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Model Steam Engine Assembly: Design and Analysis

05-05-2009, Past Projects, Muhhamad M. Raza

Methodology:

COSMOSDesignSTAR™ was used to conceive a computerized solution to each part in the assembly of the steam engine. An analysis was also conducted on the assembly. Several parts required the addition of split lines.  The purpose of the split lines was to isolate a region in the part for the purpose of applying boundary conditions. Each model was prepared in solidworks™ with fully defined dimensions and required split lines. The COSMOSDesignSTAR™ study was created using a solid mesh type for all parts. The conducted studies were all static. The material for the parts was chosen and may be referred to in appendix A for each part. Split lines were added to solidworks™ models of the clevis and piston for the area consisting of the piston rod. Split lines were added to the clevis pin for the area subjected to double shear, where the center section was connected to the connecting rod and assumed fixed.  The clevis pin required a criteria other than Von Mises stresses for convergence.  A point was chosen to be probed and was shown in figure 1 below.

The connecting rod was subject by an axial load on the clevis side, and a fixed boundary condition on the counterweight side.  Many split lines were added to the driveshaft for the area consisting of the counterweight (subjected to by a torque), and the load bearing walls (cylindrical face only restrained in the radial directions), as well as the flywheel, which was the end which the driveshaft was immovable. The fixed boundary condition was unrealistic, but necessary for a COSMOSDesignSTAR™ analysis. The driveshaft was reduced in length for analysis purposes. The actual length was not entirely subjected to a torque, thus the model would have been incorrect if it had been fixed a distance, L, more, than the accurate portrayal of the problem. No split lines were added to the pressure vessel. The pressure vessel walls required split lines for the purpose of applying a pressure on the area subjected to a water vapor pressure. The mounting holes for the pressure vessel on the walls were used to fix the walls. The base was also fixed, and the pressure was applied to the walls on the relevant area. The piston rod was subjected to an axial pressure of 200 psi.  For a worst case scenario analysis the connecting rod and counterweight were set at right angles. The counterweight was subjected to fixed boundary condition at the shaft. The counterweight was subjected to a horizontal force of 157 lbf, as calculated from a static calculation by knowing the pressure on the piston, and a vertical force of 61 lbf calculated by measuring the angle in solidworks™ between the horizontal plane of the base and the angled plane of the counterweight as 21.4 degrees.  This trigonometric solution gave a resultant of 170 lbf, and was what was used in the analysis of the connecting rod, clevis pin, and counterweight.  The driveshaft was subjected to a torque of 126 in-lbf and a force of 170 lbf as a worst case scenario from the connecting rod. All part analysis was conducted with high mesh quality. All part factor of safeties were obtained from the maximum Von Mises stress criterion.

 

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