Siheyuan: I eat melons while doing scientific research

Chapter 1237 Random Error (4k, 5k left)

Although the Russian ships from Viking City to here are available from June to September, as the first comrades to arrive on the island and endure the most harsh working environment due to their lack of experience, the plan at home is very clear: once the navigation is open, they will be picked up.

They have undertaken the most arduous and dangerous tasks and cannot be asked to work for any longer.

If the satellite camera in the sky was not in the wrong direction and was not equipped with a complex attitude adjustment system and loaded with enough fuel to "turn over", they would not have to be so anxious to start their work.

As for developing and launching a satellite specifically to turn over and take pictures, this is a bit difficult for us at the moment. After all, for star maps, the cameras on current satellites are not up to the task, and those that can handle the task must be newly developed. Without deep space exploration, the use of such satellites is somewhat narrow.

There is no way. Some promising work forms mean that the requirements for certain information are greatly advanced. We can't wait until the launch to load the data.

The comrades were ready to go and started working. While working, they talked about insignificant daily matters. One of them even took out a device that looked like a radio and started walking around.
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In a laboratory on the coast of Northeast China, a group of experimenters are conducting acoustic tube tests on a polyurethane material from the Department of Applied Chemistry.

"What's the situation?" Engineer Hong looked at the comrade who was coming over with the test report.

"Well, Mr. Hong, there is good news and bad news."

"Let me tell you the bad news first." Engineer Hong applied the principle of "good stuff should be stored at the bottom of the jar" to the fullest extent and decided to take the slap first and then eat the sweet dates.

"The results of repeated measurements of the material are not consistent and show a certain degree of randomness."

"Huh?" For Hong Gong, this news couldn't be worse. It meant that the test results might not be credible at all.

"So what's the good news?"

"The good news is that despite this randomness, the test of the covering material still shows a clear correspondence with the theoretical calculation. If this randomness can be eliminated, the performance of the covering material can be effectively tested."

"Hmm..." Engineer Hong thought for a long time and said, "Remove the covering material and test the steel backing directly! See if the reflection coefficient of the steel backing is around the ideal 1 without the material covering it."

According to their ideal covering material testing requirements, the sound reflectivity of the backing material of the covering material should be 1, that is, it is an absolute rigid body, reflecting as much as it comes. Only in this way can the specific parameters of the covering material be measured.

However, those who have studied kindergarten physics know that absolutely rigid bodies do not exist, so they chose a steel backing, and the thickness of the backing is positively correlated with the wavelength. Under this condition, the level of an ideal backing can basically be achieved.

Now Engineer Hong wants to know what specific role this steel backing plays in the measurement and how much error it introduces.

His thinking is sharp.

Not long after, the comrade in charge of the test came back with a report: "Engineer Hong, we found the reason. You are amazing! The test data of the bare steel backing showed randomness in repeated tests, and the analysis showed that this randomness was closely related to the randomness of the data in the acoustic covering material."

"Hiss..." Engineer Hong took a breath of cold air. This was the situation he least wanted to see. The necessary testing conditions were the culprit that introduced the error.

"Have you analyzed the reasons?" he asked the comrade in charge of the experiment.

"We have analyzed it and think... it's probably because the thickness of the steel backing is not enough." Since the data is random, the weight of the steel backing may not be enough to form an absolute rigid body that simulates the ideal backing?
"Not thick enough? We have already calculated the thickness according to the sound wave frequency of the test. If we want to make it thicker, it will be impossible to operate. For the 1.4kHz sound wave test, the backing needs to be nearly 900 mm thick, which is already a very difficult task."

It should be known that the sound tube is installed vertically, and the test object composed of backing and covering materials should be placed on the top of the sound tube. It needs to be frequently taken up and down, turned over and over. For an almost entirely steel test object assembly that is several hundred millimeters thick and 900 millimeters high, these operations are actually extremely difficult.

"Enlarge?"

"Increase it? There is no use in increasing it, and it will only move further and further away from an 'absolute rigid body'." For a piece of material, the larger the area, the better the elasticity, and the further away from an "absolute rigid body" it is under the same thickness.

"What should we do?"

"What should we do? The first priority now is to find out why the steel backing, which is theoretically capable of achieving total acoustic reflection, actually has such large fluctuations in the measured reflection coefficient." Engineer Hong said with a frown.

But this is really difficult. The comrades sat together and spent a long time looking at multiple sets of test data, but still couldn't figure it out.

"How about... Engineer Hong, should we make a phone call to Beijing? Isn't there a comrade there who is very knowledgeable about water acoustics?"

"This..." Engineer Hong felt a little embarrassed. He had just come back from someone's class, where the other person taught him everything he knew in theory. However, not long after he came back, he was stumped by technical details.

Seeing his expression, a colleague in the group said, "Engineer Hong, it's not shameful to do research. Besides, we learned these things from others..."

Oh, that seems to be the case. It’s okay then.

"Well, okay..."

When Gao Zhendong received the call in his office, he was a little surprised. The result came out so quickly? Not really. Even if he had guaranteed it, he believed that his comrades would not be satisfied with it.

Moreover, even if you want to get a guaranteed bottom line, it still requires a rigorous testing process to prove that it can really guarantee a bottom line before you can move on to the next step.

In any case, they shouldn't report the good news to me now. If that's the case, then there's a high probability that something has gone wrong.

"Engineer Hong, is there any problem?" Gao Zhendong went straight to the point.

Listening to Gao Zhendong's voice, Engineer Hong felt a little embarrassed: "It's like this, there was a problem with our experiment..."

Gao Zhendong felt relieved when listening to Engineer Hong's story on the phone. It turned out that he had indeed encountered this problem.

It's not that he's gloating, nor is it that he deliberately didn't say anything last time. The main reason is that this matter can't be discovered until the specific test is done, so Gao Zhendong couldn't say it at that time. Moreover, this phenomenon may not appear with different test methods.

Now that they have asked, I can "analyze" something based on their description.

"Let me think about it..."

Gao Zhendong pretended to think about it on the phone, since the call would not be disconnected anyway.

"That's right. I think there are two main reasons. One is that there is a certain randomness in the fixed state of the combination of your backing and covering materials each time." While Engineer Hong was anxiously waiting, Gao Zhendong finally spoke.

“Randomness? It’s always different every time…” At this point, he suddenly realized that since he could only say “almost”, then for the experiment, this “almost” might be very different.

You have to know that the large and heavy assembly is fixed by a set of movable parts through self-locking and other means. For the experiment, this method is inherently random.

"I see. What do you think is the second reason?"

"The water acoustic impedance of the steel backing is too different from that of water, which will also introduce errors. Relatively speaking, the samples tested by the acoustic tube test should be materials such as rubber and plastic that are not much different from the acoustic impedance of water. Using an acoustic tube to test will also cause large errors when you measure the bare backing, and this error is a systematic error and cannot be eliminated."

This made Engineer Hong frown even more tightly on the other end of the phone.

Systematic errors are difficult to eliminate unless the error source is drastically improved. It is a diode state that either does not exist or cannot be removed.

"Chief Engineer Gao, do you have any suggestions on this?" Engineer Hong did not hesitate. Things had already happened and the problem was right here, so there was nothing to be embarrassed about.

"I do have a suggestion. Don't test the one with backing. Just test the covering material itself." Gao Zhendong almost scared Engineer Hong as soon as he opened his mouth.

"Mr. Gao, isn't this a bit too revolutionary? If there are no reflected sound waves, wouldn't that be disadvantageous to the acoustic test? After all, some energy is lost."

Gao Zhendong smiled and said, "You should know that no matter how we improve it, we can never achieve an absolutely rigid body, right?"

"Correct."

"So how do you deal with the difference between this part and the theory?"

Engineer Hong answered quickly, as he was familiar with the matter: "As long as there is a correspondence between the test results and the actual data, the law can be reflected and the results we need can be obtained to some extent. Moreover, we can obtain data that is close to the results we want through physical experiments and mathematical methods."

As long as it is approximate, it is sufficient for engineering applications in many cases. What I want now is certainty. As for whether the data is weakened, as long as I can find the conversion relationship, it is not a problem.

At this point, he opened up the entire chain by himself and was very excited.

Otherwise, why do we need to consult experts? Just a simple word from them can help you clear up the fog and gain enlightenment.

"Mr. Gao, thank you so much! I will just..."

At this point, he got stuck again: "However, in this case, it is impossible to perform a pressure test, right? Measuring low frequencies is easy, but high frequencies..."

Originally there was a pressure test, in which one end of the sound tube was sealed by the sound transducer, and the other end was sealed by the strength of the steel backing. Now that the steel backing is gone, as soon as pressure is applied, the material being tested at the other end of the sound tube will not be able to withstand the high pressure no matter what, so it will collapse as soon as the pressure is applied.

When measuring low frequencies, we have to use the continuous sound wave traveling wave method/standing wave method that Chief Engineer Gao mentioned last time. One of the advantages of this method is that it can perform pressure testing. However, in order to measure high frequencies and obtain accurate data, we have to use the pulse method, which is troublesome.

Gao Zhendong smiled and said, "We can do without steel backing, but that doesn't mean we can't use steel seals. Can't you just put the test piece somewhere in the middle of the pipe? There is water below the test piece and pressurized air above it. In this way, there will be no reflected waves interfering with the data. Wouldn't that meet the requirement of no backing?"

Engineer Hong felt like a fool at this moment, but he was also happy like a fool: "Yes, yes, I was foolish. Chief Engineer Gao, thank you so much, I have to go to work now. If you are free later, come over to our place and we will treat you to fish."

It was not fashionable to call it "seafood" in those days. Seafood, which was later regarded as a high-end delicacy, was now more of a nutrition to fill the stomach. Going back to its basics, it was just fish, nothing more than sea fish.

After hanging up the phone, Engineer Hong shouted, "Comrades from the equipment team, come over here, let's discuss how to modify the equipment!"
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"Mr. Gao, we are here again!" The director of Beijing Automobile Factory shook Gao Zhendong's hand enthusiastically.

They finally finished the celebration of "exporting 2000 cars", but they were still thinking about the agreement with Gao Zhendong, who had a lot of suggestions he wanted to communicate with them.

But not only him, but also the chief engineer of the 11th Ministry of Machine Building came. This was a bit strange, because he was in charge of all technical aspects, and this was just a small part of the car.

The chief engineer of the 11th Ministry of Machine Building also shook Gao Zhendong's hand and said with a smile: "Commissioner Gao, I am here today with two tasks. One task is to learn. Don't worry about me, just do what you should do with the Beijing Automobile Factory. I am just here to listen." "Just listening" is a metaphor, which means that I will not interfere with or influence your communication, and I am here purely to learn.

"Another task is to bring you a little gift from our department. You have made such a great contribution to our automobile industry, and our department cannot just turn a deaf ear to it. This is the certificate and medal of our department's 'Gear Award' special prize, as well as the medal and certificate of our 11th Ministry of Machinery's advanced worker. I originally wanted to invite you over and thank you at the award ceremony, but the Defense Work Committee gave a heads-up, so I had to let you down a bit. So our leaders specially sent me here to express our sincere gratitude to you."

Needless to say, everyone knows what the Defense Work Committee is saying.

Although Gao Zhendong is not from the 463th Ministry of Machine Building, needless to say, a engine is enough to wipe out all sectarianism. Whoever wants to show off can come and compete with him.

The 11th Ministry of Machine Building knew very well that if they did not create an original gasoline engine of world-leading level, it would be bullying. If they could imitate an engine well without losing its main parameters, or create an original engine that was not too bad, it would be considered a capability.

Moreover, they have the results of the two-axis CNC milling machine in their hands. Although it is only in the promotion and trial period now, this thing has played a big role in the 11th Ministry of Machine Building. Apart from anything else, it has played a huge role in engine processing.

Although the engine is very complex, the two-axis milling machine can still play a role to some extent. If the number of axes is not enough, technology can make up for it. As long as the program is designed properly, it can still solve many problems.

(End of this chapter)