Determination of the orthotropic plate parameters of stiffened plates and grillages in free vibration

It is well known that the analysis of vibration of orthogonally stiffened rectangular plates and grillages may be simplified by replacing the actual structure by an orthotropic plate. This needs a suitable determination of the four elastic rigidity constants Dx, Dy, Dxy, D1 and the mass {Mathematical expression} of the orthotropic plate. A method is developed here for determining these parameters in terms of the sectional properties of the original plate-stiffener combination or the system of interconnected beams. Results of experimental work conducted on aluminium plates agree well with the results of the theory developed here.

Influence of External Light Waves on the Thermoelectric Power Under Strong Magnetic Field in Ultrathin Films, Quantum Wires and Quantum Dots of Optoelectronic Materials

In this paper, an attempt is made to study the influence of external light waves on the thermoelectric power under strong magnetic field (TPSM) in ultrathin films (UFs), quantum wires (QWs) and quantum dots (QDs) of optoelectronic materials whose unperturbed dispersion relation of the conduction electrons are defined by three and two band models of Kane together with parabolic energy bands on the basis of newly formulated electron dispersion laws in each case. We have plotted the TPSM as functions of film thickness, electron concentration, light intensity and wavelength for UFs, QWs and ODs of InSb, GaAs, Hg1-xCdxTe and In1-xGaxAsyP1-y respectively. It appears from the figures that for UFs, the TPSM increases with increasing thickness in quantum steps, decreases with increasing electron degeneracy exhibiting entirely different types of oscillations and changes with both light intensity and wavelength and these two latter types of plots are the direct signature of light waves on opto-TPSM. For QWs, the opto-TPSM exhibits rectangular oscillations with increasing thickness and shows enhanced spiky oscillations with electron concentration per unit length. For QDs, the opto-TPSM increases with increasing film thickness exhibiting trapezoidal variations which occurs during quantum jumps and the length and breadth of the trapezoids are totally dependent on energy band constants. Under the condition of non-degeneracy, the results of opto-TPSM gets simplified into the well-known form of classical TPSM equation which the function of three constants only and being invariant of the signature of band structure.

On the theory of the indentation test for the measurement of tensile strength of brittle materials

A theoretical solution has been obtained for the state of stress in a rectangular plate under a pair of symmetrically placed rigid indenters. The stress distributions along the two central axes have been calculated for a square plate assuming the pressure distribution under the indenters as uniform, parabolic and one resulting from 'constant displacement' on a semiinfinite boundary, for different ratios of indenter-width to side of square. The results are compared with those of photoelastic analysis of Berenbaum and Brodie and the validity of the solution is discussed. The solution has been extended to orthotropic materials and numerical results for one type of coal are given.

An exact analysis of free vibrations of simply-supported viscoelastic plates

In this paper an exact three-dimensional analysis for free vibrations of a class of simply-supported viscoelastic rectangular plates is given. The characteristic equation defining the eigenvalues is of closed form. Some numerical results are presented for standard linear solids. Results from thin plate and Mindlin theories are also given for the purpose of comparison.

Some pulse characteristics of atmospheric radio noise bursts at 3 MHz

An atmospheric radio noise burst represents the radiation received from one complete lightning flash at the frequency to which a receiver is tuned and within the receiver bandwidth. At tropical latitudes, the principal source of interference in the frequency range from 0.1 to 10 MHz is the burst form of atmospheric radio noise. The structure of a burst shows several approximately rectangular pulses of random amplitude, duration and frequency of recurrence. The influence of the noise on data communication can only be examined when the value of the number of pulses crossing a certain amplitude threshold per unit time of the noise burst is known. A pulse rate counter designed for this purpose has been used at Bangalore (12°58′N, 77°35′E) to investigate the pulse characteristics of noise bursts at 3 MHz with a receiver bandwidth of 3.3 kHz/6d B. The results show that the number of pulses lying in the amplitude range between peak and quasi-peak values of the noise bursts and the burst duration corresponding to these pulses follow log normal distributions. The pulse rates deduced therefrom show certain correlation between the number of pulses and the duration of the noise burst. The results are discussed with a view to furnish necessary information for data communication.

An optimum criterion for eccentrically loaded R. C. columns

An analysis of eccentrically loaded short reinforced concrete columns using a variable failure strain criterion is presented. The method dispenses with the usual procedure of assuming a fixed value for the ultimate strain in concrete. The analysis is based on the use of a simple, single equation for the complete stress-strain curve of concrete and the adoption of a process of maximisation of moment with respect to extreme fibre concrete compressive strain. Columns of rectangular section and loaded eccentrically along one axis only are considered in this paper. A good agreement is observed between the theoretical and experimental values of some test results.

A three-dimensional solution for plates and laminates

A general three-dimensional solution is presented for statics and dynamics of plates, homogeneous or laminated, of orthotropic materials. The solution is in series form. Using parts of the general solution a variety of problems, especially of rectangular configurations, can be solved. As Mindlin's approximate analysis for vibration of thick plates is often adequate for specific practical purposes, a general solution for Mindlin's analysis is also given.

A coaxial capacitive voltage divider for oscilloscopic recording of nanosecond high voltage pulses

A coaxial capacitance voltage divider with a ratio of 110 and a rise time much less than 2.5 ns was developed for use with a transmission line pulse generator capable of producing 100 kV rectangular pulses of 2 mu s duration. The low voltage arm of the divider is a 3 cm long tube of titania (TiO2) turned out from a cylindrical compact. The compact was made by first pressing titania powder using a suitable binder and then sintering at controlled temperatures. The tube was slipped over the terminating end of the pulse-forming cable to form the divider with the cable capacitance.

Stabilization of the bio-membrane by small molecules: interaction of trehalose with the phospholipid bilayer

Anhydrobiotic organisms undergo periods of acute dehydration during their life cycle. It is of interest to understand how the biomembrane remains intact through such stress. A disaccharide, trehalose, which is metabolised during anhydrobiosis is found to prevent disruption of model membrane systems. Molecular modelling techniques are used to investigate the possible mode of interaction of trehalose with a model monolayer. The objective is to maximise hydrogen bonding between the two systems. A phospholipid matrix consisting of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) is chosen to represent the monolayer. The crystal structure of DMPC reveals that there are two distinct conformers designated as A and B. An expansion of the monolayer, coplanar with its surface, results in the trehalose molecule being accommodated in a pocket formed by four B conformers. One glucose ring of the sugar rests on the hydrophobic patch provided by the choline methyls of an A conformer. Five hydrogen bonds are formed involving the phosphate oxygens of three of the surrounding B conformers. The model will be discussed with reference to relevant experimental data on the interaction.

Coplanar Capacitively Coupled Probe Fed Microstrip Antennas for Wideband Applications

The design and analysis of a coplanar capacitive fed microstrip antenna suspended above the ground plane is presented. It is demonstrated that the proposed approach can be used for designing antennas with impedance bandwidth of about 50% and a good gain to operate in various microwave bands. The model of the antenna incorporates the capacitive feed strip which is fed by a coaxial probe using equivalent circuit approach, and matches simulation and experimental results. The capacitive feed strip used here is basically a rectangular microstrip capacitor formed from a truncated microstrip transmission line and all its open ends are represented by terminal or edge capacitances. The error analysis was carried out for validity of the model for different design parameters. The antenna configuration can be used where unidirectional radiation patterns are required over a wide bandwidth.

Heat transfer correlations for PCM-based heat sinks with plate fins

Characterization of melting process in a Phase Change Material (PCM)-based heat sink with plate fin type thermal conductivity enhancers (TCEs) is numerically studied in this paper. Detailed parametric investigations are performed to find the effect of aspect ratio of enclosure and the applied heat flux on the thermal performance of the heat sinks. Various non-dimensional numbers, such as Nusselt number (Nu), Rayleigh number (Ra), Stefan number (Ste) and Fourier number (Fo) based on a characteristic length scale, are identified as important parameters. The half fin thickness and the fin height are varied to obtain a wide range of aspect ratios of an enclosure. It is found that a single correlation of Nu with Ra is not applicable for all aspect ratios of enclosure with melt convection taken into account. To find appropriate length scales, enclosures with different aspect ratios are divided into three categories, viz. (a) shallow enclosure, (b) rectangular enclosure and (c) tall enclosure. Accordingly, an appropriate characteristic length scale is identified for each type of enclosure and correlation of Nu with Ra based on that characteristic length scale is developed. (C) 2010 Elsevier Ltd. All rights reserved.

A Computationally Efficient PWM Algorithm for Multilevel Inverters

Centred space vector PWM (CSVPWM) technique is popularly used for three level voltage source inverters. The reference voltage vector is synthesized by time-averaging of the three nearest voltage vectors produced by the inverter. Identifying the three voltage vectors, and calculation of the dwelling time for each vector are both computationally intensive. This paper analyses the process of PWM generation in CSVPWM. This analysis breaks up a three-level inverter into six different conceptual two level inverters in different regions of the fundamental cycle. Control of 3-level inverter is viewed as the control of the appropriate 2-level inverter. The analysis leads to a systematic simplification of the computations involved, finally resulting in a computationally efficient PWM algorithm. This algorithm exploits the equivalence between triangle comparison and space vector approaches to PWM generation. This algorithm does not involve any 3-phase/2-phase or 2-phase/3-phase transformation. This also does not involve any transformation from rectangular to polar coordinates, and vice versa. Further no evaluation of trigonometric functions is necessary. This algorithm also provides for the mitigation of DC neutral point unbalance, and is well suited to digital implementation. Simulation and experimental results are presented.

A Smooth Finite Element Method Based on Reproducing Kernel DMS-Splines

The element-based piecewise smooth functional approximation in the conventional finite element method (FEM) results in discontinuous first and higher order derivatives across element boundaries Despite the significant advantages of the FEM in modelling complicated geometries, a motivation in developing mesh-free methods has been the ease with which higher order globally smooth shape functions can be derived via the reproduction of polynomials There is thus a case for combining these advantages in a so-called hybrid scheme or a `smooth FEM' that, whilst retaining the popular mesh-based discretization, obtains shape functions with uniform C-p (p >= 1) continuity One such recent attempt, a NURBS based parametric bridging method (Shaw et al 2008b), uses polynomial reproducing, tensor-product non-uniform rational B-splines (NURBS) over a typical FE mesh and relies upon a (possibly piecewise) bijective geometric map between the physical domain and a rectangular (cuboidal) parametric domain The present work aims at a significant extension and improvement of this concept by replacing NURBS with DMS-splines (say, of degree n > 0) that are defined over triangles and provide Cn-1 continuity across the triangle edges This relieves the need for a geometric map that could precipitate ill-conditioning of the discretized equations Delaunay triangulation is used to discretize the physical domain and shape functions are constructed via the polynomial reproduction condition, which quite remarkably relieves the solution of its sensitive dependence on the selected knotsets Derivatives of shape functions are also constructed based on the principle of reproduction of derivatives of polynomials (Shaw and Roy 2008a) Within the present scheme, the triangles also serve as background integration cells in weak formulations thereby overcoming non-conformability issues Numerical examples involving the evaluation of derivatives of targeted functions up to the fourth order and applications of the method to a few boundary value problems of general interest in solid mechanics over (non-simply connected) bounded domains in 2D are presented towards the end of the paper

Analysis of continuum using boundary compatibility conditions of integrated force method

Static and vibration problems of an indeterminate continuum are traditionally analyzed by the stiffness method. The force method is more or less non-existent for such problems. This situation is primarily due to the incomplete state of development of the compatibility conditions which are essential for the analysis of indeterminate structures by the flexibility method. The understanding of the Compatibility Conditions (CC) has been substantially augmented. Based on the understanding of CC, a novel formulation termed the Integrated Force Method (IFM) has been established. In this paper IFM has been extended for the static and vibration analyses of a continuum. The IFM analysis is illustrated taking three examples: 1. (1) rectangular plate in flexure 2. (2) analysis of a cantilevered dam 3. (3) free vibration analysis of a beam. From the examples solved it is observed that the force response of an indeterminate continuum with mixed boundary conditions can be generated by IFM without any reference to displacements in the field or on the boundary. Displacements if required can be calculated by back substitution.

Ultimate Strength of R.C. Wall Panels in Two-Way In-Plane Action

Test results of 24 reinforced concrete wall panels in two-way action (i.e., supported on all the four sides) and subjected to in-plane vertical load are presented. The load is applied at an eccentricity to represent possible accidental eccentricity that occurs in practice due to constructional imperfections. Influences of aspect ratio, thinness ratio, slendemess ratio, vertical steel, and horizontal steel on the ultimate load are studied. Two equations are proposed to predict the ultimate load carried by the panels. The first equation is empirical and is arrived at from trial and error fitting with test data. The second equation is semi-empirical and is developed from a modification of the buckling strength of thin rectangular plates. Both the equations are formulated so as to give a safe prediction of a large portion of ultimate strength test results. Also, ultimate load cracking load and lateral deflections of identical panels in two-way action (all four sides supported) and oneway action (top and bottom sides only supported) are compared.