김경종
193 lines
12 KiB
Markdown
193 lines
12 KiB
Markdown
<!-- source-page: 1331 -->
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You can specify the contact thickness of the generated particles by using the surface property assignment option for an element-based surface that includes the faces of the parent elements. This modeling choice affects contact interactions on parent elements before they convert.
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# Output
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Output requests associated with parent elements, nodes of parent elements, or contact involving faces of parent elements trigger the creation of output requests associated with the corresponding internally generated particles. For example, if you request element output for an element set that contains parent elements, Abaqus/Explicit automatically creates an additional element output request using the corresponding internal element set containing generated particles, as described in “Automatically generated sets and surfaces.”
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A field output request for the STATUS output variable is created automatically for all parent elements and generated particles. The value of the STATUS output variable is toggled automatically between a value of zero and one upon conversion for both parent and generated particles. By default, only the active elements are displayed in the Visualization module. In addition, contour and vector plots are displayed appropriately on the elements that are currently active.
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History output requests are also replicated for the generated particles. Since the actual element or node numbers of generated particles are defined internally, you can query the actual number of a particle in the Visualization module before identifying which output curve to display. For example, assume that you requested equivalent plastic strain history output for a small element set containing three C3D8R parent elements and that you requested that two particles per isoparametric direction (eight particles per parent element) are to be generated upon conversion. Before conversion you would have 3 curves to analyze; but after the three elements are converted, there are 24 curves from which to choose. You can query the element number of a particle and then select that curve from the 24 available history curves. Before conversion the curves associated with the particles have a value of zero. Upon conversion there will be a jump to the equivalent plastic strain value at the current time.
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# Limitations
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Analyses involving finite element conversion to SPH particles are subject to the following limitations:
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• Only reduced-integration continuum elements C3D8R, C3D6, and C3D4 are available for conversion.
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• Surface loads specified on the faces of parent elements that convert during the analysis are not applied after conversion to particles. However, distributed loads, such as pressure, can be applied to other finite element surfaces that do not convert (e.g., on a piston surface) that can apply a pressure onto the particle elements (e.g., the fluid pushed by the piston) via contact interactions.
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• Bodies modeled with elements that may convert to particles that were not defined using the same section definition will not interact with each other between the converted portions of the bodies. For example, body A and body B allow elements to convert to particles, but these elements are associated with different section definitions. After conversion, the particles will not interact.
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<!-- source-page: 1332 -->
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• Within a given body (part) defined via one solid section definition, gravity loads and mass scaling cannot be specified selectively on a subset of elements referenced by this definition. Instead, the two features must be applied to all the elements in the element set associated with the solid section definition.
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• Progressive conversion of finite elements into SPH particles during an analysis (based on strain, stress, or user-defined criterion) should be used only in applications that are inertia dominated and for which at any point during the analysis the strain energy is a small percentage of the total energy in the system. Specifically, progressive conversion should be used only in applications involving severe deformations, such as hypervelocity impact, blast, and crushing.
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# Input file template
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The following example illustrates a smoothed particle hydrodynamic analysis of a bottle filled with fluid being dropped on the floor using the conversion technique. The plastic bottle and the floor are modeled with conventional shell elements. The fluid is modeled with C3D4 elements that will convert to two particles per isoparametric direction (four particles per element) at the beginning of the analysis based on a time-based criterion. Material property definitions are defined as usual for both the fluid and the bottle. Contact interaction is defined using the default options. Output is requested for stresses (pressure) and density in the fluid.
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```txt
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*HEADING
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...
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*ELEMENT, TYPE=C3D4, ELSET=Fluid_Inside_The_Bottle
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...
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*SOLID SECTION, ELSET=Fluid_Inside_The_Bottle, MATERIAL=Water, CONTROLS=Time_Based_Conversion
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*SECTION CONTROLS, ELEMENT CONVERSION=YES, CONVERSION CRITERION=TIME, NAME=Time_Based_Conversion
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First data line
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Second data line
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Third data line
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2, 0.0
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*MATERIAL, NAME=Water
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Material definition for water, such as an EOS material
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*ELEMENT, TYPE=S4R, ELSET=Plastic_Bottle
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Element definitions for the shells
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**
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*INITIAL CONDITIONS, TYPE=VELOCITY
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Data lines to define velocity initial conditions
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**
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*STEP
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*DYNAMIC, EXPLICIT
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*DLOAD
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```
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<!-- source-page: 1333 -->
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Data lines to define gravity load
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```sql
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**
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*CONTACT
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*OUTPUT, FIELD
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*ELEMENT OUTPUT, ELSET=Fluid_Inside_The_Bottle
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S, DENSITY
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*END STEP
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```
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<!-- source-page: 1334 -->
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<!-- source-page: 1335 -->
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# 15.3 Particle generator
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• “Particle generator,” Section 15.3.1
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<!-- source-page: 1336 -->
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<!-- source-page: 1337 -->
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# 15.3.1 PARTICLE GENERATOR
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Products: Abaqus/Explicit Abaqus/Viewer
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# References
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• “Discrete element method,” Section 15.1.1
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• “Discrete particle elements,” Section 33.1.1
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• \*PARTICLE GENERATOR
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• \*PARTICLE GENERATOR INLET
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• \*PARTICLE GENERATOR MIXTURE
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• \*PARTICLE GENERATOR FLOW
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• \*PROBABILITY DENSITY FUNCTION
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# Overview
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The particle generator:
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• is a tool for automatically introducing discrete particles (PD3D) into the problem domain during the course of the analysis;
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• can be used during an initial step to prepare a discrete element method (DEM) model prior to the actual analysis; and
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• can be used to continuously introduce discrete particles into the model while the analysis is in progress.
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# Introduction
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The particle generator capability enables a modeling approach in which the discrete element method considers particles only after entering a region of interest. This approach can simplify model set-up and improve computational efficiency. Characteristics of this capability include:
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• particles are generated at an inlet that can vary in shape over time,
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• generated particles can have random sizes based on a user-specified probability density function,
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• multiple species of particles can be generated simultaneously by a single generator, and
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• the net mass flow rate and particle speeds at the inlet can be specified with time dependence.
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# Applications
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How you use the particle generator will depend on the process being analyzed. Two broad usage categories are as follows:
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• Model creation: In many applications the particle generator can be used to fill part of a domain with particles to establish initial conditions for subsequent studies. Figure 15.3.1–1 shows an
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<!-- source-page: 1338 -->
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example where two particle generators are filling a drum mixer with two different batches of particles prior to performing a mixing simulation. The sequence of images show the start and end of the particle generation phase.
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<details>
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<summary>text_image</summary>
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Drum mixer
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Particle generators
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(a) start of particle generation
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(b) end of particle generation
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</details>
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Figure 15.3.1–1 Model creation using particle generator.
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• Continuous generation: In another type of application a particle generator can be used to inject a continuous stream of particles into the domain while an event of interest involving particles that have been introduced is underway. Figure 15.3.1–2 shows the use of a particle generator in a sorting analysis. In this application a particle generator is continuously feeding random sized particles to a screen sorter assembly while the analysis is in progress.
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# Defining a particle generator
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To define a particle generator, you specify a name for the generator, the type of particle to be generated (only PD3D elements are supported), and the maximum number of particles that may be generated during the analysis. You must define an inlet surface, the list of particle species that will be generated, and the size distribution for each species.
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In many processes the number and speed of the particles being introduced into the domain are not constant during the analysis. You must define the time-dependent mass flow rate per unit inlet area and the particle speed at the generator inlet to control the rate of injection of particles of each species through the inlet. These specifications allow the possibility of turning the particle generator on or off during the analysis.
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<!-- source-page: 1339 -->
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<details>
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<summary>text_image</summary>
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Particle generator
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Screen sorter
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</details>
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Figure 15.3.1–2 Continuous particle generation example.
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Input File Usage: \*PARTICLE GENERATOR, NAME=generator\_name, TYPE=PD3D, MAXIMUM NUMBER OF PARTICLES=number
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# Inlet surface
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The inlet surface can be thought of as an opening through which the particles are injected into the domain. It is important that no other model feature is positioned in front of the generator inlet to obstruct the flow of particles. An element-based surface must be defined for the inlet surface. Using surface elements is appropriate in most applications. Care should be taken with respect to the positive surface normal direction at the inlet because the initial particle velocity will be in this direction. A complex inlet
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<!-- source-page: 1340 -->
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geometry as shown in Figure 15.3.1–3 may have several facets. In this example the normal direction to the inlet surface is out of the page.
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<details>
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<summary>flowchart</summary>
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```mermaid
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graph TD
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A["Inlet surface facets"] --> B["1"]
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A --> C["2"]
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A --> D["3"]
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```
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</details>
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Figure 15.3.1–3 Complex inlet geometry with multiple facets.
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The size and shape of the inlet surface can be modified during an analysis by adjusting the nodal positions of the inlet surface. The inlet surface can expand, collapse, and translate as well as undergo rigid body motions. Figure 15.3.1–4 shows the inlet surface of four different generators being subjected to different deformation and motion.
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Input File Usage: \*PARTICLE GENERATOR INLET, SURFACE=inlet\_surface\_name
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# Particle species
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In many applications several different types of particles interact with each other. For example, sand, cement, and aggregate particles are mixed together to prepare a batch of concrete. A particle generator can be used to generate one or more species of particles as shown in Figure 15.3.1–5, where the two colors represent the two species of particles that have been simultaneously generated by a particle generator. An element set name is associated with each species in the mixture. This is analogous to a regular DEM analysis where the particles are grouped into element sets.
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Input File Usage: \*PARTICLE GENERATOR MIXTURE
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element set or species 1, element set for species 2, etc.
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# Particle size distribution
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Statistical distributions are commonly used to specify the particle sizes. Statistical distributions are defined by analytical or user-specified piecewise linear tabular probability density functions (PDF). The particle generator supports the following different types of probability density functions: uniform, normal, log-normal, and piecewise linear. The normal and log-normal PDFs have well-known analytical
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