Vibration analysis of cracked aluminium plates

This research is concerned with analytical modelling of the effects of cracks in structural plates and panels within aerospace systems such as aeroplane fuselage, wing, and tail-plane structures, and, as such, is part of a larger body of research into damage detection methodologies in such systems. This study is based on generating a so-called reduced order analytical model of the behaviour of the plate panel, within which a crack with some arbitrary characteristics is present, and which is subjected to a force that causes it to vibrate. In practice such a scenario is potentially extremely dangerous as it can lead to failure, with obvious consequences. The equation that is obtained is in the form of the classical Duffing equation, in this case, the coefficients within the equation contain information about the geometrical and mass properties of the plate, the loading and boundary conditions, and the geometry, location, and potentially the orientation of the crack. This equation has been known for just over a century and has in the last few decades received very considerable attention from both the analytical dynamics community and also from the dynamical systems researchers, in particular the work of Ueda, Thompson, in the 1970s and 1980s, and Thomsen in the 1990s and beyond. An approximate analytical solution is obtained by means of the perturbation method of multiple scales. This powerful method was popularized in the 1970s by Ali H.Nayfeh, and discussed in his famous books, ‘Perturbation Methods’ (1974) and ‘Nonlinear Oscillations’ (1979, with D.T.Mook), and also by J.Murdock (1990), and M.P.Cartmell et al. (2003) and has been shown to be immensely useful for a wide range of nonlinear vibration problems. In this work it is shown that different boundary conditions can be admitted for the plate and that the modal natural frequencies are sensitive to the crack geometry. Bifurcatory behaviour of the cracked plate has then been examined numerically, for a range of parameters. The model has been tested against experimental work and against a Finite Element model, with good corroboration from both. In all events, this is a significant new result in the field and one that if implemented within a larger damage detection strategy, could be of considerable practical use

Effects of variable resistance on smart structures of cubic reconnaissance satellites in various thermal and frequency shocking conditions

Piezoelectric materials are widely used as smart structures in cubic reconnaissance satellites because of their sensing, actuating, and energy-harvesting abilities. In this study, an analytical model is developed in specific mechanical thermal shocking conditions. A special circuit and apparatus is designed for experimentation on the basis of the inverse piezoelectric effect. An equivalent circuit method is used to establish the relationship between the resistance and peak-to-peak voltage of lead zirconate titanate used as smart materials for cubic reconnaissance satellites. Various frequencies and resistance were applied in different mechanical thermal shocking conditions. Moreover, numerical simulations are conducted in various mechanical loading conditions to determine the accumulative effect. The model provides a novel mechanism to characterize the smart structures in cubic reconnaissance satellites. A rise in temperature increases peak-to-peak voltage; a rise in frequency decreases peak-to-peak voltage; and intensified resistance decreases peak-to-peak voltage. Based on experimentation and simulation, the optimum resistance is predicted for the various frequencies and temperatures. The various conditions may correspond to the different applications of smart structures for cubic reconnaissance satellites. The analytical calculations are in good agreement with experimental and numerical calculations. © 2017, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany

Analytical modeling and vibration analysis of partially cracked rectangular plates with different boundary conditions and loading

This study proposes an analytical model for vibrations in a cracked rectangular plate as one of the results from a program of research on vibration based damage detection in aircraft panel structures. This particular work considers an isotropic plate, typically made of aluminum, and containing a crack in the form of a continuous line with its center located at the center of the plate and parallel to one edge of the plate. The plate is subjected to a point load on its surface for three different possible boundary conditions, and one examined in detail. Galerkin's method is applied to reformulate the governing equation of the cracked plate into time dependent modal coordinates. Nonlinearity is introduced by appropriate formulations introduced by applying Berger's method. An approximate solution technique—the method of multiple scales—is applied to solve the nonlinear equation of the cracked plate. The results are presented in terms of natural frequency versus crack length and plate thickness, and the nonlinear amplitude response of the plate is calculated for one set of boundary conditions and three different load locations, over a practical range of external excitation frequencies

Outcomes of intubation techniques in nasolacrimal duct blockage in adult age group: a comparative study based on Sindh, Pakistan population

Background: Nasolacrimal duct obstruction is listed under the heading of congenital diseases; on other hand it is also commonly present in adult age group. In population of Sindh we found these patients frequently. Through this study we revealed the surgical options for the treatment of Nasolacrimal duct obstruction in population of Sindh provenience of Pakistan. The objective of the study was to compare the outcomes of two different intubation techniques in treatment of Nasolacrimal duct obstruction between two age groups. Comparative study was conducted in the Department of Ophthalmology Al-Ibrahim Eye Hospital Karachi from May 2018 to June 2019.Methods: Total 136 numbers of patients were included on the bases of history, clinical examination and pre-operative syringing test. Non- probability convenient sampling was applied for data collection. Total 136 numbers of patients were divided into two groups on the bases of treatment and further subgroup on the bases of age ranges. Data were analyzed by SPSS version 20.0.Results: Frequency and percentage of recovery in six months in each subgroup with application of chi-square test. Frequency and percentage of post-operative complications prolong treatment and regurgitation and patency of tube in each group and subgroups.Conclusions: The results showed significant difference between the groups. Group A showed higher success rate with minimal percentage of complications and post-operative measurements in both age ranges as compare to Group B

A Comparative Study on Electroplating of FDM Parts

Electroplating on fused deposition modeling parts through two different routes is presented in the study. One route follows the conventional method of electroplating using chromic acid for surface preparation or etching and the other route uses the novel method of electroplating using aluminium charcoal (Al-C) paste for surface preparation. Same plating conditions are used for both the routes employed. The result proposes that instead of shell cracking in few electroplated samples, Al-C route is also capable of producing good copper deposition on FDM samples. Cracks may develop in few samples electroplated through Al-C route, because of dissolution of paste at high operating condition during electroplating. Proper drying of electrolessly plated samples and adaptation of suitable operating condition reduces the risk of electroplated shell cracking

Substantial and sustained reduction in under-5 mortality, diarrhea, and pneumonia in Oshikhandass, Pakistan : Evidence from two longitudinal cohort studies 15 years apart

Funding Information: Study 1 was funded through the Applied Diarrheal Disease Research Program at Harvard Institute for International Development with a grant from USAID (Project 936–5952, Cooperative Agreement # DPE-5952-A-00-5073-00), and the Aga Khan Health Service, Northern Areas and Chitral, Pakistan. Study 2 was funded by the Pakistan US S&T Cooperative Agreement between the Pakistan Higher Education Commission (HEC) (No.4–421/PAK-US/HEC/2010/955, grant to the Karakoram International University) and US National Academies of Science (Grant Number PGA-P211012 from NAS to the Fogarty International Center). The funding bodies had no role in the design of the study, data collection, analysis, interpretation, or writing of the manuscript. Publisher Copyright: © 2020 The Author(s).Peer reviewedPublisher PD

Vibration and Modal Analysis of Low Earth Orbit Satellite

This paper presents design, modeling, and analysis of satellite model used for remote sensing. A detailed study is carried out for the design and modeling of the satellite structure focusing on the factors such as the selection of material, optimization of shape and geometry, and accommodation of different subsystems and payload. The center of mass is required to be kept within the range of (1-2) cm from its geometric center. Once the model is finalized it is required to be analyzed by the use of Ansys, a tool for finite element analysis (FEA) under given loading and boundary conditions. Static, modal, and harmonic analyses in Ansys are performed at the time of ground testing and launching phase. The finite element analysis results are also validated and compared with the theoretical predictions. These analyses are quite helpful and suggest that the satellite structure does not fail and retains its structural integrity during launch environment

DYNAMICAL SYSTEM ANALYSIS FROM NONLINEAR TRANSITION TO CHAOS FOR A CRACKED PLATE

Nonlinear vibrations for an isotropic cracked plate with different possible boundary conditions subjected to transverse harmonic excitation are evaluated. The first mode is examined in detail around the resonant region. A crack consisting of a continuous line is arbitrarily located at the middle and along the x-axis of the plate. The nonlinear dynamical systems analysis of this cracked plate model begins with the stability of the phase states, and the Poincare map followed by a study of the bifurcations that are observed from the analysis of saddle trajectories, and the estimation of the Lyapunov exponent. This leads to the emergence of strange attractors of fractal dimension, the evolution of saddle orbits into chaos, and to the observation that in this system seemingly chaotic behaviour can emerge from perfectly deterministic origins. In this study, the computational methods required are implementations of the Dynamics 2 software package, and specialized code written in Mathematical. Results shows that the system response could be extremely susceptible to changes in the control parameters, and the variation in the half crack length at the plate centre is one influence on the system s bifurcation and chaos

منتخب آپ بیتیوں میں تاریخ ،سماج اور ثقافت کی عکاسی

This article contains many angles of the human related things, which have been discussed in the autobiographies since beginning. It is fact that every literal as well as commonsense person wants to know about history of the area or the world and try to trace out which depends upon the facts and figures. But history has always shown the only the side of the kings or the dominants’ but not present the whole truth about the society. On the other hand autobiographies show the picture of whole the phenomenon and original aspects of the prevailing norms of civilization. To present the truth, authenticity and importance of the autobiographies in the literature as well as to elaborate such kind of accuracy in biographies, this research article has been written for this purpose