many parameters of the IDTs infl uence the LWs propagation, techniques for the simulation of the wave excitation and propagation are needed. In the paper, numerical tools for the computer aided design and virtual prototyping of the IDTs are presented. The simulation technique is based on the frequency-dependent transfer function of the structure, and due to its computational efficiency it can be used for fast testing of IDTs’ performance and for preliminary transducer design for further finite element simulations, and prototyping.