Drag reduction within radial turbine rotor passages using riblets

In this paper, reducing the friction losses in a radial inflow turbine rotor surface by adding engineered features (riblets) is explored. Initially, computational fluid dynamics analysis was used to study the operating mechanism of riblets and to test their ability to reduce drag within the rotor passage when running the turbine at the design point. Thereafter, riblets with different heights and spacing have been implemented at the rotor hub to study the effect of riblets geometry and arrangement on the drag reduction, which leads to determine the riblet geometry where the maximum benefit on turbine performance can be achieved. The effect of riblets on boundary layer development and on the secondary flow generation within the rotor passage has been examined. It was found that the introduction of riblets could reduce the wall shear stress at the hub surface, and on the other hand, they contribute to increasing the stream-wise vorticity within the rotor passage. The maximum wall shear reduction was achieved with riblet with relative height hrel = 2.5% equivalent to 19.3 wall units, while the maximum performance happens when using riblets with hrel = 1.5% equivalent to 11.8 wall units as the later contributes less in secondary flow generation within the passage. For riblets with height more than 19.3 wall units, the overall effect is negative, as they cause an increase in drag and give rise to secondary flow leading to lower turbine performance

Probabilistic Stress Analysis of Liquid Storage Tank

Liquefied Natural Gas transport and storage has become very important due to its ability to occupy 1/600th of the volume that compressed natural gas would occupy at room temperature and atmospheric pressure. In the present work, an LNG storage tank has been computationally simulated and probabilistically evaluated in view of the several uncertainties in the fluid, structural, material and thermal variables that govern the LNG storage tank. A finite element code ALGOR was used to couple the thermal profiles with structural design. The stresses and their variations were evaluated at critical points on the storage tank. Cumulative distribution functions and sensitivity factors were computed for stress responses due to fluid, mechanical and thermal random variables. These results can be used to quickly identify the most critical design variables in order to optimize the design and make it cost effective. The total heat gained by the liquid part in the tank has been evaluated and the amount of boil-off was calculated. Various methods have been proposed to minimize thermal stresse

Probabilistic Stress Analysis of Liquid Storage Tank

Liquefied Natural Gas transport and storage has become very important due to its ability to occupy 1/600th of the volume that compressed natural gas would occupy at room temperature and atmospheric pressure. In the present work, an LNG storage tank has been computationally simulated and probabilistically evaluated in view of the several uncertainties in the fluid, structural, material and thermal variables that govern the LNG storage tank. A finite element code ALGOR was used to couple the thermal profiles with structural design. The stresses and their variations were evaluated at critical points on the storage tank. Cumulative distribution functions and sensitivity factors were computed for stress responses due to fluid, mechanical and thermal random variables. These results can be used to quickly identify the most critical design variables in order to optimize the design and make it cost effective. The total heat gained by the liquid part in the tank has been evaluated and the amount of boil-off was calculated. Various methods have been proposed to minimize thermal stresse

RNA interference screening reveals host CaMK4 as a regulator of cryptococcal uptake and pathogenesis

ABSTRACT Cryptococcus neoformans , the causative agent of cryptococcosis, is an opportunistic fungal pathogen that kills over 200,000 individuals annually. This yeast may grow freely in body fluids, but it also flourishes within host cells. Despite extensive research on cryptococcal pathogenesis, host genes involved in the initial engulfment of fungi and subsequent stages of infection are woefully understudied. To address this issue, we combined short interfering RNA silencing and a high-throughput imaging assay to identify host regulators that specifically influence cryptococcal uptake. Of 868 phosphatase and kinase genes assayed, we discovered 79 whose silencing significantly affected cryptococcal engulfment. For 25 of these, the effects were fungus specific, as opposed to general alterations in phagocytosis. Four members of this group significantly and specifically altered cryptococcal uptake; one of them encoded CaMK4, a calcium/calmodulin-dependent protein kinase. Pharmacological inhibition of CaMK4 recapitulated the observed defects in phagocytosis. Furthermore, mice deficient in CaMK4 showed increased survival compared to wild-type mice upon infection with C. neoformans . This increase in survival correlated with decreased expression of pattern recognition receptors on host phagocytes known to recognize C. neoformans . Altogether, we have identified a kinase that is involved in C. neoformans internalization by host cells and in host resistance to this deadly infection. </jats:p

Thermal conductivity of heterogeneous mixtures and lunar soils

The theoretical evaluation of the effective thermal conductivity of granular materials is discussed with emphasis upon the heat transport properties of lunar soil. The following types of models are compared: probabilistic, parallel isotherm, stochastic, lunar, and a model based on nonlinear heat flow system synthesis

DCM+: Robust Congestion Control Protocol for Mobile Networks

This paper aims at presenting a new robust congestion control protocol for mobile networks. It also can be used for mixed networks and mobile adhoc networks (MANETs). The proposed protocol is called Dynamic Congestion Control Protocol for Mobile Networks (DCM+). It makes use of the bandwidth estimation algorithm used in Westwood+ algorithm. We evaluate DCM+ on the basis of known metrics like throughput, average delay, packet loss and Packet-Delivery-Ratio (PDR). New metrics like Normalized Advancing Index (NAI) and Complete-Transmission-Time (CTT) have been introduced for a comprehensive comparison with other congestion control variants like NewReno, Hybla, Ledbat and BIC. The simulations are done for a one-way single-hop-topology (sender->router->receiver). The findings in this paper clearly show excellent properties of our proposed technique like robustness and stability. It avoids congestions, increases performance, minimizes the end-to-end delay and reduces the transmission time. DCM+ combines the advantages of the protocols NewReno and Westwood+. The simulation results show high improvements, which make this approach extremely adequate for different types of networks