Browsing by Author "Roy, Soumyajit"

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Correlation of Singularity Analyses Based on Position and Velocity Kinematics
(IFToMM World Congress, 2015-10) Roy, Soumyajit
Singularity analyses of manipulators are performed with great concern to avoid singular configurations in which the driving motors and related hardware may face great difficulty to drive the manipulator joints further or the manipulator itself may become uncontrollable in certain regions. Position and velocity kinematics are common practices for singularity analyses. Both the kinematics serve two different purposes. Position kinematics directly proposes the singularity manifold as well as the assembly configurations. On the other hand, velocity kinematics very easily finds a singular configuration. The present research proposes a unique procedure to correlate these two methods. Inverse kinematics in case of serial manipulators and forward kinematics for parallel manipulators act as a bridge between two different singularity analyses approaches. The fact was established with relevant examples of 2-link 2-R planar serial manipulator, 3-link 3-R spatial serial manipulator and 4-bar linkage
Coupled dynamics of a viscoelastically supported infinite string and a number of discrete mechanical systems moving with uniform speed
(Elsevier, 2018-02) Roy, Soumyajit
The mutual interaction between a number of multi degrees of freedom mechanical systems moving with uniform speed along an infinite taut string supported by a viscoelastic layer has been studied using the substructure synthesis method when base excitations of a common frequency are given to the mechanical systems. The mobility or impedance matrices of the string have been calculated analytically by Fourier transform method as well as wave propagation technique. The above matrices are used to calculate the response of the discrete mechanical systems. Special attention is paid to the contact forces between the discrete and the continuous systems which are estimated by numerical simulation. The effects of phase difference, the distance between the systems and different base excitation amplitudes on the collective behaviour of the mechanical systems are also studied. The present study has relevance to the coupled dynamic problem of more than one railway pantographs and an overhead catenary system where the pantographs are modelled as discrete systems and the catenary is modelled as a taut string supported by continuous viscoelastic layer.
Dynamic interaction between multiple pantographs sliding on an overhead conductor wire: a multibody and wave-based approach
(Springer, 2021-11) Roy, Soumyajit
he interaction dynamics between a number of railway pantographs moving in contact with an overhead high-tension conductor wire has been studied. The bases of the pantographs are subjected to harmonic excitation with different phases representing track undulation. The overhead wire is modelled as a viscoelastically supported infinite taut string, and a multibody model of the pantograph is proposed. Natural coordinates and extended Hamilton’s principle are used to derive the equations of motion of the multibody system, which are then linearised about its static equilibrium state for a small amplitude of base excitation. To follow the method of substructure synthesis in determining the responses of multiple pantographs with the help of the linearised models and subsequently in estimating the contact force, the dynamic stiffness matrix associated with the continuum is analytically calculated using the wave propagation approach. It is found that the separation distance between the pantographs, the travel speed and the base excitation phase have significant influences on the collective behaviour of the pantographs. Counter-intuitively, a leading pantograph may not always affect the trailing ones. The phase of the base excitation can actually play a decisive role, as brought out in this work.
Interaction of a moving mechanical oscillator with a periodically supported infinite string
(ICSV 2018, 2018) Roy, Soumyajit
The coupled dynamics of an infinite string with heavy axial tension supported by periodic discrete supports and a three degrees of freedom mechanical oscillator moving at a uniform subcritical speed is studied using substructure synthesis method. String displacements are found by applying a well known model available in the literature, whereas, the steady state response of the oscillator is determined through computing the receptance or dynamic stiffness associated with the continuum. Results show that, near the critical speed, the coupled dynamics is quite different from a prior study by the same authors (where the string was supported by a homogeneous viscoelastic layer) due to the discrete nature of the support condition. It is concluded that this type of behaviour is owing to excessive wave scattering from each support point. The problem analysed in this present work has a great application in pantograph-catenary coupled system as well as in railway tracks
On the wave propagation in a beam-string model subjected to a moving harmonic excitation
(Elsevier, 2019-05) Roy, Soumyajit
The vibration of an infinitely long beam with a large axial tension under a point harmonic load moving at a uniform speed is studied to find out the importance of bending rigidity of the beam. It is found analytically that the effect of bending stiffness of the beam does not play any significant role in the dynamics of the continuum beyond a certain distance away from the point of application of the load. The beam-string system simply acts as a taut string in those regions. However, the bending of the beam-string plays a major part in the vicinity of the load. It is shown that the beam model neglecting the inertia term is sufficient to capture the real scenario with negligible error in the close proximity of the load. The string model also becomes insufficient, especially at the upstream side when the speed of the load approaches the critical speed. In that case the bending and the inertia terms cannot be ignored in the Euler–Bernoulli beam model. It is seen from the response that, when the speed of the load is near the critical speed, one of the four propagating waves traverses with high phase speed, high frequency and low amplitude in the portion of the beam lying upstream of the load. This phenomenon cannot be captured in a simple string model. Comparison between the string model and the complete beam model in determining loading point displacement shows that the former can only be used at low frequencies in the subcritical speed regime.