The military-industrial scientific research system of the academic master

In the first half of 1996, even the security situation in Beijing was not very good, so they did not eat too late and left the hotel before eight o'clock. Wu Yifan went to the house he rented off campus, and the other three Naturally, people go back to school together.

In college dormitories in the 1990s, entertainment activities were far less abundant.

Chang Haonan remembered that there were a few roommates in his dormitory who particularly liked playing cards. Except for a period of time before the exam, they basically had to play hard every night.

Therefore, he did not choose to go back to the dormitory directly. Instead, he went to the public phone booth and called home.

Chang Haonan almost cried when he heard his parents' voices when they were young again.

In order to prevent the second elder from hearing anything unusual, he hung up the phone without chatting for too long, saying that he was going back to the dormitory to rest.

It took almost ten minutes for Chang Haonan to finally calm down and then decided to go to the library again.

This time it is not for course design, but there are several newspaper racks in the rest area of ​​the library, which will provide the latest newspapers and magazines.

He had just been reborn and had basically no memory of recent events, and there was no developed Internet in this era, so that was the most convenient place to get news.

A few minutes later, Chang Haonan moved a stack of newspapers and sat on the bench next to him.

When reading the news, he only needs to understand a general idea, so that not knowing anything seems very strange. Therefore, he gulps down the news and flips through it very quickly.

The aftermath of the incident at the beginning of the year is still lingering, and many news reports are still related to it. Some military publications are comparing the military power between China and the United States. In this era, it goes without saying much about the results.

There have been a number of shootings in the last month.

The last module of Mir, the Nature module, was launched into orbit and successfully docked, completing all construction work of the space station.

…

They are all very contemporary content.

Just when Chang Haonan saw the crash of Valuje Air Flight 592, a familiar voice suddenly came from behind him.

"Junior Chang? You look very relaxed today?"

He turned around and found that it was Yao Mengna, the senior sister he met in the computer room that day.

"It's about combining work and rest. Students in our new era have to read books about sages and see things outside the window." Chang Haonan looked up at his watch and found that it was almost 10:30 pm when the library closed, so he stood up and turned around. He put the books and newspapers back into their places one by one, then put on his bag and left the library with Yao Mengna.

The total distance from the newspaper area to the library entrance was less than 20 meters, and Yao Mengna secretly glanced at Chang Haonan no less than five times.

She came here today to find some information about CFD simulation. A project being carried out by the research team was not going well. She and two other people tried for a long time but failed to find an efficient calculation method.

So when she saw Chang Haonan just now, Yao Mengna almost subconsciously walked over and said hello.

Subconsciously, she thought that this junior undergraduate student might be able to solve this problem.

But when the question came to her lips, Yao Mengna still hesitated.

Firstly, the problem this time was much more complicated than the previous simulation that Chang Haonan conducted in the computer room. Secondly... Chang Haonan really caused her huge psychological trauma last time.

But in the end, she decided to put aside her face issues for the sake of the research group's project.

"Junior, can I ask you a question related to computational fluid dynamics?"

After hearing this question, Chang Haonan's first reaction was disappointment.

He originally thought that Yao Mengna noticed his handsome appearance and kept peeking over here, but it turned out that the other party was attracted by his inner wisdom.

Why can't it be more superficial?

But he still nodded calmly: "Okay, let's talk."

"I am studying an aeroelastic instability problem that considers large geometric deformation factors for the aircraft wing, but it is very inefficient to solve the N-S equation and the Euler equation using a similar idea to your day, and we have tried several results, The error is also relatively large..."

"Wait a minute." Upon hearing this, Chang Haonan raised his hand and interrupted Yao Mengna's question: "What kind of wings are they?"

"Uh..." Yao Mengna was stunned: "I just want to ask about the simulation idea. Does this have a big impact?"

"There is a huge difference between a delta wing, a swept wing and a straight wing with a large aspect ratio." Chang Haonan replied expressionlessly: "Of course your research group may have confidential topics, if it is not convenient to tell me... …”

"There's nothing inconvenient about making the project public!" Listening to Chang Haonan's meaning, Yao Mengna obviously knew something about this aspect, and she immediately didn't care whether she was a junior or not.

"It is a straight wing with a large aspect ratio. We also tried to improve the Dewey-Hodges equation, but the results were not ideal either."

"That's normal." Chang Haonan shrugged, as if it were a matter of course: "The aeroelastic instability problem of a large aspect ratio straight wing is most likely a flutter problem. Computational Fluid Dynamics (CFD)/Computational Fluid Dynamics (CFD) The structural mechanics (CSD) coupling method is not suitable for this aspect of analysis."

Wing flutter has been a fatal problem almost since the birth of aircraft.

It is a self-excited vibration formed by the interaction of aerodynamic force, elastic restoring force and inertia force of the structure.

In other words, once flutter occurs, it is a self-continuous movement that does not require external force, and the vibration amplitude will become more and more severe, usually causing irreversible structural damage to the aircraft within a few cycles.

This problem is particularly evident on large aspect ratio wings.

"This..." Yao Mengna opened her red lips slightly and looked at Chang Haonan beside her. She thought about countless possibilities, but she never expected that she would go in the wrong direction from the beginning.

And such a mistake was pointed out by an undergraduate almost without thinking.

Almost her entire worldview was shaken.

For a moment, Yao Mengna even began to doubt whether she had ever attended this university.

Chang Haonan quickly spoke again:

"The large aspect ratio wing can be regarded as a beam wing in structure, so the unsteady aerodynamic force can be calculated by the dipole grid method based on subsonic speed. According to the linearization theory, the unsteady linear small perturbation velocity potential One of the basic solutions to the equation is the acceleration potential dipole. Therefore, for a wing that vibrates simply harmoniously in the airflow, an acceleration potential dipole Δp/p can be distributed on the wing. At this time, the normal force on the wing is The wash velocity amplitude must satisfy the corresponding vibration boundary conditions, so that Δp can be solved. Of course, this method is only suitable for linear problems."

Chang Haonan, who noticed Yao Mengna's stop, also stopped and looked back at her: "Do you understand?"

This tone again...

Yao Mengna's breathing suddenly became heavy.

My fists were hard.

but……

If you are not as skilled as others, you will be at a disadvantage.

She finally chose to reconcile with herself.

"I understand. Since we have to use the dipole grid method, wouldn't it be better to use the MSC.NASTRAN software?"

Yao Mengna was able to deeply participate in the big project of the research group in her second year of Ph.D., so she is certainly not an ordinary person. Before, she was just the tip of the iceberg. Besides, the dipole grid method is not a new theory. Now that she is awakened, she quickly understands it. understand Chang Haonan's meaning.

She felt that she should have found a way.

"It seems that my college experience was not in vain..." Yao Mengna comforted herself in her heart.

However, Chang Haonan's next sentence poured cold water on her newly ignited hope: "The default MSC.NASTRAN should not be easy to use. If you really want to do it well, I'm afraid you need to modify it with DAMP language rules. The solution sequence provided within the software can only be developed through secondary development, but if I can’t see the actual problem, I probably won’t be able to tell you anything more specific.”

"..."

Yao Mengna looked up at the bright moon in the sky. Although it was already late May, she felt that her mood could be described in one lyric.

Snowflakes are falling and the north wind is blowing

The world is vast~~~