Kinetostatic Analysis and Solution Classification of a Planar Tensegrity Mechanism

Tensegrity mechanisms have several interesting properties that make them suitable for a number of applications. Their analysis is generally challenging because the static equilibrium conditions often result in complex equations. A class of planar one-degree-of-freedom (dof) tensegrity mechanisms with three linear springs is analyzed in detail in this paper. The kinetostatic equations are derived and solved under several loading and geometric conditions. It is shown that these mechanisms exhibit up to six equilibrium configurations, of which one or two are stable. Discriminant varieties and cylindrical algebraic decomposition combined with Groebner base elimination are used to classify solutions as function of the input parameters.Comment: 7th IFToMM International Workshop on Computational Kinematics, May 2017, Poitiers, France. 201

Co-evolution of RDF Datasets

Linking Data initiatives have fostered the publication of large number of RDF datasets in the Linked Open Data (LOD) cloud, as well as the development of query processing infrastructures to access these data in a federated fashion. However, different experimental studies have shown that availability of LOD datasets cannot be always ensured, being RDF data replication required for envisioning reliable federated query frameworks. Albeit enhancing data availability, RDF data replication requires synchronization and conflict resolution when replicas and source datasets are allowed to change data over time, i.e., co-evolution management needs to be provided to ensure consistency. In this paper, we tackle the problem of RDF data co-evolution and devise an approach for conflict resolution during co-evolution of RDF datasets. Our proposed approach is property-oriented and allows for exploiting semantics about RDF properties during co-evolution management. The quality of our approach is empirically evaluated in different scenarios on the DBpedia-live dataset. Experimental results suggest that proposed proposed techniques have a positive impact on the quality of data in source datasets and replicas.Comment: 18 pages, 4 figures, Accepted in ICWE, 201

Deployment of a Pentagonal Hollow-Rope Tensegrity Module

Tensegrity structures are spatial reticulated structures composed of cables and struts. Tensegrity systems are good candidates for adaptive and deployable structures and thus have applications in various engineering fields. A “hollow-rope” tensegrity system composed of tensegrity-ring modules has been demonstrated by the authors to be a viable system for a pedestrian bridge. This paper focuses on the deployment of pentagonal ring modules. A geometric study is performed to identify the deployment-path space allowing deployment without strut contact. Two actuation schemes are explored for deployment: the first scheme employs only actuated cables, while the second combines actuated cables with spring elements. In both schemes, continuous cables are used to reduce the number of actuators required. Finally, the structural response of the module during deployment is studied numerically using a modified dynamic relaxation algorithm

Designing tensegrity modules for pedestrian bridges

Tensegrity systems are spatial structures composed of tensile and compression components in a self-equilibrated state of prestress. The tensegrity concept has already been studied by researchers in various fields over the past decades. A family of tensegrity modules that can offer promising solutions for civil engineering applications such as tensegrity domes, towers and bridges is analyzed. Research into tensegrity systems has resulted in reliable techniques for form finding and structural analysis. However, the tensegrity concept is not yet part of mainstream structural design. This paper presents a design study of a tensegrity-based pedestrian bridge. The structural performance of the bridge using three tensegrity modules is evaluated through parametric studies. Design requirements for pedestrian bridges and results of parametric studies are used to define a design procedure that optimizes section sizes for this type of structure. A structural efficiency indicator is proposed and used to compare proposals for feasible bridge configurations. Design results illustrate that the hollow-rope tensegrity bridge can efficiently meet typical design criteria

Deployment aspects of a tensegrity-ring pedestrian bridge

Tensegrity structures are spatial systems that are composed of tension and compression components in a self-equilibrated prestress stable state. Although tensegrity systems were first introduced in 1950s, few examples have been used for civil engineering purposes. In this paper, tensegrity-ring modules are used for a deployable pedestrian bridge. Ring modules belong to a special family of tensegrity systems composed of a single strut circuit. Assembled in a “hollow-rope” structure, ring modules were shown to be a viable system for a tensegrity pedestrian bridge. Furthermore, ring modules are deployable systems that can change shape by adjusting cable lengths (cable actuation). This paper focuses on the deployment of a tensegrity-ring pedestrian bridge. A geometric study of the deployment for a single module identified the solution space that allows deployment without strut jamming. The optimal deployment path is identified amongst hundreds of possible solutions. Moreover, the number of actuators required and their placement in the module are determined by the deployment path that is applied. Cable-based actuation often has the drawback of having to control too many cable elements. Therefore, a deployment path that minimizes the number of actuated cables was found. The number of actuated cables is further reduced by employing continuous cables. A first generation prototype made of aluminium struts and steel cables was used to verify experimentally both findings. The structural response during unfolding and folding is studied numerically using a modified dynamic relaxation algorithm. A well-known dynamic-relaxation algorithm is extended to accommodate clustered tensegrity structures (tensegrity systems with continuous cables). The deployment-analysis algorithm applies cable-length changes first, to create mechanisms allowing deployment and then, to find new equilibrium configurations. Deployment is thus carried out through an equilibrium manifold. The deployment-actuation step size is identified as a critical parameter for successful deployment. Large deployment steps lead to instable configurations while small steps are computationally expensive. Due to mechanism-based deployment, the total energy in the structural system remains nearly constant during deployment. Elastic potential energy due to cable tension is the highest energy identified while kinetic energy and the work of torque friction on strut-to-strut joints are relatively low. Finally, internal forces increase during deployment but remain low compared with service self-stress values showing that deployment is not a critical phase for the design of the bridge

Intensional Query Answering to XQuery Expressions

XML is a representation of data which may require huge amounts of storage space and query processing time. Summarized representations of XML data provide succinct information which can be directly queried, either when fast yet approximate answers are sufficient, or when the actual dataset is not available. In this work we show which kinds of XQuery expressions admit a partial answer by using association rules extracted from XML datasets. Such partial information provide intensional answers to queries formulated as XQuery expressions

Deployment analysis of a pentagonal tensegrity-ring module

Ring modules are tensegrity systems that include a single strut circuit and recently, they have been shown to be viable systems for pedestrian bridges. Furthermore, their shape can be controlled using cable actuation. This paper focuses on the deployment of a pentagonal tensegrity-ring module. A geometric study is conducted to identify the deployment-solution space without strut contact. Deployment paths and actuation requirements are explored. The structural response of the module during deployment is analyzed using a modified dynamic relaxation method

Growth dynamics and the evolution of cooperation in microbial populations

Microbes providing public goods are widespread in nature despite running the risk of being exploited by free-riders. However, the precise ecological factors supporting cooperation are still puzzling. Following recent experiments, we consider the role of population growth and the repetitive fragmentation of populations into new colonies mimicking simple microbial life-cycles. Individual-based modeling reveals that demographic fluctuations, which lead to a large variance in the composition of colonies, promote cooperation. Biased by population dynamics these fluctuations result in two qualitatively distinct regimes of robust cooperation under repetitive fragmentation into groups. First, if the level of cooperation exceeds a threshold, cooperators will take over the whole population. Second, cooperators can also emerge from a single mutant leading to a robust coexistence between cooperators and free-riders. We find frequency and size of population bottlenecks, and growth dynamics to be the major ecological factors determining the regimes and thereby the evolutionary pathway towards cooperation.Comment: 26 pages, 6 figure

Gridshell as Formwork: Proof of Concept for a New Technique for Constructing Thin Concrete Shells Supported by Gridshell as Formwork

This paper documents an empirical experiment conducted in August 2014 as proof of concept for a new method of constructing concrete shells. An idea initially presented by the first author in 2012, it uses redeployable gridshells onto which fabric is midstressed and concrete applied. Primarily, this system addresses key issues that led to their decline in use: construction methods/formwork systems were not reusable, nor were they easily customizable to create different shapes. Employing 27 man-hours over seven days, two concrete shells were achieved using the same reusable and reconfigurable formwork. Lightweight (0.6 kg) PVC gridshell formwork supported 106.92 kg of concrete to create a concrete shell that covered 1.11 m2 (floor area). The construction verifies a low-cost (£6.06/m2) efficiency and material utilization in the construction of very strong wide-spanning thin concrete structures. Detailed analysis of formwork behavior during construction and detailed measurements of resultant shell results prove this new method of deployable gridshells as a reusable and reconfigurable formwork to construct very strong concrete shells very quickly. Whilst the emphasis of the research focused on the construction process, the vaults were tested and sustained a failure load of 4.2 kN (4.32 times their deadweight), applied as a point load at the crown

Role of the electro-thermo-mechanical multiple coupling on the operation of RF microswitch

A phenomenological approach is proposed to identify some effects occurring within the structure of the microswitch conceived for radio frequency application. This microsystem is operated via a nonlinear electromechanical action imposed by the applied voltage. Unfortunately, it can be affected by residual stress, due to the microfabrication process, therefore axial and flexural behaviors are strongly coupled. This coupling increases the actuation voltage required to achieve the so-called ‘‘pull-in'' condition. Moreover, temperature may strongly affect strain and stress distributions, respectively. Environmental temperature, internal dissipation of material, thermo-elastic and Joule effects play different roles on the microswitch flexural isplacement. Sometimes buckling phenomenon evenly occurs. Literature show that all those issues make difficult an effective computation of ‘‘pull-in'' and ‘‘pull-out'' voltages for evenly distinguishing the origin of some failures detected in operation. Analysis, numerical methods and experiments are applied to an industrial test case to investigate step by step the RF-microswitch operation. Multiple electro-hermomechanical coupling is first modeled to have a preliminary and comprehensive description of the microswitch behavior and of its reliability. ‘‘Pull-in'' and ‘‘pull-out'' tests are then performed to validate the proposed models and to find suitable criteria to design the RF-MEM