Unterschiede

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--- en:berechnungen:druckverlauf [2024/07/21 13:24] – neelest
+++ en:berechnungen:druckverlauf [2026/09/17 09:24] (aktuell) – gelöscht - Externe Bearbeitung (Unbekanntes Datum) 127.0.0.1
@@ Zeile 1: / Zeile 1: @@
-======Pressure profile======
-FIXME
-===== Pressure profile =====
-In order to calculate the pressure profile it is necessary to fulfil the same conditions
-as for the throughput calculation of both the throughput and the metering time
-calculation. This also applies for all input data
-[[en:eingabe_der_schneckendaten:eingabe_der_schneckendaten|geometry]],
-[[en:materialdaten:allgemeineangaben|material data]]
-and [[en:eingabe_der_verfahrensparameter:eingabe_der_verfahrensparameter|processing parameters]].
-Additionally, the point of calculation (just //PSI//) for which the pressure
-profile of the screw length shall be calculated has to be defined.
-The pressure profile is calculated back to the point of melt pool formation (OSW). If it was not
-possible to determine the point of melt pool formation on account of missing data,
-REX/PSI will calculate up to the end of the feed section. The profile from the front
-edge of the hopper to the last point calculated is reflected by a logarithmic
-formulation.
-The pressure profile calculation starts with the screw tip. The calculated throughput is
-used to determine the pressure loss between two calculation points and this is then
-added to the previous absolute pressure. The pressure in the screw vestibule (at the
-screw tip) results from the adjusted impact pressure.
-The pressure profile is calculated isothermally at the melt temperature for each step
-and is subsequently multiplied by a correction factor. This correction factor has in
-physical terms the effect that the calculation performed at a temperature that permits
-the pressure and throughput behavior to coincide. This is necessary, since the
-throughput has to be calculated on the basis of a mixed isothermal/non-isothermal
-formulation while the pressure profile has to be calculated either isothermally or nonisothermally.
-==== Pressure profile calculation for the barrier section ====
-In order to calculate the barrier screw in the way described a constant pressure
-gradient has to be assumed. However, since every additional assumption increases
-inaccuracy, the so-called "Matrix model" was implemented to eliminate this
-assumption. Its calculation method is similar to the FEM calculation method.
-Here, single intervals are built for barrier flight, solid and melt channel and for each
-section between the individual balance points, the change in the flow is described by
-means of a linear equation. These equations form a linear system of equations. The
-equations only describe the development of the flow in the direction of the channel,
-which means that the mesh of the division of the geometry into the required intervals
-corresponds to constant conditions.
-{{ :en:berechnungen:abbildung_9_13_en.svg?700 |}}
-Before the resulting equation system can be solved with the familiar algorithms used
-to solve linear equation systems, it is first necessary to reduce the system. This
-reduction is achieved by allowing boundary conditions.
-{{ :en:berechnungen:abbildung_9_14_en.svg?700 |}}
-In the closed barrier section, the mass flow towards the first node, or away from the
-last node in the channel direction, can be taken as being equal to zero. If an open
-barrier section is calculated, by contrast, it is sufficient to alter the boundary condition
-in order to be able to calculate this design. Because of the lack of a geometrical
-separation, the pressure difference between the first and last nodes of the solids and
-melt channel is set at zero.
-For a clear-cut solution of the system it is necessary to know about the mass flow.
-Here an iterative calculation helps, i.e. in the first step, the pressure-throughput
-behavior of the standard sections is calculated for a known pressure at the screw tip
-without considering the barrier section. In the second step, this throughput is taken to
-solve the equation system for the barrier section. Since the overall pressure
-requirement for the screw is equal to the sum of the pressure requirements of the
-individual screw sections, the calculated pressure requirement for the barrier section
-can be added to the pressure requirement of the remaining screw sections that was
-calculated in the first step.
-==== Druckverlaufsberechnung für Wave-Schnecken ====
-ToDo: Anpasssen wenn MA Gödeke fertig ist