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Approximation of structural damping and input excitation force

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Frontiers of Structural and Civil Engineering 2017年第2期11卷 244-254页

作者： mohammad salavati Institute of Structural Mechanics Faculty of Civil Engineering Bauhaus University Weimar Weimar 99423 Germany

Structural dynamic characteristics are the most significant parameters that play a decisive role in structural damage assessment. The more sensitive parameter to the damage is the damping behavior of the structure. The complexity of structural damping mechanisms has made this parameter to be one of the ongoing research topics. Despite all the difficulties in the modeling of damping, there are some approaches like as linear and nonlinear models which are described as the energy dissipation throughout viscous, material or structural hysteretic and frictional damping mechanisms. In the presence of a mathematical model of the damping mechanisms, it is possible to estimate the damping ratio from the theoretical comparison of the damped and un-damped systems. On the other hand, solving the inverse problem of the input force estimation and its distribution to each SDOFs, from the measured structural responses plays an important role in structural identification process. In this paper model-based damping approximation method and a modelless structural input estimation are considered. The effectiveness of proposed methods has been carded out through analytical and numerical simulation of the lumped mass system and the results are compared with reference data. Consequently, high convergence of the comparison results illustrates the satisfactory of proposed approximation methods.

关键词： structural modal parameters damping identification method input excitation force identification Inverse problem

Investigation of material composition,design,and performance of open-graded asphalt mixtures for semi-flexible pavement:A comprehensive experimental study

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Journal of Traffic and Transportation Engineering(English Edition) 2024年第1期11卷 92-116页

作者： mohammad Taghipoor Abolfazl Hassani mohammad M.Karimi Department of Civil and Environmental Engineering Tarbiat Modares UniversityTehranIran

The primary goal of this study is the design and construction of semi-flexible pavement(SFP)mixture in accordance with the engineering and mechanical criteria.This study involves the use of a range of gradation curves,air void contents,cellulose and synthesized fibers,and neat and modified asphalt binders to prepare the open-graded asphalt(OGA)mixtures.To analyze the characteristics of these mixtures,a variety of test,namely binder drainage,semi-circular bending(SCB),Cantabro,wheel tracking,indirect tensile strength(ITS),and permeability tests were conducted.Additionally,to analyze the prepared grouting material,flexural strength,compressive strength,and fluidity tests were conducted.In the final stage,SFP was compared to HMA in terms of engineering characteristics and performance.According to the results,SFP was more resistant to skid,rutting,fire,and moisture damage,while HMA had a better performance in fracture tests,including SCB test.According to the results of the mechanical performance tests conducted on OGA mixtures,the highest and lowest values for air void content to achieve the highest mechanical performance level were 30%-35%and 25%,respectively.Also,based on the laboratory results,it was determined that the required void ratio for constructing OGA mixtures was 24%-26%based on the bitumen type and fibers amount in the mixture.Finally,SFP mixture can be regarded as a viable alternative to common pavements thanks to its high resistance to rutting and moisture damage,long freezing-thawing fatigue life,and adequate fire and skid resistance.

关键词： Semi-flexible pavement mixture Open-graded asphalt mixture Engineering properties Cantabro test Hot mix asphalt

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Ultrasensitive plasmonic sensor based on MDM waveguide containing Persian Orsi window cavities for refractive index and blood plasma sensing

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Optoelectronics Letters 2024年第7期20卷 406-411页

作者： mohammad Ghanavati mohammad Azim Karami School of Electrical Engineering Iran University of Science and Technology

We developed a plasmonic refractive index（RI） with a metal-dielectric-metal（MDM） structure that utilizes two Persian Orsi windows-like separated cavities with a high figure of merit（FoM） and ultrasensitivity. The simulated and optimized Ag-air-Ag MDM sensor for surface plasmon resonance（SPR） offers high RI sensitivity（SRI） and the ability to detect blood plasma concentration（BPC）. The results verified that structural parameters have an effect on SRI, full width at half maximum（FWHM）, FoM, sensitivity of blood plasma（Sp） for right and left peaks, whose values are 1 345.45 nm·RIU-1, 32 nm, 42.04 RIU-1, 0.26 and 0.19 nm·L·g-1, respectively. The proposed design opens a new horizon in sensor development.

关键词： A

Recent Progress in Bionic Hydrogels for Articular Cartilage:Tribological and Mechanical Characteristics

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Journal of Bionic Engineering 2024年第2期21卷 653-673页

作者： mohammad Javan Almasi Dangsheng Xiong School of Materials Science and Engineering Nanjing University of Science and TechnologyNanjing210094China

Cartilage regeneration and repair are considered clinical challenges since cartilage has limited capability for reconstruction.Although tissue-engineered materials have the ability to repair cartilage,they have weak mechanical characteristics and cannot resist long-term overload.On the other hand,surgery to replace the joint is frequently done to treat significant cartilage deterioration these days.However,the materials that are being used for replacement have high friction coefficients,lack shock absorption functions,and lack cushioning.Further research on natural articular cartilage structure and function may lead to bionic hydrogels,which have suitable physicochemical and biological characteristics(e.g.,tribological and mechanical properties and the ability to support loadbearing capability),but need improvements.Based on their tribological and mechanical characteristics,the current review highlights the most recent advancements of bionic hydrogels used for articular cartilage,highlighting both the field's recent progress and its potential for future research.For this reason,firstly,some important property improvement methods of bionic hydrogels are discussed and then,the recent findings of various research on the making of those bionic materials are provided and compared.It seems that by using some modifications such as product design,surface treatments,animal tests,controlling the isoelectric point of hydrogels,and computer simulation,the intended mechanical and tribological characteristics of natural articular cartilage may be attained by the bionic hydrogels.

关键词： Bionic hydrogel Articular cartilage Mechanical property Tribological property Lubrication

A deep energy method for functionally graded porous beams

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2021年第6期22卷 492-498页

作者： Arvin MOJAHEDIN mohammad salavati Timon RABCZUK Institute of Structural Mechanics Bauhaus-Universitat WeimarWeimar 99423Germany Institute of Material Science and Technology Department of Materials EngineeringTechnische Universitat BerlinBerlin 10623Germany Division of Computational Mechanics Ton Due Thang UniversityHo Chi Minh CityVietnam Faculty of Civil Engineering Ton Due Thang UniversityHo Chi Minh CityVietnam

We present a deep energy method(DEM)to solve functionally graded porous beams.We use the EulerBernoulli assumptions with varying mechanical properties across the thickness.DEM is subsequently developed,and its performance is demonstrated by comparing the analytical solution,which was adopted from our previous work.The proposed method completely eliminates the need of a discretization technique,such as the finite element method,and optimizes the potential energy of the beam to train the neural network.Once the neural network has been trained,the solution is obtained in a very short amount of time.

关键词： Energy-based method Multilayer perceptron methodology Functionally graded porous materials Euler-Bernoulli beam theory

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Sacrificial piles as a countermeasure against local scour around underwater pipelines

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Water Science and Engineering 2024年第2期17卷 187-196页

作者： Forough Raeisi Seyed mohammad Ali Zomorodiann Masih Zolghadr Hazi mohammad Azamathulla Department of Water Engineering Shiraz UniversityShiraz ***Iran Department of Water Sciences Engineering Jahrom UniversityJahrom ***Iran Department of Civil and Environmental Engineering The University of the West IndiesSt.Augustine CampusTrinidad 331310Republic of Trinidad and Tobago

Local scour around pipelines crossing rivers or in marine environments is a significant concern.It can lead to failure of the pipelines resulting in environmental side effects and economic losses.This study developed an experimental method to reduce local scour around pipelines with a steady flow of clear water by installing cylindrical and cubical sacrificial piles.Three sizes of sacrificial piles were examined in a linear arrangement.Sacrificial piles were installed on the upstream side of the pipeline at three distances.Maximum scour depth reduction rates below the pipeline were computed.The results showed that sacrificial piles could protect a pipeline from local scour.A portion of scoured sediment around the sacrificial piles was deposited beneath the pipeline.This sediment accumulation reduced the scour depth beneath the pipeline.Analysis of the experimental results demonstrated that the size of piles(d),the spacing between piles,and the distance between the pipe and piles(Xp)were the variables that reduced the maximum scour beneath the pipeline with a diameter of D.For the piles with d=0.40D and 0.64D,X_(p)=4OD was the optimal distance to install a group of piles,and cubical piles could mitigate scour more effectively than cylindrical piles under similar conditions.For the piles with d=D,the greatest reduction in scour depth was achieved at X_(p)=50D with any desired spacings between piles,and cylindrical piles in this dimension could protect the pipeline against scour more effectively than cubical piles.

关键词： Clear water River crossing pipeline Local scour Self-burial process Sediment transport

Developing a phenomenological model to simulate single and mixed scale formation during flow in porous media:Coupling a salt precipitation model with an ion transport equation under dynamic conditions

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Petroleum Research 2024年第1期9卷 17-36页

作者： Erfan Hosseini Dana mohammad Nazar Negar Hosseini mohammad Sarmadivaleh Exploration Directorate National Iranian Oil Company(NIOC)TehranIran Institute of Physical Chemistry and Polymer Physics Leibniz Institute of Polymer Research DresdenDresdenGermany Department of Petroleum Engineering Islamic Azad University(IAU)IlamIran WA School of Mines:Minerals Energy and Chemical EngineeringCurtin UniversityPerthWestern AustraliaAustralia

Water flooding and pressure maintenance are recommended to improve oil recovery practices after low recovery of petroleum reservoirs occurs during primary production.Salt crystal formation is a frequent occurrence when using these techniques.Several experimental,numerical,and theoretical studies have been done on the mechanisms underlying scaling and permeability reduction in porous media;however,there has not been a satisfactory model developed.This study developed a phenomenological model to predict formation damage caused by salt deposition.Compared with existing models,which provide a scaling tendency,the proposed model predicts the profile of scale deposition.The salt precipitation model simulates reactive fluid flow through porous media.A thermodynamic,kinetic,and flow hydrodynamic model was developed and coupled with the ion transport equation to describe the movement of ions.Further,a set of carefully designed dynamic experiments were conducted and the data were compared with the model predictions.Model forecasts and experimental data were observed to have an average absolute error(AAE)ranging from 0.68%to 5.94%,which indicates the model's suitability.

关键词： Improved oil recovery Water flooding Formation damage Scaling tendency Salt precipitation

Mechanical responses of pristine and defective hexagonal boron-nitride nanosheets:A molecular dynamics investigation

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Frontiers of Structural and Civil Engineering 2020年第3期14卷 623-631页

作者： mohammad salavati Arvin MOJAHEDIN Ali Hossein Nezhad SHIRAZI Institute of Structural Mechanics Bauhaus-Universitat WeimarWeimar D-99423Germany

ABSTRACT In this work we conducted classical molecular dynamics(MD)simulation to investigate the mechanical characteristics and failure mechanism of hexagonal boron-nitride(h-BN)nanosheets.Pristine and defective structure of h-BN nanosheets were considered under the uniaxial tensile loadings at various temperatures.The defective structure contains three types of the most common initial defects in engineering materials that are known as cracks,notches(with various length/size),and point vacancy defects(with a wide range of concentration).MD simulation results demonstrate a high load-bearing capacity of extremely defective(amorphized)h-BN nanosheets.Our results also reveal that the tensile strength decline by increasing the defect content and temperature as well.Our MD results provide a comprehensive and useful vision concerning the mechanical properties ofh-BN nanosheets with/without defects,which is very critical for the designing of nanodevices exploiting the exceptional physics of h-BN.

关键词： hexagonal boron-nitride mechanical properties crack notch point defects molecular dynamics

The modeling non-sequential double ionization of helium atom under highintensity femtosecond laser pulses with shielding charge approximation

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Communications in Theoretical Physics 2024年第2期76卷 151-156页

作者： Marjan Zakavi mohammad Sabaeian Department of Physics Faculty of ScienceShahid Chamran University of AhvazIran Center for Research on Laser and Plasma Shahid Chamran University of AhvazIran

In this study,we successfully extracted the‘knee structure’for non-sequential double ionization(NSDI)in the helium atom.To achieve this,for the first time,we solved the time-dependent Schrödinger equation in three dimensions for the helium atom,utilizing the shielding charge approximation.Our findings corroborate prior observations by Wang et al[Wang and Eberly,Phys.Rev.Lett.105,083001(2010)],demonstrating that NSDI occurs within a narrower time window in circular polarization compared to linear polarization.As a result,the yield of linear polarization was higher than that of circular polarization,aligning with the previously reported results.Notably,in the case of circular polarization,the time window further narrows with increasing intensity,attributed to a decrease in the time-of-flight.

关键词： NSDI knee structure TDSE shielding charge helium 3D-TDSE

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