Optimal input cross-power spectra in shake table testing of asymmetric structures

The study considers earthquake shake table testing of bending-torsion coupled structures under multi-component stationary random earthquake excitations. An experimental procedure to arrive at the optimal excitation cross-power spectral density (psd) functions which maximize/minimize the steady state variance of a chosen response variable is proposed. These optimal functions are shown to be derivable in terms of a set of system frequency response functions which could be measured experimentally without necessitating an idealized mathematical model to be postulated for the structure under study. The relationship between these optimized cross-psd functions to the most favourable/least favourable angle of incidence of seismic waves on the structure is noted. The optimal functions are also shown to be system dependent, mathematically the sharpest, and correspond to neither fully correlated motions nor independent motions. The proposed experimental procedure is demonstrated through shake table studies on two laboratory scale building frame models

Optimal cross-spectrum of road loads on vehicles: theory and experiments

The random vibration analysis of a four-wheeled vehicle traveling on parallel road tracks with random unevenness is considered. The two parallel road track roughnesses are modeled as a vector of homogeneous, non-isotropic, Gaussian random fields with known auto-power spectral density (PSD) functions but unknown cross-PSD functions. Questions on bounds on the response, when the unknown cross-PSD functions are varied over their permitted ranges, are considered. An exact solution to this problem, based on principles of random vibrations, is arrived at. Based on this theoretical solution, an experimental procedure to determine these response bounds on automotive structural response, without involving mathematical idealization of structural matrices, is developed. Illustrations involving numerical modeling and laboratory testing (using a four-post test rig) of vibratory behavior of a four-wheeled vehicle due to random road loads are presented

System reliability of randomly vibrating structures: Computational modeling and laboratory testing

The problem of determination of system reliability of randomly vibrating structures arises in many application areas of engineering. We discuss in this paper approaches based on Monte Carlo simulations and laboratory testing to tackle problems of time variant system reliability estimation. The strategy we adopt is based on the application of Girsanov's transformation to the governing stochastic differential equations which enables estimation of probability of failure with significantly reduced number of samples than what is needed in a direct simulation study. Notably, we show that the ideas from Girsanov's transformation based Monte Carlo simulations can be extended to conduct laboratory testing to assess system reliability of engineering structures with reduced number of samples and hence with reduced testing times. Illustrative examples include computational studies on a 10 degree of freedom nonlinear system model and laboratory/computational investigations on road load response of an automotive system tested on a four post Lest rig. (C) 2015 Elsevier Ltd. All rights reserved

Experimental estimation of time variant system reliability of vibrating structures based on subset simulation with Markov chain splitting

The study investigates the application of ideas from variance reduction schemes, developed in the area of computational structural reliability modelling, to the problems of experimental estimation of time variant reliability of randomly excited vibrating structures. The study considers series/parallel system reliability of vibrating systems under multi-component random excitations. An experimental protocol, based on subset simulation with Markov chain splitting, is proposed to estimate probabilities of failure as low as 10(-5) to 10(-4) with a relatively smaller number of samples and hence with reduced test times. Illustrative examples consist of earthquake shake table studies on a three-storied bending-torsion coupled building frame under bi-axial non-stationary, random earthquake support motions

Cutaneous angiomyolipoma

We report a case of cutaneous angiomyolipoma (AML) found on the anterior abdominal wall of a 3-year-old female child. Histologic examination showed a well-circumscribed nodule in the dermis composed of an intimate mixture of convoluted thick-walled blood vessels, smooth muscle, and mature fat. This lesion differs from renal AML in terms of a lack of association with tuberous sclerosis, circumscription, absence of epithelioid cells, and male predominance. We concluded that the unique features of this lesion distinguish it from other lesions such as angiomyoma, angiolipoma, myolipoma, haemangioma, and other mixed mesenchymal tumors. This case report suggests that the features considered diagnostic of AML can occur in extrarenal sites and, therefore, this diagnosis cannot be excluded on the basis of site alone

Sputum cytology in suspected cases of carcinoma of lung (Sputum cytology a poor man's bronchoscopy!)

Aims: To evaluate the role of sputum cytology in the diagnostic work-up of patients with suspected lung cancer . Settings and Design : Spontaneously produced fresh sputum was analyzed in clinically suspected cases of lung cancer. Materials and Methods: Spontaneously produced fresh sputum was analyzed in 36 clinically suspected cases of lung cancer. It was carried out using the "fresh pick and smear" method, which employs examination of sputum for blood-tinged, discolored or solid particles and preparation of thin and even smears from these selected portions. Statistical Analysis Used : Average and means. Results: Sensitivity of sputum cytology was 60%, which increased with an increase in the number of samples examined. Conclusions: Sputum cytology in suspected cases of carcinoma of lung is a useful diagnostic tool. It may be called as a poor man′s bronchoscopy