The military-industrial scientific research system of the academic master.

"Multi-body dissipative particle dynamics..."

Zhu Lan repeated the term and raised her hand to straighten her hair.

It's an unconscious movement she does when she's 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 basic 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 research at the mesoscopic scale or the macroscopic scale with a certain scale.

However, this "certain scale" refers to 100nm in the field of molecular dynamics, and will not exceed the order of 1mm at most.

If multibody 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 resolve her confusion, Zhu Lan finally decided to "have no shame in asking" - 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 that's the case 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 transformed the state equation and obtained a new control equation based on it."

"The conservative force in DPD is a purely repulsive force, and its size decreases as the distance increases. 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 density, temperature and other substances with uniform thermodynamic properties.”

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 a 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. Therefore, this form of state equation cannot essentially be numerically simulated with Fluid systems with free liquid-air interface.”

Hearing this, Zhu Lan's eyes suddenly lit up:

Although Chang Haonan has not introduced any new knowledge yet, 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 issue. It is not the kind of civil science who only wants to prove Goldbach's conjecture after learning 1+1=2, or the novice engineer who wants to get started quickly just by brainstorming.

If just now the couple 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.

Lin Guofan next to him also sat up straight involuntarily:

"So the new method you just mentioned can solve this problem?"

For Lin Guofan, who focuses on applied research, 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 and improving the weight function in DPD, we can obtain a conservative force form that can freely convert attraction and repulsion according to different distances, thus ensuring the stability of the model. Particles can gather together at a certain density to form particle clusters similar to condensed droplets..."

"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 and wrote down the last step of the calculation process on paper, 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, it is possible to numerically simulate real droplets."

……

After all, the two Jincheng University professors also have real talents and knowledge. Although they were a little confused when faced with an unknown concept at first, they 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. Come on:

"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 couldn't wait to try its application in engineering practice.

"Comrade Xiao Chang."

Lin Guofan directly interrupted his wife mid-sentence:

"If there is anything else we 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, while the specific design of the aircraft de-icing device can be left to Chief Engineer Liang and his colleagues."

Chang Haonan looked at the pieces of paper filled with formulas in front of him and said slowly:

"But I also want to take a longer-term view, rather than just focusing on the Yun 8 model."

"That is, use this theory to establish an ice accumulation model that can adapt to different environments and airfoils, or not just wings, but any solid surface. In this way, subsequent users only need to provide the characteristic factors of the environment and By studying the physical modeling of the object, we can obtain the corresponding ice shape growth process."

Lin Guofan, who was sitting opposite, was so shocked by such an ambitious goal that his breath froze:

"Do you want to come up with a tool for predicting ice accumulation that is universal across the world?"

You know, the aviation industry is not the only one that will be affected by ice damage.

Various fields such as electricity, highways, railways, and construction 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 inefficient, it is also very difficult and dangerous.

And if Chang Haonan's ambition can really be realized, then both in the design process and in the use process, targeted prevention can be achieved.

For a meteorologist, it's 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 within our country."

"However, the environmental factors here are quite complex, such as inflow speed, droplet diameter, inflow water content, ambient temperature, etc. I don't know much about this aspect. Professor Lin needs to be responsible for research and determination."

When he was cheating just now, he tried several different expression methods several times, and found that if all the development processes were completed by himself, it would require too many scientific research points, so in the end he chose to just let the system guide him. Do the most challenging and groundbreaking parts of it yourself.

"No problem, this is exactly 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 autumn and winter in the Qinling Mountains to ensure that there are no problems with your finalization work."

Nanzheng, where Factory 182 is located, is located in the Qinling region, and autumn and winter are also the most common periods for wing icing.

"Uh...that's perfect."

Just now, Chang Haonan was so excited that he almost forgot to finalize Yun 8F and Yun 8J, which was already imminent.

Thanks to Lin Guofan for still remembering the needs of Factory 182.

"As for Professor Zhu..."

Zhu Lan was a foreign aid that was not part of the plan, so Chang Haonan thought for a moment before continuing:

"In addition to active de-icing methods such as expansion or heating, it is also important to make the surface of the object less likely to freeze. So I want to test the anti-icing capabilities of materials with different surface structures and roughness. the difference."

"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:

"Then let's start right away!"