1/2004

Contents:

• N.Egidi, L.Misici, R.Piergallini and F.Tosi, The Lattice Boltzmann Method for Fluid Mixing: a Comparison with the Finite Element Method - abstract | full text
• A.K.Bin, P.M.Machniewski and L.Rudniak, Modelling of Bubble Formation with the Aid of CFD - abstract | full text
• Y.Bin and W.Keqi, Three-Dimensional Numerical Analysis of Internal Flow Phenomena in a Diagonal Rotor - abstract | full text
• A.Sowa, Flow Simulations in Cross-flow Fans Using the Finite Element and Finite Volume Methods - abstract | full text
• R.Rzadkowski and J.Sokolowski, Natural Frequencies and Modes Shapes of Two Rigid Bladed Discs on the Shaft - abstract | full text
• R.Jankowski, M.Kujawa and Cz.Szymczak, Reduction of Steel Chimney Vibrations with a Pendulum Damper - abstract | full text
• K.J.Kalinski, Computer Simulation of Vibration Surveillance of Discretely Idealised Mechanical Systems. Part I: Optimal Control at the Energy Performance Index for Open Non-stationary Systems - abstract | full text
• K.J.Kalinski, Computer Simulation of Vibration Surveillance of Discretely Idealised Mechanical Systems. Part II: Tool-workpiece Vibration in a Non-stationary Model of the Cutting Process - abstract | full text
• K.Murawski and M.Tarnowski, Sound Waves in a Wave Noise - abstract | full text
• K.Murawski and M.Selwa Numerical Simulations of Sound Wave Generation in a Random Medium - abstract | full text
• K.Malarz, J.Karpinska, A.Kardas and K.Kulakowski, Node-Node Distance Distribution for Growing Networks - abstract | full text
• L.Pasini and S.Feliziani Networks of Queues for the Simulation of Urban Flow Systems: an Intermodal Traffic System - abstract | full text

• A.Januszajtis, Family House and School of Daniel Gabriel Fahrenheit

Abstracts:

• N.Egidi, L.Misici, R.Piergallini and F.Tosi, The Lattice Boltzmann Method for Fluid Mixing: a Comparison with the Finite Element Method

  In this article we study three-dimensional mixing of an incompressible viscous fluid subjected to the force of rotating blades in a vessel, with a low Reynolds number. The results obtained with the lattice Boltzmann method are compared with the ones previously obtained using the finite element method. All the qualitative and quantitative parameters of the two simulations agree.

• A.K.Bin, P.M.Machniewski and L.Rudniak, Modelling of Bubble Formation with the Aid of CFD

  Results of a numerical simulation of the bubble formation process obtained with the aid of computational fluid dynamics (CFD) approach are presented. A solution of the momentum balance (Navier-Stokes) equations was coupled with the volume of fluid (VOF) algorithm for tracking the gas-liquid interface in 2D and 3D domains. The simulation results are compared with the experimental data regarding the influence of gas flow rate on the bubble formation regime and volume of the produced bubbles in a low-viscosity system (air-water). As the simulation results are in agreement with the experimental observations, the VOF algorithm is found to be a valuable tool for studying the phenomena of gas-liquid interaction.

• Y.Bin and W.Keqi, Three-Dimensional Numerical Analysis of Internal Flow Phenomena in a Diagonal Rotor

  A numerical analysis has been designed to study internal flow phenomena in a diagonal rotor. A calculated diagonal rotor was designed by a quasi-three-dimensional method. Its hub and casing walls were inclined 45^o and 25^o, respectively. The numerical simulation was based on the Navier-Stokes equations coupled with a k-ε turbulence model. We found that the rotor's wake was stronger near the hub and in the casing end wall region. The wake at a lower flow rate was stronger than that at a higher flow rate. Static pressure gradually increased from the hub to the casing along the height of a blade, on the rotor pressure surface and in the front 60% of the chord region of the suction surface. In the back 40% of the chord region of the suction surface, static pressure gradually decreased. A passage vortex formed in the stator flow passage and an 80% axial chord plane. It was located near the hub end-wall. The passage vortex developed into a large vortex centered near the midspan at a 99% axial chord plane of the stator. The casing wall boundary layer downstream of the rotor occupied approximately 10% of the flow passage. Along the height of a blade, the meridian velocity gradually increased upstream of rotor and decreased downstream. The calculated aerodynamic characteristic curve, the meridian velocity distribution upstream and downstream of the rotor, and the streamline distribution on the meridian surface were consistent with experimental results and design data. Our findings proved that the present numerical method is reliable and practicable. It can be used to design and analyze swept diagonal rotors in order to improve their surging and rotation stall state. The present results also provide comparative data for the design of highly-loaded swept diagonal rotors in future studies.

• A.Sowa, Flow Simulations in Cross-flow Fans Using the Finite Element and Finite Volume Methods

  Both basic computational fluid dynamics methods: the finite element method (FEM) and the finite volume method (FVM) have been used to simulate flow fields in a cross-flow fan (CFF). A review of previous numerical simulations of flow in CFF's is presented. The theorethical foundations of the applied numerical algorithms and specifications of the computer programs are given. The procedure of computations is described in detail. Computational results are shown in the form of contour and vector velocity and contour pressure plots.

• R.Rzadkowski and J.Sokolowski, Natural Frequencies and Modes Shapes of Two Rigid Bladed Discs on the Shaft

  The dynamic behavior of a rotor consisting of two bladed discs on a solid shaft is considered. The effect of shaft flexibility on the dynamic characteristics of the bladed discs and the coupling effects between the shaft and bladed disc modes are investigated. Results presented for various cases with differing blade flexibility show clearly the coupling effects in a bladed disc-shaft system. Interference diagrams are developed, from which the dynamic behavior of a system can be predicted for differing flexibility relationships between the solid shafts and the bladed discs.
  In this study, the global rotating mode shapes of flexible bladed disc-shaft assemblies have been calculated. Rotational effects such as centrifugal stiffening have been accounted for, and all the possible couplings between the flexible parts have been allowed. Gyroscopic effects have been included in the shaft with two discs. Calculated natural frequencies obtained from the blade, shaft, bladed disc and shaft with two discs have been checked to determine resonance conditions and coupling effects. The calculations have shown the influence of the shaft on the natural frequencies of the bladed discs up to one nodal diameter frequencies. The torsional frequency of the shaft with two discs is coupled with the zero nodal diameter modes of the single bladed discs. The bending modes of the shaft are coupled with one nodal diameter modes of the bladed discs. It is shown that including the shaft in the bladed discs model is important from a designer's point of view and can change the spectrum of frequencies considerably.

• R.Jankowski, M.Kujawa and Cz.Szymczak, Reduction of Steel Chimney Vibrations with a Pendulum Damper

  Karman vortices observed around chimneys may induce dangerous structural vibrations at certain wind velocities. The aim of this paper is to analyse the effectiveness of a pendulum damper in reducing vibrations of a steel chimney. A two-degree-of-freedom non-linear model is used to simulate the behaviour of the structure equipped with a damper. The results of the study show that the use of a pendulum with tuned frequency leads to significant reduction in structural response.

• K.J.Kalinski, Computer Simulation of Vibration Surveillance of Discretely Idealised Mechanical Systems. Part I: Optimal Control at the Energy Performance Index for Open Non-stationary Systems

  The paper discusses means of mechanical vibration surveillance using elements of control theory, dynamic optimisation, modern methods of computer simulation and measurement techniques. A mixed method of rigid and flexible finite elements is applied to discrete modelling of non-stationary controlled systems. A method of vibration surveillance in the time domain is elaborated, which utilises optimal control at the energy performance index with respect to the trajectory of given motion. An example is given of surveillance of transient vibration of a railway freight wagon weighing device.

• K.J.Kalinski, Computer Simulation of Vibration Surveillance of Discretely Idealised Mechanical Systems. Part II: Tool-workpiece Vibration in a Non-stationary Model of the Cutting Process

  The problems of tool-workpiece vibration surveillance during machining have been researched. The object of investigation has been analysed, and cutting dynamics and calculation model creation described. Various approaches to and computer simulations of non-stationary model vibration surveillance are explained, based upon optimal spindle speed control and step-changing spindle speed control. A procedure is developed for computer prediction of results of the programme-controlled spindle speed surveillance strategy. Performance results are compared with those measured on a VMC FADAL 4020HT milling machine.

• K.Murawski and M.Tarnowski, Sound Waves in a Wave Noise

  We examine by analytical and numerical means sound waves which propagate in a space- and time-dependent random mass density field in the form of dispersionless wave noise of its spectrum E(k,ϑ) ∼ E(k)δ(ϑ-c_rk), where c_r is a random speed. Numerical simulations are in agreement with the analytical theory which shows that at c_r=ϑ/k resonance occurs and the cyclic frequency ϑ tends to infinity. For values of c_r which are close to the resonance point, the sound waves are slowed down and attenuated (accelerated and amplified) for c_r < ϑ/k (c_r > ϑ/k).

• K.Murawski and M.Selwa Numerical Simulations of Sound Wave Generation in a Random Medium

  In turbulent media, both sound wave sources and the speed of sound can be stochastic variables. By means of numerical simulations of one-dimensional Euler equations with random source terms we have studied two cases in a homogeneous stochastic random medium for which the speed of sound and sound sources are: (1) correlated and (2) uncorrelated. The numerical simulations indicate that, if the source and the speed of sound fluctuations are uncorrelated, the acoustic field is incoherent, with a zero expectation value. The mean field is non-zero in the correlated case. The correlated and uncorrelated cases are clearly distinguishable by the mean field, but also - to some extent - in the power spectrum, which displays a modified Lorentzian profile with a shift in frequency.

• K.Malarz, J.Karpinska, A.Kardas and K.Kulakowski, Node-Node Distance Distribution for Growing Networks

  We present a simulation of the time evolution of the distance matrix. The result is a node-node distance distribution for various kinds of networks. For the exponential trees, analytical formulas are derived for the moments of distance distribution.

• L.Pasini and S.Feliziani Networks of Queues for the Simulation of Urban Flow Systems: an Intermodal Traffic System

  In this paper we introduce a queueing network model, which can be used to simulate the behaviour of specific traffic systems in an urban context. The frame of the work is that of road automation and traffic system control by queue based models simulation.