Transient cavitating flow structure and acoustic analysis of a hydrofoil with whalelike wavy leading edge

In this paper, the open source software OpenFOAM is used to perform a numerical investigation of the cavitating flow around a modified NACA63₄-021 hydrofoil with bioinspired, wavy leading edge, with particular emphasis on study of the interactions between the cavitation and the streamwise vortices and the far-field radiation noise. A modified k-ω shear-stress transport (SST) model coupled with the Schnerr-Sauer cavitation model and the Ffowcs Williams-Hawkings (FW-H) acoustic analogy approach are introduced to the simulation. The transient cavitation structure and the streamwise vortices are captured well and the results show significant interactions between the cavitation and the streamwise vortices. Cavitation can promote fragmentation of the streamwise vortices, while the streamwise vortices cause cavitation inception to occur earlier and bind the cavitation within the trough region by changing the pressure distribution on the hydrofoil. The transformation of the FW-H equation's solution indicates that the monopole noise is directly related to the cavitation volume acceleration and the dipole noise is related to the mechanical force of the hydrofoil on fluids and the rate at which this force changes. The collapse of cavitation cloud and the collision of the re-entrant jet and main flow will cause violent fluctuation of the mechanical force thus produce instantaneous extreme dipole noise values, while the monopole noise is relatively strong in the cavitation collapse stage due to significant cavitation volume acceleration. The time domain hydroacoustic characteristics are similar for the modified hydrofoil and the baseline hydrofoil.     

Prediction of commercial bank failure via multivariate statistical analysis of financial structures: The Turkish case

The objective of this paper is to propose a methodological framework for constructing the integrated early warning system (IEWS) that can be used as a decision support tool in bank examination and supervision process for detection of banks, which are experiencing serious problems. Sample and variable set of the study contains 40 privately owned Turkish commercial banks (21 banks failed during the period 1997–2003) and their financial ratios. Well known multivariate statistical technique (principal component analysis), was used to explore the basic financial characteristics of the banks, and discriminant, logit and probit models were estimated based on these characteristics to construct IEWS. Also, importance of early warning systems in bank examination was evaluated with respect to cost of failure. Results of the study show that, if IEWS was effectively employed in bank supervision, it can be possible to avoid from the bank restructuring costs at a significant amount of rate in the long run.     

Phase resolved measurements of the statistical flow behavior of a backward-facing step flow controlled by a sinusoidal Lorentz-force

In order to gain deeper inside into the behavior of a Lorentz-force controlled flow behind a backward-facing step, measurements with a laser Doppler velocity profile sensor were undertaken. By varying the frequency of the sinusoidal Lorentz-force the influence on the turbulence statistics was studied. Moreover, phase resolved measurement data is presented. The results confirm the characteristic frequency determined on basis of the momentum thickness beforehand. The aim of this study is to understand the influence of the different incitation signals and to reduce the reattachment length. The statistical results show a dependency of the turbulence degree on the excitation frequency as well as a deformation of the flow profile behind the step. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Time-harmonic acoustic propagation in the presence of a shear flow

This work deals with the numerical simulation, by means of a finite element method, of the time-harmonic propagation of acoustic waves in a moving fluid, using the Galbrun equation instead of the classical linearized Euler equations. This work extends a previous study in the case of a uniform flow to the case of a shear flow. The additional difficulty comes from the interaction between the propagation of acoustic waves and the convection of vortices by the fluid. We have developed a numerical method based on the regularization of the equation which takes these two phenomena into account. Since it leads to a partially full matrix, we use an iterative algorithm to solve the linear system.     

Prediction of the paper path in a laser printer by finite element analysis

A conventional problem of paper handling in a page-printing printer is to design a reliable paper path. Sometimes, this also affects the printing quality. The nonlinear theory of elastica has often been used to model paper deflection shape and to predict the paper path between some guiding rollers. The present paper proposes another method that can solve this problem more efficiently. Considering a piece of paper as a nonlinear beam, finite element analysis with geometric nonlinearity and manipulating the contact gap element between paper and guiding surfaces can be used to simulate the large-deflection behavior of paper. In this paper, the paper path in the vicinity of an OPC (organic photoconductive) drum is investigated with a general purpose finite element package. The effect of the electrostatic force between the OPC drum and the paper is considered, and the deformed shape of the paper for different forces lengths is obtained. According to those results an appropriate paper guide is added for an exact paper path.     

The recurrence and the gradient-like structure of a flow

In this paper, some new properties of the nonwandering set, the partial order set, the chain recurrent set and the generalized recurrent set of a flow are proved. A new characterization of the gradient-like part of a flow is given. Some results of Conley are generalized.     

Temporal analysis of a power-law liquid sheet in the presence of acoustic oscillations

The instability of a non-Newtonian liquid sheet in the presence of acoustic oscillations is investigated theoretically. The power-law model is used to describe the viscosity of the non-Newtonian liquid. The corresponding dispersion relation is obtained by linear analysis. The effects of the mean velocity of the gas, the oscillation amplitude, the oscillation frequency, and the gas density on the instability of the power-law liquid sheet are studied. The results show that the shear-thickening liquid sheet is more unstable than Newtonian and shear-thinning liquid sheets when the effects of acoustic oscillations are considered. In particular, a second unstable region appears on the shear-thickening liquid sheet at a low oscillation frequency. Especially, for the shear-thinning liquid sheet, there is a second unstable region in the dispersion curve at a high mean gas velocity. A third unstable region appears on the shear-thinning liquid sheet at a high gas density in the presence of acoustic oscillations. The unstable range of the Newtonian liquid is always the widest among these liquids.     

Determination of acoustic parameters in flow fields using OpenFOAM

In the present paper a Computational Aero Acoustics approach based on Lighthill's and Curle's Acoustic Analogies was implemented in OpenFOAM 2.1.1. The novel developed OpenFOAM application solvers acousticFoam and acousticRhoFoam can be used for transient incompressible and compressible simulations respectively. The CAA approach takes High Performance Computing environment into account and realize the computation of flow and acoustic fields within the acoustical near field on one mesh only. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of a long slender structure in turbulent flow

The dynamic behaviour of a long slender structure in turbulent flow can vary considerably, depending on the particular excitation. Regimes from simple static deformation, over periodic to irregular and chaotic behaviour are observed. An example is the self-excited periodic motion of a long slender structure in cross flow. In such cases, the fluid flow and the structure movement are strongly coupled. The paper presents a robust partitioned coupling approach based on the Immersed Boundary Method which integrates the geometrically exact Cosserat rod model. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A statistical estimate of the structure of multi-extremal problems

The solution of ak-extremal problem is defined as the set of pairs (x _i ^* , _i),i = 1, ,k, where x _t ^* isi ^th local minimum and _i is the volume of the set of attraction of this minimum. A Bayesian estimate ofk and ( ₁ , , _k ) is constructed.This paper has been written while the author was a CNR visiting professor at the Institute of Mathematics of the Milano University.     

Asymptotic analysis of the nonsteady viscous flow with a given flow rate in a thin pipe

The nonsteady Navier–Stokes equations are considered in a thin infinite pipe with the small diameter ? in the case of the Reynolds number of order ?. The time-dependent flow rate is a given function. The complete asymptotic expansion is constructed and justified. The error estimate of order O(? ^J ) for the difference of the exact solution and the J-th asymptotic approximation is proved for any real J.     

Modelling the flow of congestive heart failure patients through a hospital system

The number of hospital admissions in England due to heart failure is projected to increase by over 50% during the next 25 years. This will incur greater pressures on hospital managers to allocate resources in an effective manner. A reliable indicator for measuring the quantity of resources consumed by hospital patients is their length of stay (LOS) in care. This paper proposes modelling the length of time heart failure patients spend in hospital using a special type of Markov model, where the flow of patients through hospital can be thought of as consisting of three stages of care—short-, medium- and longer-term care. If it is assumed that new admissions into the ward are replacements for discharges, such a model may be used to investigate the case-mix of patients in hospital and the expected patient turnover during some specified period of time. An example is illustrated by considering hospital admissions to a Belfast hospital in Northern Ireland, between 2000 and 2004.     

Characterization of welding defects by fractal analysis of ultrasonic signals

In this work we apply tools developed for the study of fractal properties of time series to the problem of classifying defects in welding joints probed by ultrasonic techniques. We employ the fractal tools in a preprocessing step, producing curves with a considerably smaller number of points than in the original signals. These curves are then used in the classification step, which is realized by applying an extension of the Karhunen–Loève linear transformation. We show that our approach leads to small error rates, comparable with those obtained by using more time-consuming methods based on non-linear classifiers.     

Coherent structure in flow over a slitted bluff body

The focus of the present investigation is resolution of the coherent structure in the near wake behind a slitted bluff body. The bluff body is two-dimensional with gap ratio from 0.12 to 0.48. The evolution of the structure was numerically investigated using the renormalization group (RNG) k–ε model at Reynolds number of 470,000. Two types of coherent structure are identified: At low gap ratio 0.12, the structure is characterized by a flip–flopping gap flow; at high ratio 0.22–0.48, the gap flow deflects to one side with an asymmetrical wake. The coherent structure is divided by the gap flow into two zones called the primary recirculation zone and the secondary recirculation zone. The coherent structure is intimately related to the gap ratio, and the structure of small gap ratio is different from that of large gap ratio because the interaction between two zones relates to the gap ratio. To explain the vortex shedding, a mechanism that single vortex of large size suddenly immerses between two shear layers was proposed. Experimental results using point-to-point method and particle-image velocimetry (PIV) measurements in a close wind tunnel were also carried out to confirm the observation from the numerical study. The evidence shows that the numerical results are of good agreement with the experiments. The comparison between the RNG k–ε model and the large eddy simulation also indicates that the RNG k–ε model is adequate in computing the bluff body flow.