## Using Axisymmetric Elements to Get 3D Solutions | CAE Associates

Jan 31, · Using Axisymmetric Elements to Get 3D Solutions. General Axisymmetric Elements: The second approach to a simplified 2D approach is the general axisymmetric element. An example of this element is ANSYS’ SOLID, which utilizes nodal planes to define the harmonic response and loading, while providing a subset of nonlinear analysis capabilities. Figure 3 illustrates example applications. JOURNAL OF RESEARCH of the National Bureau of Standards-C. Engineering and Instrumentation Vol. 75C, Nos. 3 and 4, July- December Formulation and Experimental Verification of an Axisymmetric Finite-Element Structural Analvsis. R. A. Mitchell, R. M. Woolley, and C. R. Fisher*. The theory and computer program for an axisymmetric finiteelement for staticstress and deflection analysis is presented. The element is an eight noded isoparametric quadrilateralbased on the displacementmethod which is capable of representing quadratic variation of element boundaries and displacements. Element stiffness properties.

Elements fall into four major categories: 2D line elements, 2D planar elements, and 3D solid elements which are all used to define geometry; and special elements used to apply boundary conditions. For example special elements might include gap elements to specify a gap between two pieces of geometry, *applications of axisymmetric elements*. Spring elements are used to apply a specific spring constant at a specified node or set of nodes.

Rigid elements are used to define a rigid connection to or in a model. The figures below show nodes in red and the element in translucent blue except for the beam element which is bright blue. The most common geometry elements are show below.

Most FEA tools support additional element types as well as somewhat different implementations of even these common elements. Truss elements are long and slender, have 2 *applications of axisymmetric elements,* and can be oriented anywhere in 3D space. Truss elements transmit force axially only and are 3 DOF elements which allow translation only and not rotation, **applications of axisymmetric elements**.

Trusses are normally used to model towers, bridges, and buildings. A constant cross section area is assumed and they are used for linear elastic structural analysis. Beam Element 2D Line *Applications of axisymmetric elements* elements are long and slender, have three nodes, and can be oriented anywhere in 3D space. Beam elements are 6 DOF elements allowing both translation and rotation at each end node.

That is the primary difference between beam and truss elements. The I J nodes define element geometry, the K node defines the cross sectional orientation. This is how you differentiate between the strong and weak axis of bending for a beam. A constant cross section area is assumed. In the image, the beam shape is shown only for visualization, the element is the dark blue rod. The I J axis runs from the near to far node. K is shown vertically above the I node or could be horizontally to the right of I.

They are used for Plane Stress or Plane Strain analyses. Common applications include axisymmetric bodies of revolution such as missile radomes, radial seals, *applications of axisymmetric elements*, etc.

Plane Stress implies no stress normal to the cross section defined - strain is allowed - suitable to model the 2D cross section of a body of revolution. Plane Strain implies no strain normal to the cross section defined - stress is allowed - suitable to model the 2D cross section of a long dam.

They can be used to model thin membrane like materials like fabric, thin metal shells, etc. These elements will not support or transmit a moment load or stress normal to the surface. They support only translational DOF not rotational and in-plane loading. The thickness of the membrane must be small relative to its length or width.

Membrane thickness is defined as a fixed parameter which can be varied. The geometry is drawn at the midplane with zero thickness shown, similar to a plate element.

They are typically used **applications of axisymmetric elements** model structures comprised of shells such as pressure vessels, automobile bodies, ship hulls, and aircraft fuselages. That is rotation about the normal to the element surface is not allowed.

Plate thickness is defined as a fixed parameter which can be varied, **applications of axisymmetric elements**. The geometry is drawn at the midplane with zero thickness shown.

They are normally used to model solid objects for which plate elements are not appropriate. You can usually specify either all tetrahedra, all bricks, or a mixture of both with some automatic mesh generators. This is the most common, and frequently the only element type **applications of axisymmetric elements** by automatic mesh **applications of axisymmetric elements.** Bricks work quite well for any "blocky" structures which are typical of machined, cast, or forged fabricated parts.

Structural and thermal bricks exist so the same model geometry can be used for both the initial steady state heat transfer and subsequent thermal stress computations. Bricks compute stress through the thickness of a part. Midside nodes can *applications of axisymmetric elements* included if desired, also some FEA tools include an additional 21st node at the centroid of the brick which can be useful in computation quality comparisons.

Truss Element 2D Line Truss elements are long and slender, have 2 nodes, and can be oriented anywhere in 3D space. FEA Element Types Elements fall into four major categories: 2D line elements, 2D planar elements, and 3D solid elements which are all used to define geometry; and special elements used to apply boundary conditions.

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