(15b) Using Real and Imaginary Pedagogical Parts to Demonstrate Fluid Dynamics and Control Concepts

Both hands-on experience with physical systems and the use of web-based simulations have been shown to have significant pedagogical benefits.  In this work we created both a physical apparatus and its simulation in order to illustrate several important engineering concepts to our students.

The physical apparatus consists of a computer fan positioned beneath a horizontal acrylic tube, which has an ultrasonic range finder aimed up its center.  By controlling the power sent to the fan, objects in the tube may be made to levitate, and their position may be determined by the rangefinder.  Using a custom Matlab GUI, we have created a system where students may manually control the power to the fan, or create automatic controllers that measure the object’s position and use that measurement as feedback to adjust the flow rate accordingly. 

To illustrate concepts of drag, students may place objects of various shapes or weights in the tube and determine the flow rate needed to lift the object; typically weighted and perforated ping-pong balls or paper cones have been used.  Though this system is complicated by the tube wall, an approximately square root relationship was found between a spherical object’s weight and the flow rate needed to lift it, as one might anticipate from theory regarding falling spheres.

To illustrate the importance of and basic concepts behind automatic control, students may use this system to take on the role of a controller.  They may alter the power to the fan using the GUI to achieve a desired object height.  However, the most effective pedagogical use of this apparatus was found by setting the power to the fan based on the the position of the student’s hand, as detected by a webcam.  Students may achieve a very memorable and tactile experience of what it takes to properly control an integrating system by feeling a direct connection to the manipulated variable.  Once the difficulties of control have been demonstrated firsthand, then a simple PID controller may be introduced, explained, and implemented to achieve superior control.  Furthermore, the effects of poor control can be easily visualized by altering PID parameters to achieve unstable oscillations, slow response times, and so on. 

A virtual counterpart to this demonstration was also created in the form of a JavaScript applet which may run on any major browser.  This applet simulates the physical system and allows the student to alter the associated constants and witness their effect.  With this virtual system the student may also implement automatic control or act as the controller themselves, using their mouse position to adjust the power to the fan.  The simulation may be used to prepare students to work on the actual apparatus, or allow a large class to all experiment with a system similar to that used in an instructor’s demonstration.  Furthermore, use of simulations along with the physical system allows students to gain a clearer picture of the problems engineers may have in reconciling theory with practice.

These twin pedagogical tools have been successfully used as an introduction to basic concepts of control and drag forces, and they have been well received by students.  Furthermore, the system has both control and fluid dynamics components that are addressable with a range of theoretical sophistication, and thereby we have created related projects that have been challenging for both undergraduate and graduate students.  Finally, this system has been a very useful tool for high school outreach purposes, due to its interactive aspects and the relatable way in which it illustrates otherwise abstract issues of automatic control.