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This work applies resolvent analysis to incompressible flow through a rectangular duct, in order to identify dominant linear energy-amplification mechanisms present in such flows. In particular, we formulate the resolvent operator from linearizing the Navier–Stokes equations about a two-dimensional base/mean flow. The laminar base flow only has a nonzero streamwise velocity component, while the turbulent case exhibits a secondary mean flow (Prandtl’s secondary flow of the second kind). A singular value decomposition of the resolvent operator allows for the identification of structures corresponding to maximal energy amplification, for specified streamwise wavenumbers and temporal frequencies. Resolvent analysis has been fruitful for analysis of wall-bounded flows with spanwise homogeneity, and here we aim to explore how such methods and findings can extend for a flow in spatial domains of finite spanwise extent. We investigate how linear energy-amplification mechanisms (in particular the response to harmonic forcing) change in magnitude and structure as the aspect ratio (defined as the duct width divided by its height) varies between one (a square duct) and ten. We additionally study the effect that secondary flow has on linear energy-amplification mechanisms, finding that in different regimes it can either enhance or suppress amplification. We further investigate how the secondary flow alters the forcing and response mode shapes leading to maximal linear energy amplification., QC 20230508

We test a method for visualizing and measuring enterprise application architectures. The method was designed and previously used to reveal the hidden internal architectural structure of software applications. The focus of this paper is to test if it can also uncover new facts about the applications and their relationships in an enterprise architecture, i.e., if the method can reveal the hidden external structure between software applications. Our test uses data from a large international telecom company. In total, we analyzed 103 applications and 243 dependencies. Results show that the enterprise application structure can be classified as a core-periphery architecture with a propagation cost of 25%, core size of 34%, and architecture flow through of 64%. These findings suggest that the method could be effective in uncovering the hidden structure of an enterprise application architecture., QC 20191008

During the closing phase of the phonation cycle the true vocal-folds (TVF) have a convergent-divergent shape. The negative pressures generated by the flow through the glottal passage are producing closing forces acting on the TVFs. They can affect both vocal-fold vibration and voice production, since they can accelerate the closing phase. Large Eddy Simulation approach is used to investigate the intra-glottal forces generated solely by the flow during the closing phase. The influence of the gap between the false vocal-folds (FVFs) and the location of FVFs with respect to the TVFs are analyzed. Based on anatomical measurements, four different widths between the FVFs and two different distances between the true and false vocal-folds are investigated for the same trans-laryngeal pressure. The TVFs gap is kept constant. All cases exhibit a non-symmetric flow behavior in the mid-frontal plane. As the distance between the FVFs is decrease beyond a threshold value (still greater than glottal width), there is an increase in the magnitude of the closing forces acting on the TVFs. On the divergent slope of the glottis, these forces were found for some of the cases to be up to four times greater in magnitude as compared with the Baseline case., QC 20131121

This paper describes in detail a novel formulation of the method of characteristics for its application to solve one-dimensional compressible unsteady non-homentropic flow advected along porous wall channels. In particular, the method is implemented into a wall-flow monolith Diesel particulate filter model whose purpose is the pressure drop prediction. The flow inside the monolith channels is considered to be one-dimensional and the flow through the porous wall treated as a source term agree with the Darcy's law. The flow dynamic behaviour at internal nodes of the channels is solved by means of shock capturing methods, whereas the end nodes, or boundary conditions, are solved applying the method of characteristics. The derived solution in this study of the Riemann variables and the entropy level includes the variation along the space-time plane due to cross-section area changes, friction and heat transfer as traditionally stated, but also takes into account the key influence on every line of the flow leaving or entering to the channels through the porous walls. © 2011 Elsevier Inc.

This paper describes in detail a novel formulation of the method of characteristics for its application to solve one-dimensional compressible unsteady non-homentropic flow advected along porous wall channels. In particular, the method is implemented into a wall-flow monolith Diesel particulate filter model whose purpose is the pressure drop prediction. The flow inside the monolith channels is considered to be one-dimensional and the flow through the porous wall treated as a source term agree with the Darcy's law. The flow dynamic behaviour at internal nodes of the channels is solved by means of shock capturing methods, whereas the end nodes, or boundary conditions, are solved applying the method of characteristics. The derived solution in this study of the Riemann variables and the entropy level includes the variation along the space-time plane due to cross-section area changes, friction and heat transfer as traditionally stated, but also takes into account the key influence on every line of the flow leaving or entering to the channels through the porous walls. © 2011 Elsevier Inc.

The flow-acoustic interaction in a T-junction can result in both amplification and attenuation of incoming waves. The frequency ranges of amplification are mainly governed by the time scales of convection of hydrodynamic instabilities over the side branch opening. With bias flow, i.e. flow through the side branch the amplification can increase or completely vanish. In this paper this effect is studied for a T-junction of rectangular ducts, with a grazing Mach number of 0.1 and a varying bias inflow. When the bias inflow Mach number changes from 0 to 0.01 the amplification is increased severely. Further increasing the bias inflow has the effect of lower the amplification again towards zero at a bias Mach number of 0.05., QC 20101118

Since its inception in 1996, the CO2 injection operation at Sleipner has been monitored by 3D time-lapse seismic surveys. Striking images of the CO2 plume have been obtained, showing a multi-tier feature of high reflectivity, interpreted as arising from a number of thin layers of CO2 trapped beneath thin, intra-reservoir mudstones. The topmost layer of the CO2 plume can be characterized most accurately, and its rate of growth quantified. From this the CO2 flux arriving at the reservoir top can be estimated. This is mostly controlled by pathway flow through the intra-reservoir mudstones. Flow has increased steadily with time suggesting that pathway transmissivities are increasing with time, and/or the pathways are becoming more numerous. Detailed 3D history-matching of the topmost layer cannot easily reproduce the observed rate of lateral spreading. Very high reservoir permeabilities seem likely, possibly with a degree of anisotropy. Other modelling variables under investigation include topseal topography, the number of feeder pathways and CO2 properties. Detailed studies such as this will provide important constraints on longer-term predictive models of plume evolution. © 2009 Natural Environment Research Council.

A quasi-steady semi-analytical model is proposed to predict the grazing-bias flow in a perforated-pipe muffler at low Mach numbers for high Reynolds numbers based on the diameter of the perforation. This model allows both the prediction of the steady flow distribution through a muffler and the prediction of the acoustical response of the perforated pipe in terms of the impedance. The model is compared with experimental and numerical data from the literature. The incorporation of the influence of the flow in this impedance allows predicting the global acoustical response of the muffler by means of a Finite Element Method solution of the Helmholtz equation, neglecting other convective effects. This procedure is tested for two extreme cases. Firstly we consider a through flow muffler consisting of an expansion chamber mounted axis-symmetrically around a perforated pipe. Secondly a plug flow muffler is considered, which is the same muffler but with a plug placed halfway along the perforated pipe, forcing the flow through the pipe perforations. In both cases the model predicts the transmission loss of the muffler within 1 dB for Strouhal numbers (based on the perforation diameter and main flow velocity) of order unity. The performance of the through flow muffler is essentially that of an expansion chamber without major contribution of flow effects. In the plug flow muffler the flow does significantly enhances the muffler performance, but this is at the cost of a significant static pressure loss., QC 20101013

The development of microsurgery has most recently been focused upon the evolution of perforator flaps, with the aim of minimising donor site morbidity, and avoiding the transfer of functionally unnecessary tissues. The vascular basis of perforator flaps also facilitates radical primary thinning prior to flap transfer, when appropriate. Based upon initial clinical observations, cadaveric, and radiological studies, we describe a new, thin, perforator flap based upon the circumflex scapular artery (CSA). A perforator vessel was found to arise within 1.5cm of the CSA bifurcation (arising from the main trunk, or the descending branch). The perforator arborises into the sub-dermal vascular plexus of the dorsal scapular skin, permitting the elevation and primary thinning of a skin flap. This thin flap has been employed in a series of five clinical cases to reconstruct defects of the axilla (two cases of hidradenitis suppurativa; pedicled transfers), and upper limb (one sarcoma, one brachial to radial artery flowthrough revascularisation plus antecubital fossa reconstruction, and one hand reconstruction with a chimeric flap incorporating vascularised bone, fascia, and thin skin flaps; free tissue transfers). No intramuscular perforator dissection is required; pedicle length is 8-10cm and vessel diameter 2-4mm. There was no significant peri-operative complication or flap failure, all donor sites were closed primarily, patient satisfaction was high, and initial reconstructive aims were achieved in all cases. Surgical technique, and the vascular basis of the flap are described. The thin circumflex scapular artery perforator flap requires no intramuscular dissection yet provides high quality skin (whose characteristics can be varied by orientation of the skin paddle), and multiple chimeric options. The donor site is relatively hair-free, has favourable cosmesis and no known functional morbidity. This flap represents a promising addition to the existing range of perforator flaps