Dual-Based Local Search for Deterministic, Stochastic and Robust Variants of the Connected Facility Location Problem

In this dissertation, we propose the study of a family of network design problems that arise in a wide range of practical settings ranging from telecommunications to data management. We investigate the use of heuristic search procedures coupled with lower bounding mechanisms to obtain high quality solutions for deterministic, stochastic and robust variants of these problems. We extend the use of well-known methods such as the sample average approximation for stochastic optimization and the Bertsimas and Sim approach for robust optimization with heuristics and lower bounding mechanisms. This is particular important for NP-complete problems where even deterministic and small instances are difficult to solve to optimality. Our extensions provide a novel way of applying these techniques while using heuristics; which from a practical perspective increases their usefulness

NESIGURNOSTI I RIZICI PRI GEOLOŠKIM ISTRAŽIVANJIMA I NAČINI RJEŠAVANJA

The authors rewiev the main types of uncertainties occuring in connection with geological investigations. The general concept of handling these uncertainties are outlined. The particular features of scalar, spatial and spatial-temporal evaluations are presented. Limitations of the traditional mathematical approach – deterministic and probabilistic – applied to geological investigations are discused. In the second part of the paper nem mathematical methods are presented that are more suitable to handle uncertaintes that the traditional ones.The fuzzy set theory seems to be one of the most efficient for geological purposes, among these methods. The problems of uncertainty in risk analysis are shortly discussed. Finally, results of test calculations performed by fuzzy arithmetic are presented.Autori prikazuju glavne oblike nesigurnosti geoloških istraživanja. U glavnim su crtama izloženi postupci za rješavanje tih nesigurnosti. Posebno su prikazani rezultati skalarne, prostorne i prostorno-vremenske obrade. Ocijenjena su ograničenja tradicionalnih pristupa interpretaciji rezultata geoloških istraživanja – determinističkog i probabilističnog. U drugom dijelu članka prikazane su nove matematičke metode, prikladnije od tradicionalnih za obradu interpretacijskuh nesigurnosti. Čini se da je među tim metodama teorija fazi-postupka najefikasnija. Kritično su, ukratko, prikazani i problemi nesigurnosti u analizi rudarskog rizika. Konačno, prikazani su i rezultati nekih test-kalkulacija izvedenih fazi-aritmetikom

Simultaneous calibration of hydrological models in geographical space

Hydrological models are usually calibrated for selected catchments individually using specific performance criteria. This procedure assumes that the catchments show individual behavior. As a consequence, the transfer of model parameters to other ungauged catchments is problematic. In this paper, the possibility of transferring part of the model parameters was investigated. Three different conceptual hydrological models were considered. The models were restructured by introducing a new parameter η which exclusively controls water balances. This parameter was considered as individual to each catchment. All other parameters, which mainly control the dynamics of the discharge (dynamical parameters), were considered for spatial transfer. Three hydrological models combined with three different performance measures were used in three different numerical experiments to investigate this transferability. The first numerical experiment, involving individual calibration of the models for 15 selected MOPEX catchments, showed that it is difficult to identify which catchments share common dynamical parameters. Parameters of one catchment might be good for another catchment but not the opposite. In the second numerical experiment, a common spatial calibration strategy was used. It was explicitly assumed that the catchments share common dynamical parameters. This strategy leads to parameters which perform well on all catchments. A leave-one-out common calibration showed that in this case a good parameter transfer to ungauged catchments can be achieved. In the third numerical experiment, the common calibration methodology was applied for 96 catchments. Another set of 96 catchments was used to test the transfer of common dynamical parameters. The results show that even a large number of catchments share similar dynamical parameters. The performance is worse than those obtained by individual calibration, but the transfer to ungauged catchments remains possible. The performance of the common parameters in the second experiment was better than in the third, indicating that the selection of the catchments for common calibration is important

A framework for space–time modelling of rainfall events for hydrological applications of weather radar

\ua9 2024 The Author(s). High-resolution rainfall fields are a crucial tool for many hydrological and hydrodynamic applications, including flood forecasting and urban drainage design. The aim of this study is to explore and exploit the space–time properties of rainfall using Fast-Fourier transforms, to provide a new method for the generation of high-resolution synthetic rainfall grids. These fields have realistic spatio-temporal properties, parametrised using historical radar rainfall events, matching the resolution of weather radar data (1km, 5 min), for events with a duration of 0.5–6 h. Utilising spectral random field theory, simulated rainfall fields are generated with a prescribed correlation structure, anisotropy, advection and marginal rainfall rate proportions and distributions. A model for rainfall generation is demonstrated, with an enriched model parameter sampling architecture using meaningful event clustering, based on space–time event properties. This model framework performs well at recreating short-duration spatio-temporal rainfall events, both visually and statistically. The extension of a clustered rainfall model allows for larger-scale sampling of synthetic event parameters, with specific rainfall event types. There are numerous potential uses for this rainfall model, such as design storms or test cases for applications of radar rainfall estimates. These include but are not limited to nowcasting, numerical weather prediction, flash flood forecasting and machine learning model training data generation

Linking drought and wet weather in the Jordan catchment with atmospheric circulation patterns

Ponencia presentada en: VI Congreso Internacional de la Asociación Española de Climatología celebrado en Tarragona del 8 al 11 de octubre de 2008.[ES]El alcance de este estudio es la identificación de patrones de circulación sobre el Mediterráneo oriental los cuales están relacionados de una manera significativa con la precipitación extrema en la cuenca hidrográfica del Jordan. A ese fin, un método multi-objetivo de clasificación a base de lógica fuzzy se pone en practica. El método condiciona los datos de la precipitación y patrones de circulación atmosférica a gran escala diariamente. Para comenzar, se realiza la clasificación condicional de la precipitación para el período de 1961-1990 usando presión a nivel del mar y potencial geológico en 500hPa, dispuestos por el proyecto de reanálisis NCEP/NCAR. Se comprueba la plausibilidad de los patrones de circulación obtenidos para situaciones de sequia y humedas. Luego, se realiza un análisis de la frecuencia de su presencia a escala temporal de meses, años y décadas. Por último, se compara la distribución de frecuencia de los patrones de circulación para los años 1961-1990 con la distribución de frecuencia para los años 2011-2040 utilizando ECHAM5 impulsado por A1B. Se presenta y discuta el impacto del cambio climático al cambio de frecuencia en patrones de circulación en situaciones de sequia y humedas.[EN]The scope of this study is to identify circulation patterns (CPs) over the Eastern Mediterranean (EM), which are significantly linked to extreme rainfall events in the Jordan catchment. For this reason, a multi objective fuzzy logic-based classification (MOFRBC) method is applied, which conditions rainfall data to large-scale atmospheric circulation patterns on dthe aily time scale. First, the rainfall conditional classification is performed for the period 1961-1990 using Sea Level Pressure (SLP) and Geopotential Height in 500hPa (GPH500), retrieved from the NCEP/NCAR reanalysis project. The obtained drought and wet circulation patterns are checked for plausibility and a frequency analysis of their occurrence is performed on monthly, interannual and decadal time scales. Second, the CP frequency distribution of the 1961-1990 time slice is then compared to the frequency distribution of the 2011-2040 time slice using the A1B driven ECHAM5. The impact of climate change on the frequency change of droughty and wet circulation patterns is presented and discussed

Interaction of valleys and circulation patterns (CPs) on spatial precipitation patterns in southern Germany

Topography exerts influence on the spatial precipitation distribution over different scales, known typically at the large scale as the orographic effect, and at the small scale as the wind-drift rainfall (WDR) effect. At the intermediate scale (1~10 km), which is characterized by secondary mountain valleys, topography also demonstrates some effect on the precipitation pattern. This paper investigates such intermediate-scale topographic effects on precipitation patterns, focusing on narrow-steep valleys in the complex terrain of southern Germany, based on the daily observations over a 48 yr period (1960~2007) from a high-density rain-gauge network covering two sub-areas, Baden-Wuerttemberg (BW) and Bavaria (BY). Precipitation data at the valley and non-valley stations are compared under consideration of the daily general circulation patterns (CPs) classified by a fuzzy rule-based algorithm. Scatter plots of precipitation against elevation demonstrate a different behavior of valley stations comparing to non-valley stations. A detailed study of the precipitation time series for selected station triplets, each consisting of a valley station, a mountain station and an open station have been investigated by statistical analysis with the Kolmogorov–Smirnov (KS) test supplemented by the One-way analysis of variance (One-way ANOVA) and a graphical comparison of the mean precipitation amounts. The results show an interaction of valley orientation and the direction of the CPs at the intermediate scale, i.e. when the valley is shielded from the CP which carries the precipitation, the precipitation amount within the valley is comparable to that on the mountain crest, and both larger than the precipitation at the open station. When the valley is open to the CP, the precipitation within the valley is similar to the open station but much less than that on the mountain. Such phenomenon where the precipitation is "blind" to the valleys at the intermediate scale conditioned on CPs is defined as the "narrow-valley effect" in this work. Such an effect cannot be captured by the widely used elevation–precipitation relationship, which implies that the traditional geostatistical interpolation schemes, e.g. ordinary kriging (OK) or external drift kriging (EDK) applying digital elevation model (DEM) as external information, are not sufficient. An interpolation experiment applying EDK with orographic surrogate elevation defined in this paper as auxiliary information to account for the valley effects shows improvement for the cross-validation.M. Liu, A. Bárdossy, and E. Zeh