Fabio Botta

New MEMS Tweezers for the Viscoelastic Characterization of Soft Materials at the Microscale

As many studies show, there is a relation between the tissue’s mechanical characteristics and some specific diseases. Knowing this relationship would help early diagnosis or microsurgery. In this paper, a new method for measuring the viscoelastic properties of soft materials at the microscale is proposed. This approach is based on the adoption of a microsystem whose mechanical structure can be reduced to a compliant four bar linkage where the connecting rod is substituted by the tissue sample. A procedure to identify both stiffness and damping coefficients of the tissue is then applied to the developed hardware. Particularly, stiffness is calculated solving the static equations of the mechanism in a desired configuration, while the damping coefficient is inferred from the dynamic equations, which are written under the hypothesis that the sample tissue is excited by a variable compression force characterized by a suitable wave form. The whole procedure is implemented by making use of a control system.

Optimal placement of piezoelectric plates for active vibration control of gas turbine blades: experimental results

It is well known that the gas turbine blade vibrations can give rise to catastrophic failures and a reduction of the blades life because of fatigue related phenomena[1]-[3] . In last two decades, the adoption of piezoelectric elements, has received considerable attention by many researcher for its potential applicability to different areas of mechanical, aerospace, aeronautical and civil engineering. Recently, a number of studies of blades vibration control via piezoelectric plates and patches have been reported[4]-[6] . It was reported that the use of piezoelectric elements can be very effective in actively controlling vibrations. In one of their previous contributions[7] , the authors of the present manuscript studied a model to control the blade vibrations by piezoelectric elements and validated their results using a multi-physics finite elements package (COMSOL) and results from the literature. An optimal placement method of piezoelectric plate has been developed and applied to different loading scenarios for realistic configurations encountered in gas turbine blades. It has been demonstrated that the optimal placement depends on the spectrum of the load, so that segmented piezoelectric patches have been considered and, for different loads, an optimal combination of sequential and/or parallel actuation and control of the segments has been studied. In this paper, an experimental investigation carried out by the authors using a simplified beam configuration is reported and discussed. The test results obtained by the investigators are then compared with the numerical predictions [7] .

Optimal placement of piezoelectric plates to control multimode vibrations of a beam

Damping of vibrations is often required to improve both the performance and the integrity of engineering structures, for example, gas turbine blades. In this paper, we explore the possibility of using piezoelectric plates to control the multimode vibrations of a cantilever beam. To develop an effective control strategy and optimize the placement of the active piezoelectric elements in terms of vibrations amplitude reduction, a procedure has been developed and a new analytical solution has been proposed. The results obtained have been corroborated by comparison with the results from a multiphysics finite elements package (COMSOL), results available in the literature, and experimental investigations carried out by the authors.

A novel fiber-optic measurement system for the evaluation of performances of neonatal pulmonary ventilators

Published standards for the performance evaluation of pulmonary ventilators are mainly directed to manufacturers rather than to end-users and often considered inadequate or not comprehensive. In order to contribute to overcome the problems above, a novel measurement system was proposed and tested with waveforms of mechanical ventilation by means of experimental trials carried out with infant ventilators typically used in neonatal intensive care units: the main quantities of mechanical ventilation in newborns are monitored, i.e. air flow rate, differential pressure and volume from infant ventilator are measured by means of two novel fiber-optic sensors (OFSs) developed and characterized by the authors, while temperature and relative humidity of air mass are obtained by two commercial transducers. The proposed fiber-optic sensors (flow sensor Q-OFS, pressure sensor P-OFS) showed measurement ranges of air flow and pressure typically encountered in neonatal mechanical ventilation, i.e. the air flow rate Q ranged from 3 l min−1 to 18 l min−1 (inspiratory) and from −3 l min−1 to −18 l min−1 (expiratory), the differential pressure ΔP ranged from −15 cmH2O to 15 cmH2O. In each experimental trial carried out with different settings of the ventilator, outputs of the OFSs are compared with data from two reference sensors (reference flow sensor RF, reference pressure sensor RP) and results are found consistent: flow rate Q showed a maximum error between Q-OFS and RF up to 13 percent, with an output ratio Q RF/Q OFS of not more than 1.06 ± 0.09 (least square estimation, 95 percent confidence level, R 2 between 0.9822 and 0.9931). On the other hand the maximum error between P-OFS and RP on differential pressure ΔP was lower than 10 percent, with an output ratio ΔP RP/ΔP OFS between 0.977 ± 0.022 and 1.0 ± 0.8 (least square estimation, 95 percent confidence level, R 2 between 0.9864 and 0.9876). Despite the possible improvements, results were encouraging and suggested the proposed measurement system can be considered suitable for performances evaluation of neonatal ventilators and useful for both end-users and manufacturers.

A Wireless Vibration Control Technique for Gas Turbine Blades Using Piezoelectric Plates and Contactless Energy Transfer

Gas turbine blade vibrations can give rise to catastrophic failures, and cause a reduction of the blades’ life due to fatigue-related phenomena. Damping is often required to improve performance of bladed disks. Recently, the adoption of piezoelectric elements has received considerable attention by many researchers for potential applicability in different areas of mechanical, aerospace, aeronautical and civil engineering. Furthermore, studies of blades’ vibration-control via piezoelectric plates are beginning to appear. In previous contributions, the authors have proposed a model to control multimode beam vibrations using piezoelectric elements. Analytical results have been validated through comparison with the results of a multi-physics finite elements package (COMSOL), as well as with data available in the literature. Experimental investigations carried out by the authors using a cantilever beam support the proposed theory. The model defines the optimal position of the plates to damp the multimode vibrations. Different loading scenarios where different modes were excited with different percentages were considered [1]. This model has also been extended to a rotating beam, and a finite elements code has been used to obtain the optimal position of the piezo-plates at different rotating speeds ([4]). In this paper the authors report the first results of the experimental investigations performed using a rotating beam. An experimental apparatus has been designed and constructed, including a new wireless power transfer system to eliminate issues associated with the use of slip rings. A Matlab program has been developed to control the system and interpret the data. Also, a laser pointing system has been used to measure the vibrations of a single blade and, thus, the effectiveness of the system. The preliminary results obtained using the newly developed test rig are discussed after presenting the experimental setup and the acquisition system designed and implemented by the authors.Copyright

Automatic Mixing Valve for Prescribed Injection Ratio Versus Variable Fuel Flow Rate

Using water or ethanol in fuel oils (including gasoline) results in a very fine atomization of the fuel due to micro-explosions (primary, secondary and tertiary) occurring during combustion. Thus the tiny nano-particles produced during combustion may better follow the flow and less particle impingement on the surfaces (tube walls, blades, etc.) occurs. The emulsion is produced by a device on board the engines using no chemical additives. Since the above engines operate at variable fuel flow rate from idle to full power there is a broad range of flow rates of the two liquids to be mixed. This paper deals with an automatic device that is capable of producing the prescribed injection ratio of the dispersed phase into the variable fuel oil flow rate. A design model has been developed to size the device. An ample description of the model and prototype is presented. Experimental validation of the model has been performed with the results discussed in this paper. The final automatic mixing valve arrangement is presented with the experimental set up. Parametric analyses of results together with the simulations are discussed.© 2007 ASME

An accelerated test stand to assess wear in offshore wind turbines rolling bearings

Rolling bearings are universally adopted to serve as revolute joints in almost all mechanisms or machines, because they offer a convenient solution to the problem of minimizing friction and, simultaneously, providing a large load-carrying capacity at any kinematic regime, including slow or alternate rotations. However, in offshore wind turbines not only they reach large dimensions but also they move within strong electromagnetic fields created by the turbine generators. For example, considering the last amplification stadium epicyclic gearbox, they may serve to sustain elements rotating around floating shafts (planetary) which also move around a fixed principal shaft (solar). This article illustrates an original experimental test bench that simulates sliding and rolling contacts through which a test current is flowing. Unexpected and interesting results disclose how this particular field is challenging and how more investigations are still required to achieve an adequate and complete interpretation. The understanding of this phenomenon could give rise to modification to the composition and the microstructure of rollers and rings employed in offshore wind turbines.

A preliminary characterization of a whole body vibration platform prototype for medical and rehabilitation application

Whole-body vibration (WBV) is receiving increasing interest as an exercise intervention in physiology and rehabilitation. Although there are many commercial and professional WBV platforms to provide controlled vibrations, very few have actually been tested in terms of amplitude (mm), frequency spectra (Hz) and shape of the vibratory motion wave. In this regard a prototype of a novel WBV platform where the vibration amplitude can be set to three values in the frequency range 20-60 Hz is here proposed. The device has been preliminarily characterized by processing the measurement signal from a piezoelectric monoaxial accelerometer mounted in the center of the WBV plate. In particular the accelerometer signal has been processed to evaluate frequency spectrum, waveform shape and displacement. Moreover to evaluate the performance of the prototype, same tests were carried out on an equivalent professional WBV platform, so that data coming from the two platforms have been compared and commented: test results have shown that the vibrations produced by the two WBV plates are very similar, nevertheless it has been found that the prototype works with a maximum error of about 5 % in frequency, that is less than in the other devices, furthermore the greater distortion of the signal is always at the twice of the operating frequency (second harmonic). Further investigations are needed to complete the characterization of the prototype and assess the vibration amplitude is not load dependent.

A preliminary uncertainty analysis of acceleration and displacement measurements on a novel WBV platform for biologic response studies

Over the last decade, many studies have been conducted on the effects of mechanical vibration on the physical hormonal and neuromuscular responses of muscles: in some works the growth hormone response showed a dependence on the acceleration provided by Whole Body Vibration (WBV) platforms with respect to subjects responsiveness. Therefore the accuracy of acceleration measurements related to the excitation system is important and should be assessed. To this aim a preliminary study on the identification and evaluation of the measurement uncertainty sources in the measurement chain of a novel WBV platform developed by the Authors is here proposed. After the main measurement error sources have been identified, a Monte Carlo simulation Method has been implemented to obtain the uncertainty in accelerations and displacements provided by the WBV platform. Since main causes of uncertainty has been identified in the accelerometer sensitivity, its mounting and the data acquisition processing, Results of the test showed a relative uncertainty of about ±4% for acceleration and displacement measurements for frequencies between 20Hz and 60Hz.

Influence of Natural Primary Thermal-Source Temperatures on Power Consumption in Air-Conditioning Plants

This paper is focused on exploring the potential of connecting air-conditioning plants to primary thermal sources qualified by temperatures. Several connection layouts between plant components and thermal sources are investigated. Traditional systems including chillers and heat pumps, as well as systems based on chillers equipped with partial or total heat recovery devices are considered. The influence of primary thermal-source temperatures on overall design performance of such systems is deeply investigated and results focusing on power consumption and energy savings, as well as on reduction of CO2 emissions produced by the source of mechanical work, will be presented and widely discussed.Copyright