This simulation was inspired by The Slow Mo Guys’ video “90 ft. Vertical Spike Wave in Slow Mo” which shows the results of an experiment made by the FloWave Ocean Energy Research Facility. We use part of their video to compare results with our own simulation. https://www.youtube.com/watch?v=iWKFPTgkpXo&t=105s The Vertical Spike Wave The Vertical Spike Wave is the result of a concentric wave travelling towards its center. Depending on its velocity, the wave can collide in the middle and form a spike of water. This wave can be generated in a circular pool equipped of moving panels on the entire length of the perimeter that push in one coordinated motion the water towards the center. The pushers have to be activated simultaneously with the same motion in order to have the water travel in one single motion and collide at the same speed with the same energy. If the speed is high enough, the water will rise in the center of the pool in a high spike [Figure 1] and fall back splashing. Figure 1 - Vertical Spike Wave Model setup on FLOW-3D® FLOW-3D was used to setup the simulation of the Vertical Spike Wave, then the result was post-processed on FlowSight. In order to model the circular wave, the mesh was defined on cylindrical coordinates. That allowed to simulate only a part of the pool [Figure 2] then to duplicate it later on Flow Sight to make it look like the entire pool was modeled. Figure 2 - FLOW-3D setup Most of the measurements were given in The Slow Mo Guys’ video, so it was possible to give the simulation the real dimensions. The pool is about 50m wide and is equipped of 168 panels. We estimated that the pushers took 4s to motion back and forth once with an angle of 17.2°. To setup the simulation, a pool was created simply on FLOW-3D using the basic geometry provided by the software, then the panel was imported as an STL file. The pusher was setup as a moving object [Figure 3] to which a motion defined in advance was applied. The water is completely still at first, and a single push is sufficient to create the vertical spike wave. Figure 3 - Panels pushing the water Results The overall motion and energy correspond to the reality with a very good precision. Some differences can be seen only in the disrupted front of the spike: its effects are negligible for our comparison but could be taken into account with a complete 3D and 2-fluid simulation. Figure 4 - Experiment and Simulation side by side … [Read more...]
Increasing Discharge Capacity with the Piano Key Weir
Piano Key Weir Characteristics The Piano Key Weir is a particular model of the labyrinth discharge spillway. It is composed of an alternation of reclined surfaces, one is the direction of the flow, the other in the opposite direction. Each of these slopes is separated by a vertical wall that follows the geometry of the shape. Seen from above, it is a series of rectangles cut in equally sized sections widthwise. For each of these sections one of the side perpendicular to the stream is pushed down, creating a slope on which the water can either flow or accumulate, depending on which side the section is lowered. This structure tops a smaller wall. The Piano Key Weir is generally used at the outbound of a dam, the idea being to dispose of a construction that is solid enough to resist the pressure created by a high quantity of water contained in a dam or a river during flood season, that can evacuate the overflow of water, and that is simple enough not to be too expensive. Usage of the Piano Key Weir The Piano Key Weir is a free flow discharge spillway. Its geometry allows for a significantly higher evacuation capacity. The studies conducted on this type of spillway have two aims: build solid and cheap discharge spillways, as well as reinforce the older structures. This enables engineers to avoid accidents of dams that break or that don’t have the capacity to discharge water correctly and in a controlled manner when there is a flood. Usually the weir is placed after the dam and before the cities so as to allow a controlled discharge of water. This type of discharge spillway presents several crucial advantages. First it is easy to install on structures that are already there, as opposed to classic labyrinth discharge spillways. Moreover, its shape that alternates between ascending and descending slopes allows the formation of two different flows depending on whether the water arrives on one or the other slope. When the water flows over the descending slope it forms a jet that goes towards the bottom of the dam, and when it is first contained by an ascending slope it forms a kind of film which then flows towards the jet below. This division of flow slows the stream down consequently in a much more efficient way than classic dams do. Simulation results In order to observe the effects of the Piano Key Weir we used FLOW-3D® to make a simulation displaying the weir in a stream. The model setup is the most basic one, given that it has been proved that it enabled the results to be as close to reality as possible. The simulation shows the characteristic flow of the water over the “keys” of the piano as well as the decrease of the flow rate after the weir. We can see that the error percentage between experimental results and the simulation using FLOW-3D is only between 2% and 4% on average. The only determining factor is the mesh resolution when it comes to the accuracy of the simulation, but it only changes the error of 3% or 4% maximum, which means that overall the simulation doesn’t go above an error of 6%. … [Read more...]
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. … [Read more...]
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... … [Read more...]
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... … [Read more...]
