Calculation of clearances in twin screw compressors

Clearances between rotating and stationary parts in a screw compressor are set to ensure the efficient operation and allow for thermal deformation without unwanted contacts. The change in clearances is caused by both pressure and temperature changes within the machine. If clearances are too large, the increased leakage flows will reduce efficiency. However, if the nominal clearances are too small, contacts between the rotating and stationary parts can occur as a consequence of rotor and casing deformations. In order to determine the operational clearances, a numerical analysis of deformation of screw compressor rotors and casing has to be performed. This paper discusses how the temperature of rotor and casing surfaces calculated from the one-dimensional chamber model in the SCORG could be used as a boundary conditions for a steady state thermal and structural analysis of a screw compressor solid parts. Deformations of rotors and casing under temperature load were calculated using a commercial Finite Element Analysis code ANSYS. Operational clearance are estimated from these deformations and some recommendations for further work are proposed

Stark Broadening of in III Lines in Astrophysical and Laboratory Plasma

Besides the need of Stark broadening parameters for a number of problems in physics, and plasma technology, in hot star atmospheres the conditions exist where Stark widths are comparable and even larger than the thermal Doppler widths. Using the semiclassical perturbation method we investigated here the influence of collisions with charged particles for In III spectral lines. We determined a number of Stark broadening parameters important for the investigation of plasmas in the atmospheres of A-type stars and white dwarfs. Also, we have compared the obtained results with existing experimental data. The results will be included in the STARK-B database, the Virtual Atomic and Molecular Data Center and the Serbian Virtual Observatory

Development of methodology for distributed collaborative design environment

This paper describes the CODEVE (COllaborative DEsign in Virtual Environment) methodology developed in a joint educational project of four European universities called NARIP (Networked Activities for Realization of Innovative Products). The ultimate goal of the NARIP NPD course is to develop a concept and produce a physical product prototype within one academic semester. In order to expose students to real life situations the prototype is being produced in close collaboration with an industrial partner. Elements of the NARIP course comprise: (1) project definition-according to agreement with the industrial partner, (2) lectures composed and adapted to address the specific needs of the current project and which are equally distributed to partner universities, (3) project work monitored by academics, with three distinct phases and review points, and (4) the final workshop that includes prototype manufacturing, assembly and testing, final presentation and exhibition. The paper presents the structure and details of the developed methodology as well as an overview of the course development history. The core of the CODEVE methodology is a set of comprehensive guidelines for students and teachers that are specially adapted and focused to the issues and problems that arise in distributed collaborative multidisciplinary design projects. The methodology focuses on management of complex projects, emphasizing the importance of research phases, prompt clarification of any issues and balanced distribution of project tasks. The methodology also promotes the use of various virtual/on-line collaboration tools to foster discussion and exchange of 3D sketches and models

Development of methodology for distributed collaborative design environment

This paper describes the CODEVE (COllaborative DEsign in Virtual Environment) methodology developed in a joint educational project of four European universities called NARIP (Networked Activities for Realization of Innovative Products). The ultimate goal of the NARIP NPD course is to develop a concept and produce a physical product prototype within one academic semester. In order to expose students to real life situations the prototype is being produced in close collaboration with an industrial partner. Elements of the NARIP course comprise: (1) project definition-according to agreement with the industrial partner, (2) lectures composed and adapted to address the specific needs of the current project and which are equally distributed to partner universities, (3) project work monitored by academics, with three distinct phases and review points, and (4) the final workshop that includes prototype manufacturing, assembly and testing, final presentation and exhibition. The paper presents the structure and details of the developed methodology as well as an overview of the course development history. The core of the CODEVE methodology is a set of comprehensive guidelines for students and teachers that are specially adapted and focused to the issues and problems that arise in distributed collaborative multidisciplinary design projects. The methodology focuses on management of complex projects, emphasizing the importance of research phases, prompt clarification of any issues and balanced distribution of project tasks. The methodology also promotes the use of various virtual/on-line collaboration tools to foster discussion and exchange of 3D sketches and models

Grid generation methodology and CFD simulations in sliding vane compressors and expanders

The limiting factor for the employment of advanced 3D CFD tools in the analysis and design of rotary vane machines is the unavailability of methods for generation of computational grids suitable for fast and reliable numerical analysis. The paper addresses this challenge presenting the development of an analytical grid generation for vane machines that is based on the user defined nodal displacement. In particular, mesh boundaries are defined as parametric curves generated using trigonometrical modelling of the axial cross section of the machine while the distribution of computational nodes is performed using algebraic algorithms with transfinite interpolation, post orthogonalisation and smoothing. Algebraic control functions are introduced for distribution of nodes on the rotor and casing boundaries in order to achieve good grid quality in terms of cell size and expansion. In this way, the moving and deforming fluid domain of the sliding vane machine is discretized and the conservation of intrinsic quantities in ensured by maintaining the cell connectivity and structure. For validation of generated grids, a mid-size air compressor and a small-scale expander for Organic Rankine Cycle applications have been investigated in this paper. Remarks on implementation of the mesh motion algorithm, stability and robustness experienced with the ANSYS CFX solver as well as the obtained flow results are presente

Spatiotemporal Dependency of Age-Related Changes in Brain Signal Variability

Recent theoretical and empirical work has focused on the variability of network dynamics in maturation. Such variability seems to reflect the spontaneous formation and dissolution of different functional networks. We sought to extend these observations into healthy aging. Two different data sets, one EEG (total n = 48, ages 18-72) and one magnetoencephalography (n = 31, ages 20-75) were analyzed for such spatiotemporal dependency using multiscale entropy (MSE) from regional brain sources. In both data sets, the changes in MSE were timescale dependent, with higher entropy at fine scales and lower at more coarse scales with greater age. The signals were parsed further into local entropy, related to information processed within a regional source, and distributed entropy (information shared between two sources, i.e., functional connectivity). Local entropy increased for most regions, whereas the dominant change in distributed entropy was age-related reductions across hemispheres. These data further the understanding of changes in brain signal variability across the lifespan, suggesting an inverted U-shaped curve, but with an important qualifier. Unlike earlier in maturation, where the changes are more widespread, changes in adulthood show strong spatiotemporal dependenc

Induced gravitational collapse at extreme cosmological distances: the case of GRB 090423

CONTEXT: The induced gravitational collapse (IGC) scenario has been introduced in order to explain the most energetic gamma ray bursts (GRBs), Eiso=10^{52}-10^{54}erg, associated with type Ib/c supernovae (SNe). It has led to the concept of binary-driven hypernovae (BdHNe) originating in a tight binary system composed by a FeCO core on the verge of a SN explosion and a companion neutron star (NS). Their evolution is characterized by a rapid sequence of events: [...]. AIMS: We investigate whether GRB 090423, one of the farthest observed GRB at z=8.2, is a member of the BdHN family. METHODS: We compare and contrast the spectra, the luminosity evolution and the detectability in the observations by Swift of GRB 090423 with the corresponding ones of the best known BdHN case, GRB 090618. RESULTS: Identification of constant slope power-law behavior in the late X-ray emission of GRB 090423 and its overlapping with the corresponding one in GRB 090618, measured in a common rest frame, represents the main result of this article. This result represents a very significant step on the way to using the scaling law properties, proven in Episode 3 of this BdHN family, as a cosmological standard candle. CONCLUSIONS: Having identified GRB 090423 as a member of the BdHN family, we can conclude that SN events, leading to NS formation, can already occur already at z=8.2, namely at 650 Myr after the Big Bang. It is then possible that these BdHNe originate stem from 40-60 M_{\odot} binaries. They are probing the Population II stars after the completion and possible disappearance of Population III stars.Comment: 9 pages, 9 figures, to appear on A&