A CFD approach for modeling the rime-ice accretion process on a horizontal-axis wind turbine

The main objective of this paper is to model the rime-ice accretion process on a horizontal-axis wind turbine (HAWT) operating under icing conditions. The model calculation procedure was divided into two stages. The first stage consists of computing the two-phase flow that is composed of air and water phases. The two-phase flow was solved using the Eulerian–Eulerian approach with the help of Fluent, a commercial CFD code. At the end of the calculations, it is possible to obtain the local volume fraction and local water incidence velocity, which can be used to estimate the local collision coefficient. In the second stage, the thickness of the newly accreted ice layer was calculated and the geometry so obtained was processed with an in-house smoothing algorithm. From the model simulation, it is possible to obtain the 3-D ice shape, as well as the ice load on the HAWT blade, which can then be used to analyze the performance of the HAWT under icing conditions, or to help develop a feasible de-icing solution. The important model input parameters include: air speed, median volume diameter (MVD) of water droplets, liquid water content (LWC) and air temperature. The turbine under consideration is a NREL VI turbine that rotates along its axis at a constant angular speed. In the flow domain, a rotating reference frame was defined to account for the angular movement of the wind turbine. The results reveal, among other things, ice geometry information that can otherwise hardly be obtained by on-site observations.     

Iranian Medical Universities in SCIE: evaluation of address variation

Patenting and licensing is not only a significant method of university knowledge transfer, but also an important indicator for measuring academic R&D strength and knowledge utilization. The methodologies of quantitative and qualitative analysis, including a special patent h-index indicator to assess patenting quality, were used to examine university patenting worldwide. Analysis of university patenting from 1998 to 2008 showed a significant overall global increase in which Chinese academia stands out: most of the top 20 universities in patenting in 2008 were in China. However, a low rate of utilization of Chinese academic patents may have roots in: (1) university research evaluation system encourages the patent production more, rather than the utilization; (2) problems in the formal mechanisms for university technology transfer and licensing, (3) industry’s limited expectation and receptive capabilities and/or (4) a mismatch between the interests of the two institutional spheres. The next action to be taken by government, university and industry in China will be to explore strategies for improving academic patent quality and industry take-up.     

Effects of Space Charge on the Discharge Process in an Icicle/Iced-Plate Electrode System under Positive DC Voltage

Using an icicle/iced-plate system, the corona discharge at the icicle tip was investigated under positive DC voltage. The discharge pulses were recorded and analyzed. The relationship between the discharge magnitude and the time interval before the pulse was examined. The mechanisms underlying the corona discharges at icicle tips were investigated. The influence of space charge on the discharge and the effects of the applied voltage on the time interval between two pulses were also investigated. Finally, a model for calculating the drift and diffusion of the space charge cloud was presented.     

Study of the Development of Positive Streamers Along an Ice Surface

This paper presents the results of fundamental investigations on the inception and propagation of corona discharge on an ice surface stressed with a standard lightning impulse voltage. High-speed photography and photomultiplier techniques were used to observe and record the propagation of the streamers. The effects of several experimental parameters such as freezing water conductivity and HV rod electrode radius on the streamer inception parameters were investigated. Moreover, time to first streamer, inception voltage and corresponding field, as well as streamer propagation velocity and charge deposited by a streamer on ice surface were measured. The results are discussed and emphases are laid on the main factors influencing the development of positive streamers on ice surface.     

Influences of nonassociated flow rules on three-dimensional seismic stability of loaded slopes

The influences of soil dilatancy angle on three-dimensional (3D) seismic stability of locally-loaded slopes in nonassociated flow rule materials were investigated using a new rotational collapse mechanism and quasi-static coefficient concept. Extended Bishop method and Boussinesq theorem were employed to establish the stress distribution along the rupture surfaces that are required to obtain the rate of internal energy dissipation for the nonassociated flow rule materials in rotational collapse mechanisms. Good agreement was observed by comparing the current results with those obtained using the translational or rotational mechanisms and numerical finite difference method. The results indicate that the seismic stability of slopes reduces by decreasing the dilatancy angle for nonassociated flow rule materials. The amount of the mentioned decrease is more significant in the case of mild slopes in frictional soils. A nearly infinite slope under local loading, whether its critical failure surface is 2D or 3D, not only depends on the magnitude of the external load, but also depends on the dilatancy angle of soil and the coefficient of seismic load.     

Effect of ultraviolet-A radiation on surface structure,thermal, and mechanical and electrical properties of liquid silicone rubber

Liquid silicone rubber (LSR) products outdoors are often subjected to high intensity of ultraviolet (UV)-A radiation. However, the influence of UV-A radiation on LSR is rarely studied. To study the influence of UV-A radiation on LSR, the surface of LSR with UV-A aging time was characterized by tests at different detection depths [X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR)]. The operation properties (thermal stability and mechanical and electrical properties) for outdoor insulators were also analyzed. It was found that the porous surface and the loose layer of LSR increased, but the growth rate of them decreased as UV-A aging time increased. SiO₂ fillers were lost in the surface. C H bonds in  CH₃ and  CH₃ in Si CH₃ increased with aging time. The increased crosslinking density increased the thermal stability, hardness, dielectric loss tangent, relative dielectric constant, and volume resistivity and decreased elongation-at-break. The mechanical strength initially increased and then decreased. Based on the proposed aging mechanism, the UV-A resistance of LSR can be improved by reducing the amount of hydrogen-containing silicone oil and by increasing the molecular weight of raw rubber. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47652.     

Effect of electron beam irradiation dose on the rheology,morphology, and thermal properties of branched polypropylene/polybutene‐1 blend

The aim of this work is to study the influence of electron beam irradiation on the structure of polypropylene (PP)/polybutene‐1 (PB‐1) blend in the branching process. The blend with 10 wt% of PB‐1 and 0.5 wt% trimethylolpropane trimethacrylate monomer is prepared and irradiated at different doses. The rheological properties of the melts in shear and extensional mode were evaluated, and their thermal behavior, crystalline structure, and morphology are studied by differential scanning calorimetry, wide‐angle X‐ray diffraction, and scanning electron microscopy. The presence of long chain branched structure is approved by higher zero‐shear viscosity (η₀), longer relaxation time and pronounced strain‐hardening behavior in the within the range of dose tested. By increasing the irradiation dose and enhancing chain scission in the backbone and long chain branches, the decline in melting temperature, duplication of melting peak, and the decrease in zero‐shear viscosity were observed. The morphological study of the blends before and after irradiation revealed no considerable change in PB‐1 droplet size and their distribution in the PP matrix. The emulsion theoretical models could predict well the rheological behavior of all samples and no significant change was observed on the interfacial interaction of PP and PB‐1. POLYM. ENG. SCI., 54:1747–1756, 2014. © 2013 Society of Plastics Engineers     

Histopathological graded liver lesions: what role does the IVIM analysis method have?

Magnetic Resonance Materials in Physics, Biology and Medicine - This study aims to investigate three different image processing methods on quantitative parameters of IVIM sequence, as well as...     

Variation of Catechin,epicatechin and their enantiomers concentrations before and after wheat cultivar-Puccinia triticina infection

Three wheat cultivars (Boolani, Roushan and Fornota) were inoculated with Puccinia triticina strain 140 and placed in greenhouse and concentrations of catechin, epicatechin and their enantiomers were monitored in three steps; healthy leaves before and after exposed and also diseased leaves after exposed. The concentration of catechin and epicatechin in infected plant ranged from 4.43 to 11.00 and 1.65 to 3.68 times higher than those in non-infected plant, respectively. Also, the healthy leaves of infected plants had more amounts of catechin and epicatechin than diseased leaves. Study of chiral separations by cellulose column, indicated that both enantiomers of catechin were found in healthy leaves of non-infected plants. However, in the leaves of wheat which were exposed to P. triticina, the concentration of (+) catechin increased while (−)-catechin disappeared in healthy and diseased leaves of infected plants. Furthermore, only (−)-epicatechin was found in all the samples. So, infection by pathogen caused a change in the biosynthesis and accumulation of catechin and also a change in the enantiomeric ration of catechin enantiomers in the leaves.