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Practical Introduction into FEM I

APDL Code example

ET ITYPE Ename KOP1, KOP2, KOP3

- Defines a local element type from the element libary
- ITYPE: Arbitary (willkürlich) local element type number
- ET: Indicator what is implemented
- Ename: Element name (e.g Beam 188)
- KOP1, KOP2, ...Keyoptions, changing element behaviour

Practical Introduction into FEM I

Ansys Parametric Design Language (APDL)

- Imperativ scripting language of Ansys
- Most actions can be accessed via GUI-tools

Practical Introduction into FEM I

Why do we need to add fixed rotation at a beam problem? (Session 2, task 1)

Although the problem should not rotate due to nomarical inaccuracies in the solution process a rotation can occure

Practical Introduction into FEM I

Beam

- One Dimensional line element
- Based on Timoshenko beam theory which includes shear deformation effects
- DOF: UX,UY, UZ ,Rotx, Roty, Rotz
- Linear, quadratic, cubic

Practical Introduction into FEM I

*get crossection, SECP, matid, PROP, AREA

ET, matid, LINK180

SECTYPE, matid, LINK

SECDATA, crosssection

- *get: reads cross section area from geometry with ID matid and stores it into user defind variable crosssection
- matid is a variable containing the geometry ID
- ET: changes the element type ot the geometry with the ID matid to LINK180
- SECTYPE: Associates the section the type "link" (this controls what we need to give using SECDATA)
- SECDATA: Assigns cross section are stored in the variable crosssection

Practical Introduction into FEM I

Link Element

- One- dimensional line element
- Stab bzw. Seil
- to model trusses, sagging cables, links, springs
- DOF: UX, UY, UZ
- Force only along the axis
- Only compressing an pulling
- No graphic interface for Link --> needs to be enabled using APDL

Practical Introduction into FEM I

Plane stress

- All stresses orthogonal to a specific plane are zero
- assumtion used, if a thin strcutre like a triangle ruler is considered
- plane x-y: sigma_z = tau_yz = tau_xz = 0
- --> gamma_xz = gamma_yz =0
- epsilon_z os generally not cero, eliminated out of the equation system

Practical Introduction into FEM I

Tau_xy

- x: stress vector is in plane with normal vector on direction of x
- y: stress vector is in direction of y-axis

Practical Introduction into FEM I

Plane Strain

- Plane strain means that all strains orthogonal to a specific plane are zero
- Assumption of plane strain is often used, if a thik structure like a steel beam is considered
- For plane x-y: Epsilon_z = 0 = gamma_xz = gamma_yz = 0
- --> tau_xz = tau_yz = 0
- sigma_z is in general not zero. Its just eliminated out of equation system

Practical Introduction into FEM I

Plane Element

- Two dimensional element
- Linear element 4 - nodes
- Quadratic element with 8 - nodes
- DOF: UX, UY (No bending, no z - direction)
- Keyopt: Plane stress, axisymetric, plane strain

Practical Introduction into FEM I

Keyoptions

- Switches for turning on specific element options
- Every element has different keyoptions, one needs to check Anys documentation for details
- Some Keyoptions are built into the Ansys workbench GUI
- Some need to be included via APDL

Practical Introduction into FEM I

APDL Code Example

SECDATA, VAL1, VAL2, ..., VAL12

- Describes geometry of a section
- VAL1, VAL2 provides geometry information to a section (e.g. cross section)

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