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Effects of weathering depth and thickness on rock failure:Experimental approach and particle flow code simulation

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journal of Rock Mechanics and Geotechnical Engineering 2024年第11期16卷 4638-4653页

作者： Vahab Sarfarazi mehdi Torabi-Kaveh Arsham Moayedi far Mining Engineering Department Hamedan University of TechnologyHamedan57965155Iran Department of Geology Yazd UniversityYazd***Iran Montanuniversitat Leoben Franz Josef Straße 18Leoben8700Austria

This study investigated the effects of weathering depth and thickness on the failure mechanisms of rock samples through experimental and numerical *** first configuration involved conducting artificial weathering on limestone using the freezing and thawing(F-T)for 40 *** mechanical parameters of the samples were measured at the end of the 40th *** the second configuration,a series of specimens underwent salt crystallization(S-C)tests for 20 *** results were validated using discrete element method(DEM).Next,the weathered limestone model with dimensions of 108 mm54 mm were *** weathering layers were tested at four different thicknesses(i.e.2.5 mm,5 mm,7.5 mm,and 10 mm)and three different positions(at the surface,5 mm under the rock surface,and 10 mm under the rock surface).According to the results,weathering depth and thickness have a considerable effect on the failure *** results also showed a correlation between the values of compressive strength and failure mechanisms associated with the weathering *** numerical results revealed that the tension crack was the dominant ***,with increasing weathering thickness,Young's modulus,crack initiation stress,and final strength decreased in constant weathering *** results also demonstrated that the failure progress of the numerical models was similar to that observed in the laboratory.

关键词： Limestone Weathering depth Weathering thickness Failure pattern Particle flow code in two dimensions(PFC2D)

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

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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

An efficient aerodynamic shape optimization of blended wing body UAV using multi-fidelity models

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Chinese journal of Aeronautics 2018年第6期31卷 1165-1180页

作者： Parviz MOHAMMAD zadeh Mohsen SAYADI Faculty of New Sciences and Technologies University of Tehran

This paper presents a novel optimization technique for an efficient multi-fidelity model building approach to reduce computational costs for handling aerodynamic shape optimization based on high-fidelity simulation models. The wing aerodynamic shape optimization problem is solved by dividing optimization into three steps—modeling 3D（high-fidelity） and 2D（lowfidelity） models, building global meta-models from prominent instead of all variables, and determining robust optimizing shape associated with tuning local meta-models. The adaptive robust design optimization aims to modify the shape optimization process. The sufficient infilling strategy—known as adaptive uniform infilling strategy—determines search space dimensions based on the last optimization results or initial point. Following this, 3D model simulations are used to tune local meta-models. Finally, the global optimization gradient-based method—Adaptive Filter Sequential Quadratic Programing（AFSQP） is utilized to search the neighborhood for a probable optimum point. The effectiveness of the proposed method is investigated by applying it, along with conventional optimization approach-based meta-models, to a Blended Wing Body（BWB） Unmanned Aerial Vehicle（UAV）. The drag coefficient is defined as the objective function, which is subjected to minimum lift coefficient bounds and stability constraints. The simulation results indicate improvement in meta-model accuracy and reduction in computational time of the method introduced in this paper.

关键词： Adaptive filter sequential quadratic programing(AFSQP) Adaptive robust meta-model Aerodynamic shape optimization Blended wing body(BWB) Move limit strategy Unmanned aerial vehicle(UAV)

Effect of Delay Time on Microstructural Evolution during Warm Rolling of Ti-Nb-IF Steel

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journal of Materials Science & Technology 2004年第1期20卷 86-88页

作者： A. Najafi-zadeh R.Ebrahimi Department of Materials Engineering Isfahan University of Technology Isfahan 84154 IranDepartment of Materials Engineering Isfahan University of Technology Isfahan 84154 Iran

The effect of delay time with constant first finishing pass temperature (800℃) has been investigated by means of multi-pass torsion tests on Ti-Nb-IF steel. All the tests have been carried out at a strain rate of 2 s-1 with 11 passes and 0.3 strain each pass. During the final pass, dynamic recrystallization occurs to a degree that depends on the delay time. In short interpass time (1 s) and at these temperatures (T≤800℃) there is not enough time to start static recrystallization, therefore, accumulation of strain occurs and after some passes, strain reaches a critical strain for starting dynamic recrystallization. In this study, the changes of mean flow stress during each pass and also the microstructural observation confirms that dynamic recrystallization occurs after some passes in ferrite phase of this steel. The stress-strain curves with constant temperature obtained by using a kinetic model and compensation of the increasing mean flow stress with decreasing temperature. Thus, this result also confirms that dynamic recrystallization occurs in warm rolling of this IF steel.

关键词： Warm rolling Perrite rolling Thermomechanical processing IF steels

Thermomechanical Behavior of Ti-6Al-4V Alloy

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journal of Materials Science & Technology 2003年第3期19卷 217-220页

作者： K.farmanesh A.Najafi-zadeh Dept.of Materials Engineering Isfahan University of TechnologyIsfahan 85154IranDept.of Materials EngineeringIsfahan University of TechnologyIsfahan 85154Iran

Ti-6AI-4V, among the Ti alloys, is the most widely used. In the present work, the behavior of Ti-6AI-4V alloy has been investigated by the uniaxial hot isothermal compression tests and a series of dilatometric experiments were also carried out to determine the transformation temperatures at different cooling rates. Specimens for hot compression tests were homogenized at 1050℃ for 10 min and then quickly cooled to different straining temperatures from 1050 to 850℃. Cooling rates were chosen fast enough to prevent high temperature transformation during cooling. Compression tests were conducted at temperatures from 1050 to 850℃ in steps of 50℃ at constant true strain rates of 10-3 or 10-2 s-1. The apparent activation energy for compression in two-phase region was calculated 420 kj·mol-1. Partial globularization of a phase was observed in the specimen deformed at low strain rates and at temperatures near the transformation zone and annealed after deformation.

关键词： Titanium alloy Hot pressing Ti-6A1-4V Dilatometry

Effect of Strain Rate on the Ferrite Grain Refinement in a Low Carbon Nb-Ti Microalloyed Steel during Low Temperature Deformation

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journal of Materials Science & Technology 2005年第6期21卷 851-855页

作者： B.Eghbali A.Abdollah-zadeh Department of Materials Engineering Tarbiat Modarres University P.O. Box 14115-143 Tehran Iran

Grain refinement is one of the effective methods to develop new generation low carbon microalloyed steels possessing excellent combination of mechanical properties. The microstructural evolution and ferrite grain refinement at the deformation temperature of 865℃, above Ar3, with different strain rates were investigated using single pass isothermal hot compression experiments for a low carbon Nb-Ti microalloyed steel. The physical processes that occurred during deformation were discussed by observing the optical microstructure and analyzing the true stress-true strain responses. At strain rates of 0.001 and 0.01s^-1, there is no evidence of work hardening behavior during hot deformation and strain-induced transformation （SIT） leads to dynamic flow softening in flow curves. Optical microscopy observation shows that ultrafine and equiaxed ferrite with grain sizes of 2μm can be obtained by applying deformation with strain rate of 0.1 s^-1 due to SIT just after deformation. Furthermore, increasing the strain rate from 0.001 to 0.1 s^-1 reduces both the grain size of the equiaxed ferrite and the amount of deformed ferrite.

关键词： Low carbon microalloyed steel Hot compression Grain refinement Strain induced transformation

When cryptography stops data science: strategies for resolving the conflicts between data scientists and cryptographers

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Data Science and Management 2024年第3期7卷 238-255页

作者： Banaeian far Saeed Imani Rad Azadeh Research and Development Department Blockchain and Metaverse Research LabIRIran

The advent of the digital era and computer-based remote communications has significantly enhanced the applicability of various sciences over the past two decades,notably data science(DS)and cryptography(CG).Data science involves clustering and categorizing unstructured data,while cryptography ensures security and privacy *** certain CG laws and requirements mandating fully randomized or pseudonoise outputs from CG primitives and schemes,it appears that CG policies might impede data scientists from working on ciphers or analyzing information systems supporting security and privacy ***,this study posits that CG does not entirely preclude data scientists from operating in the presence of ciphers,as there are several examples of successful collaborations,including homomorphic encryption schemes,searchable encryption algorithms,secret-sharing protocols,and protocols offering conditional *** instances,along with others,indicate numerous potential solutions for fostering collaboration between DS and ***,this study classifies the challenges faced by DS and CG into three distinct groups:challenging problems(which can be conditionally solved and are currently available to use;e.g.,using secret sharing protocols,zero-knowledge proofs,partial homomorphic encryption algorithms,etc.),open problems(where proofs to solve exist but remain unsolved and is now considered as open problems;e.g.,proposing efficient functional encryption algorithm,fully homomorphic encryption scheme,etc.),and hard problems(infeasible to solve with current knowledge and tools).Ultimately,the paper will address specific solutions and outline future directions to tackle the challenges arising at the intersection of DS and CG,such as providing specific access for DS experts in secret-sharing algorithms,assigning data index dimensions to DS experts in ultra-dimension encryption algorithms,defining some functional keys in functional encryption schemes for DS experts,a

关键词： Big data Data mining Homomorphic calculation Randomized data analytic Searchable encryption

Effects of Mn and Cu on the Mechanical Properties of a High Strength Low Alloy NiCrMoV Steel

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journal of Materials Science & Technology 2005年第4期21卷 470-474页

作者： A.Abdollah-zadeh M.Belbasy Department of Materials Engineering Tarbiat Modarres University P.O. Box 14115-143 Tehran IranDepartment of Materials Engineering Tarbiat Modarres University P.O. Box 14115-143 Tehran Iran

The present study focuses on the effects of Mn and Cu on the mechanical properties, in particular, strength and toughness of a low alloy steel containing Ni, Cr, Mo and V. Specimens with different amounts of Mn （0.23%-0.85%）and Cu （0.15%-0.45%） were cast and forged, and then austenitized at 870℃ for 1h, followed by oil quenching. All specimens were tempered at 650℃ for 1h. The results show that as the amounts of Mn and Cu increase respectively from 0.35% to 0.85% and from 0.15% to 0.45%, the yield and tensile strength increase. The highest impact energies were observed in the specimen with 0.35% Mn and in the specimen with 0.25% Cu. The impact energy decreases with increasing the Mn and Cu from 0.35% to 0.85% and from 0.25% to 0.45%, respectively. Furthermore, the variation of Mn and Cu does not cause a considerable change in the tempered martensite microstructure. The optimum strength and toughness is observed in 0.35% Mn containing steel and in the 0.25% Cu containing steel.

关键词： NiCrMoV steel Cu Mn Tensile strength Impact energy

Impacts of the precision agricultural technologies in Iran: An analysis experts’ perception & their determinants

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Information Processing in Agriculture 2018年第1期5卷 173-184页

作者： Somayeh Tohidyan far Kurosh Rezaei-Moghaddam Dept.of Agricultural Extension and Education School of AgricultureShiraz UniversityIran

Nowadays agricultural methods developments that are productively,economically,environmentally and socially sustainable are required *** concept of precision agriculture is becoming an attractive idea for managing natural resources and realizing modern sustainable agricultural *** purpose of this study was to investigate factors influencing impacts of precision agriculture from the viewpoints of Boushehr Province *** research method was a cross sectional survey and multi-stage random sampling was used to collect data from 115 experts in Boushehr *** to the results,experts found underground and surface waters conservation,rural areas development,increase of productivity and increasing income as the most important impacts of precision agricultural ***’attitudes indicate their positive view toward these kinds of *** behavioral attitude has the most effect on impacts.

关键词： Sustainable agriculture Precision agriculture Impact assessment Boushehr Iran