Wind turbine speed control of a contactless piezoelectric wind energy harvester

ABSTRACT

Wind turbine control is an important task to make the electricity generation secure in terms of energy demand and machine safety. It also yields to control the desired power level and optimized energy because of the assignment of turbine speed. The contactless piezoelectric wind energy harvester (CPWEH) used in this study has three piezoelectric layers located around the shaft with 120 degrees apart and they are buckled by the magnetic force without any physical contact. The superiority of this device is to generate energy for low wind speeds such as 1.5 m/s. However, for high speeds, high total harmonic distortions (THDs) govern the waveforms, thus controlling the turbine speed becomes necessary for optimizing the output power. Encouraged by this, a small low inertia dc generator is coupled with the wind turbine, and the generator terminals are connected to a resistor through a power switch to generate a braking torque that opposes to wind speed direction. By controlling the switch properly, turbine speed is ensured to remain within a certain band, which accordingly prevents the turbine from rotating very fast at damaging wind speeds. Several experiments are performed on the developed CPWEH with/without the presented control scheme which prove the existence of promising performance of our proposal.     

Investigation of the soil amplification factor in the Adapazari region

Turkey is located on the highly active Eurasian plate. A very active strike slip fault, the North Anatolian Fault Zone (NAFZ), crosses Turkey from east to west; earthquakes occurred on this fault on August 17, 1999 (Kocaeli) and November 12, 1999 (Düzce). Regional geology and subsoil conditions can significantly change the characteristics of ground motion. For this reason, determining soil amplification during an earthquake, especially for soft soils, is a very important topic for researchers. In this study, one dimensional ground response analyses were performed for selected Adapazari sites using the August 17, 1999 Kocaeli earthquake strong ground motion record with SHAKE2000 software. Soil characteristics and depth to engineering bedrock at the selected sites are different and the observed level of structural damage at these sites during the Kocaeli earthquake was also different. Calculated soil surface response spectrums at these sites were compared with the recommended design spectra of the Turkish Earthquake Code and the Eurocode 8. According to one dimensional ground response analyses, the calculated response spectra of the selected sites exceed the recommended design spectra of the Turkish Earthquake Code and the Eurocode 8. Calculations show that higher amplification ratios occur at higher periods due to soil behaviour. Results of this study indicate that local geological conditions may amplify ground motion at some periods and, due to this amplification, the calculated response spectra may exceed the recommended design spectra. Therefore, it is clear that local site conditions must be considered for earthquake-resistant engineering designs on soft alluvial soil deposits.     

An attitude scale for smart board use in education: Validity and reliability studies

The main purpose of this study was to develop an instrument to measure the attitudes of elementary students towards smart board (SB) use in education. A sequential exploratory mixed method was used. So the study started with a qualitative approach to establish the content and face validity of the scale, followed by a quantitative approach to test the construct validity and reliability of the scale items. Ten students, one teacher trainer specialized in SB use, three teachers experienced in SB use, and a language expert participated in the qualitative part. Data from 203 elementary students from two local schools in Malatya, Turkey, were used to test the psychometric properties of ‘smart board attitude scale’ (SBAS). The exploratory factor analysis (FA) yielded a two-factor model with 10 items. The goodness of fit indices produced by confirmatory FA confirmed the fit of the model to the data. Reliability of SBAS was also proved through multi-analyses.     

Swage casting of A380 alloy

Swage casting is a new casting technique which combines the advantages of squeeze, centrifugal and semi-solid casting methods. In this new casting method, components with one rotating axis can be produced on a swage casting machine from molten metal in a one-step operation. A shape like a “bomb-body” is chosen to demonstrate the advantages of this new method by using A380 Al–Si–Cu alloy. The same alloy is also cast with centrifugal and squeeze casting methods. In this study, the swage casting method and its features are briefly described. The final microstructures, mechanical properties and amount of porosity of the cast pieces produced by squeeze, centrifugal and swage casting methods are compared. Swage cast pieces showed a different composition of microstructure that consists of fine dendritic particles at the chill ends and a mixture of spherical and rosette shaped particles at the core. The swage cast pieces also have a slightly higher mechanical strength as indicated by tensile strength and Brinell hardness values.     

Evaluation of damage to light structures erected on a fill material rich in expansive soil

The paper reports a study of the cause of defects in light structures and the toppling of a wall constructed on a fill material rich in Ankara clay. Laboratory tests were carried out on vertical and horizontal samples from boreholes and a trial pit was excavated near the damaged structures. The results showed that in the vicinity of the toppled wall, swelling pressures in the horizontal direction were greater than those measured in the vertical direction. The swelling properties of the fill material were higher than those of original Ankara clay as determined previously by other investigators, suggesting that breakdown of the cementing bonds and a change in the fabric are the main factors affecting the swelling pressure of disturbed and compacted expansive soils. The calculations to predict uplift showed a good agreement with the observations in the damaged structures. It is concluded that swelling was the main cause of the damage to the light structures at the study site and resulted from the highly expansive nature of the fill material, poor drainage, the semi-arid climate, poor construction methods and ineffective precautions. Some recommendations for minimizing the effects of swelling at the study site are briefly outlined.     

Assessment of the site amplifications and predominant site periods for Saruhanlı, in an earthquake-prone region of Turkey

An earthquake-resistant design should include the effect of local site conditions on the seismic ground motions. In this study, ground response analyses in 22 locations around the developing town of Saruhanlı in the Aegean Region of Turkey were undertaken using SHAKE software. The ground response analyses for a typical soil profile considered various modulus reduction and damping curves including effective confining stress and a plasticity index dependent model. The confining stress-dependent soil models and shear-wave velocity profile resulted in higher amplification ratios and lower predominant periods. High acceleration ratios (>3) and lower predominant site periods were found in the eastern part of the site such that buildings of ten or more storeys would be severely damaged.     

A new catalyst of AlCu@ZnO for hydrogen evolution reaction

Thin films of undoped ZnO, Al-doped ZnO, Cu-doped ZnO, and AlCu@ZnO deposited on indium tin oxide were performed by the sol-gel spin coating method. The prepared ZnO thin films were investigated for their structural and electrical properties after annealing at 500 °C for 1 h. ZnO thin films were characterized by electrochemical impedance spectroscopy, linear sweep voltammetry, scanning electron microscopy, Fourier transform infrared spectroscopy and Mott Schottky. According to the results obtained from the Nyquist diagrams of the ZnO thin films, the resistance value was found to decrease with binary doping and the resistance value was found to be lowest in AlCu@ZnO doped thin film containing 0.01 M Al and 0.1 M Cu. As ZnO thin films go to cathodic potentials, it is seen that the cathodic current value of ZnO with undoped is the lowest. It has been found that only Al and Cu doping showed less cathodic current than double doping.     

Chemical,thermal, and mechanical properties and ultraviolet transmittance of novel nano-hydroxyapatite/polyethylene terephthalate milk bottles

Polyethylene terephthalate (PET)/nano-hydroxyapatite (nHAp) composite granules were obtained using twin-screw extruder. Preforms were prepared by injection molding and then PET/nHAp bottles were produced by blow molding. For PET bottles with nHAp, the migration amounts of carboxylic acid (COOH), acetaldehyde (AA), diethylene glycol (DEG), and isophthalic acid (IPA); glass transition temperature (T_g); melting temperature (T_m); and the maximum crystallization temperature (T_cry) were measured. The load-carrying capacity, burst strength, stress cracking, and regional material distribution tests were carried out on the bottles. X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and ultraviolet transmittance analyses were conducted to explain the changes in mechanical, chemical, physical properties, and light transmission of bottles. It was found out that the COOH amount increased and the AA content decreased with increasing nHAp amount. On the other hand, no change was observed in the amounts of DEG and IPA. Although the mechanical properties such as load-carrying capacity and burst strength of the bottles have improved, it has been determined that the standard environmental stress crack resistance test procedure cannot be applied to such a composite. Experimental findings indicate that nHAp disrupts the chemical structure of PET and it isolates harmful chemicals such as AA by forming intermolecular bonds. Moreover, with the addition of up to 0.8% nHAp, PET bottles block the light transmission approximately 80% within 400–700 nm wave length zone. The study demonstrates that the PET/nHAp composite bottles can be used in the food industry, particularly in the packaging of milk and milk products which are vulnerable to light exposure.     

Use of organosolv lignin in phenol-formaldehyde resins for particleboard production: II. Particleboard production and properties

The objective of this work was to demonstrate the utility of lignin-based resins designed for application as an adhesive in the production of particleboard. Bond qualities of lignin-phenol-formaldehyde resins, phenolated-lignin-formaldehyde resins and commercial phenol-formaldehyde (PF-com) resin were assessed by using an automatic bonding evaluation system, prior to production of particleboards. In order to evaluate the quality of lignin-based resins, particleboards were produced and physical and mechanical properties were investigated. These physical properties included internal bond, modules of rupture and modulus of elasticity. Thickness swell and water absorption properties of particleboards bonded with lignin-based resins were also determined. The lignin-based resins have been reported previously in Part I of this study. The results showed that particleboards bonded with phenolated-lignin formaldehyde resins (up to 30% lignin content) exhibited similar physical and mechanical properties when compared to particleboards bonded with PF-com. The work has indicated that phenolated-lignin formaldehyde resins (up to 30% substitution level) can be used successfully as a wood adhesive for constructing particleboard. The performance of these panels is comparable to those of boards made using PF-com resin.