a. karimzadeh

In the present study the dynamic behavior of a piezoelectric flow micro sensor based on vortex-induced vibrations (VIV) is investigated. This sensor is made by a cantilever beam, piezoelectric layer and a cylinder at free end which is used to measure the fluid velocity. The proposed VIV sensors have nonlinear dynamic behavior for different flow velocities therefore in designing VIV micro sensors obtaining linear operational working range is an important parameter. In this paper the dynamic behavior of micro flow sensors based on the modified couple stress theory (MCST) is investigated and linear operational working span is derived. The coupled governing equations of silicon based and piezoelectric layer cantilever beam, gauss electric and Van der pol equation are derived. Utilizing the derived equations the dynamic behavior of the micro sensor on the basis of parameters such as damping coefficient, cantilever beam length, material length scale parameter and tip cylinder mass is analyzed. The operational work range of the micro sensor, the acceptable linear behavior domain and error of linear behavior assumption of the device is investigated. According to the results the maximum linearization error is 3.5%. In addition to that reduction in cantilever beam length and tip cylinder mass increase the operational working range of the micro sensor. Analyzing the effect of damping coefficient on the dynamic behavior of micro flow sensor show that increasing the damping coefficient decreases the beam deflection and output voltage, but has no effect on the operational working span of the system and in order to obtain precise output from this sensor the damping coefficient must be reduced. Findings indicate that parameters which make the device behave stiffer such as reduction in beam length or tip cylinder mass or considering non-classical stresses gives a wider acceptable voltage range at higher flow velocities for the micro sensor.

In the present study, the performance of a cylinder-based piezoelectric wind energy harvester attached to an elastic beam is numerically simulated. The wind flow perpendicular to beam axis causes an oscillatory aerodynamic force exerted on the beam tip. The beam and the piezoelectric layer are modeled as elastic continuous bodies, and the continuum governing equations of the solid and piezoelectric layers are extracted. Moreover, the induced lift force by the vortex shedding downstream of the cylinder is estimated by the modified van der Pol wake oscillator equation. The cantilever mode shapes and the Galerkin method is applied to solve the three transient and coupled equations of elastic deflection, electrical resistance and fluid force. Besides to verify the accuracy of the modified van der Pol equation, a moving object computational fluid dynamics (CFD) simulation is also conducted. The effect of oscillator length, cylinder diameter, resistance load, structure and piezoelectric thickness as well as the wind speed on the produced power is investigated. According to the obtained results, by increasing of the cylinder diameter from 0.05 m by 100, 200 and 300 %, the output power is increased by 219, 801 and 1502 % at the wind speed of 5 m/s.

In this study microstructure and formation of NiAl phase using a modified (single-step) high activity aluminizing at 1080°C have been compared with those of common (two-step) high activity aluminizing at 850°C. The mechanism of this process has been investigated by carrying out the aluminizing process on electroplated Nickel on 316 stainless steel substrate at 1080°C in different durations of 0.25, 1, 2, 4 and 8 h (by investigation the Ni content in NiAl). Results showed that even in a short duration of 0.25 h the NiAl phase was formed. In 0.25 h NiAl phase with more than 50%at. of Al was formed while NiAl phase with less than 50%at. of Al was formed at 1, 2, 4 and 8 h. It is concluded that the mechanism of formation of NiAl coatings takes place primarily by inward Al diffusion initially, followed by an intermediate stage when the growth involves both inward Al and outward Ni diffusion and In the final stage, the outward diffusion of Ni dominates the coating formation process. The microstructure of the coatings sections were observed by optical microscopy and scanning electron microscopy. The phase analysis and the coating composition were investigated by XRD and EDS respectively.