Towards farm-level health management of offshore wind farms for maintenance improvements

This paper studies a conceptual architecture for health management of offshore wind farms. To this aim, various necessary enablers of a health management system are presented to improve reliability and availability while optimizing maintenance costs. The main focus lies on improving existing condition monitoring systems based on concepts of condition-based maintenance and reliability centered maintenance. A brief review of the relevant state-of-the-art is presented and gaps to be filled towards realization of such health management system are discussed.     

Energy and exergy analysis in solar drying of pistachio with air recycling system

A solar drier with and without air recycling (Methods I and II) along with a sun drying system (Method III) were used to reduce the moisture content of pistachio from 40 to ～5% (wet basis) at similar weight conditions. Although the ΔT’s of ambient air in Methods I and II reached, respectively, to 18 and 14°C, it did not increase more than 2°C in Method III. The drying air of Method I obtained ～55% more enthalpy from its solar collectors and transferred ～35% more heating energy to the product than the one in Method II. Consequently it’s thermal and pickup efficiencies became, respectively, 40 and 80% more than Method II. Although the highest exergy efficiencies of Methods I and II were equal to each other (～95%), the maximum exergy loss of Method I was higher than Method II due to its higher air temperature and pressure loss (because of continuous air circulation). Although its energy utilization ratio and drying rate were, respectively, 30% more than Method II and 20% higher than Method III, its drying time was 20 and 30% less than the ones in Methods II and III. Overall, the pistachio dried with Method I used much less energy than those dried with other methods and had a higher quality than those dried with commercial driers due to drying temperature <50°C.     

Simulation of dielectric behavior in RFeO$$_{}$$ orthoferrite ceramics (R = rare earth metals)

Due to their colossal dielectric constant (CDC), \(\hbox {RFeO}_{3}\), orthoferrite ceramics (R = rare earth metal) have recently attracted much attention. In the present research, the dielectric constants of \(\hbox {RFeO}_{3}\) orthoferrite ceramics, whether with or without CDC, have been simulated. The type of synthesis method, the type of R material, temperature, and frequency as the effective parameters on the dielectric behavior are introduced to the model. Another input parameter is the ratio of \(\hbox {Fe}^{+2}/\hbox {Fe}^{+3}\) peak area (in the XPS diagram), which is the most important parameter that affects the CDC behavior. Initially, a colossal database is formed by means of WebPlotDigitizer software and 2930 experimental data, and then the simulation is carried out through gene expression programming. Two case studies are also performed on \(\hbox {PrFeO}_{3}\) and \(\hbox {NdFeO}_{3}\) orthoferrite ceramics to validate the accuracy of the presented model. \(\hbox {PrFeO}_{3}\) exhibits significant CDC behavior whereas the \(\hbox {NdFeO}_{3}\) ceramic samples possess little CDC property, both of which were precisely simulated by the model. Two-dimensional tenth-degree equations resulting from the model predict the dielectric constant variations accurately.     

A group-based security scheme for wireless sensor networks

In recent years, wireless sensor networks have been a very popular research topic, offering a treasure trove of systems, networking, hardware, security, and application-related problems. Distributed nature and their deployment in remote areas, these networks are vulnerable to numerous security threats that can adversely affect their proper functioning. The problem is more critical if its purpose is for some mission-critical applications such as in a tactical battlefield. This paper presents a security scheme for group-based distributed wireless sensor networks. Our first goal is to devise a group-based secure wireless sensor network. We exploit the multi-line version of matrix key distribution technique and Gaussian distribution to achieve this goal. Secondly, security mechanisms are proposed for such a group-based network architecture in which sensed data collected at numerous, inexpensive sensor nodes are filtered by local processing on its way through more capable and compromise-tolerant reporting nodes. We address the upstream requirement that reporting nodes authenticate data produced by sensors before aggregating and the downstream requirement that sensors authenticates commands disseminated from reporting nodes. Security analysis is presented to quantify the strength of the proposed scheme against security threats. Through simulations, we validate the analytical results.     

Synthesis route and three different core-shell impacts on magnetic characterization of gadolinium oxide-based nanoparticles as new contrast agents for molecular magnetic resonance imaging

Despite its good resolution, magnetic resonance imaging intrinsically has low sensitivity. Recently, contrast agent nanoparticles have been used as sensitivity and contrast enhancer. The aim of this study was to investigate a new controlled synthesis method for gadolinium oxide-based nanoparticle preparation. For this purpose, diethyleneglycol coating of gadolinium oxide (Gd₂O₃-DEG) was performed using new supervised polyol route, and small particulate gadolinium oxide (SPGO) PEGylation was obtained with methoxy-polyethylene-glycol-silane (550 and 2,000 Da) coatings as SPGO-mPEG-silane550 and 2,000, respectively. Physicochemical characterization and magnetic properties of these three contrast agents in comparison with conventional Gd-DTPA were verified by dynamic light scattering transmission electron microscopy, Fourier transform infrared spectroscopy, inductively coupled plasma, X-ray diffraction, vibrating sample magnetometer, and the signal intensity and relaxivity measurements were performed using 1.5-T MRI scanner.As a result, the nanoparticle sizes of Gd₂O₃-DEG, SPGO-mPEG-silane550, and SPGO-mPEG-silane2000 could be reached to 5.9, 51.3, 194.2 nm, respectively. The image signal intensity and longitudinal (r₁) and transverse relaxivity (r₂) measurements in different concentrations (0.3 to approximately 2.5 mM), revealed the r₂/r₁ ratios of 1.13, 0.89, 33.34, and 33.72 for Gd-DTPA, Gd₂O₃-DEG, SPGO-mPEG-silane550, and SPGO-mPEG-silane2000, respectively.The achievement of new synthesis route of Gd₂O₃-DEG resulted in lower r₂/r₁ ratio for Gd₂O₃-DEG than Gd-DTPA and other previous synthesized methods by this and other groups. The smaller r₂/r₁ ratios of two PEGylated-SPGO contrast agents in our study in comparison with r₂/r₁ ratio of previous PEGylation (r₂/r₁ = 81.9 for mPEG-silane 6,000 MW) showed that these new three introduced contrast agents could potentially be proper contrast enhancers for cellular and molecular MR imaging.     

Plasma effects in semiconducting nanowire growth

Three case studies are presented to show low-temperature plasma-specific effects in the solution of (i) effective control of nucleation and growth; (ii) environmental friendliness; and (iii) energy efficiency critical issues in semiconducting nanowire growth. The first case (related to (i) and (iii)) shows that in catalytic growth of Si nanowires, plasma-specific effects lead to a substantial increase in growth rates, decrease of the minimum nanowire thickness, and much faster nanowire nucleation at the same growth temperatures. For nucleation and growth of nanowires of the same thickness, much lower temperatures are required. In the second example (related to (ii)), we produce Si nanowire networks with controllable nanowire thickness, length, and area density without any catalyst or external supply of Si building material. This case is an environmentally-friendly alternative to the commonly used Si microfabrication based on a highly-toxic silane precursor gas. The third example is related to (iii) and demonstrates that ZnO nanowires can be synthesized in plasma-enhanced CVD at significantly lower process temperatures than in similar neutral gas-based processes and without compromising structural quality and performance of the nanowires. Our results are relevant to the development of next-generation nanoelectronic, optoelectronic, energy conversion and sensing devices based on semiconducting nanowires.     

Semi-active vibration control of an eleven degrees of freedom suspension system using neuro inverse model of magnetorheological dampers

A semi-active controller-based neural network for a suspension system with magnetorheological (MR) dampers is presented and evaluated. An inverse neural network model (NIMR) is constructed to replicate the inverse dynamics of the MR damper. The typical control strategies are linear quadratic regulator (LQR) and linear quadratic gaussian (LQG) controllers with a clipped optimal control algorithm, while inherent time-delay and non-linear properties of MR damper lie in these strategies. LQR part of LQG controller is also designed to produce the optimal control force. The LQG controller and the NIMR models are linked to control the system. The effectiveness of the NIMR is illustrated and verified using simulated responses of a full-car model. The results demonstrate that by using the NIMR model, the MR damper force can be commanded to follow closely the desirable optimal control force. The results also show that the control system is effective and achieves better performance and less control effort than the optimal in improving the service life of the suspension system and the ride comfort of a car.     

Employing reduced surface field technique by a P‐type region in 4H‐SiC metal semiconductor field effect transistors for increasing breakdown voltage

In this paper, we employ the Reduced Surface Field technique in metal semiconductor field effect transistors (MESFETs) by a P‐type region above the active layer near gate (PR‐MESFET). Electric field distribution can be made more uniform by a new depletion region in the active layer of the proposed structure that is created by a P‐type region. ‏‏Therefore, the electric field peak at the gate edge decreases, and the breakdown voltage increases. On the basis of our simulation results, the breakdown voltage increases as compared with the conventional bulk 4H‐SiC MESFET (CB‐MESFET) and the spacer bulk 4H‐SiC MESFET (SB‐MESFET). Detailed numerical simulations demonstrate that for proposed structure due to decrease in parasitic gate‐to‐drain capacitor, maximum oscillation frequency increases with respect to SB‐MESFET. Our simulation results show that output current slightly decreases in comparison with CB‐MESFET. Copyright © 2012 John Wiley & Sons, Ltd.     

Displacement measurement of the soil nail walls by using close range photogrammetry and introduction of CPDA method

Displacement measurement of the soil nail walls is a very important task in monitoring tiny movements in excavations to prevent disastrous accidents like wall collapsing. In building construction projects, this is usually done by either micro-geodesy or accurate instrumentation methods. In this research, for the first time, the use of close range photogrammetry in displacement measurement of the soil nail walls has been proposed and experienced. For this, a photogrammetric system was designed, implemented and evaluated. Proposed system with three separate methods for displacement measurement, which one of them was submitted for the first time (CPDA), was implemented. The evaluation results the accuracy of 3 mm is achievable in determining the point coordinates with a precision of 8 mm in displacement measurement of soil nail walls. Due to the efficiency, low cost, high accuracy, high speed of observations along with the simplicity of implementation of close range photogrammetry, it is suggested as a proper alternative to the traditional methods.     

Dynamic characterization for the dielectric electroactive polymer fundamental sheet

A study into the appropriateness of characterizing the dynamics of the dielectric electroactive polymer (DEAP) fundamental sheet has been performed. Whereby a model describing the dynamics of the DEAP fundamental sheet is developed, parameters of the models are determined using experimental/simulation results, and verification has been conducted to determine the precision of the dynamic model. The precision for the DEAP sheet-obtained dynamic model could not be verified unless some parameters characterizing the material properties are found. For this purpose, a set of preparatory experiments are done in order to find the material properties “Young’s modulus and damping”. The testing for finding the material properties is requested before doing the dynamic analysis; both material characterization and dynamic analysis tests are performed using the developed testing rig which will be described in the paper. The results of this study highlight the dependency of the material dynamics on the mechanical fixture of the material, whereby the range of operation can be reduced to lower frequencies or expanded to higher frequencies when the mechanical fixture is designed for a certain application. The test results for the material show a relatively visible error between 0 and 20 Hz, but the error diverges after this range was stimulated when exceeding the natural frequency of the system, leading to nonstable state affecting the controllability of the actuated material. The following error is established due to the static friction in the setup and mainly as expected before the ignorance of the polymer creep, as exhibited through the dynamic experimentation verified by an excellent correlation whenever viscoelastic property is considered.