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Influences of different impeller trimming methods on flow characteristics of a centrifugal pump have been studied numerically and experimentally in this research. Different cases of trimmed impellers include straight trimmed impeller with and without remained shrouds, oblique trimmed impeller, triangular trimmed impeller, semi-circular trimmed impeller and polygon-shaped trimmed impeller. Verification of computational results has been investigated through comparison of experimental and numerical data as maximum deviation of 5.4 per cent has been observed. Results revealed that impeller trimming method has profound impact on the centrifugal pump performance as the highest head value has been achieved by employing the impeller with polygon-shaped trimmed shrouds at all flow rates, which is by 5 per cent higher than that of the conventional trimmed impellers (straight trimmed ones). Furthermore, it is also seen that the efficiency of polygon-shaped trimmed impeller was reduced by 3.6 per cent at BEP (Best Efficiency Point).

Heat transfer increase has been always the industries' aim. One of the methods to increase heat transfer is to manufacture heat exchangers with specific geometries such as wavy-tube heat exchangers. In this study, effects of inserting homogenous porous media to amplitudes of a wavy-tube heat exchanger have been investigated. A pipe with a length of 4λ (λ is the wavelength) was considered. Surface waviness has been introduced by L*, which is the ratio of wavelength to half of the amplitude. The computations were repeated for three different L* values including 11, 19 and 25. Effects of surface waviness and porous media properties including porosity and Darcy number on the heat transfer and pressure drop for a fully-developed laminar flow are provided. Results show that using porous media will lead to both heat transfer and pressure drop increase. The heat exchanger's efficieny was measured by Performance Evaluation Criteria (PEC) which is the ratio of heat transfer increase to pressure drop increase. It was observed that for 10-6 ≤ Da ≤ 10-4, filling the amplitudes out with porous media with thicknesses less than the amplitude will result in the maximum PEC while for 10-4 ≤ Da ≤ 10-2, filling out thoroughly will result in the maximum PEC. In addition, it was found that there is an optimized porosity to have the maximum PEC for the constant Darcy number.

Shielding failure has long been recognized as a possible mode of lightning flashover. This paper reports the development of a method for estimating the shielding failure number of transmission lines using the charge simulation method. The effects of towers, sags of conductors, and a perfectly conducting ground are represented in 3-D computation. In addition, the stepwise descending nature of a downward negative leader-streamer system is taken into account by using an appropriate progression model. Upward leader inception and propagation is also modeled utilizing critical equivalent streamer-length criterion as well as Rizk's formula. The results of the comparison between traditional and proposed techniques with different criteria are also presented. Index Terms--Charge simulation method (CSM), leader, shielding failure number (SFN), transmission line.

In this paper, the procedure for deriving the parameters of an IEEE governor-turbine model (particularly turbine model) based on a practical study case consisting of a 200-MW tandem compound, single reheat steam unit and its available heat balance data is presented. The main focus of the work is on presenting a regular procedure and using only available heat balance data of the steam unit, to be suitable for training the principles and details of such an approach for educational purposes. Unavailable parameters are approximated with simple thermodynamic assumptions, resulting in good correspondence to typical values. The model response to step changes for special scenarios is simulated and presented as well. Index Terms--Heat balance data, steam power plant, thermodynamic process, turbine model.

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Reduced drag, increased lift and, consequently, increased vital ratio and lift-to-drag coefficients are crucial in almost all efficient micro air vehicles. Riblet geometries use a variety of air vehicles. Further investigation on micro air vehicles is, however, necessary for enhanced development. Rectangular riblets on a rectangular micro air vehicle are computationally investigated. In this study, the governing equation of fluid flow is solved numerically; the turbulent model around the NACA S5020 airfoil section is covered by riblets either on both sides or on the upper side of the wings. Results show a difference of behavior in drag reduction due to the angle of attack on the airfoil. When the lift-to-drag coefficient of an angle of attack is at its maximum, an improvement can be observed, where lift-to-drag ratio increases, and drag decreases. Results for the two-side riblets show an increase in the lift-to-drag ratio as well; although the lift-to-drag coefficient and the drag reduction of riblets on both sides were comparatively less than that for riblets on the upside. [ABSTRACT FROM AUTHOR]

In this paper a novel method is presented to investigate lightning stroke attachment to earthed overhead transmission line structures. This method is based on the dynamic simulation of lightning downward leader movement toward the ground in three dimensions. To perform the simulation, a three-dimensional model for clouds, towers, wires, and a perfectly conducting ground is created. A stepping approach is also introduced in accordance with the field observations of negative downward lightning leaders to model the downward leader movement toward the ground. In each step of the leader movement, the electric field is computed numerically in all points of the simulation space and in three dimensions. Meanwhile, stable positive upward leader inception from some test points on earthed structures is tracked by means of an adopted precise model of the leader--streamer system to find the ultimate striking point. The main computational volume is occupied by an electric field calculation, which is performed using the charge simulation method. A direct movement model for the downward leader is also simulated and compared with the stepping approach. The percentage of strokes that attach to the phase wires, ground wires, and towers is extracted using this method. The maximum return stroke current for the strokes that attach to the phase wires is also computed by this dynamic simulation and is compared with the traditional methods that are available for transmission line lightning performance investigation. [ABSTRACT FROM AUTHOR]

Background: Evaluate the patient's safety status in Iranian hospitals using the Patient safety friendly hospital initiative (PSFHI) assessment tool provided by the World Health Organization. PSFHI assessment tool of 140 patient safety standards, they are classified as mandatory (20 standards), basic (90 standards) and advanced (30 standards). Mandatory standards are necessary criteria that hospitals must meet to register for PSFHI. The first stage of the patient safety program in Iran is to achieve the implementation of the mandatory standards to enter the patient safety friendly hospital program. We aimed to evaluate the patient's safety status in Iranian hospitals in terms of implementing mandatory patient safety standards., Methods: In this systematic review, articles were searched between 2001 and 2021 in Web of Science, PubMed, Scopus Google Scholar, and Iranian SID and Magiran databases. Keywords including patient safety, quality assessment, standards, patient safety friendly hospital, Iran were performed. These articles were evaluated independently by two researchers and the contradictions were discussed with the third author., Results: Finally, 7 eligible studies were included in the study. The highest score (75%) was related to the fourth domain of safe environment and the lowest score with (47%) was related to the second domain of engaging and interacting with the patient and the community. The overall average of compliance with standards in all four areas was 70%., Conclusion: Institutionalizing a patient safety culture, paying more attention to creating a culture to identify patients, educating staff and patients, and removing legal barriers, Increases the observance of mandatory patient safety standards in the Iran., Competing Interests: Conflict of interest The authors declare that there is no conflict of interest., (Copyright © 2022 Nekoei Moghadam et al. Published by Tehran University of Medical Sciences.)