Dynamics of piezoceramics-based mass and force actuators for rotating machines

In the past decade, it has become more and more common to install active vibration control devices on rotating systems like grinding machines, tooling centers, industrial fans and drive shafts. In the present research, two innovative actuation concepts for such devices are evaluated. The first device is a force actuator based on piezoceramic fibers, which has a low power consumption and high dynamic range. The second device is a mass redistribution actuator based on two piezoelectric ultrasonic motors, which is smaller and faster than conventional electromagnetic devices. At the basis of the analysis are rotor dynamic finite element models including actuators, sensors and feedback controllers. In simulations and experiments with device one, feedback control and scheduled feedforward control are considered. It is shown experimentally that the unbalance response at a critical speed can be reduced by some 97%. In experiments with device two, the positioning speed is determined

Sensitivity of combustion driven damage mechanisms to instability

A multi-disciplinary framework is developed to evaluate the damage on gas turbine engine liners including interrelated sub-domains such as combustion dynamics, stress, modal, fracture mechanics analyses and life assessment. Comparative operation conditions for the combustion dynamics have been investigated. Excessive vibrations induced by the limit cycle operation resulted in mechanical stresses and strains on the structure. The structural integrity of both the intact and damaged test specimens have been monitored by vibration-based and thermal-based techniques during the combustion operation. The progressive damage on the damaged specimen configuration has been analyzed and linked to the combustion driven mechanisms. Damage evaluation, life assessment and physical experimental approaches have been integrated and utilized to evaluate the fatigue dominant damage in combustion liner material. This study addresses a reference in ensuring the safety and reliability of gas turbine engine combustors. The outcome provides a better understanding and a quantification of the material damage progress and the component behavior in terms of life consumption and combustion dynamics

Damage evolution by using the near-tip fields of a crack in gas turbine liners

A residual lifetime prediction study has been performed on a combustion liner metallic material exposed to elevated temperatures by simulating the evolution of plastic work fields at a crack tip under monotonically loading. The strain and stress distribution has been computed by finite element analysis. The method gives a measure of the metal degradation and enables to evaluate the failure limit of a progressive damage under the operating conditions of gas turbine components. The study allows making a correlation between the progress of damage of a combustion liner and the loading conditions, the material type and the geometry of a specimen by the parametric design construction

Agricultural Land Search Behavior: A Study of Agricultural Relocation in the Niagara Fruit Belt

This thesis identifies and examines how people look for farms. In it the actual search rather than the decision to seek additional or alternative locations is the focus. It is estimated that the sample of farmers interviewed and surveyed consists of 50 per cent of those who had undergone the process of relocation/expansion in the past two years in the Niagara region of Ontario. The analytic framework used is adopted from a case study of intra-urban mobility. Therefore, this study is an attempt to transpose those urban concepts to an agricultural situation. Five important sets of variables of farmers are examined in relation to their agricultural location decision: (1) socio-demographic and economic characteristics, (2) housing/farming history, (3) a rationalization of the reasons for moving, (4) information sources, and (5) the characteristics of the actual search. Working hypotheses were tested using the Spearman rank-corelation test as well as the Kendall test. The results indicate that a positive relationship exists between the time spent searching and the number of alternatives examined, the time spent searching and the size of the search area, and the time spent searching and the distance of the move. Furthermore, Chi square tests indicated that ‘familiarity with the area’ is important in the search and that real estate agents and direct personal contact are the major information channels used by the searchers. Nevertheless, different groups exhibit different biases toward different information sources. Barrett’s Indices of Search Behavior are presented in this thesis as well so that an analysis of the alternative locations can be made. On the whole the data on agricultural land search period is short, and restricted to a small area. The study concludes that agricultural and intra-urban search behavior differs mainly in degree rather than kind. Different types of farmers exhibited differences in their search behavior. The differences are attributed to the role of the vacancies of the market and the consequent effects of an immobile residence

Molecular Clouds as the Origin of the Fermi Gamma-Ray GeV-Excess

The so-called "GeV-excess" of the diffuse Galactic gamma-ray emission is studied with a spectral template fit based on energy spectra. The spectral templates can be obtained in a data-driven way from the gamma-ray data, which avoids the use of emissivity models to subtract the standardbackground processes from the data. Instead, one can determine these backgrounds simultaneously with any "signals" in any sky direction, including the Galactic disk and the Galactic center. Using the spectral template fit two hypothesis of the "GeV-excess" were tested: the dark matter (DM) hypothesis assuming the excess is caused by DM annihilation and the molecular cloud (MC) hypothesis assuming the "GeV-excess" is related to a depletion of gamma-rays below 2 GeV, as is directly observed in the Central Molecular Zone (CMZ). Both hypotheses provide acceptable fits, if one considers a limited field-of-view centered within 20$^\circ$ around the Galactic center and applies cuts on the energy range and/or excludes low latitudes, cuts typically applied by the proponents of the DM hypothesis. However, if one considers the whole gamma-ray sky and includes gamma-ray energies up to 100 GeV we find that the MC hypothesis is preferred over the DM hypothesis for several reasons: i) The MC hypothesis provides significantly better fits; ii) The morphology of the "GeV-excess" follows the morphology of the CO-maps, a tracer of MCs, i.e. there exists a strong "GeV-excess" in the Galactic disk also at large longitudes; iii) The massive CMZ with a rectangular field-of-view of $l \times b = 3.5^{\circ} \times 0.5^{\circ}$ shows the maximum of the energy flux per log bin in the diffuse gamma-ray spectrum at 2 GeV, i.e. the "GeV-excess", already in the raw data without any analysis. The rectangular profile contradicts the spherical morphology expected for DM annihilation.Comment: 53 pages, 8 figures (+ 42 figures in Appendices), extended version of arXiv:1610.08926 accepted for publication in PR

Design optimization applied in structural dynamics

This paper introduces the design optimization strategies, especially for structures which have dynamic constraints. Design optimization involves first the modeling and then the optimization of the problem. Utilizing the Finite Element (FE) model of a structure directly in an optimization process requires a long computation time. Therefore the Backpropagation Neural Networks (NNs) are introduced as a so called surrogate model for the FE model. Optimization techniques mentioned in this study cover the Genetic Algorithm (GA) and the Sequential Quadratic Programming (SQP) methods. For the applications of the introduced techniques, a multisegment cantilever beam problem under the constraints of its first and second natural frequency has been selected and solved using four different approaches

Experimental validation of the interaction between combustion and structural vibration

To decrease NOx emissions from combustion systems, lean premixed combustion is used. A disadvantage is the increase in sound pressure levels in the combustor, resulting in an increased excitation of the surrounding structure: the liner. This causes fatigue, which limits the life time of the combustor. To study this problem experimentally, a test setup has been built consisting of a single burner, 500kW, 5 bar combustion system. The thin structure (liner) is contained in a thick pressure vessel with optical access for a traversing laser vibrometer system to measure the vibration levels and mode shapes of the liner. The acoustic excitation of the liner is measured using pressure sensors measuring the acoustic pressures inside the combustion chamber and in the cooling passage between the liner and the pressure vessel. To validate models, measurements were performed in steps of increasing complexity. Firstly, the structural properties, obtained by modal analysis of the liner outside the pressure vessel, have been compared with a finite element model. Subsequently, results of an acoustic finite element model of the setup have been compared to acoustic measurements on the test rig to validate the acoustic properties of the model, which are made by mounting a well defined acoustic source to the rig. Finally, measured pressures and vibration levels in the presence of combustion are shown

Connecting the Vehicle with the Environment - Trends and Challenges

Innovations in automotive electronics have become increasingly complex, resulting in high-end vehicles containing more than 70 electronic control units and offering a variety of functions to the driver. In-vehicle telematics and infotainment systems provide services like digital radio, broadcast services, television, and MP3 audio. Future applications and services will integrate information sources available outside and inside the car, requiring vehicle systems connected with in-vehicle Consumer Electronics devices and the outside world. In order to realized the vision of an intelligent networked car, connected with the environment and providing the driver with information according to his demands, common efforts towards car manufacturer and supplier spanning standards for data exchange are required. The paper discusses possible approaches and future challenges