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A robust protocol to compute wind load coefficients of telecommunication towers and antennas using numerical simulation for risk and resilience assessment

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Resilient Cities and Structures 2024年第1期3卷 66-83页

作者： Mohanad Khazaali Liyang Ma keivan rokneddin Matteo Mazzotti Paolo Bocchini Research Engineer Extreme Event Solutions at VeriskLafayette City CenterBostonMA 02111USA Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education Harbin Institute of TechnologyHarbin 150090PR China Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology Harbin Institute of TechnologyHarbin 150090PR China Senior Research Scientist RenaissanceRe Risk SciencesUSA Research Associate P.M.Rady Department of Mechanical EngineeringUniversity of Colorado Boulder1111 Engineering Dr UCB 427BoulderCO 80309USA Professor Dept.of Civil and Environmental EngineeringLehigh University117 ATLSS DrBethlehemPA 18015-4729.USA Director Catastrophe Modeling CenterLehigh UniversityBethlehemPAUSA

An accurate estimation of wind loads on telecommunication towers is crucial for design,as well as for perform-ing reliability,resilience,and risk *** particular,drag coefficient and interference factor are the most significant factors for wind load *** tunnel tests and computational fluid dynamics(CFD)are the most appropriate methods to estimate these *** wind tunnel tests are generally preferred in practice,they require dedicated facilities and personnel,and can be expensive if multiple configurations of tower panels and antennas need to be tested under various wind directions(e.g.,fragility curve development for system resilience analysis).This paper provides a simple,robust,and easily accessible CFD protocol with widespread applicability,offering a practical solution in situations where wind tunnel testing is not feasible,such as complex tower configurations or cases where the cost of running experiments for all the tower-antennas configurations is prohibitively *** turbulence models,structural and fluid boundary conditions and mesh types are tested to provide a streamlined CFD modeling strategy that shows good convergence and balances accuracy,computational time,and *** protocol is calibrated and validated with experimental studies available in the *** demonstrate the capabilities of the protocol,three lattice tower panels and antennas with different configurations are analyzed as *** protocol successfully estimates the drag and lateral wind loads and their coefficients under different wind *** differences are observed between the esti-mated wind loads with this protocol and those computed by a simple linear superposition used in most practical applications,indicating the importance of tower-antenna ***,as expected,the wind loads recom-mended by design codes overestimate the simulated *** importantly,the telecommunication design codes inadequate

关键词： Generalized CFD protocol Lattice tower Tower panel Microwave antenna Wind coefficients Tower-antenna interaction

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Stress analysis of thermally affected rotating nanoshafts with varying material properties

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Acta Mechanica Sinica 2016年第5期32卷 813-827页

作者： keivan Kiani Department of Civil Engineering K.N. Toosi University of Technology

Based on the surface elasticity theory of GurtinMurdoch, thermo-elastic fields within rotating nanoshafts with varying material properties subjected to a thermal field are explicitly examined. Accounting for the surface energy effect, the nonclassical boundary conditions are enforced in the cases of fixed-free and free-free conditions. The effects of variation of material properties, temperature of the environment, angular velocity, and radius of the outer radius on the radial displacement, hoop and radial stresses are investigated. In all performed studies, the role of the surface effect on the thermo-elastic field of the nanostructure is methodically discussed.

关键词： Rotating nanoshaft Thermo-elastic field Surface energy effect Non-classical boundary conditions Analytical modeling

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On the limitations of linear beams for the problems of moving mass-beam interaction using a meshfree method

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Acta Mechanica Sinica 2012年第1期28卷 164-179页

作者： keivan Kiani Ali Nikkhoo Department of Civil Engineering Islamic Azad University Department of Civil Engineering University of Science and Culture

This paper deals with the capabilities of linear and nonlinear beam theories in predicting the dynamic response of an elastically supported thin beam traversed by a moving mass. To this end, the discrete equations of motion are developed based on Lagrange＇s equations via reproducing kernel particle method （RKPM）. For a particular case of a simply supported beam, Galerkin method is also employed to verify the results obtained by RKPM, and a reasonably good agreement is achieved. Variations of the maximum dynamic deflection and bending moment associated with the linear and nonlinear beam theories are investigated in terms of moving mass weight and velocity for various beam boundary conditions. It is demonstrated that for majority of the moving mass velocities, the differences between the results of linear and nonlinear analyses become remarkable as the moving mass weight increases, particularly for high levels of moving mass velocity. Except for the cantilever beam, the nonlinear beam theory predicts higher possibility of moving mass separation from the base beam compared to the linear one. Furthermore, the accuracy levels of the linear beam theory are determined for thin beams under large deflections and small rotations as a function of moving mass weight and velocity in various boundary conditions.

关键词： Nonlinear beam theory Moving mass-beam in- teraction Euler-Bernoulli beam theory - Reproducing kernel particle method (RKPM) Galerkin method (GM)

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Economic analysis on log damage during logging operation in Caspian Forests

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Journal of Forestry Research 2013年第3期24卷 585-589页

作者： Farshad keivan Behjou Faculty of Agriculture University of Mohaghegh ArdabiliArdabil Iran P.O.Box:56199-11367

Waste wood was studied in an economic enterprise by logging, function, tree species and log size in four Caspian hardwood sites. Dam- aged logs were recorded with additional information obtained for the location, dimensions and type of damage. The data were analyzed statis- tically to determine significant differences of damage during logging process. The results indicated that animal harvesting systems cause more volume （40.5% of log volume） and value loss （89.5 $.m^-3） to logs than mechanized harvesting systems （13.9% and 6.0 $.m^-3）, also bucking resulted in significantly more volume （9.9% of log volume） and value loss （5.5 $.m-3） when compared to skidding （0.2% of log volume and 0.2 $.m^-3）, decking （0.4% of log volume and 0.2 $.m^-3） and loading （0.2% of log＇s volume and 0.3 $.m^-3） operations. Study showed that the processes of skidding, decking and loading of logs have very little impact on dam- age levels. Volume and value losses of damaged logs are not sensitive to tree species and log size. The information from the field study is impor- tant in creating new guidelines or training to help minimize hardwood log damage during the timber harvesting process.

关键词： log damage forest operations Caspian hardwood forests

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A novel ternary half adder and multiplier based on carbon nanotube field effect transistors

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Frontiers of Information Technology & Electronic Engineering 2017年第3期18卷 423-433页

作者： Sepehr TABRIZCHI Nooshin AZIMI keivan NAVI Department of Computer Engineering Science and Research BranchIslamic Azad University Nanotechnology and Quantum Computing Lab Shahid Beheshti University

A lot of research has been done on multiple-valued logic(MVL) such as ternary logic in these years. MVL reduces the number of necessary operations and also decreases the chip area that would be used. Carbon nanotube field effect transistors(CNTFETs) are considered a viable alternative for silicon transistors(MOSFETs). Combining carbon nanotube transistors and MVL can produce a unique design that is faster and more flexible. In this paper, we design a new half adder and a new multiplier by nanotechnology using a ternary logic, which decreases the power consumption and chip surface and raises the speed. The presented design is simulated using CNTFET of Stanford University and HSPICE software, and the results are compared with those of other studies.

关键词： CNTFET-based design Ternary Half adder Multiplier Multiple-valued logic(MVL)

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Assessing dynamic response of multispan viscoelastic thin beams under a moving mass via generalized moving least square method

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Acta Mechanica Sinica 2010年第5期26卷 721-733页

作者： keivan Kiani Ali Nikkhoo Bahman Mehri Department of Civil Engineering Sharif University of Technology Department of Mathematical Sciences Sharif University of Technology

Dynamic response of multispan viscoelastic thin beams subjected to a moving mass is studied by an efficient numerical method in some detail. To this end, the unknown parameters of the problem are discretized in spatial domain using generalized moving least square method （GMLSM） and then, discrete equations of motion based on Lagrange＇s equation are obtained. Maximum deflection and bending moments are considered as the important design parameters. The design parameter spectra in terms of mass weight and velocity of the moving mass are presented for multispan viscoelastic beams as well as various values of relaxation rate and beam span number. A reasonable good agreement is achieved between the results of the proposed solution and those obtained by other researchers. The results indicate that, although the load inertia effects in beams with higher span number would be intensified for higher levels of moving mass velocity, the maximum values of design parameters would increase either. Moreover, the possibility of mass separation is shown to be more critical as the span number of the beam increases. This fact also violates the linear relation between the mass weight of the moving load and the associated design parameters, especially for high moving mass velocities. However, as the relaxation rate of the beam material increases, the load inertia effects as well as the possibility of moving mass separation reduces.

关键词： Moving mass-beam interaction - Multispan viscoelastic beam Euler-Bernoulli beam Generalized moving least square method (GMLSM)

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Strong internal resonance in a nonlinear, asymmetric microbeam resonator

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Microsystems & Nanoengineering 2021年第1期7卷 117-131页

作者： keivan Asadi Junghoon Yeom Hanna Cho Department of Mechanical and Aerospace Engineering The Ohio State UniversityColumbusOH 43210USA Department of Mechanical Engineering Michigan State UniversityEast LansingMI 48824USA

Exploiting nonlinear characteristics in micro/nanosystems has been a subject of increasing interest in the last *** others,vigorous intermodal coupling through internal resonance(IR)has drawn much attention because it can suggest new strategies to steer energy within a micro/nanomechanical ***,a challenge in utilizing IR in practical applications is imposing the required frequency commensurability between vibrational modes of a nonlinear micro/***,we experimentally and analytically investigate the 1:2 and 2:1 IR in a clamped–clamped beam resonator to provide insights into the detailed mechanism of *** is demonstrated that the intermodal coupling between the second and third flexural modes in an asymmetric structure(e.g.,nonprismatic beam)provides an optimal condition to easily implement a strong IR with high energy transfer to the internally resonated *** this case,the quadratic coupling between these flexural modes,originating from the stretching effect,is the dominant nonlinear mechanism over other types of geometric *** design strategies proposed in this paper can be integrated into a typical micro/nanoelectromechanical system(M/NEMS)via a simple modification of the geometric parameters of resonators,and thus,we expect this study to stimulate further research and boost paradigm-shifting applications exploring the various benefits of IR in micro/nanosystems.

关键词： nonlinear asymmetric clamped

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Ideals Whose First Two Betti Numbers Are Close

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Algebra Colloquium 2015年第4期22卷 671-676页

作者： keivan Borna S.H. Hassanzadeh Faculty of Mathematical Sciences and Computer Kharazmi University Tehran Iran School of Mathematics Institute for Research in Fundamental Sciences (IPM) Tehran Iran Faculty of Mathematical Sciences and Computer Kharazmi University Tehran Iran Institute of Mathematics Universidade Federal de Rio de Janeiro Brasil

For an ideal I of a Noetherian local ring （R, m, k） one hasβR1（I） -β0R（I） ≥-1. It is demonstrated that some residual intersections of an ideal I for whichβ1R（I） -β0R（I） = -1 or 0 are perfect.

关键词： Betti numbers linlkage theory perfect Gorenstein ideals residual intersection

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Effect of selective cutting type on the chainsaw productivity in Caspian Forests

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Journal of Forestry Research 2012年第4期23卷 699-702页

作者： Farshad keivan Behjou Department of Rangeland and Watershed Management Faculty of AgricultureUniversity of Mohaghegh ArdabiliArdabilIranP.O.Box:56199-11376

Time and motion studies were conducted to evaluate the impact of selective cutting type on Chainsaw productivity in Caspian forests, the selective cutting performed as single and group selection cutting in the region. The selective cutting was performed on a 42-ha tract with an average slope of 30%. The results indicate that felling time for per tree is most affected by diameter at breast height, the distance among harvested trees in single-tree selection method and diameter at breast height in group selection method. The production rate in single and group selection cutting were 21.2 m^3·h^-1 and 28.4 m^3·h^-1 for one person, respectively. Considering the gross and net production rate in single and group selection cutting, the unit cost was 1.11 USD.m^-3 and 0.88 USD.m^-3, respectively. The results indicate that group selection cutting can be more profitable than single-tree selection method.

关键词： single-tree selection Group selection manual felling unit cost

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Comparative Performance Evaluation of Large FPGAs with CNFET-and CMOS-based Switches in Nanoscale

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Nano-Micro Letters 2011年第3期3卷 178-188页

作者： Mohammad Hossein Moaiyeri Ali Jahanian keivan Navi Faculty of Electrical and Computer Engineering. Shahid Beheshti University G.C. Nanotechnology and Quantum Computing Lab. Shahid Beheshti University G. C. VLSI Design Automation Lab. Shahid Beheshti University G. C.

Routing resources are the major bottlenecks in improving the performance and power consumption of the current FPGAs. Recently reported researches have shown that carbon nanotube field effect transistors(CNFETs) have considerable potentials for improving the delay and power consumption of the modern FPGAs. In this paper, hybrid CNFET-CMOS architecture is presented for FPGAs and then this architecture is evaluated to be used in modern FPGAs. In addition, we have designed and parameterized the CNFET-based FPGA switches and calibrated them for being utilized in FPGAs at 45 nm, 22 nm and 16 nm technology *** results show that the CNFET-based FPGA switches improve the current FPGAs in terms of performance, power consumption and immunity to process and temperature variations. Simulation results and analyses also demonstrate that the performance of the FPGAs is improved about 30%, on average and the average and leakage power consumptions are reduced more than 6% and 98% respectively when the CNFET switches are used instead of MOSFET FPGA switches. Moreover, this technique leads to more than 20.31%smaller area. It is worth mentioning that the advantages of CNFET-based FPGAs are more considerable when the size of FPGAs grows and also when the technology node becomes smaller.

关键词： Carbon nanotube field effect transistor(CNFET) FPGA switches Performance evaluation Power consumption Process variation

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