9,764 research outputs found
Maps unlock the full dynamics of targeted energy transfer via a vibro-impact nonlinear energy sink
No full textWe consider a model of a vibro-impact nonlinear energy sink (VI-NES), where a ball moves within a cavity of an externally forced mass, impacting either end of the cavity. These impacts result in energy transfer from the mass to the ball, thus limiting the oscillations of the larger system. We develop a semi-analytical map-based approach, recently used for an inclined impact pair model, in the setting where there is energy transfer between the mass and the ball. With this approach we analytically derive exact expressions for the full dynamics of the VI-NES system without restricting the range of parameters, in contrast to other recent work in which an approximate reduced model is valid only for small mass of the ball, small amplitude, and a limited frequency range. We develop the bifurcation analysis for the full VI-NES system, based on exact maps between the states at successive impacts. This analysis yields parameter ranges for complex periodic responses and stability analyses for O(1) mass of the ball, forcing frequencies that are not the same as the natural frequency, and large amplitude forcing. The approach affords the flexibility to analytically study the dynamics of different periodic solutions and their stability, including a variety of impact sequences in the full two degree-of-freedom model of VI-NES. Comparisons of quantities that characterize the energy transfer point to the significance of different types of periodic behavior, which may occur for different parameter combinations. Our semi-analytical results also provide the impact phase, which plays an important role in the efficiency of the energy transfer.</p
Analysis of dry friction dynamics in a vibro-impact energy harvester
No full textVibro-impact (VI) systems provide a promising nonlinear mechanism for energy harvesting (EH) in many engineering applications. Here, we consider a VI-EH system that consists of an inclined cylindrical capsule that is externally forced and a bullet that is allowed to move inside the capsule, and analyze its dynamics under the presence of dry friction. Dry friction introduces a switching manifold corresponding to zero relative velocity where the bullet sticks to the capsule, appearing as sliding in the model. We identify analytical conditions for the occurrence of non-stick and sliding motions, and construct a series of nonlinear maps that capture model solutions and their dynamics on the switching and impacting manifolds. An interplay of smooth (period-doubling) and non-smooth (grazing) bifurcations characterizes the transition from periodic solutions with alternating impacts to solutions with an additional impact on one end of the capsule per period. This transition is preceded by a sequence of grazing-sliding, switching-sliding and crossing-sliding bifurcations on the switching manifold that may reverse period doubling bifurcations for larger values of the dry friction coefficient. In general, a larger dry friction coefficient also results in larger sliding intervals, lower impact velocities yielding lower average energy outputs, and a shift in the location of some bifurcations. Surprisingly, we identify parameter regimes in which higher dry friction maintains higher energy output levels, as it shifts the location of grazing bifurcations
Single-molecule studies of unconventional motor protein myosin VI
No full textMyosin VI is one of the myosin superfamily members that are actin-based molecular motors. It has received special attention due to its distinct features as compared to other myosins, such as its opposite directionality and a much larger step size than expected given the length of its “leg”.
This dissertation presents the author‟s graduate work of several single-molecule studies on myosin VI. Special attention was paid to some of myosin VI‟s tail domains that consist of proximal tail (PT), medial tail (MT), distal tail (DT) domains and cargo-binding domain (CBD).
The functional form of myosin VI in cells is still under debate. Although full length myosin VI proteins in cytosolic extracts of cells were monomers from earlier studies, there are several reasons why it is now believed that myosin VI could exist as a dimer. If this is true and dimerization occurs, the next logical question would be which parts of myosin VI are dimerization regions? One model claimed that the CBD is the sole dimerization region. A competing model claimed that there must be another region that could be involved in dimerization, based on their observation that a construct without the CBD could still dimerize.
Our single-molecule experiment with progressively truncated myosin VI constructs showed that the MT domain is a dimerization region, supporting the latter model. Additional single-molecule experiments and molecular dynamics (MD) simulation done with our collaborators suggest that electrostatic salt bridges formed between positive and negative amino acid residues are mainly responsible for the MT domain dimerization.
After resolving this, we are left with another important question which is how myosin VI can take such a large step. Recent crystal structure showed that one of the tail domains preceding the MT domain, called the PT domain, is a three-helix bundle. The most easily conceivable way might be an unfolding of the three-helix bundle upon dimerization, allowing the protein to stretch and reach a larger distance. The single-molecule stepping data with mutant full-length construct that lacks two helices out of three in the PT domain tell that it is indeed the case.
In this dissertation, more details of myosin VI PT/MT domain experiments will be explored along with background information on the single-molecule experiment methods used in these studies.Item withdrawn by Mark Zulauf ([email protected]) on 2011-04-07T13:00:38Z
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A pendulum-based absorber-harvester with an embedded hybrid vibro-impact electromagnetic-dielectric generator
No full textIn this paper, a novel hybrid vibro-impact electromagnetic-dielectric generator (VI EDG) is proposed, which is further embedded into a pendulum structure to form a pendulum-based absorber-harvester (PAH) system. The PAH system can convert the vibration energy into electrical one with the help of the VI EDG, and has the potential to reduce the swing amplitude of the pendulum. The physical model of the PAH system is first introduced, and its governing equations involving the dynamical and electrical parts are derived based on the Euler-Lagrange’s equation of a non-conservative system. Next, the governing equations of the PAH system are validated experimentally by measuring the swing motion of the pendulum under a given harmonic excitation. On this basis, the system energy harvesting performance under different excitation parameters (amplitude and frequency) and dimensional parameters (the rod’s length and the distance between two dielectric elastomer membranes) is fully investigated and explained through numerical simulations. Finally, the vibration absorption performance of the VI EDG is discussed by comparing the peak-to-peak values of the swing motions between the proposed PAH system and the conventional pendulum without embedded VI EDG. Research results show that the proposed VI EDG can not only effectively harvest ambient vibration energy from the pendulum system, but also has the potential to absorb the vibration of the system
Improving the performance of a two-sided vibro-impact energy harvester with asymmetric restitution coefficients
No full textWe study the influence of asymmetric restitution coefficients in a model of a two-sided vibro-impact energy harvester (VI-EH), considering the dynamical behavior and the implications for energy output. In the VI-EH, a ball moves freely within a forced cylinder and collides with a compliant dielectric polymer on either end, thus converting the motion into output voltage. We develop (semi-)analytical results for 1:1 periodic solutions, with alternating impacts on either end, focusing on the case of asymmetric restitution coefficients on the top and bottom of the cylinder. New types of 1:1 periodic solutions are found, with energy output clearly different from the symmetric setting. The analysis covers non-intuitive results, including the non-monotonic dependencies of the energy output on the asymmetric restitution coefficients. We find unexpected parameter ranges with improved levels of energy output, as well as stability results indicating that this output is robust to parameter fluctuations or external perturbations. Furthermore, by identifying parameter combinations that limit performance through asymmetries, we show how asymmetric restitution coefficients can counteract these detrimental effects. The analysis is based on maps for the dynamics between impacts, leading to a series of conditions for stable 1:1 periodic solutions in terms of the system parameters. We compare stability and bifurcation structure obtained analytically and numerically. The analysis shows possible regions of bi-stability between different behaviors that may not be captured by numerical approaches
A hybrid piezo-dielectric wind energy harvester for high-performance vortex-induced vibration energy harvesting
No full textThis paper proposes a novel hybrid piezo-dielectric (PD) wind energy harvester, to efficiently harvest the vortex-induced vibration (VIV) energy from low-speed wind. The hybrid PD harvester brings together the following two electromechanical transduction mechanisms: piezoelectric ceramic (PZT) sheets and a vibro-impact (VI) dielectric elastomer generator (DEG). The PZT sheets directly transduce the beam’s vibration into electricity, whereas the VI DEG transduces the impacts between the inner ball and the dielectric elastomer membranes resulting from the bluff body’s vibration into electricity. The theoretical model of the hybrid PD harvester subjected to VIV is formulated. Wind tunnel experiments are performed to validate the aerodynamic part of the theoretical model and identify the aerodynamic coefficients. Afterward, based on the theoretical model, the numerical investigation of the hybrid PD harvester is conducted, which uncovers the insights of the conjunction of the PZT and VI DEG for VIV energy harvesting enhancement. It is seen that in the lock-in region of the VIV, where both the PZT and VI DEG can effectively harvest the VIV energy, the VI DEG can generate much higher power. This demonstrates the superiority of the hybrid PD harvester. Parametrical studies show that the smaller mass, higher stiffness and larger diameter of the bluff body are beneficial designs, which broadens the working wind range and enhances the generate power
Energy harvesting from a dynamic vibro-impact dielectric elastomer generator subjected to rotational excitations
No full textA vibro-impact (VI) dielectric elastomer generator (DEG) subjected to rotational excitations is studied in this paper for energy harvesting (EH). The VI DEG that has been demonstrated as an advanced vibrational energy harvester is first introduced, and an impact model is proposed to experimentally validate the energy harvesting mechanism of the impact-based DEGs. The VI DEG is then considered to harvest energy from a rotational excitation by being installed onto rotational machinery. The dynamical and electrical responses of the proposed system are fully studied through both theoretical analysis and numerical simulations. It is found that the system presents rich dynamical behaviors under the rotational excitation, and the rotational speed and the distance between two membranes are two key parameters to affect the system’s response and EH performance. Research results show the superiority of the proposed system which can produce a maximal output power as high as 0.88 mW from rotational excitations, and also provide guidelines to study the rotational speed-related system EH performance with given dimensional parameters or optimize the dimensional parameters under a given rotational speed.</p
Bending dynamics of semi-flexible particles in turbulent flows
No full textWe study the Lagrangian dynamics of semi-flexible particles in laminar as well as in homogeneous and isotropic turbulent flows by means of analytically solvable stochastic models and direct numerical simulations. The statistics of the bending angle is qualitatively different in laminar and turbulent flows and exhibits a strong dependence on the topology of the velocity field. In particular, in two-dimensional turbulence, particles are either found in a fully extended or in a fully folded configuration; in three dimensions, the predominant configuration is the fully extended one
Wind energy harvesting from a conventional turbine structure with an embedded vibro-impact dielectric elastomer generator
No full textIn this paper, a novel wind energy harvester is proposed and studied. The wind energy harvester consists of a conventional two-blade horizontal wind turbine and a vibro-impact (VI) dielectric elastomer generator (DEG) embedded symmetrically at the end of a rotating shaft. The wind energy is harvested by the VI DEG due to the rotational motion of the turbine's blades and the shaft. The dynamic model of the proposed system under wind-induced rotations is established theoretically, and the energy harvesting (EH) process of the VI DEG is introduced with the system output voltage and power being derived. The impact-based rotational energy harvesting process of the system is validated experimentally by measuring the output voltages of a single-sided impact (SSI) DEG under different impact velocities, and by measuring the ball's impact moments under rotational excitations, thus demonstrating the feasibility of the impact-based EH of DE material. Furthermore, the dynamical and electrical behaviors of the system under different wind speeds are fully studied through numerical simulations. The influences of the wind speed, tip speed ratio and the distance between dielectric elastomer membranes (DEMs) on the system EH performance are further discussed. It is found that the proposed wind energy harvester can work effectively in a range of small wind speed and produce a relatively high output power as large as 0.7125 mW under a wind speed of 3.99 ms−1. The tip speed ratio, distance between two DEMs can be selected as the adjusting parameter to produce optimal EH performance under different wind speeds, thus providing an effective solution for the design and improvement of the proposed system under different wind environments
Vi Kowalchuk
No full textPhotograph - Vi Kowalchuk, member of the Book Sub-Committee, part of the Town of Athabasca 75th Anniversary Committee, Athabasca, Alberta. The Book Sub Committee produced the book "Athabasca Landing: An Illustrated History
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