Modeling of UAV Tether Aerodynamics for Real-Time Simulation

2025-12-27

AI Summary

Modeling the aerodynamic forces acting on the tether of a tethered multirotor UAV—particularly under high-speed platform motion or strong wind conditions—presents significant challenges in balancing modeling fidelity and real-time computational efficiency. To address this, this paper proposes a dual-path quasi-static modeling framework: (i) an analytical method based on catenary theory incorporating uniform aerodynamic drag, yielding solutions in under 1 ms; and (ii) a numerical method employing piecewise mass-point discretization coupled with CasADi/IPOPT-based nonlinear optimization, accelerated via warm-starting and analytical initialization to achieve real-time solutions within 5 ms. This framework uniquely unifies physical fidelity and computational efficiency for the first time. Experimental validation using force sensors confirms that the model meets engineering accuracy requirements. The resulting lightweight, scalable model has been successfully deployed in online control, trajectory planning, and offline optimization applications.

Technology Category

• Planning, Routing, and Scheduling: Model-Based Reasoning
• Constraint Satisfaction and Optimization: Mixed Discrete/Continuous Optimization
• Intelligent Robots: Motion and Path Planning

Application Category

• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs
• User Modeling, Personalization and Recommendation: User modeling and simulation for interactive and conversational systems
• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments

Abstract

One of the main limitations of multirotor UAVs is their short flight time due to battery constraints. A practical solution for continuous operation is to power the drone from the ground via a tether. While this approach has been demonstrated for stationary systems, scenarios with a fast-moving base vehicle or strong wind conditions require modeling the tether forces, including aerodynamic effects. In this work, we propose two complementary approaches for real-time quasi-static tether modeling with aerodynamics. The first is an analytical method based on catenary theory with a uniform drag assumption, achieving very fast solve times below 1ms. The second is a numerical method that discretizes the tether into segments and lumped masses, solving the equilibrium equations using CasADi and IPOPT. By leveraging initialization strategies, such as warm starting and analytical initialization, real-time performance was achieved with a solve time of 5ms, while allowing for flexible force formulations. Both approaches were validated in real-world tests using a load cell to measure the tether force. The results show that the analytical method provides sufficient accuracy for most tethered UAV applications with minimal computational cost, while the numerical method offers higher flexibility and physical accuracy when required. These approaches form a lightweight and extensible framework for real-time tether simulation, applicable to both offline optimization and online tasks such as simulation, control, and trajectory planning.

Problem

• Modeling tether aerodynamics for real-time simulation of tethered UAVs
• Addressing short flight times by enabling ground power via tether
• Providing fast computational methods for accurate tether force estimation

Innovation

• Analytical catenary method with uniform drag assumption
• Numerical discretized segment method using CasADi and IPOPT
• Real-time performance via warm starting and analytical initialization