Stochastic field processes in the mathematical modelling of damped transmission line vibrations

Wind-excited vibrations in the frequency range of 10 to 50 Hz due to vortex shedding often cause fatigue failures in the cables of overhead transmission lines. Damping devices, such as the Stockbridge dampers, have been in use for a long time for supressing these vibrations. The dampers are conveniently modelled by means of their driving point impedance, measured in the lab over the frequency range under consideration. The cables can be modelled as strings with additional small bending stiffness. The main problem in modelling the vibrations does however lay in the aerodynamic forces, which usually are approximated by the forces acting on a rigid cylinder in planar flow. In the present paper, the wind forces are represented by stochastic processes with arbitrary crosscorrelation in space; the case of a Kármán vortex street on a rigid cylinder in planar flow is contained as a limit case in this approach. The authors believe that this new view of the problem may yield useful results, particularly also concerning the reliability of the lines and the probability of fatigue damages. © 1987.

Parâmetros de erosividade da chuva e da enxurrada correlacionados com perdas de solo e erodibilidade de um Latossolo Roxo de Dourados (MS)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Soil erosion fragility assessment using an impact model and geographic information system

A study was taken in a 1566 ha watershed situated in the Capivara River basin, municipality of Botucatu, São Paulo State, Brazil. This environment is fragile and can be subjected to different forms of negative impacts, among them soil erosion by water. The main objective of the research was to develop a methodology for the assessment of soil erosion fragility at the various different watershed positions, using the geographic information system ILWIS version 3.3 for Windows. An impact model was created to generate the soil's erosion fragility plan, based on four indicators of fragility to water erosion: land use and cover, slope, percentage of soil fine sand and accumulated water flow. Thematic plans were generated in a geographic information system (GIS) environment. First, all the variables, except land use and cover, were described by continuous numerical plans in a raster structure. The land use and cover plan was also represented by numerical values associated with the weights attributed to each class, starting from a pairwise comparison matrix and using the analytical hierarchy process. A final field check was done to record evidence of erosive processes in the areas indicated as presenting the highest levels of fragility, i.e., sites with steep slopes, high percentage of soil fine sand, tendency to accumulate surface water flow, and sites of pastureland. The methodology used in the environmental problems diagnosis of the study area can be employed at places with similar relief, soil and climatic conditions.

Dynamics of experimental populations of native and introduced blowflies (Diptera: Calliphoridae): mathematical modelling and the transition from asymptotic equilibrium to bounded oscillations

The equilibrium dynamics of native and introduced blowflies is modelled using a density-dependent model of population growth that takes into account important features of the life-history in these flies. A theoretical analysis indicates that the product of maximum fecundity and survival is the primary determinant of the dynamics. Cochliomyia macellaria, a blowfly native to the Americas and the introduced Chrysomya megacephala and Chrysomya putoria, differ in their dynamics in that the first species shows a damping oscillatory behavior leading to a one-point equilibrium, whereas in the last two species population numbers show a two-point limit cycle. Simulations showed that variation in fecundity has a marked effect on the dynamics and indicates the possibility of transitions from one-point equilibrium to bounded oscillations and aperiodic behavior. Variation in survival has much less influence on the dynamics.

Characterization of Soil Surface Roughness Effects on Runoff and Soil Erosion Rates under Simulated Rainfall

This study aims at identifying the influence of soil surface roughness from small to large aggregates (random roughness) on runoff and soil loss and to investigate the interaction with soil surface seal formation. Bulk samples of a silty clay loam soil were sieved to four aggregate-size classes of 3 to 12, 12 to 20, 20 to 45, 45 to 100 mm, and packed in soil trays set at a 5% slope. Rainfall simulations using an oscillating nozzle simulator were conducted for 90 min at an average rainfall intensity of 50.2 mm h(-1). Soil surface roughness was measured using an instantaneous profile laser scanner and surface sealing was studied by macroscopic analysis of epoxy impregnated soil samples. The rainfall simulations revealed longer times to initiate runoff with increasing soil surface roughness. For random roughness levels up to 6 mm, a decrease in final runoff rate with increasing roughness was observed. This can be attributed to a decreased breakdown of the larger roughness elements on rougher surfaces, thus keeping infiltration rate high. For a random roughness larger than 6 mm, a greater final runoff rate was observed. This was caused by the creation of a thick depositional seal in the concentrated flow areas, thus lowering the infiltration rates. Analysis of impregnated soil sample blocks confirmed the formation of a structural surface seal on smooth surfaces, whereas thick depositional seals were visible in the depressional areas of rougher surfaces. Therefore, from our observations it can be learned that soil surface roughness as formed by the presence of different aggregate sizes reduces runoff but that its effect diminishes due to aggregate breakdown and the formation of thick depositional seals in the case of rough soil surfaces. Sediment concentration increased with increasing soil surface roughness, due to runoff concentration in flow paths. Nevertheless, final soil loss rates were comparable for all soil roughness categories, indicating that random roughness is only important in influencing runoff rates and the time to initiate runoff, but not in influencing sediment export through soil loss rates.

Potential use of polyacrylamide for soil erosion control in Brazil

Since soil erosion is currently a worldwide threat, its control has become a necessity. The performance and effectiveness of synthetic organic polymers such polyacrylamide (PAM), have been intensively studied, especially for erosion control in temperate climate conditions. In tropical regions, however, where climatic conditions are usually severe, very little research has been conducted. The Brazilian region is a good example, where few papers on this subject exist. In addition to the severe climatic conditions, careless land use has been prevalent for many years. The use of PAM for erosion control in Brazilian soils may be a good option to minimize the impacts of the soil degradation process, but more research is required to optimize its application.

Erosion factors and magnetic susceptibility in differet compartments of a slope in Gilbués-PI, Brazil

A erosão é a forma de degradação do solo com efeitos na produtividade das culturas e na poluição do meio ambiente. Para compreender a variabilidade espacial desse fenômeno, técnicas geoestatísticas e conceitos da relação solo-paisagem podem ser utilizados para identificar compartimentos da paisagem com diferentes potenciais de erosão. O objetivo deste trabalho foi estabelecer elementos para a compreensão dos fatores de erosão em compartimentos da paisagem e das relações com a suscetibilidade magnética (SM) dos solos de uma vertente no município de Gilbués -PI. Foram montadas malhas de amostragem nos compartimentos I e II, com 121 pontos, e compartimento III, com 99 pontos, espaçados a cada 10 m. Houve diferença significativa para erodibilidade (K) e risco de erosão (RE); a variabilidade espacial da SM foi menor do que a dos fatores de erosão do solo. As perdas de solo (A), potencial natural de erosão (PNE), RE e SM tiveram relação espacial com o fator topográfico, indicando dependência da erosão ao relevo. Concluiu-se que as perdas de solo, o potencial natural de erosão e o risco de erosão apresentaram relação espacial com o fator topográfico, comprovando a dependência dos fatores de erosão ao relevo. A suscetibilidade magnética do solo pode ser utilizada como variável auxiliar na quantificação indireta do fator erodibilidade e do risco de erosão do solo.

Fuzzy Logic and Geostatistical Techniques for Spatialization of Soil Texture in Region with Rough Terrains

From the geotechnical standpoint, it is interesting to analyse the soil texture in regions with rough terrain due to its relation with the infiltration and runoff processes and, consequently, the effect on erosion processes. The purpose of this paper is to present a methodology that provides the soil texture spatialization by using Fuzzy logic and Geostatistic. The results were correlated with maps drawn specifically for the study area. The knowledge of the spatialization of soil properties, such as the texture, can be an important tool for land use planning in order to reduce the potential soil losses during rain seasons. (c) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of Spatial Statistics 2011

Action of soil microorganisms on PCL and PHBV blend and films

Poly(hydroxybutyrate-co-valerate) (PHBV) and poly(epsilon-caprolactone) (PCL) PCL/PHBV (4:1) blend films were prepared by melt-pressing. The biodegradation of the films in response to burial in soil for 30 days was investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry (TG). The PHBV film was the most susceptible to microbial attack, since it was rapidly biodegraded via surface erosion in 15 days and completely degraded in 30 days. The PCL film also degraded but more slowly than PHBV. The degradation of the PCL/PHBV blend occurred in the PHBV phase, inducing changes in the PCL phases (interphase) and resulting in an increase of its crystalline fraction.

Space analysis of water erosion in the red-yellow latosol under conilon coffee cultivation

This work aimed to study the space behavior of the water erosion in a red-yellow latosol. Then a study was developed in an area with colinon coffee cultivation in an Experimental Farm of Bananal do Norte of INCAPER in Cachoeiro de Itapemirim - ES. Soil samples were obtained from 0,0 to 0,20 m depth in an irregular grid with 109 samples. The analyzed variables were granulometric fractions, erodibility (K), natural erosion potential (PNE), soil loss (A) and erosion risk (RE). All the variables showed space dependency with moderate index of space dependency and similar standard of space distribution. The soil loss is related with the space distribution of the granulometric fractions.

Modelling of fatigue crack growth following overloads

In variable-amplitude loading there are interaction effects between the loading history and the crack propagation rate. The most important of these effects is the retardation in the crack propagation, which may raise the life of the cracked structureconsiderably. The main objective of this research is to analyse and quantify the retardation of crack propagation in a thin plate of the high-resistance aluminium alloy 2024-T3, comparing the results obtained from the mathematical models proposed to account for the retardation effect. The specimens were tested under high-low loading sequences, for different crack sizes and overload ratios. A simplified model was developed, based on crack closure theory, that could represent the crack behaviour during retardation very well. © 1991.

Modelling of the influence of the layer pollution thickness in high voltage polluted insulators

An experimental model and a mathematical model with the introduction of a ramp in the channel of Obenaus model are presented. The aim is to present a better reproduction of the real layer pollution deposited on the HV insulators. This better reproduction is obtained from two types of thickness variation: the introduction of a ramp (soft variation) and the introduction of a step (sudden variation). The computational simulations and the experimental data suggest that the introduction of the ramp is the better reproduction of the layer pollution. The ramp approximates to the real layer pollution more than the step.

Alteração da fertilidade do solo como indicador do processo de antropização e presença de atividades não agrícolas no assentamento rural Horto Aimorés, municípios de Bauru e Pederneiras/SP =: Change of soil fertility as an indicator of the anthropization process and presence of non agricultural activities at the rural settlement Horto Aimorés, cities of Bauru and Pederneiras/ SP

Pós-graduação em Geografia - FCT

Natural and anthropogenic influence on soil erosion in a rural watershed in the Brazilian southeastern region

Human activities have been driven land cover, provoking acceleration of the erosive process and alteration on the soil characteristics. To explore the effects of human disturbance, we investigated the influences of natural and anthropogenic features on soil quality and soil erosion indicators (EI) within a Brazilian rural watershed located in Bauru Municipality, State of So Paulo. A pre-established set of soil EI was used to evaluate the influence of anthropogenic land cover categories on the presence and severity of erosion, related with spatial variations of soil attributes. On-site visits were carried out to measure the occurrence and the intensity of eleven separate EI values and to collect undisturbed topsoil samples for subsequent analyses. We registered 17 occurrences of EIs, distributed in ten locals. Occurrence and intensity of EIs were related to degree of sheet erosion. The EI qualities were more strongly associated with land cover management practices than to local topographic features. The occurrence of EIs and characteristics of soil and soil organic matter (SOM) were not significantly self-correlated. Although land cover class seems to influence soil properties and SOM attributes, we observed that the granulometric composition of the soils also contributes to the structural characteristics of the soil and consequently to the dynamic loss and gain of soil carbon. Sites covered with natural remnant vegetation (NRV) store 96.5 Mg ha(-1) of C and grassy and tilled soils stored more C than NRV, 100.1 and 142.4 Mg ha(-1), respectively. Due to the influence of soil texture over the soil C dynamic, we observe that in Bauru, pastured areas have high potential for sequestration of C if factors such as fire and/or erosion were avoided or effectively controlled. Results from this study show that human disturbance substantially affects soil properties within of southeastern region of Brazil.