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نتیجه جستجو - Finite element

تعداد مقالات یافته شده: 86
ردیف عنوان نوع
1 The physical and mechanical properties for flexible biomass particles using computer vision
خواص فیزیکی و مکانیکی ذرات زیست توده انعطاف پذیر با استفاده از بینایی کامپیوتری-2022
The combustion and fluidization behavior of biomass depend on the physical properties (size, morphology, and density) and mechanical performances (elastic modulus, Poisson’s ratio, tensile strength and failure strain), but their quantitative models have rarely been focused in previous researchers. Hence, a static image measurement for particle physical properties is studied. Combining the uniaxial tension and digital image correlation tech- nology, the dynamic image measurement method for the mechanical properties is proposed. The results indicate that the average roundness, rectangularity, and sphericity of present biomass particles are 0.2, 0.4, and 0.16, respectively. The equivalent diameter and density obey the skewed normal distribution. The tensile strength and failure stress are sensitive to stretching rate, fiber size and orientation. The distribution intervals of elastic modulus and Poisson’s ratio are 30–600 MPa and 0.25–0.307, respectively. The stress–strain curves obtained from imaging experiments agree well with the result of finite element method. This study provides the operating parameters for the numerical simulation of particles in the fluidized bed and combustor. Furthermore, the computer vision measurement method can be extended to the investigations of fossil fuels.
keywords: ذرات زیست توده | مشخصات فیزیکی | اجرای مکانیکی | تست کشش | آزمایش تصویربرداری | بینایی کامپیوتر | Biomass particle | Physical properties | Mechanical performances | Tensile testing | Imaging experiment | Computer vision
مقاله انگلیسی
2 A computer vision-based method for bridge model updating using displacement influence lines
یک روش مبتنی بر بینایی کامپیوتری برای به‌روزرسانی مدل پل با استفاده از خطوط موثر جابجایی-2022
This paper presents a new computer vision-based method that simultaneously provides the moving vehicle’s tire loads, the location of the loads on a bridge, and the bridge’s response displacements, based on which the bridge’s influence lines can be constructed. The method employs computer vision techniques to measure the displacement influence lines of the bridge at different target positions, which is then later used to perform model updating of the finite element models of the monitored structural system.
The method is enabled by a novel computer vision-based vehicle weigh-in-motion method which the coauthors recently introduced. A correlation discriminating filter tracker is used to estimate the displacements at target points and the location of single or multiple moving loads, while a low-cost, non-contact weigh-in-motion technique evaluates the magnitude of the moving vehicle loads.
The method described in this paper is tested and validated using a laboratory bridge model. The system was loaded with a vehicle with pressurized tires and equipped with a monitoring system consisting of laser displacement sensors, accelerometers, and cameras. Both artificial and natural targets were considered in the experimental tests to track the displacements with the cameras and yielded robust results consistent with the laser displacement measurements.
The extracted normalized displacement influence lines were then successfully used to perform model updating of the structure. The laser displacement sensors were used to validate the accuracy of the proposed computer vision-based approach in deriving the displacement measurements, while the accelerometers were used to derive the system’s modal properties employed to validate the updated finite element model. As a result, the updated finite element model correctly predicted the bridge’s displacements measured during the tests. Furthermore, the modal parameters estimated by the updated finite element model agreed well with those extracted from the experimental modal analysis carried out on the bridge model. The method described in this paper offers a low-cost non-contact monitoring tool that can be efficiently used without disrupting traffic for bridges in model updating analysis or long-term structural health monitoring.
keywords: Computer vision | Displacement influence line | Vehicle weigh-in-motion | Structural identification | Finite element method model | Model updating | Modal analysis | Bridge systems
مقاله انگلیسی
3 A graphics-based digital twin framework for computer vision-based post-earthquake structural inspection and evaluation using unmanned aerial vehicles
یک چارچوب دیجیتال دوقلوی مبتنی بر گرافیک برای بازرسی و ارزیابی ساختاری پس از زلزله مبتنی بر بینایی کامپیوتری با استفاده از وسایل نقلیه هوایی بدون سرنشین-2022
Rapid structural inspections and evaluations are critical after earthquakes. Computer vision-based methods have attracted the interest of researchers for their potential to be rapid, safe, and objective. To provide an end-to-end solution for computer vision-based post-earthquake inspection and evaluation of a specific as-built structure, the concepts of physics-based graphics model (PBGM) and digital twin (DT) are combined to develop a graphics-based digital twin (GBDT) framework. The GBDT framework comprises a finite element (FE) model and a computer graphics (CG) model whose state is informed by the FE analysis, representing the state of the structure before and after an earthquake. The CG model is first created making use of the FE model and the photographic survey of the structure, yielding the virtual counterpart of the as-built structure quickly and accurately. Then damage modelling approaches are proposed to predict the location and extent of structural and nonstructural damage under seismic loading, from which photographic representation of the predicted damage is realized in the CG model. The effectiveness of the GBDT framework is demonstrated using a five-story reinforced concrete benchmark building through the design and assessment of various UAV (Unmanned Aerial Vehicle) inspection trajectories for post-earthquake scenarios. The results demonstrate that the proposed GBDT framework has significant potential to enable rapid structural inspection and evaluation, ultimately leading to more efficient allocation of scarce resources in a post-earthquake setting.
keywords: بینایی کامپیوتر | مهندسی زلزله | دوقلو دیجیتال | ارزیابی پس از زلزله | دوقلو دیجیتال مبتنی بر گرافیک | مدل گرافیکی مبتنی بر فیزیک | Computer vision | Earthquake engineering | Digital twin | Post-earthquake assessment | Graphics-based digital twin | Physics-based graphics model
مقاله انگلیسی
4 Effect of CNT additives on the electrical properties of derived nanocomposites (experimentally and numerical investigation)
تأثیر افزودنی‌های CNT بر خواص الکتریکی نانوکامپوزیت‌های مشتق‌شده (بررسی تجربی و عددی)-2021
In this work, two simulations models have been developed to study the electrical percolation and the electrical conductivity of epoxy-based nanocomposite containing Multi-walled Carbon Nanotubes. The models are based on resistor-model and finite element analysis. The former was evaluated using MATLAB code and the finite element analysis using DIGIMAT software. The maximum tunneling distance and its influence on the percolation probability and final electrical conductivity were studied. Electrical measurements on the samples were conducted for numerical validation. The experimental data showed a percolation achievement around 2 wt%, which was confirmed in the numerical simulations. This study provides evidence of the effectiveness of the resistor model and finite element method approach to predict the electrical conductivity of nanocomposites.
Keywords: Polymer-matrix composites (PMCs) | Nanocomposites | Carbon nanotube | Electrical properties | Computational modelling
مقاله انگلیسی
5 Coupled elasto-viscoplastic and damage model accounting for plastic anisotropy and damage evolution dependent on loading conditions
الاستو ویسکوپلاستیک همراه و مدل آسیب محاسبه ناهمسانگردی پلاستیک و تکامل آسیب وابسته به شرایط بارگذاری-2021
This work presents an unconventional fully coupled elasto-viscoplastic and damage constitutive model that is suitable for investigating the failure mechanism of metallic materials. The constitutive equations are developed within a finite elastoplasticity framework under the assumption of hypoelastic-based plasticity. Anisotropic plastic potential and plastic-induced anisotropy are modelled by means of the Hill48 yield criterion and a Chaboche-type non-linear kinematic hardening law, respectively. A modified Voce-type law is assumed for the isotropic hardening behaviour. A novel law is proposed to account for an evolution of the damage depending on the loading directions. The proposed model was implemented via user subroutine for the commercial finite elements (FE) software Abaqus/Standard and used for the prediction of the cyclic failure of lead-free solder materials, the crack formation in anisotropic AISI 316L steel specimens and the description of the failure behaviour of carbon steel notched round bars and flat grooved plates.
Keywords: Rate-dependent plasticity | Damage anisotropic evolution | Plastic anisotropy | Kinetic logarithmic spin | Hypoelastic-based plasticity
مقاله انگلیسی
6 Natural vibrations and stability of loaded cylindrical shells partially filled with fluid, taking into account gravitational effects
ارتعاشات طبیعی و پایداری پوسته‌های استوانه‌ای بارگذاری شده تا حدی پر از مایع، با در نظر گرفتن اثرات گرانشی-2021
The paper presents the results of studying circular cylindrical shells partially filled with an ideal liquid and subjected to uniform external and internal hydrostatic pressure. The behavior of an elastic structure and a compressible fluid is described in the framework of the classical nonlinear theory of shells, based on the Kirchhoff – Love hypotheses, and the Euler equations. The problem is solved using a semi-analytical version of the finite element method. The influence of the level of fluid in the shell on the critical values of external pressure is analyzed with and without consideration of gravitational effects on the free and lateral surfaces of the fluid. Shells with different boundary conditions and linear dimensions are considered. It has been shown that for certain geometrical parameters the gravitational field can significantly affect the dynamic characteristics of the structure.
Keywords: Classical shell theory | Ideal compressible fluid | Finite element method | Gravitational field | Natural vibrations | Stability
مقاله انگلیسی
7 Adaptive finite element eye model for the compensation of biometric influences on acoustic tonometry
مدل چشم اجزای محدود تطبیقی برای جبران تأثیرات بیومتریک بر تونومتری آکوستیک-2021
Background and objective: Glaucoma is currently a major cause for irreversible blindness worldwide. A risk factor and the only therapeutic control parameter is the intraocular pressure (IOP). The IOP is determined with tonometers, whose measurements are inevitably influenced by the geometry of the eye. Even though the corneal mechanics have been investigated to improve accuracy of Goldmann and air pulse tonometry, influences of geometric properties of the eye on an acoustic self-tonometer approach are still unresolved.
Methods: In order to understand and compensate for measurement deviations resulting from the geometric uniqueness of eyes, a finite element eye model is designed that considers all relevant eye components and is adjustable to all physiological shapes of the human eye.
Results: The general IOP-dependent behavior of the eye model is validated by laboratory measurements on porcine eyes. The difference between simulation and measurement is below 8 μm for IOP levels from 5 to 40 mmHg. The adaptive eye model is then used to quantify systematic uncertainty contributions of a variation of eye length and central corneal thickness based on input statistics of a clinical trial series. The adaptive eye model provides the required relation between biometric eye parameters and the corneal deflection amplitude, which here is the measured quantity to trace back to the IOP. Implementing the relations provided by the eye model in a Gaussian uncertainty propagation calculation now allows the quantification of the uncertainty contributions of the biometric parameters on the overall measurement uncertainty of the acoustic self-tonometer. As a result, a systematic uncertainty contribution resulting from deviations in eye length dominate stochastic deviations of the sensor equipment by a factor of 3.5.
Conclusion: As perspective, the proposed adaptive eye model provides the basis to compensate for systematic deviations of (but not only) the acoustic self-tonometer.
Keywords: Corneal vibration | Transient simulation | FEM | Eye model | Intraocular pressure | Glaucoma
مقاله انگلیسی
8 Prediction of perforation into concrete accounting for saturation ratio influence at high confinement
پیش بینی سوراخ شدن در بتن برای تأثیر نسبت اشباع در محصور شدن بالا-2021
This paper provides both an analytical and a finite element models aiming at better predicting possible perfo- ration of reinforced concrete slabs submitted to impacts. Both models account for free water saturation ratio and high triaxial stress induced into concrete by the impact. Finite element simulations are performed with Abaqus explicit code using a revised constitutive model for concrete; this coupled damage plasticity model (PRM) ac- counts for strain rate effects and the influence of saturation ratio on the triaxial behavior. Complementary original analytical predictions of ballistic limit and residual velocities are provided for both hard and soft im- pacts. These predictions depend on a recent deviatoric stress-based formulation of compressive strength of concrete. Numerical and analytical results are consistent with bending and punching experimental tests.
keywords: اثرات نرم و سخت | سرعت باقی مانده | بتن آرمه | ظرفیت سوراخ کردن | نسبت اشباع | Soft and hard impacts | Residual velocity | Reinforced concrete | Perforation capacity | Saturation ratio
مقاله انگلیسی
9 A shape memory alloy helix model accounting for extension and torsion
یک مدل مارپیچ آلیاژ حافظه شکل برای محاسبه گسترش و پیچش -2021
In the present paper a mathematical model able to reproduce the mechanical response of a shape memory alloy (SMA) helical spring is presented. The proposed model is based on a simplified but effective theory of the helix that assumes small strains and large displacements. The kinematics of the helix and the related generalized strain measures are introduced, with stress resultants conjugated to them and the corresponding equilibrium equations of the curved beam. A specific constitutive law for this structural model is then presented for the SMA material, which accounts for the phase transformation due to the coupling of the shear and axial strains and to the effect of the temperature variation as well. Then, a numerical procedure, based on the backward Euler time integration algorithm and the prediction-correction technique for solving the nonlinear time step, is developed. Several numerical applications are presented to assess the reliability of the proposed SMA helix model and the imple- mented numerical procedure, and to investigate the response of the helix. Initially, the behavior of a circular SMA cross-section is studied, comparing the results obtained by the proposed modeling approach with the ones carried out by finite element analyses. Then, the helix structural element is considered and results are again compared with finite element outcomes. Finally, a sensitivity analysis is performed varying the pitch of the helix.
keywords: آلیاژ حافظه شکل | بهار | مدل Helix | روش عددی | Shape memory alloy | Spring | Helix model | Numerical procedure
مقاله انگلیسی
10 Methods for field measurement of electrical parameters of soil as functions of frequency
روش‌های اندازه‌گیری میدانی پارامترهای الکتریکی خاک به عنوان توابع فرکانس-2021
In this article, the application of four-electrode and two-electrode arrays to measure electrical parameters of soil as functions of frequency is investigated and its feasibility is evaluated by simulations and measurements. First, the experimental arrays are simulated using finite element method to solve a rigorous electromagnetic problem. New geometric factors are presented, which yield correct estimates of resistivity and permittivity even for reduced spacing. Formulas are proposed for calculating the geometric factors. Then, a series of case studies is carried out considering different soil representations, geometric parameters and excitation frequencies. It was found that increasing excitation frequency and distance between electrodes decreases accuracy. However, resistivity and permittivity of soil can be determined for frequencies up to 2 MHz when using reduced spacing. For the four-electrode array, a discrepancy of less than 3% between estimate and reference is obtained when using distance between electrodes less than 0.5 m. Next, measurements using four and two electrode methods were performed, and it was found that the four-electrode method is the most suitable for measuring soil parameters, given that it was the one that provided consistent results. An analytical equation was also proposed to represent the electrical parameters measured for this case.
Keywords: Grounding | Permittivity | Resistivity measurement | Soil electrical parameters
مقاله انگلیسی
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