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Centrifuge experiments for shallow tunnels at active reverse fault intersection

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Frontiers of Structural and Civil Engineering 2020年第3期14卷 731-745页

作者： mehdi SABAGH Abbas GHALANDARZADEH School of Civil Engineering University College of EngineeringUniversity of TehranTehran 11155-4563Iran

Tunnels extend in large stretches with continuous lengths of up to hundreds of kilometers which are vulnerable to faulting in earthquake-prone *** the interaction of soil and tunnel at an intersection with an active fault during an earthquake can be a beneficial guideline for tunnel design ***,a series of 4 centrifuge tests are planned and tested on continuous ***-slip suface faulting in reverse mechanism of 60°is modeled by a fault simulator box in a quasi-static *** mechanism,progression and locations of damages to the tunnels are assessed through a gradual increase in Permanent Ground Displacement(PGD).The ground surface deformations and strains,fault surface trace,fault scarp and the sinkhole caused by fault movement are observed *** ground surface deformations are major threats to stability,safety and serviceability of the *** to the observations,the modeled tunnels are vulnerable to reverse fault rupture and but the functionality loss is not abrupt,and the tunnel will be able to tolerate some fault *** monitoring the progress of damage states by increasing PGD,the fragility curves corresponding to each damage state were plotted and interpreted in related figures.

关键词： reverse fault rupture continuous tunnel geotechnical centrifuge ground surface deformations fragility curves

A Sliding Mode Controller Based on Robust Model Reference Adaptive Proportional-integral Control for Stand-alone Three-phase Inverter

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Journal of Modern Power Systems and Clean Energy 2021年第3期9卷 668-678页

作者： Hadi Esmaeili mehdi Asadi Arak University of Technology ArakIran

This paper proposes a sliding mode controller based on robust model reference adaptive proportional-integral(RMRA-PI)control for a stand-alone voltage source inverter(SA-VSI).The proposed controller has two control loops where the coefficients of PI controller are regulated by the adaptive sliding *** method is used to regulate the output voltage of the inverter under different load conditions and uncertainty,and adapts the output to the reference model to reduce the total harmonic distortion(THD).In this paper,the stability of the proposed controller is proven by using Lyapunov's theory and Barbalet’s *** proposed controller performs well in voltage regulation such as low THD under sudden load change and ***,the results of the proposed controller are compared with PI controller to show the effectiveness of the presented control system.

关键词： Robust model reference adaptive proportional-integral(RMRA-PI)control stand-alone inverter three-phase inverter voltage control Lyapunov's theory

Impact of nanoparticle shape on thermohydraulic performance of a nanofluid in an enhanced microchannel heat sink for utilization in cooling of electronic components

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Chinese Journal of Chemical Engineering 2021年第12期34卷 36-47页

作者： mehdi Bahiraei Ali Monavari Institute of Research and Development Duy Tan UniversityDa Nang 550000Vietnam Department of Mechanical Engineering Razi UniversityKermanshahIran

In this article,the thermal–hydraulic efficacy of a boehmite nanofluid with various particle shapes is evaluated inside a microchannel heat *** study is done for particle shapes of platelet,cylinder,blade,brick,and oblate spheroid at Reynolds numbers(Re)of 300,800,1300,and *** particle volume fraction is assumed invariant for all of the nanoparticle *** heat transfer coefficient(h),flow irregularities,pressure loss,and pumping power heighten by the elevation of the Re for all of the nanoparticle ***,the nanofluid having the platelet-shaped nanoparticles leads to the greatest h,and the nanofluid having the oblate spheroid particles has the lowest h and smallest pressure *** contrast,the nanofluid having the platelet-shaped nanoparticles leads to the highest pressure *** mean temperature of the bottom surface,thermal resistance,and temperature distribution uniformity decrease by the rise in the Reynolds number for all of the particle ***,the best distribution of the temperature and the lowest thermal resistance are observed for the suspension containing the platelet ***,the thermal resistance of the nanofluid with the platelet particles shows a 9.5%decrement compared to that with the oblate spheroid particles at Re=*** all the nanoparticle shapes,the figure of merit(FoM)uplifts by elevating the Re,while the nanofluids containing the brickand oblate spheroid-shaped nanoparticles demonstrate the highest FoM values.

关键词： Nanofluid Thermohydraulic performance Nanoparticle shape Microchannel heat sink Boehmite nanoparticles

Seismic analysis of semi-sine shaped alluvial hills above subsurface circular cavity

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Earthquake Engineering and Engineering Vibration 2020年第4期19卷 903-917页

作者： mehdi Panji Mohammad Habibivand Department of Civil Engineering Zanjan BranchIslamic Azad UniversityZanjanIran

In this study, a seismic analysis of semi-sine shaped alluvial hills above a circular underground cavity subjected to propagating oblique SH-waves using the half-plane time domain boundary element method(BEM) was carried out. By dividing the problem into a pitted half-plane and an upper closed domain as an alluvial hill and applying continuity/boundary conditions at the interface, coupled equations were constructed and ultimately, the problem was solved step-by-step in the time domain to obtain the boundary values. After solving some verification examples, a semi-sine shaped alluvial hill located on an underground circular cavity was successfully analyzed to determine the amplification ratio of the hill surface. For sensitivity analysis, the effects of the impedance factor and shape ratio of the hill were also considered. The ground surface responses are illustrated as three-dimensional graphs in the time and frequency domains. The results show that the material properties of the hill and their heterogeneity with the underlying half-space had a significant effect on the surface response.

关键词： alluvial semi-sine shaped hill half-plane BEM time domain circular cavity SH waves

Effect of the spectral shape of ground motion records on the collapse fragility assessment of degrading SDOF systems

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Earthquake Engineering and Engineering Vibration 2021年第4期20卷 925-941页

作者： Amin Norouzi mehdi Poursha Department of Civil Engineering Sahand University of TechnologyTabriz 51335-1996Iran Earthquake Engineering Research Center Sahand University of TechnologyTabriz 51335-1996Iran

The main purpose of this paper is to study the collapse capacity of single degree of freedom(SDOF)systems and to produce fragility curves as well as collapse capacity spectra while considering a broad range of structural parameters,including system degradation,the P-Δeffect,ductility capacity and the post-capping stiffness *** modified Ibarra-Krawinkler deterioration model was used to consider hysteretic behavior.A comprehensive study was conducted to extract the collapse capacity spectrum of SDOF systems with a wide range of periods,varying from 0.05 to 4 s,to cover short,intermediate and long *** dynamic analysis(IDA)was performed for SDOF systems to identify the condition in which the collapse capacity of the system is *** IDAs were performed using different sets of seismic ground *** ground motion records were categorized into different sets based on three spectral shape parameters,including the epsilon,SaRatio and N_(p).The collapse fragility curves of SDOF systems with different periods were extracted to illustrate the collapse capacity at different probability *** results show that structural degradation and ductility as well as the spectral shape parameters significantly affect the collapse capacity of SDOF *** the other hand,the post-capping stiffness ratio and small levels of the P-Δeffect do not remarkably change collapse ***,the collapse capacity of SDOF systems is more sensitive to the records categorized based on SaRatio and N_(p)than those classified based on epsilon.

关键词： collapse capacity fragility analysis degrading SDOF system IDA curve Epsilon,N_(p) SaRatio P-Δeffect

Optimization Methods of MPPT Parameters for PV Systems:Review,Classification,and Comparison

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Journal of Modern Power Systems and Clean Energy 2021年第2期9卷 225-236页

作者： Jalal Dadkhah mehdi Niroomand the Department of Electrical Engineering University of Is-fahanIsfahanIran the Department of Electrical and Computer Engineering University of ManitobaWinnipegCanada the Department of Electrical Engineering University of IsfahanIsfahanIran

To obtain efficient photovoltaic(PV)systems,optimum maximum power point tracking(MPPT)algorithms are *** efficiency of MPPT algorithms depends on two MPPT parameters,i.e.,perturbation amplitude and perturbation *** optimization of MPPT algorithms affect both the tracking speed and steady-state *** this paper,optimization methods of MPPT parameters are reviewed and classified into fixed and variable *** fixed MPPT parameters are constant during MPPT performance,and a trade-off should be made between the tracking speed and steady-state ***,the variable MPPT parameters will be changed to improve both the tracking speed and the steadystate ***,some of them are simulated,compared,and discussed to evaluate the real contributions of the optimization methods to the MPPT ***,significant features of the optimization methods,i.e.,noise immunity,robustness,and computation effort,are investigated.

关键词： Photovoltaic(PV)systems maximum power point tracking(MPPT) perturbation amplitude perturbation period

The hydrodynamic performance of a turbine in shallow free surface flow

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Journal of Hydrodynamics 2021年第4期33卷 804-820页

作者： Zeda Yin mehdi Esmaeilpour Department of Mechanical Engineering College of Engineering and Computer SciencesMarshall UniversityHuntingtonWV25755USA

The performance and flow field of hydropower turbine in shallow water can be affected by the presence of free surface. Therefore, the influence of free surface on the turbine performance was studied through transient computational fluid dynamics (CFD) analysis. The turbine included three blades made of NACA0018 hydrofoil. Submerged depths and different tip speed ratio (TSR) were two main variables in this numerical simulation. A comprehensive simulation of quantities was performed for submerged depths ranging from h / R = 1.2 to 2.0, and tip speed ratio from λ = 1.0 to 30. The results revealed that the presence of the free surface decreased the power coefficient by 19.05% for the closest submerged depth of h / R = 1.2 at optimal tip speed ratio of λ = 2.5. The wave breaking also occurred when the submerged depth was smaller than h / R = 2.0. In the case of variable pitch, the top speeds for free-to-spin cases were investigated by 6DOF method. The top speed had a 4.24% drop by comparing the largest and the smallest submerged depths. Variable pitch also improved the power coefficient by 28.09% when the free surface was far from the hydropower turbine. However, the power coefficient improvement became significantly small when the hydropower turbine was placed close to the free surface.

关键词： Hydropower turbine free surface computational fluid dynamics(CFD) Froude number tip speed ratio(TSR)

Surface oxidation study of molten Mg–Al alloys by oxide/metal/oxide sandwich method

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Journal of Magnesium and Alloys 2022年第6期10卷 1704-1717页

作者： Mohammad Mahdi Jalilvand Hassan Saghafian mehdi Divandari mehdi Akbarifar School of Materials Science and Engineering Iran University of Science and TechnologyNarmakTehran ***Iran

The dynamic oxidation of molten Mg–Al alloy was investigated via the oxide/metal/oxide(OMO)sandwich *** characteristics of sandwiches were explored using optical microscopy,scanning electron microscopy,X-ray energy dispersive spectroscopy,and X-ray diffraction *** results showed the formation of porous oxide films with varying thicknesses from 0.43 to 16.7 *** the measurements and calculations confirmed the literature findings that the oxidation product consists mainly of MgO and Mg Al_(2)O_(4)*** increase in thickness and amount of folds formed on the oxide films implies the significant effect of aluminum in reducing the oxidation resistance of magnesium.

关键词： OMO sandwich Dynamic oxidation Surface film Oxide morphology Thermodynamics Mg–Al alloys

Spatial simulation using abstraction of virtual geographic environments

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International Journal of Digital Earth 2018年第4期11卷 334-355页

作者： mehdi Mekni Department of Computer Science&Information Technology College of Science&EngineeringSt.Cloud State UniversitySt.CloudMNUSA

In this paper,we address two challenging issues underlying spatial simulation using software agents immersed in virtual geographic environments(VGE).First,the way to describe virtual VGE models using accurate spatial decomposition approaches structured using graph theory ***,the use of graph abstraction techniques to support realistic and advanced navigation and path planning capabilities for software agents considering the VGE’s *** order to illustrate our contributions to the growing field of spatial simulations,we present and discuss a case study involving an urban VGE model populated with agents who autonomously and differently interact with multiple abstractions of the same physical environment.

关键词： Virtual geographic environment spatial abstraction spatial modeling and simulation spatial information semantics