Om Prakash Sha

Three-dimensional finite element prediction of transient thermal history and residual deformation due to line heating

The parameters of the line heating process have significant effect on thermal history and the resulting residual deformation of the heated plate. The thermal transients are dependent on torch speed, torch height, gas pressure, and nozzle size, which in turn controls the residual deformation of the plate. In the present work, three-dimensional transient finite element thermomechanical analysis of line heating using oxyacetylene gas flame is presented. The analysis is carried out using temperature-dependent material properties, Newtons convection, and Gaussian distribution of heat. To reduce the computation time, a fine mesh was used along and near the heating line that was coarsened at the edges and away from the heating line. Numerical thermal transients and residual deformation were presented for various torch speeds, heat inputs, and different thicknesses of plate (6 mm, 8 mm, 10 mm, and 12 mm thick plates). The results compared fairly well with experimental and previously published results. The reduction in peak temperature, for similar heating conditions, and the increase in structural stiffness of thicker plates resulted in a reduction in out-of-plane deformation. In this work, the computational model for correlation of deformation pattern with heat input for a single heating line has been achieved. This model will further be extended to predict deformation patterns due to multiple parallel and oblique heating lines.

Uncertainty assessment for ship maneuvering mathematical model

An 8 degrees of freedom (DoF) ship maneuvering motion model for a twin-propeller twin-rudder high-speed hull form is developed from captive model experiment data available from literatures. The degrees of freedom considered are surge, sway, yaw, roll, rudder rate and propeller rate. Besides maneuvering motion model, variation of port/starboard propeller thrust and torque and port/starboard rudder normal force and rudder torque are also included in the model. An uncertainty analysis computation for the mathematical model is carried out. Uncertainties in the experimental data and the polynomial curve fitting during modeling are included in the computation. It is shown that the mathematical model uncertainty is higher than the experimental uncertainty. Uncertainty is propagated to full-scale zigzag maneuver using the conventional Monte Carlo simulation (MCS) method. The uncertainty analysis results will be useful for further improvement of mathematical model, validation of CFD simulation results of appended hull maneuvering tests, etc. The authors have also shown the utility of asymmetric operations of the twin-propeller and twin-rudder by carrying out full-scale simulation a zigzag maneuver and showing the variation of the rudder normal force and torque.

A tracing method for parametric Bezier triangular surface/plane intersection

Surface/plane intersection problem is a special case of surface/surface intersection, and is an active area of research across many disciplines in computer-aided geometric design. This paper presents, in general the setting of derivational continuities, (i.e. C0, C1, and C2), a surface/plane intersection algorithm for parametric Bezier triangular surface over triangular domain. The present algorithm is a combinatorial algorithm that is based on a tracing method, in which the intersection curves are traced out in the direction of tangent vectors at intersectionpoints. The intersection curves are represented by their piecewise polynomial approximations, given by orderedpair of surface domain points. The aim is to obtain the smallest number of ordered points that correctly represent the topology of the true intersection curves. Since the points on the intersection curves are obtained in an ordered manner, no sorting is essential. The refinement of the intersection curve may include fitting an interpolatory cubic spline, or adding and deleting points. The method has been used to compute different planar sections (i.e. intersection curves with X, Y, and Z planes) for surfaces having different derivational continuities (i.e. C0, C1 and C2).

Supplementary Article: 3-D FEM and ANN prediction of thermal history and residual deformation due to line heating by oxy acetylene gas flame

In the present work three-dimensional transient, elasto-plastic finite element thermo-mechanical analysis of line heating by oxy-acetylene gas flame has been presented. The problem was solved by considering temperature dependent material properties, Newtons convection and Gaussian distribution of heat source. To reduce the computation time, coarse mesh was generated away from the heating line and finer mesh was generated along and near the heating line. Numerical thermal history and the resulting residual deformations were estimated for line heating of 6mm, 8mm, and 10mm and 12mm thick steel plates. The estimated thermal profiles and the residual deformations were compared well with those of the experimental results. Finally the thermal history of the whole plate and the residual deformations have been predicted with the help of artificial neural network approach by using back propagation algorithm and compared with numerical and experimental results.

Artificially ventilated conventional hydrofoils - An experimental investigation

This paper presents an experimental study on the artificial ventilation of conventional hydrofoil (NACA66 2 -215) sections. The investigation includes a study of the effect of different ventilation pressures, speeds of operation, angles of attack, ventilation locations and ventilation outlet configurations on the hydrodynamic performance of the foil. The experiments have been carried out at the High Speed Towing Tank facility of the Naval Science and Technological Laboratory at Visakhapatnam in India. A 6-component foil dynamometer has been developed for conducting the tests. A set of foils has been designed and manufactured with different ventilation locations and ventilation configurations.

An investigation into design of fair surfaces over irregular domains using data-dependent triangulation

Design of fair surfaces over irregular domains is a fundamental problem in computer-aided geometric design (CAGD), and has applications in engineering sciences (in aircraft, automobile, ship science etc.). In the design of fair surfaces over irregular domains defined over scattered data, it was widely accepted till recently that the classical Delaunay triangulation be used because of its global optimum property. However, in recent times it has been shown that for continuous piecewise linear surfaces, improvements in the quality of fit can be achieved if the triangulation pattern is made dependent upon some topological or geometric property of the data set or is simply data dependent. The fair surface is desired because it ensures smooth and continuous surface planar cuts, and these in turn ensure smooth and easy production of the surface in CAD/CAM, and favourable resistance properties. In this paper, we discuss a method for construction of C1 piecewise polynomial parametric fair surfaces which interpolate prescribed ℜ3 scattered data using spaces of parametric splines defined on H3 triangulation. We show that our method is more specific to the cases when the projection on a 2-D plane may consist of triangles of zero area, numerically stable and robust, and computationally inexpensive and fast. Numerical examples dealing with surfaces approximated on plates, and on ships have been presented.

Unstructured triangular surface grid generation and intrinsic grid analysis using rational triangular patches

Purpose – To focus on grid generation which is an essential part of any analytical tool for effective discretization.Design/methodology/approach – This paper explores the application of the possibility of unstructured triangular grid generation that deals with derivationally continuous, smooth, and fair triangular elements using piecewise polynomial parametric surfaces which interpolate prescribed R3 scattered data using spaces of parametric splines defined on R2 triangulations in the case of surfaces in engineering sciences. The method is based upon minimizing a physics‐based certain natural energy expression over the parametric surface. The geometry is defined as a set of stitched triangles prior to the grid generation. As for derivational continuities between the two triangular patches C0 and C1 continuity or both, as per the requirements, has been imposed. With the addition of a penalty term, C2 (approximate) continuity can also be achieved. Since, in this work physics‐based approach has been used, th...