Mechanical Engineering

This study proposes an analytical model for vibrations in a cracked rectangular plate as one of the results from a programme of research on vibration based damage detection in aircraft panel structures. This particular work considers an isotropic plate, typically made of aluminium, and containing a crack in the form of a continuous line with its centre located at the centre 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. 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.

In this paper a theoretical relationship for the effective thermal conductivity of a multiphase transversely isotropic composite system is obtained. The Generalized Self-Consistent Method and simple energy balance principle is employed to derive a more appropriate model. In the derivation, it is assumed that the orientation of fiber within the transversely isotropic composite system is unidirectional and surrounded by two different phases of porous and matrix phase. A combined effect of these three different phases on the effective thermal conductivity of the composite system in transverse direction is studied. The effect of the interfacial contact conductance between the fibers and porous medium is also considered. Results of effective thermal conductivity are plotted against volume fraction and conductance which shows extremely good agreement.

In this paper the nonlinear vibration of an aircraft panel structure modelled as an isotropic cracked plate and subjected to transverse harmonic excitation is considered for studying the dynamic response, both analytically and experimentally. A crack is arbitrarily located at the centre of the plate, consisting of a continuous line. This mathematical model is in the form of Duffing equation with a cubic nonlinear term. The perturbation method of multiple scales is used to solve the algebraic equation, and then investigated with the results of the direct integration within Mathematica™ and finite element analysis in ABAQUS for the first mode only. In addition, experimental measurements are also carried out to verify the dependence of the cracked plate's fundamental mode shape and resonance frequency on the vibration displacement amplitude. An extermely close agreement between these results is observed.

In this study derived differential equations are examined by using one of the famous Finite Element Method (FEM) i.e. Galerkin’s method under given boundary conditions. The flow in the pipe is considered to be periodic and moves transversely towards the walls of the pipe. It has been observed that this type of flow movement in the vessel may cause dynamic instability at the boundaries or cause sudden failure. The results obtained from Galerkin’s method is compared with the exact solution and found good in agreement between the two results.

A specially designed apparatus and circuit working on the principle of inverse piezoelectricity due to the effect of polarization was used to find the relationship between resistance and peak to peak voltage of Lead Zirconate Titanate (PZT-5A4E)by shocking it at variable frequencies and at variable resistances under various thermal conditions within Curie temperature limit using equivalent circuit method. It was found that by increasing temperature, peak to peak voltage increases and similarly by increasing frequency, peak to peak voltage decreases and with the increase in resistance peak to peak voltage decreases.

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 ...

A specially designed apparatus and circuit working on the principle of inverse piezoelectricity due to the effect of polarization was used to find the relationship between resistance and peak to peak voltage of Lead Zirconate Titanate (PZT-5A4E) by shocking it at variable frequencies and at variable resistances under various thermal conditions within Curie temperature limit using equivalent circuit method. It was found that by increasing temperature, peak to peak voltage increases and similarly by increasing frequency, peak to peak voltage decreases and with the increase in resistance peak to peak voltage decreases.

Wheat is a strategic crop which is considered to be one of the most important agricultural products. Harvest Loss is a type of loss that decreases final production performance. Combine harvester loss is divided to several losses; natural loss, header loss, threshing loss, separation loss and quality loss. The major loss is attributed to header loss. Combine harvester header loss is the consequence of cutter bar strokes, height of the reel, reel peripheral speed, travel speed, width of harvest, height of cutting, crop moisture, height and density of crop, feed rate of the crop and etc. Mathematical modeling of the combine harvester is the initial step to retrofit the performance of the combine harvester. Dimensional analysis is a method that uses effective variables and forms several dimensionless equations to evaluate the issue. The variables are changed to dimensionless equations and this reduces the number of variables. Accordingly, the numbers of required experiments to determine relationship between variables are decreased. This research has developed a model using combination of theoretical combination method (dimensional analysis) and practical phase (field experiments). This method uses most of the elements that have effect on loss. There were π-terms developed out of the effective elements, and the experiments were designed based on these pi-terms. Complete randomized block design was used in practical experiments. All the experiments were done in Pars-Abad with CLAAS combine harvester. Increasing travel speed in a defined range decreased header loss. Height of cut should be optimized because of some reciprocating reasons. The obtained data in analysis stage, verified the model with relatively high (76%) correlation coefficient.

Objective: To evaluate the analgesic efficacy of a modified ultra sound guided unilateral STAP block with 0.25% bupivacaine in laparoscopic cholecystectomy compared with conventional port site and intraperitoneal infiltration of the same drug in similar amount and concentration. Study Design: Randomized clinical trial. Place and Duration of Study: Pak Emirates Military Hospital Rawalpindi, from Oct 2017 to Feb 2018. Material and Methods: 100 adult female as well as male patients were randomized by lottery method into 2 equal groups. In group A (n=50) unilateral STAP block was performed under ultrasound guidance (Xario 200 Toshiba). The 18 Hz linear probe was placed in the midline of the abdomen 2 cm below the xiphisternum and moved right laterally along the subcostal margin to the anterior axillary line and bupivacaine 0.25% 0.4 ml/kg) was injected after negative aspiration test. Group B (n=50) patients received intra peritoneal instillation of 1/3 of the total drug volume before cl...