جستجوی مقالات مرتبط با کلیدواژه « accuracy » در نشریات گروه « مکانیک »
تکرار جستجوی کلیدواژه «accuracy» در نشریات گروه «فنی و مهندسی»-
Several statistical approaches have been developed to analyze the sampling of huge data and information. There are three significant factors for comparison of the strength of these methods that are argued in this paper; the proposed method is a compatible approach to various types of sampling methods and applied to improve the sampling efficiency and decrease uncertainties to reach accuracy in results. In argued methods, each element just belongs to one category and/ or strata, but in our approach, each element includes all groups with one exception that membership values are different. The case study results show that the proposed Fuzzy Strata Sampling (FSS) method better measures uncertainty and accuracy rate than the other existing sampling methods.Keywords: Sampling Method, stratified sampling, Fuzzy approach, Fuzzy-Strata, accuracy, Uncertainty}
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In 2008, a technique was proposed to reduce run-times in analysis of semi-discretized equation of motion against dynamic excitations available in digitized format. Later, the technique was successfully adapted to reduce numbers of degrees of freedom in finite element analysis of assemblies of beam-columns subjected to static digitized loads. In this paper, attention is paid to dynamic finite element analysis of assemblies of beam-columns. It is shown that, when the mass is available in digitized format, after small modifications in the original technique, the adaptation can simplify the analysis, regardless of the models' sizes, their linearity or non-linearity, and whether the damping is classical or non-classical. The reductions in run-time and in-core memory are considerable, while the changes in accuracy can be negligible.Keywords: Reduction in space, Dynamic finite element analysis, Beam-columns, Accuracy, Computational effort}
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در این مقاله، یک روش محاسباتی دقیق برای اندازه گیری دقت نسبی حسگر ستاره پیشنهاد شده است که نیازمند ابزارها و ادوات پیچیده و پرهزینه آزمایشگاهی نیست و صرفا با استفاده از مشاهده مستقیم آسمان شب و استفاده از معادلات دقیق دوران زمین و حرکت نسبی ستارگان ناشی از آن، می تواند دقت حسگر ستاره را تا مرتبه بهتر از 1 ثانیه قوسی اثبات نماید. روال مرسوم آزمایشگاهی اندازه گیری دقت حسگر ستاره، نیازمند استفاده از شبیه ساز آسمان بهمراه ابزارآلات کمکی نظیر کولیماتور، میز چند درجه آزادی، الاینمنت دقیق و... است. این فرآیند علاوه بر پیچیده و زمانبر بودن، پرهزینه بوده و ابزارآلات کمکی نیز خطای اندازه گیری را بیشتر می کند که شناسایی و حذف آن خطاها خود پروسه ای مجزا و دشوار است. روال پیشنهادی در این مقاله از آن جا که حسگر را در محیط واقعی عملکردش، یعنی آسمان، مورد آزمون قرار می دهد و نه محیط شبیه سازی شده آزمایشگاهی، دقیق تر بوده و قابلیت اطمینان بیشتری خواهد داشت
کلید واژگان: ماهواره, حسگر ستاره, دقت, آسمان شب, شبیه ساز آسمان}In this paper, an accurate computational method is proposed to measure the relative accuracy of the star sensor, which does not require complex laboratory instruments. The proposed method uses the direct observation of the night sky along with the exact equations of motions of the Earth and stars to measure the accuracy of the star sensors in the order of 1 arcsecond. The Classical Laboratory Measurement Procedures of the star sensor’s accuracy requires at least a sky simulator along with some auxiliary tools such as a collimator, an accurate 3 DOF Rotary table, an exact alignment instruments, and so on. The classical procedure, in addition of being complex and time-consuming, is costly, and the auxiliary tools also increase the measurement error by themselves. Identifying and eliminating these errors are more difficult process. The proposed procedure is more accurate and more reliable because the sensor is tested in its actual operating environment, i.e., the sky, rather than the simulated laboratory environment.
Keywords: Satellite, Star Sensor, Accuracy, Night Sky, Sky Simulator} -
Optical spectrum is a set of wavelengths which is created by a light source. Radiation of each element or composition can be absorptive or reflective and unique. For measurement of these spectra, an apparatus known as spectrometer can be used. In reality, spectrophotometer is a machine which measures the intensity of the absorbed light as a function of wavelength. Owing to the extensiveness of the radiational energy amplitude, various spectrophotometers are used for different purposes. The main purpose of this research is to use spectrophotometer and design of a spectrometer for diagnosis and evaluation of icterus in children and measurement of blood sugar in people suffering from diabetes. Statistical population of research includes 80 newborns suffering from icterus and 160 diabetic people in Al-Zahra hospital which are selected randomly. In this method, all of the samples are evaluated with regard to the absorbed light. Results imply to the 78% accuracy for diabetes and 84% accuracy in newborns.
Keywords: Icterus, Diabetes, Spectrophotometer, Accuracy} -
اصولا برونیابی میدان موج بر مبنای حل معادله موج یکی از مراحل مهم مدل سازی لرزه ای بوده و نیازمند دقت بسیار بالایی است. برونیابی میدان موج توسط روش های مختلف عددی از جمله روش تفاضلات محدود به عنوان یک روش سنتی و مرسوم انجام می شود. از جمله محدودیت های روش تفاضلات محدود کاهش دقت و پراکندگی عددی با بزرگ تر شدن فواصل زمانی (t∆) است. یکی از راهکارهای حل این مشکل استفاده از انتگرال گیر های ترکیبی است که با توجه به نوع ساختار آنها زمان محاسبات را کاهش داده و با افزایش فواصل زمانی دچار پراکندگی عددی نشده و دقت آن به نسبت روش تفاضلات محدود بیشتر است. از این رو در این مقاله ابتدا با استفاده از روش اویلر یک انتگرال گیر ترکیبی برای برونیابی میدان موج معرفی می شود. سپس برونیابی میدان موج برای یک فاصله زمانی به نسبت بزرگ در قالب یک مدل ساده برای هر دو روش تفاضلات محدود و روش ترکیبی اویلر نشان داده شده است که بیانگر برونیابی میدان موج با کیفیت بهتر است. در نهایت دقت برونیابی هر دو روش با هم مقایسه شده است که نشان از دقت بسیار بالاتر روش ترکیبی اویلر دارد.
کلید واژگان: مدل سازی لرزه ای, تفاضلات محدود, روش اویلر, دقت, پراکندگی عددی}Wave-field extrapolation based on solving the wave equation is an important step in seismic modeling and needs a high level of accuracy. It has been implemented through a various numerical methods such as finite difference method as the most popular and conventional one. Moreover, the main drawbacks of the finite difference method are the low level of accuracy and the numerical dispersion for large time intervals (∆t). On the other hand, the symplectic integrators due to their structure can cope with this problem and act more accurately in comparison to the finite difference method. They reduce the computation cost and do not face numerical dispersion when time interval is increased. Therefore, the aim of the current paper is to present a symplectic integrator for wave-field extrapolation using the Euler method. Then, the extrapolation is implemented for rather large time intervals using a simple geological model. The extrapolation employed for both symplectic Euler and finite difference methods showed a better quality image for the proposed method. Finally the accuracy was compared to the finite difference method
Keywords: Seismic modeling, Finite difference, Euler method, Accuracy, Numerical dispersion} -
Iranian Journal of Mechanical Engineering Transactions of ISME, Volume:19 Issue: 2, Sep 2018, PP 78 -93Indentation is a new method for estimating residual stress. The plastic behavior of the materials under study can affect indentation parameters and, thus, influences the results of residual stress measurement. In this paper, the effect of yield stress and work-hardening exponent on the accuracy of residual stress measurements in steels and aluminums was studied.
Results showed that, for materials with a low strain-hardening exponent and yield strain, Lee’s model is applicable; for materials with relatively high amounts of strain-hardening exponent and yield strain, Wang’s model is more accurate; and for materials with a medium range of strain-hardening exponent and yield strain all three models can be applied. It was also found that the stresses being tensile or compressive can affect the accuracy of the calculated results for each model. The applicable range of each model is represented in the article.Keywords: residual stress, measurements, indentation, plastic behavior, accuracy} -
Investigation of residual stresses is of crucial importance due to their effect on the performance of engineering components. Recently, inverse methods have been developed for determination of the residual stresses. Inverse eigenstrain method is one of the mentioned inverse methods. The inverse eigenstrain method, which is based on the eigenstrain theory, uses limited measurements of residual elastic strains obtained from the experimental tests. In this study, effective parameters on result accuracy obtained from the 2D inverse eigenstrain method in residual stresses measurement were investigated using numerical experiment. The results indicated that in the inverse eigenstrain method the accuracy of the results increases with increasing the basis functions order and the number of the points where displacement is measured. Additionally, the result accuracy increases selecting the appropriate basis functions. Moreover, in this paper the inverse eigenstrain method was applied for an actual part. The results showed that in the real conditions too, accurate results can be obtained by selecting the appropriate parameters of the inverse eigenstrain method.Keywords: Residual stress, Eigenstrain, Accuracy, FEM}
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در این مقاله معادلات کامل ناویر- استوکس دو بعدی در جریان خارجی آشفته به طور عددی مدل سازی شده است، بدین منظور، جهت محاسبه شارهای غیر لزج از روش بالادستیAusm+up و برای مدل سازی جریان آشفته از مدل تک معادله ای اسپالارت- آلماراس استفاده شده است. مدل اسپالارت- آلماراس به کارگرفته شده، نسخه اصلاح شده این مدل آشفتگی است که از تولید لزجت دینامیکی منفی جلوگیری می کند. این مسئله کمتر در مقالات مورد توجه قرار گرفته است. اصلاحیه مطرح شده به کمک تصحیح ترم های پخش و چشمه در تک معادله مدل آشفتگی انجام شده است. جهت اعتبار سنجی دقت و پایداری مدل آشفتگی و روش محاسبه شار ها جریان کاملا آشفته با رینولدز در ماخ 799/0 در زاویه حمله 26/2 درجه و همچنین جریان با رینولدز و زوایای حمله (صفر و ده) درجه در اطراف ایرفویل NACA0012 بررسی شده است. نتایج حاصل از این پژوهش نشان می دهد، فریم محاسباتی طراحی شده تطبیق مناسبی با داده های آزمایشگاهی دارد و به علاوه تعداد تکرار لازم برای همگرایی کاهش یافته است.کلید واژگان: مدل اصلاح شده ی اسپالارت, آلماراس, ویسکوزیته دینامیکی منفی, پایداری و دقت حل}In this paper, the full two-dimensional NavierStokes equations in the external turbulent flow were numerically modeled. Thus, in order to calculate the fluxes, the Ausm method was utilized and for modeling turbulent flows, the single-equation Spalart-Allmaras model was used. The employed Spalart-Allmaras model is a modification of this turbulence model, which prevents the formation of negative dynamic viscosity, a point that has gone generally unnoticed. The suggested modification was conducted on the distributing and the source terms in the single equation of turbulence model. For validation and assessment of accuracy and stability of the turbulence model and the calculation method of fluxes, the totally turbulent flow with Reynolds number of 9106 and Mach number of 0.799 and angle of attack 2.26 and also flow with Reynolds numbers of 6106 and and Mach number of 0.15 and angles of attack zero,10 around NACA 0012 airfoil are investigate. The results of this study show that computational framework designed have a good agreement with experimental data .furthermore the number of iterations required for convergence is reduced.Keywords: Modified Spalart-Allmaras Model, Negative Daynamic Viscosity, Accuracy, Stability of Solution}
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