An Attempt to Strengthen “Outcome k” in a Mechanical Vibrations Course David Che Department of Engineering and Computer Science Geneva College Beaver Falls, PA 15010 Abstract One of the challenges in teaching undergraduate mechanical vibrations curriculum is in the necessity of extensive use of advanced math in deriving and solving differential equations (DFQ). How to engage students in this seemingly tedious theoretical development is paramount for effective teaching. There is no way to get around this theoretical development – actually the instructor not only has to engage the students with the DFQ aspect of math, but he/she also has to teach some fundamentals in dynamic modeling of mechanical systems in order to come up with these DFQ equations. How to keep this derivational work interesting to the students is a perennial challenge. Another challenge is the need to prepare our students in using ever changing engineering software and tools that are being used more widely in the industry. Commonly termed as “outcome k”, ABET accreditation pressure just adds to such needs. Having taught this course for seven years in a roll, the author had gone through several textbook changes and tried various techniques and pedagogies with varying levels of success. In this paper, a variety of tools in enhancing student learning are shared, which include the use of animation, simulation and virtual lab assignments. Examples in each category are given. For animation and simulation, Mathematica and Matlab/Simulink are used. For virtual lab development, an open access web-based resource has been adapted for use in the undergraduate level mechanical vibration curriculum. All these tools are easy to use and easy to implement in coursework. Some outcome assessment data are shared. Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education Introduction MEE 410 (Mechanical Vibrations) is a senior or junior-level engineering elective course for engineering majors at Geneva College. It has an ABET accredited general BSE program with concentrations in mechanical, civil, environmental, computer, chemical, electrical and interdisciplinary engineering. Due to the EGR 214 (Dynamics) pre-requisite, which is only an elective for concentrations other than mechanical engineering, almost all who took MEE 410 were mechanical engineering students over the past seven years (2009-2015). The course was redesigned in spring of 2009 with increased emphasis on using modern engineering tools such as MATLAB and Simulink in solving engineering vibration problems. This change was mainly motivated by the instructor’s desire that students be taught the most advanced engineering tools currently being used in the industry. Later on it was realized that this effort also helped address an ABET assessment requirement for outcome k (ability to use the techniques, skills and modern engineering tools necessary for engineering practice)1. And teaching students these software and tools is a nice change of pace from the typical theoretical derivations inherent in teaching this course. It helps engage students in classrooms and help them see the applications more clearly. One of the first challenges was finding an appropriate textbook that would support this pedagogy. Over a dozen mechanical vibrations textbooks were evaluated. Table 1 shows the results of this evaluation according to each text’s use of engineering software and other computer tools in support of the mechanical vibrations curriculum. It can be seen that Matlab is the consensus tool adopted by the majority of the authors. However, only one text used Simulink extensively in the curriculum. Many textbooks were developed using Matlab, but the books themselves did not include or only included very little coverage on how to use Matlab to solving vibration problems. Despite of its many shortcomings (for example, as the first edition, it has many typos and errors), we decided to use William J. Palm III’s text2 due to its excellent coverage of Matlab and Simulink applications. It was the first mechanical vibrations textbook that teaches Simulink, and it is still the only vibration textbook that teaches Simulink to this day, according to our knowledge. Palm’s text has a strong "system dynamics" and "feedback control" flavor because of the author's background (he authored several textbooks such as System Dynamics, Control Systems Engineering, and Modeling, Analysis, and Control of Dynamic Systems). Over the years we had tried some other textbooks, such as Benson Tongue's Principles of Vibration3 and Daniel Inman's Engineering Vibration (3rd edition)4, and used Palm's book as a supplement on teaching students how to use Simulink. Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education Table 1 Survey of Textbooks that Support the Use of Modern Engineering Software and Tools Textbook listed by author(s) Mathematica Matlab Some examples Extensive use – many examples throughout the book Recommended Matlab in the preface but no examples or coverage in the text Some examples and toolboxes William Palm III2 Benson H. Tongue3 Daniel J. Inman4 H. Benaroya & M. Nagurka5 S. Graham Kelly6 Recommended but no examples or coverage in the text Mentioned in the preface but no coverage in the text W. T. Thomson & M. D. Dahleh7 Some examples B. Balachandran & E. B. Magrab8 Some coverage provided by publisher’s website T. Schmitz & K. S. Smith9 Alok Sinha10 Singiresu S. Rao11 Some examples Simulink MathCad Extensive use – many examples Some examples Some examples Some examples The revised course description says: MEE 410 Mechanical Vibration (3 credits) Introduction to the modeling, analysis and design of mechanical vibrating systems. Steady state and transient analysis of systems with a single or multiple degrees of freedom. Free, harmonic and forced responses of such systems. Extensive use of modern engineering computational tools such as MATLAB and Simulink. Spring semester. Prerequisites: MAT 261 (Calculus III), MAT 405 (Differential Equations), EGR 214 (Dynamics). For course outcomes, the syllabus stated that after successfully completing this course, the student will: 1. Be able to use the MATLAB ode functions and/or Simulink to solve ordinary differential equations. 2. Be able to obtain the harmonic response of systems having a single degree of freedom. 3. Be able to obtain the transfer function from the equation of motion. 4. Be able to use the plots or the frequency transfer function to determine the steady-state output amplitude and phase that result from a sinusoidal input. 5. Be able to determine the resonance frequency, peak response, and bandwidth. 6. Be able to use MATLAB and/or Simulink to analyze harmonic response. 7. Be able to apply the Fourier series method to obtain the response of a linear system to a periodic forcing function and apply the amplitude spectrum plot. 8. Be able to use MATLAB and/or Simulink to obtain the response of a linear system to a variety of forcing functions, such as step, impulse and other arbitrary input functions. 9. Be able to use MATLAB and/or Simulink to obtain the response of a nonlinear system to a variety of forcing functions, both linear and nonlinear. Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education Most of the course objectives above relate to outcome k. Detailed outcome assessment data on using Matlab/Simulink is included in a later section of this paper. The reason we like Simulink is due to its versatility in handling dynamic systems. Simulink is built on top of Matlab. It has a very user-friendly Graphical User Interface (GUI). You can build a dynamic system simply by dragging and dropping and connecting some blocks of functions and operators. It is intuitive and fun to learn. Many students develop a love of mechanical vibrations as a subject thanks to the pleasures they got from using Simulink. Simulink is especially advantageous in handling nonlinear or discontinuous functions as input to dynamic systems. It is well equipped to handle periodic and non-periodic forcing functions such as a train of pulse (rectangular, triangular or trapezoidal). With a graphical interface, user can easily enter special waveforms. This saves users a lot of effort developing Fourier series of representation of these waveforms. With this tool, coverage on forcing function transformation using Fourier series could be shortened. Other uses of these tools include student capstone senior designs. Pakkala introduced a vehicle dynamics model based on Simulink for design and simulation of SAE Baja vehicles at Milwaukee School of Engineering21. Animation of System Responses Using Mathematica One of the challenges in teaching undergraduate mechanical vibrations curriculum is in the necessity of extensive use of advanced math in deriving and solving differential equations (DFQ). How to engage students in this seemingly tedious theoretical development is paramount for effective teaching. There is no way to get around this theoretical development – actually the instructor not only has to engage the students with the DFQ aspect of math, but he/she also has to teach some fundamentals in dynamic modeling of mechanical systems in order to come up with these DFQ equations. How to keep this derivational work interesting to the students is a perennial challenge. Typically the teaching of mechanical vibrations starts with introducing students to the simple harmonic motion, as represented by a sinusoidal function of the form π₯(π‘) = π΄π ππ(π€π‘ + ∅) The instructor needs to explain what each of the parameter represents in the oscillation behavior of the system. But it is kind of hard to visually demonstrate the effects or contributions of each individual parameter with mere words and equations. Previous work in this area included extensive GUI programming in either Matlab or LABView12, 13. Aung20 used an example from Wolfram to demonstrate the simulation of vibration of a string. However, it is a canned GUI and is not readily transferrable to other situations and applications. The author found a useful tool in Mathematica that could be easily adapted for a variety of applications. It is the “Manipulate” Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education function in Mathematica14. A simple command below would generate a window as shown in Figure 1. Manipulate[Plot[A*Sin[wn*t + phi], {t, 0, 10}], {A, 0, 10}, {wn, 0, 5}, {phi, 0, 100}] Figure 1 Mathematica’s Manipulate function as used in the demonstration of a sinusoidal function In the above window, students can use mouse to drag the bars and change in real time the amplitude, natural frequency, and phase angle. As these parameters are being changed, students can observe its impact on the vibration signal. It is powerful! Previously boring material like this becomes so fun to learn that it literally becomes “playing!” for the students. And once students are introduced to the use of this function, later on in the semester they can easily adapt it to observe more complex damped oscillations. Figure 2 Under-damped oscillation demonstrations Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education The following command could be used to show the typical under-damped solution π₯(π‘) = π΄π −π‘/π sin(π€π ∗ π‘ + ∅) in Mathematica: Manipulate[Plot[A*Exp[-t/tau]*Sin[wn*t + phi], {t, 0, 10}], {A, 0, 10}, {wn, 0, 5}, {phi, 0, 100}, {tau, 1, 20}] Figure 2 shows the under-damped response. Figure 3 shows a near-critically damped response. All four parameters (amplitude, natural frequency, phase angle, and time constant) could be changed by students using the slider bars on top. Figure 3 Near-critically-damped oscillation demonstrations Virtual Labs As echoed by Jouaneh and Palm23, “most mechanical engineering curricula include courses in system dynamics, controls, mechatronics and vibrations, but at most schools, these courses do not have a laboratory component. Even at schools that have such a component, laboratory access is often limited, and thus there is a need to increase students’ laboratory experience.”23 Virtual and remote laboratories are gaining popularity in engineering education due to its flexibility on staff, time and space. According to Chen, et al22, virtual laboratories are based on software such as LabVIEW, Matlab/Simulink, Java Applet, Flash or other software to simulate the lab environment. University of Colorado Boulder developed a series of online interactive teaching tools to help with teaching science and math subjects15. Termed PhET Interactive Simulations, it is a non-profit open educational resource (OER) project founded in 2002 by Nobel Laureate Carl Wieman16. PhET began with Wieman’s vision to improve the way science is taught and learned. Their stated mission is "to advance science and math literacy and education worldwide through free interactive simulations." Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education We developed two virtual mechanical vibration labs from two simulation tools provided by PhET. These are spring and mass lab (Figure 4) and pendulum lab (Figure 5). Normally these two labs are assigned during the first two weeks of the semester and students can pretty much work on these assignments with minimum instructions. It helps students visualize and get a “feel” for the mechanical vibration phenomenon at hand. Figure 4 Spring and Mass Virtual Lab17 Figure 5 Pendulum Virtual Lab18 For the spring and mass lab, students can hang masses from springs and adjust the spring stiffness and damping. Students can even slow time to help with measurements. Students can also transport the lab to different planets. It includes a chart showing the kinetic, potential, and Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education thermal energy for each spring. Unique questions were developed for this lab – due to page limits in this paper, these questions are not included here. If anyone is interested in using them, please contact the author and he would be glad to email you the questions (the author will start teaching at Anderson University in Anderson, Indiana, in the fall of 2015, so make sure you google and find his new email address at Anderson). Tables 2 and 3 give a summary of what, how and when some of the basic educational outcomes were introduced or reinforced by these lab activities. Not surprisingly, there has been some staggering of coverage, which is good to stimulate students’ thinking and reinforcement the basic concepts required of a vibrations course. Table 2 Coverage of Basic Vibration Concepts and Principles by the Spring and Mass Lab Questions Basic concepts/experimental techniques Definition of stiffness of springs (or spring rate); measurement thereof Damping/internal friction Factors contributing to oscillation frequency Free vs. forced vibration - definition Oscillation period and its measurement Conservation of energy; energy conversion Gravitational constant and its effect Initial condition and its effects Response parameters (amplitude, oscillation frequency, phase angle) Equilibrium position and its significance Appeared in these questions 1; 3; 4; 8; 10 2; 5; 7 2; 6; 8; 9; 11; 12 2 6; 8; 11; 12 7; 8; 9; 10; 12; 9; 12 10; 12 Table 3 Coverage of Basic Vibration Concepts and Principles by the Pendulum Lab Questions Basic concepts/experimental techniques Nonlinear vs. linear solutions (exact but need numerical solution vs. small angle approximation but closed-form solution) Damping/internal friction Factors contributing to oscillation frequency Velocity and acceleration Oscillation period and its measurement Conservation of energy; energy conversion Gravitational constant and its effect Initial condition and its effects Response parameters (amplitude, oscillation frequency, phase angle) Free vs. forced vibration Appeared in these questions 2; 3 7; 9 4; 6 8; 11 1; 2; 3; 4; 6; 10 7; 11 5; 10; 11 1; 10; 11 11 9; 11 Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education For the pendulum virtual lab18, one of the key concepts we try to instill in students’ mind is the non-linear response of the system. Due to small angle approximation, we can simplify the solution of the differential equation and obtain a closed-form solution. But there are errors in it. How large are the errors? We ask students to measure the oscillation periods at different initial conditions (release angles). Later on in the semester, once we get into teaching students using Matlab ode solvers to solve for the nonlinear equations, we again ask students to plot the percent difference (error) between the linear solution and nonlinear solution. Assessment The first time we implemented these two virtual labs and the use of Mathematica Manipulate function was in spring semester of 2012. There were 16 students in the class. At the end of the semester, an anonymous survey was conducted and 14 responses were collected. The results are shown in Table 4. Table 4 Student Responses to the Survey Strongly agree Agree Disagree Strongly disagree The use of “Manipulate” function in Mathematica helped me understand the contribution of various parameters in a vibration model 3 10 1 0 For the virtual labs, we only have some indirect evidence, since the survey question was on students’ reaction to the “practicum” sessions we offered in class, which included not only the virtual labs but also some problem solving activities. A majority of the students responded positively to the practicum sessions. There were, however, two students who felt the practicum sessions took valuable class time and they’d prefer it be assigned as homework. Since then we have been assigning the virtual labs as homework. From a year to year comparison of student IDEA evaluations, there has been a significant increase in scores in the areas of stimulating student interest and encouraging student involvement. In spring semester of 2013, roughly 33.8% of the overall homework grade and 64% of the final exam grade were based on a student’s performance in using Matlab/Simulink. The students were given two lectures (1 hour and 20 minutes is the typical length of each lecture) of training on using fundamentals of MATLAB at the beginning of the semester. Continued training and application of the software were conducted throughout the semester. Usually the instructor used the first 40-50 minutes of class time to teach on theory and concepts, and then devoted the remainder of the class time to hands-on use of the software to solve problems. The classroom was a fully equipped computer lab and each student had a computer to use. Most of the time students worked individually under the supervision of the instructor, with some discussions among themselves. The instructor also encouraged them to help each other out as much as Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education possible in and outside of class. Sometimes students would come to ask software related questions during office hours and the instructor would go with the student to a computer lab and help them debug their codes or teach them how to use certain features of the software. Table 5 shows the rubric that was used to assist in the Matlab/Simulink teaching effectiveness assessment process and the assessment results for various outcomes19. There were a total of nine students in spring semester of 2013, two are seniors and seven are juniors. Except for one student, who was quite proficient in using the software throughout the course, all other eight students needed some assistance and occasionally applied the tool inappropriately. Table 5 Rubric19 and Assessment Results (Numbers in the table are the number of students at the level indicated in the heading) Using Matlab to solve ordinary differential equations (ode solver) Using Matlab to find roots to polynomial equations Clueless – Unable to use tool and does not try (0) Attempts to use tool but does so incorrectly and consistently gets incorrect results (1) Proficient use of tool with minimal assistance and consistently applies tool appropriately (4) a, b, c 8 1 3.1 a, b, c 8 1 3.1 8 1 3.1 8 1 3.1 Using Simulink a, to model a b, c second order system Using Matlab a, to obtain b, c frequency response of a system a. Observation of students during lab b. Homework assignments c. Final Exam Occasionally able to use tool correctly by guess work (2) Average Score Able to use tool but needs some assistance and occasionally applies the tool inappropriately (3) Means for Observation Technique, Skill, Tool Figure 6 shows the aggregated scores (in percentage) of each student for their performance that relate to outcome k in their homework and final exam. Six of the nine performed better in the final exam than in their homework, which indicates that the majority of them show a continuous improvement in the use of these tools. Student #5 seems to have the solution manual based on the instructor’s observation from his homework (probably he purchased an illegal copy from Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education online), which explains why he did better in homework than the final exam. Figure 7 through 10 show the detailed homework evaluation results for individual outcomes as previously listed. In Figure 7, student #3 did not turn in his homework. 120% 100% 80% 60% homework 40% final exam 20% 0% 1 2 3 4 5 6 7 8 9 Figure 6 Aggregate percent scores for each of the 9 students in portions of the homework and final exam that are related to the use of MATLAB and Simulink software 120% 100% 80% 60% 40% 20% 0% 1 2 3 4 5 6 7 8 9 Figure 7 Percent scores for each of the nine students in a homework assignment that is related to the use of MATLAB ode solver Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education 100% 95% 90% 85% 80% 75% 70% 1 2 3 4 5 6 7 8 9 Figure 8 Percent scores for each of the nine students in a homework assignment that is related to the use of Simulink and Laplace transform to obtain forced response of a second order dynamic system 120% 100% 80% 60% 40% 20% 0% 1 2 3 4 5 6 7 8 9 Figure 9 Percent scores for each of the nine students in a homework assignment that is related to the use of Matlab/Simulink to find bandwidth of a dynamic system and plot amplitude spectrum 120% 100% 80% 60% 40% 20% 0% 1 2 3 4 5 6 7 8 9 Figure 10 Percent scores for each of the nine students in a homework assignment that is related to the use of Matlab/Simulink to solve a dynamic system with either a nonlinear model or a nonlinear input Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education Overall, it can be concluded that the entire class achieved a satisfactory outcome in mastering the use of these software tools. It can also be shown that students’ critical thinking and problem solving skills are enhanced with the use of these tools. Summary Using animation, simulation and virtual labs is an economical way of enhancing student learning in classes where traditionally a lot of “dry” theoretical derivation and equation solving are involved. It has no limitation in terms of lab space and lab hours. As long as students have access to a computer, they can do the virtual labs on their own time and at their own pace. The lab questions help them dig deep into the course materials. The staggered coverage of fundamental concepts and principles help reinforce what was covered in class. As long as the school has Mathematica software, the use of “Manipulate” function proves to be easy to implement in class demonstration of complex mathematical or physical relationships. Students need not know how to use Mathematica beforehand. The learning curve is virtually non-existent, but the benefit is significant in helping students to visualize what they are learning in theory. Another part of the simulation activities we had engaged the students with was the extensive use of Matlab and Simulink later in the semester. As evidenced by the assessment data, this enhanced students’ learning. As part of the engineering curriculum renewal effort at Geneva College this year, all mechanical engineering students will be required to take a Matlab-based programming course to substitute the traditional C++ based programming course. This will further enhance the effort to strengthen outcome k in the mechanical engineering curriculum. References 1. ABET, Criteria for Accrediting Engineering Programs, page 3, http://www.abet.org/uploadedFiles/Accreditation/Accreditation_Process/Accreditation_Documents/Current /eac-criteria-2012-2013.pdf, accessed on 3/7/2014 2. William J. Palm III, Mechanical Vibration, John Wiley & Sons, Inc., 2006 nd 3. Benson H. Tongue, Principles of Vibration, 2 edition, Oxford University Press, 2002 4. Daniel Inman, Engineering Vibration, 3rd edition, Prentice Hall, 2008 5. Haym Benaroya & Mark L. Nagurka, Mechanical Vibration – Analysis, Uncertainties, and Control, 3rd edition, CRC Press, 2010 6. S. Graham Kelly, Mechanical Vibrations – Theory and Applications, Cengage Learning, 2012 7. William T. Thomson & Marie D. Dahleh, Theory of Vibration with Applications, 5th edition, Prentice Hall, 1998 8. B. Balachandran & E. B. Magrab, Vibrations, 2nd edition, Cengage Learning, 2009 9. T. Schmitz & K. S. Smith, Mechanical Vibrations – Modeling and Measurement, Springer, 2011 10. Alok Sinha, Vibration of Mechanical Systems, Cambridge University Press, 2010 11. Singiresu S. Rao, Mechanical Vibrations, 5th edition, Pearson and Prentice Hall, 2011 Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education 12. Thomas Nordenholz, Animation as the Final Step in the Dynamics Experience, ASEE Annual Conference, 2006 13. Peter Avitabile, Jeffrey Hodgkins, Development of Visualization Tools for Response of 1 st and 2nd Order Dynamic Systems, ASEE Annual Conference, 2006 14. Wolfram Mathematica 9 Documentation Center, Manipulate, http://reference.wolfram.com/mathematica/ref/Manipulate.html, accessed on 3/7/2014 15. http://phet.colorado.edu, accessed on 3/7/2014 16. http://en.wikipedia.org/wiki/PhET_Interactive_Simulations, accessed on 3/7/2014 17. http://phet.colorado.edu/en/simulation/mass-spring-lab, accessed on 3/7/2014 18. http://phet.colorado.edu/sims/pendulum-lab/pendulum-lab_en.html, accessed on 3/7/2014 19. Robe Liljestrand, Dave Clark, Proposal for Assessing Student Outcome k, Geneva College Department of Engineering Internal Communication, 2013 20. Kendrick T. Aung, Teaching Advanced Engineering Mathematics to Graduate Students: Lessons Learned, Proceedings of the ASEE Annual Conference, 2011 21. John E. Pakkala, A Vehicle Dynamics Design and Simulation Tool for Capstone Projects, Proceedings of the ASEE Annual Conference, 2011 22. X. Chen, G. Song and Y. Zhang, Virtual and Remote Laboratory Development: A Review, Proceedings of Earth and Space 2010, pp. 3843-3852, Honolulu, HI, March, 2010 23. Musa Jouaneh, William Palm, System Dynamics and Control Take-home Experiments, Proceedings of the ASEE Annual Conference, 2010 DAVID CHE Dr. Che currently serves as Associate Professor of Mechanical Engineering at Geneva College in Beaver Falls, PA. He also serves as Director of the Pinkerton Center for Technology Development at the college. His research interests are manufacturing engineering, quality control, and precision engineering. Starting in fall of 2015, Dr. Che will be teaching at Anderson University in Anderson, Indiana. Proceedings of the 2015 ASEE Gulf-Southwest Annual Conference Organized by The University of Texas at San Antonio Copyright © 2015, American Society for Engineering Education