1,721,095 research outputs found
Electrical method to measure the dynamic behaviour and the quadrature error of a MEMS gyroscope sensor
No full textThe electronics on board of a vibrating MEMS sensor is able to compensate only for small changes in the mechanical characteristics of the
device. Thus, it is of great importance to find an easy and fast way to evaluate the mechanical parameters, such as the resonance frequency and the
damping coefficient, of a MEMS sensor before putting the device on the market [A. Cigada, E. Leo, M. Vanali, Optical and electrical methods to
measure the dynamic behaviour of aMEMSgyroscope sensor, Proceedings of IMECE2005 ASME International Mechanical Engineering Congress
and Exposition 2005, Orlando, Florida, USA [14]]. Moreover, for a vibrating MEMS gyroscope also the quadrature error, i.e. [Y.Y. Bao, C.L. Yung,
Modelling and compensation of quadrature error for silicon MEMS microgyroscope], has to be kept below a given threshold in order to be able to
acurately measure low angular speeds.
Verification tests are usually carried out at the end of the production process, i.e. when the package is complete. Thus, only electrical measurements
are possible. In the present paper, a reliable approach to determine mechanical parameters as well as the quadrature error of the MEMS device
through electrical measurements is proposed and results are compared to more traditional optical measurements
Wind action on the london eye cables. Part 2: damping device design and field measurements
Full text linkThis paper is part two in the description of the London Eye panoramic wheel damping system design. The system is meant to protect the structure against the wind action, mainly the aeolian vibrations and ice galloping. A particular accent on the experimental techniques and their critical review is put in this second section
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Phase change material cellulosic composites for the cold storage of perishable products: From material preparation to computational evaluation
No full textWarm temperature spikes represent one of the main spoilage causes of perishable good-stuffs. The development of packaging materials with thermal buffering properties represents a powerful solution to address the problems arising from an uncontrollable interruption during cold-chain logistic.
Here, we propose the use of phase change material (PCM) composites for the design of cold storage packaging. Two different concentrations (25 and 50% w/w) of commercially available micro-encapsulated PCM were homogeneously dispersed in paper matrix via conventional negative filtration techniques. The possibility of obtaining composites with different latent heats in the 4-10 degrees C range has been demonstrated via differential scanning calorimetry measurements. Heat transmission tests, simulating the heating processes typical of the removal from a cold room, were performed on a suitable multilayer configuration. The obtained materials show the ability to maintain the inner temperature for a duration up to 10-fold longer in time, when compared to a similar cellulose material with a thickness of 2 cm. Experimental results have been numerically assessed by considering the material thermal parameters as homogeneous.
Both experimental and computational approaches here discussed offer an easy way for the design of micro-encapsulated PCM-cellulose composite as building blocks in cold storage packaging design
Effects of an asymmetrical confined flow on a rectangular cylinder
No full textThe effects of an asymmetric confined flow on a cylinder of rectangular cross-section are investigated and discussed. Experiments are performed in a wind tunnel by placing cylinders of different cross-sections at various elevations from the floor of the test section. The Reynolds number is varied within the range 6E+3-4E+4. Forces exciting the cylinder are measured by built-in dynamometers placed inside the cylinder structure. The flow is characterized by mean and fluctuating local velocity components to define the inflow distribution and the ensuing wake region.
The mean dimensionless force coefficients are then calculated and analyzed. The frequency analysis of the force components acting on the cylinder provides the dynamic characterization of the loading and of the wake shedding.
The experimental results highlight that the presence of the wall strongly influences the system dynamics also when the cylinder is placed at a relatively large elevation from the wall itself. The cylinder aspect ratio governs effects of the wall condition on the force coefficients and the Strouhal number
Evaluation of performances and reliability of a wavelet based modal parameter estimation method applied on the modal identification of the Meazza stadium grandstands in Milan
No full textStructural monitoring is a crucial aspect for the safety management of large civil structures. A vibrationmeasurement-based monitoring system allows to estimate the structure's modal parameter and their change in time which is an indicator of possible damages. Operational modal analysis is the proper tool to this prupose, allowing a continuous monitoring of the parameters evolution with no needs for external excitation. A reliable modal analysis technique is therefore fundamental: in this paper a wavelet based modal parameter estimation method is analyzed. The method has been adopted in the modal parameters estimation of the grandstands of the G. Meazza stadium in Milan. It is a famous huge concrete structure composed of three different sub-structures built in different decades: the stadium can host about 80000 people. The Department of Mechanics of Politecnico di Milano since summer 2003 looks after the vibration monitoring of the Meazza stadium: measurement are available for different sorts of event, such as big concerts and important football matches and also a traditional modal analysis of one of the grandstands has been performed, loading the structure with an inertial electromechanical shaker. This allows to compare the wavelet based modal parameter estimation results with those from more commonly adopted methods such as the Least Square Complex Exponentials (LSCE, Prony's solution) and the Poly Reference Least Square Frequency Domain (known as POLYMAX), not only with unknown ambient excitation but also with a known one
One year of structural health monitoring of the Meazza Stadium in Milan: analysis of the collected data
No full textThe interest about all the topics related to security and safety of people is increasing. In particular great attention is devoted to the health monitoring of large civil structures like high-rise buildings and sports arenas. Among these the Giuseppe Meazza is one of the biggest stadium in Italy and the municipality decided to develop and implement a system devoted to monitor its structural health. Since September 2007 the first portion of the system covering part of the Meazza grandstands is installed and working. At the moment about 1/5 of the structure is continuously monitored by means of vibration measurement devices. Even if only a part of the stadium is covered by the system a huge amount of data has been collected and their manual analysis by an operator is not affordable. The system should therefore guarantee an automatic detection of significant events without human supervision. Analysis of the first data has a crucial relevancy: the most significant parameters and the associated threshold levels must be established. This paper faces the first results analysis, pointing out the most significant parameters and a statistical analysis of their evolution during the first year of monitoring. © 2009 Society for Experimental Mechanics Inc
Experimental investigation of the pre-tension effects on the modalparameters of a slender pre-tensioned concrete beam
No full textSlender pre-tensioned concrete structures are nowadays of common use, due to their unique features. Slender beam can be used to sustain large structures and important loads leaving the architects a lot possibilities in the structure design. The health of such structures is strictly related to the conditions of the tendon that, in many cases, are not accessible. Visual inspection is the most used technique to assess the tendon condition even if in many cases access to the inspection points is very difficult or impossible This paper investigates the possibility of detecting a pre-stress loss or a tendon failure by means of modal analysis. A pre-stressed concrete beam has been built and tested under laboratory conditions, varying the applied pre-stress and the number of active tendon. Modal analysis has been performed in each of the experimental condition and attention has been focussed on the variation of all identified modal parameters, frequency, damping and mode shapes. Furthermore a set of damage indexes have been computed to highlight the most sensible magnitude able to identify a change on the structure. Obtained results showed that an accurate analysis is needed in order to identify a change in modal parameters due to variations in the pre-stress, while tendon failure leads to more important changes in the identification results. The performed study are the starting point in order to properly tune a numerical model of the beam useful to accurately interpreter structural changes. ©2010 Society for Experimental Mechanics Inc
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