Rozhovor s vedoucím redaktorem PMFA
On fuzzy input data and the worst scenario method
In practice, input data entering a state problem are almost always uncertain to some extent. Thus it is natural to consider a set of admissible input data instead of a fixed and unique input. The worst scenario method takes into account all states generated by and maximizes a functional criterion reflecting a particular feature of the state solution, as local stress, displacement, or temperature, for instance. An increase in the criterion value indicates a deterioration in the featured quantity....
Optimal design of an elastic beam on an elastic basis
An elastic simply supported beam of given volume and of constant width and length, fixed on an elastic base, is considered. The design variable is taken to be the thickness of the beam; its derivatives of the first order are bounded both above and below. The load consists of concentrated forces and moments, the weight of the beam and of the so called continuous load. The cost functional is either the -norm of the deflection curve or the -norm of the normal stress in the extemr fibre of the beam. Existence...
Editorial
Editorial
Hybrid variational formulation of an elliptic state equation applied to an optimal shape problem
A recovered gradient method applied to smooth optimal shape problems
A new postprocessing technique suitable for nonuniform triangulations is employed in the sensitivity analysis of some model optimal shape design problems.
Programs and Algorithms of Numerical Mathematics 13 in honor of Ivo Babuška’s 80th birthday
Ivan Hlaváček passed away
A note on factorization of the Fermat numbers and their factors of the form
We show that any factorization of any composite Fermat number into two nontrivial factors can be expressed in the form for some odd and , and integer . We prove that the greatest common divisor of and is 1, , and either or , i.e., for an integer . Factorizations of into more than two factors are investigated as well. In particular, we prove that if then and .
Elements of uncertainty modeling
The goal of this contribution is to introduce some approaches to uncertainty modeling in a way accessible to non-specialists. Elements of the Monte Carlo method, polynomial chaos method, Dempster-Shafer approach, fuzzy set theory, and the worst (case) scenario method are presented.
An application of the averaged gradient technique
On the optimal setting of the -version of the finite element method
The goal of this contribution is to find the optimal finite element space for solving a particular boundary value problem in one spatial dimension. In other words, the optimal use of available degrees of freedom is sought after. This is done through optimizing both the mesh and the polynomial degree of the basis functions. The resulting combinatorial optimization problem is solved in parallel by a Matlab program running on a cluster of multi-core personal computers.
On cumulative C breath tests: An effort to improve the accuracy of test results revealed a substantial uncertainty in input data
A cumulative C breath test can be used to detect a pancreatic disorder, for example. The test is burdened by uncertain input data. Among them, the estimation of CO production rate is a key issue. An established estimate based on the body surface area could be replaced by an estimate using the basal metabolic rate. Although the latter estimate might be considered more appropriate than the former, the differences between them are large in some sex and agegroups. Such disagreements pose a danger...
Identification of parameters in initial value problems for ordinary differential equations
Scalar parameter values as well as initial condition values are to be identified in initial value problems for ordinary differential equations (ODE). To achieve this goal, computer algebra tools are combined with numerical tools in the MATLAB environment. The best fit is obtained through the minimization of the summed squares of the difference between measured data and ODE solution. The minimization is based on a gradient algorithm where the gradient of the summed squares is calculated either numerically...
Hydrological applications of a model-based approach to fuzzy set membership functions
Since the common approach to defining membership functions of fuzzy numbers is rather subjective, another, more objective method is proposed. It is applicable in situations where two models, say and , share the same uncertain input parameter . Model is used to assess the fuzziness of , whereas the goal is to assess the fuzziness of the -dependent output of model . Simple examples are presented to illustrate the proposed approach.
The impact of uncertain parameters on ratchetting trends in hypoplasticity
Perturbed parameters are considered in a hypoplastic model of granular materials. For fixed parameters, the model response to a periodic stress loading and unloading converges to a limit state of strain. The focus of this contribution is the assessment of the change in the limit strain caused by varying model parameters.
Modelled behaviour of granular material during loading and unloading
The main aim of this paper is to analyze numerically the model behaviour of a granular material during loading and unloading. The model was originally proposed by D. Kolymbas and afterward modified by E. Bauer. For our purposes the constitutive equation was transformed into a rate independent form by introducing a dimensionless time parameter. By this transformation we were able to derive explicit formulas for the strain-stress trajectories during loading-unloading cycles and compare the results...
On models of long-term behavior of concrete
Long-term behavior of concrete is modeled by several widely accepted models, such as B3, MC 2010, or ACI 209 whose input parameters and output values are not identical to each other. Moreover, the input and, consequently, the output values are uncertain. In this paper, fuzzy input parameters are considered in uncertainty quantification of each model response and, finally, the sets of responses are analyzed by elementary tools of evidence theory. That is, belief and plausibility functions are proposed...
Preface
Page 1 Next