Research starts with PhD students

Chapter 106 Arrival at the base, Rocket's Pogo vibration problem!

"Is there something wrong with the Second Academy of Aerospace?"

"What exactly happened?"

After Sheng Zhenhua finished speaking, Tan Youming couldn't help but ask in confusion.

Sheng Zhenhua said, "It seems to be a problem with the test launch of a large rocket. I don't know the details. Professor Du Bin just asked us to go over."

He asked Xiang Zhangshuo, "Didn't you receive the call?"

Zhang Shuo shook his head and subconsciously scanned his phone, and found that there was an unknown call coming in.

When the call was connected, the person on the other end asked, "Is this Professor Zhang Shuo?"

"I'm Zhang Shuo, hello."

"I'm Du Bin from the Power Group of the Second Academy of Aerospace. Do you remember me? We met at Soochow University."

Du Bin continued, "I'm calling to invite you to come to the Second Academy of Aerospace Science and Technology. We have encountered some problems and urgently need experts in computational mathematics and dynamics."

"When?" Zhang Shuo asked.

"The sooner the better!"

Zhang Shuo talked to Du Bin for a few more words, put down the phone and said to Sheng Zhenhua, "It seems that Professor Du is really anxious..."

"Let's go then!"

It was not only Sheng Zhenhua who went to the Second Academy of Aerospace Science and Technology, but also Deng Qiang from the Institute of Science and Engineering, and Zhang Shuo and his group, a total of three people.

They went not to the research institute of the Second Academy of Aerospace Science and Technology, but to a scientific research base near a rocket launch base.

The three flew to Xijing.

On the way, Sheng Zhenhua also said, "I guess something went wrong during the rocket test launch."

He said to Zhang Shuo, "Deng Qiang and I are involved in the computational simulation of jet propulsion. You may go to the power group. Du Bin is the head of the power group of the Second Academy of Aerospace."

Zhang Shuo had never participated in this kind of work before. He asked in confusion, "Go to the power group and be assigned some computing work?"

"Maybe." Sheng Zhenhua added, "It's just a guess. I haven't encountered such a situation before."

The flight arrived in Xijing.

After walking out of Xijing Airport, they got on the car sent by the Second Academy of Aerospace Science and Technology to pick them up, and it took two hours to reach their destination.

This is a scientific research base very close to the rocket launch base. From the outside, it looks like a very empty factory. The car entered the main gate of the base and drove for another two or three kilometers before we saw a few office buildings.

The car stopped at the main entrance of an office building.

Zhang Shuo, Sheng Zhenhua and Deng Qiang got out of the car and waited for a while before seeing Du Bin coming out.

Du Bin led the three people into the office building and introduced the situation along the way. "A few days ago, we conducted a test launch of a large carrier rocket and found a serious Pogo vibration problem."

"Its severity has reached a level that could directly affect the rocket's normal separation at high altitude."

"The expert group believes that they can try to adjust the nozzle structure, but they are not sure. The rocket's Pogo vibration is a difficult problem in the world's aerospace industry. The structure of large launch vehicles is too complicated, and no one can come to an accurate conclusion."

Zhang Shuo understood after Du Bin simply explained it.

Pogo vibrates!

If you have watched a rocket launch up close at the satellite launch center, you will have a common feeling: that is, when the rocket is ignited, the ground within a radius of several hundred meters will vibrate violently.

This is what it feels like to be on the ground.

The vibration reflected on the rocket is Pogo vibration, which means that the rocket as a whole will shake violently.

No one can be sure of the cause of Pogo vibration, but professionals believe that the pulsating thrust of each engine is difficult to maintain stability, resulting in the coupling of the rocket body structure and the dynamic characteristics of the propulsion system, resulting in longitudinal unstable vibration.

The underlying reason is that the pressure fluctuation of the propellant in the delivery pipeline causes the engine thrust pulsation, resulting in the vibration of the rocket body structure, which in turn aggravates the pressure fluctuation in the pipeline, forming a positive feedback loop and causing the structural vibration to be amplified.

Pogo vibration is a big problem.

If the Pogo vibrates severely, it is very likely to cause launch failure.

Even if the vibration is not serious and does not pose a threat to the rocket structure, the instruments and equipment on the rocket and the lives of the astronauts will be threatened.

Now is the serious situation.

Du Bin said that the situation was serious enough that it might affect the rocket's high-altitude separation, which would directly lead to the failure of the launch mission.

After conducting fault analysis, they found a large number of experts in computational mathematics and dynamics to conduct computational research on the dynamic balance of rocket engine thrust to see if the Pogo vibration problem could be reduced by improving the nozzle structure.

Reduction is not a solution.

Pogo vibration is bound to exist, and improving the nozzle does not necessarily solve the problem.

The structure of large launch vehicles is too complicated.

The rocket has been equipped with a variable energy pressure storage device, which is a special solution to Pogo vibration, but the effect is obviously not good.

After Du Bin finished his brief speech, he took Zhang Shuo to the power group.

Sheng Zhenhua's guess was quite accurate. Du Bin invited Zhang Shuo to join the power group to help with some complex calculations.

The expert group of the Second Academy of Aerospace Science and Technology believes that adjusting and improving the rocket's nozzle structure may help reduce Pogo vibration, but adjusting the rocket nozzle requires a large amount of dynamic calculations.

One is to ensure that the nozzle structure does not affect the thrust provided by the engine.

The second is to maximize stability in all directions, and in the case that each engine may have unstable pulsating thrust, stability can be achieved as much as possible by adjusting the nozzle structure.

The power group is an area that occupies half of a floor, and there are people working hard in every office.

Du Bin took Zhang Shuo to the second to last office and called out the person inside, "Zhou Bing!" A middle-aged man wearing round-frame glasses and looking a little bloated walked out.

Du Bin helped to introduce Zhang Shuo and assigned him to Zhou Bing.

Zhou Bing took Zhang Shuo into the office and said, "Professor Zhang Shuo, I have heard of your great name for a long time. You are really young."

"Excellent."

There were three people in the office, and they briefly introduced themselves to each other. Some of them were curious to see Zhang Shuo, but they continued to be busy with their work.

Zhou Bing said directly, "Our team is already overwhelmed. You are really a timely help. I will get straight to the point."

He took out a piece of paper with a bunch of written equations on it. "These calculation problems are assigned to us. You can do them according to your own needs. Make sure to ensure accuracy."

He said with a light breath.

The power group needs to solve comprehensive problems and will assign a large amount of calculations to the following groups.

Their team was short of one person before, but there was a lot of work to be done.

Now there is one more person, Zhang Shuo, who is said to have a good level of computational mathematics and has published relevant papers in top journals, but his computing ability is also uncertain. In any case, it is always good to have one more person.

Zhang Shuo found an empty desk and sat down. He turned on his computer and began to read the contents on the paper.

In short, it's just a bunch of complicated equations.

These equations have a common characteristic, which is that they have serious nonlinear characteristics or are very complex.

Another one is the set of fluid dynamics equations.

Zhang Shuo felt a bit of a headache after taking a look at it. Similar equations or systems of equations need to be calculated using numerical methods, and the requirement is to be as precise as possible. No wonder so many computational mathematics experts have to be found.

He pressed his forehead hard and had no choice but to start working.

Before officially starting work, use the system to create a task——

【Task 1】

[Research project name: Numerical solution of partial differential equations (difficulty assessment: E). ]

(The mission can be upgraded to C level.)
【Progress: 0.301%.】

(The task can be canceled. Currently, the number of scientific research coins required to cancel the task is 0.)
(The remaining progress requires 1 scientific research coins.)
"One question, one research coin?"

Zhang Shuo wanted to complete it directly by spending coins, but after thinking about it, it was too extravagant, so he decided to use scientific research coins to help improve his status.

【Scientific Research Coin-1】

Officially enter working state!
The numerical solution of partial differential equations does not rely on manual calculations, but still requires the assistance of computer software.

Generally, discrete transformation is performed with the aid of a computer first, and then methods are found to substitute numerical values ​​based on the results. Computers are also needed for calculation and analysis in the middle.

Zhang Shuo felt a headache looking at the question. In fact, it was not complicated for him. With the help of the scientific research coins and the direction correction of the task system, and the use of a computer, it took him about five minutes to complete the calculation of an equation, and the verification result was relatively accurate.

He then proceeded to build up the task and continue with the calculations.

It took about half an hour to complete the calculation of all the equations on the paper.

At this time, Zhang Shuo also had time to think about the problem of Pogo vibration.

The Pogo vibration of rocket launch is a world problem in the aerospace field. The research on Pogo vibration abroad has a history of 70 to 80 years, and the research in China has also lasted for more than 50 years.

Pogo vibration usually occurs when a problem is encountered and solved.

Some scholars also specialize in studying the theory of Pogo vibration. For example, Robin Brown has been dealing with Pogo vibration all his life and is also the founder of Pogo vibration research.

However, some of the theories Robin-Brown has studied and the solutions he has adopted to the Pogo vibration problem are still limited to a few types of rockets.

For example, his early research focused only on tandem rockets.

Later, as rockets became more and more complex, he proposed using the state space method to describe Pogo vibrations and obtain the criterion for the stability of Pogo vibrations by solving the eigenvalues ​​of the state space.

These theories are difficult to apply in practice.

Rocket technology is constantly evolving, and as the demand for launch increases, rockets become more and more complex.

At the same time, the cost of rockets is also increasing.

It is normal for the manufacturing cost of a large launch vehicle to reach hundreds of millions of dollars. After it is designed and manufactured, it is unlikely that major adjustments will be made internally, which means that the Pogo vibration problem cannot be solved from the inside.

The expert group is considering reducing the Pogo vibration problem to a certain extent by adjusting the nozzle structure.

Zhang Shuo was considering another issue. "Pogo vibration is related to the stability of engine injection, but it is also caused by many factors."

"For this test launch, can we find the cause of Pogo vibration from the perspective of jet power alone?"

He thought about it and created a task——

【Task 1】

[Research project name: Research on the problem of Pogo vibration caused by jet power in test firing experiments (difficulty assessment: B).]

【Progress: 0.003%.】

(The task can be canceled. Currently, the number of scientific research coins required to cancel the task is 0.)
(The remaining progress requires 200 scientific research coins.)
"A B-level mission worth 200 coins?"

“Not that high.”

Zhang Shuo thought, "It seems that I need to find some data on the rocket's engine performance and power, otherwise it will be impossible to complete the research."

(End of this chapter)