Surface-based fluid cavities

This problem contains basic test cases for one or more Abaqus elements and features.

This page discusses:

ProductsAbaqus/Explicit

Features tested

This section provides basic verification tests to define:

  • Fluid behavior for a surface-based cavity

  • Fluid exchange

  • Fluid exchange activation

  • Fluid exchange in or out of a fluid cavity

  • Fluid inflator

  • Fluid inflator activation

  • Fluid inflator property

  • Gas species used for a fluid inflator

  • Molar heat capacity

  • Molecular weight

  • Surface-based fluid cavity

Fluid behavior

Problem description

In this test the following three types of fluid behaviors are tested:

  • Fluid cavity filled with a mixture of gases (pneumatic fluids) under isothermal conditions.

  • Fluid cavity filled with a mixture of gases (pneumatic fluids) under adiabatic conditions with optional temperature dependence of heat capacity.

  • Fluid cavity filled with an hydraulic fluid with optional temperature dependence of fluid density.

Five independent fluid cavities (no fluid exchange) are modeled using the surface-based fluid cavity capability, each with a different fluid behavior.

Results and discussion

The test verifies that Abaqus/Explicit accurately addresses the relationship between fluid pressure, fluid temperature, and fluid volume. In addition, the test also verifies the use of the magnitude of the additional and minimum volumes for the fluid.

Gas structure interaction

Elements tested

  • B21
  • CAX3
  • CAX4R
  • C3D4
  • C3D6
  • C3D8R
  • C3D10M
  • CPE3
  • CPE4R
  • CPS3
  • CPS4R
  • M3D3
  • M3D4R
  • RAX2
  • R2D2
  • R3D3
  • R3D4
  • S3R
  • S4R
  • SAX1
  • SC6R
  • SC8R
  • SFM3D3
  • SFM3D4R
  • T2D2

Problem description

A fluid cavity is primarily defined to consider the coupling between the deformation of the structure and the pressure exerted by the fluid on the structure. These tests verify the capability of Abaqus/Explicit to model this interdependence accurately by defining a fluid cavity based on the surfaces of the structure. The structure enclosing the fluid cavity is modeled using different feasible combinations of finite elements. The volume of the cavity is changed intentionally during the analysis by prescribing displacement boundary conditions on a particular set of nodes, which results in a change in the cavity pressure.

Results and discussion

The results indicate that the change in cavity pressure gets correctly transferred to the elements of the structure and is reflected as a change in the nodal reaction forces.

Input files

gasstructure_3d.inp

The structure enclosing the fluid cavity is modeled using different three-dimensional finite elements available in Abaqus/Explicit.

gasstructure_c3d10m.inp

The structure enclosing the fluid cavity is modeled using C3D10M elements.

gasstructure_2d.inp

The structure enclosing the fluid cavity is modeled using different two-dimensional finite elements available in Abaqus/Explicit.

gasstructure_axi.inp

The structure enclosing the fluid cavity is modeled using different axisymmetric finite elements available in Abaqus/Explicit.

Fluid exchange

Problem description

In this test fluid flow between a cavity and its environment or between two fluid cavities is modeled. Test cases include flow of a single gas, flow of a mixture of gases, and flow of hydraulic fluids. For pneumatic fluids, both isothermal and adiabatic behaviors are tested.

Results and discussion

The analysis results closely match with the analytical results, which are obtained using the governing equations described in Fluid Exchange Definition.

Input files

fluidexchange_pneumatic.inp

Flow between a single cavity and its environment and between two fluid cavities filled with either a single gas (pneumatic fluid) or a mixture of gases (pneumatic fluids) modeled using all fluid exchange property options.

fluidexchange_hydraulic.inp

Flow between a single cavity and its environment and between two fluid cavities filled with an hydraulic fluid modeled using all fluid exchange property options.

fluidexchange_usereffarea.inp

Flow between a single cavity and its environment with leakage area defined using user subroutine VUFLUIDEXCHEFFAREA.

fluidexchange_cavitypres.inp

Application of fluid pressure on the fluid exchange surface.

Fluid inflators

Problem description

This test verifies the fluid inflator properties that can be defined in Abaqus/Explicit to simulate the flow characteristics of the actual inflators. The inflator mass flow rate and inflator temperature are assumed to be linearly varying with time for the mass flow rate and inflator gas temperature type of fluid inflator property. For the tank volume type of inflator property, the tank volume and tank pressure are set to be the same as the cavity volume and cavity pressure obtained in the mass flow rate and inflator gas temperature case. For the dual pressure type of fluid inflator property definition, the tank volume and tank pressure data are taken from the tank volume case and the inflator pressures at different inflation times are determined from the equations given in Inflator Definition. The data necessary to define the mass flow rate and inflator pressure type of inflator property are obtained from the previous three cases. In the test a total of ten fluid cavities are modeled using the surface-based fluid cavity capability. Fluid cavities 1–8 and 10 are inflated with the same ideal gas or a mixture of ideal gases that are initially present in the cavity. However, the molar mass fractions of the gases inflating the fluid cavity filled with a mixture are considered to be different from the initial molar mass fractions. In the case of cavity 9, the constituents of the gas mixture inflating the cavity are considered to be different from the constituents present in the cavity initially.

Results and discussion

The results for the mass flow rate and gas inflator temperature type of fluid inflator property are in agreement with the analytical results. The results for both the tank volume and mass flow rate and inflator pressure type of inflator properties, as expected, are almost the same as for the mass flow rate and gas inflator temperature type of inflator property. However, for the dual pressure type of inflator property, the results do not match the results of the previous cases since the heat capacity for the ideal gases is considered to be dependent on temperature.