Design of New Materials for Passive Vibration Control

The objective of this contribution is to extend the models of cellular/composite material design to nonlinear material behaviour and apply them for design of materials for passive vibration control. As a first step a computational tool allowing determination of optimised one-dimensional isolator behaviour was developed. This model can serve as a representation for idealised macroscopic behaviour. Optimal isolator behaviour to a given set of loads is obtained by generic probabilistic metaalgorithm, simulated annealing. Cost functional involves minimization of maximum response amplitude in a set of predefined time intervals and maximization of total energy absorbed in the first loop. Dependence of the global optimum on several combinations of leading parameters of the simulated annealing procedure, like neighbourhood definition and annealing schedule, is also studied and analyzed. Obtained results facilitate the design of elastomeric cellular materials with improved behaviour in terms of dynamic stiffness for passive vibration control.

Design of New Materials for Passive Vibration Control

The aim of this contribution is to extend the techniques of composite materials design to non-linear material behaviour and apply it for design of new materials for passive vibration control. As a first step a computational tool allowing determination of macroscopic optimized one-dimensional isolator behaviour was developed. Voigt, Maxwell, standard and more complex material models can be implemented. Objective function considers minimization of the initial reaction and/or displacement peak as well as minimization of the steady-state amplitude of reaction and/or displacement. The complex stiffness approach is used to formulate the governing equations in an efficient way. Material stiffness parameters are assumed as non-linear functions of the displacement. The numerical solution is performed in the complex space. The steady-state solution in the complex space is obtained by an iterative process based on the shooting method which imposes the conditions of periodicity with respect to the known value of the period. Extension of the shooting method to the complex space is presented and verified. Non-linear behaviour of material parameters is then optimized by generic probabilistic meta-algorithm, simulated annealing. Dependence of the global optimum on several combinations of leading parameters of the simulated annealing procedure, like neighbourhood definition and annealing schedule, is also studied and analyzed. Procedure is programmed in MATLAB environment.

Ground Vibrations Induced by High-Speed Trains in Regions with Sudden Foundation Stiffness Change

In this paper analytical transient solutions of dynamic response of one-dimensional systems with sudden change of foundation stiffness are derived. In more details, cantilever dynamic response, expressed in terms of vertical displacement, is extended to account for elastic foundation and then two cantilever solutions, corresponding to beams clamped on left and right hand side, with different value of Winkler constant are connected together by continuity conditions. The internal forces, as the unknowns, can be introduced by the same values in both clamped beam solutions and solved. Assumption about time variation of internal forces at the section of discontinuity must be adopted and originally analytical solution will have to include numerical procedure.

SENSITIVITY ANALYSIS OF TRACK VIBRATIONS DUE TO VERTICAL STIFFNESS VARIATION IN HIGH-SPEED RAILWAYS

High speed trains, when crossing regions with abrupt changes in vertical stiffness of the track and/or subsoil, may generate excessive ground and track vibrations. There is an urgent need for specific analyses of this problem so as to allow reliable esimates of vibration amplitude. Full understanding of these phenomena will lead to new construction solutions and mitigation of undesirable features. In this paper analytical transient solutions of dynamic response of one-dimensional systems with sudden change of foundation stiffness are derived. Results are expressed in terms of vertical displacement. Sensitivity analysis of the response amplitude is also performed. The analytical expressions presented herein, to the authors’ knowledge, have not been published yet. Although related to one-dimensional cases, they can give useful insight into the problem. Nevertheless, in order to obtain realistic response, vehicle- rail interaction cannot be omitted. Results and conclusions are confirmed using general purpose commercial software ANSYS. In conclusion, this work contributes to a better understanding of the additional vibration phenomenon due to vertical stiffness variation, permitting better control of the train velocity and optimization of the track design.

Efectividade de um programa de exercício aquático na osteoartrose do joelho

RESUMO: A osteoartrose do joelho é uma condição clínica cuja prevalência tem aumentado nos últimos anos na população idosa. Trata-se de uma condição que pode ser bastante incapacitante para o idoso, gerando um forte impacto social e económico. O exercício aquático tem sido identificado como um factor de promoção da melhoria do quadro clínico nesta população, mas a sua efectividade não está, ainda, determinada. Objectivo: investigar a efectividade, a curto e médio prazo, de um programa de exercício aquático, realizado em grupo, com a duração de 8 semanas, na amplitude articular, dor e rigidez do joelho, e na função física e qualidade de vida, em idosos com osteoartrose do joelho. Metodologia: Recorreu-se a um estudo quase-experimental, double-blind, controlado, sem aleatorização, cuja amostra, constituída por 43 sujeitos, foi selecionada por conveniência. Os sujeitos do grupo experimental (n=22) foram submetidos ao programa de exercício aquático e os do grupo de controlo (n=21) foram submetidos ao programa de exercício no solo. Ambos os programas foram definidos de acordo com as recomendações internacionais para a prática de exercício físico em idosos com osteoartrose (Arthritis Foundation, 2009a, 2009b). Todo o grupo foi avaliado no início do programa, no final do mesmo (8 semanas) e após 6 semanas de follow-up, nos seguintes indicadores: amplitude articular do joelho (através do goniómetro), dor, rigidez, função e qualidade de vida (através do KOOS). Resultados: A amostra deste estudo foi constituída por sujeitos maioritariamente do género feminino (76,7%), com uma média de 72,7 anos (DP=5,49). O programa de exercício aquático implementado demonstrou um aumento da amplitude articular passiva de flexão (p<0,0001) e extensão (p=0,016) do joelho, uma diminuição da dor e da rigidez articular (p<0,0001), um aumento da função nas AVD’s (p<0,0001) e no desporto/lazer (p=0,031), e ainda, um aumento da qualidade de vida (p<0,0001). Contudo, apenas os níveis de amplitude articular passiva de extensão do joelho (p=0,083) e de função no desporto/lazer (p=0,244) se mantiveram ao longo das seis semanas de follow-up. Conclusões: Apesar de algumas limitações, considera-se que este estudo é de grande importância para a comunidade científica e para os fisioterapeutas preocupados com a crescente prevalência da osteoartrose e dos custos associados. O exercício aquático parece ser uma estratégia importante na melhoria do estado de saúde dos idosos com osteoartrose do joelho.----------------- ABSTRACT: The osteoarthritis of the knee is a clinical condition that has been increasing among the elderly population over the past few years. It’s a condition that can be fairly disabling to the elderly individual, and which generates a strong social and economic impact. Aquatic exercise has been named as a promotional factor in the improvement of the clinical picture in this population, but its effectiveness is yet to be determined. Objective: To investigate the effectiveness, in a short and medium term, of an aquatic exercise program undertaken by a group over eight weeks, in the joint amplitude, pain and stiffness of the knee, and in the physical function and quality of life in elderly people who suffer from knee osteoarthritis. Methodology: was used a double-blind, quasi-experimental study with no randomization and its 43 subjects were selected as a matter of convenience. The subjects of the experimental group (n=22) were subjected to an aquatic exercise program and those of the control group (n=21) were subjected to a land-based exercise program. Both programs have followed international recommendations on the practice of physical exercise in elderly people who suffer from osteoarthritis (Arthritis Foundation, 2009a, 2009b). The entire group was evaluated in the beginning and at the end of the program (8 weeks later), and after a 6 week follow-up, in these parameters: knee range of motion (through a goniometer), pain, stiffness, function and quality of life (through KOOS). Results: This sample was predominantly female (76,7%) with a mean age of 72,7 years (SD=5,49). Aquatic exercise resulted in increase of passive joint flexion (p<0,0001) and knee extension (p=0,016), in the decline of pain and stiffness (p<0,0001), in the increase of function in the ADLs (p<0,0001). However, only the knee extension amplitude (p=0,083) and the function in sports/leisure (p=0,244) were kept through the six-week follow-up. Conclusions: Despite some limitations, this study is of great importance to the community and to the physiotherapists concerned with the growing prevalence of osteoarthritis and the associated costs. Aquatic exercise appears to be an important strategy in the improvement of the health condition of patients who suffer from knee osteoarthritis.

Dynamic stiffness of the piled foundation of a onshore wind turbine

One of today's biggest concerns is the increase of energetic needs, especially in the developed countries. Among various clean energies, wind energy is one of the technologies that assume greater importance on the sustainable development of humanity. Despite wind turbines had been developed and studied over the years, there are phenomena that haven't been yet fully understood. This work studies the soil-structure interaction that occurs on a wind turbine's foundation composed by a group of piles that is under dynamic loads caused by wind. This problem assumes special importance when the foundation is implemented on locations where safety criteria are very demanding, like the case of a foundation mounted on a dike. To the phenomenon of interaction between two piles and the soil between them it's given the name of pile-soil-pile interaction. It is known that such behavior is frequency dependent, and therefore, on this work evaluation of relevant frequencies for the intended analysis is held. During the development of this thesis, two methods were selected in order to assess pile-soil-pile interaction, being one of analytical nature and the other of numerical origin. The analytical solution was recently developed and its called Generalized pile-soil-pile theory, while for the numerical method the commercial nite element software PLAXIS 3D was used. A study of applicability of the numerical method is also done comparing the given solution by the nite element methods with a rigorous solution widely accepted by the majority of the authors.