Before entering Cai Xingquan's scientific research team, Du Xiaodi only had a junior Chinese credential, but he had a more solid foundation than Feng Xiaochen, a junior high school student. For more than a year, she worked as a welding experimenter in Cai Xingquan's team, and under the guidance of several graduate students assigned by Cai Xingquan and Feng Xiaochen, she tutored high school and university courses, and finally was admitted to Cai Xingquan's graduate school with excellent results.

The subject that Cai Xingquan handed over to Du Xiaodi this time was quite difficult. Du Xiaodi's self-blame is actually being demanding of himself. Although the Rosenthal-Rykalin analytical formula mentioned by Feng Xiaochen has been mentioned as early as the 40s, considering the complex boundary conditions, heat source distribution, nonlinearity and other problems, it is still a serious challenge for scholars with excellent mathematical skills to use this formula to solve practical problems.

Because of the great difficulty of deriving formulas, most of the solutions to this problem in practice are numerical simulations, that is, using various numerical values to try repeatedly and collide with the final result. For example, if you haven't learned how to open a root number, then if you ask for the square root of 2, you can only try it.

You can start by assuming that the square root is 1.4, but the square of 1.4 is 1.96, which is smaller than 2, so it needs to be increased. Then suppose that the square root is 1.5 and its square is 2.25, which is greater than 2. In this way, you can take the compromise point between 1.4 and 1.5 1.45, and calculate that the square is still larger than 2, and then the compromise is 1.425...... , and after repeated attempts, you can finally find a result that is relatively close to the real one, such as 1.414.

That's how numerical simulation works. But to do numerical simulation, you have to count some simple calculations many times, and the workload is very scary. The widespread use of numerical simulations came after the invention of computers, because computers are tireless, and they are able to follow a program and try again and again to do things that these humans cannot do.

Formula derivation and numerical simulation are the two methods of solving equations. Du Xiaodi didn't understand these things in the past, but after more than a year in Cai Xingquan's scientific research team, he at least mastered this knowledge. The equations involved in the low-temperature welding process of 16MnR steel, which she was working on, were so complex that she thought from the beginning that she should do a numerical simulation. But numerical simulations require the use of computers, and this obstacle stumped her.

In this era, microcomputers have been widely used, and Cai Xingquan's laboratory has an IBM286 computer. But for complex numerical simulations, this computer is not enough, and you have to use a small or medium-sized computer. The computing center of the University of Technology has an IBM370 that can do these calculations, but the problem is that there are so many teachers and graduate students in the whole school who need to use this computer that the computing center has to assign machines to various departments, and you can only use it when it is your turn. In order to make the most of this computer, the computing center is scheduled 24 hours a day, but even at 12 o'clock in the middle of the night, the demand is in short supply.

Du Xiaodi belongs to Cai Xingquan's research group, Cai Xingquan belongs to the teacher of the Department of Materials, and the time assigned by the computing center to the Department of Materials has to be distributed a second time among the teachers, and the time that falls under Cai Xingquan's name is very limited. Du Xiaodi knew this situation, so it was naturally inconvenient for him to compete with his teachers or senior brothers and sisters for these precious opportunities. Since the way of numerical simulation did not work, she thought that it was better to go back to the way of solving equations, and wanted to find the analytical solution of this set of formulas with her own efforts. But who would have thought that solving such an equation is not something that ordinary people can do at all, and there may be some hope for a mathematical genius like Gauss or Kolmogorov, and Du Xiaodi is just a welder with a junior high school background after all.

"Xiaochen, am I too stupid?" Du Xiaodi took Feng Xiaochen's arm and asked aggrievedly. She had been tossing and turning around with these equations for days, and she was exhausted, and finally had a chance to talk, and she almost cried.

Feng Xiaochen patted her arm and comforted: "Xiaodi, it's not that you're stupid, it's that you underestimate the difficulty of this matter. It has long been decided that this equation is impossible to solve. You see, these foreign literatures are also solved by numerical simulation, these people are all big-name professors, with deep academic skills, and there are doctoral and master's teams, even they can't solve the equations, how can you solve them?"

"Really?" Du Xiaodi asked, she pondered it carefully, and it seemed that Feng Xiaochen's explanation really made some sense. However, she was not relieved by this, she frowned and said: "However, if I don't solve this equation, I can't prove that the process we designed is better than the one used for comparison, although the photomicrograph can see the difference, but it is not possible without theoretical proof." ”

"You can do numerical simulations, why do you have to hang yourself on a tree?" Feng Xiaochen asked.

"Didn't I just say that we don't have the time. Du Xiaodi said.

Feng Xiaochen stroked her hair with a smile and said, "I have trouble finding a husband, haven't I told you many times? There are several large factories in Beijing that have our equipment systems, and they all have large or medium-sized machines imported from the United States. Their usual computing tasks are not heavy, so I contacted them and borrowed their machine, and there was no problem. Anyway, your project is also entrusted by the Heavy Equipment Office, which is not a fake public benefit. ”

"Really?" Du Xiaodi's eyes suddenly lit up, "Xiaochen, is it really not against the principle to do this?"

Feng Xiaochen shook his head firmly and said, "Absolutely not violating principles. In addition to your task, if you Professor Cai have anything that needs to be calculated, you can also take it, which is called the full use of resources. ”

"Great!" Du Xiaodi smiled, and she said: "Since that's the case, then I won't be busy for now." I'll go to the vegetable market now and buy meat, and I'll give you stew to eat later. ”

"Forget it. Feng Xiaochen grabbed Du Xiaodi, who was about to change his clothes and go out, and said, "You are tired like this, your eyes have become panda eyes, so let's go to sleep first." I'll just take care of the cooking, and your task now is to sleep. ”

"Well, okay then. Only then did Du Xiaodi feel tiredness from the inside out, just like a person who had walked dozens of miles suddenly stopped, covered with indescribable exhaustion.

"I'll clean up my bed...... For the past two days, I slept on my desk. Du Xiaodi said embarrassedly, and prepared to clean up the materials on the bed.

Feng Xiaochen dragged her from behind, and it was a princess hugging her, hugged her, and said, "What else to pack up, you can go to my room to sleep, these materials will be sorted out when you fall asleep." Let's go, I'll carry you over. ”

"Don't!" Du Xiaodi protested, but at the same time stretched out his hand to wrap his arms around Feng Xiaochen's neck, making himself safer in Feng Xiaochen's arms.

Feng Xiaochen carried Du Xiaodi out of her room, came to his room, and put her on his bed, only to find that Du Xiaodi had fallen asleep deeply. Perhaps, she felt that Feng Xiaochen's embrace was safe and warm, which could make her forget all her worries at once.

Du Xiaodi slept from morning to evening, and when she opened her eyes, she smelled an enticing fragrance in her nose, which was the smell of stewed chicken.

Du Xiaodi came to the courtyard with his clothes on, and saw Feng Xiaochen sitting in the corner of the courtyard, with a small round table in front of him, and he was lying on the round table writing something. Hearing Du Xiaodi's movement going out, Feng Xiaochen raised his head and asked with a smile:

"Woke up, do you feel better?"

"Okay!" Du Xiaodi said a little embarrassed, she couldn't even remember when she fell asleep, she only felt that she had slept so soundly this night, and the tiredness accumulated over the past few days had been swept away.

"You wash up and get ready to eat. Feng Xiaochen said, "I went to the vegetable market in the morning to buy a chicken, which has been stewed for several hours, and I will make up for you." ”

Du Xiaodi smiled: "I don't dare to make up for it casually, I have gained several pounds in the capital for more than a year." If you continue to be fat like this, you won't be able to drill into the pipe in the future. ”

Most people don't use drilling pipes as a goal to keep in shape, but Du Xiaodi is a welder, and she is a welder who works on pressure vessels, and drilling pipes is her most common job. In many cases, female welders are stronger than male welders because they are more slender and able to drill into small spaces for electric welding operations, while male welders with big shoulders and round waists can only sigh at such times.

Hearing Du Xiaodi talk about drilling pipes, Feng Xiaochen asked with a smile: "You have all studied for graduate school, do you still want to drill pipes in the future?"

Du Xiaodi replied very seriously: "Of course I have to drill, I am a graduate student in electric welding, how can I lose my profession?"

"However, your current business is to calculate the heat equation of welding, Professor Cai probably won't burn electric welding, right?" Feng Xiaochen said.

Du Xiaodi said: "Professor Cai can burn electric welding, but he usually doesn't do much, and he is not very proficient. I told Professor Cai that no matter whether I am a graduate student or not, I will continue to work as a welding experimenter, in fact, I prefer to burn electric welding. ”

"Well, let's keep drilling the pipe, but I'm sure you won't be able to drill it one day. ”

"Why?"

"Because sooner or later, you're going to ......," Feng Xiaochen said this, pausing deliberately while gesturing a ball shape on his stomach with his hand.

Du Xiaodi didn't understand for a while, and after a long while, he realized what he was referring to from the expression on Feng Xiaochen's face, and he couldn't help but blush with shame. She pounced forward, slammed her fists into a violent blow, and scolded coquettishly as she struck:

“…… You're going to die!