Ranjith Mohan

Bio: Ranjith Mohan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Dynamic soaring & Floquet theory. The author has an hindex of 3, co-authored 19 publications receiving 62 citations. Previous affiliations of Ranjith Mohan include Indian Institutes of Technology.

Fourier Pseudospectral Method for Trajectory Optimization with Stability Requirements

Abstract: Periodic trajectories that satisfy stability-based requirements are useful in many engineering applications. In this work, a time-domain approach using Fourier collocation for solving the Floquet e...

A novel guidance algorithm and comparison of nonlinear control strategies applied to an indoor quadrotor

Abstract: In this paper we propose a cascaded approach for the full control of a quadrotor operating in indoor spaces. Sliding mode controller with a saturation function is applied to achieve robust attitude tracking performance without control chattering. A novel guidance algorithm and a feedback-linearization based position controller is proposed, which ensures that the MAV follows the shortest path between the waypoints. Also, we discuss the on-board implementation of state-estimation and 3D localization techniques for an MAV. The robustness and effectiveness of the proposed control law are validated through simulations and experiments under external disturbances. Further, the test-bench results are compared with those obtained from PI-PID and backstepping control.

Detection and control of ground resonance using phase of fuselage attitude rates

Abstract: Ground resonance is a type of aeromechanical instability that occurs when the helicopter is in contact with the ground. It may occur due to coalescence between frequencies of two modes of the system if damping is insufficient. In this paper, we analyze the phase relations between the fuselage states corresponding to the least damped mode (regressive lag mode) and its correlation with frequency coalescence. The phase of fuselage states (attitude or attitude rates), which are easily measurable, is observed to exhibit certain trends with variation in parameters like rotor speed and landing gear stiffness. The phase data can aid in the design of a stability augmentation system for ground resonance. It can serve as a parameter to detect the possibility of instability and in systems with uncertainties in parameters, like landing gear stiffness, it can aid in selecting the appropriate feedback gain for stabilization. The model we have primarily considered has isotropic rotor and anisotropic hub, hence multiblade coordinate transformation is used and the stability analysis is done in fixed frame. The analysis is further extended to incorporate dynamic inflow effects and anisotropy in rotor blades, where Floquet method is used for stability analysis. Air resonance instability is also investigated on similar lines and the proposed method is found to be good for its detection.

Mixed convection in a partially heated triangular cavity filled with nanofluid having a partially flexible wall and internal heat generation

Abstract: Numerical study of mixed convection in a partially heated nanofluid-filled lid driven cavity with internal heat generation and having a partial flexible wall was performed. The bottom wall of the triangular enclosure is moving with constant speed and left vertical wall is partially heated. The inclined wall of the cavity is cooled and partially flexible. The governing equations are solved with Galerkin weighted residual finite element method. The effects of Richardson number (between 0.05 and 50), internal Rayleigh number (between 10 4 and 10 8 ), size and elastic modulus of the partial flexible wall and nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and heat transfer were numerically investigated. It was observed that the local and averaged heat transfer reduce as the value of the Richardson number and internal Rayleigh number increase. As the value of the elastic modulus of the inclined wall and nanoparticle volume fraction increase, local and average heat transfer enhance. The discrepancy between the averaged Nusselt number increase for different sizes for the lower values of elastic modulus of the flexible wall. When heat transfer process is effective adding nanoparticles to the base fluid is advantageous.