Power harvesting in a helicopter lag damper

In this paper a new power harvesting application is developed and simulated. Power harvesting is chosen within the European Clean Sky project as a solution to powering in-blade health monitoring systems as opposed to installing an elaborate electrical infrastructure to draw power from and transmit signals to the helicopter body. Local generation of power will allow for a ‘plug and play’ rotor blade and signals may be logged or transmitted wirelessly.\ud The lag damper is chosen to be modified as it provides a well defined loading due to the re-gressive damping characteristic. A piezo electric stack is installed inside the damper rod, effec-tively coupled in series with the damper. Due to the well defined peak force generated in the damper the stack geometry requires a very limited margin of safety. Typically the stack geometry must be chosen to prevent excessive voltage build-up as opposed to mechanical overload.\ud Development and simulation of the model is described starting with a simplified blade and piezo element model. Presuming specific flight conditions transient simulations are conducted using various power harvesting circuits and their performance is evaluated. The best performing circuit is further optimized to increase the specific power output. Optimization of the electrical and mechanical domains must be done simultaneously due to the high electro-mechanical cou-pling of the piezo stack. The non-linear electrical properties of the piezo material, most notably the capacitance which may have a large influence, are not yet considered in this study.\ud The power harvesting lag damper provides sufficient power for extensive health monitoring systems within the blade while retaining the functionality and safety of the standard component. For the 8.15m blade radius and 130 knots flight speed under consideration simulations show 7.5 watts of power is generated from a single damper

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

Succesful teaching of experimental vibration research

For more than 20 years, master students have been offered a practical training on experimental vibration research by the Structural Dynamics & Acoustics Section of the University of Twente. The basic theoretical knowledge, necessary to attend this practical training, is provided for the Master part of their study and it consists of a series of lectures on advanced dynamics, measurement techniques and the concept of modal analysis. The practical training consists of performing vibration experiments on a well defined simple structure. Use is made of a digital signal processing (DSP) Siglab system, together with ME'scope as analysis tool. In order to guarantee maximal transfer of knowledge toward the participants, small groups consisting of two students are formed. These groups are supervised by an experienced tutor, who intensively monitors the progress of the practical training. It lasts one day and the students have to write down their findings in a report. In order to attend the practical training in an efficient way, students have to study the theoretical basics of experimental vibration research in advance. In order to achieve an optimal preparation to the practical, a ‘virtual’ vibration measurement based on Labview is developed for the next academic year. Students will thus be able to run this experiment remotely from behind their PC by activating a real-life test case placed in the laboratory. In this paper the content and execution of the practical training is described. The experience of the authors is that the vast amount of interesting educational ingredients contributes to a profound understanding of both theoretical and experimental vibration research for Mechanical Engineering students

An optimization method for dynamics of structures with repetitive component patterns

The occurrence of dynamic problems during the operation of machinery may have devastating effects on a product. Therefore, design optimization of these products becomes essential in order to meet safety criteria. In this research, a hybrid design optimization method is proposed where attention is focused on structures having repeating patterns in their geometries. In the proposed method, the analysis is decomposed but the optimization problem itself is treated as a whole. The model of an entire structure is obtained without modeling all the repetitive components using the merits of the Component Mode Synthesis method. Backpropagation Neural Networks are used for surrogate modeling. The optimization is performed using two techniques: Genetic Algorithms (GAs) and Sequential Quadratic Programming (SQP). GAs are utilized to increase the chance of finding the location of the global optimum and since this optimum may not be exact, SQP is employed afterwards to improve the solution. A theoretical test problem is used to demonstrate the method

Design Optimization Utilizing Dynamic Substructuring and Artificial Intelligence Techniques

In mechanical and structural systems, resonance may cause large strains and stresses which can lead to the failure of the system. Since it is often not possible to change the frequency content of the external load excitation, the phenomenon can only be avoided by updating the design of the structure. In this paper, a design optimization strategy based on the integration of the Component Mode Synthesis (CMS) method with numerical optimization techniques is presented. For reasons of numerical efficiency, a Finite Element (FE) model is represented by a surrogate model which is a function of the design parameters. The surrogate model is obtained in four steps: First, the reduced FE models of the components are derived using the CMS method. Then the components are aassembled to obtain the entire structural response. Afterwards the dynamic behavior is determined for a number of design parameter settings. Finally, the surrogate model representing the dynamic behavior is obtained. In this research, the surrogate model is determined using the Backpropagation Neural Networks which is then optimized using the Genetic Algorithms and Sequential Quadratic Programming method. The application of the introduced techniques is demonstrated on a simple test problem

Near-source error sensor strategies for active vibration isolation of machines

Due to lightweight construction of vehicles and ships, the reduction of structure borne interior noise problems with passive isolation of engine vibrations might be not sufficient. To improve the isolation, a combination of passive and active isolation techniques can be used (so-called hybrid isolation). This paper focusses on the influence of the sensor positions on the performance of the active isolation. In general two strategies can be distinguished: sensors located in the accommodation with a direct minimization of the sound field and sensors located near the source of vibration. In this paper attention will be paid to an effective weighting of the near-source sensors in such a way that the interior noise in the vehicle is reduced. Also the nearsource strategy of minimization of the injected power is considered. The latter strategy is theoretically very attractive, but is much more difficult to implement in practice. The techniques are explained and compared to each other with the help of numerical models

Фінансова політика держави і розвиток фінансового ринку в Україні

Розглянута координуюча роль інституту – держави через реалізацію відповідної фінансової політики у формуванні ефективно функціонуючого фінансового ринку в сучасній економічній системі