Pradeep Raj

Accurate Computing of Higher Vibration Modes of Thin Flexible Structures

Motivated by the need for high-fidelity modeling and accurate control of future hypersonic vehicles subjected to complex aerothermomechanical loads and many other such applications, a novel scheme is proposed to accurately compute higher modes of vibration for one-dimensional structures by coupling the classic Ritz method as a predictor and the linear two-point boundary value problem solver SUPORE as a corrector. The Ritz method is used to compute a preliminary estimate of the natural frequencies for the desired modes. These estimates are then used as initial guesses by SUPORE, which employs superposition and reorthonormalization to accurately solve the governing boundary value problem. Compared to a high-fidelity Ritz approximation or a highly refined finite element modeling procedure, this is a simple, computationally less expensive, and yet highly accurate method to compute mode shapes for applications that require higher modes. This scheme is used to compute mode shapes within an absolute and relative...

A Novel Scheme to Accurately Compute Higher Vibration Modes using the Ritz Method and a Two-point BVP Solver

Motivated by the control of future hypersonic vehicles subjected to complex aero-thermo-mechanical loads and many other such applications, we propose a novel scheme to compute higher modes of vibration accurately for one-dimensional stuctures, that couples the classic Ritz method as a predictor and the linear two-point boundary value problem (BVP) solver SUPORE as a corrector. The Ritz method is used to compute a preliminary estimate of the natural frequencies for the desired modes. These estimates are then used as initial guesses by SUPORE, which employs superposition and reorthonormalization to accurately solve the governing boundary value problem. Compared to a high fidelity Ritz approximation or a highly refined finite element modeling, this is a simple, computationally less expensive, and yet highly accurate method to compute mode shapes for applications that require higher modes. This scheme is used to compute mode shapes within an error tolerance of 10−6 for the idealized case of a free-free Euler Bernoulli beam and a typical air-breathing hypersonic vehicle modeled as a thin-walled structure taking into account deformations due to bending, shear, and torsion.

Stability Derivative Computation of Tailless Aircraft using Variable-Fidelity Aerodynamic Analysis and Wind-Tunnel Experiments

In aircraft design, tailless aircraft are an attractive concept for their aerodynamic efficiency. However, because of their unusual shape, a tailless configuration has disadvantages in stability and control (SC static derivatives, steady dynamic derivatives, and unsteady dynamic derivatives. For accurate and efficient stability estimation, several aerodynamic and numerical methods were introduced to calculate aerodynamic derivatives. These values were compared with the wind tunnel data for the validation. Finally, the stability characteristics of certain steady conditions were calculated from the results of the numerical method, and the stability performance was evaluated.

Computational Simulation of Turbulent (Jocaj Vortex Merger and Decay

The interaction and eventual merger of corotational vortices and the decay of a single vortex have been studied by employing zero-, one- and two-equation turbulent-flow models in order to gain a better understanding of the role of turbulence. An implicit finite-difference procedure is used to integrate the unsteady, two-dimensional equations in a cross-plane. The zero- and one-equation formulations utilize a mixing-length model, which incorporates the streamline curvature effect by prescribing a spatially-varying mixing-length. In the two-equation model, the turbulence kinetic energy equation and a modified rate of dissipation equation which includes a streamline curvature correction are solved. Computational results of different models applied to various flow-configurations are presented and compared with available experimental data whenever possible.