arXiv subjects

Tri Ngo

Publications and source records attributed to Tri Ngo.

5 recordsLinked to original sources

arXiv2026

Cost of Sensing in Optimal Control: Basic Formulations, Examples, and Applications

Incorporating a notion of cost of sensing, or sensing-cost, within the optimal control framework is beneficial in controlling systems where the duration of sensing, and/or the cost of sensors themselves, have a considerable impact on the overall cost. In this regard, this paper presents multiple methods for incorporating an integral sensing-cost into the optimal control framework for Linear Time-Invariant (LTI) systems. Sensing-cost is traded off against the conventional costs of control and stabilization. Optimal sensing intervals are derived by applying the Pontryagin's Minimum Principle. Other formulations of the sensing-cost problem, and extension to nonlinear systems, are possible. The theoretical developments of this paper are validated through numerical solutions and demonstrated through simulations. A reduced-form expression for the infinite-horizon multi-dimensional case with single switching point is derived, and a closed-form solution is obtained for the infinite-horizon first-order case. Additionally, a Shrinking Horizon method is demonstrated for practical implementation of the proposed theory and as a means to address uncertainties. A practical case study of a wastewater treatment plant is introduced to examine the applicability of sensing-cost considerations in a real-world setting.

eess.SY↗

arXiv2026

Adaptive Model Predictive Control of Nonlinear Generic Urban Air Mobility Using Linear Parameter-Varying Systems

This paper presents an adaptive model predictive control (MPC) framework for nonlinear urban air mobility (UAM) vehicles operating across the full flight envelope. The proposed approach leverages a linear parameter-varying (LPV) representation to update the predictive model online, enabling accurate capture of strongly nonlinear and time-varying dynamics associated with distributed electric propulsion (DEP) eVTOL aircraft. To systematically address the high-dimensional and coupled nature of MPC tuning, a multi-objective evolutionary optimization strategy based on NSGA-II is employed, incorporating proper normalization of states and control inputs to ensure balanced weighting and meaningful exploration of the design space. The resulting controller explicitly accounts for actuator constraints and enables reconfigurable control allocation for fault-tolerant operation. The framework is evaluated in nonlinear simulations using NASA's Generic Urban Air Mobility (GUAM) model and benchmarked against a robust servomechanism linear quadratic regulator (RSLQR). Results demonstrate that the proposed adaptive MPC achieves improved trajectory tracking and enhanced robustness under both nominal conditions and actuator degradation scenarios, including partial motor failure, while maintaining constraint satisfaction throughout all flight regimes.

eess.SY↗

arXiv2025

Enhanced Hydrodynamic Modeling of Offshore Wind Turbines using Morison's Equation with Frequency-Dependent Coefficients

This paper presents a novel approach for implementing frequency-dependent hydrodynamic coefficients in Morison's equation, which is widely used in hydrodynamics modeling. Accurate hydrodynamic predictions using Morison's equation necessitate the incorporation of frequency-dependent drag coefficients due to their variation with wave frequency. To address this, the proposed method segments the frequency domain into different regions, such as low-frequency (resonance) and high-frequency (wave) regions. Instead of using a constant drag coefficient across the entire spectrum, different drag coefficients are assigned to these regions. To implement this, a fifth-order low-pass Butterworth velocity filter is applied for the resonance zone, while a first-order high-pass Butterworth velocity filter is applied for the wave-dominated zone. The approach is validated using the INO WINDMOOR 12MW semisubmersible offshore wind turbine, comparing the simulation results against the experimental data. By incorporating frequency-dependent drag coefficients, the model shows improved agreement with experimental surge motion data across both frequency regions, demonstrating the effectiveness of the proposed method.

physics.ao-ph↗

arXiv2025

Modeling and Verification of Lumped-Parameter, Multibody Structural Dynamics for Offshore Wind Turbines

This paper presents the modeling and verification of multibody structural dynamics for offshore wind turbines. The flexible tower and support structure of a monopile-based offshore wind turbine are modeled using an acausal, lumped-parameter, multibody approach that incorporates structural flexibility, soil-structure interaction, and hydrodynamic models. Simulation results are benchmarked against alternative modeling approaches, demonstrating the model's ability to accurately capture both static and dynamic behaviors under various wind and wave conditions while maintaining computational efficiency. This work provides a valuable tool for analyzing key structural characteristics of wind turbines, including eigenfrequencies, mode shapes, damping, and internal forces.

eess.SY↗

arXiv2025

Hydrodynamic Modeling Improvements for Floating Offshore Wind Turbines with Validation Results

This study presents key enhancements in hydrodynamic modeling using the strip-based Morison's equation approach to enable rapid simulations of Floating Offshore Wind Turbines (FOWT). The modeling framework employs the relative form of the Morison equation, incorporating nonlinear irregular wave kinematics, vertical wave stretching, and diffraction corrections based on MacCamy-Fuchs (MCF) theory for large-scale, non-slender structures. Wave kinematics are iteratively applied at dynamically displaced structural nodes to accurately capture fluid-structure interaction. Additionally, a discretization scheme is introduced to improve hydrodynamic load distribution across large horizontal structures of floaters. These enhancements are validated against experimental data from the Floating Offshore Wind and Controls Advanced Laboratory (FOCAL), which conducted a 1:70 scale test of the IEA-Wind 15MW reference turbine on the VolturnUS-S platform. Results demonstrate that the incorporation of nonlinear wave kinematics significantly improves low-frequency response accuracy. Furthermore, the vertical wave stretching and MCF corrections lead to surge response predictions that closely align with experimental measurements, while the improved load discretization significantly enhances heave and pitch response fidelity in wave-dominant frequency ranges.

physics.ao-ph↗