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DAM-BREAK SHOCK WAVES WITH FLOATING DEBRIS: EXPERIMENTALANALYSIS AND TWO-PHASE MODELLING  [cached]
Stefano Mambretti,Daniele De Wrachien,Enrico Larcan
Journal of Agricultural Engineering , 2008, DOI: 10.4081/jae.2008.2.7
Abstract: To predict floods and debris flow dynamics a numerical model, based on 1D De Saint Venant (SV) equations, was developed. The McCormack – Jameson shock capturing scheme was employed for the solution of the equations, written in a conservative law form. This technique was applied to determine both the propagation and the profile of a two – phase debris flow resulting from the instantaneous and complete collapse of a storage dam. To validate the model, comparisons have been made between its predictions and laboratory measurements concerning flows of water and homogeneous granular mixtures in a uniform geometry flume reproducing dam – break waves. Agreements between computational and experimental results are considered very satisfactory for mature (non – stratified) debris flows, which embrace most real cases. To better predict immature (stratified) flows, the model should be improved in order to feature, in a more realistic way, the distribution of the particles of different size within the mixture. On the whole, the model proposed can easily be extended to channels with arbitrary cross sections for debris flow routing, as well as for solving different problems of unsteady flow in open channels by incorporating the appropriate initial and boundary conditions.
Jams, Waves, and Clusters  [PDF]
Dirk Helbing,Martin Treiber
Physics , 1998,
Abstract: Have you been suffering from traffic jams lately and asking yourself why freeways are no free ways anymore? After several great advances in traffic theory, Korean physicists have now offered an interpretation of a recently discovered state of congested traffic, called ``synchronized'' traffic. Their fluid-dynamic simulations can be a useful tool for an optimization of traffic flow on motorways.
Emergent Traffic Jams  [PDF]
Kai Nagel,Maya Paczuski
Physics , 1995, DOI: 10.1103/PhysRevE.51.2909
Abstract: We study a single-lane traffic model that is based on human driving behavior. The outflow from a traffic jam self-organizes to a critical state of maximum throughput. Small perturbations of the outflow far downstream create emergent traffic jams with a power law distribution $P(t) \sim t^{-3/2}$ of lifetimes, $t$. On varying the vehicle density in a closed system, this critical state separates lamellar and jammed regimes, and exhibits $1/f$ noise in the power spectrum. Using random walk arguments, in conjunction with a cascade equation, we develop a phenomenological theory that predicts the critical exponents for this transition and explains the self-organizing behavior. These predictions are consistent with all of our numerical results.
Microscopic features of moving traffic jams  [PDF]
Boris S. Kerner,Sergey L. Klenov,Andreas Hiller,Hubert Rehborn
Physics , 2005, DOI: 10.1103/PhysRevE.73.046107
Abstract: Empirical and numerical microscopic features of moving traffic jams are presented. Based on a single vehicle data analysis, it is found that within wide moving jams, i.e., between the upstream and downstream jam fronts there is a complex microscopic spatiotemporal structure. This jam structure consists of alternations of regions in which traffic flow is interrupted and flow states of low speeds associated with "moving blanks" within the jam. Empirical features of the moving blanks are found. Based on microscopic models in the context of three-phase traffic theory, physical reasons for moving blanks emergence within wide moving jams are disclosed. Structure of moving jam fronts is studied based in microscopic traffic simulations. Non-linear effects associated with moving jam propagation are numerically investigated and compared with empirical results.
Decisive Markov Chains  [PDF]
Parosh Aziz Abdulla,Noomene Ben Henda,Richard Mayr
Computer Science , 2007, DOI: 10.2168/LMCS-3(4:7)2007
Abstract: We consider qualitative and quantitative verification problems for infinite-state Markov chains. We call a Markov chain decisive w.r.t. a given set of target states F if it almost certainly eventually reaches either F or a state from which F can no longer be reached. While all finite Markov chains are trivially decisive (for every set F), this also holds for many classes of infinite Markov chains. Infinite Markov chains which contain a finite attractor are decisive w.r.t. every set F. In particular, this holds for probabilistic lossy channel systems (PLCS). Furthermore, all globally coarse Markov chains are decisive. This class includes probabilistic vector addition systems (PVASS) and probabilistic noisy Turing machines (PNTM). We consider both safety and liveness problems for decisive Markov chains, i.e., the probabilities that a given set of states F is eventually reached or reached infinitely often, respectively. 1. We express the qualitative problems in abstract terms for decisive Markov chains, and show an almost complete picture of its decidability for PLCS, PVASS and PNTM. 2. We also show that the path enumeration algorithm of Iyer and Narasimha terminates for decisive Markov chains and can thus be used to solve the approximate quantitative safety problem. A modified variant of this algorithm solves the approximate quantitative liveness problem. 3. Finally, we show that the exact probability of (repeatedly) reaching F cannot be effectively expressed (in a uniform way) in Tarski-algebra for either PLCS, PVASS or (P)NTM.
PHYSICOCHEMICAL QUALITY OF SELECTED STRAWBERRY JAMS WITH FRUCTOSE  [cached]
Dorota Ga?kowska,Teresa Fortuna,Weronika Prochwicz Zagórska
Potravinarstvo : Scientific Journal for Food Industry , 2010, DOI: 10.5219/46
Abstract: Four different commercially available strawberry jams with fructose were characterized in relation to acidity and reducing sugar, ash, micro- and macroelement contents. The results showed that the jams differed in active and total acidity, ash, as well as reducing sugar content. Differences between the jams were more pronounced for microelements than for macroelements. doi:10.5219/46
Dynamics of traffic jams: order and chaos  [PDF]
Michael Blank
Physics , 2001,
Abstract: By means of a novel variational approach we study ergodic properties of a model of a multi lane traffic flow, considered as a (deterministic) wandering of interacting particles on an infinite lattice. For a class of initial configurations of particles (roughly speaking satisfying the Law of Large Numbers) the complete description of their limit (in time) behavior is obtained, as well as estimates of the transient period. In this period the main object of interest is the dynamics of `traffic jams', which is rigorously defined and studied. It is shown that the dynamical system under consideration is chaotic in a sense that its topological entropy (calculated explicitly) is positive. Statistical quantities describing limit configurations are obtained as well.
Discharge estimation in a backwater affected meandering river
H. Hidayat, B. Vermeulen, M. G. Sassi, P. J. J. F. Torfs,A. J. F. Hoitink
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2011,
Abstract: Variable effects of backwaters complicate the development of rating curves at hydrometric measurement stations. In areas influenced by backwater, single-parameter rating curve techniques are often inapplicable. To overcome this, several authors have advocated the use of an additional downstream level gauge to estimate the longitudinal surface level gradient, but this is cumbersome in a lowland meandering river with considerable transverse surface level gradients. Recent developments allow river flow to be continuously monitored through velocity measurements with an acoustic Doppler current profiler (H-ADCP), deployed horizontally at a river bank. This approach was adopted to obtain continuous discharge estimates at a cross-section in the River Mahakam at a station located about 300 km upstream of the river mouth in the Mahakam delta. The discharge station represents an area influenced by variable backwater effects from lakes, tributaries and floodplain ponds, and by tides. We applied both the standard index velocity method and a recently developed methodology to obtain a continuous time-series of discharge from the H-ADCP data. Measurements with a boat-mounted ADCP were used for calibration and validation of the model to translate H-ADCP velocity to discharge. As a comparison with conventional discharge estimation techniques, a stage-discharge relation using Jones formula was developed. The discharge rate at the station exceeded 3250 m3 s 1. Discharge series from a traditional stage-discharge relation did not capture the overall discharge dynamics, as inferred from H-ADCP data. For a specific river stage, the discharge range could be as high as 2000 m3 s 1, which is far beyond what could be explained from kinematic wave dynamics. Backwater effects from lakes were shown to be significant, whereas interaction of the river flow with tides may impact discharge variation in the fortnightly frequency band. Fortnightly tides cannot easily be isolated from river discharge variation, which features similar periodicities.
Discharge estimation in a backwater affected meandering river
H. Hidayat,B. Vermeulen,M. G. Sassi,P. J. J. F. Torfs
Hydrology and Earth System Sciences Discussions , 2011, DOI: 10.5194/hessd-8-2667-2011
Abstract: Variable effects of backwaters complicate the development of rating curves at hydrometric measurement stations. In areas influenced by backwater, single-parameter rating curve techniques are often inapplicable. To overcome this, several authors have advocated the use of an additional downstream level gauge to estimate the longitudinal surface level gradient, but this is cumbersome in a lowland meandering river with considerable transverse surface level gradients. Recent developments allow river flow to be continuously monitored through velocity measurements with an acoustic Doppler current profiler (H-ADCP), deployed horizontally at a river bank. This approach was adopted to obtain continuous discharge estimates at a cross-section in the River Mahakam at a station located about 300 km upstream of the river mouth in the Mahakam delta. The discharge station represents an area influenced by variable backwater effects from lakes, tributaries and floodplain ponds, and by tides. We applied both the standard index velocity method and a recently developed methodology to obtain a continuous time-series of discharge from the H-ADCP data. Measurements with a boat-mounted ADCP were used for calibration and validation of the model to translate H-ADCP velocity to discharge. As a comparison with conventional discharge estimation techniques, a stage-discharge relation using Jones formula was developed. The discharge rate at the station exceeded 3300 m3 s 1. Discharge series from a traditional stage-discharge relation did not capture the overall discharge dynamics, as inferred from H-ADCP data. For a specific river stage, the discharge range could be as high as 2000 m3 s 1, which is far beyond what could be explained from kinematic wave dynamics. Backwater effects from lakes were shown to be significant, whereas the river-tide interaction may impact discharge variation in the fortnightly frequency band. Fortnightly tides cannot easily be isolated from river discharge variation, which features similar periodicities.
Life-Times of Simulated Traffic Jams  [PDF]
K. Nagel
Physics , 1993, DOI: 10.1142/S012918319400074X
Abstract: We study a model for freeway traffic which includes strong noise taking into account the fluctuations of individual driving behavior. The model shows emergent traffic jams with a self-similar appearance near the throughput maximum of the traffic. The lifetime distribution of these jams shows a short scaling regime, which gets considerably longer if one reduces the fluctuations for driving at maximum speed but leaves the fluctuations for slowing down or accelerating unchanged. The outflow from a traffic jam self-organizes into this state of maximum throughput.
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