The effect of different tornado wind fields on the response of transmission line structures

Nima Ezami,Nima Ezami,Ahmed Hamada,Mohamed Hamada 한국풍공학회 2022 Wind and Structures, An International Journal (WAS Vol.34 No.2

Majority of transmission line system failures at many locations worldwide have been caused by severe localized wind events in the form of tornadoes and downbursts. This study evaluates the structural response of two different transmission line systems under equivalent F2 tornadoes obtained from real incidents. Two multi-span self-supported transmission line systems are considered in the study. Nonlinear three-dimensional finite element models are developed for both systems. The finite element models simulate six spans and five towers. Computational Fluid Dynamics (CFD) simulations are used to develop the tornado wind fields. Using a proper scaling method for geometry and velocity, full-scale tornado flow fields for the Stockton, KS, 2005 and Goshen County WY, 2009 are developed and considered together with a previously developed tornado wind field. The tornado wind profiles are obtained in terms of tangential, radial, and axial velocities. The simulated tornadoes are then normalized to the maximum velocity value for F2 tornadoes in order to compare the effect of different tornadoes having an equal magnitude. The tornado wind fields are incorporated into a three-dimensional finite element model. By varying the location of the tornado relative to the transmission line systems, base shears of the tower of interest and peak internal forces in the tower members are evaluated. Sensitivity analysis is conducted to assess the variation of the structural behaviour of the studied transmission lines associated with the location of the tornado relative to the tower of interest. The tornado-induced forces in both lines due to the three different normalized tornadoes are compared with corresponding values evaluated using the simplified load case method recently incorporated in the ASCE-74 (2020) guidelines, which was previously developed based on the research conducted at Western University

Qualified sperm selection based on the rheotaxis and thigmotaxis in a microfluidic system

Nima Ahmadkhani,Maryam Saadatmand,Somaieh Kazemnejad,MohammadJafar Abdekhodaie 대한의용생체공학회 2023 Biomedical Engineering Letters (BMEL) Vol.13 No.4

Microfluidic systems with the ability to mimic the female reproductive tract (FRT) and sperm features have emerged aspromising methods to separate sperm with higher quality for the assistant reproductive technology. Thereby, we designed andfabricated a microfluidic system based on FRT features with a focus on rheotaxis and thigmotaxis for passive sperm separation. In this regard, four various geometries (linear, square, zigzag, and sinusoidal) were designed, and the effect of rheotaxisand thigmotaxis were investigated. Although separated sperm in all microchannels were 100% motile, non-linear geometrieswere more effective than linear geometry in the term of separating the progressive sperm with high quality. In the presenceof upstream flow, periodical changes in the slope of walls (in non-linear geometries) give rise to the periodical facing spermwith a high flow rate in the middle of microchannels, which was a reason for the high quality of separated sperm. However,because of sharp corners in the square and zigzag microchannels that create dead zones with a lack of upstream flow, whichis noticeable via simulation results, these geometries have obstacles against sperm swimming toward the outlet, whichwas proved by image analysis. The sinusoidal geometry showed the highest enhancement level of the designed geometriescompared to the linear geometry. Separated sperm exhibited 34.7% normal morphology, 100% motility, and 100% viabilityin the sinusoidal geometry. Therefore, the periodic change in the position of sperm from one wall to another wall can be astrategy for separating sperm with high quality.

Synergistic interactions with a high intraoperative expander fill volume increase the risk for mastectomy flap necrosis

Nima Khavanin,Sumanas Jordan,Francis Lovecchio,Neil A. Fine,John Kim 한국유방암학회 2013 Journal of breast cancer Vol.16 No.4

Purpose: Prosthetic-based breast reconstruction is performedwith increasing frequency in the United States. Major mastectomyskin flap necrosis is a significant complication with outcomesranging from poor aesthetic appearance to reconstructivefailure. The present study aimed to explore the interactionsbetween intraoperative fill and other risk factors on the incidenceof flap necrosis in patients undergoing mastectomy with immediateexpander/implant-based reconstruction. Methods: A retrospectivereview of 966 consecutive patients (1,409 breasts) whounderwent skin or nipple sparing mastectomy with immediatetissue expander reconstruction at a single institution was conducted. Age, body mass index, hypertension, smoking status,premastectomy and postmastectomy radiation, acellular dermalmatrix use, and application of the tumescent mastectomy techniquewere analyzed as potential predictors of flap necrosis bothindependently and as synergistic variables with high intraoperativefill. The following three measures of interaction were calculated:relative excess risk due to interaction, attributable proportionof risk due to interaction, and synergy index (SI). Results: Intraoperativetissue expander fill volume was high (≥66.7% of themaximum volume) in 40.9% (576 of 1,409 breasts) of cases. Theunadjusted flap necrosis rate was greater in the high intraoperativefill cohort than in the low fill cohort (10.4% vs. 7.1%, p=0.027). Multivariate logistic regression did not identify high intraoperativefill volume as an independent risk factor for flap necrosis(odds ratio 1.442, 95% confidence interval 0.973-2.137, p=0.068). However, four risk factors were identified that interactedsignificantly with intraoperative fill volume, namely tumescence,age, hypertension, and obesity. The SI, or the departure from additiverisks, was largest for tumescence (SI, 25.3), followed byhypertension (SI, 2.39), obesity (SI, 2.28), and age older than 50years (SI, 1.17). Conclusion: In the postmastectomy, hypovascularmilieu, multiple risk factors decreasing flap perfusion interactwith high intraoperative fill volume to cross a threshold and synergisticallyincrease the risk of flap necrosis.

ZMP Analysis for Dynamic Walking of a Passivity-based Biped Robot with Flat Feet

Nima Fatehi,Adel Akbarimajd,Masoud Asadpour 제어로봇시스템학회 2010 제어로봇시스템학회 국제학술대회 논문집 Vol.2010 No.10

Zero moment point has been usually employed for balance keeping and walking analysis of active biped robots with bent knees, while balance and walking stability analysis of passive robots has been done using cyclic analysis approaches. While the problem in general is common, the two approaches have been separated in the literature for two different classes of passivity-based and ZMP-based robots. In this paper we have made a ZMP analysis for a passivity-based biped robot. The robot has been simulated using MSC Adams and Matlab/Simulink and a stable walking is achieved for a defined walking policy which is based on passivity-based walking with hips and ankles actuated and knee joints considered passive. The trajectory of ZMP is extracted and discussed during a stable walking. The role of Achill"s spring on ZMP is discussed and the overall profile of ZMP trajectory and its changes at specific crucial events, like knee strike and heel strike, is analyzed.

Energy-Aware Service Composition Mechanism in Grid Computing Using an Ant Colony Optimization Algorithm

Nima Jafari Navimipour,Saied Asghari 대한전자공학회 2017 대한전자공학회 학술대회 Vol.2017 No.1

In the past few years, with the extension of distribution systems such as the Internet and web services, grid systems emerged to be one of the utilizable solutions to response the huge computing needs. Grid systems offer a vast amount of calculating resources from multiple administrative domains to reach the main goal. One of the main challenges in these systems is to choose the appropriate services for combination. According to the service-oriented architecture paradigm, the composite service consists of a set of abstract tasks interconnected by various workflow constructs. Consumed energy in these systems is an important issue; however, in many of the previous methods, it is not considered. Therefore, this paper proposes a new service composition mechanism based on an ant colony optimization algorithm (ACO) to reduce the consumed energy. The ACO algorithm is a famous meta-heuristic algorithm where ants try to select the best node for moving in each iteration. Java programming language is used to evaluate the proposed method in terms of the consumed energy and execution time. The obtained results showed better performance of the proposed algorithm in comparison with the greedy algorithm.

4E Analysis and Design of a Combined Cycle with a Geothermal Condensing System in Iranian Moghan Diesel Power Plant

Nima Norouzi 대한설비공학회 2020 International Journal Of Air-Conditioning and Refr Vol.28 No.3

Considering the new issues human society faces now, environmental issues, and climate change is one of the primary and most essential phenomena which have been caused by the unsustainable lifestyle of men over the last two centuries. Power and energy are some of the leading role players of today’s human lifestyle and one of the most effective in which the environment is affected. This article represents the results of research over the possibility of recovering waste heat and determination of design parameters of a waste heat steam generator for medium speed set of diesel generators, with the rated 42 MW capacity and are used for power generation. The main goals of this study are to manage the waste heat of the engines and to help the severe water leakage of the power plant. In this paper, for managing the waste heat, a combined steam cycle is being designed for this process. This system added 19 MW the overall electricity generation, and the exergy and energy efficiencies of the system are being increased by 29.2% and 32.8%. Moreover, finally, a geothermal condensing system (GCS) is designed to control the water shortages of the steam power unit condensing system. The GCS condensing system developed in this paper helps to reduce the water evaporation losses in the cooling water by more than 79% compared to the wet cooling towers.

Aeroelastic testing of a self-supported transmission tower under laboratory simulated tornado-like vortices

Nima Ezami,Ashraf El Damatty,Ahmed Hamada,Horia Hangan 한국풍공학회 2022 Wind and Structures, An International Journal (WAS Vol.34 No.2

The current study investigates the dynamic effects in the tornado-structure response of an aeroelastic self-supported lattice transmission tower model tested under laboratory simulated tornado-like vortices. The aeroelastic model is designed for a geometric scale of 1:65 and tested under scaled down tornadoes in the Wind Engineering, Energy and Environment (WindEEE) Research Institute. The simulated tornadoes have a similar length scale of 1:65 compared to the full-scale. An extensive experimental parametric study is conducted by offsetting the stationary tornado center with respect to the aeroelastic model. Such aeroelastic testing of a transmission tower under laboratory tornadoes is not reported in the literature. A multiaxial load cell is mounted underneath the base plate to measure the base shear forces and overturning moments applied to the model in three perpendicular directions. A three-axis accelerometer is mounted at the level of the second cross-arm to measure response accelerations to evaluate the natural frequencies through a free-vibration test. Radial, tangential, and axial velocity components of the tornado wind field are measured using cobra probes. Sensitivity analyses are conducted to assess the variation of the structural dynamic response associated with the location of the tornado relative to the lattice transmission tower. Three different layouts representing the change in the orientation of the tower model relative to the components of the tornado-induced loads are considered. The structural responses of the aeroelastic model in terms of base shear forces, overturning moments, and lateral accelerations are measured. The results are utilized to understand the dynamic response of self-supported transmission towers to the tornado-induced loads.

Tabbed Tissue Expanders Improve Breast Symmetry Scores in Breast Reconstruction

Nima Khavanin,Madeleine J Gust,David W Grant,Khang T Nguyen,John YS Kim 대한성형외과학회 2014 Archives of Plastic Surgery Vol.41 No.1

Background: Achieving symmetry is a key goal in breast reconstruction. Anatomically shaped tabbed expanders are a new tool in the armamentarium of the breast reconstruction surgeon. Suture tabs allow for full control over the expander position and thus inframammary fold position, and, in theory, tabbed expanders mitigate many factors responsible for poor symmetry. The impact of a tabbed expander on breast symmetry, however, has not been formally reported. This study aims to evaluate breast symmetry following expander-implant reconstruction usingtabbed and non-tabbed tissue expanders. Methods: A chart review was performed of 188 consecutive expander-implant reconstructionsthat met the inclusion criteria of adequate follow-up data and postoperative photographs. Demographic, oncologic, postoperative complication, and photographic data was obtained for each patient. The photographic data was scored using a 4-point scale assessing breast symmetry by three blinded, independent reviewers. Results: Of the 188 patients, 74 underwent reconstruction with tabbed expanders and 114 with non-tabbed expanders. The tabbed cohort had significantly higher symmetry scores thanthe non-tabbed cohort (2.82/4±0.86 vs. 2.55/4±0.92, P=0.034). Conclusions: The use of tabbed tissue expanders improves breast symmetry in tissue expander−implant−based breast reconstruction. Fixation of the expander to the chest wall allows for more precise control over its location and counteracts the day-to-day translational forces that may influence the shape and location of the expander pocket, mitigating many factors responsible for breast asymmetry.

Hydrogen production in the light of sustainability: A comparative study on the hydrogen production technologies using the sustainability index assessment method

Nima Norouzi 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.4

Hydrogen as an environmentally friendly energy carrier has received special attention to solving uncertainty about the presence of renewable energy and its dependence on time and weather conditions. This material can be prepared from different sources and in various ways. In previous studies, fossil fuelshave been used in hydrogen production, but due to several limitations, especially the limitation of theaccess to this material in the not-too-distant future and the great problem of greenhouse gas emissionsduring hydrogen production methods. New methods based on renewable and green energy sources asenergy drivers of hydrogen production have been considered. In these methods, water or biomass materials are used as the raw material for hydrogen production. In this article, after a brief review ofdifferent hydrogen production methods concerning the required raw material, these methods areexamined and ranked from different aspects of economic, social, environmental, and energy and exergyanalysis sustainability. In the following, the current position of hydrogen production is discussed. Finally,according to the introduced methods, their advantages, and disadvantages, solar electrolysis as a methodof hydrogen production on a small scale and hydrogen production by thermochemical method on a largescale are introduced as the preferred methods.

DO EXPLORATORY AND EXPLOITATIVE MARKETING CAPABILITIES REALLY BENEFIT FROM MARKET KNOWLEDGE DEVELOPMENT AND EXTERNAL TIES IN NEW PRODUCT SUCCESS?

Nima Heirati,Aron O’Cass 글로벌지식마케팅경영학회 2014 Global Marketing Conference Vol.2014 No.10

While the necessity of closing the marketing capabilities gap is an important issue, little is known about the mechanisms that enable firms create and refine marketing capabilities to market new products. Although it is suggested that market knowledge enables firms to create and refine marketing capabilities, little is known about why some firms are better at generating market knowledge or the extent market knowledge development impacts marketing capabilities. We advance the literature by showing that the development of market knowledge through internal processes is not sole or main foundation, external ties are also required to facilitate closing the marketing capabilities gap. Building on the literature on organizational ambidexterity, relational governance, and positional advantages, we examine the extent that external ties facilitate the effect of the firm’s market knowledge development processes (MKD) on exploratory and exploitative marketing capabilities. We use the positional advantage principle (Day & Wensley, 1988) to uncover the path that exploratory and exploitative marketing capabilities drive new product success through. Data from a sample of 169 industrial firms using a multi-informant design shows that the interplay between MKD and external ties provide the foundation to build exploratory and exploitative marketing capabilities to successfully market new products. Given the differences in the nature (e.g., goal convergence, longevity) and knowledge embedded in business and political ties, we draw attention to the different impacts that business and political ties have in helping to build exploratory and exploitative marketing capabilities. Our findings reveal that business ties promote the positive effect of MKD on exploitative marketing, indicating that business ties promote a firm’s capacity to improve its existing marketing routines. Political ties, however, enhance the positive effect of MKD on exploratory marketing, indicating that political ties provide support required to create new marketing initiatives (e.g., new distribution channel). Further, we show that distinct positional advantages, differentiation and cost efficiency, help explain how exploratory and exploitative marketing capabilities may be more or less effective in driving new product success. Our results suggest that while both new product differentiation and cost efficiency are significant drivers of NPP, their antecedents are different. Hence, achieving fit between the preferred positional advantage(s) and the type of marketing capabilities represents a critical determinant of new product success.