Model Uncertainties of FEM Nonlinear Analyses of Concrete Structures

2016 ◽  
Vol 249 ◽  
pp. 197-202 ◽  
Author(s):  
Lukáš Kadlec ◽  
Vladimir Červenka
Keyword(s):  
Numerical Simulations ◽  
Model Uncertainty ◽  
Structural Reliability ◽  
Constitutive Relations ◽  
Nonlinear Analyses ◽  
Model Uncertainties ◽  
Flexural Failure ◽  
Literary Sources ◽  
Near Future

Advanced numerical simulations are more often used due to the increasing possibilities of computer technology. For material descriptions, generally nonlinear constitutive relations are employed. It is expected that in the near future the reliability of structures will be assessed by use of these sophisticated calculations. For this purpose, it is firstly necessary to evaluate the model uncertainty of the numerical model, because the structural reliability is directly affected by the model uncertainty. Recommended values of model uncertainties differ in individual scientific literary sources. In standard codes the partial safety factor for model uncertainty is set by relatively low value. This value was assessed by empirical way and it seems that such value is valid only for flexural failure. Contemporary numerical simulations indicate larger model uncertainties. Moreover, the value of model uncertainty should be related to particular failure mode. This paper presents a comprehensive procedure for the determination of model uncertainties of nonlinear analyses. In the second part, the value of model uncertainties is derived for punching of slabs.

Modulation instability in nonlinear chiral fiber

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Demissie Jobir Gelmecha ◽  
Ram Sewak Singh
Keyword(s):  
Theoretical Model ◽  
Numerical Simulations ◽  
Pulse Propagation ◽  
Modulation Instability ◽  
Constitutive Relations ◽  
Gain Spectrum ◽  
Circularly Polarized ◽  
Left Handed ◽  
Simulation Results ◽  
The Difference

AbstractIn this paper, the rigorous derivations of generalized coupled chiral nonlinear Schrödinger equations (CCNLSEs) and their modulation instability analysis have been explored theoretically and computationally. With the consideration of Maxwell’s equations and Post’s constitutive relations, a generalized CCNLSE has been derived, which describes the evolution of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) components propagating through single-core nonlinear chiral fiber. The analysis of modulation instability in nonlinear chiral fiber has been investigated starting from CCNLSEs. Based on a theoretical model and numerical simulations, the difference on the modulation instability gain spectrum in LCP and RCP components through chiral fiber has been analyzed by considering loss and chirality into account. The obtained simulation results have shown that the loss distorts the sidebands of the modulation instability gain spectrum, while chirality modulates the gain for LCP and RCP components in a different manner. This suggests that adjusting chirality strength may control the loss, and nonlinearity simultaneously provides stable modulated pulse propagation.

Methodology of Estimation of Fire Separation Distances between Construction Facilities by Calculation

2020 ◽  
Vol 1006 ◽  
pp. 93-100
Author(s):  
Vadym Nizhnyk ◽  
Yurii Feshchuk ◽  
Volodymyr Borovykov
Keyword(s):  
Mathematical Model ◽  
Heat Flux ◽  
Linear Regression ◽  
Ignition Temperature ◽  
Oil Products ◽  
Regression Equations ◽  
Fire Load ◽  
Literary Sources ◽  
Tabular Method

Based on analysis of appropriate literary sources we established that estimation of fire separation distances was based of two criteria: heat flux and temperature. We proposed to use “ignition temperature of materials” as principal criterion when determining fire separation distances between adjacent construction facilities. Based on the results derived while performing complete factorial we created mathematical model to describe trend of changing fire separation distances depending on caloric power of fire load (Q), openings factor of the external enclosing structures (k) and duration of irradiation (t); moreover, its adequacy was confirmed. Based on linear regression equations we substantiated calculation and tabular method for the determination of fire separation distances for a facility being irradiated which contains combustible or otherwise non-combustible façade and a facility where liquid oil products turn. We developed and proposed general methodology for estimation of fire separation distances between construction facilities by calculation.

Influence of Human Error on Structural Reliability

2017 ◽  
Author(s):  
Eric Brehm ◽  
Robert Hertle ◽  
Markus Wetzel
Keyword(s):  
Human Error ◽  
Structural Reliability ◽  
Failure Modes ◽  
Structural Model ◽  
Limit State ◽  
Design Procedure ◽  
Material Strength ◽  
Limit States ◽  
The Impact

In common structural design, random variables, such as material strength or loads, are represented by fixed numbers defined in design codes. This is also referred to as deterministic design. Addressing the random character of these variables directly, the probabilistic design procedure allows the determination of the probability of exceeding a defined limit state. This probability is referred to as failure probability. From there, the structural reliability, representing the survival probability, can be determined. Structural reliability thus is a property of a structure or structural member, depending on the relevant limit states, failure modes and basic variables. This is the basis for the determination of partial safety factors which are, for sake of a simpler design, applied within deterministic design procedures. In addition to the basic variables in terms of material and loads, further basic variables representing the structural model have to be considered. These depend strongly on the experience of the design engineer and the level of detailing of the model. However, in the clear majority of cases [1] failure does not occur due to unexpectedly high or low values of loads or material strength. The most common reasons for failure are human errors in design and execution. This paper will provide practical examples of original designs affected by human error and will assess the impact on structural reliability.

In search of an optimum plutonium density measurement fluid

2009 ◽  
Vol 97 (4-5) ◽  
Author(s):  
K. M. Dziewinska ◽  
A. M. Peters ◽  
J. A. La Verne ◽  
P. Martinez ◽  
J. J Dziewinski ◽  
...  
Keyword(s):  
National Laboratory ◽  
Density Measurement ◽  
Chemical Properties ◽  
Decomposition Products ◽  
Los Alamos National Laboratory ◽  
Corrosion Rates ◽  
Physical And Chemical ◽  
Near Future ◽  
Plutonium Metal

AbstractDensity measurements of plutonium metal and its alloys are performed at Los Alamos National Laboratory (LANL) using a technique based on the Archimedes principle. The goal is to find and characterize a fluid for density determination of large objects made of plutonium to replace the currently used monobromobenzene. Physical and chemical properties must be considered while selecting the fluid. Chemical properties of the fluid must ensure low corrosion rates and good resistance to radiological decomposition. The study was carried on to evaluate the corrosion rates of Pu metal cause by FC-43 and the FC-43 decomposition products of radiolysis. The results of these studies proved favourable for this application. The evaluation of the surface reactions between FC-43 and Pu metal will be conducted in the near future.

(GE/m**3). According to this definition one odour unit is the amount of odorants in one cubic meter of air at odour thres­ hold level. The new definition is a real concentration and gives a better form of input parameter for dispersion models. On the basis of guideline VDI 3881 parts 1, 2, and 3 ringtests were carried out with different odorants. The results can be summerized as follows: -The dispersion of results varies and depends on the compo­ sition of the participants and on problems of sampling and preparation of odorous sample. Lower dispersion is obtained when results with obvious errors in application of guide­ lines or with large deviations from mean value are excluded. -Participants of the Netherlands get systematically lower threshold values than the others. The reason has to be investigated. -All findings of the ringtests lead to the conclusion that it is possible to determine odour thresholds which do not differ by more than factor 10. At present another ringtest is in preparation. This test will be carried out in summer 1985. The French collegues will also participate in this test. Experience of all ringtests will be reported in part 4 of guideline VDI 3881. Guideline VDI 3882 deals with the determination of odour intensity and hedonic tone. The members of the working group "odorous substances" assume that odour threshold and odour concentration are insufficient for the characterization of odorous perception. They recommend to judge the odour inten­ sity and the hedonic tone by category estimation. Moreover, it is their opinion that the odour determination with olfacto­ meters is not suitable to assess odour in ambient air. There­ fore they are preparing two guidelines dealing with these problems. Guideline VDI 3883 gives instructions on the regis­ tration of nuisance by interviews with nearby residents of emitting plants or inhabitants of industrial areas. Addition­ ally guideline VDI 3940 describes the determination of odour in ambient air by inspection panels based on the following idea: During constant conditions as to the class of weather, wind speed, and wind direction each local point is charac­ terized by a frequency of odour perception representing the probability to perceive an odour. The situation at a local point will be have to determine the portion of a year with a frequency of odorous perception greater than 5 % in a random test. Both guidelines, VDI 3882 and 3940, should give corres­ ponding results. Guideline VDI 3781 part 5 completes the complex of odour determination and judgement with the calculation of disper­ sion models. The calculation methode and odour determination by panelists should give comparable results. The following summery can be given. Odour measurements with olfactometers is only a small part of the whole field of odour determination in ambient air and the measurement of odour nuisance must be approached in the near future with appropriate urgency.

1986 ◽  
pp. 76-94
Keyword(s):  
Input Parameter ◽  
Ambient Air ◽  
Mean Value ◽  
Hedonic Tone ◽  
Local Point ◽  
Odour Threshold ◽  
Real Concentration ◽  
Category Estimation ◽  
Near Future

scholarly journals Determination of braking force on the aerodynamic brake by numerical simulations

2014 ◽  
Vol 42 (2) ◽  
pp. 106-111 ◽  
Author(s):  
Mirjana Puharic ◽  
Dusan Matic ◽  
Suzana Linic ◽  
Slavica Ristic ◽  
Vojkan Lucanin
Keyword(s):  
Numerical Simulations ◽  
Braking Force ◽  
Aerodynamic Brake

scholarly journals Unscented Kalman filter for airship model uncertainties and wind disturbance estimation

PLoS ONE ◽  
2021 ◽  
Vol 16 (11) ◽  
pp. e0257849
Author(s):  
Muhammad Wasim ◽  
Ahsan Ali ◽  
Mohammad Ahmad Choudhry ◽  
Faisal Saleem ◽  
Inam Ul Hasan Shaikh ◽  
...  
Keyword(s):  
Kalman Filter ◽  
Precision Agriculture ◽  
Model Uncertainty ◽  
Unscented Kalman Filter ◽  
Estimation Method ◽  
Wind Disturbance ◽  
Model Uncertainties ◽  
Nonlinear Simulation ◽  
Lumped Model ◽  
Disturbance Estimation

An airship is lighter than an air vehicle with enormous potential in applications such as communication, aerial inspection, border surveillance, and precision agriculture. An airship model is made up of dynamic, aerodynamic, aerostatic, and propulsive forces. However, the computation of aerodynamic forces remained a challenge. In addition to aerodynamic model deficiencies, airship mass matrix suffers from parameter variations. Moreover, due to the lighter-than-air nature, it is also susceptible to wind disturbances. These modeling issues are the key challenges in developing an efficient autonomous flight controller for an airship. This article proposes a unified estimation method for airship states, model uncertainties, and wind disturbance estimation using Unscented Kalman Filter (UKF). The proposed method is based on a lumped model uncertainty vector that unifies model uncertainties and wind disturbances in a single vector. The airship model is extended by incorporating six auxiliary state variables into the lumped model uncertainty vector. The performance of the proposed methodology is evaluated using a nonlinear simulation model of a custom-developed UETT airship and is validated by conducting a kind of error analysis. For comparative studies, EKF estimator is also developed. The results show the performance superiority of the proposed estimator over EKF; however, the proposed estimator is a bit expensive on computational grounds. However, as per the requirements of the current application, the proposed estimator can be a preferred choice.

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