The Use of Optimally Shaped Piezo-electric Film Sensors in the Active Control of Free Field Structural Radiation, Part 2: Feedback Control

1996 ◽  
Vol 118 (1) ◽  
pp. 112-121 ◽  
Author(s):  
S. D. Snyder ◽  
N. Tanaka ◽  
Y. Kikushima
Keyword(s):  
Feedback Control ◽  
Control Strategies ◽  
Free Field ◽  
Low Frequency ◽  
Acoustic Power ◽  
State Equations ◽  
Subsequent Increase ◽  
Low Frequencies ◽  
Control Approach ◽  
Iir Filters

Feedback control of free field structural radiation is considered. State equations are formulated with a transformation which decouples the acoustic power error criterion. Using the resultant equations, expressed in terms of “transformed mode” states, the order of the state equations can be significantly reduced at low frequencies. Two experimental implementations of feedback control strategies using shaped piezoelectric polymer film sensors to measure the transformed system states are described. The first of these is a simple analog implementation. The second implementation is in discrete time, where an adaptive algorithm for optimizing the weights of IIR filters for practical use is described. It is shown that by using the outlined control approach significant levels of low frequency acoustic power attenuation can be obtained with no control spillover and subsequent increase in higher frequency acoustic power output.

Frequency-Weighted Variable-Length Controllers Using Anytime Control Strategies

2011 ◽  
Author(s):  
Gundula B. Runge ◽  
Al Ferri ◽  
Bonnie Ferri
Keyword(s):  
Time Scale ◽  
Weighting Function ◽  
Control Strategies ◽  
Low Frequency ◽  
Low Frequencies ◽  
High Frequencies ◽  
Frequency Components ◽  
Computational Resources ◽  
Weighted Variable ◽  
Selection Of

This paper considers an anytime strategy to implement controllers that react to changing computational resources. The anytime controllers developed in this paper are suitable for cases when the time scale of switching is in the order of the task execution time, that is, on the time scale found commonly with sporadically missed deadlines. This paper extends the prior work by developing frequency-weighted anytime controllers. The selection of the weighting function is driven by the expectation of the situations that would require anytime operation. For example, if the anytime operation is due to occasional and isolated missed deadlines, then the weighting on high frequencies should be larger than that for low frequencies. Low frequency components will have a smaller change over one sample time, so failing to update these components for one sample period will have less effect than with the high frequency components. An example will be included that applies the anytime control strategy to a model of a DC motor with deadzone and saturation nonlinearities.

Acoustic Barriers Based on Sonic Crystals

2007 ◽  
Author(s):  
V. Romero-Garci´a ◽  
E. Fuster-Garcia ◽  
L. M. Garci´a-Raffi ◽  
J. V. Sa´nchez-Pe´rez
Keyword(s):  
Geometric Distribution ◽  
Free Field ◽  
Low Frequency ◽  
Optimization Methods ◽  
Band Gaps ◽  
High Symmetry ◽  
Low Frequencies ◽  
Periodic Arrays ◽  
Sonic Crystals ◽  
High Sound

Environmental noise problems become an standard topic across the years. Acoustic barriers have been purposed as a possible solution because they can act creating an acoustic attenuation zone which depends on the sound frequency, reducing the sound transmission through it. It was demonstrated that at high sound frequencies the effect of the barriers is more pronounced than at low frequencies, due to the diffraction in their edges. Sonic Crystals (SCs) are periodic arrays of scatterers embedded in a host material with strong modulation of its physical properties, that produces band gaps attenuation in frequencies related with their geometry. These frequencies are explained by the well known Bragg’s diffraction inside the crystal. SCs present different high symmetry directions, where the Bragg’s peaks appears in different frequencies ranges due to the variation of the geometry in each direction. Recently, some authors have studied the possibility to use SCs to reduce noise in free-field condition. Also, it was showed that SCs built by trees are acoustic systems that present acoustic band gaps in low frequency range due to the geometric distribution of the trees. These results led us think that these structures are a suitable device to reduce noise, this means SCs could be use as acoustic barriers. Nevertheless the technological application of these devices for controlling the noise present some problems. First, the angular dependence of the frequencies attenuated when the sound impinges over the SC. Second, the fact that the necessary space to put the SC is bigger than in the case of the traditional acoustic barriers. Finally, the necessity of some robust and long-lasting materials to use them outdoors. In this paper we show the possibility to use different materials (rigid, mixed or soft) to make scatterers, explaining their advantages or disadvantages. These materials in conjunction with some optimization methods will allow us find some solutions to the problems mentioned above. We will relate both acoustic systems, acoustic barriers and SCs, making a comparison of the main properties of each one and then, we will present the technological possibilities to design acoustic barriers based on SCs.

Predictive Time-Based Feedback Control Approach for Managing Freeway Incidents

2000 ◽  
Vol 1710 (1) ◽  
pp. 79-84 ◽  
Author(s):  
Omar B. Sawaya ◽  
Dung L. Doan ◽  
Athanasios K. Ziliaskopoulos
Keyword(s):  
Feedback Control ◽  
Traffic Management ◽  
Control Strategies ◽  
Compliance Rate ◽  
Dynamic Control ◽  
Route Guidance ◽  
Control Approach ◽  
Real Time Traffic ◽  
Freeway Incidents ◽  
Alternate Routes

A feedback control approach is introduced that produces dynamic control strategies in the form of alternate routes around freeway incidents and in response to the prevailing traffic conditions. The approach is based on the equalization of predictive travel times on alternate routes. The methodology is intended to be used as a decision-aid tool for real-time traffic management applications, more specifically for route guidance via variable message signs. The approach is implemented and tested computationally on an example network in a simulated environment under various scenarios of system disturbances. The results indicate that the performance of this approach is fairly robust to uncertainties in demand, compliance rate, and incident severity. It also performs better than an anticipatory approach and an instantaneous time–based feedback control approach.

The Use of Optimally Shaped Piezo-electric Film Sensors in the Active Control of Free Field Structural Radiation, Part 1: Feedforward Control

1995 ◽  
Vol 117 (3A) ◽  
pp. 311-322 ◽  
Author(s):  
S. D. Snyder ◽  
N. Tanaka ◽  
Y. Kikushima
Keyword(s):  
Vibration Control ◽  
Polymer Film ◽  
Active Control ◽  
Computer Simulations ◽  
Basis Function ◽  
Feedforward Control ◽  
Free Field ◽  
Acoustic Power ◽  
Low Frequencies ◽  
Piezo Electric

Feedforward active control of free field structural radiation using vibration control sources and piezo-electric polymer film error sensors is considered. The problem of what should be measured by the sensors is first examined, where it is shown that orthonormal decomposition of the equation governing the acoustic power output of the structure will define the optimal quantities, which are described using the in vacuo structural modes as a basis function. Computer simulations show that by using only a few of these quantities as error signals, practically the maximum levels of acoustic power attenuation can be obtained at low frequencies. Tonal and broadband experimental results are presented using the shaped piezo-electric polymer film sensors which demonstrate the effectiveness of the described approach.

Active Control of a Circular Membrane to Reduce Transient Noise Transmission

1995 ◽  
Vol 117 (3A) ◽  
pp. 252-258 ◽  
Author(s):  
J. L. van Niekerk ◽  
B. H. Tongue
Keyword(s):  
Feedback Control ◽  
Active Control ◽  
Sliding Mode ◽  
Control Strategies ◽  
Circular Membrane ◽  
Velocity Feedback ◽  
Circular Duct ◽  
Control Approach ◽  
Noise Transmission

An active control approach that reduces transient noise transmission through a membrane in a circular duct is presented. Discrete sections of piezo-electrical film, PVDF, are used as actuators to adjust the tension of the membrane. Different control strategies, such as optimal, sliding mode and velocity feedback control, are investigated analytically and then implemented experimentally. It is shown that velocity feedback control is the more effective, stable controller for this application.

Active Control of Low Frequency Modes in an Aircraft Fuselage Using Spatially Weighted Arrays

2000 ◽  
Vol 122 (3) ◽  
pp. 227-234 ◽  
Author(s):  
Steven A. Lane ◽  
Robert L. Clark ◽  
Steve C. Southward
Keyword(s):  
Three Dimensional ◽  
Pressure Sensors ◽  
Low Frequency ◽  
Single Mode ◽  
Open Loop ◽  
H2 Control ◽  
Low Frequencies ◽  
Control Approach ◽  
Aircraft Fuselage ◽  
Transducer Arrays

Acoustic enclosures such as aircraft cabins often display lightly damped modal behavior at low frequencies where passive treatments are impractical due to mass and volume constraints. This work presents a feedback control approach using dynamic H2 controllers implemented with spatially weighted arrays of collocated pressure sensors and constant volume-velocity actuators. The open-loop system is shaped using spatially weighted transducer arrays to yield increased pole-zero separation, which results in better closed-loop performance. The transducer arrays are weighted to emphasize coupling to a particular acoustic mode or modes, which facilitates global control of the targeted dynamics. This work presents a method to determine the spatial weighting vectors for the transducer arrays from frequency response measurements. The development and implementation of low-order, dynamic H2 control laws is also discussed. Experimental results are presented for a single-mode and a multiple-mode controller implemented on an aircraft fuselage section, and demonstrate significant reduction of the targeted acoustic modes. To the best of the authors’ knowledge, this is the first experimental implementation of a feedback controller of this type capable of achieving such levels of global reduction in a three-dimensional acoustic system. [S0739-3717(00)02303-5]

scholarly journals Very low-frequency IEPE accelerometer calibration and application to a wind energy structure

2021 ◽  
Author(s):  
Clemens Jonscher ◽  
Benedikt Hofmeister ◽  
Tanja Grießmann ◽  
Raimund Rolfes
Keyword(s):  
Measurement Data ◽  
Low Frequency ◽  
Calibration Procedure ◽  
Low Noise ◽  
Energy Structure ◽  
Frequency Range ◽  
Low Frequencies ◽  
Iir Filters ◽  
Very Low Frequency ◽  
Ac Response

Abstract. In this work, we present an experimental setup for very low-frequency calibration measurements of low-noise Integrated Electronics Piezo Electric (IEPE) accelerometers and a customised signal conditioner design for using IEPE sensor down to 0.05Hz. AC-response IEPE accelerometer and signal conditioners have amplitude and phase deviations at low frequencies. As the standard calibration procedure in the low-frequency range is technically challenging, IEPE accelerometers with standard signal conditioners are usually used in frequency ranges above 1 Hz. Vibrations on structures with low eigenfrequencies like wind turbines are thus often monitored using DC-coupled micro-electro-mechanical systems (MEMS) capacitive accelerometers. This sensor type suffers from higher noise levels compared to IEPE sensors. To apply IEPE sensors instead of MEMS sensors, in this work the calibration of the entire measurement chain of three different IEPE sensors with the customised signal conditioner is performed with a low-frequency centrifuge. The IEPE sensors are modelled using IIR filters to apply the calibration to time-domain measurement data of a wind turbine support structure. This procedure enables an amplitude and phase-accurate vibration analysis with IEPE sensors in the low-frequency range down to 0.05 Hz.

Sound absorptive light comprising nanofibrous resonant membrane applicable in room acoustics

2017 ◽  
Vol 39 (3) ◽  
pp. 362-370 ◽  
Author(s):  
Klara Kalinova
Keyword(s):  
Broad Band ◽  
Low Frequency ◽  
Acoustic Power ◽  
Acoustic Properties ◽  
Room Acoustics ◽  
Sound Waves ◽  
Final Thickness ◽  
Low Frequencies ◽  
Perforated Sheet ◽  
Lower Frequencies

Room acoustic solutions are based on measurements of the acoustic power of the room and acoustic elements with different functions (absorption tiles, absorption ceilings, absorption bodies, diffusers, barriers). This work is focused only on absorption elements with an emphasis on addressing lower-middle frequencies. The design of the material is based on broad band noise. Damping of lower frequencies is restricted to a certain extent by the final thickness of the acoustic material. Nanofibrous resonant membranes will be used in the design to achieve higher sound absorption at lower frequencies in comparison with commercially available materials. The principle of the acoustic system is to use combination of a perforated sheet covered by a nanofibrous resonant membrane, which is brought into forced vibration upon impact of sound waves of low frequency. Practical application:To absorb sounds of high frequencies, porous materials are used. To absorb sounds of low frequencies, resonant membranes are employed. However, these structures absorb only sounds of certain frequency. Nanofibrous layers have unique acoustic properties due to the large specific surface area of the nanofibres, where viscous losses may occur, and also the ability to resonate at its own frequency. The advantage of this technology is the space between the acoustic element with a thickness of 1–2 mm and the wall/ceiling, which can be used for the installation of lighting/audio speakers, etc. The acoustic light prototype has been made.

Frequency-Weighted Variable-Length Controllers Using Anytime Control Strategies

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Bonnie H. Ferri ◽  
Aldo A. Ferri ◽  
Gundula B. Runge
Keyword(s):  
Weighting Function ◽  
Control Strategies ◽  
Low Frequency ◽  
Low Frequencies ◽  
High Frequencies ◽  
Frequency Components ◽  
Computational Resources ◽  
Weighted Variable ◽  
Sample Time ◽  
Selection Of

This paper develops an optimal frequency-weighted strategy to design anytime controllers that can react to changing computational resources. The selection of the weighting function is driven by the expectation of the situations that would require anytime operation. For example, if the anytime operation is due to occasional and isolated missed deadlines, then the weighting on high frequencies should be larger than that for low frequencies. Low frequency components will have a smaller change over one sample time, so failing to update these components for one sample period will have less effect than with the high frequency components. Additional considerations explored in this paper are stability analyses, architectural issues, and transient management. Two examples are included that demonstrate the methodology.

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