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Analytical Formulations (analytical + formulations)

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Engineering100%

Selected Abstracts

Development and validation of a metallic haunch seismic retrofit solution for existing under-designed RC frame buildings

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2006
Stefano Pampanin
Abstract The feasibility and efficiency of a seismic retrofit solution for existing reinforced concrete frame systems, designed before the introduction of modern seismic-oriented design codes in the mid 1970s, is conceptually presented and experimentally investigated. A diagonal metallic haunch system is introduced at the beam,column connections to protect the joint panel zone from extensive damage and brittle shear mechanisms, while inverting the hierarchy of strength within the beam,column subassemblies and forming a plastic hinge in the beam. A complete step-by-step design procedure is suggested for the proposed retrofit strategy to achieve the desired reversal of strength hierarchy. Analytical formulations of the internal force flow at the beam,column-joint level are derived for the retrofitted joints. The study is particularly focused on exterior beam,column joints, since it is recognized that they are the most vulnerable, due to their lack of a reliable joint shear transfer mechanism. Results from an experimental program carried out to validate the concept and the design procedure are also presented. The program consisted of quasi-static cyclic tests on four exterior, , scaled, beam,column joint subassemblies, typical of pre-1970 construction practice using plain round bars with end-hooks, with limited joint transverse reinforcement and detailed without capacity design considerations. The first (control specimen) emulated the as-built connection while the three others incorporated the proposed retrofitted configurations. The experimental results demonstrated the effectiveness of the proposed solution for upgrading non-seismically designed RC frames and also confirmed the applicability of the proposed design procedure and of the analytical derivations. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Analytical modelling of users' behaviour and performance metrics in key distribution schemes

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 1 2010
Massimo Tornatore
Access control for group communications must ensure that only legitimate users can access the authorised data streams. This could be done by distributing an encrypting key to each member of the group to be secured. To achieve a high level of security, the group key should be changed every time a user joins or leaves the group, so that a former group member has no access to current communications and a new member has no access to previous communications. Since group memberships could be very dynamic, the group key should be changed frequently. So far, different schemes for efficient key distribution have been proposed to limit the key-distribution overhead. In previous works, the performance comparison among these different schemes have been based on simulative experiments, where users join and leave secure groups according to a basic statistical model of users' behaviour. In this paper, we propose a new statistical model to account for the behaviour of users and compare it to the modelling approach so far adopted in the literature. Our new model is able to to lead the system to a steady state (allowing a superior statistical confidence of the results), as opposed to current models in which the system is permanently in a transient and diverging state. We also provide analytical formulations of the main performance metrics usually adopted to evaluate key distribution systems, such as rekey overheads and storage overheads. Then, we validate our simulative outcomes with results obtained by analytical formulations. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Propagation of drought through groundwater,a new approach using linear reservoir theory

HYDROLOGICAL PROCESSES, Issue 15 2003
E. Peters
Abstract The effect of drought on groundwater heads and discharge is often complex and poorly understood. Therefore the propagation of a drought from groundwater recharge to discharge and the influence of aquifer characteristics on the propagation was analysed by tracking a drought in recharge through a linear reservoir. The recharge was defined as a sinusoid function with a period of 1 year. The decrease in recharge owing to drought was simulated by multiplying the recharge during 1 year with a drought fraction between 0 and 1, which represents a decrease in the recharge of 100 to 0%, respectively. The droughts were identified using the threshold level approach, with a threshold that is constant in time. For this case analytical formulations were derived, which express the drought duration and deficit in the groundwater discharge in terms of the decrease in recharge, the reservoir coefficient that characterizes aquifer properties and the height of the threshold level. The results showed that the delay in the groundwater system caused a shift of the main part of the decrease in recharge from the high-flow to the low-flow period. This resulted in an increase in drought deficit for discharge compared with the drought deficit for recharge. Also the development of multiyear droughts caused an increase in drought deficit. The attenuation in the groundwater system caused a decrease in drought deficit. In most cases the net effect of these processes was an increase of drought deficit as a result of the propagation through groundwater. Only for small droughts the deficit decreased from recharge to discharge. The amount of increase or decrease depends on the reservoir coefficient and the severity of the drought. Under most conditions a maximum in the drought deficit occurred for a reservoir coefficient of around 200 days. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Bending of fluid-saturated linear poroelastic beams with compressible constituents

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2009
Zhi-Hua Wang
Abstract Analytical solutions are presented for fluid-saturated linear poroelastic beams under pure bending. The stress-free boundary condition at the lateral surfaces is satisfied in the St Venant's sense and the Beltrami,Michell compatibility conditions are resolved rigorously, rendering the flexure of the beams analytically tractable. Two sets of formulations are derived based on the coupled and uncoupled diffusion equations respectively. The analytical solutions are compared with three-dimensional finite element simulations. Both sets of analytical formulations are capable of capturing exactly both the initial (undrained) and the steady-state (fully drained) deflection of the beams. However, the analytical solutions are found to be deficient during the transient phase. The cause for the deficiency of the transient analytical solutions is discussed. The accuracy of the analytical solutions improves as Poisson's ratio and the compressibility of the constituents of the porous beam increase, where the St Venant's edge effect at the lateral surfaces is mitigated. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Coplanar to microstrip transitions for on-wafer measurements

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2007
Yi Wang
Abstract Two types of via-free coplanar line to microstrip transitions are designed and tested for on-wafer measurements. The transitions are designed to fit coplanar ground-signal-ground probes. They are taper transitions with capacitive ground patches and radial stub transitions. Both structures are easy implemented and exhibit wideband transmission. The performance of the optimized taper transition is among the best demonstrated in terms of a return loss of less than ,20 dB from 5 to 15.5 GHz; this is even superior to the radial stub designs. Design information is given, which is based on full-wave simulations for the taper transition, and analytical formulations for the radial stub. The increasing bandwidth with increased angle of the radial stub is observed. The transition structures and design guidelines addressed can be used for on-wafer measurements of a wide range of microstrip circuits. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 100,103, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22056 [source]