Variable Annealing Length and Parallelism in Simulated Annealing

In this paper, we propose: (a) a restart schedule for an adaptive simulated annealer, and (b) parallel simulated annealing, with an adaptive and parameter-free annealing schedule. The foundation of our approach is the Modified Lam annealing schedule, which adaptively controls the temperature parameter to track a theoretically ideal rate of acceptance of neighboring states. A sequential implementation of Modified Lam simulated annealing is almost parameter-free. However, it requires prior knowledge of the annealing length. We eliminate this parameter using restarts, with an exponentially increasing schedule of annealing lengths. We then extend this restart schedule to parallel implementation, executing several Modified Lam simulated annealers in parallel, with varying initial annealing lengths, and our proposed parallel annealing length schedule. To validate our approach, we conduct experiments on an NP-Hard scheduling problem with sequence-dependent setup constraints. We compare our approach to fixed length restarts, both sequentially and in parallel. Our results show that our approach can achieve substantial performance gains, throughout the course of the run, demonstrating our approach to be an effective anytime algorithm.Comment: Tenth International Symposium on Combinatorial Search, pages 2-10. June 201

The effect of generalized force correlations on the response statistics of a harmonically driven random system

If the physical properties of a structural component are sufficiently random then the statistical distribution of the natural frequencies and mode shapes tends to a universal distribution associated with the Gaussian Orthogonal Ensemble (GOE) of random matrices. Previous work has exploited this result to yield expressions for the relative variance of the energy of the response of a random system to harmonic excitation. The derivation of these expressions employed random point process theory, and in the theoretical development it was assumed that the modal generalised forces were uncorrelated. Although this assumption is often valid, there are cases in which correlations between the generalised forces can significantly affect the response variance, and in the present work the existing theory is extended to include correlations of this type. The extended theory is applicable to both single frequency responses and to band average responses, and the developed closed form expressions are validated by comparison with direct simulations for a random plate structure.Elke Deckers contribution was funded through The Research Fund KU Leuve

Aerodynamic performance of a periodically oscillating vertical axis wind turbine.

To ensure successful modeling of a floating wind turbine, its aerodynamic behaviour has to be investigated. At the time of writing, the only relevant studies on the topic are about vertical axis wind turbines (VAWTs) in skewed flow. There is lack of experimental, numerical or theorical studies about floating turbines. In the following thesis, the aerodynamic performance of a periodically oscillating VAWT is investigated through computational and theorical means. The complex dynamics of a floating turbine was simplified to a sinusoidal pitch motion, assuring simplicity without losing meaningfullness. A theory is given to predict the aerodynamic torque of an oscillating VAWT, obtaining it from the one of the same fixed axis turbine. A blade-element model was developed to achieve this result, taking into account the effect of oscillation on key parameters affecting the torque, that is angles of attack and relative wind speed. The core idea of the method, is to use blade element theory not as a prediction itself, but as a mean to correct the aerodynamic torque of the fixed axis turbine. The latter may be the result of both experiments, or numerical simulations. Theorical predictions were compared against data from CFD URANS simulations, for two different oscillation frequencies. These were chosen in the typical range of wave energy spectrum, in order to test representative conditions for floating applications. CFD simulations were also performed to obtain the torque of the fixed axis turbine, which was validated against experimental data from the 17m Darrieus-type rotor studied by SANDIA laboratories. Numerical simulations showed aerodynamic forces are deeply affected by oscillation. As intuition suggests, torque increases when the turbine pitches in the opposite direction of the wind, and decreases when it pitches in the same direction. This periodic oscillation causes significant ripple and maximum torque increase. For the higher oscillation frequency, which represents the most extreme condition, maximum torque was more than 2 times the one of the fixed turbine. Mean torque was found to be almost unaffected or slightly increased. For the higher oscillation frequency a 4.4% increase was observed. The theorical model was able to reproduce the behaviour of the oscillating turbine with satisfactory accuracy. To quantify the matching, absolute error was divided by the peak torque of the fixed axis turbine. For the lower oscillation frequency worst accuracy is 13.8%, while mean accuracy is 5.3%. As the frequency grows the hypothesis which the model is based on become less valid, so for the higher oscillation frequency precision decreases, in fact worst accuracy is 29.0% while mean is 9.1%. The theory proved to attain reasonably accurate results notwithstanding its simplicity, making it a cost-effective tool for quick analysis or optimization. Moreover, the theory could insight the way in which oscillation affects the torque. Considering relative wind speed separately showed that it has little influence, so it can be concluded that torque is affected by oscillation mainly by the change in the angles of attack. By comparing theorical and computational results, it was possible to show the dynamic effect on the downwind blade created by the wake of the upwind passage, a phenomenon which momentum models tailored for floating turbines should take into account. Finally some conclusions are drawn on the advantages and disadvantages of the aerodynamic features of Darrieus type VAWTs

Em busca das origens da «qualidade do vinho». Interação agrícola e desenvolvimento tecnológico na viticultura de Mendoza durante 1960-1990

The relationship between science, technology and agriculture for Mendoza viticulture goes through different stages depending on economic and political situations since the late nineteenth century. This historical process is also characterized by the interaction of various social actors, both public and private, generating spaces of tension and synergy related to productivity. During the second half of the twentieth century, the foundations were laid for the restructuring of wine caused by an extend and deep crisis in the sector (accentuated at the end of the 70s), which stimulated the reorientation of some producers towards the international market through new innovative knowledge and technological devices on the productive framework.This historical study intends to explain how the adoption of new tools, techniques, productive processes, selection of species or forms of harvest in the wine economic field generates a new position of the social actors and relevant institutions, to resignify the wine "quality" in Mendoza during 1960-1990. The analysis of historical sources such as the newspaper Los Andes de Mendoza, the magazine Vinos y Viñas, the publications of INV, Ministry of Agriculture of the Nation, INTA and Center of Winemakers, will allow to identify these positions and interactions that feed the social construction of quality and "good taste" from the development of a regional product with international significance.La relación entre ciencia, tecnología y agro para la vitivinicultura mendocina transita distintas etapas sujetas a las coyunturas económicas y políticas desde fines del siglo XIX. Dicho proceso histórico se caracteriza también por la interacción de diversos actores sociales, tanto públicos como privados, generando espacios de tensiones y sinergia en relación con la productividad. Durante la segunda mitad del siglo XX, se establecen las bases para la reestructuración vitivinícola ocasionada por una prolongada y profunda crisis del sector (acentuada a fines de los años setenta), que estimula la reorientación de algunos productores hacia el mercado internacional a través de nuevos conocimientos innovadores y artefactos tecnológicos sobre la trama productiva.Este estudio histórico procura explicar cómo la adopción de nuevas herramientas, técnicas y procesos de producción, selección de especies o formas de cosecha en el campo económico vitivinícola genera una nueva posición de los actores sociales e instituciones relevantes, para resignificar la «calidad» vitivinícola en Mendoza durante 1960-1990. El análisis de fuentes históricas como ser el periódico Los Andes de Mendoza, la revista Vinos y Viñas, las publicaciones del INV, del Ministerio de Agricultura de la Nación, del INTA y del Centro de Bodegueros, permitirán identificar dichas posiciones e interacciones que nutren a la construcción social de calidad y el «buen gusto» desde el desarrollo de un producto regional de alcance internacional. Imagen de portada: Verónica Ríos. "Cola caballo", 2022.A relação entre ciência, tecnologia e agricultura para a viticultura de Mendoza passa por diferentes etapas sujeitas às conjunturas econômicas e políticas desde o final do século XIX. Esse processo histórico também se caracteriza pela interação de diversos atores sociais, públicos e privados, gerando espaços de tensão e sinergia em relação à produtividade. Na segunda metade do século XX, foram lançadas as bases para a reestruturação vitivinícola provocada por uma prolongada e profunda crise do setor (acentuada no final da década de 1970), que estimulou a reorientação de alguns produtores para o mercado internacional através de novos conhecimentos inovadores e artefatos tecnológicos sobre a linha de produção.Este estudo histórico procura explicar como a adoção de novas ferramentas, técnicas e processos de produção, seleção de espécies ou formas de colheita no campo econômico do vinho gera uma nova posição de atores sociais e instituições relevantes, para ressignificar a "qualidade" do vinho em Mendoza durante 1960-1990. A análise de fontes históricas como o jornal Los Andes de Mendoza, a revista Vinos y Viñas, as publicações do INV, Ministério da Agricultura da Nação, INTA e Centro de Enólogos, permitirá identificar essas posições e interações que nutrem o construção de qualidade e "bom gosto" a partir do desenvolvimento de um produto regional com relevância internacional

Spider dynamics under vertical vibration and its implications for biological vibration sensing

Often overlooked, vibration transmission through the entire body of an animal is an important factor in understanding vibration sensing in animals. To investigate the role of dynamic properties and vibration transmission through the body, we used a modal test and lumped parameter modelling for a spider. The modal test used laser vibrometry data on a tarantula, and revealed five modes of the spider in the frequency range of 20–200 Hz. Our developed and calibrated model took into account the bounce, pitch and roll of the spider body and bounce of all the eight legs. We then performed a parametric study using this calibrated model, varying factors such as mass, inertia, leg stiffness, damping, angle and span to study what effect they had on vibration transmission. The results support that some biomechanical parameters can act as physical constraints on vibration sensing. But also, that the spider may actively control some biomechanical parameters to change the signal intensity it can sense. Furthermore, our analysis shows that the parameter changes in front and back legs have a greater influence on whole system dynamics, so may be of particular importance for active control mechanisms to facilitate biological sensing functions

Bayesian system identification for structures considering spatial and temporal correlation

The decreasing cost and improved sensor and monitoring system technology (e.g. fiber optics and strain gauges) have led to more measurements in close proximity to each other. When using such spatially dense measurement data in Bayesian system identification strategies, the correlation in the model prediction error can become significant. The widely adopted assumption of uncorrelated Gaussian error may lead to inaccurate parameter estimation and overconfident predictions, which may lead to sub-optimal decisions. This paper addresses the challenges of performing Bayesian system identification for structures when large datasets are used, considering both spatial and temporal dependencies in the model uncertainty. We present an approach to efficiently evaluate the log-likelihood function, and we utilize nested sampling to compute the evidence for Bayesian model selection. The approach is first demonstrated on a synthetic case and then applied to a (measured) real-world steel bridge. The results show that the assumption of dependence in the model prediction uncertainties is decisively supported by the data. The proposed developments enable the use of large datasets and accounting for the dependency when performing Bayesian system identification, even when a relatively large number of uncertain parameters is inferred.Comment: 33 pages, 16 figures; Revised after reviewer comments, corrected typos, recreated figure