R. A. S. Moreira

Constrained Damping Layer Treatments: Finite Element Modeling:

In this paper we assess the performance of finite element models in modeling structures with sheer damping treatments. We analyze the finite element modeling of constrained layer damping (CLD) and integrated layer damping (ILD) treatments using viscoelastic materials, devoting special attention to the spatial modeling of the treatment and to the characterization of the viscoelastic material properties. In this work, we used a finite element commercial software (MSC.Nastran) to simulate the dynamic response of aluminum plates with both treatment configurations (CLD and ILD). The spatial modeling of the treatment was devel-oped using three different models, all based on a layered assembly of plate/brick conventional finite elements. The dynamic properties of the viscoelastic material were taken into account in the numerical simulation using the complex modulus approach. The numerical results are correlated with experimental data obtained for four treated specimens by direct comparison of the frequency response functions (FRFs) and by using FRF-based correlation indicators. The analyzed finite element models are found to provide very reliable results when compared with experimental acquired data.

PARTIAL CONSTRAINED VISCOELASTIC DAMPING TREATMENT OF STRUCTURES: A MODAL STRAIN ENERGY APPROACH

The constrained viscoelastic layer damping treatment is an effective means for the passive vibration control of plate and beam-kind structures. In order to reduce the treatment cost, while minimizing structural modifications, particularly the increase in mass, constrained viscoelastic treatments can be successfully applied in a partial and localized manner. The effectiveness of these treatments depends on their extension and relative location with respect to the target mode shape, which is not usually expeditiously established. In order to minimize the cost of the numerical optimization of the partial treatments, an efficient numerical methodology based on the ratio between the modal strain energy of the treated area and that of the structure is hereby proposed. This method is used in the analysis of the location and extension effects of partial constrained viscoelastic treatments on the modal damping of thin plates. The numerical results are verified through an experimental study on specimens with partial constrained viscoelastic layer damping treatments.

Application of Cork Compounds in Sandwich Structures for Vibration Damping

The remarkable damping over a broad temperature range and thermal insulation properties of cork make it a suitable material to be applied on integrated and surface damping treatments in sandwich structures, improving its dynamic behavior. Experimental analysis and numerical modeling of sandwich structures with cork compound layers is therefore essential for a better understanding of the cork compound influence on the dynamic properties of a layered structure. In this article, an evaluation study on the dynamic properties of a set of sandwich plates with cork compound cores inside two aluminium faces is performed. For this purpose, three test samples were assembled following the described configuration, using cork compounds with different properties (density, granulometry and thickness). To numerically simulate these layered plates, a partial layerwise plate finite element (FE), with a multilayer configuration, was developed and integrated in a MATLAB FE code. The constitutive relation of the cork compounds is included in the FE model by using the material complex modulus in a direct frequency analysis procedure. For the different cork compounds hereby considered, the extensional complex modulus was previously identified by using a specific experimental methodology which simulates a semidefinite two degrees of freedom system, where the cork compound test sample represents the complex stiffness. From the complex modulus data, both extensional storage modulus and loss factor of the cork compound were obtained. The experimental evaluation of the dynamic properties of the sandwich plates was performed carrying out an experimental modal analysis on each test specimen, being measured a set of frequency response functions (FRFs). Additionally, the developed layerwise plate element was validated through the comparison between the measured driving point FRFs and the FE method predicted ones.

Multilayer Damping Treatments: Modeling and Experimental Assessment

The sandwich panels with viscoelastic cores, which represent the physical application of the viscoelastic integrated damping treatment concept, associate different materials, each one having a specific structural contribution, where the outside faces, usually made from a stiff material, guarantee the stiffness of the composite structure whereas the viscoelastic and soft core provides the damping capability. The application of soft cores, specially the thick ones, into sandwich plates produces an important decoupling effect, leading to a significant flexural stiffness reduction of the sandwich plate, as experimental and numerical results evidence. From this observation and pursuing a solution to minimize such effect, the partitioning of the core layer into multiple layers separated by thin constraining layers is hereby considered. Taking advantage of the application of the multiple viscoelastic layers in the sandwich core, it is also analyzed the potential use of different viscoelastic materials in order to spread out the efficient temperature range of the damping treatment. To verify and evaluate the effects of the multilayer and multi-material viscoelastic cores in sandwich panels, an experimental and a numerical study were conducted on specimens representative of these design concepts. The results achieved from this study demonstrate the applicability of the two multiple layer configurations, evidencing the effect of the partitioning procedure of the core onto the reduction of the bending stiffness decay and the efficient temperature range enlargement when adopting viscoelastic materials with different transition temperatures.

Prognostic of feature interactions between independently developed pervasive systems

Statistics show an aging trend in the world population, which will progressively overload existing health systems. Therefore, we believe that ubiquitous computing will play an important role in domicile settings, coping with the growing need for automated home healthcare support, especially for the sick and elderly. The integration of independently developed off-the-shelf systems (e.g., health-monitoring, entertainment, communications, home automation, etc.) may cause unplanned interactions between them (cf. feature interactions). This is a major concern since the correct/expected behavior of an isolated system may not be the same when deployed in conjunction with other systems, causing interferences, i.e., unexpected outcomes or misbehaviors. The Safe Home Care project tackles this problem to pursuit the safe deployment and reconfiguration of home healthcare smart-spaces. We propose the use of state graphs to represent off-the-shelf systems and predict the occurrence of intra-systems feature interactions. We use pre-deployment simulations to forecast feature interactions before deployment. We assess the applicability and correctness of this approach through a set of simulated home assisted living scenarios.

Experimental Identification of GHM and ADF Parameters for Viscoelastic Damping Modeling

Viscoelastic materials can be used as an effective means of controlling the dynamics of structures, reducing and controlling the structural vibrations and noise radiation. They can be used as surface mounted or embedded damping treatments, utilizing passive viscoelastic materials alone, the so-called passive treatments, or in an unified way with active materials such as piezoelectrics, the so-called hybrid treatments. The use of these materials in damping treatments provides high damping capability over wide temperature and frequency ranges. The extensive use of passive or hybrid treatments using viscoelastic materials has motivated the development of damping models to be used and integrated into commercial or home-made finite element (FE) codes. The implementation of the Golla-Hughes- McTavish (GHM) and anelastic displacement fields (ADF) models in a general FE model with viscoelastic damping is presented and discussed in this paper. Additionally, a direct frequency analysis (DFA) is also described and employed.

The design of a washing machine prototype

The design process for a washing machine prototype is described. The prototype was developed within the final-year project of the Mechanical Engineering course at the University of Aveiro. Professional designers at the School of Arts and Design of Matosinhos carried out conceptual studies and the CAD modelling. To develop the appliance, different design and engineering aspects were carefully studied, namely concept studies, scaled model prototyping, structural engineering, materials selection, CAD/CAM mould making, advanced sandwich composite manufacturing structures, automation (programming and control) and testing. Within the project, pedagogic objectives were also set. In fact, these types of projects incorporate extra teaching and learning values because they involve students in more practical learning of engineering topics.

Development of a hybrid humanoid platform and incorporation of the passive actuators

This paper describes the design and development of a new hybrid humanoid platform conceived to use both active and passive actuators. Power efficiency and mechanical response capability of the robot were the main concerns driving this development. Maintaining the use of off-the-shelf RC servomotors, due to their limited cost and commercial availability, the platform was nonetheless custom-designed for lightness, mechanical stiffness and prone to vast sensorial enrichment for future advanced control. Low-cost actuators may degrade and perform poorly and erroneously in demanding conditions; therefore, one major inspiration for this work relies on the potential energy storage mechanism, using elastic elements to overcome the motors limitation, avoiding their operation near the limits, while saving energy and wearing, and also obtain faster responses of the overall platform in various motion schemes and gaits. A standard simulation environment allows the initial design and future tuning of the passive actuators for several joints in motion tasks. The early simulation results show that the elastic elements approach indeed eases the actuators tasks and is a must in the future development of the new platform now presented.

LoCoBoard: Low-Cost Interactive Whiteboard Using Computer Vision Algorithms

In the current digital age, the adoption of natural interfaces between humans and machines is increasingly important. This trend is particularly significant in the education sector where interactive tools and applications can ease the presentation and comprehension of complex concepts, stimulate collaborative work, and improve teaching practices. An important step towards this vision, interactive whiteboards are gaining widespread adoption in various levels of education. Nevertheless, these solutions are usually expensive, making their acceptance slow, especially in countries with more fragile economies. In this context, we present the low-cost interactive whiteboard (LoCoBoard) project, an open-source interactive whiteboard with low-cost hardware requirements, usually accessible in our daily lives, for an easy installation: a webcam-equipped computer, a video projector, and an infrared pointing device. The detection software framework offers five different Pointer Location algorithms with support for the Tangible User Interface Object protocol and also adapts to support multiple operating systems. We discuss the detailed physical and logical structure of LoCoBoard and compare its performance with that of similar systems. We believe that the proposed solution may represent a valuable contribution to ease the access to interactive whiteboards and increase widespread use with obvious benefits.

Mechatronic Design of a New Humanoid Robot with Hybrid Parallel Actuation

Humanoid robotics is unquestionably a challenging and long-term field of research. Of the numerous and most urgent challenges to tackle, autonomous and efficient locomotion may possibly be the most underdeveloped at present in the research community. Therefore, to pursue studies in relation to autonomy with efficient locomotion, the authors have been developing a new teen-sized humanoid platform with hybrid characteristics. The hybrid nature is clear in the mixed actuation based on common electrical motors and passive actuators attached in parallel to the motors. This paper presents the mechatronic design of the humanoid platform, focusing mainly on the mechanical structure, the design and simulation of the hybrid joints, and the different subsystems implemented. Trying to keep the appropriate human proportions and main degrees of freedom, the developed platform utilizes a distributed control architecture and a rich set of sensing capabilities, both ripe for future development and research.