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121.
Jin-sung Kim Jong-hyun Jeon Hoon Heo 《Journal of Mechanical Science and Technology》2013,27(2):549-556
The operation of a wind turbine generator involves natural uncertainty due to aerodynamic characteristics, resulting in a system that performs inefficiently. In general, the conventional controller now in wide use is not suitable for every operating point, because its tuning parameters and set-points do not meet the varying system characteristics. A study into an optimal control technique is conducted to reduce the negative effects of inherent uncertainty in system operation. In order to resolve the uncertainty problem, an optimal control method for an effective wind turbine generator is designed on the basis of a sensorless frame by utilizing a hybrid of the direct search optimization method (DSO) and the genetic algorithm (GA). This method is easy to implement and computation of functional derivatives is not necessary. The conventional GA is well known for its high performance in global optimization and its effectiveness in making ideal choices for control variables. The proposed DSO-GA hybrid differs from the conventional GA in terms of the sampling survey and the crossover operation. Moreover, the proposed multivariable optimal control strategy is a sensorless optimization technique that determines the pitch angle of the blades and the yaw angle of the nacelles to produce stable maximum power from a wind turbine system under steady-state operation. The proposed DSO-GA controller is implemented for a lab-scale wind turbine generator exposed to artificial wind, and the experimental results constitute a 3-D performance surface model of output voltage, which is used as an objective function for simulation. The optimization procedure with the objective function is carried out by means of the conventional and proposed methods, whose results reveal that the proposed DSO-GA optimizer yields far better performance in terms of generation number, convergence rate, and robustness. Both techniques are applied to a wind power generator through simulation and experiments. The performances are compared, and conclusions are drawn for each case. 相似文献
122.
Polypyrrole (PPy) microstructures with diverse shapes were synthesized in an aqueous inorganic salt medium including organic crystals and pyrrole (Py). A series of sulfobenzoic acid salt forms with various cations (K+, Na+, Li+, NH4+) in different positions (para, meta, ortho) of the sulfonate group on the benzene ring were used to form organic crystals as sacrificial templates. Using these crystals, we produced five different shapes of PPy microstructures (hexagonal microplates, curled nanofibers, lozenge-shaped microplates, rigid rods, parallelogram microplates), which replicated the shapes of the organic crystal templates through electrostatic interaction between the anionic crystal surfaces and the cationic PPy chains. In contrast, PPy that was polymerized without crystals showed bulky agglomerates of 200-500 nm size. The electrical properties were dictated by the molecular structures of the organic salt molecules used. While the highest conductivity (200.3 Scm−1) was observed in PPy using crystals of para-linked 4-sulfobenzoic acid monopotassium salt, the lowest conductivity (0.8 Scm−1) was observed in PPy prepared in the presence of crystals of ortho-linked 2-sulfobenzoic acid monoammonium salt. 相似文献
123.
Ultra-thin polypyrrole nanosheets (UPNSs) are fabricated by organic crystal surface-induced polymerization (OCSP) of pyrrole in an aqueous suspension containing hydrated crystals of sodium decylsulfonate (C10SO3Na) below the Krafft temperature using FeCl3 as an oxidant. The hydrated C10SO3Na crystals are used as templates through electrostatic binding of the cationic polypyrrole (PPy) chains oxidized by Fe(III) ions on the anionic C10SO3Na crystal surface. The resulting UPNSs have a single layer thickness of ∼21 nm, widths between 2 and 6 μm, and lengths greater than 10 μm. The UPNSs are composed of a single continuous PPy domain. Moreover, the UPNSs exhibit higher conductivity (30.6 Scm−1) and longer conjugation lengths than the PPy nanoparticles (2.4 Scm−1) prepared using emulsion polymerization. We systematically investigate the UPNSs as gas sensors for detecting and quantifying toxic gases such as HCl and NH3. The UPNSs exhibit much higher gas sensitivity and faster response times compared with the PPy nanoparticles. 相似文献
124.
A method and device for measuring glucose concentration in a scattering medium have been developed. A spectral range of 800-1800 nm is considered for wavelength selection because of its deeper penetration into biological tissue and the presence of a glucose absorption band. An algorithm based on selected wavelengths is proposed to minimize interference from other components. The optimal distance between the light source and the detector for diffuse reflectance measurement minimizes the influence of medium scattering. The proposed algorithm and measuring device are tested with a solution containing milk with added glucose. Glucose concentrations between 0 and 2000 mg/dl are determined with a correlation coefficient of 0.977. We also investigate the influence of concentration variations of other substances such as water, hemoglobin, albumin, and cholesterol when they are mixed in a scattering medium. 相似文献
125.
During steady state crack growth by diffusive cavitation at grain boundaries, crack tip fields are relaxed due to the presence of a cavitation zone. In the present analysis, analytic solutions for the actual crack tip stress fields and the crack velocity in the presence of cavitation zone consisting of continuously distributed cavities ahead of the crack tip are derived using the smeared volume concept. Results indicate that the r
–1/2 singularity is now attenuated to r
–1/2 + (0<<1/2) singularity. The singularity attenuation parameter is a function of the crack velocity and material parameters. The crack growth rate is related to the mode I stress intensity factor K by K
2 at relatively high load, K
n at intermediate load, and approaches zero at small load near K
th. Meanwhile, the cavitation zone extends further into the material due to the stress relaxation at the crack tip and the subsequent stress redistribution. Such relaxation effects become very distinct at low crack velocity and low applied load.
Key words: Creep crack growth, brittle material, diffusive cavity growth, sintering stress, crack tip stress field. 相似文献
126.
Shin H Lee KM Moon WK Jeon JU Lim G Pak YE Park JH Yoon KH 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2000,47(4):801-807
The feasibility of utilizing PZT films as future data storage media was investigated using a modified AFM. Applying voltages between a conductive AFM tip and the PZT films causes the switching of ferroelectric domains. The domains are observed using an EFM imaging technique. The experimental results and calculations revealed that the electrostatic force generated between the polarized area and the tip is a main contributor for the imaging of the polarized domains. The written features on ferroelectric films were less than 100 nm in diameter, implying the possibility of realizing data storage devices with ultra-high area density. The disappearance of the polarized images without any applied voltage was observed, which is a drawback in this application of PZT thin films. 相似文献
127.
A new technique for designing linear phase quadrature mirror filters (QMF) filters is proposed. These filters have the frequency responses of sharp and symmetrical transition characteristics, and the properties of perfect reconstruction and simple implementation.<> 相似文献
128.
Sangook Jun Yong-Hee Jeon Joohyun Rho Dong-ho Lee 《Journal of Mechanical Science and Technology》2006,20(1):133-146
Collaborative optimization(CO) is a multi-level decomposed methodology for a large-scale multidisciplinary design optimization(MDO).CO is known to have computational and organizational advantages. Its decomposed architecture removes a necessity of direct communication
among disciplines, guaranteeing their autonomy. However,CO has several problems at convergence characteristics and computation time. In this study, such features are discussed and
some suggestions are made to improve the performance ofCO. Only for the system level optimization, genetic algorithm is used and gradient-based method is used for subspace optimizers.
Moreover, response surface models are replaced as analyses in subspaces. In this manner,CO is applied to aero-structural design problems of the aircraft wing and its results are compared with the multidisciplinary
feasible (MDF) method and the original CO. Through these results, it is verified that the suggested approach improves convergence
characteristics and offers a proper solution. 相似文献
129.
130.