Yoshihiro Kikushima

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

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.

Vortex structural power flow in a thin plate and the influence on the acoustic field

This article examines the characteristics of real vibrational power flow in a simply supported rectangular panel under the action of feedforward vibration control, induced by a control source input which is slightly suboptimal such that the primary source is producing a slight amount of real vibrational power, and the control source is absorbing the same amount. It is found that the path of the power flow is a combination of translations and rotations, the rotations induced by the interference of two modes which produces a ‘‘vortex generating block.’’ A qualitative formula for predicting the number of power flow vortices, as well as the discussion of the vortex period, is put forward. A novel method to induce a vortex at an arbitrary location of the plate is also shown, which may have practical applications in controlling the path of vibrational power flow in systems of large extent. Moreover, the influence of the induced vortex power flow on the plate onto the acoustic intensity distribution is investiga...

One-dimensional distributed modal sensors and the active modal control for planar structures

This paper discusses distributed parameter sensors designed to extract vibration modes of a structure, as well as its active modal control. Compared to conventional point sensors such as accelerometers or displacement sensors, the distributed parameter sensors are superior to point sensors provided that they are properly designed. First, this paper overviews a conventional modal filter method using point sensors, and enumerates the problems they possess. To overcome the drawbacks of the point sensor-based modal filtering, a novel modal filtering technique based upon distributed parameter PVDF film sensors is proposed. This paper begins by discussing a design methodology for modal filtering using two-dimensional distributed sensors. Then, taking into consideration the applicability of the sensors, a design procedure for modal filtering using one-dimensional sensors is presented, the number, location, and shaping functions for the one-dimensional modal sensors being clarified. Furthermore, the modal filteri...

Active control of streak structures in wall turbulence using an actuator array producing inclined wavy disturbances

By using a piezo-ceramic actuator array, turbulent flow control in a two-dimensional water channel was attempted at the flow Reynolds number of 7500. Eight piezo-ceramic actuators were installed sp...

Detection of missing fastener based on vibration mode analysis using fiber Bragg grating (FBG) sensors

We propose a damage detection method based on frequency responses measured by FBG sensors during vibration tests. When random noise vibrates a laminated composite panel and a stiffener fastened with bolts, the peak gain of the resonance frequencies can be obtained. We calculated the correlation coefficient of the normalized gain for the frequency responses, and then predicted the location of a missing bolt. This method will make possible to predict the location of damage with a limited number of FBG sensors while a structure is vibrating even if the excitation point changes.

Experimental considerations on fabrication of a smart actuator for vibration control using shape memory alloy (SMA)

Despite its great potentials, having a large displacement and force compared to traditional electro-hydraulic servo mechanical actuators or to PZT actuators, there are not so many studies on SMA active actuator. The main reasons are considered as following; (1) SMA has transformation only in one direction, (2) the response is quite slow, and (3) vibration control requires punctual thermo control in real time. In the study at our laboratory, the vibration can be clearly separated into different modes by distributed cluster system. SMA actuators are, then, proposed to use with PZT actuators for control of low and high frequency modes, respectively, to realize all-round actuation. The purpose of this paper is to realize SMA active actuator for low frequency modes. First of all, actuators using SMA wires, partly embedded in CFRP, were fabricated in consideration of SMA/FRP interfacial strength. Their thermo-mechanical behavior had been studied with cooling system. These lightweight actuators were placed on beam structure made of CFRP. Recovery force of beam structure itself was used as reactive force against force generated by SMA. As a result, actuator which is favorable for low frequency vibration modes control, i.e. having a large displacement and a large force, was obtained.

Fabrication and tests of a MEMS-based double-beam cantilever flow sensor with clarifying of temperature effect

This paper presents the fabrication process of a MEMS-based cantilever flow sensor (CFS) with double cantilever beams and the test results of CFS in a wind-tunnel. Four boron-doped piezoresistive strain gauges at the base of each cantilever beam compose the four arms of the Wheatstone bridge. The output of CFS will change signs as piezoresistors at the base of the cantilever beam undergo compressive or tensile stresses. Analyses and experimental results suggest that double-beam CFS can be applied not only as a flow direction discriminator but also as a wall skin-friction sensor, which could be used in the system of active flow control for drag reduction and separation suppression in the boundary layers on a wing section. Temperature effect is commonly encountered in the application of MEMS-based piezoresistive strain gauges. By comparing the outputs of CFS when front side and back side of it facing the flow respectively, we are able to clarify the contribution of temperature effect on the output of CFS sensor and give more accurate results on flow measurement.

Active modal control of a truss structure considering displacement constraint

For the purpose of reducing the cost, a control system for a truss structure with a simplified controller equipped with amplifying function alone is proposed. In order to realize a sensor in consideration of system stability, the sensor is provided with multiplication-addition capability and a distributed modal filter capable of isolating multiple vibration modes. Then, a control system is built up to amplify the sensor output through a power amplifier, by using a moment actuator which can exert actuation comparable to that of the velocity feedback for damping the system. Finally, the control system is incorporated to the truss structure and the vibration control effect through direct feedback is studied.

Offshore wind profile measurements using a Doppler LIDAR at the Hazaki Oceanographical Research Station

Vertical wind speed profiles near the coast were observed using a Doppler Light Detection and Ranging (LIDAR) system at the Hazaki Oceanographical Research Station (HORS) from September 17 to 26, 2013. The accuracies of the theoretical wind profile models of the log profile model and the Monin-Obukov similarity (MOS) theory were examined by comparing them to those of the observed wind profiles. As a result, MOS, which takes into account the stability effects during wind profile calculations, successfully estimated the wind profile more accurately than the log profile model when the wind was from a sea sector (from sea to land). Conversely, both models did not estimate the profile adequately when the wind was from a land sector (from land to sea). Moreover, the wind profile for the land sector was found to include an obvious diurnal cycle, which is relevant to the stability change over land. Consequently, it is found that the atmospheric stability plays an important roll to determine the offshore wind speed profiles near the coast for not only the sea sector but also the land sector.

Fabrication technique of SMA/CFRP smart composites

In recent years, pre-strained TiNi shape memory alloys (SMA) have been used for fabricating smart structure with carbon fibers reinforced plastics (CFRP). However, since the curing temperature of CFRP is higher than the reverse transformation temperatures of TiNi SMA, special fixture jigs have to be used for keeping the pre-strain during fabrication, which restricted its practical application. We have developed a new method to control the transformation temperatures of SMA by proper thermo-mechanical treatments and composition adjustment, which is suitable to fabricate SMA/CFRP smart composite with a curing temperature of 130C. Furthermore, we tried to develop a new fabrication technique which is also suitable to fabricate SMA/CFRP smart composite with a curing temperature of 180C. It was found that by using cold drawn ultra-thin TiNi wires, TiNi/CFRP composites with a curing temperature of 180C could be fabricated without special fixture jigs. The damage suppression effect by embedded ultra-thin wires in the smart composite was confirmed.