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.
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.
KEYWORDS: Control systems, Sensors, Actuators, Ferroelectric materials, Fiber Bragg gratings, Digital signal processing, Finite element methods, Ferroelectric polymers, Composites, Vibration control
A new vibration control system, named 'block-by-block' distributed cluster control system, is presented with a CFRP board with stiffeners. Distributed cluster control system which had been applied for flat simple board is a control system includes 'cluster sensing' which classified numberless vibration modes into some limited number of clusters by using a group of sensors, and 'cluster actuation' which can actuate only specific cluster. It means, this system controls only target clusters. When the system is applied to complex structure such as this CFRP board with stiffeners, it is not possible to applied directly since the forms of vibration modes are not as simple as the one of flat board but there exist three blocks; 2 side blocks and one center block between two stiffeners. In this paper, after a rough explanation of distributed cluster control system, the idea of 'block-by-block' control is explained and verified experimentally with FEM analysis using some kinds of sensors and actuator.
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.
During construction of extra high structures such as a skyscraper or a main tower of a long bridge, just a slight wind can generate low frequency vibration, and the maximum displacement at the top of structure can increase up to a few meters. Occurrence of low frequency vibration causes a fear of operators and it deteriorates awfully safeness. The purpose of this paper is a control of low frequency vibration above-mentioned with a development of small-lightweight actuator which can control a big displacement and that of control system which guarantees a stable control. As a first step, beam structure is estimated. Design of modal sensor using PVDF film sensor is explained. For an actuator, SMA/CFRP hybrid moment actuator is used. This actuator has been developed in the recent studies by authors with special consideration on the interfacial strength between SMA wires and matrix. Basic characteristics of this actuator is presented in this paper. To drive this moment actuator smoothly, punctual temperature control in real time which includes rapid heating, exact current control and some cooling control is required. Adaptive feedforward control system is, therefore, designed here for this actuator aiming to apply to beam structure. As a result, control effect on beam structure is demonstrated experimentally. Verification of performance of this actuator is also shown.
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.
Low frequency modes of tower structure generated by a strong wind or by an earthquake occur deterioration or a collapse of structure because stress concentration happens at the root of structure. High frequency modes, on the other hand, are often possible to be disregarded because they can be damped immediately. In general, all vibration modes which are generated in the structure are tried to be suppressed when it is said as 'vibration control'. There remind, however, a lot of problems to realize a stable control in this case.
The object of present paper is a pick up and a suppression of specific vibration modes which occur such problems, it means here low frequency modes, among all of generated vibration modes in structure.
First of all, a design of modal sensor made of PVDF film is proposed to pick up only low frequency modes separately by using FEM analysis. Then, an applied method of SMA/CFRP hybrid actuator, which can generate great force in a field of low frequency, is explained. By using these PVDF modal sensor and SMA moment actuator, vibration model can be simplified by means of modification to low dimensions. Consequently, modal control system, which suppresses only low frequency vibration modes, is constructed. At the end of the present paper, effect of this control system is demonstrated experimentally.
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.
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.
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