André de Boer

Power harvesting in a helicopter rotor using a piezo stack in the lag damper

A piezoelectrically augmented helicopter lag damper has been simulated for the purpose of harvesting electrical energy within the rotor of the aircraft. This energy can then be consumed locally for sensing, processing, and transmission of data to the cockpit. An 8.15-m radius rotor is considered, and in-plane rigid lagging motion forms the prime excitation of the damper. The piezoelectric stack is installed within the rod of the damper in such a manner that the stack is submitted to all damper loads. MATLAB and Simulink are used to simulate a simplified blade model. A number of electrical harvesting circuits are investigated, and the piezo stack is optimized for each circuit. Also the effect of nonlinear capacitance of the piezo material is investigated revealing a profound effect. The important design parameters are identified and optimized resulting in a power output of 5.1 W for a steady 130-knot forward flight profile.

Finite element models applied in active structural acoustic control

This paper discusses the modeling of systems for active structural acoustic control. The finite element method is applied to model structures including the dynamics of piezoelectric sensors and actuators. A model reduction technique is presented to make the finite element model suitable for controller design. The reduced structural model is combined with an acoustic model which uses the radiation mode concept. For a test case consisting of a rectangular plate with one piezo patch the model reduction technique is validated. The results show that the an accurate prediction of both the structural and acoustic response is predicted by the reduced model. The model is compact requiring small simulation times, which makes it attractive for control system design. Finally the control performances for both structural and acoustic error criteria are presented.This paper discusses the modeling of systems for active structural acoustic control. The finite element method is applied to model structures including the dynamics of piezoelectric sensors and actuators. A model reduction technique is presented to make the finite element model suitable for controller design. The reduced structural model is combined with an acoustic model which uses the radiation mode concept. For a test case consisting of a rectangular plate with one piezo patch the model reduction technique is validated. The results show that the an accurate prediction of both the structural and acoustic response is predicted by the reduced model. The model is compact requiring small simulation times, which makes it attractive for control system design. Finally the control performances for both structural and acoustic error criteria are presented.

Influence of Multiphysical Effects on the Dynamics of High Speed Minirotors—Part I: Theory

In Part I of this work, a theoretical analysis showed that the surrounding air in the closed confinement between rotor and casing has a significant effect on the dynamic behavior of high speed minirotors. In order to validate the developed theoretical model, an experimental setup is designed and the dynamic behavior of the rotor with medium gap confinement is studied. The experimental setup has flexible supports, which consist of beams with adjustable length. The support stiffness is changed by altering the beam length. Modal analysis of the rotor is done in free-free conditions in order to test the capability of the rotordynamic model without the supports and multiphysical effects. The experimental and simulation results agree well with a difference of 1%. Then modal analysis of the whole structure is done at standstill and during operation in the absence of the casing. In this way, multiphysical effects are eliminated and only support effects on the dynamics of the structure are observed. The supports appear to have significant effect on the natural frequencies of the flexural modes of the system. Different support modeling techniques are studied and adequate equivalent models are obtained. These models are then implemented into the structural model of the rotor. Finally, multiphysical effects are tested at different speeds with different support stiffnesses. Experiments are performed with and without the casing for determining the change in the natural frequencies and onset of instability. The surrounding fluid has a significant effect on the stability of the system while the natural frequencies do not change significantly. The experimental and theoretical results are in fair agreement for predicting the natural frequencies and the onset of instability.

Life assessment by fracture mechanics analysis and damage monitoring technique on combustion liners

A methodology has been developed and tested including a multi-disciplinary framework towards integrated analysis of gas turbine combustors. The sub-elements consist of combustion dynamics, stress and modal analysis, fracture mechanics and structural health monitoring have been interlinked indicating the damage evaluation to life assessment. The interaction between the interrelated combustion driven flame dynamics, acoustic pressure fluctuations and liner wall vibration has been investigated in the laboratory combustor test system. During the operation, the combustion, acoustics and wall vibrations have been coupled together. The dynamic combustion process generates high amplitude pressure oscillations resulting in vibration of the liner structure at about constant elevated temperature in base load operation. The thermo-acoustic instabilities have a significant destructive impact on the life of the liner material due to high cyclic vibration levels at high temperature. A structural health monitoring (SHM) method has been established to identify the damage, detect the flaw existence and determine the location, severity and progress of the damage for the combustion liners. Vibration-based and acoustic emission (AE) techniques have been applied in the test system to assess the structural behavior. The applicability of the technique has been tested by examining the dynamic modal parameters of the structure. The method enables a reliable assessment on the liner specimen at elevated temperatures by means of non-destructive evaluation under continuous operation of the combustor. The combustion liner specimen material has been assessed by calculating the near-tip fields at the crack tip by finite element based stress and fracture mechanics analysis. An algorithm based on J-Integral has been utilized to analyze the crack growth behavior under various loading conditions considering both linear and non-linear elastic fracture mechanics concepts. The location and the direction of the cracking on the liner specimen have been predicted. The presented work interrelates the different mechanisms in gas turbine combustors and the applicability of the concepts has been verified and validated in the test systems.

Designing PV powered LED products - sensing new opportunities for advanced technologies

This study covers the design of innovative product concepts based on a combination of PV and LED technology. The products were developed in a project that took place in 2008 and 2009 during a cooperation of the University of Twente with Philips Lighting. It is shown that surprisingly unpredictable - yet technically feasible - PV powered LED products can be designed by carefully selected industrial design methods and an open view towards potential applications. In this scope innovation is not just a matter of implementing advanced technology in existing products, but particularly a matter of sensing new opportunities which are created by the combination of new technologies such as LEDs and PV technology. The PV powered LED product concepts range from small products, like watches, remote controls and other electronic handhelds, to large-sized products such as tents. In this paper it is shown how the concepts have been developed and they will be visualized by high key renderings. Also attention will be paid to the prototyping a few product concepts to evaluate their functional requirements.

THERMAL MODELING OF A MINI ROTOR-STATOR SYSTEM

In this study the temperature increase and heat dissipation in the air gap of a cylindrical mini rotor stator system has been analyzed. A simple thermal model based on lumped parameter thermal networks has been developed. With this model the temperature dependent air properties for the fluid-rotor interaction models have been calculated. Next the complete system has also been modeled by using computational fluid dynamics (CFD) with Ansys-CFX and Ansys. The results have been compared and the capability of the thermal networks method to calculate the temperature of the air between the rotor and stator of a high speed micro rotor has been discussed.

A contact solver suitable for tyre/road noise analysis

Road traffic noise is a major environmental problem in modern society. The interaction between tyre and road surface, the major noise source, is non‐linear and is best described in the time domain. The currently used contact models for acoustic analyses have problems with either accuracy or calculation speed. At the Structural Dynamics and Acoustics group of the University of Twente an alternative contact algorithm has been developed. The characteristic feature of this algorithm is that, while solving the set of equations, the contact condition, i.e. the condition stating that there is no overlap between the bodies, is satisfied exactly. Hence, there is no need for contact elements or contact parameters. The possibility to optimize and speed up the algorithm, using multigrid is the major advantage of the new approach. In this paper the contact algorithm is applied to a two‐dimensional finite element model. Coulomb friction is taken into account. Some test simulations illustrate the ease of the algorithm. ...

Sensitivity of Combustion Driven Structural Dynamics and Damage to Thermo-Acoustic Instability: Combustion-Acoustics-Vibration

The dynamic combustion process generates high amplitude pressure oscillations due to the thermo-acoustic instabilities, which are excited within the gas turbine. The combustion instabilities have a significant destructive impact on the life of the liner material due to the high cyclic vibration amplitudes at elevated temperatures. This paper presents a methodology developed for mechanical integrity analysis relevant to gas turbine combustors and the results of an investigation of combustion-acoustics-vibration interaction by means of structural dynamics. In this investigation, the combustion dynamics was found to be very sensitive to the thermal power of the system and the air-fuel ratio of the mixture that feed into the combustor. The unstable combustion caused a dominant pressure peak at a characteristic frequency, which is the first acoustic eigenfrequency of the system. Besides, the higher-harmonics of this peak were generated over a wide frequency-band. The frequencies of the higher-harmonics were observed to be close to the structural eigenfrequencies of the system. The structural integrity of both the intact and damaged test specimens mounted to the combustor were monitored by vibration-based and thermal-based techniques during the combustion operation. The flexibility method was found to be accurate to detect, localize and identify the damage. Furthermore, a temperature increase was observed around the damage due to the hot gas leakage from the combustor that can induce detrimental thermal stresses to consume the lifetime.

Design of an Experimental Setup for Testing Multiphysical Effects on High Speed Mini Rotors

Recently, there have been numerous research projects on the development of minirotating machines. These machines mostly operate at speeds above the first critical speed and have special levitation systems. Besides, the multiphysical effects become significant in small scale. Therefore, advanced modeling approaches should be developed and innovative experimental rigs with the foregoing requirements should be constructed in order to test the developed techniques. In the current study, the design of an experimental setup for testing the multiphysical effects has been outlined. First, the previously developed multiphysical models (Dikmen, E., van der Hoogt, P., de Boer, A., and Aarts, R., 2010, “Influence of Multiphysical Effects on the Dynamics of High Speed Minirotors—Part I: Theory,” J. Vibr. Acoust., 132, p. 031010; Dikmen, E., van der Hoogt, P., de Boer, A., and Aarts, R., 2010, “Influence of Multiphysical Effects on the Dynamics of High Speed Minirotors—Part II: Results,” J. Vibr. Acoust., 132, p. 031011) for the analysis of small scale rotors are described briefly for background information. Second, an analysis of the effect of the rotor parameters (diameter, length, rotation speed, etc.) on the dynamics of the rotor under multiphysical effects is presented. Afterward the design process which includes the design decisions based on these results, the availability, simplicity, and applicability of each component is presented in detail. Finally, the experimental results have been presented and the efficiency of the design has been evaluated. In summary, the design requirements for an experimental setup for testing multiphysical effects on minirotors have been analyzed. The design procedure and evaluation of the design have been presented.

Vibration Isolation by an Actively Compliantly Mounted Sensor Applied to a Coriolis Mass-Flow Meter

In this paper, a vibration isolated design of a Coriolis mass-flow meter (CMFM) is proposed by introducing a compliant connection between the casing and the tube displacement sensors, with the objective to obtain a relative displacement measurement of the fluid conveying tube, dependent on the tube actuation and mass-flow, but independent of external vibrations. The transfer from external vibrations to the relative displacement measurement is analyzed and the design is optimized to minimize this transfer. The influence of external vibrations on a compliant sensor element and the tube are made equal by tuning the resonance frequency and damping of the compliant sensor element and therefore the influence on the relative displacement measurement is minimized. The optimal tuning of the parameters is done actively by acceleration feedback. Based on simulation results, a prototype is built and validated. The validated design shows more than 24 dB reduction of the influence of external vibrations on the mass-flow measurement value of a CMFM, without affecting the sensitivity for mass-flow.