Presented work concerns with a sensitivity analysis of a harmonically excited bending vibration of a rotating couple of blades with a friction element with regard to the parameters of the friction characteristic. Either of the blades is discretized by FEM using beam elements and continuously distributed weight is concentrated in nodal points. The friction in central contact points between blade shrouds and the friction element is approximated by a continuous function depending on slip velocities of the shrouds relative to the friction element. Considered friction characteristic respects the micro-slip phase at the very low slip velocities and the macro-slip (full-slip) phase at the higher slip velocities. The values of the friction characteristic parameters are identified by comparison of the numerical simulations of a transient vibration with experiments used in IT AS CR. and Obsahuje seznam literatury
Study about the mechanical energy balance and the energy loss of 3-D turbulent flows in open-channels has its own complexities. The governing equation of the mechanical energy in turbulent flows has been previously known and includes turbulence parameters that their calculations or measurements are not easy. In this study, a form of the total mechanical energy equation that leads to a number of significant physical insights is analytically investigated, from which analytical relationships for the energy loss estimation in 3-D turbulent flows are defined. The effect of different turbulence parameters is reflected on the new relationships and analyzed by equalizations replacing unknown correlations with closure approximations using the numerical turbulence simulation. In order to investigate the application of the analytical relationships, numerical simulations are performed by using OpenFOAM software to solve the Navier-Stokes equations with the RSM turbulence model in open-channels with different geometries. Then, the contribution of the turbulence parameters to the total mechanical energy balance is evaluated in uniform and nonuniform turbulent flows and their difference is analyzed, that leads to identify the parameters affecting the friction and local losses. The results demonstrate that the magnitudes of the turbulent diffusion, the work done by the viscous stresses pertaining to the mean motion and the viscous diffusion of the turbulence energy are substantially smaller than the other terms of the total energy equation for turbulent flows in open-channels with different geometries, while the effect of the variations of the turbulence kinetic energy and the work done by the turbulence stresses, that has not been considered in the previous mechanical energy equations, is more important in complex flows. From a practical viewpoint, in order to study the details of the total mechanical energy balance and the energy loss in 3-D turbulent flows with the presence of the secondary currents, the proposed method can be useful.
The gob side entry retaining with high water material is often used in coal mines. To study the stress evolution characteristics of surrounding rock and asymmetric support control technology of gob side entry retaining with high water material, the evolution law of stress and deformation of surrounding rock in gob side entry retaining during working face mining is studied by theoretical analysis, numerical simulation and field measurement. According to the stress variation of overlying strata during the mining process of the working face, the mechanical models before and after the basic roof fracture were established respectively. The stress and deformation of the filling body and the roof on the side of the filling body are larger, and the stress and deformation of the solid coal and the roof on the side of solid coal are smaller. The maximum stress is at 3 m away from the roadway. The first weighting step distance is 40 m and the periodic weighting step distance is 30 m. Based on the stress and deformation characteristics of the roadway surrounding, the roadway surrounding support is divided into filling bodyside, solid coal side, and middle part of roadway roof. The asymmetric support technology of "filling body+ double row hydraulic prop+ I-beam+ high-strength pretension anchor cable+ high-strength bolt" is proposed. The field engineering practice shows that the surrounding rock control effect of asymmetric support technology with high water material is good., Qiyuan Shan, Yongli Liu, Tao Li and Zhupeng Jin., and Obsahuje bibliografii
This paper deals with studying of two topics – measuring of velocity profile deformation behind a over-flooded construction and modelling of this velocity profile deformation by computational fluid dynamics (CFD). Numerical simulations with an unsteady RANS models - Standard k-ε, Realizable k-ε, Standard k-ω and Reynolds stress models (ANSYS Fluent v.18) and experimental measurements in a laboratory flume (using ADV) were performed. Results of both approaches showed and affirmed presence of velocity profile deformation behind the obstacle, but some discrepancies between the measured and simulated values were also observed. With increasing distance from the obstacle, the differences between the simulation and the measured data increase and the results of the numerical models are no longer usable.
This presented work is concerned with a friction element impact and detuning mass impact of the bending oscillation of a couple of blades with a friction element embodied between the blade shrouds. Either of the blades is discretized by FEM using beam elements and continuously distributed weight is concentraed in nodal points. One of the blades is excited by harmonic varying force. The friction element, which is considered as a rigid body, is pulled using constant tension force into a wedge gap between the blade shrouds. The detuning of this system is caused by an additional mass mounting on one of the blade shrouds. Numerical simulation results are compared with results of the equivalent linearization method. The effects of the friction and detuning on the blades vibration suppression are analyzed. and Obsahuje seznam literatury
During the extraction of coal from thick seams in deep longwall faces, both high in-situ stress and a massive main roof are common. The progressive fracturing in this massive main roof leads to an increase in the front abutment stress and changes in the strain energy of the coal seam which can lead to dynamic disasters such as rockbursts. Based on the mining conditions observed in Panel 5301 of the Xinhe Coal Mine, microseismic (MS) and borehole stress monitoring, along with numerical simulations, was used to propose an evolution law for coal mine roof fracture, front abutment stress, and strain energy. Results indicate that as the roof collapses during the progress of extraction, the transmission point for overburden load moves forward such that the peak front abutment stress advances to 20–25 m in front of the working face. The coal mass within 22–90 m in front of the working face was observed to accumulate 176.2 kJ of strain energy, with the peak strain energy increasing from 80.15 kJ to 136 kJ. The data collected and analyzed in this research provides a theoretical basis for forecasting the location of mining-induced rockburst based on observed fracturing in the main roof.
The present work investigates the effect of the flow profile induced by an inlet condition on the roll-wave evolution in turbulent clear-water flows. The study employs theoretical and numerical analyses. Firstly, the influence of the inlet condition on the spatial evolution of a single perturbation in a hypercritical flow is examined through the expansion near a wavefront analysis. The results show that an accelerated unperturbed profile reduces the disturbance spatial growth. A decelerated profile causes an increase. The effect of the flow profile on the spatial evolution of rollwave trains is then numerically investigated solving the Saint Venant equations with a second-order Runge-Kutta Total Variation Diminishing (TVD) Finite Volume scheme. The numerical simulations comply with the analytical results for the initial and transition phases of the roll-wave development. The unperturbed profile influences even the roll-waves statistical characteristics in the final stage, with a more evident effect in case of accelerated profiles. The influence of the flow profile should be therefore accounted for in the formulation of predictive criteria for roll-waves appearance based on the estimation of the disturbance spatial growth rate.
The paper deals with the design of stator channels of the aerator using CFD code ANSYS Fluent. The main problem is to design proper inclination of the channels corresponding with the direction of flow at the impeller outlet. The direction of flow is variable along the channel and represented by the absolute velocity angle. Therefore, this angle is computed first, and according to it, the inclination of stator channels is designed. Numerical simulations are made as single-phase flow for two different shapes of channels and for two different channel incllnations - for already computed ones and for ones used in older type of aerator which this work develops. Stator channels inclined by computed angle that corresponded with the direction of flow had the best results. On the other hand, the channels inclined by the same angle as the channels of older aerator had the worst efficiency. The decrease of aerator efficiency was caused by the large vortexes in the stator channels. and Obsahuje seznam literatury a názvosloví
Semi finished glass pieces are moulded in the furnace to template forms not only to fit their shape but also to reduce internal stresses. Thermal differences are unwanted and have to be minimized in the cooling procedure of the glass pieces. Simulations of various types and sizes of shaping forms and complex model cooling were accomplished. The aim of these simulations was to optimise geometric parameters, clamping conditions and material of the form, so that thermal differences at glass are minimized during the cooling. and Článek se zabývá numerickým modelováním změn teplotního pole v materiálu skleněných výlisků v průběhu jejich chlazení po tvarování v elektrické peci. Cílem simulací bylo optimalizovat geometrické vlastnosti, způsob uchycení a materiál formy pro tvarování skleněných výlisků tak, aby teplotní diference ve skle byly co nejmenší.
Study is focused on the numerical modeling of fly-ash transport in three sands, which was experimentally studied in the laboratory. Sands were packed in glass cylinders with diameter of 5.52 cm and height of 18 cm. Sands were also packed in plastic cylinders with diameter of 30 cm and height of 40 cm. The fly-ash and pulse infiltrations were applied on the top of all cylinders. Visually observed and gravimetrically evaluated fly-ash migration in small cylinders corresponded to fly-ash mobility in large columns detected using the SM400 Kappameter. The HYDRUS-1D code was used to simulate observed fly-ash transport. Parameters of soil hydraulic functions were either obtained using the Tempe cells and the RETC program or estimated using numerical inversion of transient water flow data measured in both types of columns using HYDRUS-1D. Parameters characterizing colloid transport in sands were then estimated from the final fly-ash distribution in sandy columns using attachment/detachment concept in HYDRUS-1D. Fly-ash mobility increased with increasing sand particle sizes, e.g. pore sizes. Particle sizes and pore water velocity influenced the attachment coefficient, which was calculated assuming filtration theory. The same longitudinal dispersivity, sticking efficiency and detachment coefficient sufficiently characterized fly-ash behavior in all sands. and Studie je zaměřena na numerické modelování transportu úletového popílku ve třech píscích, který byl experimentálně studován v laboratoři. Písky byly nahutněny ve skleněných válcích o průměru 5,52 cm a výšce 18 cm. Písky byly také nahutněny v plastových válcích o průměru 30 cm a výšce 40 cm. Na povrchu válců byly aplikovány jednorázové infiltrace vody s popílkem. Migrace úletového popílku pozorovaná vizuálně a zjištěná gravimetricky v malých válcích odpovídala mobilitě úletového popílku detekované Kappametrem SM400 ve velkých válcích. Pozorovaný transport úletového popílku byl simulován programem HYDRUS-1D. Parametry hydraulických funkcí byly získány buď pomocí Tempských cel a programu RETC nebo odhadovány numerickou inverzí transientních data měřených na obou typech válců programem HYDRUS-1D. Parametry charakterizující transport koloidů v píscích byly potom odhadovány z konečné distribuce úletového popílku v písčitých sloupcích užitím konceptu attachment/detachment (připojení/odpojení) v programu HYDRUS-1D. Mobilita úletového popílku se zvyšovala se zvyšující se velikostí písčitých zrn, tj. s velikostí pórů. Velikost zrn a pórová rychlost ovlivnila depoziční (attachment) koeficient, který byl počítán na základě filtrační teorie. Stejné hodnoty podélné disperze, efektivity blokování (sticking efficiency) a mobilizačního (detachement) koeficientu charakterizovaly chování úletového popílku ve všech píscích.