Exploitation of hard coal seams by roadway system is applied by two coal mines in southern Poland in Upper Silesian Basin. It is a secondary mining exploitation carries out in safety pillars of urban areas and shafts within mining areas of closed coal mines. Roadway system is the excavation process of gateways which are made in parallel order leaving coal pillars between them. An optimal width of coal pillar makes roadway stable and reduces subsidence of terrain surface. The article presents results of subsidence simulation caused by partial extraction using empirical and numerical methods on the example of one exploitation field of “Siltech” coal mine. The asymptotic state of subsidence was considered after mining ceased in the study area. In order to simulate of subsidence, numerical model of rock mass and model of Knothe-Budryk theory were calibrated. Simulation of vertical displacements in numerical method was carried out using RS3 program by Rocscience based on finite element method. The assumption was made that model of rock mass is transversely isotropic medium, in which panels were designed according to order of extraction of coal seams. The results of empirical and numerical methods were compared with measured values of subsidence at benchmarks along drawn lines (subsidence profiles).
Modern regulations concerning railway bridges are based on the approach of structural dynamics, which is described in PN-EN standards. This paper presents the results of theoretical dynamic analysis of the HSLM-A train set loading on the structure of a pre-stressed concrete arch bridge - the first railway bridge of its type which was built in Poland (completed in 1959). The recommendations of PN-EN have been followed and modal analysis was carried out to define the sensitivity of the structure to chosen eigenforms. Additionally the paper presents a course of calculations and the conclusions obtained from the analysis of displacements, accelerations, and bending moments induced in the structure through a simulated passage of a high-speed train in the context of the requirements of PN-EN Standards. The conclusions from the current calculations can be used for dynamic analysis of bridges of similar structural solutions.
This study aims to design a novel air cleaning facility which conforms to the current situation in China, and moreover can satisfy our demand on air purification under the condition of poor air quality, as well as discuss the development means of a prototype product. Air conditions in the operating room of a hospital were measured as the research subject of this study. First, a suitable turbulence model and boundary conditions were selected and computational fluid dynamics (CFD) software was used to simulate indoor air distribution. The analysis and comparison of the simulation results suggested that increasing the area of air supply outlets and the number of return air inlets would not only increase the area of unidirectional flow region in main flow region, but also avoid an indoor vortex and turbulivity of the operating area. Based on the summary of heat and humidity management methods, the system operation mode and relevant parameter technologies as well as the characteristics of the thermal-humidity load of the operating room were analyzed and compiled. According to the load value and parameters of indoor design obtained after our calculations, the airflow distribution of purifying the air-conditioning system in a clean operating room was designed and checked. The research results suggested that the application of a secondary return air system in the summer could reduce energy consumption and be consistent with the concept of primary humidity control. This study analyzed the feasibility and energy conservation properties of cleaning air-conditioning technology in operating rooms, proposed some solutions to the problem, and performed a feasible simulation, which provides a reference for practical engineering.
This paper presents a complex study of anhydrite interbeds influence on the cavern stability in the Mechelinki salt deposit. The impact of interbeds on the cavern shape and the stress concentrations were also considered. The stability analysis was based on the 3D numerical modelling. Numerical simulations were performed with use of the Finite Difference Method (FDM) and the FLAC3D v. 6.00 software. The numerical model in a cuboidal shape and the following dimensions: length 1400, width 1400, height 1400 m, comprised the part of the Mechelinki salt deposit. Three (K-6, K-8, K-9) caverns were projected inside this model. The mesh of the numerical model contained about 15 million tetrahedral elements. The occurrence of anhydrite interbeds within the rock salt beds had contributed to the reduction in a diameter and irregular shape of the analysed caverns. The results of the 3D numerical modelling had indicated that the contact area between the rock salt beds and the anhydrite interbeds is likely to the occurrence of displacements. Irregularities in a shape of the analysed caverns are prone to the stress concentration. However, the stability of the analysed caverns are not expected to be affected in the assumed operation conditions and time period (9.5 years).
This article describes stability issues of main excavations in deep copper mines in Poland, from the perspective of mining work safety. To protect main transportation and ventilation routes, parts of rock are left untaken to form so-called protective pillars. The problem was to determine the size of main excavations protective pillars in deep underground copper mines in which provide stability of main excavations. The results of numerical simulations of the stability of protective pillars under specific geological and mining conditions are presented, covering: underground depth and width of protective pillar, number, size and layout geometry of protected excavations, as well as the impact of parameters of surrounding gob areas. Problem was solved applying numerical simulations based on the finite element method which were performed in a plane state of strain by means of Phase2 v. 8.0 software. The behavior of the rock mass under load was described by an elastic-plastic model. The Mohr-Coulomb criterion was used to assess the stability of the rock mass. The results of numerical modeling have practical applications in the designing of protective pillars primarily in determining their width. These results were used to prepare new guidelines for protective pillars in Polish copper mines in the Legnica-Glogow Copper District.
The cohesion and internal friction angle were characterized as quadratic functions of strain and were assumed to follow the Mohr-Coulomb criterion after the yield of peak strength. These mechanical parameters and their variations in post-peak softening stage can be exactly ascertained through the simultaneous solution based on the data points of stress-strain curves of triaxial compression tests. Taking the influence of the fault into account, the variation of strata pressure and roadway convergence with coal advancement, the temporal and spatial distribution of axial bolt load were numerically simulated by FLAC3D (Fast Lagrangian Analysis of Continua) using the ascertained post-peak mechanical parameters according to the cohesion weakening and friction strengthening model. The change mechanism of axial load of single rock bolt as abutment pressure changes was analyzed, through the comparison analysis with the results of axial bolt load by field measurements at a coal mine face. The research results show that the simulated results such as the period of main roof weighting, temporal and spatial distribution of axial bolt load are in accordance with field measurement results, so the validity of the numerical model is testified. In front of the working face, the front abutment pressure increases first and then decreases, finally tends to be stable. A corresponding correlation exists between the variation of axial bolt load and rock deformation along the bolt body. When encountered by a fault, the maximum abutment pressure, the influential range of mining disturbance and the roadway convergence between roof and floor before the working face are all increased. In the roadways along the gob, axial bolt loads on the side of the working face decrease, while the other side one increases after the collapse of the roof. As superficial surrounding rock mass is damaged, the anchoring force of rock bolts will transfer to inner rock mass for balancing the tensile load of the bolts.
The paper presents a numerical model of the novel design of the axial magnetic bearing with six cylindrical poles. The motivation behind this idea was to eliminate vibrations in rotating machinery due to the axial load. Common conception of such a bearing provides a single component of the electromagnetic force, which is not enough to reduce transverse and lateral vibrations of the armature. The proposed design allows for avoiding wobbling of the disc with the use of a few axial force components that are able to actively compensate the axial load and stabilise the disc in a balanced position. Before a real device is manufactured, a virtual prototype should be prepared. The accurate numerical model will provide essential knowledge about the performance of the axial magnetic bearing.
This study, describing computer simulation of a glider crash against a non-deformable ground barrier, is a part of a larger glider crash modeling project. The studies were intended to develop a numerical model of the pilot - glider - environment system, whereby the dynamics of the human body and the composite cockpit structure during a crash would make it possible to analyze flight accidents with focus on the pilot's safety. Notwithstanding that accidents involving glider crash against a rigid barrier (a wall, for example) are not common, establishing a simulation model for such event may prove quite useful considering subsequent research projects. First, it is much easier to observe the process of composite cockpit structure destruction if the crash is against a rigid barrier. Furthermore, the use of a non-deformable barrier allows one to avoid the errors that are associated with the modeling of a deformable substrate, which in most cases is quite problematic. Crash test simulation, carried out using a MAYMO package, involved a glider crash against a wall positioned perpendicularly to the object moving at a speed of 77 km/h. Computations allowed for determination of time intervals of the signals that are required to assess the behavior of the cockpit and pilot's body - accelerations and displacements in selected points of the glider's structure and loads applied to the pilot's body: head and chest accelerations, forces at femur, lumbar spine and safety belts. Computational results were compared with the results of a previous experimental test that had been designed to verify the numerical model. The glider's cockpit was completely destroyed in the crash and the loads transferred to the pilot's body were very substantial - way over the permitted levels. Since modeling results are fairly consistent with the experimental test, the numerical model can be used for simulation of plane crashes in the future.
Eutectoid growth, as the important reaction mechanism of the carbon steel heat treatment, is the basis to control the microstructure and performance. At present, most studies have focused on lamellar growth, and did not consider the nucleation process. Mainly due to the nucleation theory is inconclusive, a lot of research can support their own theory in a certain range. Based on the existing nucleation theory, this paper proposes a cooperative nucleation model to simulate the nucleation process of eutectoid growth. In order to ensure that the nucleation process is more suitable to the theoretical results, different correction methods were used to amend the model respectively. The results of numerical simulation show that when the model is unmodified, the lateral growth of single phase is faster than that of longitudinal growth, so the morphology is oval. Then, the effects of diffusion correction, mobility correction and ledges nucleation mechanism correction on the morphology of nucleation and the nucleation rate were studied respectively. It was found that the introduction of boundary diffusion and the nucleation mechanism of the ledges could lead to a more realistic pearlite.
The absorption of sound in air represents one of the main problems of the scale model measurements. This absorption, especially at higher frequencies, is considerably greater than the value determined by the law of acoustical similarity between the full scale and the scale model. Different alternatives are applied for compensation of the excess air absorption including a numerical compensation. In this paper, a modified approach to numerical compensation is proposed. It is based on compensation of the sound decay only, and not background noise. As a consequence, there is no an increase of background noise in the compensated impulse response. The results obtained by the proposed procedure are compared to the corresponding ones obtained by the other procedures.
This paper constitutes the sensitivity study of application the Polar WRF model to the Svalbard area with testing selected parameterizations, including planetary boundary layer, radiation and microphysics schemes. The model was configured, using three one-way nested domains with 27 km, 9 km and 3 km grid cell resolutions. Results from the innermost domain were presented and compared against measured wind speed and air temperature at 10 meteorological stations. The study period covers two months: June 2008 and January 2009. Significant differences between simulations results occurred for planetary boundary layer (PBL) schemes in January 2009. The Mellor-Yamada-Janjic (MYJ) planetary boundary layer (PBL) scheme resulted in the lowest errors for air temperature, according to mean error (ME), mean absolute error (MAE) and correlation coefficient values, where for wind speed this scheme was the worst from all the PBL schemes tested. In the case of June 2008, shortwave and longwave radiation schemes influenced the results the most. Generally, higher correlations were obtained for January, both for air temperature and wind speed. However, the model performs better for June in terms of ME and MAE error statistics. The results were also analyzed spatially, to summarize the uncertainty of the model results related to the analyzed parameterization schemes groups. Significant variability among simulations was calculated for January 2009 over the northern part of Spitsbergen and fjords for the PBL schemes. Standard deviations for monthly average simulated values were up to 3.5°C for air temperature and around 1 m s-1 for wind speed.
The modelling of colloidal fouling and defouling of hollow fibre membranes in the presence of membrane oscillations is analysed by means of numerical simulations as an effect of complex coupling between hydrodynamic and surface forces. To describe the latter the Derjaguin-Landau- Vervey-Overbeek (DLVO) model has been employed. We have investigated the influence of various parameters of the process like flow rate, mean particle diameter, amplitude and frequency of the oscillations, and others, on the efficiency of the defouling process. The investigated parameters is close to that of a silica suspension in , a typical system modelling used to investigate membrane separation. On the basis of numerical simulation results e have defined an optimal set of parameters preventing membrane fouling.
The aim of this work is to develop a numerical model capable of predicting the grain density in the Mg-based matrix phase of an AZ91/SiC composite, as a function of the total mass fraction of the embedded SiC particles. Based on earlier work in a range of alloy systems, we assume an exponential relationship between the grain density and the maximum supercooling during solidification. Analysis of data from cast samples with different thicknesses, and mass fractions of added SiCp, permits conclusions to be drawn on the role of SiCp in increasing grain density. By fitting the data, an empirical nucleation law is derived that can be used in a micro model. Numerical simulation based on the model can predict the grain density of magnesium alloys containing SiC particles, using the mass fraction of the particles as inputs. These predictions are compared with measured data.
A cross-flow, tube and fin heat exchanger of the water – air type is the subject of the analysis. The analysis had experimental and computational form and was aimed for evaluation of radiative heat transfer impact on the heat exchanger performance. The main element of the test facility was an enlarged recurrent segment of the heat exchanger under consideration. The main results of measurements are heat transfer rates, as well as temperature distributions on the surface of the first fin obtained by using the infrared camera. The experimental results have been next compared to computational ones coming from a numerical model of the test station. The model has been elaborated using computational fluid dynamics software. The computations have been accomplished for two cases: without radiative heat transfer and taking this phenomenon into account. Evaluation of the radiative heat transfer impact in considered system has been done by comparing all the received results.
A mathematical model of the steam superheater exchanger with distributed parameters has been developed. Scale deposits were assumed to be present on the internal tube surfaces. It was assumed that the inner tube surfaces are covered by a thin layer of scale deposits. The finite volume method was used to solve partial differential equations describing flue gas, tube wall and steam temperature. The developed modeling technique can especially be used for modeling tube heat exchangers when detail information on the tube wall temperature distribution is needed. The numerical model of the superheater developed in the paper can be used for modeling of the superheaters with complex flow arrangement accounting scales on the internal tube surfaces. Using the model proposed the detailed steam, wall and flue gas temperature distribution over the entire superheater can be determined. The steam pressure distribution along its path flow and the total heat transfer rate can also be obtained. The calculations showed that the presence of scale on the internal surfaces of the tubes cause the steam temperature decrease and the heat flow rate transferred from the flue gas to the steam. Scale deposits on the inner surfaces of the tubes cause the tube wall temperature growth and can lead to premature wear of tubes due to overheating.
On the basis of mathematical modeling of fluid flow in vortex devices verification of use of detached-eddy simulation method in the swirling flows in vortex chamber superchargers is made. Research of a flow with use of different turbulence models was made for vortex chamber supercharger in two working points of the characteristic: with the open exit channel and closed. Verification has been spent on integrated parameters, and also on kinematic, by comparison of static pressure value of on the top end cover of the device. It is received that the hybrid turbulence model DES does not allow, as well as model SST precisely to predict value of vacuum on an axis of the vortex chamber. The error makes an order of 20 %. However, DES predicts almost correct, on 20 % big, than model SST, values of vacuum on an axis in a throat axial diffuser on an input in the vortex chamber. Besides, by means of DES it is possible to describe more adequately unsteady structures near to an axis of the vortex chamber, and also vortex core precession that does not allow to make SST turbulence model. By optimization of vortex devices, and vortex chamber superchargers in particular, simulation time essentially is better to use SST turbulence model with rotation-curvature correction.
In the paper the thermal processes proceeding in the solidifying metal are analyzed. The basic energy equation determining the course of solidification contains the component (source function) controlling the phase change. This component is proportional to the solidification rate ¶ fS/¶ t (fS Î [0, 1], is a temporary and local volumetric fraction of solid state). The value of fS can be found, among others, on the basic of laws determining the nucleation and nuclei growth. This approach leads to the so called micro/macro models (the second generation models). The capacity of internal heat source appearing in the equation concerning the macro scale (solidification and cooling of domain considered) results from the phenomena proceeding in the micro scale (nuclei growth). The function fS can be defined as a product of nuclei density N and single grain volume V (a linear model of crystallization) and this approach is applied in the paper presented. The problem discussed consists in the simultaneous identification of two parameters determining a course of solidification. In particular it is assumed that nuclei density N (micro scale) and volumetric specific heat of metal (macro scale) are unknown. Formulated in this way inverse problem is solved using the least squares criterion and gradient methods. The additional information which allows to identify the unknown parameters results from knowledge of cooling curves at the selected set of points from solidifying metal domain. On the stage of numerical realization the boundary element method is used. In the final part of the paper the examples of computations are presented.
This paper presents a three-dimensional model of an airbag located outside of a small city car at the front bumper, which is intended to protect the vehicle against the effects of road traffic collisions. Results of numerical simulations of airbag operation in case of collision with two types of obstacles are presented: a flat, vertical wall and a circular pillar with a diameter of 200 mm. The paper presents the physical model, which is the subject of simulation, along with its mathematical description and the numerical calculation scheme used.
The main work of this paper focuses on the simulation of binary alloy solidification using the phase field model and adaptive octree grids. Ni-Cu binary alloy is used as an example in this paper to do research on the numerical simulation of isothermal solidification of binary alloy. Firstly, the WBM model, numerical issues and adaptive octree grids have been explained. Secondary, the numerical simulation results of three dimensional morphology of the equiaxed grain and concentration variations are given, taking the efficiency advantage of the adaptive octree grids. The microsegregation of binary alloy has been analysed emphatically. Then, numerical simulation results of the influence of thermo-physical parameters on the growth of the equiaxed grain are also given. At last, a simulation experiment of large scale and long-time has been carried out. It is found that increases of initial temperature and initial concentration will make grain grow along certain directions and adaptive octree grids can effectively be used in simulations of microstructure.
The generic mathematical model and computational algorithm considering hydrodynamics, heat and mass transfer processes during casting and forming steel ingots and castings are offered. Usage domains for turbulent, convective and non-convective models are determined depending on ingot geometry and thermal overheating of the poured melt. The expert system is developed, enabling to choose a mathematical model depending on the physical statement of a problem.
The paper discusses the influence of the initial parameters on the strength parameters of S235JR steel at low stress triaxiality. The analysis was performed using the Gurson-Tvergaard-Needlem (GTN) material model, which takes into consideration the material structure. The initial material porosity was defined as the void volume fraction f₀. The fully dense material without pores was assumed and the typical and maximum values of porosity were considered for S235JR steel in order to analyse the porosity effect. The strength analysis of S235JR steel was performed basing on the force-elongation curves obtained experimentally and during numerical simulations. Taking into consideration the results obtained, the average values of the initial void volume fraction f₀ = 0.001 for S235JR steel is recommended to use in a common engineering calculations for elements operating at low stress triaxiality. In order to obtain more conservative results, the maximum values of f₀ = 0.0024 may be used.
The effect of the initial porosity on the material response under multi-axial stress state for S235JR steel using the Gurson-Tvergaard-Needleman (GTN) material model was examined. Three levels of initial porosity, defined by the void volume fraction f₀, were considered: zero porosity for fully dense material without pores, average and maximum porosity according to the metallurgical requirements for S235JR steel. The effect of the initial porosity on the material response was noticed for tensile elements under multi-axial stress state defined by high stress triaxiality σₘ/σe = 1.345. This effect was especially noticeable at the range of the material failure. In terms of the load-bearing capacity of the elements, the conservative results were obtained when maximum value of f₀ = 0.0024 was used for S235JR steel under multi-axial stress state, and this value is recommended to use in the calculations in order to preserve the highest safety level of the structure. In usual engineering calculations, the average porosity defined by f₀ = 0.001 may be applied for S235JR.