Questa simulazione è stata ispirata dal video "90 ft. Vertical Spike Wave in Slow Mo" che mostra i risultati di un esperimento condotto dal FloWave Ocean Energy Research Facility. Utilizziamo parte del loro video per confrontare i risultati con la nostra simulazione. https://www.youtube.com/watch?v=iWKFPTgkpXo&t=105s Onda con picco verticale La Vertical Spike Wave è il risultato di un'onda concentrica che viaggia verso il suo centro. A seconda della sua velocità, l'onda può collidere nel mezzo e formare un picco d'acqua. Quest'onda può essere generata in una vasca circolare dotata di pannelli mobili su tutta la lunghezza del perimetro che spingono in un unico movimento coordinato l'acqua verso il centro. I pannelli devono essere attivati simultaneamente con lo stesso movimento per far sì che le onde viaggino in un unico movimento e si scontrino alla stessa velocità e con la stessa energia. Se la velocità è abbastanza alta, il livello dell'acqua al centro della piscina aumenterà notevolmente generando uno stretto ed alto picco [Figura 1], per poi ricadere a mo’ di fontana. Onda con picco verticale Configurazione del modello su FLOW-3D® FLOW-3D è stato utilizzato per impostare la simulazione della Vertical Spike Wave ed il risultato è stato elaborato su FlowSight. Per modellare l'onda circolare la mesh è stata definita in coordinate cilindriche: questo ha permesso di simulare solo una parte della piscina [Figura 2] e di duplicarla successivamente su FlowSight per dare l’impressione che l'intera piscina sia stata modellata. Figura 2 - Setup FLOW-3D La maggior parte delle misure sono note dal video di The Slow Mo Guys, così è stato possibile dare alla simulazione le dimensioni reali. La piscina è larga circa 50 metri ed è dotata di 168 pannelli. Abbiamo stimato che i pannelli impieghino all’incirca 4s per compiere un movimento completo avanti e indietro, inclinandosi di un angolo di 17.2°. Per impostare la simulazione, è stato creato la vasca direttamente su FLOW-3D utilizzando le capacità di modellazione geometrica di base fornite dal software, mentre il pannello è stato importato come file STL [Figura 3]. Quest’ultimo è stato configurato come oggetto in movimento a cui è stato applicato il movimento definito in precedenza. All'inizio l'acqua è completamente immobile e si è verificato che una sola spinta è sufficiente per creare il picco d’onda cercato. Pannelli di spinta dell'acqua Risultati Il movimento complessivo e l'energia corrispondono alla realtà con un'ottima precisione. Alcune differenze sono visibili solo nella parte superiore del picco, che nella realtà frange: questi effetti sono trascurabili per il nostro confronto, ma potrebbero essere presi in considerazione con una simulazione completa 3D e 2 fluidi. Figura 4 - L'esperimento e la simulazione fianco a fianco … [Leggi di più...]
(English) Increasing Discharge Capacity with the Piano Key Weir
Ci spiace, ma questo articolo è disponibile soltanto in Inglese Americano e Francese. … [Leggi di più...]
Sleeve filling and slow shot phase analysis with FLOW-3D Cast
High pressure Die Casting is a complex field of foundry. The liquid hot metal is generally poured into a shot sleeve for few seconds, until the desired volume is reached. Then, after a short waiting time, the plunger pushes the metal into the die cavity. First a slow shot phase is performed to avoid air entrainment in the sleeve, then a final high speed phase that fill the casting part in a very short amount of time. One of the targets of any producer is to find the best compromise between a fast process, to increase the productivity and to reduce the heat losses, and a slow filing and shot necessary to minimize the air entrainment. FLOW-3D Cast, due to its capabilities, is one of the best software to analyse this process. It can combine easily moving objects, mass sources, heat transfer and solidification, everything in fast and accurate simulations. Several studies were already done to determine the best plunger velocity curve, also coupling FLOW-3D Cast to numerical optimization software. The aim of the present simulation, instead, is to focus on the sleeve filling, underlining the possibility to control also this phase and the defects that could arise from a not-optimal solution. https://www.youtube.com/watch?v=cGQUmH8EHZ0 In the video both fluid and walls are coloured by temperature, with two different colour scales. The heat transfer coefficients have been artificially increased to emphasize the temperature change. Thanks to this fact, it is possible to notice that some drops of metal flow on the beginning of the runner system, solidifying and influencing the casting phase until they are melted again. It is possible also to notice the big waves generated when the filling is finished, and how this waves contribute to entrain some big air bubbles that are pushed into the casting part, generating defects. … [Leggi di più...]
Investigation of Mould Leakages in a Gravity Casting
This article was contributed by Gabriele Taricco of CM Taricco and Stefano Mascetti of XC Engineering. Mould design is a very complex undertaking that must consider not only fluid dynamics and metal solidification patterns, but problems that may arise from the mould itself and how it reacts to stresses from heat transfer. CM Taricco, a mould maker company based in Italy, recently encountered a problem of metal leakages at the bottom of one of their new moulds. The cause of the mould leakages was initially obscure and only appeared after a few process cycles. It was evident that the problem was critical, since it would compromise the production timeline and dramatically increase the costs to cast the part. Investigation of an idea The process itself was a gravity casting, with well-controlled pouring dynamics and overflow designs, so the problem could not come from the fluid dynamics part. The hypothesis of Gabriele Taricco (owner of CM Taricco) was that the metal leakages were resulting from a bad design of the thermal dissipation of the mould, causing a non-uniform distribution of temperature and hence large and unwanted deformations at the bottom of the mould, that were enforced cycle after cycle up to the opening of a critical area where metal could flows out. To verify this and to find a quick solution to the problem, a FLOW-3D simulation was run to exactly visualize what was happening to the mould as it was being heated. The analysis After a filling simulation, to ensure a good filling pattern, the focus of the simulation was redirected to a thermal die cycling analysis. The setup in this case is fast and straightforward requiring only 1 hour to reproduce 10 production cycles on a common desktop machine (i7 5930K, commercial value 1500 dollars). The result confirmed CM’s initial hypothesis: by looking at the temperature field, from various points of view and cross sections in a single image using FlowSight, it was clear that the temperature distribution of the mould would easily cause the expected deformations and metal leakages. Simulation of the mould’s temperature during the die cyclings Further analysis with the Fluid-Structure Interaction module Once the problem was identified and the technical staff could start designing an improved mould, CM Taricco wanted to have a final confirmation running a FEM analysis of stresses and deformations on the die. To perform this analysis, XC Engineering Srl helped CM in setting up and performing the calculation. The result of the analysis showed exactly what CM thought was happening: FLOW-3D was able to reproduce with extreme accuracy the same location and size of the real deformations found on the mould after few pouring cycles. This was good news for CM, and enforces an additional recommendation to use the FSI module at the design stage to predict the real die deformations based on the real casting conditions. Deformation of the mould during the die cyclings, simulated using the Fluid Structure Interaction model. Deformations are amplified x20. Read more... … [Leggi di più...]
Improving High Pressure Die Casting Designs
The content for this article was contributed by Mark Littler of Littler Diecast Corporation. Littler Diecast Corporation, a producer of high pressure die castings, was recently able to redesign and die cast an electrical switch frame for an aerospace application. Formerly produced by a different manufacturer, there were defect problems in a high number of the castings and a new design was needed to achieve a lower scrap rate. Littler Diecast was able to demonstrate that they could pinpoint the defects through simulation without previous knowledge of the problems. This impressed the client enough to land them the job. Identifying the Problem The switch is cast from A380 aluminum and is approximately 1 ¼” x 1” x 1/2” in size. Littler Diecast found that porosity problems were plaguing the part in two locations: the plate and the chimney. This was confirmed by the customer. Holes were forming in each of the locations because of the way the part filled. The flow would enter through a single gate as shown in Figure 1, jet to the far side of the plate and then backfill, trapping air pockets that do not always close due to early solidification. The same problem was found in the chimney: fluid would jet to its furthest extent and then backfill, creating trapped air that could not vent through the parting line. X-ray of original part, showing porosity problemsFigure 1: Original design with a single gate. Plot colored by velocity magnitude.Figure 2: Final design with three gates. Plot colored by velocity magnitude. The Original Part Design There were other problems with the original design of the part. There was a lot of die erosion around the slot for the lock washer and the sealing surfaces on the bottom of the plate. The overflows located at the corners of the part were not large enough to allow defects to flow out. Using FLOW-3D, Littler Diecast was able to analyze the flow behavior and visually determine what was occurring. With such a small part, early solidification is a problem due to the rapid cooling in thin sections. If flow jets across the part and back, the fluid has more time to cool and create entrapped air. It is best to have the hottest liquid coming in last. With this in mind, Littler Diecast was able to test a number of ideas and achieved a design that minimized the potential for problems and maximized the process window. Read more... … [Leggi di più...]
