Numeričko istraživanje utjecaja radijalne zračnosti na performanse kompresora s kombiniranim tokom

In mixed-flow compressor, the leakage flow through the tip clearance generates the tip leakage vortex by the interaction with the main flow, and consequently makes the flow in the impeller passage more complex. Different tip clearances generate different intensity of disturbance to main flow. In this paper, numerical analysis is performed using a commercial code to investigate tip clearance effects on main flow. The performance of mixed-flow impeller with four different clearances between impeller and stationary shroud are evaluated and compared with experimental results. The impeller performance curves are obtained for different mass flow parameters with different tip clearances at design speed. The results show that the tip leakage flow strongly interacts with main flow and contributes to total pressure loss and performance reduction. The pressure and performance decrement are approximately linearly proportional to the gap between impeller and stationary shroud. Though the velocity vectors distribution, the computed results reveal that the intensity of the disturbance generated by the leakage flow interacts with the main flow has rather a large influence over efficiency. And the quantity of backflow is minimum when the tip clearance is 0.5 mm, while the 0.75mm tip clearance, by contrast, has a considerable effect on main flow by the interaction with leakage flow.Kod kompresora s kombiniranim tokom, protok rasipanja kroz radijalnu zračnost stvara vršni vrtlog rasipanja zbog interakcije s glavnim tokom te uzročno tok u prolazu rotora čini kompleksnijim. Različite veličine radijalne zračnosti uzrokuju različiti intenzitet smetnje glavnom toku. U ovom članku, numerička analiza provodi se korištenjem komercijalnog koda kako bi se istražio utjecaj radijalne zračnosti na glavni tok. Ocjenjene su performanse rotora kombiniranog toka sa četiri različite radijalne zračnosti između rotora i stacionarnog kućišta te su uspoređene s eksperimentalnim rezultatima. Krivulje performansa rotora dobivene su za različite parametre masenog protoka sa različitim radijalnim zračnostima pri konstrukcijskoj brzini. Rezultati pokazuju kako protok vršnog rasipanja ima snažno međudjelovanje s glavnim tokom i da pridonosi potpunom gubitku tlaka i smanjenju performansa. Smanjenje tlaka i performansi približno je linearno proporcionalno razmaku između rotora i stacionarnog kućišta. Kroz raspored vektora brzine, računalni izračuni otkrivaju kako intenzitet smetnja koje se stvaraju kod međudjelovanja protoka rasipanja i glavnog toka, ima priličan utjecaj na efikasnost. Kvantiteta protutoka je minimalna kad radijalna zračnost iznosi 0.5mm, a usporedno tome, kad je radijalna zračnost 0.75mm, ima značajan utjecaj na glavni tok kroz međudjelovanje s protokom rasipanja

Decomposing and Coupling Saliency Map for Lesion Segmentation in Ultrasound Images

Complex scenario of ultrasound image, in which adjacent tissues (i.e., background) share similar intensity with and even contain richer texture patterns than lesion region (i.e., foreground), brings a unique challenge for accurate lesion segmentation. This work presents a decomposition-coupling network, called DC-Net, to deal with this challenge in a (foreground-background) saliency map disentanglement-fusion manner. The DC-Net consists of decomposition and coupling subnets, and the former preliminarily disentangles original image into foreground and background saliency maps, followed by the latter for accurate segmentation under the assistance of saliency prior fusion. The coupling subnet involves three aspects of fusion strategies, including: 1) regional feature aggregation (via differentiable context pooling operator in the encoder) to adaptively preserve local contextual details with the larger receptive field during dimension reduction; 2) relation-aware representation fusion (via cross-correlation fusion module in the decoder) to efficiently fuse low-level visual characteristics and high-level semantic features during resolution restoration; 3) dependency-aware prior incorporation (via coupler) to reinforce foreground-salient representation with the complementary information derived from background representation. Furthermore, a harmonic loss function is introduced to encourage the network to focus more attention on low-confidence and hard samples. The proposed method is evaluated on two ultrasound lesion segmentation tasks, which demonstrates the remarkable performance improvement over existing state-of-the-art methods.Comment: 18 pages, 18 figure

Study of vibration characteristics of the short thin cylindrical shells and its experiment

The short thin cylindrical shells are important component used in rotating machinery and its function is to connect shafts and transmitted torque. The kind of components is always destroyed due to vibrational state, so it is necessary to further research on the vibration characteristics. In this paper, the vibration characteristics of short thin cylindrical shells are solved using the beam function method, the transfer matrix method and the finite element method respectively. The solving results of three calculating methods are compared by simulation in the clamped-free and clamped-clamped boundary conditions. The simulation results show that the solving results of the transfer matrix method are close to the results of finite element method, but the deviation of the results of the beam functions method is larger than the other two methods. Furthermore, the experiments of the short thin cylindrical shell in the clamped-free boundary conditions are studied. The experimental results verify that the transfer matrix method and the finite element method are applicability to solve the vibration characteristics of the short thin cylindrical shells