The gating system and the overflow system were designed according to the casting structure during high pressure die casting(HPDC) process. The simulation was carried out by ProCAST software to visualize the injection ...The gating system and the overflow system were designed according to the casting structure during high pressure die casting(HPDC) process. The simulation was carried out by ProCAST software to visualize the injection chamber pre-crystallization and the flow of molten metal. The main work is to research four die casting process parameters, i.e. injection temperature, low-pressure velocity, high-and low-pressure velocity’s switching position, and high-pressure velocity. Experimental results show that the higher injection temperature and lowpressure velocity can mitigate the pre-crystallization of the injection chamber. However, when the low-pressure velocity exceeds 0.2 m·s-1, the air entrapment in the chamber occurs. Besides, when the high-pressure velocity is greater than 2.5 m·s-1, the overflow channel at the final filling position is covered by the liquid metal too early. Finally, the injection temperature of 650 °C, the low-pressure velocity of 0.2 m·s-1, the high-and low-pressure velocity’s switching position of 320 mm and the high-pressure velocity of 2 m·s-1 are obtained as the optimal parameters by the software simulation, which has been verified by actual production.展开更多
With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based ...With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10^(-6) when the signal-to-noise ratio is larger than-10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.展开更多
The mold friction(MDF)is an important parameter reflecting the lubrication between the mold and slab quantitatively.The mold/slab friction was detected using an online monitoring system on a slab continuous caster equ...The mold friction(MDF)is an important parameter reflecting the lubrication between the mold and slab quantitatively.The mold/slab friction was detected using an online monitoring system on a slab continuous caster equipped with hydraulic oscillators.Wavelet entropy theory was introduced to describe the fluctuation characteristics of the MDF signal in order to quantitatively estimate the mold/slab lubrication.Furthermore,MDF signal and its wavelet entropy were analyzed under typical casting conditions,such as normal casting,different models(to control the relationship among the amplitude,the frequency and the casting speed),changing casting speeds and breakout.The results showed that the wavelet entropy could accurately reflect the overall changing trend of the mold friction as well as the local variation features.Besides,the wavelet entropy of the hydraulic cylinder force and the MDF was compared and analyzed,and the relationship between them was further discussed.展开更多
基金financially supported by the National Key Research and Development Program of China(No.2016YFB0301003)
文摘The gating system and the overflow system were designed according to the casting structure during high pressure die casting(HPDC) process. The simulation was carried out by ProCAST software to visualize the injection chamber pre-crystallization and the flow of molten metal. The main work is to research four die casting process parameters, i.e. injection temperature, low-pressure velocity, high-and low-pressure velocity’s switching position, and high-pressure velocity. Experimental results show that the higher injection temperature and lowpressure velocity can mitigate the pre-crystallization of the injection chamber. However, when the low-pressure velocity exceeds 0.2 m·s-1, the air entrapment in the chamber occurs. Besides, when the high-pressure velocity is greater than 2.5 m·s-1, the overflow channel at the final filling position is covered by the liquid metal too early. Finally, the injection temperature of 650 °C, the low-pressure velocity of 0.2 m·s-1, the high-and low-pressure velocity’s switching position of 320 mm and the high-pressure velocity of 2 m·s-1 are obtained as the optimal parameters by the software simulation, which has been verified by actual production.
基金Project supported by the National Natural Science Foundation of China(Nos.61431005,51409235,and 61401111)the Fundamental Research Funds for the Central Universities,China(No.201213004)
文摘With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10^(-6) when the signal-to-noise ratio is larger than-10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.
基金The project was supported by the National Natural Science Foundation of China(No.51204063)the Anhui Provincial Natural Science Foundation(No.1308085QE72).
文摘The mold friction(MDF)is an important parameter reflecting the lubrication between the mold and slab quantitatively.The mold/slab friction was detected using an online monitoring system on a slab continuous caster equipped with hydraulic oscillators.Wavelet entropy theory was introduced to describe the fluctuation characteristics of the MDF signal in order to quantitatively estimate the mold/slab lubrication.Furthermore,MDF signal and its wavelet entropy were analyzed under typical casting conditions,such as normal casting,different models(to control the relationship among the amplitude,the frequency and the casting speed),changing casting speeds and breakout.The results showed that the wavelet entropy could accurately reflect the overall changing trend of the mold friction as well as the local variation features.Besides,the wavelet entropy of the hydraulic cylinder force and the MDF was compared and analyzed,and the relationship between them was further discussed.
