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The maximum undercooling that has been achieved for Ni-Cu alloy, by using molten glass purification and cyclic super-heating technology, is 270 K. With the help of high-speed photography, the solidification front images of Ni-Cu alloy at various typical undercooling were obtained. Two grain refinements occurred in the range of 60 K< ΔT < 100 K and ΔT > 170 K, the solidification front became smoother, and the solidification position appeared randomly. With the increase of undercooling, the transition from solute diffusion to thermal diffusion leads to the transition from coarse dendrite to directional fine dendrite. At large undercooling, considerable stress is accumulated and some dislocations exist in the microstructure. However, the proportion of high-angle grain boundaries is as high as 89%, with twin boundaries of 13.6% and most strain-free structures, and the microhardness decreases sharply. This indicates that the accumulated stress at large undercooling causes the plastic strains in the microstructure, and in the later stage of recalescence, part of the plastic strains is dissipated by the system and acts as the driving force to promote the recrystallization of the microstructure.

The solidification microstructure evolution of Ni-25 at.% Cu alloys under different undercooling degrees were studied by the cladding method and cyclic superheating method. Two grain refinement phenomena were observed in the obtained undercooling. In the low undercooling condition, dendrite remelting is the main reason for grain refinement in the recalescence process, while in the high undercooling condition, the stress accumulated in the recalescence process leads to recrystallization in the later stage of recalescence. Under the condition of high undercooling, the solidification structure is composed of complete equiaxed grains with relatively uniform grain size, which indicates that grain boundary migration occurs during grain growth.

Sodium caseinate (SC)/dextran conjugates were prepared via Maillard reaction under controlled dry-heating conditions. Moreover, the nanoparticles of phytosterols (PS) encapsulated by SC or SC/dextran were produced using the emulsion evaporation method. The encapsulation efficiency (78.81 ± 5.22%) of PS in SC/dextran nanoparticles was higher than that (73.5 ± 2.78%) in SC nanoparticles. Compared with the compact and dense structure of SC nanoparticles, SC/dextran nanoparticles existed as relatively loose aggregates. The result of differential scanning calorimetry demonstrated that the encapsulation of PS greatly decreased its crystallinity. The released rates of PS from SC and SC/dextran nanoparticles under acidic gastric conditions were 8.59% and 4.73%, respectively. After 7 h of intestinal digestion, the released rate (52.19%) of PS from SC/dextran nanoparticles was significantly higher than that from SC (32.67%) nanoparticles. Therefore, SC/dextran conjugates prepared by the Maillard reaction are more suitable to be used as wall material for the nano-encapsulation of PS.

A cylinder test was designed for the CL-20-based aluminized explosives to study the influence of aluminum (Al) powder properties on the explosives' metal driving performance in the direction perpendicular to detonation wave propagation. The research results showed that: in the direction perpendicular to detonation wave propagation, as the Al powder particle size became larger (in the range of 2–43 μm), the metal driving performance of the explosives grew stronger; the CL-20-based explosive containing 25% Al was much less capable of accelerating the metal than the formulation containing 15% Al. Considering the two-dimensional flow characteristics of the detonation products in the radial and axial directions as the aluminized explosive expands and drives the cylinder, a quasi-isentropic theoretical model for the aluminized explosive driving the cylinder was proposed. In the model, the calculation methods for the variations of the cylinder expansion velocity, Al reaction degree, and detonation product parameters with time, axial space, and radial space were developed. According to the experimental data of the cylinder test, the correctness of the proposed quasi-isentropic theoretical model was verified; the variation laws of the physical parameters, such as the pressure and temperature of the detonation products under different radial distributions in the cylinder with time and axial positions, were calculated. It was found that the pressure and temperature of the detonation products in the non-inner-wall place of the cylinder were significantly higher than those on the inner wall of the cylinder at the same axial position; the pressure and temperature of the detonation products on the inner wall decreased rapidly at the early timeframes; as the Al reaction proceeded, the pressure gradually turned to a constant value, and the temperature dropped slowly; for the CL-20-based explosives with 15% Al, the temperature of the detonation products in the non-inner-wall place rose slightly at first and then decreased slowly; for the formulation with 25% Al, the temperature of the detonation products in the non-inner-wall place kept rising at a small rate.

With the widespread use of composite structures in ship superstructures, their vibro-acoustic response under transient impact loads is of increasing concern. This paper studies the vibro-acoustic behavior of a carbon fibre reinforced composite laminate under transient impact excitation based on the time-domain hybrid FEM/BEM method. Firstly, the numerical method is verified through the model test of a homogeneous plate. Subsequently, the vibration and sound radiation characteristics of composite laminates are studied. It was found that the impact noise energy mainly concentrated in the low-frequency range of 10~200Hz, and the peak noise spectrum was 9dB lower than that of the steel plate. The variation of lay-up orientations causes differences in the structural properties of the laminates, resulting in differences in their vibro-acoustic radiation performance. In this study, the laminate with the [0°/90°]5s orthogonal lay-up scheme has better acoustic radiation performance under the impact load.

Protective clothing is very important to guarantee the safety of emergency rescuers. And proper construction design of clothing will improve the rescue efficacy. This study developed a new set of emergency rescue protective clothing (NC) and evaluated its performance. Clothing fit test, freedom of movement, and rationality of pocket tests were conducted. The results showed that the amount of slippage at the hem, waist of pants, and leg opening of NC has been greatly reduced. The NC had provided better cloth fit and dynamic comfort. The storage capacity of the pockets had been increased, the position and angle design of the pocket made it easier to take and keep the rescue tools.

A post-treatment of hydrothermal process was conducted to evaluate its effects on the material characteristics and mechanical properties of plasma-sprayed pure HA and HA/20% YSZ coatings. Surface morphology and microstructural changes, relative element contents as well as phase transformations were analyzed by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry. Both microhardness and Young’s modulus were measured. CaCO3 was found existing before and after the whole process of post-treatment. Peaks of impurity phases such as CaO, TCP, and TTCP of as-sprayed coatings were observed to disappear while HA peaks show a tendency of getting higher and wider over time. Surface morphology of SEM analysis presents a clear deposition behavior of ultrafine HA crystallized particles and cross-sectional analysis exhibits a dense and fine structure. Mechanical properties of HA/20%YSZ coatings are found to be significantly higher than those of pure HA coatings and both of which displayed an overall increase with the heating time, indicating enhanced performances.

Variable flow ducted rockets are excellent candidates for propulsion systems in hypersonic vehicles. However, the anti-regulation characteristics of the gas flow not only decrease the stability of ducted rockets but also create difficulties in the control system design. In this study, a model predictive control (MPC)–based compound control algorithm that suppresses the anti-regulation is proposed. First, a mathematical model involving a gas flow regulation system was developed to describe and analyse the anti-regulation. Next, a fused feedback variable that included both the gas flow and the gas generator pressure signal was constructed. An MPC control system with the fused feedback variable was also designed. Then, to accurately predict the gas flow and the anti-regulation, a nonlinear disturbance observer was constructed. To evaluate the performance of the controller, two scenarios that were regulated by a tracking differentiator proportional–integral–derivative controller and a model reference adaptive control controller were constructed and compared. The theoretical results demonstrate that the proposed method exhibited a superior performance compared to previous methods by overcoming the supposed trade-off between the response rate and the anti-regulation of gas flow systems.

Freezing injury is one of the main restriction factors for winter wheat production, especially in the northern part of the Winter Wheat Region in China. It is very important to assess the risk of winter wheat-freezing injury. However, most of the existing climate models are complex and cannot be widely used. In this study, Zunhua which is located in the northern boundary of Winter Wheat Region in China is selected as research region, based on the winter meteorological data of Zunhua from 1956 to 2016, seven freezing disaster-causing factors related to freezing injury were extracted to formulated the freezing injury index (FII) of wheat. Referring to the historical wheat-freezing injury in Zunhua and combining with the cold resistance identification data of the National Winter Wheat Variety Regional Test (NWWVRT), consistency between the FII and the actual freezing injury situation was tested. Furthermore, the occurrence law of freezing injury in Zunhua during the past 60 years was analyzed by Morlet wavelet analyze, and the risk of freezing injury in the short term was evaluated. Results showed that the FII can reflect the occurrence of winter wheat-freezing injury in Zunhua to a certain extent and had a significant linear correlation with the dead tiller rate of wheat (P = 0.014). The interannual variation of the FII in Zunhua also showed a significant downward trend (R2 = 0.7412). There are two cycles of freezing injury in 60 years, and it showed that there’s still exist a high risk in the short term. This study provides reference information for the rational use of meteorological data for winter wheat-freezing injury risk assessment.

The response difference between the classical mathematical model of a ducted rocket and a real experiment is compared in this study, and a new revised method is proposed based on the free v...

When a viscous fluid flows over the surface of an object, different regions of the wall form different boundary layers. Fluctuating pressure in this boundary layer acts on the surface of the structure, causing it to vibrate and radiate noise; simultaneously, structural deformations will also have an impact on the flow field, and boundary layer pressure fluctuation is the most important component of flow noise. The characteristic parameters of a model, such as its wall thickness and the length of its parallel body section, will affect the pressure fluctuations it experiences. However, most studies treat the structure of the model as a rigid body. Therefore, this paper conducted experiments to examine the influences of the wall thickness and the parallel body length of a model on the pressure fluctuations it experiences. It was found that the fluctuating pressure at a given measuring position increases with decreasing wall thickness, and it decreases with increasing parallel body length. Then, this study demonstrated through comparative experiments that elastic and scale effects are important factors that cannot be ignored in calculations and experiments relating to pressure fluctuations. In addition, according to the characteristics of pressure fluctuation test values in different regions, the pressure-fluctuation prediction empirical formulas for different regions of the boundary layer were established or improved on the basis of previous research on pressure fluctuation in different regions of the boundary layer. Finally, by pasting a flow exciter at the transition position in the boundary layer of the model can keep its flow noise down, the experimental results show that rough particles can split the large vortex into smaller vortices and reduce flow noise by more than 5 dB. These results and empirical formulas provide references for numerical and experimental research examining pressure fluctuations.

New rapid compression machine (RCM) ignition delay data for dimethyl ether (DME), methanol (MeOH), and their blends are acquired at engine-relevant conditions (T = 600 K–890 K, P = 15 bar and 30 bar, and equivalence ratios of ϕ = 0.5, 1.0, and 2.0 in synthetic dry air). The data are then used to validate a detailed DME/MeOH model in conjunction with literature RCM and shock tube data for DME and MeOH. This detailed DME/MeOH model, constructed by systematically merging literature models for the combustion of the individual fuel constituents, is capable of accurately predicting the experimental ignition delay data at a wide range of temperatures and pressures. The experiments and simulations both show a non-linear promoting effect of DME addition on MeOH autoignition. Additional analyses are performed using the merged DME/MeOH model to gain deeper insight into the binary fuel blend autoignition, especially the promoting effect of DME on MeOH. It is found that the unimolecular decomposition of HO2CH2OCHO plays an essential role in low temperature DME/MeOH blend autoignition. The accumulation of HO2CH2OCHO before the first-stage ignition and later quick consumption not only triggers the first-stage ignition, but also causes the non-linear promoting effect by accumulating to higher levels at higher DME blending ratios. These analyses suggest the rate parameters of HO2CH2OCHO unimolecular decomposition are critical to accurately predict the first-stage and overall ignition delay times as well as the first-stage heat release profile for low temperature DME/MeOH oxidation.

Modular multilevel converter (MMC) has broad application prospects in new energy transmission. When a MMC is connected to an active AC grid, it is necessary to calculate the three-phase symmetrical short-circuit current contribution of MMC to ensure the safety of power system. The existing method used in actual engineering projects consider MMC as a current source of which the amplitude is the current limiting amplitude of current limiter. It is safe but has too much margin to be accurate. This paper proposes a new method to calculate short-circuit current that can be used in actual engineering project. This paper analyses the characteristics of MMC short-circuit current first, and proposes the key factors affect short-circuit current contributed by MMC during an actual operating condition. On this basis, simulation trials on advanced digital power system simulator (ADPSS) are designed to get the characteristic curves of short-circuit current which can be used to calculate short-circuit current in actual operation of the engineering project. Finally, this paper uses Zhangbei MMC-HVDC project as an example to apply the new method and show the effectiveness and superiority of the method proposed by this paper.

Cooling workwear using phase change materials (PCMs) was designed for miners in hot underground mines. A new arrangement of PCM packs was introduced that used 15 °C PCMs as the inner layer and 23 °C PCMs as the outer layer (15&23). Its performance was investigated using thermal manikin and human subject tests by comparison with clothing without PCMs (CON), with 15 °C PCMs (15&15) and with melted PCMs (mPCM) in a climate chamber (30 °C, 80% relative humidity). The PCM cooling workwear significantly increased the manikin heat loss, attenuated the rise of skin temperatures and improved thermal sensation and comfort. The cooling duration was extended in 15&23 as compared with 15&15. The added PCMs did not affect the perceptual exertion and body mobility. In summary, cooling workwear using PCMs with different temperatures can be an effective option for miners' personal cooling in a hot and humid environment.

A hysteresis model was built to describe the backlash of the flow regulator in a solid ducted rocket, and its influence on the engine control was also analyzed in this study. An adaptive backlash compensation method was proposed under two challenges: limited information and backlash state variation caused by the harsh environment in the gas generator. The touch state is designed and its observation is used to get the state of backlash, and a compensation control method using the existing information was carried out combined with the motion intention. This method greatly shortened the time during the transition and reduced the hysteresis effect on the control system. Furthermore, the compensation method is improved and acquires a self-learning ability, the compensation parameter changes adaptively during the process of flow regulation, and it is able to meet the challenge of an unknown and variable state of backlash. Finally, the validation of the compensation method was carried out with two simulations.

There are many storage and transportation stations in China. The large-scale construction of oil and gas pipelines has a length of tens of thousands of kilometers. The intelligent construction of stations and pipelines needs to be improved and improved urgently. It is necessary to improve the intelligent management level and strengthen the intelligent data application processing functions. The intelligent construction of the station library and the pipeline needs to realize the intelligent perception of the pipeline. At the perception layer, comprehensive perception of the pipeline body, key equipment, external environment and maintenance resources and other information is realized to realize the integration of collection, processing and transmission. Artificial intelligence is trained using data samples, and artificial intelligence algorithms are used to mine data in depth at the algorithm layer to extract fault information, predict operating conditions, and optimize resource allocation. Realize intelligent pipeline operation through specific business function platforms. The main functions are unified data standards, accurate and visible data collection, unified system software and hardware interconnections, protocol data standard matching, intelligent judgment management and efficient, predictive and early warning situation judgments are accurate and reliable.