LNG Tank Analysis and Design System

Software Tour

LNG tank model and analysis types supported

The models created by the LNG tank wizards are optimised according to intended use. Due to the circular nature of tanks, the creation and use of 2D axisymmetric models may be appropriate in some situations, resulting in smaller models and correspondingly faster solution times than 3D models. In cases where these cannot be used, appropriate 3D models may be created instead. 

Model / analysis types supported include:

  • 2D Axisymmetric Static Structural Analysis

  • 2D Axisymmetric Construction Stage Analysis

  • 2D Axisymmetric Thermal Analysis

  • 3D Shell Static Structural Analysis

  • 3D Shell Eigenvalue Analysis

  • 2D Beam-Stick FSSI Seismic Analysis

Examples of models created by the wizards are shown below.

2D Axisymmetric Static Structural Analysis

Model features are defined in individual groups for easier updating of the model and processing of results. Only the outer concrete tank is modelled, and is investigated using 16 static loadcases.

2D Axisymmetric Construction Stage Analysis

In addition to the groups of features defined in the 2D static model, extra groups are set-up to simplify the activation and deactivation of features when modelling the construction stages. Up to thirteen construction stages are automatically created by the wizard, and the nonlinear analysis sequence used ensures that the stresses and strains from a previous stage are inherited in the following stage.

2D Axisymmetric Thermal Analysis

Used to obtain the temperature variation through the thickness of the structure and to obtain the thermal stress and strains induced by the temperature gradient. Typically followed by a structural analysis that uses the temperature distribution as its input loading - commonly known as a thermo-mechanical coupled analysis.

3D Shell Static Structural / Eigenvalue Analysis 

Used when tank loadings are not axisymmetric. All loading defined for the 2D axisymmetric model is also used for this model, and wind loading is also applied.

2D Beam-Stick FSSI Seismic Analysis

A lumped mass beam-stick model is used to perform a dynamic analysis under earthquake conditions. The adopted arrangement of components captures the complex seismic behaviour of the liquid tank system in a simplified but accurate model. A response spectrum corresponding to ASCE is defined by the wizard by default, but others and user-defined spectrums are available.

Some loadings specified or generated from some 2D analyses (such as applied loading, live loadings, thermal or seismic effects) may be converted into equivalent structural or temperature and used in a 3D model.


Models created

Models created by the wizards are generated with all mesh, geometric properties, attributes, supports and loadings assigned to the model, and with features grouped according to type.

Results

Once solved:

  • View results for all or selected parts of a model using separate layers for diagram, contour, vector and discrete value data.
  • Select loadcases individually for each view window, and display multiple views of the model, with each window showing results for different loadcases.
  • Manually specify basic load combinations, defining loadcases to be included and load factors to be used.
  • Use Smart Combinations to generate maximum and minimum results, reducing the number of combinations and envelopes required.
  • Define envelopes of multiple loadcases to provide maximum and minimum results.
  • Plot bending moment and shear force diagrams and visualise structural deflections.
  • Control contour ranges and vector/diagram scales individually for each view window, or set globally to apply to all view windows.
  • Display results in global or local directions, in element directions, or at any specified orientation.
  • Plot results on deformed or undeformed mesh plots and on fleshed or unfleshed beam sections.
  • Selectively output results to spreadsheet applications for additional calculation and graphing uses.
  • For concrete modelling, plot crack width contours, crack patterns and values for supported design codes.
  • Use inspection locations to obtain results for user-defined positions of interest on a model.
  • Transform and display results in global or local directions, in element directions, or at any specified orientation.

Transformed results plots of component Nx and Ny are shown below.

Graphs showing, for example, the variation of moment Mx with wall height can be generated from selections made on the model.


Exporting of forces to spreadsheets

In addition to on-screen viewing of results, wizards also exist to automatically convert stress distributions at chosen slicing locations on models into section forces and output to a spreadsheet. For example, for a 2D axisymmetric model, slices taken through a wall section for component SY can be used to compute vertical axial forces and bending moment.

For a 3D shell model similar section forces based upon angular values are extracted by that wizard and exported to a spreadsheet

 


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Any modelling, design and analysis capabilities described are dependent upon the LUSAS software product, version and option in use.