CFD Simulation of Flow Features and Vorticity Structures in Tuna-Like Swimming

The theoretical research on the propulsive principle of aquatic animal becomes more important and attracted more researchers to make efforts on it. In the present study, a computational fluid dynamic （CFD） simulation of a three-dimensional traveling-wave undulations body of tuna has been developed to investigate the fluid flow features and vorticity structures around this body when moving in a straight line. The undulation only takes place in the posterior half of the fish, and the tuna-tail is considered as a lunate fin oscillating with the mode combined swaying with yawing. A Reynolds-averaged Navier-Stokes （RANS） equation is developed, employing a control-volume method and a k-omega SST turbulent model; meanwhile an unstructured tetrahedral grid, which is generated for the three-dimensional geometry, is used based on the deformation of the hind parts of the body and corresponding movement of the tail. We calculated the hydrodynamic performance of tuna-like body when a tuna swims in a uniform velocity, and compared the input power coefficient, output power coefficient and propulsive efficiency of the oscillating tuna-tail with or without body vortex shedding. Additionally, the load distribution on the body, flow features and vorticity structures around the body were demonstrated. The effect of interaction between the body-generated vortices and the tail-generated vorticity on the hydrodynamic performance can be obtained.

Hepatocyte culture in a radial-flow bioreactor with plasma polypyrrole coated scaffolds

We have designed and evaluated a radial-flow bioreactor for three-dimensional liver carcinoma cell culture on a new porous coated scaffold.We designed a culture chamber where a radial flow of culture medi-um was continuously delivered through it.Once this system was established,flow was simulated using flow dy-namics software based on numeric methods to solve Navier-Stockes flow equations.Perfusion within cell culture scaffolds was simulated using a flow velocity of 7 mL/min and found that cell culture medium was distributed unhindered in the bioreactor chamber.Afterwards,the bioreactor was built according to the simulated design and was tested with liver carcinoma cells(HepG2)cultured over an L-polylactic acid scaffold whose surface was modified with iodine-doped polypyrrole.The bioreactor was tested under non-flow and in radial flow condi-tions.Cell density under radial flow conditions was almost double than that under static conditions and both total protein and albumin output was also increased under radial flow conditions.

DDoS Attack Detection via Multi-Scale Convolutional Neural Network

Distributed Denial-of-Service(DDoS)has caused great damage to the network in the big data environment.Existing methods are characterized by low computational efficiency,high false alarm rate and high false alarm rate.In this paper,we propose a DDoS attack detection method based on network flow grayscale matrix feature via multi-scale convolutional neural network(CNN).According to the different characteristics of the attack flow and the normal flow in the IP protocol,the seven-tuple is defined to describe the network flow characteristics and converted into a grayscale feature by binary.Based on the network flow grayscale matrix feature(GMF),the convolution kernel of different spatial scales is used to improve the accuracy of feature segmentation,global features and local features of the network flow are extracted.A DDoS attack classifier based on multi-scale convolution neural network is constructed.Experiments show that compared with correlation methods,this method can improve the robustness of the classifier,reduce the false alarm rate and the missing alarm rate.

Importance guided stream surface generation and feature exploration

Exploring flow features and patterns hidden behind the data has received extensive academic attention in flow visualization.In this paper,we introduce an importance-guided surface generation and exploration scheme to explore the features and their connections.The features are expressed as an importance field,which can either be derived from a scalar field or be specified as a flow pattern.Guided by the importance field,we sample a pool of seeding curves along the binormal direction and construct stream surfaces to fit the regions of high-importance values.Our scheme evaluates candidate seeding curves by collecting importance scores from the curve and corresponding streamlines.The candidate seeding curves are refined using the high-score segments to identify the optimal surfaces.Comparative visualization among different kinds of flow features across time steps can be easily derived for flow structure analysis.In order to reduce the visual complexity,we leverage SurfRiver to achieve clearer observation by flattening and aligning the surface.Finally,we apply our surface generation scheme guided by flow patterns and scalar fields to evaluate the effectiveness of the proposed tool.

SOME FEATURES OF MUD ROCK FLOW AND LANDSLIDE CAUSED BY STORM RAINFALL IN CHINA

Storm rainfall and severe storm rainfall can directly cause flood, and usually cause a series of secondary disasters. In mountain areas, the abrupt mud rock flow and landslide disasters motivated by storm rainfall are especially serious. So, it is negligible content to pay more attention and strengthen the study of storm rainfall secondary disasters in studying storm rainfall disaster.In the National Key Project 85-906-09,we have developed these aspects’studies, which not be ignored by some relevant sections

Numerical Simulation on Flow and Heat Transfer at Shell-Side of Flat-Tube Heat Exchangers

The fluid flow and heat transfer of the shell-side in one type of flat-tube heat exchangers（FHE） were studied through numerical simulation and experimental methods.In the numerical simulation,hot/cold air was set as working fluid,and the standard k-ε turbulence model supplemented by boundary conditions was used,and also the control volume method was used to the discrete control equations.Compared with the same type of circular-tube heat exchangers（CHE）,the numerical simulation results show that the pressure drop at the shell-side of FHE decreases by 12%-20%,and heat transfer coefficient increases by about 24%.The coefficient of integral performance Nu/ζ 0.29 has an increment of 22%-34%.Under the same conditions,the experimental results of temperature and the overall pressure drop show that the deviation percentage with those of numerical simulation are less than 8% and 25%,respectively.Both results verify that the heat transfer efficiency and flow resistance characteristics of FHEs are superior to that of CHEs.

Clinical Relevance of Coronary Fractional Flow Reserve： Art-of-state

Objective：The objective was to delineate the current knowledge of fractional flow reserve （FFR） in terms of definition,features,clinical applications,and pitfalls of measurement of FFR.Data Sources：We searched database for primary studies published in English.The database of National Library of Medicine （NLM）,MEDLINE,and PubMed up to July 2014 was used to conduct a search using the keyword term ＂FFR＂.Study Selection：The articles about the definition,features,clinical application,and pitfalls of measurement of FFR were identified,retrieved,and reviewed.Results：Coronary pressure-derived FFR rapidly assesses the hemodynamic significance of individual coronary artery lesions and can readily be performed in the catheterization laboratory.The use of FFR has been shown to effectively guide coronary revascularization procedures leading to improved patient outcomes.Conclusions：FFR is a valuable tool to determine the functional significance of coronary stenosis.It combines physiological and anatomical information,and can be followed immediately by percutaneous coronary intervention （PCI） if necessary.The technique of FFR measurement can be performed easily,rapidly,and safely in the catheterization laboratory.By systematic use of FFR in dubious stenosis and multi-vessel disease,PCI can be made an even more effective and better treatment than it is currently.The current clinical evidence for FFR should encourage cardiologists to use this tool in the catheterization laboratory.