Exploring Offshore Hydrodynamics and Mooring Dynamics through a Coupled Ansys Workflow.
Challenges
The offshore industry is moving into deeper waters and harsher environments, where traditional methods are no longer enough. Analyses that treat hydrodynamic loads and structural response as separate problems often fail to capture the true behavior of floating structures, especially moored vessels exposed to dynamic ocean conditions.
- Complex Multi-Physics Interactions. Offshore systems are subject to wave forces, structural deformations, and mooring dynamics that interact in nonlinear and time-dependent ways. These coupled effects drive resonance, transient responses, and load amplification that simplified approaches simply miss.
- Mooring System Integrity. Mooring failures remain one of the greatest risks in offshore operations. Uncoupled analyses tend to underestimate peak tensions and overlook how structural flexibility combines with wave excitation, leading to unsafe predictions of fatigue life.
- Operational Efficiency. Without coupled hydrodynamic–structural analysis, it is difficult to define realistic operating limits. Operators often compensate with conservative margins that reduce efficiency and profitability.
- Regulatory Demands. Industry standards and classification societies increasingly require advanced methodologies that demonstrate structural integrity under extreme conditions. Coupled time-domain analysis is becoming the new benchmark, as traditional methods cannot reliably predict offshore system behavior.
Engineering Solutions
Methods
Coupled time-domain analysis brings hydrodynamics, structural response, and mooring dynamics into a single simulation framework. By integrating Ansys Aqwa and Ansys Mechanical, engineers can capture the full behavior of offshore systems under realistic environmental conditions—something traditional, decoupled approaches cannot achieve.
- Ansys Aqwa applies boundary element methods to model wave–structure interaction in both frequency and time domains. It accounts for first- and second-order wave loads, as well as wind and current effects. Its built-in mooring module simulates line dynamics and seabed contact with high fidelity, making it a robust tool for offshore hydrodynamics.
- Ansys Mechanical complements this with finite element structural analysis. It handles nonlinear materials, large deformations, and transient dynamics, while offering fatigue assessment under variable amplitude loading. Detailed connection modeling enables engineers to evaluate complex structures with accuracy, from global response to local stress concentrations.
Solutions
An example of this coupled workflow is presented in this blog through the simulation of a 200-meter ship hull floating in 50 meters of water depth. The vessel is held in position by six mooring lines—three on each side—anchored to the seabed.
The process begins in Ansys Aqwa with a diffraction analysis. This step is essential because it establishes how incident waves interact with the hull geometry, providing the hydrodynamic coefficients required for stability and time-domain studies. Once diffraction data is obtained, the stability and time-domain analyses can follow, ensuring that the vessel’s global motion response is well captured before transferring results to Ansys Mechanical.
For this case study:
- Diffraction analysis. Wave frequencies between 0.01592 to 0.39461 Hz, all directions.
- Environmental conditions for Hydrodynamic response. Irregular wave train defined by the Pierson–Moskowitz spectrum.
- Wave parameters for time domain. Significant height of 4 m and zero-crossing period of 4 s, applied along the X+ direction (physical meaning: Continuous, random wave excitations with average crests of 4 m occurring roughly every 4 seconds).
- Simulation time. Time-domain analysis of 300 s in Aqwa.
- Data transfer. Hydrodynamic outputs exported every 50 s to Mechanical for structural evaluation.
To see the workflow in action, watch the demonstration video below and download the ZIP file containing the two geometries used in this simulation.
You can download the ZIP file with the ship hull geometries used in this example from this link.
Ozen Engineering Expertise
Ozen Engineering Inc. leverages its extensive consulting expertise in CFD, FEA, optics, photonics, and electromagnetic simulations to achieve exceptional results across various engineering projects, addressing complex challenges like multiphase flows, erosion modeling, and channel flows using Ansys software.
We offer support, mentoring, and consulting services to enhance the performance and reliability of your systems. Trust our proven track record to accelerate projects, optimize performance, and deliver high-quality, cost-effective results for both new and existing water control systems. For more information, please visit https://ozeninc.com.
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