Shahin S. Nudehi

Design, Fabrication and Control of Spherobot: A Spherical Mobile Robot

In the literature, Spherobot refers to a mobile robot with a spherical exo-skeleton and a propulsion mechanism that uses unbalance masses in a tetrahedral arrangement. A modified design of Spherobot, that is better suited to fabrication, is presented in this paper. The modified propulsion mechanism and other components of the design are discussed in detail to highlight the challenges of fabrication. An adaptive estimation and control algorithm used for position control of the unbalance masses and a steering algorithm used for motion control of Spherobot are also discussed. Experimental results of the Spherobot navigating a hallway with bends is presented.

Thermal electrolytic production of Mg from MgO: Reflections on commercial viability

We are exploring the commercial viability for producing Mg from MgO for which thermal energy is supplied to the cell as a substitute for some electric energy. The thermal input source may be concentrated sunlight or natural gas. Laboratory-scale electrochemical studies near 1250 K for two cell concepts show that we reached current densities above 0.5 A-cm−2at an overvoltage of 1.0 V. Current efficiency values exceeded 80%. The discussion of the relationship between these bench-top experimental results and the industrial potential of the process has been initiated.

A High-Flux Solar Furnace for Undergraduate Engineering Education and High-Temperature Thermochemistry Research

The optical design and engineering features of a 10 kW solar furnace now operational at Valparaiso University are described. The solar furnace is anticipated to achieve a mean concentration ratio of 3000 suns over a 6 cm diameter focus. It will support high-temperature solar chemistry research and undergraduate engineering pedagogy. Many of the components of the solar furnace were designed and constructed by undergraduate engineering students. Some of these students cite their participation in the solar furnace project as the motivating factor for continuing to work in the area of energy science in industry or graduate school.Copyright

A Control Systems Laboratory for Undergraduate Mechanical Engineering Education

This article describes seven laboratory experiments that have been developed for the automatic controls course at Valparaiso University. It also presents the results of a self-assessment survey taken by the students after they had done these laboratory experiments. Automatic controls recently became a required course for all undergraduate mechanical engineering students. When taught as an elective, it was noticed that many students tended to struggle with this class. Most students perceive this class to be a collection of different mathematical tools without any application or use in their future careers. To alleviate this situation and assist students in visualizing control systems in practical situations, a half-credit elective control laboratory, which consists of five experiments and two laboratory projects, has been developed. These experiments will help students to understand the application of this topic and to learn to develop appropriate mathematical models and control routines in closed-loop systems with computers in the loop.

Tailoring Plate Thickness of a Helmholtz Resonator for Improved Sound Attenuation

A Helmholtz resonator with flexible plate attenuates noise in exhaust ducts, and the transmission loss function quantifies the amount of filtered noise at a desired frequency. In this work the transmission loss is maximized (optimized) by allowing the resonator end plate thickness to vary for two cases: 1) a nonoptimized baseline resonator, and 2) a resonator with a uniform flexible endplate that was previously optimized for transmission loss and resonator size. To accomplish this, receptance coupling techniques were used to couple a finite element model of a varying thickness resonator end plate to a mass-spring-damper model of the vibrating air mass in the resonator. Sequential quadratic programming was employed to complete a gradient based optimization search. By allowing the end plate thickness to vary, the transmission loss of the non-optimized baseline resonator was improved significantly, 28 percent. However, the transmission loss of the previously optimized resonator for transmission loss and resonator size showed minimal improvement.

A Tunable Helmholtz Resonator for Active Noise Control

In this study, a tunable Helmholtz resonator is proposed for active noise cancelation in a primary acoustic system. In the tunable Helmholtz resonator, the resonator’s top wall is replaced by a flexible membrane and four actuators are mounted on the side of the resonator. These actuators are connected to the membrane in order to tune its radial force (tension) by pulling or releasing the membrane during the operation. This causes the resonant frequency of the modified Helmholtz resonator to change due to the change in the membrane tension. The maximum noise attenuation is achieved when the the resonant frequency of the active resonator matches with the noise frequency in the primary system. In this paper, first mathematical modeling is used to derive nonlinear coupled differential equations for the tunable Helmholtz resonator with the membrane. The differential equations were linearized to obtain an analytical formulation for the resonant frequency of the tunable resonator in terms of the membrane tension. The analytical formulation for the resonant frequency was verified via simulation of the original nonlinear differential equations. Finally, to demonstrate the validity of the mathematical modeling of the tunable resonator, experimental results are provided.Copyright

Perturbation Analysis of a Nonlinear Resonator

A perturbation analysis of a Helmholte type resonator with one of the resonator ends replaced by a membrane is studied in this work. A membrane is known to exhibit nonlinear behavior under certain conditions, and thus when attached to a resonator system modifies the dynamic characteristics of the original system. This modified Helmholtz resonator system modeled by coupled nonlinear differential equations is investigated by using the singular perturbation theory. The resonant frequency of nonlinear resonator in the primary resonance case is analytically obtained by using the first order approximate solutions. A good agreement is seen when the frequency response of first order approximate system is compared with the numerically simulated results.Copyright

Cantilever Beam Vibration Suppression Using Modal Energy Redistribution

Modal energy redistribution is utilized to suppress vibrations of a cantilever beam. The energy redistribution between the modes of the beam is achieved by switching on/off an end force which causes varying stiffness nof the beam. The control methodology to suppress all the modes relies on continuously funneling the energy from the higher to the lower modes with the end force and dissipating the energy associated with the fundamental mode. We npresent an analytical framework for control design exploiting the modal energy redistribution and verify the results through simulations and experiments.

Optimal Design of a Helmholtz Resonator With a Flexible End Plate

A multi-objective optimization formulation to design a Helmholtz resonator with a flexible end plate is studied. The optimization formulation generates a Pareto curve of design solutions that quantify the trade-off between the optimization goals: minimum resonator volume and maximum transmission loss across a specified frequency range. The optimization problem is formulated and solved in the following manner. First, a mathematical formulation for the transmission loss of the Helmholtz resonator with a flexible plate is completed based on the design parameters. Then, the weighted transmission loss across a specified frequency range and a minimum resonator volume are defined as optimization objectives. Finally, the Pareto curve of optimum design solutions is calculated using a gradient-based approach via the e-constraint method. The optimization results allow the designer to select resonator design parameters that meet the requirements for both transmission loss and resonator volume. To validate the optimization results, one optimal Helmholtz resonator is manufactured and experimentally confirmed.Copyright