277 research outputs found
SLDV technology for measurement of mistuned bladed disc vibration
Bladed discs are very sensitive structures and the amplitude vibration of each
blade can vary significantly from blade to blade due to a series of factors such as
geometrical inhomogeneity between blades or material properties. These factors
lead to bladed disks mistuned thus the forced response amplitudes can be much
higher than the level predicted for a tuned assembly.
Designed models need to be “validate” to predict the response of a real bladed
disc within the tolerances set by the manufactures and this process is very
expensive as well as difficult. The validation process needs “reference data” as
fundamental input against what all predictions can be compared and validated.
Data that can be provided both under stationary conditions and under rotating
conditions and the latter is the most difficult to achieve, especially for bladed
disc assemblies which are very sensitive to any structural modification as it
could be attaching a transducer to measure vibrations. There are contact-less
measurement techniques available which, however, provide limited information
because they can measure only limited areas of the vibrating structures.
The aim of this study is to design measurement methods, using a standard
Scanning Laser Doppler Vibrometer (SLDV) and to integrate it into a software
platform which will be able to handle a series of measurement tasks both under
stationary and rotating conditions. The main contribution of this thesis is to
extend the use of Continuous Scanning LDV (CSLDV) to the rotating structures,
such as bladed discs, thus to perform synchronous measurements. Hence, a
bladed disc is needed to be designed to perform vibration predictions and
measurements and a mathematical model of the measurement test to control,
critically, all possible sources of errors involved in measurement under rotating conditions; all these to produce a robust measurement method. While the
primary focus is the measurement method, the study also extends to evaluation
of the sensitivity properties of the bladed disk test pieces that are the object of
the measurement tool
Bloom filter variants for multiple sets: a comparative assessment
In this paper we compare two probabilistic data structures for association
queries derived from the well-known Bloom filter: the shifting Bloom filter
(ShBF), and the spatial Bloom filter (SBF). With respect to the original data
structure, both variants add the ability to store multiple subsets in the same
filter, using different strategies. We analyse the performance of the two data
structures with respect to false positive probability, and the inter-set error
probability (the probability for an element in the set of being recognised as
belonging to the wrong subset). As part of our analysis, we extended the
functionality of the shifting Bloom filter, optimising the filter for any
non-trivial number of subsets. We propose a new generalised ShBF definition
with applications outside of our specific domain, and present new probability
formulas. Results of the comparison show that the ShBF provides better space
efficiency, but at a significantly higher computational cost than the SBF
An anonymous inter-network routing protocol for the Internet of Things
With the diffusion of the Internet of Things (IoT), computing is becoming increasingly pervasive, and different heterogeneous networks are integrated into larger systems. However, as different networks managed by different parties and with different security requirements are interconnected, security becomes a primary concern. IoT nodes, in particular, are often deployed “in the open”, where an attacker can gain physical access to the device. As nodes can be deployed in unsurveilled or even hostile settings, it is crucial to avoid escalation from successful attacks on a single node to the whole network, and from there to other connected networks. It is therefore necessary to secure the communication within IoT networks, and in particular, maintain context information private, including the network topology and the location and identity of the nodes. In this paper, we propose a protocol achieving anonymous routing between different interconnected networks, designed for the Internet of Things and based on the spatial Bloom filter (SBF) data structure. The protocol enables private communication between the nodes through the use of anonymous identifiers, which hide their location and identity within the network. As routing information is encrypted using a homomorphic encryption scheme, and computed only in the encrypted domain, the proposed routing strategy preserves context privacy, preventing adversaries from learning the network structure and topology. This, in turn, significantly reduces their ability to gain valuable network information from a successful attacks on a single node of the network, and reduces the potential for attack escalation
Response phase mapping of nonlinear joint dynamics using continuous scanning LDV measurement method
AIP PublishingInternational audienceThis study aims to present a novel work aimed at locating discrete nonlinearities in mechanical assemblies. The long term objective is to develop a new metric for detecting and locating nonlinearities using Scanning LDV systems (SLDV). This new metric will help to improve the modal updating, or validation, of mechanical assemblies presenting discrete and sparse nonlinearities. It is well established that SLDV systems can scan vibrating structures with high density of measurement points and produc e highly defined Operational Deflection Shapes (ODSs). This paper will present some insights on how to use response phase mapping for locating nonlinearities of a bolted flange. This type of structure presents two types of nonlinearities, which are geometr ical and frictional joints. The interest is focussed on the frictional joints and, therefore, the ability to locate which joint s are responsible for nonlinearity is seen highly valuable for the model validation activities
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