9 research outputs found
Distributed simulation of city inundation by coupled surface and subsurface porous flow for urban flood decision support system
We present a decision support system for flood early warning and disaster
management. It includes the models for data-driven meteorological predictions,
for simulation of atmospheric pressure, wind, long sea waves and seiches; a
module for optimization of flood barrier gates operation; models for stability
assessment of levees and embankments, for simulation of city inundation
dynamics and citizens evacuation scenarios. The novelty of this paper is a
coupled distributed simulation of surface and subsurface flows that can predict
inundation of low-lying inland zones far from the submerged waterfront areas,
as observed in St. Petersburg city during the floods. All the models are
wrapped as software services in the CLAVIRE platform for urgent computing,
which provides workflow management and resource orchestration.Comment: Pre-print submitted to the 2013 International Conference on
Computational Scienc
Slope Instability of the Earthen Levee in Boston, UK: Numerical Simulation and Sensor Data Analysis
The paper presents a slope stability analysis for a heterogeneous earthen
levee in Boston, UK, which is prone to occasional slope failures under tidal
loads. Dynamic behavior of the levee under tidal fluctuations was simulated
using a finite element model of variably saturated linear elastic perfectly
plastic soil. Hydraulic conductivities of the soil strata have been calibrated
according to piezometers readings, in order to obtain correct range of
hydraulic loads in tidal mode. Finite element simulation was complemented with
series of limit equilibrium analyses. Stability analyses have shown that slope
failure occurs with the development of a circular slip surface located in the
soft clay layer. Both models (FEM and LEM) confirm that the least stable
hydraulic condition is the combination of the minimum river levels at low tide
with the maximal saturation of soil layers. FEM results indicate that in winter
time the levee is almost at its limit state, at the margin of safety (strength
reduction factor values are 1.03 and 1.04 for the low-tide and high-tide
phases, respectively); these results agree with real-life observations. The
stability analyses have been implemented as real-time components integrated
into the UrbanFlood early warning system for flood protection
Identifying Self-excited Vibrations with Evolutionary Computing
AbstractThis study uses differential evolution to identify the coeffic ients of second-order differentia l equations of self-e xc ited vibrations fro m a time signal. The motivation is found in the ample occurrence of this vibration type in engineering and physics, in particu lar in the real -life proble m of v ibrations of hydraulic structure gates. In the proposed method, an equation structure is assumed at the level of the ordinary differentia l equation and a population of candidate coefficient vectors undergoes evolutionary training. In this way the numerical constants of non-linear terms of various self-e xc ited vibration types were recovered fro m the time signal and the velocity value only at the initial t ime. Co mparisons are given regarding accuracy and computing time. Dependency of the test errors on the algorith m para meters is studied in a sensitivity analysis. The presented evolutionary method shows good promise for future applicat ion in engineering systems, in particular operational early -wa rning systems that recognise oscillations with negative damping before they can cause damage
Evolutionary Design of Numerical Methods: Generating Finite Difference and Integration Schemes by Differential Evolution
Classical and new numerical schemes are generated using evolutionary
computing. Differential Evolution is used to find the coefficients of finite
difference approximations of function derivatives, and of single and multi-step
integration methods. The coefficients are reverse engineered based on samples
from a target function and its derivative used for training. The Runge-Kutta
schemes are trained using the order condition equations. An appealing feature
of the evolutionary method is the low number of model parameters. The
population size, termination criterion and number of training points are
determined in a sensitivity analysis. Computational results show good agreement
between evolved and analytical coefficients. In particular, a new fifth-order
Runge-Kutta scheme is computed which adheres to the order conditions with a sum
of absolute errors of order 10^-14. Execution of the evolved schemes proved the
intended orders of accuracy. The outcome of this study is valuable for future
developments in the design of complex numerical methods that are out of reach
by conventional means.Comment: 19 pages, 7 figures, 10 tables, 4 appendice
Reducing cross-flow vibrations of underflow gates: experiments and numerical studies
An experimental study is combined with numerical modelling to investigate new
ways to reduce cross-flow vibrations of hydraulic gates with underflow. A
rectangular gate section placed in a flume was given freedom to vibrate in the
vertical direction. Holes in the gate bottom enabled leakage flow through the
gate to enter the area directly under the gate which is known to play a key
role in most excitation mechanisms. For submerged discharge conditions with
small gate openings the vertical dynamic support force was measured in the
reduced velocity range 1.5 < Vr < 10.5 for a gate with and without holes. The
leakage flow through the holes significantly reduced vibrations. This
attenuation was most profound in the high stiffness region at 2 < Vr < 3.5.
Two-dimensional numerical simulations were performed with the Finite Element
Method to assess local velocities and pressures for both gate types. A moving
mesh covering both solid and fluid domain allowed free gate movement and
two-way fluid-structure interactions. Modelling assumptions and observed
numerical effects are discussed and quantified. The simulated added mass in
still water is shown to be close to experimental values. The spring stiffness
and mass factor were varied to achieve similar response frequencies at the same
dry natural frequencies as in the experiment. Although it was not possible to
reproduce the vibrations dominated by impinging leading edge vortices (ILEV) at
relatively low Vr, the simulations at high Vr showed strong vibrations with
movement-induced excitation (MIE). For the latter case, the simulated response
reduction of the ventilated gate agrees with the experimental results. The
numerical modelling results suggest that the leakage flow diminishes the
whipping effect of fluctuations at the trailing edge associated with the
streamwise pressure drop across the gate and the body's vertical oscillatory
motion.Comment: 27 pages, 15 figures, 2 table
Optimal floodgate operation for river flood management: The case study of Padova (Italy)
Study region: A large, densely populated area nearby Padova (Veneto Region, Italy) is exposed to floods owing to the Brenta-Bacchiglione river network, which is formed by two main rivers and by a set of interconnected channels, control structures and pump stations. Study focus: The Brenta and Bacchiglione rivers suffer from an increasing pressure in terms of flood events, especially for urban sprawl, anthropogenic modifications of drainage networks, and climate change. Finding and implementing effective remedies is hard in developed countries due to the presence of several constraints. Optimal flood management in complex river networks is then a way to reduce flood hazard, at a relatively low cost compared to structural measures. Hence, optimal operation rules for floodgates at an existing control structure are searched for to control the upstream water level and to divert a proper amount of the Bacchiglione discharge into the Brenta River. The operation rules have been endorsed by the Civil Engineering Department in charge of flood management and have been implemented in the flood forecasting Early Warning System of the Regional Civil Protection Office. New hydrological insights: The proper operation of control structures allows reducing flood risk by balancing the water discharge in the river networks. The engagement of end-users proves beneficial as it fosters exchange of knowledge and allows for the effective adoption of research outcomes in decision making
Free-surface flow simulations for discharge-based operation of hydraulic structure gates
We combine non-hydrostatic flow simulations of the free surface with a discharge model based on elementary gate flow equations for decision support in the operation of hydraulic structure gates. A water level-based gate control used in most of today's general practice does not take into account the fact that gate operation scenarios producing similar total discharged volumes and similar water levels may have different local flow characteristics. Accurate and timely prediction of local flow conditions around hydraulic gates is important for several aspects of structure management: ecology, scour, flow-induced gate vibrations and waterway navigation. The modelling approach is described and tested for a multi-gate sluice structure regulating discharge from a river to the sea. The number of opened gates is varied and the discharge is stabilized with automated control by varying gate openings. The free-surface model was validated for discharge showing a correlation coefficient of 0.994 compared to experimental data. Additionally, we show the analysis of CFD results for evaluating bed stability and gate vibrations
Free-surface flow simulations for discharge-based operation of hydraulic structure gates
We combine non-hydrostatic flow simulations of the free surface with a discharge model based on elementary gate flow equations for decision support in the operation of hydraulic structure gates. A water level-based gate control used in most of today's general practice does not take into account the fact that gate operation scenarios producing similar total discharged volumes and similar water levels may have different local flow characteristics. Accurate and timely prediction of local flow conditions around hydraulic gates is important for several aspects of structure management: ecology, scour, flow-induced gate vibrations and waterway navigation. The modelling approach is described and tested for a multi-gate sluice structure regulating discharge from a river to the sea. The number of opened gates is varied and the discharge is stabilized with automated control by varying gate openings. The free-surface model was validated for discharge showing a correlation coefficient of 0.994 compared to experimental data. Additionally, we show the analysis of CFD results for evaluating bed stability and gate vibrations