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- 2015 (51) (remove)
Steel profiles with slender cross-sections are characterized by their high susceptibility to instability phenomena, especially local buckling, which are intensified under fire conditions. This work presents a study on numerical modelling of the behaviour of steel structural elements in case of fire with slender cross-sections. To accurately carry out these analyses it is necessary to take into account those local instability modes, which normally is only possible with shell finite elements. However, aiming at the development of more expeditious methods, particularly important for analysing complete structures in case of fire, recent studies have proposed the use of beam finite elements considering the presence of local buckling through the implementation of a new effective steel constitutive law. The objective of this work is to develop a study to validate this methodology using the program SAFIR. Comparisons are made between the results obtained applying the referred new methodology and finite element analyses using shell elements. The studies were made to laterally restrained beams, unrestrained beams, axially compressed columns and columns subjected to bending plus compression.
Some caad packages offer additional support for the optimization of spatial configurations, but the possibilities for applying optimization are usually limited either by the complexity of the data model or by the constraints of the underlying caad system. Since we missed a system that allows to experiment with optimization techniques for the synthesis of spatial configurations, we developed a collection of methods over the past years. This collection is now combined in the presented open source library for computational planning synthesis, called CPlan. The aim of the library is to provide an easy to use programming framework with a flat learning curve for people with basic programming knowledge. It offers an extensible structure that allows to add new customized parts for various purposes. In this paper the existing functionality of the CPlan library is described.
In this paper we present some rudiments of a generalized Wiman-Valiron theory in the context of polymonogenic functions. In particular, we analyze the relations between different notions of growth orders and the Taylor coefficients. Our main intention is to look for generalizations of the Lindel¨of-Pringsheim theorem. In contrast to the classical holomorphic and the monogenic setting we only obtain inequality relations in the polymonogenic setting. This is due to the fact that the Almansi-Fischer decomposition of a polymonogenic function consists of different monogenic component functions where each of them can have a totally different kind of asymptotic growth behavior.
VARIATIONAL POSITING AND SOLUTION OF COUPLED THERMOMECHANICAL PROBLEMS IN A REFERENCE CONFIGURATION
(2015)
Variational formulation of a coupled thermomechanical problem of anisotropic solids for the case of non-isothermal finite deformations in a reference configuration is shown. The formulation of the problem includes: a condition of equilibrium flow of a deformation process in the reference configuration; an equation of a coupled heat conductivity in a variational form, in which an influence of deformation characteristics of a process on the temperature field is taken into account; tensor-linear constitutive relations for a hypoelastic material; kinematic and evolutional relations; initial and boundary conditions. Based on this formulation several axisymmetric isothermal and coupled problems of finite deformations of isotropic and anisotropic bodies are solved. The solution of coupled thermomechanical problems for a hollow cylinder in case of finite deformation showed an essential influence of coupling on distribution of temperature, stresses and strains. The obtained solutions show the development of stressstrain state and temperature changing in axisymmetric bodies in the case of finite deformations.
Known as a sophisticated phenomenon in civil engineering problems, soil structure interaction has been under deep investigations in the field of Geotechnics. On the other hand, advent of powerful computers has led to development of numerous numerical methods to deal with this phenomenon, resulting in a wide variety of methods trying to simulate the behavior of the soil stratum. This survey studies two common approaches to model the soil’s behavior in a system consisting of a structure with two degrees of freedom, representing a two-storey frame structure made of steel, with the column resting on a pile embedded into sand in laboratory scale. The effect of soil simulation technique on the dynamic behavior of the structure is of major interest in the study. Utilized modeling approaches are the so-called Holistic method, and substitution of soil with respective impedance functions.
A central issue for the autonomous navigation of mobile robots is to map unknown environments while simultaneously estimating its position within this map. This chicken-eggproblem is known as simultaneous localization and mapping (SLAM). Asctec’s quadrotor Pelican is a powerful and flexible research UAS (unmanned aircraft system) which enables the development of new real-time on-board algorithms for SLAM as well as autonomous navigation. The relative UAS pose estimation for SLAM, usually based on low-cost sensors like inertial measurement units (IMU) and barometers, is known to be affected by high drift rates. In order to significantly reduce these effects, we incorporate additional independent pose estimation techniques using exteroceptive sensors. In this article we present first pose estimation results using a stereo camera setup as well as a laser range finder, individually. Even though these methods fail in few certain configurations we demonstrate their effectiveness and value for the reduction of IMU drift rates and give an outlook for further works towards SLAM.
With the advances of the computer technology, structural optimization has become a prominent field in structural engineering. In this study an unconventional approach of structural optimization is presented which utilize the Energy method with Integral Material behaviour (EIM), based on the Lagrange’s principle of minimum potential energy. The equilibrium condition with the EIM, as an alternative method for nonlinear analysis, is secured through minimization of the potential energy as an optimization problem. Imposing this problem as an additional constraint on a higher cost function of a structural property, a bilevel programming problem is formulated. The nested strategy of solution of the bilevel problem is used, treating the energy and the upper objective function as separate optimization problems. Utilizing the convexity of the potential energy, gradient based algorithms are employed for its minimization and the upper cost function is minimized using the gradient free algorithms, due to its unknown properties. Two practical examples are considered in order to prove the efficiency of the method. The first one presents a sizing problem of I steel section within encased composite cross section, utilizing the material nonlinearity. The second one is a discrete shape optimization of a steel truss bridge, which is compared to a previous study based on the Finite Element Method.
SELECTION AND SCALING OF GROUND MOTION RECORDS FOR SEISMIC ANALYSIS USING AN OPTIMIZATION ALGORITHM
(2015)
The nonlinear time history analysis and seismic performance based methods require a set of scaled ground motions. The conventional procedure of ground motion selection is based on matching the motion properties, e.g. magnitude, amplitude, fault distance, and fault mechanism. The seismic target spectrum is only used in the scaling process following the random selection process. Therefore, the aim of the paper is to present a procedure to select a sets of ground motions from a built database of ground motions. The selection procedure is based on running an optimization problem using Dijkstra’s algorithm to match the selected set of ground motions to a target response spectrum. The selection and scaling procedure of optimized sets of ground motions is presented by examining the analyses of nonlinear single degree of freedom systems.
Entwicklung eines Sommerreferenzjahres zur Bestimmung der sommerlichen Überhitzung von Gebäuden
(2015)
Die Ableitung von sommer-fokussierten warmen Referenzjahren aus langjährigen Klimadaten erfolgt in Europa bisher nach unterschiedlichen, länderspezifischen Methoden, die sich in der Regel allein auf die Trockentemperatur beziehen und in der Auswahl eines zusammenhängenden realen Sommerhalbjahres resultieren. Simulationsergebnisse zur sommerlichen Überhitzung von natürlich belüfteten Gebäuden in Deutschland und Großbritannien zeigen jedoch für einige Wetterstationen weniger Überhitzung für Simulationen mit dem sommer-fokussierten Referenzjahr als für solche mit dem entsprechenden Testreferenzjahr (TRY) für den gleichen Ort. Dies gilt insbesondere dann, wenn einzelne Monate miteinander verglichen werden. Neben der Wahl eines kompletten Halbjahres, das sowohl extrem warme als auch vergleichsweise kühle Monate beinhalten kann, liegt dies vor allem begründet in der fehlenden Berücksichtigung der Solarstrahlung bei der Auswahl eines warmen Referenzjahres, die jedoch eine wichtige Rolle für sommerliche Überhitzungserscheinungen in Gebäuden spielt. Eine verlässliche, allgemein anerkannte Methode zur Erstellung von sommer-fokussierten Referenzjahren erscheint daher auch im Hinblick auf die rechtlichen Rahmenbedingungen in der Europäischen Union, die Strategien zur natürlichen Belüftung von Neubauten und Sanierungen begünstigen, erforderlich. Diese Arbeit präsentiert einen Ansatz zur Erstellung eines Sommerreferenzjahres (Summer Reference Year – SRY) aus dem TRY eines gegebenen Ortes und langjährigen Klimadaten. Die existierenden TRY-Daten werden hierbei skaliert, um den Bedingungen für Trockentemperatur und Solarstrahlung von nah-extremen Kandidatenjahren zu entsprechen, die separat über einen statistischen Ansatz ausgewählt werden. Anschließend werden Feuchttemperatur, Windgeschwindigkeit und Luftdruck des TRY durch lineare Korrelationen mit der Trockentemperatur angepasst, um die entsprechenden SRY-Daten zu erhalten. Der Vorteil dieser Methode liegt darin, dass das grundlegende Wettermuster des TRY erhalten bleibt und somit eine klare Relation zwischen SRY und TRY besteht, die eine Vergleichbarkeit von Simulationsergebnissen gewährleistet. Über vergleichende Gebäudesimulationen mit dem zugrundeliegenden TRY und langjährigen Klimadatensätzen kann nachgewiesen werden, dass sich das SRY zur Ermittlung sommerlicher Überhitzungserscheinungen in natürlich belüfteten Gebäuden eignet. Weiterhin kann gezeigt werden, dass das SRY im Gegensatz zur direkten Nutzung eines Kandidatenjahres für einen nah-extremen Sommer die Möglichkeit eines monatsscharfen Vergleichs mit dem TRY erlaubt und frei von wenig repräsentativen Besonderheiten ist, die in den entsprechenden Kandidatenjahren vorhanden sein können.
A topology optimization method has been developed for structures subjected to multiple load cases (Example of a bridge pier subjected to wind loads, traffic, superstructure...). We formulate the problem as a multi-criterial optimization problem, where the compliance is computed for each load case. Then, the Epsilon constraint method (method proposed by Chankong and Haimes, 1971) is adapted. The strategy of this method is based on the concept of minimizing the maximum compliance resulting from the critical load case while the other remaining compliances are considered in the constraints. In each iteration, the compliances of all load cases are computed and only the maximum one is minimized. The topology optimization process is switching from one load to another according to the variation of the resulting compliance. In this work we will motivate and explain the proposed methodology and provide some numerical examples.