J. N. Reddy

Bio: J. N. Reddy is an academic researcher from Texas A&M University. The author has contributed to research in topics: Finite element method & Plate theory. The author has an hindex of 106, co-authored 926 publications receiving 66940 citations. Previous affiliations of J. N. Reddy include Instituto Superior Técnico & National University of Singapore.

Fluid-Structure Transient Gust Sensitivity using Least-Squares Continuous Sensitivity Analysis

Abstract: A least-squares continuous sensitivity analysis method is developed for flui d-structure interacti on transient gust res ponse problems to support computationally efficient analysis and opti mization of aeroelastic design problems. In continuous sensitivity methods, one computes design or shape parameter gradients from the continuous system of parti al di fferential equati ons instead of the discretized system. The continuous sensitivity equati ons are a linear boundary-val ue problem which render computationally efficient design parameter gradients without needi ng to deri ve and code the problematic mesh sensitivities of discrete sensitivity methods. The coupled flui d-structure physics and conti nuous sensitivity system equations for a representati ve nonlinear gust response problem are posed in first-order form. The boundary condi tions for the sensitivity system are deri ved from a least-squares formulation of the underlying flui d-structure problem. The conti nuous sensitivity boundary val ue problem is then solved using a high-order pol ynomial leastsquares finite element model. An i mportant distincti on is made between l ocal and total deri vati ves at materi al points of the structure and a method for c onverting the local sensitivities to material deri vati ves is developed. Continuous sensitivity results for both the local and total material deri vati ves are presented and compared to gradients obtai ned by finite-di fference methods.

Least-squares finite element processes in h, p, k mathematical and computational framework for a non-linear conservation law

Abstract: This paper considers numerical simulation of time-dependent non-linear partial differential equation resulting from a single non-linear conservation law in h, p, k mathematical and computational framework in which k=(k1, k2) are the orders of the approximation spaces in space and time yielding global differentiability of orders (k1−1) and (k2−1) in space and time (hence k-version of finite element method) using space–time marching process. Time-dependent viscous Burgers equation is used as a specific model problem that has physical mechanism for viscous dissipation and its theoretical solutions are analytic. The inviscid form, on the other hand, assumes zero viscosity and as a consequence its solutions are non-analytic as well as non-unique (Russ. Math. Surv. 1962; 17(3):145–146; Russ. Math. Surv. 1960; 15(6):53–111). In references (Russ. Math. Surv. 1962; 17(3):145–146; Russ. Math. Surv. 1960; 15(6):53–111) authors demonstrated that the solutions of inviscid Burgers equations can only be approached within a limiting process in which viscosity approaches zero. Many approaches based on artificial viscosity have been published to accomplish this including more recent work on H(Div) least-squares approach (Commun. Pure Appl. Math. 1965; 18:697–715) in which artificial viscosity is a function of spatial discretization, which diminishes with progressively refined discretizations. The thrust of the present work is to point out that: (1) viscous form of the Burgers equation already has the essential mechanism of viscosity (which is physical), (2) with progressively increasing Reynolds (Re) number (thereby progressively reduced viscosity) the solutions approach that of the inviscid form, (3) it is possible to compute numerical solutions for any Re number (finite) within hpk framework and space–time least-squares processes, (4) the space–time residual functional converges monotonically and that it is possible to achieve the desired accuracy, (5) space–time, time marching processes utilizing a single space–time strip are computationally efficient. It is shown that viscous form of the Burgers equation without linearizing provides a physical and viablemechanism for approaching the solutions of inviscid form with progressively increasing Re. Numerical studies are presented and the computed solutions are compared with published work. Copyright © 2008 John Wiley & Sons, Ltd.

Finite-Element Analysis of Adhesive Joints

Abstract: Adhesive bonding is increasingly used to fasten metallic to metallic or metallic to composite structural components together. This is because in many present-day applications, conventional fasteners such as bolts, rivets, welds, etc., are unsuitable, especially if the components are made of polymeric or composite materials. The sonar transducer adhesively bonded acoustical window, the likely necessity of the repair of the composite structural components of carrier-based aircraft, and door inner assembly to outer panel, main body frame joints, trunk lid inner to outer and sealants in an automobile provide examples of such applications. Penetration methods (i.e., drilling holes, etc.) cause high stress concentrations and, in the case of composites, sever the fiber reinforcement which in turn reduces the strength of the joint. On the other hand, bonded joints tend to be damage-tolerant due to the high damping behavior of the adhesive layer and less expensive due to lower fabrication cost. The use of adhesives increases the joint strength, distributes the loads more evenly, and enables alternative jointing methods to be reduced or eliminated. Dissimilar materials (e.g., steel, aluminum, plastics, glass, etc.) can be joined together by bonding even where it is impossible to gain access to either side of the joint, thereby increasing the design flexibility.

An Initial and Progressive Failure Analysis for Cryogenic Composite Fuel Tank Design

Abstract: Thermal residual stresses, internal pressure stresses, and acceleration stresses during launch were evaluated and quantified for cryogenic composite fuel tank design. Both failure initiation and progression of graphite/epoxy laminate system (IM7/977-2) [0/90/90/0/0/90]s and graphite/BMI laminate system (IM7/5250-4) [0/90/90/0/0/90]s were investigated using the non-isothermal classical laminate and plate theory (CLPT) and the maximum stress failure criterion. The thermal residual stresses in the transverse direction are the dominant stresses on each ply in the launch stage. After initial ply cracking, through-the-thickness temperature change of a laminate related to fuel leakage as well as a laminate stiffness matrix change was applied to the progressive failure analysis. The fuel leakage-based progressive analysis shows a higher number of initial ply cracking does not necessarily mean a higher chance of matrix cracking in all plies. The graphite/BMI laminate has such an advantage as transverse thermo-mech...

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Robot dynamics and control

Abstract: From the Publisher: This self-contained introduction to practical robot kinematics and dynamics includes a comprehensive treatment of robot control. Provides background material on terminology and linear transformations, followed by coverage of kinematics and inverse kinematics, dynamics, manipulator control, robust control, force control, use of feedback in nonlinear systems, and adaptive control. Each topic is supported by examples of specific applications. Derivations and proofs are included in many cases. Includes many worked examples, examples illustrating all aspects of the theory, and problems.

A Simple Higher-Order Theory for Laminated Composite Plates

Abstract: A higher-order shear deformation theory of laminated composite plates is developed. The theory contains the same dependent unknowns as in the first-order shear deformation theory of Whitney and Pagano (1970), but accounts for parabolic distribution of the transverse shear strains through the thickness of the plate. Exact closed-form solutions of symmetric cross-ply laminates are obtained and the results are compared with three-dimensional elasticity solutions and first-order shear deformation theory solutions. The present theory predicts the deflections and stresses more accurately when compared to the first-order theory.