Concrete constitutive model, calibration and applications

A methodology has been developed for characterising the mechanical behaviour of concrete, based on the damaged plasticity model, enriched with a user subroutine (V)USDFLD in order to capture better the ductility of the material under moderate confining pressures. The model has been applied in the context of the international benchmark IRIS_2012, organised by the OECD/NEA/CSNI Nuclear Energy Agency, dealing with impacts of rigid and deformable missiles against reinforced concrete targets. A slightly modified version of the concrete damaged plasticity model was used to represent the concrete. The simulation results matched very well the observations made during the actual tests. Particularly successful predictions involved the energy spent by the rigid missile in perforating the target, the crushed length of the deformable missile, the crushed and cracked areas of the concrete target, and the values of the strains recorded at a number of locations in the concrete slab.

Evaluation and improvement of empirical models of global solar irradiation: Case study northern Spain

This paper presents a new methodology to build parametric models to estimate global solar irradiation adjusted to specific on-site characteristics based on the evaluation of variable im- portance. Thus, those variables higly correlated to solar irradiation on a site are implemented in the model and therefore, different models might be proposed under different climates. This methodology is applied in a study case in La Rioja region (northern Spain). A new model is proposed and evaluated on stability and accuracy against a review of twenty-two already exist- ing parametric models based on temperatures and rainfall in seventeen meteorological stations in La Rioja. The methodology of model evaluation is based on bootstrapping, which leads to achieve a high level of confidence in model calibration and validation from short time series (in this case five years, from 2007 to 2011). The model proposed improves the estimates of the other twenty-two models with average mean absolute error (MAE) of 2.195 MJ/m2 day and average confidence interval width (95% C.I., n=100) of 0.261 MJ/m2 day. 41.65% of the daily residuals in the case of SIAR and 20.12% in that of SOS Rioja fall within the uncertainty tolerance of the pyranometers of the two networks (10% and 5%, respectively). Relative differences between measured and estimated irradiation on an annual cumulative basis are below 4.82%. Thus, the proposed model might be useful to estimate annual sums of global solar irradiation, reaching insignificant differences between measurements from pyranometers.

Remote sensing of LAI, chlorophyll and leaf nitrogen pools of crop- and grasslands in five European landscapes.

Leaf nitrogen and leaf surface area influence the exchange of gases between terrestrial ecosystems and the atmosphere, and play a significant role in the global cycles of carbon, nitrogen and water. The purpose of this study is to use field-based and satellite remote-sensing-based methods to assess leaf nitrogen pools in five diverse European agricultural landscapes located in Denmark, Scotland (United Kingdom), Poland, the Netherlands and Italy. REGFLEC (REGularized canopy reFLECtance) is an advanced image-based inverse canopy radiative transfer modelling system which has shown proficiency for regional mapping of leaf area index (LAI) and leaf chlorophyll (CHLl) using remote sensing data. In this study, high spatial resolution (10–20 m) remote sensing images acquired from the multispectral sensors aboard the SPOT (Satellite For Observation of Earth) satellites were used to assess the capability of REGFLEC for mapping spatial variations in LAI, CHLland the relation to leaf nitrogen (Nl) data in five diverse European agricultural landscapes. REGFLEC is based on physical laws and includes an automatic model parameterization scheme which makes the tool independent of field data for model calibration. In this study, REGFLEC performance was evaluated using LAI measurements and non-destructive measurements (using a SPAD meter) of leaf-scale CHLl and Nl concentrations in 93 fields representing crop- and grasslands of the five landscapes. Furthermore, empirical relationships between field measurements (LAI, CHLl and Nl and five spectral vegetation indices (the Normalized Difference Vegetation Index, the Simple Ratio, the Enhanced Vegetation Index-2, the Green Normalized Difference Vegetation Index, and the green chlorophyll index) were used to assess field data coherence and to serve as a comparison basis for assessing REGFLEC model performance. The field measurements showed strong vertical CHLl gradient profiles in 26% of fields which affected REGFLEC performance as well as the relationships between spectral vegetation indices (SVIs) and field measurements. When the range of surface types increased, the REGFLEC results were in better agreement with field data than the empirical SVI regression models. Selecting only homogeneous canopies with uniform CHLl distributions as reference data for evaluation, REGFLEC was able to explain 69% of LAI observations (rmse = 0.76), 46% of measured canopy chlorophyll contents (rmse = 719 mg m−2) and 51% of measured canopy nitrogen contents (rmse = 2.7 g m−2). Better results were obtained for individual landscapes, except for Italy, where REGFLEC performed poorly due to a lack of dense vegetation canopies at the time of satellite recording. Presence of vegetation is needed to parameterize the REGFLEC model. Combining REGFLEC- and SVI-based model results to minimize errors for a "snap-shot" assessment of total leaf nitrogen pools in the five landscapes, results varied from 0.6 to 4.0 t km−2. Differences in leaf nitrogen pools between landscapes are attributed to seasonal variations, extents of agricultural area, species variations, and spatial variations in nutrient availability. In order to facilitate a substantial assessment of variations in Nl pools and their relation to landscape based nitrogen and carbon cycling processes, time series of satellite data are needed. The upcoming Sentinel-2 satellite mission will provide new multiple narrowband data opportunities at high spatio-temporal resolution which are expected to further improve remote sensing capabilities for mapping LAI, CHLl and Nl.

Evaluación de parámetros que influyen en el transporte de cloruros en hormigón parcialmente saturado

El deterioro del hormigón debido a la presencia del ion cloruro es causa frecuente de problemas en estructuras localizadas en ambiente marino y alta montaña. Su principal efecto consiste en la despasivación del acero de refuerzo embebido en el hormigón y su consecuente inicio de la corrosión del mismo. El ingreso del ion cloruro al interior del hormigón, está condicionado por una serie de parámetros de origen medioambiental e intrínsecos del hormigón. En función de estos parámetros el ingreso de cloruros en el hormigón puede deberse principalmente a los siguientes mecanismos: difusión y succión capilar. El estudio y evaluación de la resistencia del hormigón frente a cloruros, se ha desarrollado principalmente en condiciones saturadas del hormigón. Lo que ha significado que parámetros de importancia no sean considerados. Debido a esto, distintos procesos que suceden en estructuras reales no han sido identificados y estudiados correctamente. En este trabajo, se diseñó un programa de investigación para evaluar los parámetros que influyen en el transporte cloruros en hormigones no saturados. Para esto se diseñaron tres dosificaciones diferentes de hormigón. En la primera se empleó únicamente cemento portland, para el resto se utilizaron adiciones minerales (humo de sílice y escoria de alto horno). El empleo de adiciones se debió a que tienen un papel importante en la durabilidad de hormigones frente a cloruros. Los hormigones fueron dosificados con una relación agua/material cementício de 0,40 para el hormigón elaborado únicamente con cemento portland y 0,45 para las mezclas con adiciones. Para evaluar las propiedades de los hormigones en estado fresco y endurecido se realizaron ensayos vigentes en las normativas. Con los resultados obtenidos se determinaron parámetros de resistencia mecánica, microestructurales, resistencia al transporte de cloruros e higroscópicos. Una vez caracterizados los hormigones, se diseñó una propuesta experimental para estudiar los principales parámetros presentes en estructuras reales con presencia de cloruros. Tanto la concentración de cloruro como las condiciones ambientales se han variado teniendo como referencia las situaciones reales que podrían producirse en ambientes de alta montaña en la zona centro de España. La propuesta experimental consistió en tratar de evaluar la capacidad de los hormigones al transporte de iones en ambientes de alta montaña con presencia de sales fundentes. Para esto se establecieron 5 fases experimentales donde los principales parámetros ambientales y la presencia de iones agresivos sufrieron variaciones. Al término de cada fase se obtuvieron perfiles de penetración de cloruros en los hormigones y se evaluó la influencia de los parámetros presentes en cada fase. Los resultados experimentales se implementaron en un modelo numérico basado en la teoría de elementos finitos, desarrollado por el grupo de investigación del Departamento de Materiales de Construcción. Para esto fue necesario realizar la calibración y validación del modelo numérico para cada hormigón. El calibrado del modelo precisa de datos químicos y microestructurales de cada hormigón, tales como: capacidad de combinación de cloruros y propiedades difusivas e higroscópicas. Para la validación del modelo numérico se realizaron simulaciones de la propuesta experimental. Los resultados obtenidos se compararon con los valores experimentales. Con el objeto de poder estudiar en mayor profundidad la influencia del grado de saturación del hormigón durante la difusión de cloruros, se llevó a cabo una campaña experimental que consideró distintos grados de saturación en los hormigones. Para esto se establecieron en los hormigones cuatro grados de saturación distintos (50%, 60%, 80% y 100%, aproximadamente), posteriormente se expusieron a cloruro de sodio finamente molido. Una vez transcurrido el tiempo necesario se obtuvieron experimentalmente los perfiles de penetración de cloruros para cada grado de saturación y se calcularon los coeficientes de difusión. Los datos obtenidos durante la campaña experimental han demostrado la influencia positiva que ejercen las adiciones en las mezclas de hormigón. Sus principales ventajas son el refinamiento de la red porosa y el aumento en la capacidad de combinación de cloruros, además de mejorar sus propiedades mecánicas. La porosidad total en las mezclas no presentó grandes cambios, sin embargo, el cambio en la distribución del tamaño de poros es importante en las muestras con adiciones. En especial las fabricadas con humo de sílice. Los coeficientes de difusión y migración de cloruros para las mezclas con adiciones disminuyeron significativamente, igual que los valores de resistividad eléctrica. En los ensayos de penetración del agua bajo presión, fueron las muestras con adiciones las que mostraron las menores penetraciones. Los resultados obtenidos al final de la propuesta experimental permitieron estudiar los distintos parámetros involucrados. Se observó claramente que el proceso de difusión provoca el mayor transporte de cloruros hacia el interior del hormigón. Así mismo se comprobó que el lavado superficial y el secado de las probetas, trasladan cloruros hacia las zonas externas del hormigón. El primero debido a una baja concentración de cloruros externa, mientras que el secado provoca el movimiento de la solución de poro hacia las zonas de secado depositando cloruros en ellas. Las medidas higroscópicas permitieron determinar la existencia de dos zonas distintas en el interior del hormigón. La primera se localizó en el rango de 0-10mm, aproximadamente, en ésta se puso de manifiesto una mayor sensibilidad a los cambios experimentados en el exterior de las probetas. La segunda zona se localizó a una profundidad mayor de 10mm, aproximadamente. Se observó claramente una baja influencia de los cambios externos, siendo la difusión de cloruros el principal mecanismo de transporte presente en ella. En cuanto al estudio de la influencia del grado de saturación en la difusión de cloruros, se observó claramente una marcada diferencia entre los coeficientes de difusión de cloruro obtenidos. Para grados de saturación mayores del 80% el mecanismo de penetración de cloruros por difusión existe de forma significativa. Mientras que para valores inferiores los resultados revelaron que las vías de acceso disminuyen (poros conectado con agua) considerablemente limitando en un alto grado la penetración del agresivo. Para grados de saturación inferiores del 50% los valores del coeficiente de difusión son despreciables. The deterioration of concrete due to chloride ions is a frequent problem identified in structures located in marine and high-mountain environments. After entering the outer layer of the concrete, the chlorides tend to penetrate until they reach and then depassivate the steel bars. Subsequently, this induces the deterioration process of the reinforced concrete. This chloride penetration depends on the environmental conditions and intrinsic parameters of the concrete. Several transport mechanisms, such as diffusion, capillary suction and permeability can be present into the concrete. While recent research into the study and evaluation of concretes with chloride presence has been carried out in saturated concrete, it has not considered certain parameters that can modify this condition. Consequently, at the time of writing several processes that take place in real structures have not been identified and studied. In this work a research programme is designed to evaluate the parameters that influence chloride transport into non-saturated concrete. For this, three concrete mixes were designed by using high-early-strength Portland cement and mineral admixtures (silica fume and blast-slag furnace). The water-cement ratio was 0.40 for the concrete made solely with Portland cement and 0.45 for the concretes that used mineral admixtures as a cement replacement. A set of experimental tests were performed to evaluate the concrete properties both in fresh and hardened state. In addition, an experimental simulation was carried out under laboratory conditions in which the main objective was to assess resistance of concrete to chloride penetration under high-mountain conditions with the presence of de-icing salts. The environmental conditions and surface chloride concentration of the concrete used during the experimental simulation were chosen by considering conditions found in the high-mountain environment in central Spain. For the experimental simulation five phases were designed by varying the environmental parameters and concrete surface concentration. At the end of each phase a chloride profile was obtained with the aim of assessing the influence of the parameters on chloride transport. The experimental results were then used to calibrate and validate a numerical model based on finite element theory developed by the research team from the Construction Materials Department in a previous work. In order to carry out model calibration chemical and microstructural data for the concretes was required, such as binding capacity and the diffusive and hygroscopic properties. The experimental results were compared with the numerical simulations and provided a good fit. With the objective of studying the influence of the degree of concrete saturation on chloride diffusion, an experimental programme was designed. This entailed four saturation degrees (50%, 60%, 80% and 100%) being established in several concrete samples. The samples were then exposed to ground sodium chloride. Once the time required was achieved, the chloride profiles and diffusion coefficients were obtained for each saturation degree. The results obtained from the experimental program revealed a positive influence of the mineral admixtures on the concretes. Their effects were reflected in the pore-network refinement and the increase of chloride binding capacity, together with the improvement of the mechanical properties of the concretes. Total porosity did not reveal any notable change, though the pore-size distribution showed a significant degree of change in the concretes with mineral admixtures, specifically the samples prepared through use of silica fume. The chloride diffusion and migration coefficient, as well as the electrical resistivity values, decreased significantly in the concretes with admixtures. In the water penetration under pressure test, the concretes with admixtures presented the lowest penetration depth. The results obtained in the experimental simulation allowed study of the main parameters involved during the chloride penetration processes in non-saturated concretes in the presence of chlorides. According to the results, the diffusion process was the transport mechanism that transferred the greatest amount of chlorides into the concrete samples. In addition, a chloride movement toward external zones of the concrete, caused by the washing of concrete surface and the drying processes, was identified. The washing occurred when the concrete surface came into contact with a low-chloride concentration solution which initiated the outward movement of chloride diffusion. The drying processes corresponded to a movement of pore solution launched by water evaporation from the outer layer. Furthermore, hygroscopic measurements made in the concrete allowed two areas with distinct behavioural patterns to be identified. The first one, located in the range of approximately 0-10mm, showed a greater degree of influence regarding the changes of the external conditions. The second, situated at depths greater than 10mm, displayed a low influence of external conditions. The main process in this area was diffusion. Study of the influence of the degree of concrete saturation on chloride diffusion showed a clear difference among the chloride diffusion coefficients obtained. For degrees of concrete saturation higher than 80%, chloride penetration by diffusion tends to be significant. However, in the case of extent of saturation of lower than 80%, the results revealed that the access zone through which chlorides can penetrate decreased considerably. For degrees of concrete saturation lower than 50%, the chloride diffusion coefficients were negligible.

Using floating car data to analyse the effects of ITS measures and eco-driving

The road transportation sector is responsible for around 25% of total man-made CO2 emissions worldwide. Considerable efforts are therefore underway to reduce these emissions using several approaches, including improved vehicle technologies, traffic management and changing driving behaviour. Detailed traffic and emissions models are used extensively to assess the potential effects of these measures. However, if the input and calibration data are not sufficiently detailed there is an inherent risk that the results may be inaccurate. This article presents the use of Floating Car Data to derive useful speed and acceleration values in the process of traffic model calibration as a means of ensuring more accurate results when simulating the effects of particular measures. The data acquired includes instantaneous GPS coordinates to track and select the itineraries, and speed and engine performance extracted directly from the on-board diagnostics system. Once the data is processed, the variations in several calibration parameters can be analyzed by comparing the base case model with the measure application scenarios. Depending on the measure, the results show changes of up to 6.4% in maximum speed values, and reductions of nearly 15% in acceleration and braking levels, especially when eco-driving is applied.

Geografía del carbono en alta resolución en bosque tropical amazónico del Ecuador mediante sensores aerotransportados

La estimación de la biomasa de la vegetación terrestre en bosque tropical no sólo es un área de investigación en rápida expansión, sino también es un tema de gran interés para reducir las emisiones de carbono asociadas a la deforestación y la degradación forestal (REDD+). Las estimaciones de densidad de carbono sobre el suelo (ACD) en base a inventarios de campo y datos provenientes de sensores aerotransportados, en especial con sensores LiDAR, han conducido a un progreso sustancial en el cartografiado a gran escala de las reservas de carbono forestal. Sin embargo, estos mapas de carbono tienen incertidumbres considerables, asociadas generalmente al proceso de calibración del modelo de regresión utilizado para producir los mapas. En esta tesis se establece una metodología para la calibración y validación de un modelo general de estimación de ACD usando LiDAR en un sector del Parque Nacional Yasuní en Ecuador. En el proceso de calibración del modelo se considera el tamaño y la ubicación de las parcelas, la influencia de la topografía y la distribución espacial de la biomasa. Para el análisis de los datos se utilizan técnicas geoestadísticas en combinación con variables geomorfométricas derivadas de datos LiDAR, y se propone un esquema de muestreo estratificado por posiciones topográficas (valle, ladera y cima). La validación del modelo general para toda la zona de estudio presentó valores de RMSE = 5.81 Mg C ha-1, R2 = 0.94 y sesgo = 0.59, mientras que, al considerar las posiciones topográficas, el modelo presentó valores de RMSE = 1.67 Mg C ha-1, R2 = 0.98 y sesgo = 0.23 para el valle; RMSE = 3.13 Mg C ha-1, R2 = 0.98 y sesgo = - 0.34 para la ladera; y RMSE = 2.33 Mg C ha-1, R2 = 0.97 y sesgo = 0.74 para la cima. Los resultados obtenidos demuestran que la metodología de muestreo estratificado por posiciones topográficas propuesto, permite calibrar de manera efectiva el modelo general con las estimaciones de ACD en campo, logrando reducir el RMSE y el sesgo. Los resultados muestran el potencial de los datos LiDAR para caracterizar la estructura vertical de la vegetación en un bosque altamente diverso, permitiendo realizar estimaciones precisas de ACD, y conocer patrones espaciales continuos de la distribución de la biomasa aérea y del contenido de carbono en la zona de estudio. ABSTRACT Estimating biomass of terrestrial vegetation in tropical forest is not only a rapidly expanding research area, but also a subject of tremendous interest for reducing carbon emissions associated with deforestation and forest degradation (REDD+). The aboveground carbon density estimates (ACD) based on field inventories and airborne sensors, especially LiDAR sensors have led to a substantial progress in large-scale mapping of forest carbon stocks. However, these carbon maps have considerable uncertainties generally associated with the calibration of the regression model used to produce these maps. This thesis establishes a methodology for calibrating and validating a general ACD estimation model using LiDAR in Ecuador´s Yasuní National Park. The size and location of the plots are considered in the model calibration phase as well as the influence of topography and spatial distribution of biomass. Geostatistical analysis techniques are used in combination with geomorphometrics variables derived from LiDAR data, and then a stratified sampling scheme considering topographic positions (valley, slope and ridge) is proposed. The validation of the general model for the study area showed values of RMSE = 5.81 Mg C ha-1, R2 = 0.94 and bias = 0.59, while considering the topographical positions, the model showed values of RMSE = 1.67 Mg C ha-1, R2 = 0.98 and bias = 0.23 for the valley; RMSE = 3.13 Mg C ha-1, R2 = 0.98 and bias = - 0.34 for the slope; and RMSE = 2.33 Mg C ha-1, R2 = 0.97 and bias = 0.74 for the ridge. The results show that the stratified sampling methodology taking into account topographic positions, effectively calibrates the general model with field estimates of ACD, reducing RMSE and bias. The results show the potential of LiDAR data to characterize the vertical structure of vegetation in a highly diverse forest, allowing accurate estimates of ACD, and knowing continuous spatial patterns of biomass distribution and carbon stocks in the study area.

Risk-based methodology for parameter calibration of a reservoir flood control model

Flash floods are of major relevance in natural disaster management in the Mediterranean region. In many cases, the damaging effects of flash floods can be mitigated by adequate management of flood control reservoirs. This requires the development of suitable models for optimal operation of reservoirs. A probabilistic methodology for calibrating the parameters of a reservoir flood control model (RFCM) that takes into account the stochastic variability of flood events is presented. This study addresses the crucial problem of operating reservoirs during flood events, considering downstream river damages and dam failure risk as conflicting operation criteria. These two criteria are aggregated into a single objective of total expected damages from both the maximum released flows and stored volumes (overall risk index). For each selected parameter set the RFCM is run under a wide range of hydrologic loads (determined through Monte Carlo simulation). The optimal parameter set is obtained through the overall risk index (balanced solution) and then compared with other solutions of the Pareto front. The proposed methodology is implemented at three different reservoirs in the southeast of Spain. The results obtained show that the balanced solution offers a good compromise between the two main objectives of reservoir flood control management

Initializing the DSSAT-Century model: inverse calibration of carbon pools from apparent soil N mineralization

The CENTURY soil organic matter model was adapted for the DSSAT (Decision Support System for Agrotechnology Transfer), modular format in order to better simulate the dynamics of soil organic nutrient processes (Gijsman et al., 2002). The CENTURY model divides the soil organic carbon (SOC) into three hypothetical pools: microbial or active material (SOC1), intermediate (SOC2) and the largely inert and stable material (SOC3) (Jones et al., 2003). At the beginning of the simulation, CENTURY model needs a value of SOC3 per soil layer which can be estimated by the model (based on soil texture and management history) or given as an input. Then, the model assigns about 5% and 95% of the remaining SOC to SOC1 and SOC2, respectively. The model performance when simulating SOC and nitrogen (N) dynamics strongly depends on the initialization process. The common methods (e.g. Basso et al., 2011) to initialize SOC pools deal mostly with carbon (C) mineralization processes and less with N. Dynamics of SOM, SOC, and soil organic N are linked in the CENTURY-DSSAT model through the C/N ratio of decomposing material that determines either mineralization or immobilization of N (Gijsman et al., 2002). The aim of this study was to evaluate an alternative method to initialize the SOC pools in the DSSAT-CENTURY model from apparent soil N mineralization (Napmin) field measurements by using automatic inverse calibration (simulated annealing). The results were compared with the ones obtained by the iterative initialization procedure developed by Basso et al., 2011.

Dynamic chanel model LMS updating for RSS-based localization

Received signal strength-based localization systems usually rely on a calibration process that aims at characterizing the propagation channel. However, due to the changing environmental dynamics, the behavior of the channel may change after some time, thus, recalibration processes are necessary to maintain the positioning accuracy. This paper proposes a dynamic calibration method to initially calibrate and subsequently update the parameters of the propagation channel model using a Least Mean Squares approach. The method assumes that each anchor node in the localization infrastructure is characterized by its own propagation channel model. In practice, a set of sniffers is used to collect RSS samples, which will be used to automatically calibrate each channel model by iteratively minimizing the positioning error. The proposed method is validated through numerical simulation, showing that the positioning error of the mobile nodes is effectively reduced. Furthermore, the method has a very low computational cost; therefore it can be used in real-time operation for wireless resource-constrained nodes.

A method for Kinematic Calibration of a Parallel Robot by using one camera in hand and a spherical object

The main purpose of robot calibration is the correction of the possible errors in the robot parameters. This paper presents a method for a kinematic calibration of a parallel robot that is equipped with one camera in hand. In order to preserve the mechanical configuration of the robot, the camera is utilized to acquire incremental positions of the end effector from a spherical object that is fixed in the word reference frame. The positions of the end effector are related to incremental positions of resolvers of the motors of the robot, and a kinematic model of the robot is used to find a new group of parameters which minimizes errors in the kinematic equations. Additionally, properties of the spherical object and intrinsic camera parameters are utilized to model the projection of the object in the image and improving spatial measurements. Finally, the robotic system is designed to carry out tracking tasks and the calibration of the robot is validated by means of integrating the errors of the visual controller.

A simple genetic algorithm for calibration of stochastic rock discontinuity networks

Este artículo propone un método para llevar a cabo la calibración de las familias de discontinuidades en macizos rocosos. We present a novel approach for calibration of stochastic discontinuity network parameters based on genetic algorithms (GAs). To validate the approach, examples of application of the method to cases with known parameters of the original Poisson discontinuity network are presented. Parameters of the model are encoded as chromosomes using a binary representation, and such chromosomes evolve as successive generations of a randomly generated initial population, subjected to GA operations of selection, crossover and mutation. Such back-calculated parameters are employed to make assessments about the inference capabilities of the model using different objective functions with different probabilities of crossover and mutation. Results show that the predictive capabilities of GAs significantly depend on the type of objective function considered; and they also show that the calibration capabilities of the genetic algorithm can be acceptable for practical engineering applications, since in most cases they can be expected to provide parameter estimates with relatively small errors for those parameters of the network (such as intensity and mean size of discontinuities) that have the strongest influence on many engineering applications.

Calibration of WAVE in irrigated maize: fallow vs. cover crops.

Nitrate leaching decreases crop available N and increases water contamination. Replacing fallow by cover crops (CC) is an alternative to reduce nitrate contamination, because it reduces overall drainage and soil mineral N accumulation. A study of the soil N and nitrate leaching was conducted during 5 years in a semi-arid irrigated agricultural area of Central Spain. Three treatments were studied during the intercropping period of maize (Zea mays L.): barley (Hordeum vulgare L.), vetch (Vicia villosa L.), and fallow. Cover crops, sown in October, were killed by glyphosate application in March, allowing direct seeding of maize in April. All treatments were irrigated and fertilised following the same procedure. Soil water content was measured using capacity probes. Soil Nmin accumulation was determined along the soil profile before sowing and after harvesting maize. Soil analysis was conducted at six depths every 0.20m in each plot in samples from 0 to 1.2-m depth. The mechanistic water balance model WAVE was applied in order to calculate drainage and plant growth of the different treatments, and apply them to the N balance. We evaluated the water balance of this model using the daily soil water content measurements of this field trial. A new Matlab version of the model was evaluated as well. In this new version improvements were made in the solute transport module and crop module. In addition, this new version is more compatible with external modules for data processing, inverse calibration and uncertainty analysis than the previous Fortran version. The model showed that drainage during the irrigated period was minimized in all treatments, because irrigation water was adjusted to crop needs, leading to nitrate accumulation on the upper layers after maize harvest. Then, during the intercrop period, most of the nitrate leaching occurred. Cover crops usually led to a shorter drainage period, lower drainage water amount and lower nitrate leaching than the treatment with fallow. These effects resulted in larger nitrate accumulation in the upper layers of the soil after CC treatments.

An Inexpensive Method for Kinematic Calibration of a Parallel Robot by Using One Hand-Held Camera as Main Sensor

This paper presents a novel method for the calibration of a parallel robot, which allows a more accurate configuration instead of a configuration based on nominal parameters. It is used, as the main sensor with one camera installed in the robot hand that determines the relative position of the robot with respect to a spherical object fixed in the working area of the robot. The positions of the end effector are related to the incremental positions of resolvers of the robot motors. A kinematic model of the robot is used to find a new group of parameters, which minimizes errors in the kinematic equations. Additionally, properties of the spherical object and intrinsic camera parameters are utilized to model the projection of the object in the image and thereby improve spatial measurements. Finally, several working tests, static and tracking tests are executed in order to verify how the robotic system behaviour improves by using calibrated parameters against nominal parameters. In order to emphasize that, this proposed new method uses neither external nor expensive sensor. That is why new robots are useful in teaching and research activities.

Calibration of calculation models of wooden guardrails with Operational Modal Analysis

This study analyses the differences between two calculation models for guardrails on building sites that use wooden boards and tubular steel posts. Wood was considered an isotropic material in one model and an orthotropic material in a second model. The elastic constants of the wood were obtained with ultrasound. Frequencies and vibration modes were obtained for both models through linear analysis using the finite element method. The two models were experimentally calibrated through operational modal analysis. The results obtained show that for the three types of wood under analysis, the model which considered them as an orthotropic material fitted the experimental results better than the model which considered them as an isotropic material.

Spatially-Explicit Testing of a General Aboveground Carbon Density Estimation Model in aWestern Amazonian Forest Using Airborne LiDAR

Mapping aboveground carbon density in tropical forests can support CO2 emissionmonitoring and provide benefits for national resource management. Although LiDAR technology has been shown to be useful for assessing carbon density patterns, the accuracy and generality of calibrations of LiDAR-based aboveground carbon density (ACD) predictions with those obtained from field inventory techniques should be intensified in order to advance tropical forest carbon mapping. Here we present results from the application of a general ACD estimation model applied with small-footprint LiDAR data and field-based estimates of a 50-ha forest plot in Ecuador?s Yasuní National Park. Subplots used for calibration and validation of the general LiDAR equation were selected based on analysis of topographic position and spatial distribution of aboveground carbon stocks. The results showed that stratification of plot locations based on topography can improve the calibration and application of ACD estimation using airborne LiDAR (R2 = 0.94, RMSE = 5.81 Mg?C? ha?1, BIAS = 0.59). These results strongly suggest that a general LiDAR-based approach can be used for mapping aboveground carbon stocks in western lowland Amazonian forests.