检索结果-南通市图书馆

Application of perfectly matched layer to soil-foundation interaction analysis

在线全文

学校读者我要写书评

暂无评论

Journal of Rock Mechanics and Geotechnical Engineering 2018年第4期10卷 753-768页

作者： mohammad Davoodi Abbas Pourdeilami Hosein Jahankhah mohammad kazem Jafari International Institute of Earthquake Engineering and Seismology TehranIran

Despite of the limitation in modeling infinite space, the finite element method(FEM) is one of the most used tools to numerically study the geotechnical problems regarding the capacity of simulating different geometries, conditions and material behaviors. A kind of absorbing layer named perfectly matched layer(PML) has been applied to modeling the radiation damping using FEM, which makes the dynamic analysis of soil-structure interaction more accurate. The PML is capable of absorbing incident waves under any angle and frequency, ensuring them to pass through the model boundaries without *** this context, a new FEM program has been written and the PML formula has been implemented by rewriting the dynamic equation of motion and deriving new properties for the quadrilateral *** analysis of soil-foundation interaction by applying the PML is validated by the evaluation of impedance/compliance functions for different ground conditions. The results obtained from the PML model match the extended mesh results, even though the domain is small enough that other types of absorbing boundaries can reflect waves back to the foundation. The mechanism of the wave propagation in the region shows that the forced vibrations can be fully absorbed and damped by the boundaries surrounded by PMLs which is the role of radiation damping in FEM modeling.

关键词： Perfectly matched layer (PML) Finite element method (FEM) Wave propagation Impedance/compliance

Transient Stability Analysis of Grid-connected Converters in Wind Turbine Systems Based on Linear Lyapunov Function and Reverse-time Trajectory

在线全文

学校读者我要写书评

暂无评论

Journal of Modern Power Systems and Clean Energy 2024年第3期12卷 782-790页

作者： mohammad kazem Bakhshizadeh Sujay Ghosh Guangya Yang Łukasz Kocewiak Ørsted Wind Power A/S Nesa Allé12820Denmark Technical University of Denmark Anker Engelunds Vej 12800Denmark

As the proportion of converter-interfaced renewable energy resources in the power system is increasing,the strength of the power grid at the connection point of wind turbine generators(WTGs)is gradually *** research has shown that when connected with the weak grid,the stability of the traditional grid-following controlled converters will deteriorate,and they are prone to unstable phenomena such as *** to the limitations of linear analysis that cannot sufficiently capture the stability phenomena,transient stability must be *** far,standalone time-domain simulations or analytical Lyapunov stability criteria have been used to investigate transient ***,the time-domain simulations have proven to be computationally too heavy,while analytical methods are difficult to formulate for larger systems,require many modelling assumptions,and are often conservative in estimating the stability *** paper proposes and demonstrates an innovative approach to estimating the transient stability boundary via combining the linear Lyapunov function and the reverse-time trajectory *** proposed methodology eliminates the need of time-consuming simulations and the conservative nature of Lyapunov *** study brings out the clear distinction between the stability boundaries with different post-fault active current ramp rate *** the same time,it provides a new perspective on critical clearing time for wind turbine *** stability boundary is verified using time-domain simulation studies.

关键词： Lyapunov direct method non-autonomous system phase-locked loop(PLL) time trajectory reversal transient stability assessment wind turbine converter system

New supervised learning classifiers for structural damage diagnosis using time series features from a new feature extraction technique

在线全文

学校读者我要写书评

暂无评论

Earthquake Engineering and Engineering Vibration 2022年第1期21卷 169-191页

作者： Masoud Haghani Chegeni mohammad kazem Sharbatdar Reza Mahjoub Mahdi Raftari Department of Civil Engineering Khorramabad BranchIslamic Azad UniversityKhorramabadIran*** Faculty of Civil Engineering Semnan UniversitySemnanIran***

The motivation for this article is to propose new damage classifiers based on a supervised learning problem for locating and quantifying damage.A new feature extraction approach using time series analysis is introduced to extract damage-sensitive features from auto-regressive *** approach sets out to improve current feature extraction techniques in the context of time series *** coefficients and residuals of the AR model obtained from the proposed approach are selected as the main features and are applied to the proposed supervised learning classifiers that are categorized as coefficient-based and residual-based *** classifiers compute the relative errors in the extracted features between the undamaged and damaged ***,the abilities of the proposed methods to localize and quantify single and multiple damage scenarios are verified by applying experimental data for a laboratory frame and a four-story steel *** analyses are performed to validate the superiority of the proposed methods over some existing *** show that the proposed classifiers,with the aid of extracted features from the proposed feature extraction approach,are able to locate and quantify damage;however,the residual-based classifiers yield better results than the coefficient-based ***,these methods are superior to some classical techniques.

关键词： structural damage diagnosis statistical pattern recognition feature extraction time series analysis supervised learning classification

Experimental study of flow field distribution over a generic cranked double delta wing

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2016年第5期29卷 1196-1204页

作者： Mojtaba Dehghan Manshadi Mehdi Eilbeigi mohammad kazem Sobhani Mehrdad Bazaz Zadeh mohammad Ali Vaziry Department of Mechanical and Aerospace Engineering Malek Ashtar University of Technology

The flow fields over a generic cranked double delta wing were investigated. Pressure and velocity distributions were obtained using a Pitot tube and a hot wire anemometer. Two different leading edge shapes, namely ＂sharp＂ and ＂round＂, were applied to the wing. The wing had two sweep angles of 55° and 30°. The experiments were conducted in a closed circuit wind tunnel at velocity 20 m/s and angles of attack of 5°- 20° with the step of 5°. The Reynolds number of the model was about 2 - 105 according to the root chord. A dual vortex structure was formed above the wing surface. A pressure drop occurred at the vortex core and the root mean square of the measured velocity increased at the core of the vortices, reflecting the instability of the flow in that region. The magnitude of power spectral density increased strongly in spanwise direction and had the maximum value at the vortex core. By increasing the angle of attack, the pressure drop increased and the vortices became wider; the vortices moved inboard along the wing, and away from the surface; the flow separation was initiated from the outer portion of the wing and developed to its inner part. The vortices of the wing of the sharp leading edge were stronger than those of the round one.

关键词： Cranked double delta wing Flow field Hot wire Leading edge shape Vortical flow

Early differentiation in biomass production and carbon sequestration of white poplar and its two hybrids in Central Iran

在线全文

学校读者我要写书评

暂无评论

Journal of Forestry Research 2015年第1期26卷 65-69页

作者： Hormoz Sohrabi mohammad kazem Parsapour Ali Soltani Yaghoub Iranmanesh Department of Forestry Faculty of Natural Resources and Marine SciencesTarbiat Modares University Department of Forestry Faculty of Natural Resources and Earth ScienceUniversity of ShahrekordShahrekordIran Research Center of Agriculture and Natural Resources ShahrekordChahar-Mahal and BakhtiariIran

We assessed the potential of white poplar（Populus alba L.） and its inter-sectional hybridization with euphrates poplar（P. euphratica Oliv.） for carbon storage and sequestration in central Iran. Trials were established at planting density of 2,500 trees per hectare in block randomized design with three replicates. After 6 years, we measured the above-ground biomass of tree components（trunk, branch, bark, twig and leaf）, and assessed soil carbon at three depths. P. alba 9 euphratica plantation stored significantly more carbon（22.3 t ha-1） than P. alba（16.7 t ha-1） and P. euphratica 9 alba（13.1 t ha-1）.Most of the carbon was accumulated in the above-ground biomass（61.1 % in P. alba, 72.4 % in P. alba 9 euphratica and 56.0 % in P. euphratica 9 alba）. There was no significant difference in soil carbon storage. Also, biomass allocation was different between white poplar P. alba and its inter-sectional hybridization. Therefore, there was a yield difference due to genomic imprinting, which increased the possibility that paternally and maternally inherited wood production alleles would be differentially expressed in the new crossing.

关键词： Carbon storage Hybridization Biomass allocation Euphrates poplar Populus alba 9 euphratica

Comparison of different turbulence models in predicting cohesive fluid mud gravity current propagation

在线全文

学校读者我要写书评

暂无评论

International Journal of Sediment Research 2020年第5期35卷 504-515页

作者： Seyed-mohammad-kazem Emami Sayed-Farhad Mousavi Khosrow Hosseini Hesam Fouladfar Majid mohammadian Faculty of Civil Engineering University of Semnan Iran Water & Power Resources Development Company 3. Department of Civil Engineering University of Ottawa

A numerical study of propagation of cohesive fluid mud gravity currents in the form of lock-exchange was done using the OpenFOAM open source *** Eulerian approach solution for three separate phases was developed by incorporating a rheological model to predict the front position of cohesive fluid mud gravity *** model also simulates features in the complete movement phases including slumping,self-similar,and viscous in which the dynamics of propagation are affected by the balance of viscous and buoyancy forces,and the inertia force is *** influence of using different turbulence models containing sub-grid scale(SGS),modified SGS,detached eddy simulation(DES),delayeddetached eddy simulation(DDES),Launder-R eece-Rodi(LRR),and k-ε models on the accuracy of simulation results was evaluated by comparing with available experimental *** results show that the selection of the proper turbulence model is one of the most important issues for this type of the numerical *** more efficient turbulence model was suggested and tabulated for each stage of propagation and different selected concentrations of 1,045,1,140,and 1,214 g/*** different turbulence models(except k-ε) lead to front propagation dynamic simulation results that are in good agreement with the experimental measurements in the early stage of propagation for low concentrations,only DES,SGS,and modified SGS are able to capture the Kelvin-Helmholtz instability vortex shapes at the dense fluid interface,which is the main characteristic of the gravity current through the slumping *** calculated accuracies of SGS and modified SGS in predicting gravity current propagation for the both self-similar and viscous phases also are slightly better than DES,DDES,and LRR model *** results of this study confirmed the performance and efficiency of the modified SGS model in which the interaction coefficients between phases are calibrated for the numerical modeling of fluid mud

关键词： Gravity current Turbulence model Numerical simulation Cohesive particles Rheology

Sustainability criteria of apicultural industry:evidence from Iran

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Ecosystem Health and Sustainability 2020年第1期6卷 617-629,616页

作者： mohammad kazem Rahimi Enayat Abbasi Masoud Bijani Gholamhosein Tahmasbi Ali Akbar Azimi Dezfouli Department of Agricultural Extension and Education College of AgricultureTarbiat Modares University(TMU)TehranIran Animal Science Research Institute(ASRI) Agricultural ResearchEducation and Extension Organization(AREEO)KarajIran Agricultural Planning Economicsand Rural Development Research Institute(APERDRI)Ministry of Agriculture-JihadTehranIran

This study aimed to determine the sustainability criteria of the beekeeping industry in Iran,which was performed using three-stage classical Delphi *** participants were 32 experts in beekeeping industry who were purposefully selected using the snowball sampling *** criteria identified,after three Delphi stages,consisted of 70 items,which were categorized into 13 general criteria and into four economic,environmental,social,and institutional *** general criteria were presented in the form of a conceptual model,including:farmers’environmental behavior quality,beekeepers'environmental behavior quality,the quality of marketing and sales of beekeeping productions,productivity and performance improvement,amount of monetization from pollinations'right,the amount of monetization of byproducts and value added,employment rate and job stability,the level of social development of stakeholders,the quality of the role-playing of non-governmental stakeholders,the quality of extension and education new sciences and technologies to stakeholders,comprehensiveness of laws and programs,quality of role-playing of stakeholder non-governmental organizations,and the quality of the roleplaying of governmental institutions *** them,a comprehensive perception of the necessary criteria for the sustainability of Iran's beekeeping industry can be obtained and a comprehensive program can be designed for its implementation.

关键词： Sustainable apiculture agricultural sustainability conceptual model Delphi technique

The Effect of Lateral Guiding Mechanism on Noise Characteristics in Semiconductor Lasers

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

光学学报 2003年第S1期23卷 465-466页

作者： Abbas Zarifkar Afsaneh Falahatpisheh mohammad kazem Moravvej-Farshi Ebrahim Mortazy Iran Telecommunication Research Center (ITRC) P. O. Box 14395-897 Tehran IranIran Telecommunication Research Center (ITRC) P. O. Box 14395-897 Tehran IranIran Telecommunication Research Center (ITRC) P. O. Box 14395-897 Tehran IranIran Telecommunication Research Center (ITRC) P. O. Box 14395-897 Tehran Iran

A comparison between intensity noise spectra and also the line shapes of gain-guided, weakly-index-guided, and strongly-index-guided semiconductor lasers are made using numerical solution of Maxwell-Bloch equations in... 详细信息

关键词： of in The Effect of Lateral Guiding Mechanism on Noise Characteristics in Semiconductor Lasers 林乙 on

Analysis of MPN, MHN and Phase Noise of a Two-Mode Semiconductor Laser

在线全文

学校读者我要写书评

暂无评论

光学学报 2003年第S1期23卷 473-474页

作者： Ebrahim Mortazy Vahid Ahmadi mohammad kazem Moravvej-Farshi Abbas Zarifkar Iran Telecommunication Research Center (ITRC) P. O. Box 14155-3961 Tehran IranDepartment of Electronic Engineering Tarbiat Modares University P. O. Box 14115-143 Tehran IranDepartment of Electronic Engineering Tarbiat Modares University P. O. Box 14115-143 Tehran IranIran Telecommunication Research Center (ITRC) P. O. Box 14155-3961 Tehran Iran

Intensity noise including Mode Partition Noise (MPN) and Mode Hopping Noise (MHN), and Phase/Frequency Noise Spectrum (FNS) are calculated for a two-mode semiconductor laser. RIN is derived considering of MPN and MHN ... 详细信息

关键词： mode in RIN MHN and Phase Noise of a Two-Mode Semiconductor Laser Analysis of MPN of