Orlando Maeso

Single- and multi-objective shape design of Y-noise barriers using evolutionary computation and boundary elements

The optimum shape design of Y-noise barriers is carried out using single and multi-objective evolutionary algorithms and the Boundary Element Method (BEM). Reduction of noise impact efficiency (using the insertion loss-IL-magnitude) and cost of the barrier (using its total length magnitude) are considered. A two-dimensional problem of sound propagation in the frequency domain is handled, defined by a fixed position emitting source, which pulses in a frequency range, and receptor. A noise barrier (limiting its maximum effective height) is situated between both. Its shape is modified to minimize the receptor measured sound level, which is calculated using BEM. Results of an inverse problem using the IL barrier curve as reference are successfully performed to validate the methodology. The proposed methodology is then used to obtain Y-barriers with 15% and 30% improved IL spectrum. Finally, six non-dominated solutions of the multi-objective optimum design problem are presented in detail.

Robust Design of Noise Attenuation Barriers with Evolutionary Multiobjective Algorithms and the Boundary Element Method

Multiobjective shape design of acoustic attenuation barriers is handled using a boundary element method modeling and evolutionary algorithms. Noise barriers are widely used for environmental protection near population nucleus in order to reduce the noise impact. The minimization of the acoustic pressure and the minimization of the cost of the barrier -considering its total length- are taken into account. First, a single receiver point is considered; then the case of multiple receiver locations is introduced, searching for a single robust shape design where the acoustic attenuation is minimized simultaneously in different locations using probabilistic dominance relation. The case of Y-shaped barriers with upper absorbing surface is presented here. Results include a comparative between the strategy of introducing a single objective optimum in the initial multiobjective population (seeded approach) and the standard approach. The methodology is capable to provide improved robust noise barrier designs successfully.

Multi-Building Interactions and Site-City Effect: An Idealized Experimental Model

This chapter aims at identifying, describing and quantifying multi-building interactions and site-city effects through experimental, theoretical and numerical crossed-analysis. Multiple Structure-Soil-Structure interactions are investigated through an idealized experimental model of a city on a soft layer the properties of which are simple enough to be reproduced in numerical and theoretical models. The experimental set-up is designed to provide a good matching between the fundamental frequencies of the city and of the layer. Experimental results show (i) drastic changes in the layer’s response with two low amplitude resonance peaks favorable to longer coda and beatings and (ii) unconventional depolarization effects. The resulting data is compared with the theoretical city-impedance model derived by homogenization methods (Boutin and Roussillon, Bull Seismol Soc Am 94(1):251–268, 2004) and with a 2D hybrid BEM-FEM numerical model (Padron et al., Calculo de estructuras de barras incluyendo efectos dinamicos de interaccion suelo-estructura. Master thesis, Universidad de Las Palmas de G.C., Spain. http://hdl.handle.net/10553/10472, 2004). The specific features of multiple interactions are successfully reproduced by both models providing a qualitative and quantitative agreement with experimental results and with one another.

THREE-DIMENSIONAL BE-FE MODEL OF BUCKET FOUNDATIONS IN POROELASTIC SOILS

Abstract. A three-dimensional BE–FE model for the time harmonic analysis of bucket foundations in poroelastic soils is presented. The soil follows the Biot’s poroelasticity and is discretized using the BEM. The skirt of the bucket is modeled as a degenerated shell finite element. The soil-structure interaction is taken into account assuming a crack-like boundary from the soil point of view, where the Dual BEM is applied. It is shown that this simple representation is accurate and efficient. This model is applied to an analysis of the impedances of bucket foundations, where the influences of the foundation geometry and soil properties are studied. The study shows that, when considering realistic seabed soils, a poroelastic model should be used for the low-frequency range ( < 1− 6 Hz depending on the seabed soil). It is shown that this is particularly true for bucket foundations with small length to diameter ratios.

DYNAMIC RESPONSE OF REAL OFFSHORE WIND TURBINES ON MONOPILES IN STRATIFIED SEABED

This paper studies the influence of the superstructure and foundation parameters of offshore wind turbine (OWT) systems, as well as of the soil profile, on the magnitude of the associated soil-structure interaction (SSI) phenomena. The analyses are carried out by assuming characteristic properties of real OWTs and of soil profiles based on North Sea boreholes. To do so, a simplified substructuring model is proposed for the computation of the fundamental frequency and equivalent damping of OWTs founded on monopiles including the SSI effects. The whole superstructure is reduced to a three-degrees-of-freedom system through its modal mass and height, while the foundation stiffness is represented by impedance functions. The pile impedance functions are computed by a time-harmonic integral model that makes use of Green’s Functions for the layered halfspace to represent the soil behaviour, while the pile is represented by finite elements as a Timoshenko beam and treated as a load-line within the soil. The obtained results confirm the necessity of considering the SSI effects for an accurate estimation of both the fundamental frequency and equivalent damping of the soil-structure system. Regarding the pile dimensions, the pile diameter plays a significant role on the magnitude of the SSI effects, while the pile length has almost no influence. On the other hand, the results highlight the importance of a good knowledge of the soil profile, as high differences are produced between the homogeneous and variable-with-depth profiles, even when both present the same mean shear velocity. The superficial soil layers are found to be the ones of crucial importance when evaluating the SSI effects on the dynamic properties of OWT systems. Guillermo M. Álamo, Juan J. Aznárez, Luis A. Padrón, Alejandro E. Martı́nez-Castro, Rafael Gallego and Orlando Maeso

A Comparative Study on Design Optimization of Polygonal and Bézier Curve-Shaped Thin Noise Barriers Using Dual BEM Formulation

The inclusion of sound barriers for abating road traffic noise is a broadly used strategy that is often constrained by the requirements associated with its effective height. Due to this fact, the searching process has to deal with compromise solutions between the effective height and the acoustic efficiency of the barrier, assessed by the insertion loss (IL) in this paper. Two different barrier designs are studied herein for two different receivers configurations and for three clearly distinguishable regions in terms of closeness to the barrier. These models are based on the optimization of the IL of thin-cross section profiles proposed by an Evolutionary Algorithm. The special nature of these sorts of barriers makes necessary the implementation of a dual BEM formulation in the optimization process. Results obtained show the usefulness of representing complex thin-cross section barrier configurations as null boundary thickness-like models.

A Procedure for Improving the Acoustic Efficiency of Top-Edge Devices on Noise Barriers: An Application of Genetic Algorithms and Boundary Elements

A procedure for improving the acoustic efficiency of barriers featuring top-edge devices is conducted. This methodology is based on the maximization of the insertion loss of candidate profiles proposed by an evolutionary algorithm. The complexity normally associated with these devices raises the need to consider some geometric simplifications in order to ease the shape optimization processes. In this way, the overall barrier configuration is modeled as both thickness and non-thickness bodies (the boundary thickness is neglected), as representatives of very thin elements. Such an idealization requires a complementary formulation to the classical Boundary Element Method (BEM) that allows the problem to be solved. Numerical results are presented both validating the formulation and on the basis of simulations on noise barriers with complex diffuser-type tops by using a 2D Dual BEM code. Results obtained show the suitability of idealizing complex barrier configurations as models featuring thickness and non-thickness boundaries.