RELIABILITY OF MACHINE ELEMENTS IN WIND TURBINES

Worldwide electrical energy production generated by wind turbines grows at a rate of 30 percent. This doubles the total production every three years. At the same time the power of individual stations goes up by 20 percent annually. Whereas today the towers, rotors and drive trains have to handle 5 MW, in about six to eight years they might produce up to fifteen MW. As a consequence, enormous pressure is put on the wind turbine manufacturers, the component suppliers and the operators. And because prototype and field testing is limited by its expense, the design of new turbines demands thorough analysis and simulation. Looking at the critical components of a wind turbine this paper describes advanced design tools which help to anticipate failures, but also assists in optimizing reliability and service life. Development of the software tools has been supported by research activities in many universities

NOVEL NEW MODELING PROCEDURE FOR INDUSTRIAL MACHINERY WITH NONLINEAR CONNECTIONS

Given current timelines for rolling out production at volume, the ability to model portions of the production process is of paramount importance. To model production, high-fidelity models of production assets must be obtained. The production assets are comprised of linear and nonlinear structures. The linear structures are well understood and defined. Significant work has, and is, being done to understand the nonlinear components. This work focuses on developing and correlating a model of a nonlinear component. The component studied and modeled is a linear guide. Linear guides are bearings which facilitate translational motion of machine axes. An accurate model of a linear guide is necessary to achieve an accurate model of a machine tool (production asset). Concepts of nonlinear structural dynamics are utilized and extended for use with linear guides. This work provides an accurate model of linear guides. The linear guides are fully tested to extract the nonlinear characteristics. The guides are found to exhibit a softening nonlinearity. Upon characterization of the nonlinearity, additional testing and validation are performed to develop a model. The harmonic balance method is utilized to conduct a numerical simulation of a set of linear guides The model is then correlated

Optimal design of vehicle with internal space frame structure subjected to high impact load

Armored military vehicles are heavily used in modern warfare. These vehicles are subjected to lethal attacks from projectiles and land mines. The shocks from these attacks may risk the safety of the occupants and damage the electronic instruments within the vehicle. Extensive research on the analysis and reduction of shocks on civilian vehicles has been performed. Fewer researchers addressed these problems in the case of military vehicles. Space frames are usually used to enhance structural strength of the vehicle while reducing its overall weight. These frames comprise of beams connected together at joints. Recently, space frames were incorporated in military vehicles. In this dissertation, a finite element model of a military vehicle with an internal space frame is developed. The space frame is composed of hollow square cross-section bars and angle sections. These frame members are bolted to the joints. The space frame is enclosed by uniform-thickness armor, except at the turret. The vehicle is subjected to high impact load that simulates a projectile hit. The vehicle design is optimized to reduce the overall mass, and shock at critical locations of the space frame. A lab-scale space frame structure derived from the military vehicle space frame is designed and built. The lab-scale space frame is subjected to non-destructive shock propagation tests. A finite element model of this structure is developed with the objective of matching the experimental results

Control Implementation of Dynamic Locomotion on Compliant, Underactuated, Force-Controlled Legged Robots with Non-Anthropomorphic Design

The control of locomotion on legged robots traditionally involves a robot that takes a standard legged form, such as the anthropomorphic humanoid, the dog-like quadruped, or the bird-like biped. Additionally, these systems will often be actuated with position-controlled servos or series-elastic actuators that are connected through rigid links. This work investigates the control implementation of dynamic, force-controlled locomotion on a family of legged systems that significantly deviate from these classic paradigms by incorporating modern, state-of-the-art proprioceptive actuators on uniquely configured compliant legs that do not closely resemble those found in nature. The results of this work can be used to better inform how to implement controllers on legged systems without stiff, position-controlled actuators, and also provide insight on how intelligently designed mechanical features can potentially simplify the control of complex, nonlinear dynamical systems like legged robots. To this end, this work presents the approach to control for a family of non-anthropomorphic bipedal robotic systems which are developed both in simulation and with physical hardware. The first is the Non-Anthropomorphic Biped, Version 1 (NABi-1) that features position-controlled joints along with a compliant foot element on a minimally actuated leg, and is controlled using simple open-loop trajectories based on the Zero Moment Point. The second system is the second version of the non-anthropomorphic biped (NABi-2) which utilizes the proprioceptive Back-drivable Electromagnetic Actuator for Robotics (BEAR) modules for actuation and fully realizes feedback-based force controlled locomotion. These systems are used to highlight both the strengths and weaknesses of utilizing proprioceptive actuation in systems, and suggest the tradeoffs that are made when using force control for dynamic locomotion. These systems also present case studies for different approaches to system design when it comes to bipedal legged robots

Numerical Investigation of Residual Stresses in Welded Thermoplastic CFRP Structures

Using thermoplastics as the matrix in carbon fiber-reinforced polymers (CFRP) offers the possibility to make use of welded joints, which results in weight savings compared to conventional joining methods using mechanical fasteners. In this paper, the resulting temperature distribution in the material due to resistance welding is investigated by transient finite element (FE) simulations. To examine the effects on the component structure, a numerical modeling approach is created, which allows determining the residual stresses caused by the welding process. It is shown that the area of the structure, especially near the joining zone, is highly affected by the process, especially in terms of residual stresses. In particular, the stresses perpendicular to the fiber direction show failure relevant values up to a maximum of 221 MPa, which might lead to the formation of microcracks in the matrix. In turn, that is assumed to be critical in terms of the fatigue of welded composite structures. Thus, the suggested modeling approach provides residual stresses that can be used to determine their effects on the strength, structural stability, and fatigue of such composite structures. In a subsequent step, these findings could play an important role in the design process of thermoplastic composite structures

Knowledge-based automated mechanical design of a robot manipulator

Design methods have been improving with an increasing level of algorithmic support for some time. The most recent advances include generative design and various optimization methods. However, the automated design tools are often focused on a single stage of the design process, for example, kinematics design, mechanical topology, or drive selection. In this paper, we show the whole design process of a robotic manipulator in an automated workflow. The method consisted of two main parts: a genetic optimization of the kinematic structure and an iterative automated CAD design. The method was then applied to a case study in which a manipulator with five degrees of freedom for a handling task was designed.Web of Science1212art. no. 589

A Lower Limb Prosthesis with Active Alignment for Reduced Limb Loading

Over the past decade, the growing field of robotics has created new possibilities in lower limb prostheses. The focus of these new prostheses has been replicating the dynamics of the lost limb in order to restore gait of individuals with lower limb amputations to healthy norms. This places demanding loads on the residual limb. Compensation by the rest of body is high, causes overloading of intact joints and can lead to deterioration of mobility and overall health. Abnormalities remain present in the person’s gait, stemming from the loading of soft tissue and the altered anatomy of the affected limb. In this dissertation, an experimental prosthesis is developed with systematic, simulation based techniques. Kinematics and kinetics of the prosthesis design are altered in order to actively realign the limb in relation to the center of pressure during stance, allowing positive power to be generated by the prosthesis while actively reducing the magnitude of the sagittal moment transferred to the residual limb. Initial findings show that during walking with the experimental device compared to a daily use prosthesis, peak pressures on the residual limb are lowered by over 10% while maintaining walking speed

Experimental and Computational Analysis of Progressive Failure in Bolted Hybrid Composite Joints

Composite materials are strong, lightweight, and stiff making them desirable in aerospace applications. However, a practical issue arises with composites in that they behave unpredictably in bolted joints, where damage and cracks are often initiated. This research investigated a solution to correcting the problem with composite bolted joints. A novel hybrid composite material was developed, where thin stainless steel foils were placed between and in place of preimpregnated composite plies during the cure cycle to reinforce stress concentrations in bolted joints. This novel composite was compared to control samples experimentally in quasi-static monotonic loading in double shear configuration in 9-ply and 18-ply layups. It was also investigated in quasi-static loading in single shear configuration using 18-ply samples in both protruding head and countersunk head configurations. Progressive failure samples were compared to data to explain which phenomenon in the material caused certain features in experimental curves. The final goal of the experimental effort was to perform an initial cycle fatigue comparison between the novel hybrid and control materials. The parallel research effort explored creating finite element models that could correctly represent and predict the behavior of this hybrid system. This was the first effort employing numerical failure criterion alongside a rigorous experimentation across multiple configurations. Hybridizing the composite material increased yield by as much as 25% and increased ultimate load capacity as much as 42%. The finite element models employed Hashin failure criteria and proved the ability to predict the yield load capacity to within 6.5% error

Elastic timber gridshells. from the finding form process to the erection of efficient lightweight structures

Doctoral Thesis (International Doctoral Programme in Sustainable Built Environment)Elastic timber gridshells emerged in the last century, essentially related to ephemeral buildings, setting a ‘new’ benchmark for lightweight, cost-effective, sustainable and temporary constructions. Timber gridshells are adaptable and can be used in rehabilitated buildings as well as, new buildings, new systems like roofs, or as small additions in nonstructural elements and act as a simple partition. However, the main feature is not its use, but its shape and how it allows some freedom in its design; an attractive characteristic for designers due to its structural behaviour. Based on the advantages of the structural system, it should be expected that timber gridshells have a wider presence in contemporary architecture. However, this is not the case, there are very few examples being built. One reason why this happens, is because of the difficulty to reach the desired design since there is a lack of information about the tools that can help to define such complex systems. Until today, the design and construction of elastic, or post-formed timber gridshells, have only been based on a case to case basis and have not been studied or used as a type of structure that can be repeated in several different applications. The aim of this thesis is to contribute to answer this difficulty, i.e. working on overcoming the lack of design guidelines, by presenting a state of the knowledge on elastic timber gridshells and by case studies analysing the process involved in building this kind of a structures. The thesis is addressing elastic timber gridshells, from the design phase to the construction phase. The results obtained show that this type of structure can be very interesting at a functional level with numerous tectonics characteristics that make elastic timber gridshells attractive as a structural solution in contemporary architecture.As malhas elásticas de madeira surgiram no século passado, essencialmente relacionadas com construções temporárias, estabelecendo uma "nova" referência para construções leves, econômicas, sustentáveis e efêmeras. As malhas de madeira são adaptáveis e podem ser usadas em edifícios a reabilitar, bem como, novos edifícios, coberturas, ou em pequenas modificações como elementos não estruturais. No entanto, a principal característica não é seu uso, mas sua geometria e como isso permite uma enorme liberdade formal torna-se uma característica atraente para todos os projetistas. Com base nas vantagens deste sistema estrutural, é de esperar que as malhas elásticas de madeira tivessem uma presença mais ampla na arquitetura contemporânea. Contudo, não é o caso, existem poucos exemplos construídos. Um motivo para isso acontecer é a dificuldade em projetar as formas desejadas, pois existe uma lacuna de informação sobre as ferramentas que podem ajudar a definir estas geometrias complexas. Por exemplo, as ferramentas baseadas em softwares computacionais têm um grande potencial para o processo de projeção das malhas de madeira nas fases de projeto e construção, onde a localização da malha e a otimização ocorrem, seguidas por um processo de produção industrial. Até hoje, o projeto e a construção destas estruturas, foram estudados apenas de caso a caso e não foram estudados ou usados como um tipo de solução que pode ser repetida em várias aplicações diferentes. O objetivo desta dissertação é contribuir para a resolução desse problema, ou seja, trabalhar na superação da falta de diretrizes de projeto, apresentando um estado do conhecimento sobre as malhas elásticas de madeira e analisando e explicando o processo envolvido na construção deste tipo de estruturas. Esta tese aborda as malhas elásticas de madeira, desde a fase de projeto até à fase de construção. Os resultados obtidos mostram que este tipo de estrutura pode ser muito interessante a um nível funcional, com numerosas características com valor tectônico que tornam as malhas elásticas de madeira atrativas como uma solução estrutural na arquitetura contemporânea.This work it was financed by FEDER funds through the Competitively Factors Operational Programme - COMPETE and by national funds through FCT – Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633. The support of the Foundation for Science and Technology (FCT) through doctoral fellowship SFRH/BD/104677/2014 is grateful