17,307 research outputs found
An experimental validation of the fatigue damaging events extracted using the wavelet bump extraction (WBE) algorithm
This paper describes an experimental validation of the fatigue damaging events that were identified and
extracted using a wavelet-based fatigue data editing technique. This technique, known as the Wavelet Bump
Extraction (WBE) algorithm, is specifically designed to summarise a long record of fatigue variable amplitude
(VA) loading whilst preserving the original load cycle sequence. Using WBE the fatigue damaging events were
identified and extracted in order to produce a mission signal. In order to validate the effectiveness of WBE in
practical applications a VA road load time history that was measured on a road vehicle suspension arm was
taken as a case study. Uniaxial fatigue tests were performed using the original signal, the WBE mission signal
and the individual WBE extracted segments. A mirror polished specimen of SAE 1042 steel was tested using a
servo-hydraulic machine. The fatigue lives measured for these VA loadings were then compared to the fatigue
lives calculated from a VA strain loading fatigue damage model. The results show a good fatigue life
correlation at the coefficient of 0.98 between the prediction and experiment. For the road load time history
considered, the WBE mission signal was found to be only 40% the time duration of the original time history
while maintaining 60% of the fatigue damage according to analytical calculation and 87% according to experimental testing
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Bump extraction algorithm for variable amplitude fatigue loading
This paper presents the development of a fatigue mission synthesis algorithm, called Wavelet Bump Extraction (WBE), for summarising long records of fatigue road load data. This algorithm is used to extract fatigue damaging events or bumps in the record that cause the majority of the fatigue damage, whilst preserving the load cycle sequences. Bumps are identified from characteristic frequency bands in the load spectrum using the 12th order Daubechies wavelet. The bumps are combined to produce a mission signal which has equivalent signal statistics and fatigue damage to the original signal. The WBE accuracy has been evaluated by observing the cycle sequence effects of the bump loadings. The WBE was compared with the time domain fatigue data editing method, so that the effectiveness of WBE can be verified. Using WBE, a substantial compression of the load-time history could be achieved for the purpose of accelerated fatigue tests in the automotive industry
Development of response models for the Earth Radiation Budget Experiment (ERBE) sensors. Part 3: ERBE scanner measurement accuracy analysis due to reduced housekeeping data
The accuracy of scanner measurements was evaluated when the sampling frequency of sensor housekeeping (HK) data was reduced from once every scan to once every eight scans. The resulting increase in uncertainty was greatest for sources with rapid or extreme temperature changes. This analysis focused on the mirror attenuator mosaic (MAM) baffle and plate and scanner radiometer baffle due to their relatively high temperature changes during solar calibrations. Since only solar simulator data were available, the solar temperatures were approximated on these components and the radiative and thermal gradients in the MAM baffle due to reflected sunlight. Of the two cases considered for the MAM plate and baffle temperatures, one uses temperatures obtained from the ground calibration. The other attempt uses temperatures computed from the MAM baffle model. This analysis shows that the heat input variations due largely to the solar radiance and irradiance during a scan cycle are small. It also demonstrates that reasonable intervals longer than the current HK data acquisition interval should not significantly affect the estimation of a radiation field in the sensor field-of-view
The Fourier finite element method for the corner singularity expansion of the Heat equation
Near the non-convex vertex the solution of the Heat equation is of the form u = (c star epsilon) chi r(pi/omega) sin(pi theta/omega) + omega, omega is an element of L-2(R+; H-2), where c is the stress intensity function of the time variable t,* the convolution, epsilon (x, t) = re(-r2/4t)/2 root pi t(3), chi a cutoff function and omega the opening angle of the vertex. In this paper we use the Fourier finite element method for approximating the stress intensity function c and the regular part omega, and derive the error estimates depending on the regularities of c and omega. We give some numerical examples, confirming the derived convergence rates. (C) 2014 Elsevier Ltd. All rights reserved.X111Ysciescopu
On the Security of Millimeter Wave Vehicular Communication Systems using Random Antenna Subsets
Millimeter wave (mmWave) vehicular communica tion systems have the potential
to improve traffic efficiency and safety. Lack of secure communication links,
however, may lead to a formidable set of abuses and attacks. To secure
communication links, a physical layer precoding technique for mmWave vehicular
communication systems is proposed in this paper. The proposed technique
exploits the large dimensional antenna arrays available at mmWave systems to
produce direction dependent transmission. This results in coherent transmission
to the legitimate receiver and artificial noise that jams eavesdroppers with
sensitive receivers. Theoretical and numerical results demonstrate the validity
and effectiveness of the proposed technique and show that the proposed
technique provides high secrecy throughput when compared to conventional array
and switched array transmission techniques
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