A Zachary Trimble

A Device for Harvesting Energy From Rotational Vibrations

A new device designed to harvest rotational vibration energy is presented. The device is modeled as a spring-mass-damper system connected to a vibration source where a torsion rod is used as a spring element and a shearing electromagnetic induction circuit as the energy harvesting element. The device is inherently a resonant type harvester. A prototype device is tested using a purely sinusoidal vibration input and more realistic inputs consisting of wider bandwidths, multiple resonance peaks, and low amplitude noise. The performance of the prototype to realistic inputs verifies the ongoing challenge to vibration energy harvesting, namely, sig n ificant loss of performance when using broadband inputs with resonant based devices.

Variable buoyancy control for a bottom skimming autonomous underwater vehicle

Two feedback controllers are presented that utilize data averaging and model-based estimation to offset the effects of sensor noise and achieve precise control of an autonomous underwater vehicle (AUV) variable buoyancy system (VBS). Operation of the bottom skimming AUV requires a constant reaction force between the seabed and the vehicle. While performing a mission, variable seafloor topography and a changing payload weight requires the use of a VBS to maintain the reaction force. Two traits of the VBS system that make this a challenging problem are the presence of sensor noise and fast on/off actuation relative to the sensor update rate. It was discovered that both controllers function under these conditions but the model-based controller provides more precise control of the system. This paper presents a comparison between these two control algorithms based on both simulation results and field experiments in a coastal environment.

Investigating the Feasibility of Tuning the Natural Frequency of an Electromagnetically-Transduced Energy Harvester Using Passively-Controlled Inductance

As the required power for wireless, low-power sensor systems continues to decrease, the feasibility of a fully self-sustaining, onboard power supply, has increased interest in the field of vibration energy harvesting — where ambient kinetic energy is scavenged from the surrounding environment. Current literature has produced a number of harvesting techniques and transduction methods; however, they are all fundamentally similar in that, the harmonic excitation frequency must fall within the resonant bandwidth frequency of the harvesting mechanism to maintain acceptable energy output. The purpose of this research is to investigate the potential for natural frequency tuning by means of passive electrical components, that is, using an imposed electrical inductance to adjust the equivalent stiffness, and resulting resonant frequency of a vibration energy harvester. In past literature, it was concluded that an “active” frequency tuning mechanism would be infeasible, as the power required by an equivalent “stiffening transducer” would require more power to maintain the system at resonance, than the system would actually produce as a result of maintaining resonance, i.e., a net energy loss (Roundy and Zhang 2005). It is believed that the model used in this conclusion can be improved by directly modeling changes in system stiffness as an equivalent mechanical spring, instead of an external inertial loading. Due to the conservative nature of the harmonic spring, the compliance of a harvesting mechanism can be theoretically altered without energy losses, whether the actuation is applied using “active” or “passive” means. This revised model departs from the traditional, base excitation model in most vibration energy harvesting systems, and includes additional stiffness, and damping elements, representative of induced mechanical spring, and related losses. We can validate the feasibility of this technique, if it can be shown that the natural frequency of an energy harvester can be altered, and still maintain energy output similar to its “untuned” natural frequency. If feasible, this tuning method would provide a viable alternative to other bandwidth-increasing techniques in literature, e.g., wideband harvesting, bandwidth normalizing, high-damping, etc. In this research, a change in natural frequency of the experimental energy harvesting system of 0.5 Hz was demonstrated, indicating that adjusting the natural frequency of a vibration energy harvesting system is possible; however, there are many new challenges associated with the revised energy harvesting model, related to the new introduced losses to the system, as well as impedance matching between the mechanical and electrical domains. Further research is required to better quantitatively characterize the relationship between natural frequency shift, and imposed electrical inductance.Copyright

Development of multifunctional nanocomposites with 3-D printing additive manufacturing and low graphene loading

Fused filament fabrication (FFF) or fused deposition modeling is an additive manufacturing (AM) process commonly used for geometric modeling and rapid prototyping of parts called three-dimensional (3-D) printing. Commonly used thermoplastic materials in FFF 3-D printing AM are acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polybutylene terephthalate (PBT). However, these materials exhibit relatively low strength and toughness. Therefore, it is desirable to improve various properties of thermoplastics in 3-D printing AM by employing nanotechnology. The combination of 3-D printing and nanotechnology opens new venues for the manufacture of 3-D engineered materials with optimized properties and multifunctionality (e.g. mechanical, electrical, and thermal properties). Hence, in this work, the multifunctional property improvement effects of graphene oxide (GO) on thermoplastic materials suitable for 3-D printing AM are investigated. Low loading of GO with carboxyl and hydroxyl surface functional groups is incorporated into thermoplastic materials suitable for 3-D printing AM by a special mixing technique. ABS is chosen in this study due to its availability. Graphene nanosheets are employed to improve the properties of the developed nanocomposites by 3-D printing AM. GO is chosen to improve the dispersion of graphene nanosheets into the thermoplastic system to increase their interfacial adhesion. A multifunctional property improvement is observed in the developed nanocomposite with less than 0.1 wt% GO. Employing ASTM standard tests, it was found that at a very small loading of 0.06% by weight, GO could improve the properties of the thermoplastic in terms of strength, strain-to-failure, and toughness, while maintaining the stiffness, rendering the developed nanocomposites suitable for various applications of static and dynamic loading. GOs are now commercially available at low prices. At such low loadings, these graphene-type materials become economically feasible components of nanocomposites.

An experimentally validated analytical model for the coupled electromechanical dynamics of linear vibration energy harvesting systems

Recent technological advancements in the efficiency of microprocessors, sensors, and other digital logic systems have increased research effort in vibration energy harvesting, where trace amounts of energy are scavenged from the ambient environment to provide power. Due to the complexity and nonlinearity of most vibration energy harvesting systems, existing research has relied primarily on numerical and finite element methods for harvester design and validation. Although these methods are useful, a vetted analytical model provides intuitive understanding of the governing dynamics and is useful for obtaining rough calculations when designing vibration energy harvesting systems. In this article, an analytical framework for linear electromechanical transducer modeling is developed into the coupled electromechanical model; a transfer function characterizing the dynamics of second-order VEH systems, which includes inputs for mechanical and electrical domain lumped parameters as complex impedances. The coupled electromechanical model transfer function is validated against frequency sweep data from a linear vibration energy harvesting experimental setup. The experimental setup demonstrated good correlation with the coupled electromechanical model, with not more than 0.9% error in natural frequency overall, 6% error in damping ratio for purely resistive loads, and 11% for reactive loads.

VERIFICATION OF A MARINE POLLUTANT SURFACE PLUME MODEL FOR USE IN THE DEVELOPMENT OF AUTONOMOUS VEHICLE TRACKING SYSTEMS

ABSTRACT A marine pollutant spill environmental model that can accurately predict fine scale pollutant concentration variations on a free surface is needed in early stages of testing robotic contro...