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1
Content available remote Performance analysis of Gough Stewart platform with 6 limbs
Chandrashekhar A., Satish Babu G.
Mechanics and Mechanical Engineering
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2018
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Vol. 22, nr 1
133--141
EN
This paper concentrates on widespread study of parallel manipulator. It focuses on optimal designing of manipulator which has a large number of application fields. Optimal design is an important criterion to improve the accuracy of a robot. Through optimal design a robot can achieve isotropic configurations where the condition number of its jacobian matrix equals one. In this we are also concentrating on transmission index and stiffness index along with their plots, which can affect the kinetostatic performance of the robot. In this the singularity of Gough Stewart platform is also studied.
2
Content available remote Effect of Two Temperatures and Thermal Phase-lags in a Thick Plate due to a Ring Load with Axisymmetric Heat Supply
Kumar J., Sharma N., Lata P.
Computational Methods in Science and Technology
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2016
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Vol. 22, No. 3
153--162
EN
The present investigation concerns thermomechanical interactions in a homogeneous isotropic thick plate in the light of the two-temperature thermoelasticity theory with dual phase lag due to a ring load. The upper and lower ends of the thick plate are traction free and subjected to an axisymmetric heat supply. The solution is obtained by using Laplace and Hankel transform techniques. The analytical expressions of displacement components, stresses, conductive temperature, temperature change and cubic dilatation are computed in a transformed domain. The numerical inversion technique has been applied to obtain the results in the physical domain. Numerically simulated results are depicted graphically. The effect of thermal phase-lags and two temperatures are shown on the various components. Some particular cases of the result are also deduced from the present investigation.
3
Content available remote Surface Deformation due to Loading of a Layered Elastic Half-space : Constructing the Solution for a General Polygonal Load
Bevis M., Pan E., Zhou H., Han F., Zhu R.
Acta Geophysica
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2015
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Vol. 63, no. 4
957--977
EN
We describe an algorithm for rapidly computing the surface displacements induced by a general polygonal load on a layered, isotropic, elastic half-space. The arbitrary surface pressure field is discretized using a large number, n, of equally-sized circular loading elements. The problem is to compute the displacement at a large number, m, of points (or stations) distributed over the surface. The essence of our technique is to reorganize all but a computationally insignificant part of this calculation into an equivalent problem: compute the displacements due to a single circular loading element at a total of m n stations (where m n is the product m × n). We solve this “parallel” problem at high computational speed by utilizing the sparse evaluation and massive interpolation (SEMI) method. Because the product m n that arises in our parallel problem is normally very large, we take maximum possible advantage of the acceleration achieved by the SEMI algorithm.
4
Content available Uniqueness, reciprocity theorems and plane wave propagation in different theories of thermoelasticy
Kumar R., Gupta V.
International Journal of Applied Mechanics and Engineering
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2013
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Vol. 18, no. 4
1067--1086
EN
In this work, a compact form of different theories of thermoelasticity is considered. The governing equations for particle motion in a homogeneous isotropic thermoelastic medium are presented. Uniqueness and reciprocity theorems are proved. The plane wave propagation in a homogeneous isotropic thermoelastic medium is studied. For a three dimensional problem there exist four waves, namely a P-wave, two transverse waves (S1, S2) and a thermal wave (T). From the obtained results the different characteristics of waves such as the phase velocity and attenuation coefficient are computed numerically and presented graphically. Some special cases are also discussed.
5
Content available Free vibration analysis of isotropic rectangular plates on Winkler foundation using differential transform method
Kumar Y.
International Journal of Applied Mechanics and Engineering
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2013
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Vol. 18, no. 2
589--597
EN
A differential transform method (DTM) is used to analyze free transverse vibrations of isotropic rectangular plates resting on a Winkler foundation. Two opposite edges of the plates are assumed to be simply supported. This semi-numerical-analytical technique converts the governing differential equation and boundary conditions into algebraic equations. Characteristic equations are obtained for three combinations of clamped, simply supported and free edge conditions on the other two edges, keeping one of them to be simply supported. Numerical results show the robustness and fast convergence of the method. Correctness of the results is shown by comparing with those obtained using other methods.
6
Content available remote Eigenvalue approach to coupled thermoelasticity with temperature dependent modulus of elasticity in an isotropic elastic medium with a cylindrical hole
Lahiri A., Das B.
International Journal of Applied Mechanics and Engineering
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2011
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Vol. 16, no 2
411-423
EN
The fundamental equations of coupled thermoelasticity in an isotropic elastic medium with a cylindrical cavity under the dependence of the modulus of elasticity on the reference temperature have been written in the form of a vector-matrix differential equation and solved by the eigenvalue approach. The normal mode analysis is used to obtain the expressions for stresses and temperature when the lateral surface of the cylinder is kept at ambient temperature. Finally, numerical computations of the stresses and temperature have been made and presented graphically. Comparisons are made with the results obtained in the case of temperature independent modulus of elasticity.
7
Content available remote Effect of rotation on surface wave propagation in a elastic layer lying over a thermodiffusive elastic half-space having imperfect boundary
Kumar R., Chawla V.
International Journal of Applied Mechanics and Engineering
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2011
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Vol. 16, no 1
37-55
EN
The present investigation deals with the propagation of surface waves at an imperfect boundary between an isotropic elastic layer of finite thickness and a homogenous isotropic thermodiffusive elastic half- space with rotation in the context of generalized theory of thermoelastic diffusion. Lord and Shulman (L-S) theory in which thermal and thermo-mechanical relaxation time is governed by time constant and diffusion relaxation time is governed by other different time constants is selected for the study. The secular equation for surface waves in a compact form is derivied after developing the mathematical model. The phase velocity and attenuation coefficient are obtained for stiffness and then deduced for normal stiffness, tangential stiffness and welded contact. The dispersion curves for these quantities are illustrated to depict the effect of stiffness and thermal relaxation times. The amplitudes of displacements, temperature and concentration are computed at the free plane boundary and depicted graphically. Specific loss of energy is obtained and presented graphically. The effects of rotation are shown for phase velocity, attenuation coefficient and amplitudes of displacements, temperature change and concentration. Some special cases of interest are also deduced and compared with known results.
8
Content available remote Effect of rotation on Rayleigh waves in an isotropic generalized thermoelastic diffusive half-space
Kumar R., Kansal T.
Archives of Mechanics
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2008
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Vol. 60, nr 5
421-443
EN
he present investigation is a study of the effect of rotation on the characteristics of Rayleigh waves propagation in a homogeneous, isotropic, thermoelastic diffusive half-space in the framework of different theories of thermoelastic diffusion, including the Coriolis and Centrifugal forces. The medium is subjected to stress-free, thermally insulated/isothermal and chemical potential boundary conditions and is rotating about an axis perpendicular to its plane. Secular equations of surface wave propagation in the considered media are derived. The phase velocities and attenuation coefficients of surface wave propagation have been computed by using the irreducible case of Cardano's method, with the help of DeMoivre's theorem known from the secular equations. The amplitudes of surface displacements, temperature change, concentration and the specific loss of energy are computed numerically. Rotation effect on the phase velocity, attenuation coefficient, amplitudes of surface wave propagation and specific loss of energy are presented graphically in order to illustrate and compare the analytically obtained results. Some special cases of frequency equation are also deduced from the present investigation.
9
Estymacja parametrów termofizycznych ciał izotropowych za pomocą metody filtracji dynamicznej oraz przedziałowego uśredniania wyników pomiarów
Kucypera S.
Modelowanie Inżynierskie
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2007
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T. 3, nr 34
73-78
PL
Prawdziwe wartości parametrów cieplnych w procesie estymacji z zastosowaniem metody filtracji dynamicznej otrzymuje się, dążąc do zmniejszenia macierzy kowariancji błędów ocen, czyli im mniejsza jest ta macierz, a szczególnie jej elementy diagonalne, tym oceny są dokładniejsze. Należy podkreślić, że w procesie estymacji norma tej macierzy dąży do normy macierzy kowariancji błędów pomiarowych. Stąd wynika, że błędy ocen będą określone błędami pomiarowymi. Dlatego w pracy w celu zmniejszenia błędów pomiarowych i poprawienia dokładności estymacji parametrów termofizycznych badanego materiału wyniki pomiarów wygładzano przed estymacją. Przedstawiono wybrane wyniki analizy.
EN
The actual values of the thermal parameters by means of dynamic filtration method are obtained approaching to decreasing of the covariance matrix of estimated errors. That is this matrix in particular her diagonal elements are lesser the estimates are more precise. It should be underline, that in the estimation process the norm of this matrix approaches the norm of the covariance matrix of the measurement errors. Hence it results, that the estimation errors are determined by measurement errors. In order to decreasing the measurement errors and to improve a precise of estimated parameters of thermophysical investigated material, the measurement results has been smoothed before estimation. Selected results of this analysis have been presented.
10
Content available remote Studium odwzorowania strukturalnego w ośrodku anizotropowym VTI
Kostecki A., Półchłopek A.
Prace Instytutu Nafty i Gazu
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2006
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nr 137
49-60
PL
W artykule zaprezentowano rezultaty zero-offset migracji głębokościowej MG(F-K) w dziedzinie liczb falowych i częstotliwości obowiązującej w ośrodku izotropowym zastosowanej do modeli pola falowego w ośrodku anizotropowym, tj. pionowo-transwersalnie izotropowego (VTI). Ten model pola falowego został obliczony według koncepcji Alkhalifa. Analiza wykazała, że decydujący wpływ na dokładność odwzorowania ma parametr Thomsena delta.
EN
In this paper we present some results of zero-offset depth migration MG(F-K) in domain wavenumber (K) - frequency (F) obtained in anizotropic VTI medium by "isotropic" version of migration. We used an efficient modeling technique for transversely isotropic, inhomogeneous media proposed by T. Alkhalif. The numerical calculations confirmed that the Thomsen parameter have dominant meaning in range "weak" anisotropy.
11
Content available remote Modelling of isotropic double negative media for microwave applications
Vendik I., Vendik O., Kolmakov I., Odit M.
Opto-Electronics Review
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2006
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Vol. 14, No. 3
179-186
EN
A composite medium consisting of two sublattices of dielectric spherical particles of high permittivity and different radii embedded in a dielectric matrix of smaller permittivity are considered. It has been shown that such a composite medium reveals properties of an isotropic double negative media (DNG) in a limited frequency range, when resonance oscillations of HIII mode in one kind of particles and EIII mode in another kind of particles are excited simultaneously. The EIII resonance and the HIII resonance give rise to the magnetic dipole momentum and the electric dipole momentum correspondingly. Averaging the magnetic momentum and the electric momentum over the cells belonging to the appropriate spherical particles gives the negative permittivity and permeability. The model of diffraction of a plane electromagnetic wave on a dielectric sphere is presented and compared with the mixing rule based consideration. The results obtained are rather close. Distribution of the electromagnetic wave outside the sphere is calculated. Influence of the dispersion of the sphere size and the dielectric permittivity on the effective parameters of the DNG material is estimated.
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