1. ME 114 Computer Assignment #1
Charles Svoboda

2. Problem Statement Problem 19.169:
A 400-kg motor supported by four springs, each of constant 150 kN/m, and a dashpot of constant c = 6500 N-s/m, is constrained to move vertically. Knowing that the unbalance of the rotor is equivalent to a 23-g mass located at a distance of 100 mm from the axis of rotation, determine for a speed of 800 rpm (a) the amplitude of the fluctuating force transmitted to the foundation, (b) the amplitude of the vertical motion of the motor.

3. Problem Solving Steps Model the problem in Working Model 2-D software.
Run simulation in software and measure all necessary results.
Determine the solution to the problem using the simulation results.

4. Step 1: The first thing I did was model the problem in WorkingModel 2-D, using simple geometric shapes for the motor and base as well as four springs and one dashpot, given the same property values as stated in the problem. I used slotted joints to ensure the vertical constraint of the system’s displacement.

5. Step 2: I then replicated the unbalance of the rotor by placing a 23 g object .1 m away from the center using a motor with an angular velocity of 800 rpm, which I calculated as being rad/s (see zoomed image below).

6. Step 3: I then commanded the model to measure the force on the base as well as its displacement during the simulation.

7. Step 4: I then ran the simulation and determined that the amplitude of the fluctuating force on the base was about 2.6 N and that its displacement amplitude was almost zero.

8. Conclusion: My results did not exactly match the answer to the problem as shown on the problem page. I was not able to show the displacement of the base in a small enough increment to get an answer so small, although I believe my model accurately demonstrates such a small displacement. I believe that the mass of the base contributed to a different answer for the forces, especially considering that the example assumes that the base has no mass. I have found that this software, WorkingModel 2-D, does not allow for mass-less bodies.