ABE 4803: Biosystems Simulation

Modeling as a Design Tool

Introduction

The last 2 classes (not counting the quiz) were devoted to getting a good start on your first modeling project. If your 3 sensor truth table was written correctly (I'll respond via email to let you know if there are problems after I see your homework), and if you implement it properly, the rest of Project 1 should be pretty easy. All you will have to do is implement a heater. See the Project 1 document for the equation that describes the heating process. Remember that the heater size is 1200 kW. Since a Watt is 1 J/s, and your model time step is 1 minute, you will also have to make sure that your heater units are correct in your model.

Last class you had the opportunity to see how VisSim could be used to model water conservation in aquaculture and left ventricle function in a human heart. These models are somewhat complex and took a while to implement (although it was a lot less time than it would have taken in a traditional programming language!). You will be implementing models like these in the coming months.

Modeling can also be useful for less complex problems that have multiple solutions, require the use of real data, or pertain to dynamic (constantly changing) systems. In this document, you will have the opportunity to solve some problems of this kind.

A note on the exercises: These exercises are designed to help you see how modeling can be a useful tool for an engineer. They are also there to help you learn basic "nuts and bolts" operations in VisSim. Be sure you see how the various modeling operations are performed. If you don't understand something, please ask! Solutions are due January 22.

The Stormwater Impoundment

Near shopping centers and housing developments, you may have noticed grassy depressions with storm drains leading into them. They are stormwater impoundments and are used to trap run-off from paved areas to limit the flow of water and pollutants into area streams. There is one located behind the Starkville Wal-Mart.

In this exercise, you will be using a 12 year weather record to design a stormwater impoundment. Your boss wants 3 options having maximum depths of 4 feet, 7 feet, and 10 feet, respectively (i.e., depth should never exceed the maximum depth). Your job is to determine the areas of the required impoundments for these options. Adjust the area of the impoundments in the model in order to make your recommendations.

The Automobile Transmission

The average automobile engine turns its crankshaft about 3000 times per minute (i.e., rpm = 3000). The average tire has a circumference of 9 feet. If the tire on the car made a complete revolution each time the engine did (final drive ratio = 1:1), the car would travel at about 270 mph. Typically, there is a gear reduction that occurs in the transmission and then a final gear reduction that occurs in the differential.

Your job is to design a 3 speed transmission which results in speeds of 10 mph, 35 mph, and 60 mph at an engine speed of 3000 rpm. The gear reduction in the differential is 3:1 . Find the gear reductions of each of the 3 gears of the transmission.

The Sperm Whale

Sperm whales (which are air breathing mammals) hunt giant squid at depths in excess of 3,000 feet (the theoretical maximum is about 3,700 feet). They can stay submerged for periods of up to 2 hours (they accomplish this by cutting off circulation to most of their bodies, thereby conserving oxygen for the most critical systems). Estimates of squid size based on tentacle sucker scars found on the whales suggest that giant squids can grow to more than 60 feet in length.

Your starting point for this exercise models a 3,700 foot dive. The verticle velocity in the downward direction becomes less as depth increases. On the return trip, the verticle velocity increases as the whale approaches the surface (what math function governs velocity in both directions?). Your task in this exercise is to

  1. understand how the model was implemented; then
  2. keep the whale at 3,700 ft so that, by the time it gets back to the surface it has stayed under water for the whole 2 hours.

When you finish with the second part, your plot will look like this:

For this exercise, you should turn in the entire finished model. You may turn in the numerical solutions for the first 2 exercises in the text part of the email. Send the model of the third part as an attachment.

Things to Know