Fernando G. Branco

3D acoustic scattering from an irregular fluid waveguide via the BEM

The BEM is used to calculate the variation in the pressure field generated by a dilatational point load inside a channel filled with a homogeneous fluid, in the presence of an irregular floor. The Greens functions are defined in the frequency domain and obtained by superposing virtual acoustic sources combined so as to generate the boundary conditions of the free or rigid surfaces of the channel. The responses in the time domain are obtained by means of Fourier transforms, making use of complex frequencies. The main features and spectral representation of the signals scattered by irregular floors are then described and used to elucidate the most important aspect of wave acoustics, which can provide the basis for the development of non-destructive testing and imaging methods.

Adaptive policies for multi-mode project scheduling under uncertainty

In this paper we propose an adaptive model for multi-mode project scheduling under uncertainty. We assume that there is a due date for concluding the project and a tardiness penalty for failing to meet this due date, and that several distinct modes may be used to undertake each activity. We define scheduling policies based on a set of thresholds. The starting time of the activity is compared with those thresholds in order to define the execution mode.

Dynamic analysis of submerged fluid-filled pipelines subjected to a point pressure load

Abstract This paper analyses the wave scattering generated by point pressure loads in the vicinity of infinite fluid-filled circular pipelines submerged in a homogeneous fluid medium. The pipeline has a constant cross-section and is modelled as a homogeneous elastic material. The three-dimensional (3-D) response is formulated in the frequency domain, and is obtained as a discrete summation of the 2-D solutions found for different axial wavenumbers. Time solutions are computed by means of inverse Fourier transforms. Complex frequencies are used to avoid aliasing phenomena. The main focus of the paper is on the dynamic analysis of the stresses generated inside and at the surface of the pipeline by a point pressure load placed in the surrounding medium. Different positions of both the source and the receivers are considered. The effect of the relation of the wall thickness to the radius of the pipeline is also studied.

Steady-state moisture diffusion in curved walls, in the absence of condensate flow, via the BEM: a practical Civil Engineering approach (Glaser method)

The influence of the curvature radius of curved walls on the condensation patterns across a single panel homogeneous wall is analysed under steady-state conditions. Condensation is defined according to the Glaser approach, which is a practical tool in building design, recommended by the DIN 4108 and prEN ISO 13788 standards. This methodology uses an iterative process, which requires the resolution of temperature equilibrium and several vapour pressure equilibrium problems. Each of these potential problems is solved using the Boundary Element Method (BEM). The iterative process is first implemented and validated by applying it to the definition of condensation patterns across a hollow cylinder, for which the solution is calculated analytically. The BEM is then applied to the curved wall models, identifying the zones where condensation occurs and quantifying the amount of liquid water generated.

ACOUSTIC SCATTERING FROM A 2-D FLUID WAVEGUIDE WITH AN IRREGULAR FLOOR VIA THE BEM

This work focuses on the way the pressure field generated by a dilatational load changes inside a channel waveguide filled with a homogeneous fluid, in the presence of an irregular floor. The problem is solved in the frequency domain using the boundary element method. The Greens functions used are obtained by superposing virtual acoustic sources defined so as to generate the free or rigid surfaces of the fluid channel. The responses in the time domain are obtained by means of Fourier transforms, using complex frequencies. Irregular floors of varying sizes are modeled. The main features and spectral representation of the signals scattered by these inclusions are described. They are used to elucidate the most important aspect of wave acoustics, which can be used as the basis for the development of nondestructive testing and imaging methods.

ACOUSTIC INSERTION LOSS PROVIDED BY RIGID ACOUSTIC BARRIERS OF DIFFERENT SHAPES

The present article studies what effect the shape of a rigid acoustic barrier has on the acoustic insertion loss provided by the barrier. The Boundary Element Method (BEM), formulated in the frequency domain, is used to evaluate the sound propagation around acoustic screens in the vicinity of a tall building. The acoustic screen is assumed to be non-absorbing, and the building is modeled as an infinite barrier. Signals in the time domain are obtained from the frequency domain computations by applying inverse Fourier transforms. In the examples provided, the height of the acoustic barrier remains constant, but different geometric shapes are modeled. The results obtained for a vertical barrier are used as a reference.

Formulation of Kansa's method in the frequency domain for the analysis of transient heat conduction

Purpose – A number of works have been published in the scientific literature proposing the solution of heat diffusion problems by first transforming the relevant partial differential equation to the frequency domain. The purpose of this paper is to present a mesh-free strategy to assess transient heat propagation in the frequency domain, also allowing incorporating initial non-zero conditions. Design/methodology/approach – The strategy followed here is based in Kansas method, using the MQ RBF as a basis function. The resulting method is truly mesh-free, and does not require any domain or boundary integrals to be evaluated. The definition of good values for the free parameter of the MQ RBF is also addressed. Findings – The strategy was found to be accurate in the calculation of both frequency and time-domain responses. The time evolution of the temperature considering an initial non-uniform distribution of temperatures compared well with a standard time-marching algorithm, based on an implicit Crank-Nicho...

Estratégias de mitigação da retração em betões autocompactáveis

RESUMO O betão auto-compactável (BAC) apresenta propriedades especiais, que justificam a sua preferência em muitas aplicações. No entanto, são conhecidos vários casos de comportamento inadequado, devido principalmente ao comportamento deficiente deste material durante o processo de hidratação e secagem. A retração tem uma importância significativa na conceção, dimensionamento, processo construtivo e comportamento em serviço das estruturas de betão. As exigências normativas não consideram de forma adequada a influência dos fatores existentes. Além disso, a possibilidade de utilização de novos materiais limita fortemente a aplicação do conhecimento existente. De modo a contribuir para a resolução de uma das principais desvantagens deste material – a sua elevada retração, foi realizada uma campanha de ensaios, tendo em vista a avaliação dessa propriedade. Foi dada especial importância à utilização de adjuvantes redutores de retração e adições expansivas. Com base nos resultados obtidos foi possível avaliar a eficiência da utilização desses materiais. Obtiveram-se melhoramentos que permitiram formular uma hierarquização das estratégias de mitigação utilizadas.

Pombaline Buildings—Consequences of Some Rehabilitation Interventions

The Pombaline buildings of downtown Lisbon have undergone some forms of adulteration across time with a greater impact in recent years due to an increase in tourist activity. After the great earthquake of 1755, this area has been rebuilt according to an innovative, enlightened urban plan. The buildings have been built in a short period of time using a standardization and prefabrication system and also an innovative anti-seismic technique—the “Pombaline cage”—which was an unparalleled Portuguese contribution to construction technology and anti-seismic engineering. The recent conversion of historic buildings in hotels has led, in many cases, to total internal demolition while maintaining the facade in its original condition. This solution is not recommended in the case of historic centres because the maintenance of the internal structure and original materials of buildings is crucial to protect its authenticity. It may also undermine the performance of buildings throughout the quarter in the event of a major earthquake. This paper describes the original structure of a Pombaline building and the major alterations that these buildings have undergone as well as the implications on their overall performance in the event of an earthquake.

Stress analysis in pipelines submerged in a fluid medium subjected to a point pressure load

This work analyses the stresses in an infinite fluid-filled circular pipeline submerged in a homogeneous fluid medium when subjected to the incidence of waves generated by a point pressure load, The wall of the pipeline is modeled with constant thickness and assumed to behave elastically. This model leads to the resolution of what is commonly called a 2-l/2-D problem which allows the 3D solution to be obtained as a discrete summation of 2D problems with different spatial wavenurnbers. This procedure is defined by means of Fourier transformation in the direction in which the geometry does not vary, and considering an infinite number of virtuaI point sources equally spaced along the pipeline axis. The solution for each 2D problem is solved using analytical solutions. Calculations are first performed in the frequency domain and time solutions are then obtained using inverse Fourier transforms.