In the field of naval architecture, accurately predicting vessel performance is critical for optimizing designs and improving operational efficiency. This case study explores how integrating HydroComp’s NavCad® software with Orca3D Marine CFD significantly improves the accuracy of marine resistance and propulsion simulations. Orca3D Marine CFD is a computational fluid dynamics (CFD) software configured specifically for marine applications. The subject of the study is a 12.7-meter offshore planing craft designed for 30-knot operation. The investigation showcases how a hybrid approach, combining parametric modeling with computational fluid dynamics (CFD), offers a more robust analysis toolset for naval architects.
NavCad provides a steady-state simulation framework that models the Vessel–Propulsor–Drive system under the assumption that all forces and moments are in equilibrium. In this model, the vessel’s resistance is balanced by the thrust generated by the propulsor, and the torque on the propulsor is matched by the power input from the drive system. These relationships form the foundation of NavCad’s two key analysis modes: resistance analysis, which predicts the thrust demand, and propulsion analysis, which simulates the full system, as well as simultaneously allowing for propeller optimization.
NavCad has a synergistic relationship with CFD. Simulation accuracy and usefulness increase when both products are used together. NavCad’s semi-empirical parametric methods may be used to establish benchmark values for vessel resistance, heave, and pitch, which help to ensure that costly CFD calculations are being configured and run correctly. Parametric methods can also be used to estimate propulsor thrust-line and lift forces, which can be applied within CFD models to improve the physical accuracy of the simulation. High-precision CFD data can be used to analyze complex flow characteristics at full scale and enhance NavCad resistance predictions in order to develop a more refined system simulation.
Once thrust demands have been modeled, propeller sizing can be carried out and the KTKQ performance curves can be produced. These curves are used to describe the thrust and torque of the propeller across different combinations of forward speed and rotational RPM. KTKQ data developed using NavCad is automatically corrected to account for oblique flow characteristics induced by shaft angle or hull geometry, and may be used for realistic self-propulsion simulations.
The vessel analyzed in this case study – a twin-screw, shaft-driven offshore planing craft – was first evaluated using NavCad to generate baseline resistance data. These parametric results served as benchmark figures for the CFD modeling process in Orca3D. The study revealed that incorporating the propulsor’s thrust-line (TPROP) and vertical lift forces (LPROP) in the parametric model had a considerable impact on both resistance and trim behavior in the hump-speed regime (volume Froude numbers from 1 to 3). The lift generated by each propeller was significant, rivalling the influence of stern lift devices like trim tabs and interceptor wedges.
To align the CFD model with this insight, TPROP and LPROP were implemented into the CFD simulation as force vectors originating from the propeller position using Orca3D’s setup wizard. This step ensured that critical forces affecting vessel behavior were not excluded from the high-fidelity numerical simulation. The CFD resistance predictions closely matched those from NavCad, validating the effectiveness of the parametric analysis and demonstrating the power of a hybrid modeling approach.
Next, a self-propulsion analysis was conducted using an actuator disk with KT/KQ curves developed using NavCad. These curves were generated for a propeller optimized for this project, and modified to account for both rise of run and the 12 degree shaft angle. This correction increased the accuracy of the CFD model and allowed for more complete analysis of vessel behavior under real-world physical conditions.
The integration of NavCad with Orca3D Marine CFD is a highly effective methodology for vessel performance analysis. NavCad offers trusted resistance prediction methods which can be used to establish benchmarks and calculate critical supplemental data for CFD calculations. The analytical data developed by CFD software can then be applied in the NavCad space to develop sophisticated vessel-propulsor-drive system simulations. Together, these tools provide a comprehensive design and analysis platform that supports more confident decision-making throughout the ship design process.
Copyright © , HydroComp Inc. | All Rights Reserved