Efficient Time-Domain Simulation of USV Motions in Short-Crested Irregular Waves Using an IRF-Based Framework

2026-06-23

AI Summary

This study addresses the high computational cost of conventional time-domain simulations of ship motions in irregular waves, which hinders real-time applications for unmanned surface vehicles (USVs). To overcome this limitation, the authors propose an efficient yet high-fidelity simulation method based on impulse response functions (IRFs). The approach transforms frequency-domain hydrodynamic forces—including Froude-Krylov, diffraction, and radiation components—into the time domain and reconstructs wave loads via convolution. Weakly nonlinear restoring forces are accounted for through instantaneous wetted-surface pressure integration. For the first time, this framework is systematically applied to predict USV motions in short-crested irregular seas. A novel directional spectrum discretization strategy is introduced, significantly reducing computational overhead while preserving accuracy. Simulation results demonstrate excellent agreement with experimental data in both statistical characteristics and time histories, with a 30° directional interval offering an optimal trade-off between fidelity and efficiency, thereby enabling practical real-time USV simulation and control.

Abstract

Traditional time-domain prediction of vessel motions in irregular waves usually relies on superposing responses from many regular-wave components, which is computationally expensive for long-duration simulation and real-time applications. This issue is particularly relevant to unmanned surface vehicles (USVs), for which efficient and realistic motion prediction is needed for seakeeping assessment, simulation-based testing, and control-system development. This study applies an impulse response function (IRF)-based time-domain framework to predict vessel motions in short-crested irregular waves. Froude-Krylov, diffraction, and radiation loads are obtained from frequency-domain analysis and transformed into the time domain. Instantaneous responses are then evaluated directly through convolution-based force reconstruction, reducing the need for repeated regular-wave simulations. Weak nonlinear restoring effects are included by instantaneous wetted-surface pressure integration, and directional wave spectra are used to represent realistic sea states. The framework is validated against model-test measurements of an offshore supply vessel in long-crested beam irregular waves and full-scale measurements of a USV operating in real sea conditions. Predicted significant amplitudes, mean zero-crossing periods, standard deviations, and motion time histories agree well with measurements. The effect of directional-spectrum discretization is also examined. Results show that motion amplitudes are moderately sensitive to directional resolution, whereas motion periods are relatively insensitive. A 30 deg directional interval provides a practical balance between prediction accuracy and computational cost. The proposed framework offers an efficient tool for high-fidelity time-domain prediction of USV motions in realistic directional irregular seas.

Problem

• USV motions
• irregular waves
• time-domain simulation
• computational efficiency
• seakeeping

Innovation

• impulse response function
• time-domain simulation
• short-crested waves
• unmanned surface vehicle
• directional wave spectrum