A dynamic modelling of safety nets

The nonlinear dynamic modelling of safety net systems is approached at different scales. For this purpose, the fundamental rope dynamic tests are the reference for two basic tools. One hand an anaytical bidimensional model with explicit geometrical nonlinearity and bilnear material law is proposed for preliminary design. On the other hand, a nonlinear explicit finite element is defined for numerical modelling of net systems. Semi-scale and full scale dynamic tests are performed to validate complete finite element models, suitable for global qualification of safety systems. The direct applications of these tools deal with explicit certification of safety systems for high-speed sport, such as downhill competitions

Variational problem for hydrogenerator thrust bearing

Reversible and irreversible heavy loaded thrust bearings of a hydrogenerator are investigated. The problem of oil wedge microgeometry profiling for load capacity optimization is considered. The analysis is based on optimization methods using variational calculus. The results of oil wedge microgeometry optimization for reversible and irreversible thrust bearings are presented

The effective bandwidth problem revisited

The paper studies a single-server queueing system with autonomous service and $\ell$ priority classes. Arrival and departure processes are governed by marked point processes. There are $\ell$ buffers corresponding to priority classes, and upon arrival a unit of the $k$th priority class occupies a place in the $k$th buffer. Let $N^{(k)}$, $k=1,2,...,\ell$ denote the quota for the total $k$th buffer content. The values $N^{(k)}$ are assumed to be large, and queueing systems both with finite and infinite buffers are studied. In the case of a system with finite buffers, the values $N^{(k)}$ characterize buffer capacities. The paper discusses a circle of problems related to optimization of performance measures associated with overflowing the quota of buffer contents in particular buffers models. Our approach to this problem is new, and the presentation of our results is simple and clear for real applications.Comment: 29 pages, 11pt, Final version, that will be published as is in Stochastic Model

Simulation Modelling Application for Balancing Epidemic and Economic Crisis in the Region

The new coronavirus pandemic has had a major impact on worldwide economic development. Many infection-countering measures have imposed restrictions on economic activities. At the same time, economic sectors contribute unequally to both the disease's spread and to regional economic development. This article proposes a method for assessing the consequences of partial regional isolation. Simulation modelling and system dynamics are applied to assess both epidemiological and economic consequences. The classic “Susceptible - Exposed - Infected - Recovered” disease spread model has been modified with the addition of a new group: Isolated Individuals. This modified model allows the size of the receptive population and the frequency of their contact to be regulated based on scenarios of partial regional isolation in the context of economic sectors. The model is tested in St. Petersburg. Changes in the region's infected population are forecasted as the result of the establishment and removal of partial isolation measures in the context of individual economic sectors. © 2020. All Rights Reserved

Nature of the sites of dissociative adsorption of dihydrogen and light paraffins in ZnHZSM-5 zeolite prepared by incipient wetness impregnation

A DRIFT study of ZnHZSM-5 zeolites with Si/Al ratios of 15 or 41 and a Zn loading of 0.8 wt% revealed a high thermal stability of bridging OH groups that was practically the same as in the pure hydrogen forms. It was concluded that the incipient wetness impregnation of NH(4)ZSM-5 zeolite with zinc nitrate and the subsequent high-temperature treatment results only in a minor amount of ion exchange. A considerable part of the modifying zinc forms nanometric ZnO clusters inside the channels of the zeolite. The use of the low-temperature adsorption of dihydrogen as a probe indicated the appearance, after high-temperature vacuum pretreatment, of three different Lewis acid sites connected with coordinatively-unsaturated Zn2+ ions. The strongest Lewis sites, with an H-H stretching frequency of adsorbed molecular hydrogen of 3940 cm(-1), dissociatively adsorbed hydrogen, methane and propane at both room and elevated temperatures. These sites are represented either by Zn2+ ions on the walls of the main channels of the zeolite (alpha sites according to Mole et al.) or by Lewis-base pairs on the surface of nanometric clusters of zinc oxid

Nature of the sites of dissociative adsorption of dihydrogen and light paraffins in ZnHZSM-5 zeolite prepared by incipient wetness impregnation

A DRIFT study of ZnHZSM-5 zeolites with Si/Al ratios of 15 or 41 and a Zn loading of 0.8 wt% revealed a high thermal stability of bridging OH groups that was practically the same as in the pure hydrogen forms. It was concluded that the incipient wetness impregnation of NH(4)ZSM-5 zeolite with zinc nitrate and the subsequent high-temperature treatment results only in a minor amount of ion exchange. A considerable part of the modifying zinc forms nanometric ZnO clusters inside the channels of the zeolite. The use of the low-temperature adsorption of dihydrogen as a probe indicated the appearance, after high-temperature vacuum pretreatment, of three different Lewis acid sites connected with coordinatively-unsaturated Zn2+ ions. The strongest Lewis sites, with an H-H stretching frequency of adsorbed molecular hydrogen of 3940 cm(-1), dissociatively adsorbed hydrogen, methane and propane at both room and elevated temperatures. These sites are represented either by Zn2+ ions on the walls of the main channels of the zeolite (alpha sites according to Mole et al.) or by Lewis-base pairs on the surface of nanometric clusters of zinc oxid

On the role of zinc oxide nanometric clusters in preparation of ZnNaY zeolite by ion exchange

Dehydration of Zn2+ exchanged NaY zeolite was studied by means of DRIFT spectra of adsorbed dihydrogen and carbon monoxide as molecular probes. Unlike alkaline earth forms of faujasites dehydration of ZnY zeolite at moderately high temperatures results in the formation of bridging protons and nanometric ZnO or mixed hydroxylated ZnO microclusters instead of bridging hydroxy groups and MeOH+ cations. After subsequent dehydration at above 573 K the zinc oxide clusters interact with acidic protons resulting in Zn2+ ions localized at SII sites. These sites adsorb hydrogen in its molecular form. Heterolytic dissociative adsorption does not take place even at elevated temperatures