Integration Settings for a Derived Value
Select a Method: Auto (the default), Integration, or Summation.
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Auto — the default method, which computes the integral for fields by numerical integration and for reaction forces by summation. Predefined quantities for reaction forces use summation instead of integration. Also, if an expression is specified for the integrand using the reacf operator, the automatic setting chooses the summation method.
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 Integration — the standard numerical integration method (quadrature).
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 Summation — a summation method is useful for calculating reaction forces. The summation method finds all nodes on the boundary, evaluates the expression in the nodes, and sums up the values. Reaction force variables are predefined in the structural mechanics interfaces.
COMSOL Multiphysics determines an appropriate Integration order for the expression when you use integration. To change the order, select the check box and enter an integer (0 or larger; default: 4). The COMSOL Multiphysics software performs the integration elementwise using numeric quadrature of the selected order.
2D Axisymmetric Models
For 2D axisymmetric models, Volume Integration and Surface Integration are available. COMSOL Multiphysics multiplies the expression (integrand) with 2*pi*r prior to integration to compute the corresponding volume or surface integral if you do the next step.
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For Surface Integration, select the Compute volume integral check box.
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For Line Integration, select the Compute surface integral check box.
Reaction force variables in axisymmetry include the 2πr factor, so summation over them always gives you the revolved surface force or volume force.