Active vibration control in building-like structures submitted to earthquakes using multiple positive position feedback and sliding modes

This work deals with the structural and dynamic analysis of a building-like structure consisting of a three-story building with one passive/active vibration absorber. The base of the structure is perturbed using a shaker, providing excitation forces and noisy excitations emulating ground transportation, underground railways and earthquakes, quite common in Mexico City. It is considered a realistic seismic record of 8.1Mw occurred at Mexico City, containing some resonant frequencies of the structure. The mechanical structure is modeled using Euler-Lagrange methodology and validated using experimental modal analysis techniques. The active control scheme is synthesized to actively attenuate the noise and vibration system response, caused by noisy excitation forces acting on the base, by employing Multiple Positive Position Feedback and Sliding Mode Control to improve the closed-loop system response and, simultaneously, attenuate three vibration modes. Simulation and experimental results describe the overall system performance

ONLINE PARAMETRIC IDENTIFICATION OF MASS-SPRING-DAMPER MECHANICAL SYSTEMS USING ACCELERATION MEASUREMENTS

AbstractImplementation of active vibration control schemes, failure detection and monitoring tasks of the suitable operation of flexible mechanical structures can require the use of on-line parametric identification techniques. Measurements of acceleration signals are preferred in several applications of parameter identification of vibrating mechanical systems. In this article, an on-line parameter estimation approach in time domain is proposed for linear mass-spring-damper mechanical systems of n degrees of freedom using acceleration measurements solely. Integration by parts is properly used in the synthesis of the proposed parameter identification method. In this fashion, a priori knowledge of the initial conditions of the system becomes unnecessary. The introduced identification method can be extended for real-time parametric estimation of nonlinear fully actuated or under-actuated nonlinear vibrating mechanical systems. Some numerical results are provided to show the effectiveness of the on-line estimation approach of the mass, stiffness and damping parameters combined with closed-loop reference trajectory tracking tasks specified for the vibrating mechanical system.Keywords: Active vibration control, mass-spring-damper systems, mechanical vibration systems, parameter identification.IDENTIFICACIÓN PARAMÉTRICA EN LÍNEA DE SISTEMAS MECÁNICOS DE MASA-RESORTE-AMORTIGUADOR UTILIZANDO MEDICIONES DE ACELERACIÓNResumenImplementación de esquemas de control activo de vibraciones, detección de fallas o tareas de monitoreo de la operación adecuada de estructuras mecánicas flexibles pueden requerir el uso de técnicas de identificación paramétrica ejecutadas en línea. Mediciones de señales de aceleración se usan en varias aplicaciones de identificación de parámetros en sistemas mecánicos vibratorios. En este artículo se propone un enfoque para estimación de parámetros en línea en el dominio del tiempo para sistemas mecánicos del tipo masa-resorte-amortiguador de n grados de libertad, usando únicamente mediciones de aceleración. Se usa integración por partes en la síntesis del método de identificación de parámetros propuesto. De esta manera, conocimiento previo de las condiciones iniciales del sistema son innecesarias. El método de estimación propuesto se puede extender para estimación paramétrica en tiempo real para sistemas mecánicos vibratorios no lineales, completamente actuados o sub-actuados. Se incluyen algunos resultados de simulación numérica para mostrar la efectividad del enfoque de estimación de parámetros de masa, rigidez y amortiguamiento, combinado con tareas de seguimiento de trayectorias de referencia en lazo-cerrado especificadas para el sistema mecánico vibratorio.Palabras Claves: control activo de vibraciones, identificación de parámetros, sistemas mecánicos vibratorios, sistemas masa-resorte-amortiguador

A food web approach reveals the vulnerability of biocontrol services by birds and bats to landscape modification at regional scale

Pest control services provided by naturally occurring species (the so-called biocontrol services) are widely recognized to provide key incentives for biodiversity conservation. This is particularly relevant for vertebrate-mediated biocontrol services as many vertebrate species are of conservation concern, with most of their decline associated to landscape modification for agricultural purposes. Yet, we still lack rigorous approaches evaluating landscape-level correlates of biocontrol potential by vertebrates over broad spatial extents to better inform land-use and management decisions. We performed a spatially-explicit interaction-based assessment of potential biocontrol services in Portugal, using 1853 pairwise trophic interactions between 78 flying vertebrate species (birds and bats) and 53 insect pests associated to two widespread and economically valuable crops in the Euro-Mediterranean region, olive groves (Olea europaea subsp. europaea) and vineyards (Vitis vinifera subsp. vinifera). The study area was framed using 1004 square cells, each 10 × 10 km in size. Potential biocontrol services were determined at all those 10 × 10 km grid-cells in which each crop was present as the proportion of the realized out of all potential pairwise interactions between vertebrates and pests. Landscape correlates of biocontrol potential were also explored. Our work suggests that both birds and bats can effectively provide biocontrol services in olive groves and vineyards as they prey many insect pest species associated to both crops. Moreover, it demonstrates that these potential services are impacted by landscape-scale features and that this impact is consistent when evaluated over broad spatial extents. Thus, biocontrol potential by vertebrates significantly increases with increasing amount of natural area, while decreases with increasing area devoted to target crops, particularly olive groves. Overall, our study highlights the suitability of our interaction-based approach to perform spatially-explicit assessments of potential biocontrol services by vertebrates at local spatial scales and suggest its utility for integrating biodiversity and ecosystem services in conservation planning over broad spatial extents.This work was supported by the projects ECOLIVES (PTDC/AAG-REC/6480/2014) and OLEAdapt (PTDC/ BIA-CBI/1365/2020) both funded by the Portuguese National Public Agency for Science, Technology and Innovation, and the project SHOWCASE (ref. 862480) funded by the Horizon 2020 Research and Innovation programme from the European Union. and the project NORTE 01-0246-FEDER-000063, funded by Norte Portugal Regional Operational Programme (NORTE2020),under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF) JMH and FM were supported, respectively, by the contracts IF/00001/2015 and IF/01053/2015 funded by the FCT. JRP was supported by ‘la Caixa’ and ‘Caja Navarra’ Foundations, under agreement LCF/PR/PR13/51080004 in the framework of UPNA’s ‘Captación de Talento’ program. BS, GJ-N, SV and RM were supported, respectively, by the PhD studentships SFRH/BD/137803/2018, SFRH/BD/133017/2017, SFRH/BD/121388/2016 and SFRH/BD/99746/2014 funded by the FCT

Disentangling the seasonal effects of agricultural intensification on birds and bats in Mediterranean olive groves

Assessing the spatio-temporal impact of agricultural intensification on species and communities is key for biodiversity conservation. Here, we investigated the seasonal effects of olive grove intensification at both local (farming practices and grove structural complexity) and landscape scale (land-cover diversity) on birds and bats, at species and community-level. Both groups were surveyed during spring, summer, and autumn in 60 sites representing varying levels of olive grove intensification throughout the Alentejo region (southern Portugal). At the local scale, the number of chemical applications was used as a proxy for the intensification of farming practices and a Structural Index, which accounted for within-grove variability in tree density and features, was used as a measure of grove structural complexity. At landscape scale, we quantified the proportion of the major land-cover types potentially affecting birds and bats. We found that the abundance of ca. 77% of the species analyzed (ca. 84% and 55% of birds and bats respectively) was negatively related to olive grove intensification in at least one season. The Structural Index was the most influential factor at both species and community-levels, especially for birds, with a consistent and strong effect across seasons. Chemical applications had a stronger negative effect on birds, whereas the amount of olive grove cover had a stronger detrimental effect on bats. Birds and bats showed a variable response to predictor variables depending on the season, particularly for the bat community. Our study shows differences in bird and bat responses associated with the spatio-temporal variability of the agricultural intensification components. On the one hand, birds and bats showed a seasonal pattern of association with the different components of olive grove intensification, probably due to their ecological and biological requirements. On the other hand, the responses of both groups also appear to be scale-dependent: while birds seem to respond to in-farm or local intensification more strongly, bats seem to be more influenced by landscape-scale simplification. Overall, we highlight the importance of the structural complexity of olive groves for birds and bats, an aspect that should be considered in the design of agricultural policies aiming to promote biodiversity conservation.11 página

Canopy arthropod declines along a gradient of olive farming intensification

Arthropod declines have been linked to agricultural intensification. However, information about the impacts of intensification is still limited for many crops, as is our understanding of the responses of different arthropod taxa and trophic groups, thus hindering the development of effective mitigation measures. We investigated the impacts of olive farming intensification on canopydwelling arthropods in the Mediterranean region. Intensification involves the increased use of agrochemicals, mechanisation and irrigation, but also structural changes from traditional orchards with low densities of large and old trees, to intensive and superintensive orchards with high to very high densities of smaller and younger trees, respectively. Canopy arthropods were vacuumsampled at 53 sites representing the three orchard intensification levels, in spring, summer and autumn 2017. We evaluated how the arthropod community varied across intensification levels, and in response to orchard structure, management and landscape context. We found no changes in the diversity of arthropod taxa across intensification levels after correcting for sample coverage, but arthropod abundance declined markedly along the intensification gradient. Decreased abundance was associated with changes in orchard structure, lower herbaceous cover, and higher herbicide and insecticide use. The abundance of a specialized olive pest was lower in landscapes with higher woodland cover. The negative effects of intensification were stronger in spring and summer than in autumn, and parasitoids and predators were particularly affected. Overall, results suggest that retaining herbaceous cover, reducing agrochemical inputs and preserving natural woody elements in the landscape, may contribute to mitigate impacts of olive farming intensification on canopy arthropods, particularly on beneficial speciesinfo:eu-repo/semantics/publishedVersio