Archive for August 2014

Using particle feeders in Energy2D for advection simulations

August 30th, 2014 by Charles Xie
Fig. 1: Particle advection behind two obstacles.
Advection is a transport mechanism in which a substance is carried by the flow of a fluid. An example is the transport of sand in a river or pollen in the air. Advection is different from diffusion, whereas the more commonly known term, convection, is the combination of advection and diffusion.

Our Energy2D can simulate advection as it integrates particle dynamics in the Lagrangian frame and fluid dynamics in the Eulerian frame. Particles in Energy2D do not spontaneously diffuse -- they are driven by gravity or fluid, though we can introduce Brownian particles in the future by incorporating the Langevin Equation into Energy2D.

Fig. 2: Blowing away particles.
Over this weekend, I added a new object, the particle feeder, for creating continuous particle flow in the presence of open mass boundary. A particle feeder can emit a specified type of particle at a specified frequency. All these settings can be adjusted in its property window, which can be opened by right-clicking on it and selecting the relevant menu.

Figure 1 shows a comparison of particle advection behind a turbulent flow and a streamlined flow. Have you ever seen these kinds of patterns in rivers?

Figure 2 shows how particles of different densities separate when you blow them with a fan. There are six particle feeders at the top that continually drop particles. A fan is placed not far below the feeders.

With these new additions to Energy2D, we hope to be able to simulate more complex atmospheric phenomena (such as pollutant transport through jet streams) in the future.

Simulating cool roofs with Energy3D

August 20th, 2014 by Charles Xie
Fig. 1: Solar absorption of colors.
Cool roofs represent a simple solution that can save significant air-conditioning cost and help mitigate the urban heat island effect, especially in hot climates. Nobel Prize winner and former Secretary of Energy Steven Chu is a strong advocate of cool roofs. It was estimated that painting all the roofs and pavements around the world with reflective coatings would be "equivalent to getting 300 millions cars off the road!"

With Version 4.0 of Energy3D (BTW, this version supports 200+ worldwide locations -- with 150+ in the US), you can model cool roofs and evaluate how much energy you can save by switching from a dark-colored roof to a light-colored one. All you need to do is to set the colors of your roofs and other building blocks. Energy3D will automatically assign an albedo value to each building block according to the lightness of its color.

Figure 1 shows five rectangles in different gray colors (upper) and their thermal view (lower). In this thermal view, blue represents low energy absorption, red represents high energy absorption, and the colors in-between represents the energy absorption at the level in-between.

Now let's compare the thermal views of a black roof and a white roof of a cape code house, as shown in Figure 2. To produce Figure 2, the date was set to July 1st, the hottest time of the year in northern hemisphere, and the location was set to Boston.

Fig. 2: Compare dark and white roofs.
How much energy can we save if we switch from a perfectly black roof (100% absorption) to a perfectly white roof (0% absorption)? We can run the Annual Energy Analysis Tool of Energy3D to figure this out in a matter of seconds. The results are shown in Figure 3. Overall, the total yearly energy cost is cut from 6876 kWh to 6217 kWh for this small cape code house, about 10% of saving.

Figure 3 shows that the majority of savings comes from the reduction of AC cost. The reason that the color has no effect on heating in the winter is because the passive solar heat gains through the windows in this well-insulated house is enough to keep it warm during the sunshine hours. So the additional heat absorbed by the black roof in the same period doesn't offset the heating cost (it took me quite a while to figure out that this was not a bug in our code but actually the case in the simulation).

Fig. 3: Compare heating and AC costs (blue is white roof).
Of course, this result depends on other factors such as the U-value and thermal mass of the roof. In general, the better the roof is insulated, the less its color impacts the energy cost. With Energy3D, students can easily explore these design variables.

This new feature, along with others such as the heat flux visualization that we have introduced earlier, represents the increased capacity of Energy3D for performing function design using scientific simulations.

Here is a video that shows the heating effect on roofs of different colors.

Visualization of heat flux in Energy3D using vector fields

August 14th, 2014 by Charles Xie
Fig. 1: Winter in Boston
One of the strengths of our Energy3D CAD software is its 3D visualizations of energy transfer. These visualizations not only allow students to see science concepts in action in engineering design, but also provide informative feedback for students to make their design choices based on scientific analyses of their design artifacts.

Fig. 2: Summer in Boston
A new feature has been added to Energy3D to visualize heat transfer across the building envelope using arrays of arrows. Each arrow represents the heat flux at a point on the surface of the building envelope. Its direction represents the direction of the heat flux and its length represents the magnitude of the heat flux, calculated by using Fourier's Law of Heat Conduction. Quantitatively, the length is proportional to the difference between the temperatures inside and outside the building, as well as the U-value of the material.

Fig. 3: Winter in Miami
The figures in this post show the heat flux visualizations of the same house in the winter and summer in Boston and Miami, respectively. Like the solar radiation heat map shown in the figures, the heat flux is the daily average. The U-value of the windows is greater than those of the walls and roof. Hence, you can see that the heat flux vectors in the winter sticking out of the windows are much longer than those sticking out of the walls or roof. In the summer, the heat flux vectors point into the house but they are much shorter, agreeing with the fact that Boston's summer is not very hot.

Fig. 4: Summer in Miami
Now move the same house to Miami. You can see that even in the winter, the daily average heat flux points inside the house, agreeing with the fact that Miami doesn't really have a winter. In the summer, however, the heat flux into the house becomes significantly large.

These visualizations give students clear ideas about where a house loses or gains energy the most. They can then adjust the insulation values of those weak points and run simulations to check if they have been fixed or not. Compared with just giving students some formulas or numbers to figure out what they actually mean to science and engineering practices, experiential learning like this should help students develop a true understanding of thermal conduction and insulation in the context of building science and technology.

Here is a YouTube video of the heat flux view.

A 16-year-old’s designs with Energy3D

August 13th, 2014 by Charles Xie
This post needs no explanation. The images say it all.

All these beautiful structures were designed from scratch (NOT imported from other sources) by Cormac Paterson using our Energy3D CAD software.

He is only 16 years old. (We have his parents' permission to reveal his name and his work.)

Using fans to create fluid flows in Energy2D

August 10th, 2014 by Charles Xie
Fig. 1: Swirling flows form between two opposite fans.
A new type of object, "fan", has been added to Energy2D to create and control fluid flows. This fan replaces the original implementation of fan that assigns a velocity to a solid part (which doesn't allow the fluid to flow through). For the CFD folks who are reading this post, this is equivalent to an internal velocity boundary.

To add a fan to the scene, use the Insert Menu to drop a fan to the last clicked location. You can then drag it anywhere and resize it any way. By default, the velocity of a fan is zero. You will need to set its velocity in the popup window that can be opened using the right-click popup menu. Currently, however, rotation has not been implemented, so a fan can only blow in four directions: left, right, up, or down -- the direction depends on the aspect ratio of the fan's shape and the value of the velocity.

Fig. 2: Eddy formation in a hole.
With this new feature, we can create a directional flow in Energy2D to simulate things such as a river or wind field. Then we can easily simulate various kinds of eddy flow and visualize them using the streamline feature of Energy2D.

For example, Figure 1 shows the continuous formation of swirling flows between two fans that blow wind in the opposite direction. If you move the fans further apart, you will find that the swirling pattern will not form. Could the mechanism shown in this simulation be related to the formation of certain types of twisters?


Fig. 3: Eddy formation behind a fin.
Figures 2 and 3 show the formation of an eddy in a hole and behind an obstacle, respectively. These eddies are common in fast-flowing rivers. Experienced fishermen know there is a higher chance to find fish in these eddies.

Accurate prediction of solar radiation using Energy3D: Part III

August 6th, 2014 by Charles Xie
Predicted and measured average daily insolation for 80 cities.
In Parts I and II, we have documented our progress on solar radiation modeling with our Energy3D CAD software. In the past few weeks, our summer interns Siobhan Bailey from Rensselaer Polytechnic Institute and Shiyan Jiang from University of Miami, and I have collected data for 167 worldwide locations. We analyzed 100 US locations among them and compared the insolation data calculated by Energy3D for a horizontal surface and a south-face vertical surface with 30 years of data collected by the US Department of Energy. The results show that, on average, the calculated mean daily insolation is within ±14% of error range compared with the measured results for a horizontal surface and ±10% of error range compared with the measure results for a south-facing vertical surface, respectively. The calculation of the average accuracy is based on both temporal data of 12 months over a year and spatial data of 100 locations in the US.

With this crystal ball in the hand to predict solar radiation anywhere anytime with a reasonable accuracy, Energy3D can be used by professional engineers for real-world applications related to solar energy, such as passive solar architecture, urban planning, solar park optimization, solar thermal power plants, and so on. Stay tuned for our future reports of those applications.

Go to Part I and Part II.

From conceptual design to detailed design with Energy3D

August 1st, 2014 by Charles Xie
Figure 1: Empire State Building
An important objective of our Energy3D software is to explore how to create CAD software that support students to practice the full cycle of engineering design from conceptual design to detailed design in a single piece of software. We believe that interactive 3D visualizations and simulations provided by CAD tools are cognitively important for K-12 students who have little prior knowledge about the subject of design or the process of design to develop some sense of them -- through practice. Instantaneous visualizations of the results of their actions within the CAD software can give students some concrete clues to develop, share, and refine their ideas directly within a visual design space.

Although there have been some cautions about the use of CAD software in design education, my take is that, in the very early stage of grassroots design education, the problem is not that students are handicapped by a design tool; the problem is that they lack ideas to start with or skills to put their ideas into actions and should be aided by an intelligent design tool (in addition to a teacher, of course). A good CAD tool will be very instructive in this stage. Only after students rise to a certain expert level will the limitations of the CAD software begin to emerge. Often in the K-12 settings, the time constraint does not allow the majority of students to reach that level through conventional instruction, however. Hence, it is likely that the positive effects of using CAD software in K-12 engineering education will outweigh the negative effects, letting alone that students will learn important computer design and modeling skills that will be extremely useful to their future STEM careers.
Figure 2: Freedom Tower

But not all CAD software were created equal. Many CAD software have been developed for professional engineers and are not appropriate for K-12 applications, even though many software vendors have managed to enter the K-12 market in recent years. Given the rise of engineering in K-12 schools, it is probably the right time to rethink how to develop a CAD platform that supports design, learning, and assessment from the ground up.

Our Energy3D CAD software has provided us a powerful platform to ponder about these questions. From the beginning of this project back in 2010, we had been envisioning a CAD platform that integrates conceptual design, detailed design, collaborative design, numerical analysis, designer modeling, machine learning, and digital fabrication. After four years' continuous work, the software can now do not only conceptual design like a sketch tool but also detailed design like a production CAD program (look at the details in Figure 3). In terms of education, this means that it has a very short learning curve that allows all students to translate their ideas into computer models in a short amount of time and, meanwhile, a very deep design space that allows some of the willing students to advance to an expert level. With these capacities, we are now conducting leading-edge data mining research to investigate how to facilitate the transition. The research will eventually translate into novel software features of the CAD program.
Figure 3: Kendall Square

Cormac Paterson, a brilliant high school student from Arlington, MA, has demonstrated these possibilities. He has created many designs with Energy3D that are showcased in our model repository, including all the designs shown in the figures of this post.