Budapest University of Technology and Economics
Budapest, Hungary

The Budapest University of Technology and Economics , in Hungarian abbreviated as BME, English official abbreviation BME, is the most significant University of Technology in Hungary and is also the oldest Institute of Technology in the world, having been founded in 1782. Wikipedia.

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Szekrenyes A.,Budapest University of Technology and Economics
European Journal of Mechanics, A/Solids | Year: 2015

The problem of free vibration of delaminated composite beams is revisited in this paper by showing the existence of parametric excitation, bifurcation and stability. Why and when the delaminated part buckles during the vibration? To answer this question, first a finite element model is developed for the uncracked beam portion using the theory of layered beams and the so-called system of exact kinematic conditions. Second, a transition element is developed to establish the kinematic connection and continuity among the delaminated and uncracked portions. Thirdly, the delaminated beam portions are modeled by simple layered beam elements. The coupling between the flexural and longitudinal vibration is taken into consideration in the delaminated part and therefore it is shown that this part is loaded by periodic normal forces during the free vibration of the system. The time dependent stiffness because of the normal forces does not influence the frequencies globally at all, however, locally delamination buckling can take place, as well. The bifurcation and stability of the delaminated parts are analyzed using the harmonic balance method and the critical forces in delaminated layered beams under dynamic stability are determined. The free vibration mode shapes in the state of instability are predicted based on the critical dynamic force and the condition of constant arc length of the delaminated parts. Finally the phase plane portraits of the motion of the midpoint in the delaminated region are presented giving a global view on the behavior of composite beams under harmonic vibration.© 2014 Elsevier Masson SAS. All rights reserved.

Rozvany G.I.N.,Budapest University of Technology and Economics
Structural and Multidisciplinary Optimization | Year: 2011

The aim of this article is to initiate an exchange of ideas on symmetry and non-uniqueness in topology optimization. These concepts are discussed in the context of 2D trusses and grillages, but could be extended to other structures and design constraints, including 3D problems and numerical solutions. The treatment of the subject is pitched at the background of engineering researchers, and principles of mechanics are given preference to those of pure mathematics. The author hopes to provide some new insights into fundamental properties of exact optimal topologies. Combining elements of the optimal layout theory (of Prager and the author) with those of linear programming, it is concluded that for the considered problems the optimal topology is in general unique and symmetric if the loads, domain boundaries and supports are symmetric. However, in some special cases the number of optimal solutions may be infinite, and some of these may be non-symmetric. The deeper reasons for the above findings are explained in the light of the above layout theory. © Springer-Verlag 2010.

In this paper, flexural buckling of pin-ended thin-walled columns is discussed. The classical formulae for the critical force are based on a beam model. The simplest formulae use the classical Euler-Bernoulli beam theory, but solutions based on the shear-deformable beam theory are also known. In the presented research alternative formulae are derived. The column is modeled as a set of flat plane elements, and the in-plane membrane shear deformations are explicitly considered. The derivations can be carried out in various, slightly different ways, leading to different formulae. The derived critical force formulae are discussed through theoretical considerations and numerical studies. © 2013 Elsevier Ltd.

Nagy A.,Budapest University of Technology and Economics
Annals of Physics | Year: 2012

We construct an algorithm to simulate imaginary time evolution of translationally invariant spin systems with local interactions on an infinite, symmetric tree. We describe the state by symmetric infinite-Tree Tensor Network (iTTN) and use translation-invariant operators for the updates at each time step. The contraction of this tree tensor network can be computed efficiently by recursion without approximations and one can then truncate all the iTTN tensors at the same time. The translational symmetry is preserved at each time step that makes the algorithm very well conditioned and stable. The computational cost scales like O(D q+1) with the bond dimension D and coordination number q, much favorable than that of the iTEBD on trees [D. Nagaj, E. Farhi, J. Goldstone, P. Shor, I. Sylvester, Phys. Rev. B 77 (2008) 214431]. Studying the transverse-field Ising model on the Bethe lattice, the numerics indicate a ferromagnetic-paramagnetic phase transition, with a finite correlation length even at the transition point. © 2011 Elsevier Inc.

Insperger T.,Budapest University of Technology and Economics
International Journal of Machine Tools and Manufacture | Year: 2010

The full-discretization method recently proposed by Ding et al. (2010) [1] for the stability analysis of milling processes is shown to be related to the semi-discretization method in the sense that both methods approximate the original DDE by a series of ODEs. Rate of convergence estimates are provided for the full-discretization method, for the zeroth-order, and for the first-order semi-discretization methods. Computation times are analyzed and compared for low and high spindle speed domains. © 2010 Elsevier Ltd. All rights reserved.

Kollar L.,University of Pécs | Keglevich G.,Budapest University of Technology and Economics
Chemical Reviews | Year: 2010

Homogeneous catalysis reactions of some 3, 4, 5, 6, and 7-membered P-heterocyclic ligands of unprecedented structure, are reviewed. A highly stable polycyclic phosphirane can be synthesized in a few steps from dibenzosuberone, which is found to act as a relatively good electron donor. The radical ring-opening polymerization of methylphosphirane, phosphetane, and phospholane, is found to be the fastest with phosphetanes, reflecting the compromise between the strain in the transition structure and the strain released by the partially broken bond. Phospholes of related structure react readily with maleic acid derivatives such as amides and anhydrides. P-Chloro-2-phospholenes are reacted with amino acid esters, resulting in the corresponding 1-L-α-amino acid derivatives of phospholene oxides as chiral P-N phospholenes.

Van Do T.V.,Budapest University of Technology and Economics
Computers and Operations Research | Year: 2010

The Dynamic Host Configuration Protocol (DHCP) is designed to provide an automatic mechanism for the allocation, configuration and management of IP addresses and TCP/IP protocol stack parameters of computers and devices in IP networks. The important feature of DHCP is a "dynamic allocation" mechanism, which assigns an IP address to a client for a limited period of time (called a lease time). Therefore, a previously allocated IP address can automatically be assigned to another host by a DHCP server upon the expiration of the lease time if a host does not renew the use of an allocated IP address. This paper proposes a retrial queueing model to approximate the performability of the DHCP dynamic allocation mechanism. An efficient computational algorithm is developed to calculate the steady state probabilities of a continuous time discrete state Markov process. A comparison of our approximate model with a detailed simulation model of the DHCP dynamic allocation mechanism shows an excellent agreement between the analytical and the simulation results. The impact of the lease time parameter on the performability of the DHCP dynamic allocation mechanism is also illustrated through a numerical study. © 2009 Elsevier Ltd. All rights reserved.

Modla G.,Budapest University of Technology and Economics
Energy | Year: 2013

In this work two energy saving methods are presented for the separation of a minimum boiling point azeotrope by using an intermediate entrainer. Extractive distillation column configurations with conventional, thermally integrated and dividing-wall columns are used for comparison. These configurations are designed, rigorously simulated and optimized to minimize the Total Annual Cost and to reduce the energy requirement. A novel simple method is proposed based on a Genetic Algorithm to determine the main design and operation parameters of the dividing-wall column. The optimization algorithm is written in Excel Macro interconnected with the ChemCad process flow-sheet simulator. In terms of total annual costs, the extractive dividing-wall column was found to be the most economical scheme, followed by the thermally integrated and conventional extractive distillation methods. © 2012 Elsevier Ltd.

Szekrenyes A.,Budapest University of Technology and Economics
European Journal of Mechanics, A/Solids | Year: 2014

In this work the third-order shear deformation theory by Reddy is applied and modified to analyze delaminated orthotropic composite plates. The delaminated plate portion is captured by Reddy's traditional theory, while a novel double-plate system is developed for the undelaminated part. It is shown that in the uncracked part four conditions are required to satisfy in symmetrically delaminated plates. The conditions involve the imposition of traction-free boundaries and the interface constraints. These four conditions enable the reduction of the parameters from nine to five in the displacement field. The governing equations show significant coupling among the stress resultants of the uncracked portion, that has to be considered in the continuity conditions between the delaminated and undelaminated parts. To demonstrate the application of the present model a simply-supported delaminated plate subjected to a concentrated force is analyzed. The distribution of the mode-II and mode-III energy release rates and their ratio are calculated using the 3-dimensional J-integral. The finite element model of the plate is also created using brick-type elements. The comparison of the analytical and finite element results shows very good agreement. It is shown that the deformations around the delamination front can be captured by the third-order plate theory with high accuracy. © 2013 Elsevier B.V. All rights reserved.

Szekrenyes A.,Budapest University of Technology and Economics
International Journal of Solids and Structures | Year: 2012

The classical laminated plate theory is applied to calculate the stresses and energy release rate function in symmetrically delaminated orthotropic plates. First, the equilibrium of classical plate forces, moments and interfacial shear stresses is formulated. Second, the displacement continuity between the interface plane of a double-plate model was considered. The governing equation system of the double-plate model consists of ten equations. As an example a delaminated, orthotropic, simply-supported plate subjected to a point force is analyzed. The distribution of the plate forces as well as the interlaminar shear stresses over the uncracked part were determined. Moreover, the mode-II and mode-III energy release rate distributions along the crack front were calculated by the J-integral. The 3D finite element model of the delaminated composite plate was also created. The results indicate a reasonably good agreement between analysis and numerical calculation. © 2012 Elsevier Ltd. All rights reserved.

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