James E. Hubbard

Bio: James E. Hubbard is an academic researcher from Texas A&M University. The author has contributed to research in topics: Aerodynamics & Actuator. The author has an hindex of 22, co-authored 118 publications receiving 2957 citations. Previous affiliations of James E. Hubbard include National Institute of Aerospace & Massachusetts Institute of Technology.

Distributed Piezoelectric-Polymer Active Vibration Control of a Cantilever Beam

Abstract: An active vibration damper for a cantilever beam was designed using a distributed-parameter actuator and distributed-parameter control theory. The distributed-parameter actuator was a piezoelectric polymer, poly (vinylidene fluoride). Lyapunov's second method for distributed-parameter systems was used to design a control algorithm for the damper. If the angular velocity of the tip of the beam is known, all modes of the beam can be controlled simultaneously. Preliminary testing of the damper was performed on the first mode of the cantilever beam. A linear constant-gain controller and a nonlinear constant-amplitude controller were compared. The baseline loss factor of the first mode was 0.003 for large-amplitude vibrations (± 2 cm tip displacement) decreasing to 0.001 for small vibrations (±0.5 mm tip displacement). The constant-gain controller provided more than a factor of two increase in the modal damping with a feedback voltage limit of 200 V rms. With the same voltage limit, the constant-amplitude controller achieved the same damping as the constant-gain controller for large vibrations, but increased the modal loss factor by more than an order of magnitude to at least 0.040 for small vibration levels.

Patient activity monitor

Abstract: A patient activity monitoring system that allows caregivers of multiple patients to work more efficiently and with reduced cost, while increasing the quality and level of patient care The system includes a plurality of remote monitoring subsystems, a plurality of user notification units, and a central monitoring unit with a Graphical User Interface (GUI) communicably coupled between the remote monitoring and user notification units Each remote monitoring subsystem includes a remote monitoring unit, and a sensor device associated with a respective patient that detects one or more activity and/or physiological parameters of the patient A simplified user interface including the GUI and the user notification units provides indications of the type and level of assistance required by one or more patients to caregivers at centralized and remote locations

Active vibration control of a simply supported beam using a spatially distributed actuator

Abstract: The application of a spatially shaped distributed actuator for the vibration control of a simply supported beam is studied both analytically and experimentally. The actuator consists of a layer of polyvinylidene fluoride (PVF 2 ) bonded to one face of the beam. A summary of the underlying theory is presented, with emphasis on how controllability requirements affect the choice of the film's spatial distribution. The requisite film controller has a linearly varying spatial distribution that facilitates the control of both even- and odd-order vibrational modes. Experimental results are presented for the control of the beam's first three modes, using both the linearly varying as well as a uniform spatial distribution. The linearly varying distribution is shown to be effective in controlling both even- and odd-order modes, serving to increase the modal loss factors by up to a factor of 4.5. In addition, the experimental results are found to corroborate a simplified computer model of the controller.

Nonlinear Control of a Distributed System: Simulation and Experimental Results

Abstract: A nonlinear active vibration damper has been developed which uses a spatially distributed piezoelectric actuator, polyvinylidene flouride, to achieve active vibration control of a cantilever beam. The control algorithm was derived using Lyapunov’s Second Method. All modes of the beam can be controlled simultaneously if the angular velocity of the tip of the beam is known. A simulation algorithm was developed to predict the effect of the control on the free decay of a single mode. A parameter study for the first mode was performed and compared to experimental results. The active damper has been tested successfully on two different scale structures.

Regression Diagnostics: Identifying Influential Data and Sources of Collinearity

Abstract: 1. Introduction and Overview. 2. Detecting Influential Observations and Outliers. 3. Detecting and Assessing Collinearity. 4. Applications and Remedies. 5. Research Issues and Directions for Extensions. Bibliography. Author Index. Subject Index.

Use of piezoelectric actuators as elements of intelligent structures

Abstract: This work presents the analytic and experimental development of piezoelectric actuators as elements of intelligent structures, i.e., structures with highly distributed actuators, sensors, and processing networks. Static and dynamic analytic models are derived for segmented piezoelectric actuators that are either bonded to an elastic substructure or embedded in a laminated composite. These models lead to the ability to predict, a priori, the response of the structural member to a command voltage applied to the piezoelectric and give guidance as to the optimal location for actuator placement. A scaling analysis is performed to demonstrate that the effectiveness of piezoelectric actuators is independent of the size of the structure and to evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure. Three test specimens of cantilevered beams were constructed: an aluminum beam with surface-bonded actuators, a glass/epoxy beam with embedded actuators, and a graphite/epoxy beam with embedded actuators. The actuators were used to excite steady-state resonant vibrations in the cantilevered beams. The response of the specimens compared well with those predicted by the analytic models. Static tensile tests performed on glass/epoxy laminates indicated that the embedded actuator reduced the ultimate strength of the laminate by 20%, while not significantly affecting the global elastic modulus of the specimen.

Structural control: past, present, and future

Abstract: This tutorial/survey paper: (1) provides a concise point of departure for researchers and practitioners alike wishing to assess the current state of the art in the control and monitoring of civil engineering structures; and (2) provides a link between structural control and other fields of control theory, pointing out both differences and similarities, and points out where future research and application efforts are likely to prove fruitful. The paper consists of the following sections: section 1 is an introduction; section 2 deals with passive energy dissipation; section 3 deals with active control; section 4 deals with hybrid and semiactive control systems; section 5 discusses sensors for structural control; section 6 deals with smart material systems; section 7 deals with health monitoring and damage detection; and section 8 deals with research needs. An extensive list of references is provided in the references section.

A Self-Sensing Piezoelectric Actuator for Collocated Control:

Abstract: A technique has been developed which allows a single piece of piezoelec tric material to concurrently sense and actuate in a closed loop system. The motivation behind the technique is that such a s...