János Józsa - Academia.edu (original) (raw)
Papers by János Józsa
Österreichische Wasser- und Abfallwirtschaft, 2005
Kurzfassung Bei der Dimensionierung von Nachklärbecken (NKB) nach den aktuellen Bemessungsvorsch... more Kurzfassung Bei der Dimensionierung von Nachklärbecken (NKB) nach den aktuellen Bemessungsvorschriften werden die beckeninternen Prozesse und die Betriebsweise kaum berücksichtigt, auch wenn diese großen Einfluss auf eine wirksame Abscheidung besitzen. Die Strömungs- und lónzentrationsverteilungen eines NKB können anhand vonIN SITU, hochauflösenden Geschwindigkeits- und Konzentrations messungen detailliert beobachtet werden. Die gewonnenen Messdaten liefern die Grundlage zur Kalibrierung und Validierung eines numerischen Nachklärbecknmodells. Mit diesem Modell kann die Geometrie und die Betriebsweise des NKB optimiert werden. Mit einer guten Einlaufgeometrie und angepassten Rücklaufschlammförderung kann die Beckenleistung wesentlich gesteigert werden. Dieser Beitrag behandelt Ultraschall Doppler Geschwindigkeitsmessungen und optische Konzentrationsmessungen in einem NKB auf der Kläranlage Graz. Die Untersuchungen zeigeninteressante Details im Hinblick auf die Strömungsvorgänge und Turbulenzen sowie die Veränderungen der Schlammoberfläche und den Feststofftransport im untersuchten NKB. Mit Hilfe eines numerischen Simulationsmodells erfolgte im zweiten Schritt die Abbildung und Analyse der Systemverhältnisse.
... Arvind Kumar Lecturer, YMCA Institute of Engineering, Faridabad, and Research Scholar, IIT De... more ... Arvind Kumar Lecturer, YMCA Institute of Engineering, Faridabad, and Research Scholar, IIT Delhi, India ... Flat velocity and volume fraction of liquid and solid phases were introduced at the inlet condition of this pipe: that is, vm vs vf Vf , Uf Æf Vf , Æs Cvf and Æf 1 Ā Cvf ...
ABSTRACT The main goal of this paper is to introduce a suitable procedure for the assessment of r... more ABSTRACT The main goal of this paper is to introduce a suitable procedure for the assessment of reach-scale hydro-morphological conditions of rivers. For this purpose a 4 km long reach of River Tisza in Hungary was chosen and investigated by means of comprehensive field measurements and three-dimensional numerical modelling. The river can be characterized with an average depth of 6 m and an average width of 150 m, whereas the mean annual discharge is around 800 m3/s. The bed material is sand with a d50 of 0.2 mm. In the shallow zones of the river bed forms are migrating with a typical length of 20 m and amplitude of 0.3 m. The study reach has recently been surveyed in 2008 and 2010. The river bed evolution occurred during the two years is assessed by difference maps of the river bathymetry. Furthermore, moving and fixed ADCP measurements were carried out in order to reveal the spatial flow structure. Suspended sediment and bed material samples were also collected yielding the sediment discharge and characteristic grain size distributions. Moreover, the bed movement was also quantified in some locations of the reach based on the deviation between bottom track and GPS positions collected during fixed ADCP measurements. Parameterizing with the detailed field data a three-dimensional flow and sediment transport model was applied to carry out morphological simulations. The numerical model solves the Reynolds averaged Navier-Stokes equations (RANS) using a k-epsilon turbulence closure. The empirical formulas of van Rijn were used to estimate sediment concentration close to the bed. Moreover, the flow resistance due to bed forms was also considered using an empirical approach. A comparative analysis of the measured and simulated velocity field, sediment concentration and river bed migration was accomplished to introduce model capabilities. Furthermore, three-dimensional flow structure accounting for the development of local, unique morphological features is analysed. The coupled field and numerical investigations can greatly contribute to the establishment of the sediment budget for the study reach, however, further research is needed, e.g. analysis of high water regimes or the study of long term changes in the sediment transport and river morphology.
ABSTRACT Shallow lakes and reservoirs often present extended reed cover with significant spatial ... more ABSTRACT Shallow lakes and reservoirs often present extended reed cover with significant spatial complexity. These zones (mostly as littoral ones) differ significantly from pelagic areas as to their aerodynamic, hydro-, sediment as well as thermodynamic conditions, thus various, gradient-driven interaction and exchange mechanisms take place at the littoral-pelagic interface strongly affecting both zones and consequently the whole lake. The aims of our ongoing research are to reveal the main interaction factors between the littoral and pelagic zones of Lake Fertő (Neusiedler See) as case study, and investigate the dynamics of the processes in the interface zones. In order to do so, two measurement stations have been deployed in both zones near the boundary, where high-frequency synchronised measurements have been conducted to systematically reveal the driving factors and the consequences of the interface zone mechanisms. As the main driving factor of exchange processes is definitely the wind, to capture its effect, the wind speed and direction were measured with a number of 2- and 3D anemometers at both measurement stations, along with recording also the wind-driven lake currents at several characteristic points of the ambient lake water. Large-scale circulations as well as seiche motion were clearly present during the measurement period depending on the actual wind conditions. In addition, from the lake currents measured at the reed border it was possible to evaluate the water exchange across the interface of the two zones. For further investigation of the driving effect of wind, the wind profile above the reed canopy was quantified. Friction velocity, aerodynamic roughness height and displacement height were derived and found to be in the order of magnitude of 0.3 m/s, 0.1 m and 3 m, respectively. In long term, calm conditions, the exchange flow cannot be induced by the wind, in turn, it is thermally driven. In fact, the emergent reed causes different shading compared to the open water, which results in different heating of the surface layers of the water. The horizontal temperature differences developed in such a way cause then horizontal water density gradients thus generating convective motion across the interface zone. To investigate this process, air and water temperature measurements were conducted on multiple heights and depths, respectively, at both measurement stations, based on the data of which vertical thermal stratification and horizontal temperature differences could be analysed. The data analysis of two measurement periods (May-July and October-November 2012) are expected to provide novel information on the development of occasionally strong horizontal gradients of the above mentioned features at the interface zone. Nevertheless, further measurement campaigns are also planned with modified sensor locations and arrangements, with hopefully even more completed instrumentation set-up.
Österreichische Wasser- und Abfallwirtschaft, 2005
Kurzfassung Bei der Dimensionierung von Nachklärbecken (NKB) nach den aktuellen Bemessungsvorsch... more Kurzfassung Bei der Dimensionierung von Nachklärbecken (NKB) nach den aktuellen Bemessungsvorschriften werden die beckeninternen Prozesse und die Betriebsweise kaum berücksichtigt, auch wenn diese großen Einfluss auf eine wirksame Abscheidung besitzen. Die Strömungs- und lónzentrationsverteilungen eines NKB können anhand vonIN SITU, hochauflösenden Geschwindigkeits- und Konzentrations messungen detailliert beobachtet werden. Die gewonnenen Messdaten liefern die Grundlage zur Kalibrierung und Validierung eines numerischen Nachklärbecknmodells. Mit diesem Modell kann die Geometrie und die Betriebsweise des NKB optimiert werden. Mit einer guten Einlaufgeometrie und angepassten Rücklaufschlammförderung kann die Beckenleistung wesentlich gesteigert werden. Dieser Beitrag behandelt Ultraschall Doppler Geschwindigkeitsmessungen und optische Konzentrationsmessungen in einem NKB auf der Kläranlage Graz. Die Untersuchungen zeigeninteressante Details im Hinblick auf die Strömungsvorgänge und Turbulenzen sowie die Veränderungen der Schlammoberfläche und den Feststofftransport im untersuchten NKB. Mit Hilfe eines numerischen Simulationsmodells erfolgte im zweiten Schritt die Abbildung und Analyse der Systemverhältnisse.
... Arvind Kumar Lecturer, YMCA Institute of Engineering, Faridabad, and Research Scholar, IIT De... more ... Arvind Kumar Lecturer, YMCA Institute of Engineering, Faridabad, and Research Scholar, IIT Delhi, India ... Flat velocity and volume fraction of liquid and solid phases were introduced at the inlet condition of this pipe: that is, vm vs vf Vf , Uf Æf Vf , Æs Cvf and Æf 1 Ā Cvf ...
ABSTRACT The main goal of this paper is to introduce a suitable procedure for the assessment of r... more ABSTRACT The main goal of this paper is to introduce a suitable procedure for the assessment of reach-scale hydro-morphological conditions of rivers. For this purpose a 4 km long reach of River Tisza in Hungary was chosen and investigated by means of comprehensive field measurements and three-dimensional numerical modelling. The river can be characterized with an average depth of 6 m and an average width of 150 m, whereas the mean annual discharge is around 800 m3/s. The bed material is sand with a d50 of 0.2 mm. In the shallow zones of the river bed forms are migrating with a typical length of 20 m and amplitude of 0.3 m. The study reach has recently been surveyed in 2008 and 2010. The river bed evolution occurred during the two years is assessed by difference maps of the river bathymetry. Furthermore, moving and fixed ADCP measurements were carried out in order to reveal the spatial flow structure. Suspended sediment and bed material samples were also collected yielding the sediment discharge and characteristic grain size distributions. Moreover, the bed movement was also quantified in some locations of the reach based on the deviation between bottom track and GPS positions collected during fixed ADCP measurements. Parameterizing with the detailed field data a three-dimensional flow and sediment transport model was applied to carry out morphological simulations. The numerical model solves the Reynolds averaged Navier-Stokes equations (RANS) using a k-epsilon turbulence closure. The empirical formulas of van Rijn were used to estimate sediment concentration close to the bed. Moreover, the flow resistance due to bed forms was also considered using an empirical approach. A comparative analysis of the measured and simulated velocity field, sediment concentration and river bed migration was accomplished to introduce model capabilities. Furthermore, three-dimensional flow structure accounting for the development of local, unique morphological features is analysed. The coupled field and numerical investigations can greatly contribute to the establishment of the sediment budget for the study reach, however, further research is needed, e.g. analysis of high water regimes or the study of long term changes in the sediment transport and river morphology.
ABSTRACT Shallow lakes and reservoirs often present extended reed cover with significant spatial ... more ABSTRACT Shallow lakes and reservoirs often present extended reed cover with significant spatial complexity. These zones (mostly as littoral ones) differ significantly from pelagic areas as to their aerodynamic, hydro-, sediment as well as thermodynamic conditions, thus various, gradient-driven interaction and exchange mechanisms take place at the littoral-pelagic interface strongly affecting both zones and consequently the whole lake. The aims of our ongoing research are to reveal the main interaction factors between the littoral and pelagic zones of Lake Fertő (Neusiedler See) as case study, and investigate the dynamics of the processes in the interface zones. In order to do so, two measurement stations have been deployed in both zones near the boundary, where high-frequency synchronised measurements have been conducted to systematically reveal the driving factors and the consequences of the interface zone mechanisms. As the main driving factor of exchange processes is definitely the wind, to capture its effect, the wind speed and direction were measured with a number of 2- and 3D anemometers at both measurement stations, along with recording also the wind-driven lake currents at several characteristic points of the ambient lake water. Large-scale circulations as well as seiche motion were clearly present during the measurement period depending on the actual wind conditions. In addition, from the lake currents measured at the reed border it was possible to evaluate the water exchange across the interface of the two zones. For further investigation of the driving effect of wind, the wind profile above the reed canopy was quantified. Friction velocity, aerodynamic roughness height and displacement height were derived and found to be in the order of magnitude of 0.3 m/s, 0.1 m and 3 m, respectively. In long term, calm conditions, the exchange flow cannot be induced by the wind, in turn, it is thermally driven. In fact, the emergent reed causes different shading compared to the open water, which results in different heating of the surface layers of the water. The horizontal temperature differences developed in such a way cause then horizontal water density gradients thus generating convective motion across the interface zone. To investigate this process, air and water temperature measurements were conducted on multiple heights and depths, respectively, at both measurement stations, based on the data of which vertical thermal stratification and horizontal temperature differences could be analysed. The data analysis of two measurement periods (May-July and October-November 2012) are expected to provide novel information on the development of occasionally strong horizontal gradients of the above mentioned features at the interface zone. Nevertheless, further measurement campaigns are also planned with modified sensor locations and arrangements, with hopefully even more completed instrumentation set-up.