Quality- and cost-driven assembly technique selection and geometrical tolerance allocation for mechanical structure assembly

The assembly process planning has been the subject of extensive scientific work, mainly due to the multiple aspects involved from geometrical matters to operational research concerns. However, very few issues about assembly technique selection are addressed. The aim of this paper is to propose a method to select an assembly technique for each joint of a product and to allocate geometrical tolerances accordingly. This is achieved by solving a multi-objective optimization problem to minimize the cost and the non-conformity associated with the assembly plan. The potential benefits of the method are illustrated on a case study representing the assembly of a simple mechanical structure.     

La modélisation de la turbulence dans une enceinte avec ouvertures et sources chaudes localisées

The air circulation inside an enclosure with multiple openings and local heat sources was studied by means of a mathematical model. After a number of comparisons to studies in an experimental apparatus, it was concluded that a turbulence model should be introduced in order to improve the mathematical simulation. Two turbulence models, one based on the algebraic and the other on the differential (K-?-G) model of the turbulent viscosity, were investigated. The differential model provided only small improvements in the results and increased the running costs substantially when compared to the algebraic model. Hence the utilisation of the differential model was not justified in these simulations. The combined effect of the forced convection through the enclosure and the natural convection from the heat sources was simulated in an attempt to study the air circulation and the air temperature inside the building of an aluminum reduction plant.     

Simulation Mathématique de la Circulation de I'Air dans une Enceinte avec Ouvertures et Sources Chaudes Localisées

A mathematical simulation of the air circulation and the temperature inside a rectangular enclosure with multiple openings and with localised rectangular heat sources was made. Finite difference techniques and a simple turbulence model were used to solve the time-averaged partial differential equations for the conservation of mass, momentum and energy. The computations were carried out for a Prandtl number of 0.7, for an Archimedes number of about 34 and for Grashof numbers up to 3 × 10⁹. Comparison of the numerical results to flow visualization and temperature studies in an experimental apparatus indicated good agreement. The combined effect of natural convection from the heat sources and the forced convection through the enclosure creates a complex flow pattern inside the enclosure. These conditions were simulated in an attempt to study the air circulation pattern and the air temperature inside the building of an aluminum reduction plant.     

The Effect of Salts on Ozone Oxidation Processes

Much research on ozone oxidation is performed using model wastewaters, containing a number of organic compounds to be degraded. In some cases they contain low concentrations of inorganic buffers to stabilize the pH during the experiments. In practical applications, however, salts and detergents may be present as well. The effect of such compounds on the process has to be investigated to prevent unexpected results in pilot- or full-scale applications. To quantify these effects, experiments have been performed on model waste waters in the absence and the presence of high concentrations of several inorganic salts. The oxidation selectivity in these experiments was interpreted using Hammett free-energy relationships. The effect of the different salt concentrations on the oxidation selectivity when considering reactions in the bulk of the liquid was seen to be small. This implicates the design of an ozone-based oxidation system can often be based on literature or calculated data regarding reaction rates. However, the effect of increased salt concentrations on ozone solubility and bubble size distribution may have implications for the reactor design, as these factors affect the mass transfer efficiency.     

Two-Dimensional Compact Third-Order Polynomial Reconstructions. Solving Nonconservative Hyperbolic Systems Using GPUs

We present a new kind of high-order reconstruction operator of polynomial type, which is used in combination with the scheme presented in Castro et al. (J. Sci. Comput. 39:67?C114, 2009) for solving nonconservative hyperbolic systems. The implementation of the scheme is carried out on Graphics Processing Units (GPUs), thus achieving a substantial improvement of the speedup with respect to normal CPUs. As an application, the two-dimensional shallow water equations with geometrical source term due to the bottom slope is considered.     

Rover-Based Autonomous Science by Probabilistic Identification and Evaluation

Autonomous science augments the capabilities of planetary rovers by shifting the identification and selection of science targets from remote operators to the rover itself. This shift frees the rover from wasteful idle time and allows for more selective data collection. This paper presents an approach to autonomous science that is comprised of three components: a Bayesian network that uses image data to identify features; an evaluation algorithm that selects the best features; and, a path-planning algorithm that guides the rover to the most scientifically valuable features. Within this framework, the effectiveness of pairing a larger prime rover with a smaller scout rover to improve autonomous science is investigated. Laboratory-based experiments were used to validate the effectiveness of the Bayesian network for feature identification and the scoring algorithm that has been developed for feature evaluation. Simulations were used to compare the traditional use of a solo prime rover to that of also employing a scout. The results presented here indicate that the inclusion of a scout rover can allow the prime rover to avoid pitfalls or routes with low scientific value.     

Evaluation of the process of integration in a transdisciplinary landscape study in the Pajottenland (Flanders, Belgium)

In order to preserve the overall landscape values in the Pajottenland, the province of Vlaams-Brabant initiated a campaign to raise awareness of local authorities and stakeholders and to stimulate co-coordinated actions. As very few scientific studies exist for the region, an interdisciplinary study was commissioned from the University of Ghent, involving archaeologists, historians, geographers and planners. This article evaluates the process of integration between the scientific disciplines and between the researchers (interdisciplinary) and program team and stakeholders (transdisciplinary) involved in this project. Potentials and difficulties encountered in the successive phases are evaluated and discussed. The interdisciplinary trajectory worked relatively smoothly as it was focused upon the realization of the first integrated landscape biography for the region. This biography includes scientific results as well as an integration of the complex legal and administrative instruments, which are necessary for the implementation of the study. Also, a methodology was developed for assessing landscape values at the municipal level, to be carried out by local stakeholders. This methodology was demonstrated with the case study of Gooik. The transdisciplinary integration encountered a series of difficulties, which mainly related to the unclear and shifting objectives of the program team and to aspects of communication between the partners and the lack of a common language.     

Optimized spatial correlations for broadband light trapping nanopatterns in high efficiency ultrathin film a-Si:H solar cells

Nanophotonic structures have attracted attention for light trapping in solar cells with the potential to manage and direct light absorption on the nanoscale. While both randomly textured and nanophotonic structures have been investigated, the relationship between photocurrent and the spatial correlations of random or designed surfaces has been unclear. Here we systematically design pseudorandom arrays of nanostructures based on their power spectral density, and correlate the spatial frequencies with measured and simulated photocurrent. The integrated cell design consists of a patterned plasmonic back reflector and a nanostructured semiconductor top interface, which gives broadband and isotropic photocurrent enhancement.     

Resource checking and event handling within the W7-X segment control framework

ITER, Wendelstein 7-X, LHD, and TORE SUPRA are experimental facilities designed to lead the way to steady state fusion devices. These experiments require strategies to sustain a discharge in case of unforeseen events, e.g. heat overloads of plasma facing components or the failure of a plasma heating source. A recovery strategy is needed to get the discharge back for physics exploitation. For this purpose the W7-X segment control framework provides means for automated event detection along with options to formulate and initiate a recovery strategy. Besides handling of failures and degradation there are events that represent a desired plasma physical effect. An example for this kind of event is a transition to from Low to High-Confinement mode. These events indicate that a certain plasma state is reached and scientific examination can be altered thus enabling event-driven multiple experiments per discharge. Examples of both kinds of events will be presented and compared to other approaches in the community.