Siheyuan: I eat melons while doing scientific research

Chapter 1210: Too much, surrender! (5k)

It's no wonder that after Gao Zhendong's explanation, Engineer Hong and his team really got a more intuitive understanding of the sound-absorbing tiles, and they felt that it wasn't that difficult to make.

At least if you have one of these four types of tiles, then based on the known characteristics, it won't be a problem to try to get one or two of them. For example, the Alberich material is not good for sound absorption, but it doesn't seem so useless for vibration damping and sound insulation.

This is like taking apart a car with good NVH features. There are vibration damping plates on the bottom of the cabin, and sound-absorbing cotton on the engine compartment partitions and hood. Their functions are different, but ultimately they are all for NVH.

Gao Zhendong is sure that even though the Russians will start installing anechoic tiles on their submarines next year, their research on anechoic tiles has definitely not reached such an in-depth level.

After explaining the four types, Gao Zhendong asked, "Comrades, should we make four types of tiles now?"

Engineer Hong thought about it and replied excitedly: "No need! I think given the limited conditions, we can just make three!"

Comrades are amazing. As long as we open the door to the treasure, they will find the treasure themselves. Gao Zhendong asked with a smile: "Which three do you think we should do?"

"Sound-absorbing tiles, damping tiles, decoupling tiles! Sound-insulating tiles and decoupling tiles are highly overlapping here, so there is no need to make them separately. The difference between the two is their function, but they can be the same in specific design and manufacturing."

Gao Zhendong nodded: "Well, that makes sense. Why do damping tiles and decoupling tiles overlap, but we need to make special damping tiles?"

For Engineer Hong, the master has shown him the way, and now it is up to him to practice. He is very confident: "Because the damping pad does not need to consider sound absorption, the structure can be much simpler and the cost is low. Moreover, if the submarine has a double hull, the damping pad is limited by the size between the inner and outer hulls and cannot be made very thick. Therefore, it is necessary to specially research a damping pad with high damping and low thickness, and it is not difficult to do this."

Double-hull and single-hull hulls were once a major debate among military fans decades later, but in fact, each has its own advantages, but at least one thing is that for a long time, double-hulls were our main submarine structure. Engineer Hong also understood this, so he specifically considered the situation of double-hulled submarines.

As for the single-hull submarine, it is actually simple. Just stick the decoupling tiles on.

To put it bluntly, even if you just stick a layer of rubber sheet tightly on the bulkhead, it can provide a good damping effect. This thing can be said to be cost-effective.

At this time, the comrades truly felt how scientific it was to divide the functions of the anechoic tiles. If you want to do everything, you often can't do anything well. Under limited conditions and technology, professional people and equipment should do professional things. This rule is always useful.

Before they knew it, the team members realized that this had solved almost a quarter of the problem. And it was a complete solution!
The comrades were all happy, a good start!

Seeing the expressions of his comrades, Gao Zhendong smiled and said, "However, I can give you a suggestion. Add fillers to the sound-absorbing material, such as lead powder, aluminum powder, hollow glass beads, glass fiber and other materials, or even foam them in the middle to make small bubbles. This can transform the longitudinal waves entering the material into shear waves, which can increase the sound loss capacity of the material. This is useful for all types of tiles. Here I recommend glass fiber, which is cheap, has good process performance, and good results."

In fact, the reason why Gao Zhendong chose fiberglass is very simple. Apart from the reasons he mentioned himself, there is only one main reason - the tiles that the American guys first pasted on their nuclear submarines were made of added fiberglass.

Before entering the 21st century, Citibank was highly selective and trustworthy. As for the reasons, they were all conclusions drawn by Gao Zhendong after he got the answers.

Look, the cheaters are so amazing.

He was so happy, and his comrades were also so happy. Hurry up and write it down! Engineer Hong wrote down these materials one by one in his notebook, and then circled the word "fiberglass".

At this moment, he remembered that the comrade in front of him was a materials scientist. This occasional exposure of his talent made him sigh that professionals are really good. If Gao Zhendong hadn't mentioned this, he would have thought that the comrade in front of him was an acoustician.

However, Gao Zhendong gave him more surprises in terms of materials: "As for rubber substrates, in addition to natural rubber, you can focus on polyurethane. This material has good acoustic and process properties, and its acoustic impedance is easy to match with water. This suggestion is valid for all types of tiles."

Well, the problem of basic sound-absorbing materials has been solved at once, and the comrades feel as happy as flowers.

It's just that up to now, Chief Engineer Gao has not entered the real theoretical part. But Engineer Hong and his team are not worried. If Chief Engineer Gao doesn't master certain theories, he probably won't be able to come up with the above conclusions. The reason why he hasn't entered it yet is probably because he hasn't reached that stage yet. All they have to do is follow Chief Engineer Gao's pace.

As for how he, a materials scientist, mastered these theories and had the time and resources to research these things, it is unknown. Anyway, comrades just need to enjoy the results.

"Chief Engineer Gao, from an acoustic point of view, basic materials are important, but acoustic structure is also important, right?" asked Engineer Hong.

Gao Zhendong nodded: "Yes, that's right. So I considered two structures, one is simpler and the other is more complicated. The decoupling tile we just mentioned has already started to involve things in this area. Theoretically, the design of the decoupling tile is simpler than that of the sound-absorbing tile. Its sound insulation and vibration suppression performance are very good. As long as the occasion does not require sound-absorbing tiles, the decoupling tile can be used. Of course, where damping tiles can be used, it is better to use damping tiles to save money."

The comrades all laughed, saying that Chief Engineer Gao was very thoughtful.

Gao Zhendong continued: "The decoupling tile design is simpler because it does not have broadband sound absorption requirements starting from low frequencies, but only needs to absorb sound in the most obvious limited frequency band inside the submarine. Most of these frequency bands are medium and high frequencies. With good sound insulation and vibration damping performance, it can complete the task well."

After listening to Gao Zhendong's words, Engineer Hong said: "In theory, Alberich materials have the basis for decoupling tiles, but in dealing with the problem of multiple frequency points, further research is needed."

"Yes, considering that the main purpose is to absorb mid- and high-frequency sounds, it is more appropriate for decoupling tiles to use resonant cavities for sound absorption. In fact, we all know that when the resonant cavity absorbs sound, the diameter of the cylindrical hole in the material determines the material's sound absorption frequency band. So we might as well stack up sound-absorbing panels with resonant cavities of different diameters and separate them in the middle. Alternatively, we can use materials similar to Alberich to stack multiple layers, but with different resonant cavity diameters in each layer. In this way, we can meet the sound absorption requirements for sounds in a limited number of frequency bands."

As Gao Zhendong spoke, he drew two different structures on the blackboard. This kind of stacking game is very intuitive and easy to understand.

His words and pictures helped Engineer Hong find the direction immediately: "Yes, and each layer is staggered according to the resonance frequency and acoustic impedance matching. The layer close to the steel plate has the lowest resonance frequency. And like the Alberich material, a certain amount of small cavities are added to increase the flexibility and loss factor of the rubber material, further enhancing the effect of adding glass fiber to the base material as you just mentioned!"

The comrades are still very capable and can draw inferences from what they have learned.

At this point, Engineer Hong scratched his head and said, "But how big a resonant cavity should I choose? I haven't figured out how to calculate it. My theoretical foundation is still too weak. But it's not a big problem. At most, I can just give an exhaustive example."

Gao Zhendong smiled and shook his head: "If you use exhaustive methods, then you will have a hard time. You will be sick of doing experiments with different thicknesses and different perforation coefficients. It's not that you can't do it, but it's not necessary. This thing can still be analyzed using mathematical methods, and you can roughly calculate a basically reliable result. It will be much easier to do experiments based on this result."

"Really?" Engineer Hong's guess was verified. Chief Engineer Gao had indeed studied theoretical things a long time ago.

"Yes, but we will talk about this later. Now let's talk about the second structure, the non-resonant composite gradient structure. If this structure is designed properly, it can achieve broadband sound absorption performance from low frequency to high frequency. This structure is most suitable for the outermost sound-absorbing tiles."

Non-resonant composite gradient structure? The name sounds impressive: "Chief Engineer Gao, what does this structure look like?"

According to Engineer Hong's estimation, Chief Engineer Gao would most likely start drawing the picture when he heard this question.

But this time he guessed wrong. Gao Zhendong did not start drawing. Instead, he smiled and said, "Comrades, have you all learned calculus?"

This question is asked despite knowing the answer. All the comrades here have studied this. All of them are majoring in science and engineering.

"Yeah, what does calculus have to do with this?"

Gao Zhendong said: "In calculus, integration is to treat a figure as a series of rectangles stitched together to calculate the area. The same is true for this non-resonant composite gradient sound absorption structure..."

Having said this, he deliberately emphasized the word "gradually".

Engineer Hong understood the elegant meaning of the music and suddenly realized: "I understand. By stacking up resonant cavities with continuously changing radius and small enough change, like integration, we can obtain a horn-shaped cavity that has an absorption effect on a wider frequency band." Chief Engineer Gao's metaphor is really vivid, and it is a metaphor exclusively for comrades in science and engineering. However, it is not necessarily true that there are also people in the humanities who study calculus.

Gao Zhendong smiled and said: "The specific mechanism is not that simple, but we can think about it this way, which is more vivid and intuitive. I have done simulation calculations, and this sound absorption structure has good broadband sound absorption performance. But it should be noted that this speaker cavity is really a complete speaker shape."

"What is a complete horn shape?" Gao Zhendong's words left his comrades stunned. They could understand each word, but it felt weird when they were put together.

Gao Zhendong then drew a picture on the blackboard: "You all know about suona, right? It's the instrument that can be used from birth to death. Look, do you see this? The tail of this structure is really the same as suona, with the pipe at the back, not just a bell."

Chief Engineer Gao is good at making analogies, but this analogy sounds a bit weird, the comrades thought to themselves.

"Well, I see. What is the function of this bell?"

Gao Zhendong said the same thing: "We will talk about this later. Now you just need to have a basic understanding of this structure. The specific theory will be introduced later."

At this time, Engineer Hong suddenly found that the sound-absorbing tiles were not so difficult to make. At least in terms of technical route and specific plan, Chief Engineer Gao had almost solved it.

He has almost figured out the classification, materials, and basic theoretical structures of various types of sound-absorbing tiles. Although there are still many details that need to be studied, such as the production process, mechanical properties, specific structural composition, dimensions, etc., those can be solved slowly with the help of existing technical conditions. Even details like structure and dimensions can be solved with good results by using the exhaustive method.

However, for Hong Gong and others, theory is undoubtedly very important. Knowing the results but not the reasons behind them is not the result they want.

But their hopes were doomed to be dashed for the time being. Gao Zhendong looked at his watch and said with a smile, "Comrades, it's almost time. Let's eat first."

After a morning, the comrades gained a lot, but they also spent a lot of time.

As soon as Gao Zhendong finished speaking, several comrades from the Internal Security Department of the Third Branch Factory knocked on the door of the reception room and walked in with a pile of lunch boxes.

Gao Zhendong enthusiastically distributed lunch boxes to the comrades and said with a smile: "According to the convention, we should invite the comrades to the small canteen to have a good meal, but considering the specific circumstances of the comrades, it is not appropriate to go to a crowded place, so I asked the comrades from the internal security to go and get it, and everyone can make do with it."

The so-called specific situation is that the comrades' confidentiality level is relatively high, but they do not have people around them like Gao Zhendong, so it is better not to show up if possible.

As for the words "make do with it", Gao Zhendong was just being modest. Although they were all lunch boxes, the things in the lunch boxes were still made by Comrade He Yuzhu, the famous chef of the 17th Ministry of Machine Building's canteen, the number one wok chef of the Third Rolling Mill, a man who cultivated both Sichuan and Shandong, and a pioneer of self-heating food in the logistics of the three armed forces.

The comrades ate with great relish, their mouths drooling with joy.

"Comrades, do you think you need to take a break?" Gao Zhendong asked for his comrades' opinions.

Comrades, you look at me and I look at you, our eyes full of expectation.

Engineer Hong said, "Chief Engineer Gao, you go and take a rest. We are fine. Let's digest our harvest."

What this means is probably "If you want to rest, you can rest. We won't rest anyway."

Gao Zhendong shook his head upon hearing this: "If that's the case, then let's not rest. We'll continue to work hard, and there's still a lot to come."

What we want is more things, the more the better! Hong Gong and his team were very excited.

Gao Zhendong then introduced the basic theoretical knowledge and important parameters related to anechoic tiles.

Comrades may know it, or may not know it all. Anyway, Gao Zhendong doesn’t care about it. This is a systematic thing, and he can’t break it down and talk about it.

Fortunately, although most of the book is theory, precisely because it is pure theory, Gao Zhendong can understand it very quickly, and it is basically enough to teach his comrades.

Because he has a good brain, a wide range of knowledge, and is good at math.

"...For the sound absorption calculation theory of sound-absorbing structures, I have three types of methods..."

Although the content of this monograph is important, it is not very long, only about 200 pages, and a large part of it is not necessary to talk about it for the time being, such as some examples and charts.

Most of these charts are not suitable for discussion at the moment. One reason is that they have not reached that level or do not conform to the current situation. There is another important reason.

Some of these charts are anonymized. Some of the charts have coordinate systems drawn out, the meaning of the coordinates are also indicated, and there are curves, but there are no units or numbers. These things cannot be manipulated at all.

However, this situation made Gao Zhendong even happier. Those who understand will know what the charts and data that need to be desensitized represent.

Therefore, Gao Zhendong mainly talked about pure theories and mathematical formulas.

Students who have taken college courses know that when the teacher stretches the class quickly, he or she is really able to finish a book in a relatively short period of time.

Not to mention that the "students" here are all the top scientific researchers in this field. For a lot of knowledge, Gao Zhendong only needs to mention the beginning, explain the knowledge points used, and write the final conclusion.

As for the process, comrades can push it themselves.

"... We have already mentioned the analytical mathematical model. Whether it is a one-dimensional or two-dimensional model, it is a mathematical analysis method based on the principles of viscoelasticity..."

At this time, many comrades were already a little overwhelmed. Damn, the knowledge was all good stuff, and Chief Engineer Gao taught seriously, but he gave a little too much.

The result of the epiphany is indeed refreshing, but the process seems a bit unbearable.

The brand new knowledge, which was not particularly difficult but had very complicated principles and calculations, made the comrades feel a little overwhelmed.

Including Engineer Hong, he now regretted not taking a break just now. He remembered at this moment that although Chief Engineer Gao in front of him has profound skills and extensive knowledge, he is younger than most people here!
They were careless. Chief Engineer Gao's ability made them ignore the fact that he was much older and more energetic than theirs.

When it was almost time for dinner, Engineer Hong raised his hand and said, "Chief Engineer Gao, let's go back to the guesthouse and spend two days digesting today's gains. We are afraid that we may miss something. At the same time, we should also find out what we didn't understand today so that we can come back to consult you and lay a more solid foundation for our work."

The implication of his words was probably surrender, surrender. If he raised his hands, it would better reflect the meaning of his words.

(End of this chapter)