1,721,021 research outputs found
Development of a computational fluid dynamics simulation tool for lubrication studies on cycloidal gear sets
No full textIn the last decades, the growing mechatronic sector has promoted the development of more and more compact and efficient gearboxes. The margins of improvement are still big even if, sometimes, finding the optimal solutions is a trial and error procedure. For this reason, the development of dedicated tools for the optimization of the geometry and configuration of gearboxes can significantly increase the development effectiveness and help in reducing design costs. Moreover, having a more efficient solution could also reduce thermal problems during operation and increase the system reliability. The so-called 'thermal limit', i.e. the maximum transmittable power without an overheating of the systems, is particularly critical for high power density and compact solutions. Those relies mainly on planetary, harmonic and cycloidal architectures. While many empirical or analytical prediction models can be found in literature for the prediction of the power losses associated with the gear meshing and the bearing, few reliable models are nowadays available for the losses associated with the interaction with the lubricant, i.e. hydraulic losses. Experimental and computational fluid dynamics studies on parallel axis as well as planetary gear sets have been presented in the past. The goal of this research is the extension of the applicability range of those numerical approached to cycloidal kinematics for which no studies at all are available with respect to the hydraulic losses. The main challenge in numerically simulate the lubricant splashing in a cycloidal reduced is related to the topological modification of the computational domain during operation. For this purpose, a specific mesh handling technique, based on a 2.5D mesh, capable to handle the variations of the geometry of the domain was developed in the OpenFOAM® environment. The capability to analytically control the mesh generation at each time step ensures a very high numerical stability and a very high computational efficiency of the solution. Eventually, the approach was systematically applied to a real geometry and the results compared with those obtained for other gear architectures with comparable performances in terms of dimensions and reduction ratios
From the extraction of currently fulfilled requirements to value curves: a case-study in the field of harvesting machines for shell fruits and lessons learnt in engineering design
Full text linkThe market for agricultural machinery is characterized by products with a high degree of maturity in the product life cycle. Consequently, current improvements in new machinery are predominantly incremental and new projects basically use solutions that are already consolidated. This makes this domain appropriate for benchmarking existing systems and envisioning new value propositions. The present paper deals primarily with the former and uses the value curves as a means to structure the comparison among different families of technical systems; in particular, harvesting machines for shell fruits from the ground surface, e.g., chestnuts, walnuts, and hazelnuts, were investigated here. The process of building value curves requires the identification of currently fulfilled requirements. Despite the attention paid by engineering design research to requirements, a structured process is lacking to extract relevant information and create value curves or other representations useful for benchmarking. The present paper approaches this problem and presents how the authors have individuated relevant knowledge for characterizing different categories of harvesting machines. Namely, after an extensive search of the scientific literature and patents, a critical review of existing machines, aimed at individuating their functioning principles, architecture, and attitude in fulfilling specific design requirements, was performed. Then, existing machines were classified in 8 main categories, and their strengths and weaknesses were identified with reference to 11 competing factors. The consequent construction of value curves enabled the identification of possible points of intervention by hypothesizing possible future evolutions of such machinery, both in a structural and in a value-based perspective. Limitations about the repeatability of the followed approach and possible repercussions on design research are discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Preliminary geochemical exploration in semiarid climate: a case of porphyry type occurrence in Sardinia (Italy)
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