In this work, the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping (LENS) process is analyzed. Firstly, the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made. Then, the establishment process of the multi-physical field model of the melt pool is introduced in detail. It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile, space temperature gradient, and time temperature gradient. Meanwhile, some parameters, such as the 3D morphology and surface fluid field of the melt pool, which are not obtained in the online measurement experiment, are analyzed. Finally, the influence of changing the scanning speed on the profile, peak temperature, and temperature gradient of the single-line melt pool is also analyzed, and the following conclusions are obtained: With the increase in scanning speed, the profile of the melt pool gradually becomes slender; The relationship between peak temperature and scanning speed is approximately linear in a certain speed range; The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed, and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.
The methodology developed by Siddiqui and Drnevich (1995) for measuring soil water content and density using Time Domain Reflectometry (TDR) was extended for routine use in the quality control testing of compacted soils. The objectives of the study were to develop computer software to automate data interpretation and data reduction, develop prototype equipment for field use, compare the results of the TDR method with the sand cone and nuclear density methods on actual construction sites and develop draft specifications for ASTM and AASHTO. New prototype equipment was developed for compaction quality control testing. Waveform interpretation and data reduction were automated by incorporating developed algorithms into a WindowsTM based computer program that is used on a palm top computer connected to the TDR apparatus. Over 150 laboratory and field tests were performed to evaluate the TDR equipment and procedure for use in the determination of moisture content and density of compacted soil.Under field conditions it was shown that the TDR method is more accurate than the nuclear density gage in estimating water content when compared to oven drying, with standard errors of 1.1% and 1.8%, respectively. The ability to assess the accuracy of the TDR method for determining density was limited because the true density of the compacted soil is not known. The sand cone test was used as a basis for comparing the TDR and nuclear density tests on several sites while accepting that the sand cone test is not an exact method. The time required to perform the TDR test under field conditions is approximately 15 to 20 minutes. The sand cone test can also be performed in approximately 15 minutes, while the nuclear density test can be performed in approximately two minutes. The time required to complete the TDR test relative to the nuclear density test, is viewed as its greatest limitation. In general, the nuclear gage provides estimates of density and water content much more rapidly than the sand cone or TDR tests, is less accurate than the TDR test in estimating water content, and must be calibrated for a specific soil using sand cone tests. Moreover, the nuclear gage uses a hazardous source requiring operators to take safety training and leading to expenses associated with equipment maintenance and disposal. The sand cone test is time consuming, and can not provide estimates of water content. The TDR test is also time consuming, but does provide accurate estimates of water content. At the present stage of the research, the TDR test has not shown great advantage in the measurement of water content and density relative to the nuclear density test. However, progress is being made in the development of an approach to use other features of the reflected waveform, in addition to the apparent dielectric constant, within the interpretation process. It is anticipated that the additional information that can be obtained from the reflected waveform will allow a more accurate estimate of density to be obtained while eliminating the need to...
Compared RNG and Realizable model with experiment results in numerical simulation in inlet passage，conclusion Realizable k-e model is better reasonable in simulation can be pertained. In order to obtain ideal flow pattern ,Realizable k-e model could be using to simulate the passage and analyze flow pattern. Based on the simulation passage configuration can be modified to pursue ideal flow pattern, which can result in ideal inlet of pump and improve pump operating condition, vibration and noise in pumping station. Inlet passage flow pattern can be modified by using triangle piers,comparing different configuration can obtain the ideal results.
In recent years, many scholars have been committed to improving the security and practicability of chaotic image encryption. In addition, their proposed schemes mainly focus on two aspects, new or improved chaotic systems and new or improved encryption processes. However, according to cryptanalysis works of scholars, encryption processes of chaotic image encryption schemes deserve more attentions. In this paper, a recently reported chaotic image encryption scheme named the 2D logistic-adjusted-sine-map-based image encryption scheme is comprehensively investigated, and some security, practicability, and rationality problems are found. Therefore, we first point out these problems existing in the reported encryption scheme and make some improvements in practicability and rationality. Next, under the conditions of chosen plaintext attack, we cryptanalyze it and propose a corresponding attack algorithm. For our attack algorithm, simulation test results show that it can completely recover plain images without knowing any secret key related information. Finally, we also present some possible improvements for the security problems of chaotic image encryption scheme under study.
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