Study of adhesion and cohesion in vacuum Final report

Vacuum metal-metal bonding tests to determine conditions of accidental adhesion of spacecraft structural material

Size-Dependent Tile Self-Assembly: Constant-Height Rectangles and Stability

We introduce a new model of algorithmic tile self-assembly called size-dependent assembly. In previous models, supertiles are stable when the total strength of the bonds between any two halves exceeds some constant temperature. In this model, this constant temperature requirement is replaced by an nondecreasing temperature function $\tau : \mathbb{N} \rightarrow \mathbb{N}$ that depends on the size of the smaller of the two halves. This generalization allows supertiles to become unstable and break apart, and captures the increased forces that large structures may place on the bonds holding them together. We demonstrate the power of this model in two ways. First, we give fixed tile sets that assemble constant-height rectangles and squares of arbitrary input size given an appropriate temperature function. Second, we prove that deciding whether a supertile is stable is coNP-complete. Both results contrast with known results for fixed temperature.Comment: In proceedings of ISAAC 201

Walking a Mile in Your Shoes

At first glance, Americans seem obsessed with other people. From magazines like People to television shows like Access Hollywood, we seem to have an insatiable appetite for the details of other people’s lives. Reality television differs from scripted television because it gives us the illusion that we are peering into the real life of other people. Much contemporary news coverage has a voyeuristic feel to it. We learn the details of the lives of people like Jerry Sandusky (child sexual abuser), Snookie (celebrity) and Whitney Houston (pop star) whether these details are relevant to an original story or not. I might assert that all this information gives us insight into the lives and perspectives of these people. From the popularity of these stories I might conclude that Americans are among the most empathic people on Earth. Data from psychological research, however, do not support this conclusion. Why not? Because people are consuming this information from a detached, objective perspective. At best, people feel sympathy for (some) of these people. But more often than not these stories provide the sweet sense of righteousness that we find so delectable. Passing judgment on others when they have done wrong is an addiction we have no interest in breaking. This addiction, like many others, has both benefits and costs. Fortunately, there is an antidote for this addiction: true empathy

Study of adhesion and cohesion in vacuum summary report 1 jul. 1963 - 30 jun. 1964

Adhesion and cohesion of metal couples in vacuum chambe

Exploring the application domain of adaptive structures

Using a previously developed design methodology it was shown that optimal material distribution in combination with strategic integration of the actuation system lead to significant whole-life energy savings when the design is governed by rare but strong loading events. The whole-life energy of the structure is made of an embodied part in the material and an operational part for structural adaptation. Instead of using more material to cope with the effect of loads, the actuation system redirects the internal load-path to homogenise the stresses and change the shape of the structure to keep deflections within limits. This paper presents a systematic exploration of the domain in which adaptive two-dimensional pin-jo inted structures are beneficial in terms of whole-life energy and monetary costs savings. Two case studies are considered: a vertical cantilever truss representative of a multi-storey building supported by an exoskeleton structure and a simply supported truss beam which is part of a roof system. This exploration takes five directions studying the influence of: (1) the structural topology (2) the characteristics of the load probability distribution (3) the ratio of live load over dead load (4) the aspect ratio of the structure (e.g. height-to-depth) (5) the material energy intensity factor. Results from the main five strands are combined with those from the monetary cost analysis to identify an optimal region where adaptive structures are most effective in terms of both energy and monetary savings. It was found that the optimal region is broadly that of stiffness-governed structures. For the cantilever case, the optimal region covers most of the application domain and it is not very sensitive to either live-to-dead-load or height-to-depth ratios thus showing a wide range of applicability, including ordinary loading scenarios and relatively deep structures

Shape control and whole-life energy assessment of an 'infinitely stiff' prototype adaptive structure

A previously developed design methodology produces optimum adaptive structures that minimise the whole-life energy which is made of an embodied part in the material and an operational part for structural adaptation. Planar and complex spatial reticular structures designed with this method and simulations showed that the adaptive solution achieves savings as high as 70% in the whole-life energy compared to optimised passive solutions. This paper describes a large-scale prototype adaptive structure built to validate the numerical findings and investigate the practicality of the design method. Experimental results show that (1) shape control can be used to achieve 'infinite stiffness' (i.e. to reduce displacements completely) in real-time without predetermined knowledge regarding position, direction and magnitude (within limits) of the external load; (2) the whole-life energy of the structure is in good agreement with that predicted by numerical simulations. This result confirms the proposed design method is reliable and that adaptive structures can achieve substantive total energy savings compared to passive structures

Infinite stiffness structures via active control

Active control has been used in civil engineering structures for a variety of purposes. Although the potential for using deflection-control adaptation to save material has been investigated by a few other authors, little attention has been given to assessing whether these material savings outweigh the energy consumed through control and actuation. Our paper seeks to address this gap, presenting experimental work on a truss with effective infinite stiffness which builds on earlier theoretical studies. Senatore previously developed a design method that produces an optimum adaptive structure that minimises the total energy spent throughout the whole life of the structure (embodied in the materials + operational for the control) (Senatore, et al., 2013). The method was used to design a range of structures from trusses to space frames, both determinate and indeterminate, and it was shown that it allows energy saving up to 70% compared to state of the art optimisation methods. A large scale prototype structure has now been built to validate the numerical findings and investigate the practicality of the method. This paper discusses recent experimental findings and the making of the prototype. Using the insight acquired after the making and testing of the prototype the authors will discuss potential applications of adaptive structures in selection of different scenarios, ranging from cantilever seating tiers in sports stands to lightweight roofs to slender beams with 80:1 span/depth ratio