This section describes the theory and assumption behind the Structure-Pipe Connection multiphysics coupling. The coupling is an extension of the transition type couplings in
Solid-Beam Connection and
Shell-Beam Connection to also account for radial deformation of the pipe caused by the fluid pressure and the temperature distribution over the cross section. For a more general background to the coupling of beam type elements to solids and shells, see
Connection Between Shells and Solids and
Connection Between Shells and Beams in the Shell documentation.
where us is the displacement of the solid,
νs is Poisson’s ratio of the solid,
up is the displacement of the pipe,
θp is the rotation of the pipe,
r the distance from the center of the pipe, and
eyl and
ezl are the base vectors of the local
yl-axis and
zl-axis. The first four terms in
Equation 11-3 are identical to the transition type coupling in the Solid-Beam Connection, while the last one is added to account for the fluid pressure and the temperature difference in the pipe. The radial displacement
uradial included in
Equation 11-3 is computed from the radial deformation
ur of the pipe as
where T is a matrix the describes the transformation from the local coordinates of the pipe to global coordinates. Above,
dy and
dz are the distances, in local coordinates, and
R is the radial distance from the center of the pipe. The radial displacement is given by
where Es is Young’s modulus of the solid,
αp is its coefficient of thermal expansion,
Ri and
Ro are its inner and outer radii, and
Tref is its volume reference temperature. The stresses in the pipe due to the temperature difference between the inside and outside temperatures
Tin and
Tout, and the fluid pressure
p on the inside surface of the pipe are given by the following analytical expressions
where a is the shell normal displacement, and
t1 and
t1 are the shell tangents. Also, the expression for the radial deformation
ur in
Equation 11-4 is simplified, and it is for a shell connection given by
Here sp and
sT are scaling factors, which are necessary to avoid abrupt changes in
uradial.