Research starts with PhD students

Chapter 108 I found the reason!
Check for half an hour in the morning and calculate for half an hour in the afternoon.

I will also help other members of the team during the process, and the total working time will not exceed two hours.

Zhou Bing, Zhang Zhihui and others were too embarrassed to ask Zhang Shuo for help.

They are so old now, and they have to ask young people for help with mathematical calculations. It is embarrassing for them, so they prefer to do the calculations themselves.

Zhang Shuo's job is still very easy.

The rest of the time, I will think more about the problem of Pogo vibration caused by jet power. After six days of research, the mission progress has reached '71%'.

The rocket expert group of the Second Academy of Aerospace Science and Technology is also studying this issue. Their research is based on data calculated by the power group.

The calculated data describes the injection position of each part of the rocket engine, along with the energy and thrust changes generated by time changes. This is used to transform the structure of the propellant delivery pipeline and the nozzle to make the unstable injection more stable.

This part of the work will not only be done by the rocket expert group, but all experts will have to be gathered together to study it in the end.

Zhang Shuo is also one of the invited experts.

Du Bin invited Zhang Shuo not just to do power calculations, as calculations were only preliminary work. After the calculations were completed, the summarized data had to be analyzed, and then they would work together to study improvements to the structure of the propellant pipes and nozzles.

There is no fixed method for this kind of research.

Even if an improvement plan is drawn up based on the summarized data, it may not necessarily have a positive benefit on the pogo vibration problem. Everyone expresses their own opinions on the improvement, and finally the rocket expert group finalizes the improvement plan.

The research on the improvement plan starts with the summary of the power group data. After the data summary work is completed, a technical meeting is held.

There were dozens of people attending the meeting.

They include the rocket expert group, as well as the heads of various work units and technical team leaders, and the others are experts who were invited to work.

Zhang Shuo arrived at the conference hall early and met Sheng Zhenhua and Deng Qiang again. They sat together and talked about their work over the past few days.

There's not much to say about Zhang Shuo's work, it's just constant calculations.

Sheng Zhenhua and Deng Qiang's work is even more interesting. They assist in jet power simulation, which means inputting some calculated data into the computer to simulate the jet conditions during rocket launch.

"Any progress?" Zhang Shuo asked curiously.

Deng Qiang pursed his lips and whispered, "Basically, there is nothing to find. It seems that we can't find the cause just from the spray."

Sheng Zhenhua followed up, "The Pogo vibration problem is too complicated. Often the main cause is inside the rocket, including the engine and propellant, which can cause Pogo vibration."

"They wanted to find the cause from the jet power, but it seemed too difficult."

He then said to Zhang Shuo, "This time you come here, just watch and listen more. It's a rare opportunity to participate in the research of such a major issue."

"This is also considered as doing something for the country. It will be recorded in the archives and will be very beneficial for future development."

After he finished speaking, he leaned over and whispered, "When in a meeting, listen more and talk less. Don't seek to achieve anything, but seek to avoid making mistakes..."

Zhang Shuo listened and nodded, but still asked, "Why?"

Sheng Zhenhua said, "Our computer team's simulation did not find any problems, which means that the power team's calculations may not be accurate. In other words, the rocket expert team's initial judgment may not be accurate."

"If you make a suggestion and it's not adopted, that's fine. But if it's adopted and the transformation doesn't work, you don't have to take responsibility, but the impact will still be bad. It's better not to make a suggestion."

He sighed lightly, shook his head slightly, and said carefully, "In short, it's best not to make suggestions..."

Zhang Shuo nodded thoughtfully.

……

The meeting started.

The meeting was chaired by Zhou Yongchang, chief engineer of the large launch vehicle project.

He talked about the serious pogo vibration problem that occurred during the test firing experiment, talked about the work in the past week, and thanked all the invited experts for coming.

The next step is to get straight to the point.

Du Bin took the stage and showed everyone the summary of the power group's calculation data. "In the past week, we have done a lot of calculations on rocket jet propulsion. Now we are showing the key parameters and analysis results."

Data charts, as well as several curve graphs and distribution diagrams were displayed on the projection screen.

He explained them one by one.

"This is the distribution diagram of the injection fluid. We can see that the injection fluid remains stable and the deviation is in line with expectations, but the injection hot fluid shows intermittent fluctuations, which may be related to the performance of the engine."

"But normally, intermittent fluctuations would not cause such a large pogo vibration in the rocket."

"Next is the pressure distribution..."

Du Bin explained each chart and everyone in the meeting room listened attentively.

Zhang Shuo also learned about the power group's calculation data, and he found that the data was helpful for research.

As Du Bin explained, the progress of the task continued to improve.

[Task 0.532, progress +%. ]

[Task 0.377, progress +%. ]

[Task 0.3, progress +...]

After Du Bin's explanation, three experts came to the stage and talked about engine injection, propellant pipeline transportation, computer simulation and other issues. Next, they conducted various analyses and everyone could raise their hands to speak and talk about their ideas.

Zhang Shuo listened very carefully the whole time.

He really seemed to be here to learn, just to be a qualified listener, but in fact, he was constantly thinking in his mind.

After combining a lot of data, the problem of jet-powered pogo vibration seems to have become clear.

He was thinking, and suddenly took out a pen and paper to start calculating.

Sheng Zhenhua noticed his movements and asked in confusion, "What are you calculating?"

Deng Qiang also looked over.

"Calculate the key points of the jet power causing the pogo vibration." Zhang Shuo gave a simple explanation and then plunged into the complex calculations.

Sheng Zhenhua and Deng Qiang looked at each other in confusion.

On the other side, Zhou Yongchang, Du Bin and several technical leaders were discussing in low voices while listening to other people's speeches.

Zhou Yongchang frowned, full of worry. "I can't find the key problem! I thought I could solve it by adjusting the nozzle, but I found nothing in the calculations."

Du Bin shook his head and frowned, "We have studied all the data and everything is normal. Do we have to add a pressure accumulator? That will increase the weight of the rocket, and the effect may not be very good."

There are accumulators inside current rockets. Accumulators are devices used to study pogo vibration problems. They can change the natural frequency of the propellant piping system and eliminate the effects of longitudinal coupling vibration instability by changing the frequency and reducing the amplitude. In addition, energy accumulators can effectively absorb the energy generated by fuel vibration, thereby avoiding pogo vibration.

Du Bin said that we need to add accumulators, which means increasing the number of accumulators.

This method is definitely effective, but there are already accumulators inside the rocket, and there are more than one, so increasing the number may not be effective.

"The most important thing is to find out the root cause of the expansion of pogo vibration!" Zhou Yongchang said with a sigh.

It’s not easy to find the reason.

The structure of large launch vehicles is too complicated. Perhaps the problem does not lie with the jet power. Looking for the cause from the inside will make the problem more complicated.

Zhou Yongchang felt a headache as he thought about it.

In the past week, he slept no more than five hours a day, analyzing various data to find out the problem.

As a result, nothing was found.

At this moment, a young voice suddenly came over, "I found the reason!"

Zhou Yongchang looked over with confusion, and his first impression when he saw Zhang Shuo standing up was "so young".

The vast majority of people at the scene were over 40 years old, with some relatively young people firmly over 30, and faces in their twenties standing out.

Zhou Yongchang also knew who the other party was.

Du Bin told him that he had invited a very young computational mathematics expert, Zhang Shuo, who frequently appeared in the media and had completed research on general algorithms for PDE equations.

Others also looked over.

"What did you say just now?" Zhou Yongchang asked.

Zhang Shuo stood up with a serious expression and said seriously, "In terms of jet power, I have found the cause of the increased pogo vibration. I have calculated the key location, which is on the exit cone of the nozzle."

This sentence leaves most people confused.

The data of the power group has been summarized. If the problem could be found through calculation, wouldn’t it have been found long ago?
Why do you suddenly say that?

Exit cone?
What does it matter?
The exit cone, to put it simply, is the inverted conical metal disk under the rocket, which controls the hot flow from the nozzle to spray in one direction.

Zhang Shuo handed the calculation content to Deng Qiang and signaled Deng Qiang to hand it over to the rocket expert group in front.

Deng Qiang took it and handed it over immediately.

The calculation results were sent to Zhou Yongchang, who immediately started to read them carefully. After just a quick glance, he exclaimed in amazement, "Resonance at the same frequency!"

"That's right!"

Zhang Shuo said, "After the rocket ignited, the expansion section of the exit cone experienced a frequency resonance phenomenon, which is also the reason for the severe pogo vibration."

"The same-frequency resonance of the expansion section of the exit cone will trigger a series of chain reactions inside the rocket, causing the originally mild pogo vibration to become extremely severe. As the rocket takes off, the amplitude continues to expand under the conduction effect."

After Zhang Shuo finished speaking, everyone in the meeting immediately started discussing.

"This is possible. The resonance at the nozzle and the conduction effect will definitely greatly increase the pogo vibration problem."

"This is the best case scenario. There are countless ways to improve it."

"The question is, how did he calculate that?"

"He must be Zhang Shuo, right? He has a general algorithm for second-order PDEs, and a lot of physics algorithm results. He is really extraordinary!"

"A bunch of experts at the Second Hospital couldn't find the problem. How did he calculate it?"

"Whether it's right or not, it's impressive to have the guts to speak up..."

"..."

(End of this chapter)