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EN
This paper presents results of a field investigation conducted to examine the bed sediment, riverbed morphology and flow structure over dunes in natural and regulated channels. Field measurements using an acoustic Doppler current profiler (ADCP) have been carried out on two parts of lowland Wilga River in Poland. It is shown that the bedforms with a low angle of lee side develop more frequently than asymmetrical dunes with high lee-side angles, which are mostly associated with the occurrence of local scours and river meanders. Wavenumber analysis of bed elevation confirms the existence of scaling region in the longitudinal wavenumber spectrum, with “–3” scaling exponents for the natural and regulated channels as well. Moreover, the results of flow velocity field are presented in the form of a 2-D streamwise-vertical vector field, showing several similarities to previous laboratory and field investigations conducted on much deeper rivers than the Wilga. The experimental campaign and methods used to obtain the results are also presented briefly. In addition, a short database of fluvial dunes statistics is provided.
EN
A 3D Lagrangian model of the saltation of solid spherical particles on the bed of an open channel flow, accounting for turbulence-induced mechanisms, is proposed and employed as the key tool of the study. The differences between conventional 2D models and a proposed 3D saltation model are discussed and the advantages of the 3D model are highlighted. Particularly, the 3D model includes a special procedure allowing generation of 3D flow velocity fields. This procedure is based on the assumption that the spectra of streamwise, vertical and transverse velocity components are known at any distance from the bed. The 3D model was used to identify and quantify effects of turbulence on particle entrainment and saltation. The analysis of particle trajectories focused on their diffusive nature, clarifying: (i) the effect of particle mobility parameter; (ii) the effect of bed topography; and (iii) the effect of turbulence. Specifically, the results of numerical simulations describing the abovementioned effects on the change in time of the variance are presented. In addition, the change in time of the skewness and kurtosis, which are likely to reflect the turbulence influence on the spread of particles, are also shown. Two different diffusion regimes (local and intermediate) for each of the investigated flow conditions are confidently identified.
3
Content available remote Searching for the best optimizer for an automated CAD system
EN
Choice of a robust and universal optimization procedure is one of the crucial design decision for many Computer Aided Design systems. Evolutionary Algorithms are commonly advised in such situations. This paper shows, that such choice is not always the best one. Use of a classical deterministic procedure may lead to better results which are obtained much faster. Example CAD system for electromagnetic flow meters design is used as a practical example illustrating the problem.
PL
Komputerowe systemy wspomagające projektowanie wymagają od swoich twórców wyboru właściwej: uniwersalnej i odpornej na błędy użytkownika, procedury optymalizacji. Często proponowanym rozwiązaniem jest wykorzystanie w takich systemach algorytmów ewolucyjnych. W tym artykule próbujemy pokazać, że taki wybór nie zawsze jest właściwy. Zastosowanie klasycznego algorytmu deterministycznego prowadzi bowiem do lepszego rozwiązania, które ponadto jest znajdowane znacznie szybciej. Rozważania zostały zilustrowane przykładem systemu wspomagającego projektowanie przepływomierzy elektromagnetycznych.
4
Content available remote The Determination of Apples Bruise Resistance by the Multiple Impact Method
EN
In this paper an attempt was undertaken aiming at establishing a methodology determining bruise resistance and the influence of apple storage time on its value and variability. The bruise resistance is a quotient bruise energy to bruise volume. The method applied to determine bruise resistance is the method of multiple drop at a constant height. It consists in multiple dropping of a tested fruit at a constant height up to stabilizing of a rebound height. The research was carried out in two time limits. The first time limit directly after the harvest and the second time limit after a four-month storage period. The measurements were performed on Melrose variety apples. On the basis of the experimental studies of apples mechanical properties under impact loading conditions, the small variability of the bruise volume in the separate research time limits was obtained. In connection with it, the main factor of the bruise resistance variability is the bruise energy.
PL
W pracy podjęto próbę określenia metodyki wyznaczenia odporności na obicie oraz wpływu czasu przechowywania jabłek na jej wartość oraz zmienność. Odporność na obicie jest to stosunek energii obicia do objętości obicia. Metoda stosowana do wyznaczania odporności na obicie to metoda wielokrotnego zrzutu ze stałej wysokości. Polega na kilkukrotnym zrzucaniu badanego owocu ze stałej wysokości aż do ustabilizowania się wysokości odbicia. Badania wykonano w dwóch terminach: termin pierwszy - bezpośrednio po zbiorze, termin drugi - po czteromiesięcznym okresie przechowywania. Pomiary przeprowadzono na jabłkach odmiany Melrose. Na podstawie badań eksperymentalnych właściwości mechanicznych jabłek w warunkach obciążeń udarowych uzyskano małą zmienność objętości obicia w poszczególnych terminach badań. W związku z tym głównym czynnikiem zmienności odporności na obicie jest energia obicia.
PL
W pracy przedstawiono analizę możliwości wykorzystania technik pomiaru progu obicia i energii obicia jako parametrów charakteryzujących odporność na obicia jabłek. Badania doświadczalne przeprowadzono na urządzeniu działającym na zasadzie wahadła. Stwierdzono wysoką czułość obu technik co pozwoliło między innymi na różnicowanie owoców świeżych i po przechowaniu. Przyjęta wysokość zrzutu 50 mm umożliwiła osiągnięcie stabilizacji powierzchni obicia już przy piątym udarze. Proponowane techniki pozwalają także na określenie wartości maksymalnego naprężenia dynamicznego przenoszonego przez tkanki jabłka bez wywoływania dalszych zniszczeń.
EN
The paper contains a feasibility study for techniques of measuring bruise threshold and bruise energy as the parameters characterizing resistance of apples to bruise. The experiments were made with the aid of a pendulum-based apparatus. High sensitivity of both techniques was found, which made it possible to distinguish between fresh and stored fruits. The 50 mm fall height assumed allowed to achieve stabilisation of bruise surface only at the fifth impact. Proposed techniques allow also to determine the maximum dynamic stress, transferred by an apple tissues without further damage.
EN
Various methods for determination of shear velocity and bed shear stress in hydraulic research are discussed, comprising gravity method, logarithmic profile method, near-bed Reynolds-stress method, turbulent kinetic energy method, Prandtl based method, Saint Venant method, power law method, pipe flow method, Shields method, and direct methods. These methods are, where applicable, used to estimate shear velocity and/or bed shear stress in different fields of hydraulic research, ranging from flows in compound channels, gravel bed rivers, and cohesive sediment erosion studies to flows under unsteady conditions.
9
Content available remote Badania eksperymentalne własności turbulencji rzecznej w Polsce
EN
The present paper provides an overview of experimental investigations of the structure of river turbulence in open channels and lowland rivers in Poland. Domestic results were presented against the background of the selected investigations from the very rich world literature. In Poland only the information on on-dimensional properties of turbulence in lowland sand-bed rivers was obtained (Świder, Wilga, Marew and Wisła rivers). However, very interesting topics were considered like the influence of sand waves motions on the turbulence properties, the structure of river turbulence behind discharges from power stations, as well as unique experiments during the passage of flood waves in rivers. Laboratory studies embraced regular investigations in rectangular channels as well as the investigations in compound channels with vegetated flood plains among others. In most studies the main characteristics of turbulence and basic hydraulic and morphometric, quantities were computed. The analyses concerned the spatial distributions of velocity values, kinetic energy of turbulence, turbulence intensity and the dissipation rate of energy. The quantitative estimations of the scales of turbulence were carried out on the basis of analysis of frequency spectra, auto-correlation , and structure functions. Various empirical formulae were derived and checked. The investigated velocity spectra and structure functions were usually characterized by the existence of the inertial sub-range. We assert that further studies are necessary and they should include three-dimensional structure of river turbulence together with generated coherent structures.
10
Content available remote Wybrane metody dynamiki chaotycznej w hydrologii
EN
In this paper outline of modern methodology in the area of chaotic dynamics, applied in hydrological sciences and necessary in the analysis of nonlinear problems, is presented. The studies concerning chaos generated by turbulent flows in rivers, daily inflows to retention reservoirs and rainfall series, river sediment transport, and others are briefly discussed. The heuristic definitions are given for attractor and correlation dimension, conceptions indispensable for determination of time, for which the predictibility based on historical data is reasonable. Estimates of the dimensions of strange attractors for turbulent flows in rivers with various bed forms as well daily inflows to the considered Wupper Reservoir System are presented. Based on them the degree of complexity of the considered processes is evaluated.
EN
Unsteady longitudinal turbulence characteristics are studied in natural conditions in small, lowlad Wilga River in Poland. Two controlled flood waves were discherged in the river reach and their dynamics was discussed in the paper. Instantaneous velocities were measured continuously at selected points. The Fourier component method was utilized to obtain basic time-dependent characteristics of turbulence, namely: mean velociyies, root mean square of fluctuating velocities. Turbulent intensity, skewness and flatness. The modulation of turbulence by flood waves was also presented.
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