Going beyond this PTB-3 example, a 3D FEA study will have data points with 6 stress components: S11, S22, S33 and S12 as discussed above, with the addition of S13 and S23 (shear components not shown in the above diagram). Of these two new components, S23 produces a torsion of the SCL and is included. S13 is not perpendicular and is removed.
Results
PTB-3 does not discuss convergence of results or quality of the mesh. We used the Error plot built into SWS to determine if the model is adequately converged at the mesh size used. Acceptable mesh errors in non discontinuity zones is 5%. Discontinuity areas often have higher errors. For this model the error is less than 1% except at SCL 1 at the base of the flange to nozzle weld discontinuity where it is an acceptable 5%. ABAQUS does not have an error plot so it was only run in SWS.
PTB-3 does not discuss convergence of results or quality of the mesh. We used the Error plot built into SWS to determine if the model is adequately converged at the mesh size used. Acceptable mesh errors in non discontinuity zones is 5%. Discontinuity areas often have higher errors. For this model the error is less than 1% except at SCL 1 at the base of the flange to nozzle weld discontinuity where it is an acceptable 5%. ABAQUS does not have an error plot so it was only run in SWS.
We obtained displacement and stress plots from both SWS and ABAQUS that substantially matched the results published in PTB-3.
A comparison of our SCL results from SWS and ABAQUS vs PTB-3 is presented in Table 1. Our results matched PTB-3 within 4% of full scale stresses. Given the assumptions we had to make in modelling this comparison, we consider this to be a bulls eye. Our SWS results matched our ABAQUS results within 0.4%. We split the model at the SCL locations to remove sampling location errors between the two programs. Even so, we did not expect results this close, as this ABAQUS analysis is based on 4 sided elements with 8 nodes while SWS is based on 3 sided elements with 6 nodes. However, the model is highly converged as shown in the SWS error plot so the closeness of the results should not have been surprising.
SWS and ABAQUS in daily use
We use SolidWorks Simulation and ABAQUS for a variety of design tasks in our office. The programs have different characteristics that lead them to be suitable for different applications. SWS is a much easier to use program, usually resulting in finished results in half the time, however it does not have built in linearization results that are compatible with ASME methods. We wrote our own tool to get around this shortcoming.
ABAQUS allows a lot of control over the generated mesh vs SWS. This extra control also requires more effort. The ABAQUS quadralateral mesh is expected to be more accurate than the SWS triangular mesh, but for this overrefined example, the difference is turned out to be negligible. Without a doubt ABAQUS has the better results plots where screen updates happen much much faster than SWS’s leisurely pace. And for non-linear analysis, ABAQUS provides results more often and is more stable than SWS.
We use SolidWorks Simulation and ABAQUS for a variety of design tasks in our office. The programs have different characteristics that lead them to be suitable for different applications. SWS is a much easier to use program, usually resulting in finished results in half the time, however it does not have built in linearization results that are compatible with ASME methods. We wrote our own tool to get around this shortcoming.
ABAQUS allows a lot of control over the generated mesh vs SWS. This extra control also requires more effort. The ABAQUS quadralateral mesh is expected to be more accurate than the SWS triangular mesh, but for this overrefined example, the difference is turned out to be negligible. Without a doubt ABAQUS has the better results plots where screen updates happen much much faster than SWS’s leisurely pace. And for non-linear analysis, ABAQUS provides results more often and is more stable than SWS.
FEA is used for frequency and vibration analysis to determine the natural frequency of objects which cannot be obtained from classical calculations. The natural frequency can then be compared to the system resonance to ensure large amplitude oscillations will not occur. The natural frequency may also be used with building codes to determine a base shear force which can then be input to a stress analysis to validate designs subject to seismic or other oscillating conditions. A complete engineering report is available below representing a typical seismic analysis and report completed by Pressure Vessel Engineering.
Description:
Gimbal Expansion Joints are designed to allow angular movement in any plane by the use of two pairs of hinges affixed to a common floating gimbal ring. The gimbal ring, hinged and pins are designed to restrain the pressure thrust due to internal pressure and shear forces.
A gimbal ring is either round or square. For round gimbals the torsional moment shall be considered and for square gimbals the instability due to the bending shall be considered.
Gimbal Expansion Joints are designed to allow angular movement in any plane by the use of two pairs of hinges affixed to a common floating gimbal ring. The gimbal ring, hinged and pins are designed to restrain the pressure thrust due to internal pressure and shear forces.
A gimbal ring is either round or square. For round gimbals the torsional moment shall be considered and for square gimbals the instability due to the bending shall be considered.
Features:
1-Absorbs angular movements in all planes
2-Restrains pressure thrust forces
3-Transmits shear and wind loads
4-Supports dead weight
5-Avoid twisting the bellows
6-No main anchors required
1-Absorbs angular movements in all planes
2-Restrains pressure thrust forces
3-Transmits shear and wind loads
4-Supports dead weight
5-Avoid twisting the bellows
6-No main anchors required
The capacit y of the Gimbal Expansion Joints to absorb angular movements in any plane is usually applied by using two Gimbal Expansion Joints as shown in the diagram. Only two intermediate fixed points are requiered owing to the fact that the Gimbal system absorbs the thrust produced by the internal pressure. This system of two Gimbal Expansion Joints means that any vertical expansion of the pipes is absorbed by the bend in the horizontal sections of piping and it may therefore be necessary to install spring hangers in both sections.
When it is either impossible or undesirable for the horizontal sections of piping to absorb the expansion of the vertical section, a system composed of two Gimbal Expansion Joints plus one Hinged Expansion Joint must be used as shown in the diagram. The use of a Hinged Expansion Joint is justified by the fact that movement in the vertical section only occurs in one plane.
Description:
These expansion joints are made of one single bellows element fitted with welding ends or flanges plus a system of articulated supports which allow for angular movement in one plane only. The hinge mechanism is designed to accept full pressure thrust.
These units do not allow axial movement however, some types of hinge systems can be provided with holes for the hinge pin that are slotted to allow limited axial displacement. These “slotted hinge” types can not resist the pressure thrust forces and therefore proper anchorage must be provided.
These expansion joints are made of one single bellows element fitted with welding ends or flanges plus a system of articulated supports which allow for angular movement in one plane only. The hinge mechanism is designed to accept full pressure thrust.
These units do not allow axial movement however, some types of hinge systems can be provided with holes for the hinge pin that are slotted to allow limited axial displacement. These “slotted hinge” types can not resist the pressure thrust forces and therefore proper anchorage must be provided.
Features:
1-Absorbs angular movements in a single plane
2-Restrains pressure thrust forces
3-Transmits shear and wind loads
4-Supports dead weight
5-Avoid twisting the bellows
6-No main anchors required
1-Absorbs angular movements in a single plane
2-Restrains pressure thrust forces
3-Transmits shear and wind loads
4-Supports dead weight
5-Avoid twisting the bellows
6-No main anchors required