ANSYS Asas software is a general-purpose structural finite element system containing industry-specific features to address the needs of offshore and marine engineers. ANSYS Asas provides the capabilities required to perform global structural assessment of most types of marine structures, including jackets, jack-ups, risers, offshore wind farms, and floating systems such as FPSOs, SPARs and semi-submersibles.

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Direct Results Access from Microsoft Excel & Mathcad Direct Results Access from Microsoft Excel & Mathcad

As part of the ANSYS ASAS installation, functional interfaces enable all ANSYS ASAS results to be accessed and retrieved using Microsoft® Excel® and Mathcad®.

This facility provides a number of major benefits. It allows the user to perform further post-processing using Excel (including Visual Basic®) and Mathcad. It also allows a user to design his or her own report templates. Once designed, templates can be re-used, thus saving considerable effort.

A Microsoft Windows® dynamic-link library provides a toolkit of functions that may be called by user-created executable programs that permit access to the ANSYS ASAS results.

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Code Checking & Fatigue Calculations Code Checking & Fatigue Calculations

A major requirement for many civil engineering designs (including offshore structures) is the need to satisfy regulatory codes of practice for frame and shell-like structures. ANSYS ASAS software provides the capability to undertake checks against the most commonly used codes. Three categories of code checks may be undertaken:

  • Beam member checks for strength and buckling
  • Tubular joint connections
  • Hydrostatic collapse

Present and past codes are available, including API WSD and LRFD, AISC WSD and LRFD, ISO 19902, NORSOK, BS5950 and DS449.

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Member utilizations
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Joint check utilizations 

To compliment code checking, ANSYS ASAS provides a fatigue capability that provides for operational life evaluation in environments in which fatigue issues have been identified (for example, in the offshore industry). Spectral, deterministic and time history fatigue analysis options are available. Stress concentration factors either can be explicitly defined or utilized with a set of empirical formulations, including the Efthymiou influence function approach. S-N curves may also be explicitly defined, or use one of the predefined curves commonly adopted. Thickness correction effects can be included.

Nonlinear & Extended Solution Capabilities Nonlinear & Extended Solution Capabilities

ANSYS ASAS software offers a standard set of features that allows simulation beyond simple linear elastic analysis, such as: 

  • Large displacement 
  • Nonlinear elastic material behavior 
  • Plasticity 
  • Laminated composite failure behavior 
  • Soil and rock-like material behavior 
  • Nonlinear boundary conditions, such as gaps and rigid surface contact 
  • Creep 
  • Nonlinear transient dynamics 
  • Stability (buckling loads) 
  • Steady-state heat 
  • General field analysis 

There is a special application for investigating pile behavior using nonlinear soil properties and interaction with attached structural members (so called pile–structure interaction). This employs an efficient solution based upon P-Y and T-Z soil curves, either explicitly defined or by providing basic soil parameters such as unit weight or shear strength. Pile group effects are automatically included to account for the interaction between the piles through the soil. Pile code checks to API can be requested. 

While conventional analysis of framed structures assumes rigid joint connections between adjoining members, there is much evidence that the effects of including the inherent flexibility at the joints provides for a more rigorous solution. This allows simple beam models to account for chord wall flexibility and the effects of adjacent members, potentially obviating the need for detailed shell models in critical areas. This application is based on simple parametric formulations that describe the load-deformation characteristics for various joint types.

Interfaces to ANSYS Aqwa Interfaces to ANSYS Aqwa

Pressures and motions from a diffraction/radiation analysis in ANSYS Aqwa software can be transferred to an ANSYS Asas model. Each combination of wave frequency, heading, height and phase becomes a quasi-static load case. This feature can be used in transferring wave loads for structures composed of both diffracting and tubular elements, such as what may occur in semi-submersibles or truss-spars.

Meshes for the ANSYS Aqwa and ANSYS Asas models can be developed independently, since structural requirements are quite different from the much-simpler hydrodynamic model. The mapping feature automatically interpolates the correct pressures at the structural nodes. For structural elements that cut the water surface, corrections are made to the resulting pressures to ensure that the total loads applied are correct.

ANSYS Aqwa can be used as a source of response amplitude operator (RAO) information for simulation of large floating body response to a wave environment.

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 Hull pressure plot and stress resultants in ANSYS Asas application after pressure mapping

Analysis of Offshore Wind Turbines Analysis of Offshore Wind Turbines

ANSYS ASAS is increasingly used in the design and certification process of offshore wind turbines (OWTs). In addition, the technology has been used over the last four decades in the oil and gas industry to analyze a large variety of offshore structures. The software's extensive and well-proven set of FEA capabilities enable comprehensive and reliable design and certification. In particular, ANSYS ASAS is used to simulate the overall OWT system: A number of effects can be analyzed simultaneously, including wave loads (from regular and irregular sea states and currents), elastic behavior of the support structure (ranging from monopiles to jackets), soil characteristics of the local sea bed, and loads from turbulent wind fields and turbine control systems when coupled with specialized wind programs such as Flex5, ADCoS and FAST. Hundreds of load cases can be easily set up, as required, and from these cases ANSYS ASAS can derive probabilistic-based rainflow-counting fatigue data, such as fatigue life, usage factors, damage per wave and stress histograms.

Courtesy REpower Systems AG.

Coupled Wave Structure Interaction with Regular & Random Waves Coupled Wave Structure Interaction with Regular & Random Waves

ANSYS ASAS software can be used to generate environmental loading for conventional quasi-static analyses. In addition, the technology includes a feature that integrates the wave loading capabilities with the large deflection solver available in the nonlinear product. This facilitates full hydroelastic coupling and makes it suitable for jack-ups, compliant structures, manifold installation and riser analysis.

Features include:

  • Wave, current and wind load
  • Regular waves, airy, Stokes 5th, cnoidal, stream function plus user-defined wave grid
  • Random sea states, JONSWAP, Pierson-Moskowitz and user-defined plus shell new wave 
  • Wave loading within the API code of practice including effects of current on the wave period, current stretching, current blockage factor and wave kinematics factor
  • Tube and beam elements with facilities for modeling appurtenances, anodes, etc. 
  • Flooded or sealed members
  • Marine growth
  • Reynolds/KC number effects
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Jacket structure with coupled wave–structure interaction

Model Generation Using ANSYS Structural Mechanics or FEMGV Model Generation Using ANSYS Structural Mechanics or FEMGV

Models can be created for analysis in ANSYS ASAS software using the ANSYS DesignModeler tool and ANSYS structural mechanics products. The model transfer includes all aspects of the analytical model, including finite element mesh, material and geometric properties, boundary conditions, and loading.

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 Geometry generated in ANSYS DesignModeler

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 Model meshed with ANSYS structural/sechanical application

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Model transferred to ANSYS ASAS via ANSYS macro 

The ANSYS ASAS solver has been integrated with FEMGV® to provide powerful finite element analysis facilities including both modeling and post-processing.

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