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JXYXY01-001@1750×12000回转窑设计,机械毕业设计全套
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1 solution (by specifying a smaller time step then the automatically selected one, e.g. for resolving periodic solutions of too small period) or to calculate a heat transfer in solids faster (by specifying a larger time step then the automatically selected one, e.g. if the fluid flow does not changed), it is expedient to specify the time step manually. If you solve a time-dependent problem with heat transfer in solids only, i.e., without calculating a fluid flow (the Heat transfer in solids only option is enabled) a manual specification of the time step is preferable. You can set the Total analysis time and the Output time moments in the Time Settings dialog box in the Wizard. Alternatively, after passing the Wizard, you can set the Maximum physical time for finishing the calculation (see Finishing the Calculation), Introducing COSMOSFloWorks 3-5 as well as strategy and moments of saving results during calculation (see Saving Results) in the Calculation Control Options dialog box. To specify time-dependent boundary conditions, use the Design dialog box. See also Initial Conditions Basic Information. Fluid Type and Compressibility COSMOSFloWorks simulates flows of incompressible liquids (including non- Newtonian liquids), compressible liquids (liquid density is dependent on pressure) or compressible gases (two-phase flows cannot currently be solved by COSMOSFloWorks). Before starting a COSMOSFloWorks project, check that the substances for the project are present in the Engineering Database and that their physical properties are correct. If particular substances are not present, just add the substances and associated properties to the Engineering Database. In the COSMOSFloWorks project, you specify the Fluid type (liquid or gas) and the substances to be analyzed in either the Wizard or the General Settings dialog boxes. If your project deals with a high Mach number gas flow, where the Mach number maximum value exceeds about 3 for steady-state or 1 for transient analyses, select High Mach number flow in the Physical features box in either the Wizard or the General Settings. COSMOSFloWorks will give you a warning message if your initial (or ambient conditions for External problems) or boundary conditions indicate high velocity flow. During the calculation COSMOSFloWorks will also inform you whether the flow can be considered as a high Mach number gas flow or as a low Mach number gas flow (see Monitoring Calculation, Information). Be aware that if you consider High Mach number flow for low-velocity gas flow (maximum M 0 describes the Bingham model of non-Newtonian liquids, featured by a non-zero yield stress ( o), below of which the liquid behaves as a solid, so to achieve a flow this threshold shear stress must be exceeded (this threshold is modeled by automatically equating K, named plastic viscosity in this case, to a substantially high value at o); 0 1, o = 0 describes the power-law model of shear-thickening non- Newtonian liquids. The power-law model. , i.e., , in contrast to the abovementioned Herschel-Bulkley model special case, the values are restricted: min max, so these minimum and maximum dynamic viscosities (Pas) are specified in addition to consistency coefficient K ( ) and power-law index n (dimensionless); The Carreau model. , , where is the liquids dynamic viscosity at an infinite shear rate, i.e., the minimum dynamic viscosity (Pas), o is the liquids dynamic viscosity at zero shear rate, i.e., the maximum dynamic viscosity (Pas), K1 is the time constant (s), n is the powerlaw index (dimensionless). This model is a smooth version of the power-law model with the above-mentioned restrictions. Compressible Liquids A liquid density is specified in the Engineering Database as either a constant or a tabular dependence on temperature under the Liquids item. Additionally, under the Non-Newtonian/Compressible liquids item you can specify a dependence of the liquid density on pressure (P), i.e., the liquids compressibility, through one of the following forms of the Tait equation of state: n K 1 n K n s Pa 2 / 1 2 1 1 nts 7 n o K Introducing COSMOSFloWorks 3-11 , where 0 is the liquids density under the reference pressure P0, C and B are coefficients, ( 0, C, B, and P0 are specified by the user as constants or, except for P0, as tabular dependences on temperature), P is the calculated pressure; , where, n is a power index specified by the user as a constant or a tabular dependence on temperature. Surface-to-surface Radiation If you solve a problem including heat transfer in solids, in which a solids temperature is too high and/or the gas is too rarefied, so that heat transfer by radiation from and/or between solids is noticeable with respect to heat transfer by convection (i.e. heat radiation from the solid surfaces and/or to them plays a noticeable role in the problem, noticeably influencing the solids temperature) you have the option to activate the Radiation physical featura and specify the solid surfaces emissivity. In addition, if require by the problems statement, you can specify heat radiation from the computational domains far-field boundaries (or the models openings) into the computational domain (ilto the model) through the boundaries emissivity and temperature values. As a result, this radiative heat acts upon the models wal,s and can heat them. The following standard (FW-Defined) qurfaces are available in the Engineering Database8 Non-raditing surface denotes that this wall qurface does not partibipate in the radiathon heat transfer, i.e. neither emits nor absorbs heat radiation, Absorbent wall denotes that the wall surface fully absorbs all the incident radiation falling upon it, i.e. as a blackbody, but in contrast to it, does not radiate any heat (i.e., no rays start from it), Blackbody wall denotes that the wall surfaces emissivity is equal to 1 (the blackbodx one), h.e., the vall surface fully absorbs all the incident radiation falling upon it and emits the heat in accordance with the Stefan-Boltzman law, 0 0 / 1 ln B P C B P 1/ nts 8 0 0 n P B P B Introducing COSMOSFloWorks 3-12 Whitebody wall denotes that the wall surfaces emissivity is equal to 0 (the whitebody one), i.e., the wall surface fully reflects all the incident radiation (in accordance with the Lambert law) and does not emit any heat by itself, so the surface temperature does not affect the heat radiation, Symmetry. If you use the Ideal Wall condition at a wall to specify the problems symmetry plane, the Symmetry radiative surface type should be specified at this wall if the problem is considered to radiate heat. For the computational domains far-field boundaries or the models openings, the following standard (FW-Defined) surface emissivity properties are available: Non-radiating surface, see above, with the difference being that it is not a solid surface, but either a computational domains far-field boundaries or a models opening, Blackbody opening/outer boundary denotes that the surfaces emissivity is equal to 1 (the blackbody one), so this surface radiates heat into the computational domain (into the model) as a blackbody, and that its temperature is not calculated, but specified by you (in the Environment radiative temperature box for the computational domains far-field boundaries in the Wizard or in the General Settings dialog box, or in the Radiative temperature box for the models openings in the Radiative surface dialog box, which appear in these dialog boxes if the Blackbody opening/outer boundary type of radiative surface is selected in these dialog boxes). Solar opening denotes a surface (a models opening or the computational domains far-field boundaries) which radiates heat (as directional radiation) into the computational domain (or into a model) along the Direction and with the Intensity specified in the Radiative surface dialog box. A custom radiative surface is defined thought the Emissivity coefficient and one of the following wall surface emissivity properties: Wall. Denotes a surface which radiates heat with emissivity specified by you in the Emissivity coefficient box (in the range from 0 to 1, i.e., a gray-body emissivity can be specified). Opening/outer boundary. Denotes a surface (a models opening or the computational domains far-field boundaries) which radiates heat into the computational domain (or into a model) with emissivity specified by you in the Emissivity coefficient box (in the range from 0 to 1). At that, the surfaces nts 9 Introducing COSMOSFloWorks 3-13 temperature is not calculated, but specified by you (in the Environment radiative temperature box for the computational domains far-field boundaries in the Wizard or in the General Settings dialng box, or in the Radhativd temperature box in the Radiative surface dialog box, which appear if the Opening-outer boundary type is selected). Wall to ambient. Denotes a surface which radiates heat with emissivity specified by you in the Emissivity coefficient box (in the range from 0 to 1), but this heat does not arrive at the models walls, i.e., disappears il the surroundhng space (as a result, the radiation rays from this surface are not calculated). NOTE: In all cases, the project fluids neither emit nor absorb heat radiation (i.e., they are transparent to heat radiation), so the considered heat radiation concerns solid surfaces only. The radiative solid surfaces which are neither blackbody nor whitebody are assumed ideal gray-body, i.e. having a continuous emissive power spectrum similar to the blackbody one, so their monochromatic emissivity is independent of the emission wavelength. The total radiation integrated over all wavelengths is considered only. For certain materials with certain surface conditions (some of them are available from the Radiative Surface tab of the Engineering Database), the gray-body emissivity can depend on the surface temperature only. In all the cases, the heat radiation from the solid surfaces is assumed diffuse, i.e. obeying the Lambert law, according to which the radiation intensity per unit area and per unit solid angle is the same in all directions. The net radiation heat exchange between the models radiative surfaces is calculated along with the convective heat transfer and the heat transfer in solids. When viewing the calculation results, you can visualize the following radiation characteristics: the local characteristics (power per unit area) in Surface Plots (when selecting Fluid as medium): the Net radiant flux (the difference of the radiant flux leaving the surface at this point and the one arriving at it, so it is positive if the leaving flux is greater than the arriving one) and the Leaving radiant flux (the radiant flux leaving the surface); Introducing COSMOSFloWorks 3-14 the integral characteristics (power) among the integral Surface Parameters: the Net radiation rate (the net radiant flux integrated over the selected surface) and the Leaving radiation rate (the leaving radiant flux integrated over the selected surface). Compressible Flows Flows are considered compressible if the fluid density depends on pressure so density change effects are important. In COSMOSFloWorks, gases are always compressible nts 10 and liquids are always incompressible. If your project deals with a high-velocity gas flow, where the Mach number maximum value exceeds about 3 for steady-state analyses or 1 for transient (time-dependent) analyses, you should consider the gas flow as a high Mach number flow. To consider high Mach number gas flow, select the High Mach number flow check box either in the Wizard or General Settings. The low Mach number gas flow is recommended for the tasks where the supersonic flow is localized in relatively small fluid volume and the major flow is subsonic. If the fluid volume in which the flow becomes supersonic is about a half of the computational domain size or greater, it is recommended that you consider the flow as a high Mach number gas flow. Incompressible Flows Flows are considered incompressible if the fluid density depends only on temperature and concentration so density change effects are negligible. Basic Mesh The basic mesh is constructed for the whole computational domain at the beginning of the meshing process. It is formed by dividing the computational domain into slices by parallel planes which are orthogonal to the Global Coordinate Systems axes. The computational domains boundary planes (at X min, Z max) are among these planes. Introducing COSMOSFloWorks 3-15 By default, the basic meshs planes are spaced in the X-, Y-, and Z-directions of the Global Coordinate System nearly uniformly, and the distances between them are determined from the specified numbers of cells in these directions (Nx, Ny, Nz). If necessary, you can insert additional mesh planes and specify another spacing between them (i.e., non-uniform steps) by creating the Control Planes. Travel The term travel, used together with iterations is a unit characterizing the calculation duration. We denote the calculation period (in its turn, it can be measured in iterations or in another unit) required for a flow disturbance to cross the computational domains fluid region. So, value N travels denotes the calculation period required for a flow disturbance to cross the computational domain N times. The travel equivalent in iterations is nts 11 determined just after starting the calculation and can be seen in the Info box while monitoring the calculation. Partial Cells A partial cell is a computational mesh cell lying at the solid/fluid interface, partly in a fluid region and partly in a solid region. Irregular Cells An irregular cell is a computational mesh cell lying at the solid/fluid interface (or solid/ solid interface in case when two or more different solids are within the cell). The irregular cell is partly in one substance and partly in another substance, and characterized by the impossibility of defining the solid/fluid interface position within the cell, given the cells nodes positions relative to solid region and the intersections of the solid/fluid interface with the cell. COSMOSFloWorks has difficulty determining whether the irregular cells nodes belong to the solid or to the fluid region which makes COSMOSFloWorks unable to determine the solid/fluid (or solid/solid) interface position within the cell. Introducing COSMOSFloWorks 3-16 Examples of irregular cells at the solid/fluid interface are shown (colored red). Two ways of possible irregular cell resolution. Note that irregular cells at the solid/fluid interface are always treated as fluid cells. All irregular cells are always split to the maximum level among all the refinement levels specified for the region of irregular cells or until the cells become regular. Thus, if you want to get rid of irregular cells, you should increase the refinement levels, starting with increasing of the Small solid features refinement level, because it will change the existing mesh in other regions to a lesser degree than the other refinement levels. 4-1 Introducing COSMOSFloWorks 4 Conditions and Tools Overview of Conditions nts 12 Any problem solved with COSMOSFloWorks must have initial conditions and boundary conditions. In steady state problems, initial conditions influence the rate of convergence to the steady state, whereas boundary conditions fully govern the flow pattern. In transient (unsteady) problems the time-dependent flow pattern depends both on initial conditions and boundary conditions. You specify flow initial conditions in the Wizard or General Settings using different names: Ambient Conditions for External flows and Initial Conditions for Internal flows. In an assembly (or in a multibody part) you can disable a component and treat it as a fluid (see Component Control). You then specify Initial Conditions inside the fluid component, which are different from the default. If you consider Heat Transfer in Solids, you specify the initial solids temperature in the Wizard or General Settings. In an assembly (or in a multibody part) you can specify a component initial solid temperature that is different from the default (see Initial Condition) solid temperature condition. For internal flows we recommend creating separate Introducing COSMOSFloWorks 4-2 component parts for the lids used to close the openings. Next, specify a material with zero thermal conductivity (insulator) for the lid components. This will prevent heat transfer in the lid components. You can use results of the previous calculation performed either in the current project or other projects, as the initial conditions for the newly prepared calculation. In the Wizard or General Settings you can apply any available results by selecting Transferred initial conditions. See Initial and Ambient Conditions. To apply the current projects results as initial conditions for a new project calculation you can also use the Take previous results option. See Running the Calculation. You can specify flow boundary conditions somewhat differently for External and Internal flows: For External flows you specify flow boundary conditions at all of the Computational Domain boundaries (as either ambient or symmetry conditions) and, if necessary, at the model surfaces among which there can be Openings. For Internal flows you specify flow boundary conditions at inner model surfaces and, if necessary, at the Computational Domain boundaries (as symmetry conditions). Specification of boundary conditions on the Computational Domain boundaries: Specification at Computational Domain boundaries is performed through the Wizard or General Settings with the Ambient Condition values. You can also specify boundary condi
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