Chapter 154 Universal Ice Growth Model
"Multi-body dissipative particle dynamics..."
Zhu Lan repeated the term and raised his hand to straighten his hair.
This is an unconscious action she does when thinking.
As a professor of surface physics, Zhu Lan has naturally been exposed to computational simulations related to molecular dynamics very early.
Naturally, this also includes dissipative particle dynamics (DPD), a numerical simulation method that has only been proposed in recent years to deal with mesoscopic particle motion.
But what is this multi-body dissipative particle dynamics?
The elementary particles in DPD are not originally single atoms or molecules in molecular dynamics, but coarse-grained particles representing molecular groups.
Since the trouble of describing all molecules in molecular dynamics is eliminated, the degree of freedom of the system is greatly reduced, and the amount of calculation is also reduced exponentially. It is very suitable for mesoscopic scale or macroscopic scale of a certain scale. scale research.
However, this "certain scale" refers to 100nm in the field of molecular dynamics, and will not exceed the order of 1μm at most.
If multi-body means to continue to expand the scale of research, then it means increasing the number of molecular groups that need to be studied, which is contrary to the original intention of establishing the DPD method...
Unable to solve the confusion, Zhu Lan finally decided "Don't be ashamed to ask" - Neither she nor Lin Guofan were from within the aviation industry system, so they naturally had no impression of the name Chang Haonan.
So in their opinion, the person in front of them should be just a young engineer from Factory 182 who is mainly responsible for improving the de-icing device of Yun-8.
At least for now.
“Okay, is there any relationship between the multi-body dissipative particle dynamics you are talking about and the dissipative particle dynamics I am familiar with, and what is the difference?”
In fact, at this time, Chang Haonan had just sorted out the knowledge that instantly poured into his mind. Regarding the basic principles of MDPD, he only knew about the basic principles of MDPD about two minutes earlier than Zhu Lan, who was sitting next to him.
“The biggest difference is that MDPD has transformed the state equation and obtained a new control equation based on it.”
“The conservative force in DPD is a purely repulsive force. Its size decreases as the distance increases, and the particles controlled by such a force will continue to move away from each other and eventually fill the entire calculation space, forming a mass of matter with uniform density, temperature and other thermodynamic properties."
< br>After speaking, Chang Haonan took the pen and paper from the side and wrote down the state equation of DPD.
p=kT+A^2
The reason for doing this is not only to make it easier for Lin Guofan and Zhu Lan to understand, but also to deepen Chang Haonan's own understanding and to sort out the theoretical principles of MDPD.
“The highest order term of the fluid density in this equation of state is the quadratic term, and the equation of state used to describe the internal pressure of the liquid needs to contain the cubic term of the fluid density, so this form of state equation is essentially It is impossible to numerically simulate a fluid system with a free liquid-gas interface.”
Hearing this, Zhu Lan’s eyes suddenly lit up:
Although Chang Haonan has not started to introduce anything yet. New knowledge, but he was able to clearly explain DPD, which is still a cutting-edge theoretical framework so far, and directly pointed out its biggest problem. It is obvious that he has really studied this problem, and is not someone who has only studied 1+ 1=2 is a civilian who wants to prove Goldbach's conjecture, or a novice engineer who wants to get started quickly just by brainstorming.
If just now, the couple still had a somewhat condescending view and wanted to see how much valuable things such a young engineer could say.
So now, at least Chang Haonan has been regarded as a peer who can conduct equal academic exchanges.
Next to him, Lin Guofan sat up involuntarily:
“So the new method you just mentioned can solve this problem?”
For Lin Guofan, who focuses on application-oriented research In fact, the significance of this matter is even greater.
Because the simulation of DPD is a bit too ideal, it can almost only be used for gaseous systems and full-pipe systems where the fluid evenly fills the entire restricted confined space.
In the real environment, there are not many situations that meet these two requirements. Almost all research objects are in open spaces and have free liquid-gas interfaces.
“Of course.” Chang Haonan tapped the pen on the paper in front of him:
“While researching the literature, I found that by combining cubic spline curves, the By improving the weight function, a conservative force form can be obtained that can freely convert attraction and repulsion according to different distances. This can ensure that the particles in the model can gather together at a certain density to form a condensed droplet-like form. Particle cluster..."
"After adding the higher order term of fluid density to the equation of state of the conservative force, the equation of state of MDPD is obtained."
Chang Haonan said on the paper. I wrote down the last step of the calculation process, which is the transformation result of the conservative force equation:
p=kT+A^2+2Br^4^2(-c)
After completing the last symbol, he showed a satisfied smile and gently put the pen aside.
“Based on its control equations, real droplets can be numerically simulated.”
……
After all, the two Jincheng University professors also have real talents. Although he was a little confused when faced with an unknown concept at first, he quickly grasped the key points. "As long as the trajectory and impact characteristics of water droplets can be calculated, it will be easier to understand the phase change process on the solid surface." After understanding Chang Haonan's explanation, Zhu Lan's frowning eyebrows gradually relaxed. Li Kailai:
"In addition, I think a series of algorithms such as time iteration and boundary condition settings need to be determined later. In this regard..."
Obviously, after seeing a brand new dynamic theory , she can’t wait to try its application in engineering practice.
“Comrade Xiao Chang.”
Lin Guofan directly interrupted his wife mid-sentence:
"Whatever else the two of us need to do later, you can just assign the work."
"The theoretical improvement of MDPD and the algorithms involved in the specific implementation process can be completed by me, except for the aircraft." The specific design of the ice device can be left to Chief Liang and the others."
Chang Haonan looked at the pieces of paper filled with formulas in front of him and said slowly:
"But I still want to look at it. Take a longer-term view, rather than just focusing on the Y-8 model."
"That is, use this theory to build a model that can adapt to different environments and airfoils, or not just wings. It is an ice growth model on any solid surface, so that subsequent users can obtain the corresponding ice growth process as long as they provide the characteristic factors of the environment and the physical modeling of the research object.”
Lin Guofan, who was sitting opposite, was shocked by such an ambitious goal:
“You want to come up with a universal ice accumulation prediction tool around the world?”
You know, the aviation industry is not the only one that will be affected by ice damage.
Electricity, highways, railways, construction and other fields are actually troubled by this.
However, due to the instability of climate conditions, it has always been difficult to predict the time, location and specific form of ice damage, and naturally there is no pre-control.
Often, a large number of manpower can only be dispatched for inspection and repair when ice damage occurs or is about to occur.
Not only is it very inefficient, it is also very difficult and dangerous.
If Chang Haonan's ambition can really be realized, then both in the design process and in the use process, we can be targeted and make targeted prevention in advance.
For a meteorologist, it is a dream come true.
“That’s right.” Chang Haonan nodded:
"Of course, we don't need to be so radical at the beginning. We just need to deal with a few typical scenarios in our country."
"However, the environmental factors here are quite complex, such as inflow speed, droplet diameter, I don’t know much about the flow water content, ambient temperature, etc. Professor Lin needs to be responsible for research and determination.”
When he was cheating just now, he used several different expressions. After trying it several times, I found that if all the development process was completed by myself, it would require too many scientific research points, so in the end I chose to only let the system guide me to complete the most challenging and groundbreaking part.
“No problem, this happens to be what I’m good at.”
Lin Guofan already showed an eager expression:
"In addition, nationwide work cannot be completed overnight. Many places require on-site inspections. I can first determine the environmental factors in the Qinling area in autumn and winter to ensure that there are no problems with your finalization work."
Nanzheng, where the 182 factory is located, is located in the Qinling region, and autumn and winter are also the periods when wing icing is most common.
"Uh...that couldn't be better."
Just now Chang Haonan was so excited that he almost forgot to finalize the Yun 8F and Yun 8J.
Thanks to Lin Guofan for still remembering the needs of Factory 182.
"As for Professor Zhu..."
Zhu Lan is a foreign aid that is not included in the plan, so Chang Haonan thought for a moment before continuing:
"In addition to active elimination such as expansion or heating, In addition to ice protection, it is also important to make the surface of an object less likely to freeze, so I wanted to test the specific differences in anti-icing capabilities of materials with different surface structures and roughness.”
"No problem. We are currently studying the impact of solid surface columnar and hemispherical microstructures on liquid wettability. Some ideas and results can be transferred here."
"Very good." Chang Haonan stood up. , and took a deep breath at the same time:
"Then let's start right away!"
(End of this chapter)