Modelización numérica del comportamiento estructural cíclico de barras esbeltas de acero con pandeo restringido

This work presents a numerical model of the cyclic structural behavior of dissipative buckling-restrained braces, commonly used as an alternative to classical concentric braces for seismic protection of building frames and other structures. Such devices are usually composed of a slender steel core embedded in a stockiest casing that is intended to prevent its buckling when it is under compression. The casing is made either of mortar or steel, and a sliding interface is interposed between the core and the casing to prevent excessive shear stress transfer. The behavior of the steel core is described by a damage and plasticity model; the behavior of the mortar casing is described by an isotropic damage model and the sliding behavior of the interface is described by a contact penalty model. These 3 models are implemented in the Abaqus software package following an explicit formulation. In a previous article (published in an earthquake engineering journal) the model was briefly described, its ability to reproduce the cyclical behavior of buckling-restrained braces was preliminarily pointed out and their results were satisfactorily compared with those of experimental tests. The aim of this paper is to describe the model thoroughly and to present new judgments about its usefulness.     

Coupled spring equations

Coupled spring equations for modelling the motion of two springs with weights attached, hung in series from the ceiling are described. For the linear model using Hooke's Law, the motion of each weight is described by a fourth-order linear differential equation. A nonlinear model is also described and damping and external forcing are considered. The model has many features that permit the meaningful introduction of many concepts including: accuracy of numerical algorithms, dependence on parameters and initial conditions, phase and synchronization, periodicity, beats, linear and nonlinear resonance, limit cycles, harmonic and subharmonic solutions. These solutions produce a wide variety of interesting motions and the model is suitable for study as a computer laboratory project in a beginning course on differential equations or as an individual or a small-group undergraduate research project.     

The Use of a Simple Multiple-Criteria Model to Assist in Selection from a Shortlist

The use of a simple multiple-criteria model to assist in decision making is described. The model, a hierarchical additive weighted value-function, was used as a part of a decision-making process to select, from a shortlist of three, the company with which to place a contract for the development of a computerized financial management system. The multiple-criteria model and its use are described in detail. To conclude, there is a discussion on the contribution of the model to the decision-making process as perceived by the decision-making group.     

Non-probabilistic Bayesian update method for model validation

Model validation is the principal strategy to evaluate the accuracy and reliability of computational simulations. A systematic model validation procedure including uncertainty quantification, model update and prediction is described based on a non-probabilistic interval model. The crucial technical challenge in model validation is limited data, thus the non-probabilistic interval model is adopted to describe uncertain parameters. To establish the model update formula, the concepts of the interval escape rate and interval coverage rate are first described. Then, not only can the possibility of failure be estimated but also the credibility of the possibility of failure based on the proposed model validation method. The data in the validation experiment are used to update the credibility of each interval model, while the data from the accreditation experiment are used to conduct a final check of the validated models. To demonstrate that the proposed method can be applied to model validation problems successfully, a validation benchmark, the static frame challenge problem, is implemented. In addition, a practical aviation structure engineering validation problem is described. The results of these two validation problems show the feasibility and effectiveness of the proposed model validation method. The theoretical framework proposed in this paper is also suitable for model validation of computational simulations in other research fields.     

Bifurcations in a Two-Dimensional Population Evolution Model

We consider a two-dimensional model for the evolution of a population consisting of two subgroups. The model is described by a system of differential equations. A qualitative analysis of the system is conducted for various parameter values. Bifurcations of phase portraits are described. An example is considered.     

A Microcomputer-Based Simulation Study of a Port

A microcomputer-based simulation model is described which was developed to aid in the planning of future berth requirements at a third-world port. The port handles a variety of incoming and outgoing cargoes, using a mixture of specialized and general berths. Some of the complications of the ship-to-berth allocation rules are described, and how they were modelled. The help that the model provided to the consultants is briefly outlined.     

Some Models for a Hierarchical Manpower System

This paper is an extension of previous work which described a model for a hierarchical manpower system with two grades. The model is first extended to a system with several grades, and then to a system with several types of entrant or in which the type of entrant has changed over time. Finally, a calculation is described which can be used to determine the best mix of qualifications amongst the entrants.     

Using a Neural Network to Enhance the Decision Making Quality of a Visual Interactive Simulation Model

The use of a neural network to represent the results of a simulation model is described. The neural network is implemented as an interaction within a visual interactive simulation model. All results obtained from the simulation are offered to the neural network. After a suitable period of training the quality of results obtained from the network matches those obtained by running the original simulation model. An example which embeds a neural network as an interaction within a visual interactive simulation model is described. The example shows how the combined system may enhance the decision making quality of a visual interactive simulation model.     

Conceptual modelling for simulation Part I: definition and requirements

Conceptual modelling is probably the most important aspect of a simulation study. It is also the most difficult and least understood. Over 40 years of simulation research and practice have provided only limited information on how to go about designing a simulation conceptual model. This paper, the first of two, discusses the meaning of conceptual modelling and the requirements of a conceptual model. Founded on existing literature, a definition of a conceptual model is provided. Four requirements of a conceptual model are described: validity, credibility, utility and feasibility. The need to develop the simplest model possible is also discussed. Owing to a paucity of advice on how to design a conceptual model, the need for a conceptual modelling framework is proposed. Built on the foundations laid in this paper, a conceptual modelling framework is described in the paper that follows.     

Hybrid neural network shock absorber model

A hybrid neural network model is presented and described. The model is composed of a mechanical and thermodynamical part. The mechanical part is described by Akima spline in combination with a feed-forward neural network, while in the case of the thermodynamic part differential equation of dissipative heating is formulated. The interface between both part is provided by the neural network. To identify a proper parameter set of the hybrid model a shock absorber of a middle class passenger car is measured on a servo-hydraulic testing machine. As an excitation a stochastic signal with a predefined power spectral density (PSD) is used. Subsequently the hybrid shock absorber is implemented into a full vehicle model in ADAMS/Car to test its numerical performance and influence on the vertical vehicle dynamics. As reference a standard spline shock absorber model is taken. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On intrinsic time measure concept with application to the modeling of smart materials

In this paper, the cyclic behavior of a Nitinol cubic block is described by using the Bouc-Wen model [2] coupled to the intrinsic time measure, other than the clock time which governs the behavior of the materials [4]. The modified Bouc-Wen model consists from the classical Bouc-Wen model coupled to the intrinsic time measure, other than the clock time which governs the behaviour of the materials. As a consequence, the thermodynamic admissibility of the Bouc–Wen model is provided by the endochronic theory of plasticity. The role of the intrinsic time measure is described by capturing the stiffness and strength degradation and the opposite phenomena. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamical analysis of a delayed singular prey–predator economic model with stochastic fluctuations

This article studies a delayed singular prey–predator economic model with stochastic fluctuations, which is described by differential‐algebraic equations due to a economic theory. Local stability and Hopf bifurcation condition are described on the delayed singular prey–predator economic model within deterministic environment. It reveals the sensitivity of the model dynamics on gestation time delay. A phenomenon of Hopf bifurcation occurs as the gestation time delay increases through a certain threshold. Subsequently, a singular stochastic prey–predator economic model with time delay is obtained by introducing Gaussian white noise terms to the above deterministic model system. The fluctuation intensity of population and harvest effort are calculated by Fourier transforms method. Numerical simulations are carried out to substantiate these theory analysis. © 2013 Wiley Periodicals, Inc. Complexity 19: 23–29, 2014     

Fibrin polymerization as a phase transition wave: A mathematical model

A mathematical model of fibrin polymerization is described. The problem of the propagation of phase transition wave is reduced to a nonlinear Stefan problem. A one-dimensional discontinuity fitting difference scheme is described, and the results of one-dimensional computations are presented.     

An operator splitting strategy for fluid–structure interaction problems with thin elastic structures in an incompressible Newtonian flow

We present a computational framework based on the use of the Newton and level set methods to model fluid–structure interaction problems involving elastic membranes freely suspended in an incompressible Newtonian flow. The Mooney–Rivlin constitutive model is used to model the structure. We consider an extension to a more general case of the method described in Laadhari (2017) to model the elasticity of the membrane. We develop a predictor–corrector finite element method where an operator splitting scheme separates different physical phenomena. The method features an affordable computational burden with respect to the fully implicit methods. An exact Newton method is described to solve the problem, and the quadratic convergence is numerically achieved. Sample numerical examples are reported and illustrate the accuracy and robustness of the method.     

Anisotropic solution of the holographic model of light quarks with an external magnetic field

Theoretical and Mathematical Physics - We find a black hole solution in a five-dimensional fully anisotropic holographic model of light quarks. The model is described by the Einstein action with a...     

On a contact problem for a system of parabolic equations in the thermal conductivity of electric machines: I

Thermal phenomena arising in some electric motors are described (physical model) and an adequate mathematical model is constructed. The model, in the form of a contact problem, is then approximated in a numerical way. The stability of the difference scheme obtained is investigated.     

Anisotropic solutions for a holographic heavy-quark model with an external magnetic field

Theoretical and Mathematical Physics - We find a solution of the black hole type for a five-dimensional fully anisotropic holographic model for heavy quarks. The model is described by the Einstein...     

Modelling the Pulsating Process

We continue research on machine-oracle modelling of second-order arithmetic. The pulsating process described in [1, 2] is simulated using oracles of so-called autonomous hierarchies. The outcome is constructing a generalized constructive model for a fragment of second-order arithmetic described in [2].     

Analysis of lumped models with contact and friction

We consider two mathematical models that describe the vibrations of spring-mass-damper systems with contact and friction. In the first model, both the contact and frictional boundary conditions are described with subdifferentials of nonconvex functions. In the second model, the contact is modeled with a Lipschitz continuous function, and the restitution force is described by a differential equation involving a Volterra integral term. The two models lead to second-order differential inclusions with and without an integral term, in which the unknowns are the positions of the masses. For each model, we prove the existence of a solution by using an abstract result for first-order differential inclusions in finite dimensional spaces. For the second model, in addition, we prove the uniqueness of the solution by using a fixed point argument. Finally, we provide examples of systems with contact and friction conditions for which our results are valid.     

On one class of dynamic transportation models

A model is studied that describes the process of good transportation occurring in some technologies. Transportation regimes satisfying a given management system are examined. Such regimes are described by traveling-wave solutions to a nonlinear finite-difference analogue of a parabolic equation. Possible transportation regimes are described, and the stability of stationary regimes is analyzed.