Tuned mass dampers are a common method implemented to control structure’s vibrations. Most tuned-mass dampers only transfer the mechanical energy of the primary system to a secondary system, but it is desirable to convert the primary systems’ mechanical energy into usable electric energy. This study achieves this by using a piezoelectric energy harvester as a tuned-mass damper. Additionally, this study focuses on improving the amount of energy harvested by including amplitude stoppers. Mechanical stoppers have been investigated to sufficiently widen the response of piezoelectric energy harvesters. Furthermore, magnetic stoppers are compared to the mechanical stopper’s response. A nonlinear reduced-order model using Galerkin discretization and Euler-Lagrange equations is developed. The goal of this study is to maximize the energy harvested from the absorber without negatively affecting the control of the primary structure.
A popular technique to control dynamical systems is the implementation of tuned-mass dampers. Most tuned-mass dampers only transfer the mechanical energy of the primary system to a secondary system, but it is desirable to convert the primary systems’ mechanical energy into usable electric energy. A piezoelectric energy harvester is used in this study. Furthermore, amplitude stoppers are included to possibly generate a broadband region by causing a nonlinear interaction. Mechanical stoppers have been investigated to sufficiently widen the response of piezoelectric energy harvesters. The effectiveness of the stoppers type is also investigated by comparing magnetic stoppers to mechanical stoppers. A nonlinear reduced-order model using Galerkin discretization and Euler-Lagrange equations is developed. The goal of this study is to maximize the energy harvested from the absorber without negatively affecting the control of the primary structure.
Self-excited vibrations are a major problem for rotary drilling. They may be mitigated by introducing adjustable compliance near the bottom of the drillstring, but it is challenging to identify the appropriate stiffness, particularly in situ and with limited available data on the rapidly-changing overall system dynamics. We describe an approach to modeling and simulating self-excited vibrations in drillstrings. Our approach uses impedance and admittance port functions to represent and systematically combine subsystems, and integrates established models for drillstring vibrations and rock / bit interactions. Simulations predict that intermediate stiffnesses provide better stability than either compliant or stiff extremes, which aligns with results from earlier work. Results also indicate that at least two different mechanisms limit stability in different stiffness regimes, producing significant differences in the relationship between vibration frequency and controlled module stiffness. This suggests a potential means of developing autonomous stiffness controllers that depend only on measurements taken at the variable stiffness module, without requiring a dynamic model of the rest of the drillstring.
The dynamic stability of deep drillstrings is challenged by an inability to impart controllability with ever-changing conditions introduced by geology, depth, structural dynamic properties and operating conditions. A multi-organizational LDRD project team at Sandia National Laboratories successfully demonstrated advanced technologies for mitigating drillstring vibrations to improve the reliability of drilling systems used for construction of deep, high-value wells. Using computational modeling and dynamic substructuring techniques, the benefit of controllable actuators at discrete locations in the drillstring is determined. Prototype downhole tools were developed and evaluated in laboratory test fixtures simulating the structural dynamic response of a deep drillstring. A laboratory-based drilling applicability demonstration was conducted to demonstrate the benefit available from deployment of an autonomous, downhole tool with self-actuation capabilities in response to the dynamic response of the host drillstring. A concept is presented for a prototype drilling tool based upon the technical advances. The technology described herein is the subject of U.S. Patent Application No. 62219481, entitled "DRILLING SYSTEM VIBRATION SUPPRESSION SYSTEMS AND METHODS", filed September 16, 2015.
This document summarizes research performed under the SNL LDRD entitled - Computational Mechanics for Geosystems Management to Support the Energy and Natural Resources Mission. The main accomplishment was development of a foundational SNL capability for computational thermal, chemical, fluid, and solid mechanics analysis of geosystems. The code was developed within the SNL Sierra software system. This report summarizes the capabilities of the simulation code and the supporting research and development conducted under this LDRD. The main goal of this project was the development of a foundational capability for coupled thermal, hydrological, mechanical, chemical (THMC) simulation of heterogeneous geosystems utilizing massively parallel processing. To solve these complex issues, this project integrated research in numerical mathematics and algorithms for chemically reactive multiphase systems with computer science research in adaptive coupled solution control and framework architecture. This report summarizes and demonstrates the capabilities that were developed together with the supporting research underlying the models. Key accomplishments are: (1) General capability for modeling nonisothermal, multiphase, multicomponent flow in heterogeneous porous geologic materials; (2) General capability to model multiphase reactive transport of species in heterogeneous porous media; (3) Constitutive models for describing real, general geomaterials under multiphase conditions utilizing laboratory data; (4) General capability to couple nonisothermal reactive flow with geomechanics (THMC); (5) Phase behavior thermodynamics for the CO2-H2O-NaCl system. General implementation enables modeling of other fluid mixtures. Adaptive look-up tables enable thermodynamic capability to other simulators; (6) Capability for statistical modeling of heterogeneity in geologic materials; and (7) Simulator utilizes unstructured grids on parallel processing computers.
The acoustic field generated during a Direct Field Acoustic Test (DFAT) has been analytically modeled in two space dimensions using a properly phased distribution of propagating plane waves. Both the pure-tone and broadband acoustic field were qualitatively and quantitatively compared to a diffuse acoustic field. The modeling indicates significant non-uniformity of sound pressure level for an empty (no test article) DFAT, specifically a center peak and concentric maxima/minima rings. This spatial variation is due to the equivalent phase among all propagating plane waves at each frequency. The excitation of a simply supported slender beam immersed within the acoustic fields was also analytically modeled. Results indicate that mid-span response is dependent upon location and orientation of the beam relative to the center of the DFAT acoustic field. For a diffuse acoustic field, due to its spatial uniformity, mid-span response sensitivity to location and orientation is nonexistent.