Search

In order to study the influence of different factors on the temperature field of the freezing wall of connecting passage, and to evaluate the effect of different influencing factors, four groups of analyses were carried out through three-dimensional finite element software, including the influence of brine temperature, the influence of freezing pipe diameter, the influence of freezing pipe spacing, and the influence of soil water content. The analysis shows that the finite element method based on the thermodynamics theory can better simulate the freezing temperature field and formation law of the freezing wall of each section. Among the influencing factors, the brine temperature and the freezing pipe spacing have the greatest influence on the temperature field of the freezing wall. The thickness of the freezing wall increases linearly with the increase in the freezing time. At the same time, the thickness of the freezing wall increases with the increase in the diameter of the freezing tube and the decrease in the spacing between the freezing tubes. With the decrease in brine temperature and water content, the difference of freezing wall thickness at different levels becomes larger and larger with the increase in freezing time. The influence of various factors on the freezing wall is in the order of brine temperature, freezing tube spacing, and freezing tube diameter. At present, the saltwater temperature in the freezing project of the metro shield tunnel is generally controlled at −28~−30 °C. Generally, from the perspective of actual engineering, it is better to control the spacing of freezing pipes at 1.0~1.3 m, and the diameter of the freezing pipe of the connecting channel is generally more than 89 mm. By comparing the numerical simulation value with monitoring data, the numerical calculation result is consistent with the monitoring temperature change rule. [ABSTRACT FROM AUTHOR]

As one of the main filled materials of the Lianghekou (LHK) rockfill dam, the strength and deformation characteristics of LHK rockfill is of great interest for hydraulic and geotechnical engineers. Correct interpretation of the state-dependent behavior of LHK rockfill is necessary for the design, construction, and operation of the dam. Therefore, a series of large-scale triaxial tests on LHK rockfill with different initial states were carried out in this study, where the state-dependent strength and deformation behaviors of LHK rockfill were investigated. It was found that both the phase transformation state and peak state of LHK rockfill are dependent on the material state. To capture such state-dependent behavior, two elastoplastic models (i.e., α1-model and α2-model) based on different stress–fractional concepts were developed and compared. It was found that the fractional order (α1) in α1-model exhibits insignificant dependence on the material state of LHK rockfill, whereas the fractional order (α2) in α2-model is dependent on the material state. As the fractional order determines the plastic flow direction of rockfill, it should be identified carefully, otherwise, an overestimation or underestimation of the critical-state stress may occur when using α2-model. Further validation against the large-scale triaxial data of LHK rockfill shows that without using additional plastic potentials, the two models can reasonably reproduce the state-dependent behavior of LHK rockfill. A slightly better performance on simulating the stress–strain response is observed when using α1-model, whereas α2-model works better when simulating the stress–dilatancy response. [ABSTRACT FROM AUTHOR]

Chang'e-5 (CE-5) mission is expected to land and sample in the Rümker region, north of the Oceanus Procellarum. To select optimal sampling points, the microwave radiation features in this mare unit are analyzed, and the dielectric constant and thickness of lunar regolith are retrieved based on Chang'e lunar microwave sounder (CELMS) data. According to the microwave brightness temperature (TB) maps, TB varying with frequency at noon and midnight are different, in which noon TB increases with frequency, but midnight TB does not follow this rule. Moreover, there are differences among TB distributions at the three higher frequencies, especially in the southern part. In addition, a great TB difference between noon and midnight can be seen in Rümker E that shows higher daytime temperature but lower nighttime temperature The inversion results reveal that the dielectric constant is lower in the west and north, higher in the middle and east, and the largest value occurs in Rümker E. As for the regolith thickness, most areas are uniform and no more than 4 m, with the thickest and thinnest regolith appearing in the northwest and Rümker E, no less than 6 m and about 2.5 m, respectively. Considering the safety and operability of landing and sampling, the northwest with thick regolith is recommended, while the Rümker E should be eluded. [ABSTRACT FROM AUTHOR]

ABSTRACT A terahertz substrateless transmitarray antenna using four layers of slot type elements is presented. Because the element contains no dielectric substrate, reflection loss on the surface of dielectric and transmission loss in the dielectric could be effectively avoided at terahertz band. A terahertz transmitarray antenna working at 340 GHz is designed and fabricated by photolithography technique and electroplating processes. DRIE process and wet anisotropic etching technique were used to remove the substrate. The measured directivity of the antenna prototype is 34.9 dB, and half power beam width (HPBW) of E-plane and H-plane are 3.3° and 3.4°, respectively. The measured sidelobe level is below −22 dB. The measured results show that good radiation characteristics are achieved by the proposed design and microfabrication processes. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2096-2100, 2016 [ABSTRACT FROM AUTHOR]

The amount of particle breakage of Tacheng rockfill material (TRM) in the process of shearing was quantitatively measured by a relative breakage index. The fractal dimension of TRM at the final state of the tests was found to be linearly related to the void ratio and logarithm of the confining pressure. The influences of the relative breakage index on the friction angle, modulus, and deformation were investigated based on a series of large-scale triaxial compression tests on TRM. An increase in the relative breakage index leads to an increase in the volumetric strain and to decreases in the peak state friction angle, critical state friction angle, deviatoric strain, and critical state void ratio. The test results were used to propose simple formulations pertaining to the relative breakage index for the strength and deformation indexes (e.g., peak state friction angle, critical state friction angle, initial elastic modulus, secant modulus at 50% of the peak strength, volumetric strain, deviatoric strain, and critical state void ratio). [ABSTRACT FROM AUTHOR]

A series of large-scale triaxial compression tests were conducted to investigate the strength and deformation behaviors of Tacheng rockfill material (TRM) in relation to the initial void ratio and initial confining pressure. The critical state friction angle of TRM was expressed as a linear function of the logarithm of the initial confining pressure. The excess peak state friction angle and excess characteristic state friction angle of TRM were formulated as linear equations of a revised relative dilatancy index to capture the influences of density and pressure on the peak state and characteristic state friction angles. The initial elastic modulus, tangent modulus, and secant modulus of TRM were dependent on the initial void ratio and initial confining pressure. In addition, a formulation incorporating density and pressure was proposed to simulate the initial elastic modulus of TRM. The volumetric and deviatoric strains of TRM at the critical state were also dependent on density and pressure. The critical state line of TRM in the space descended with a decrease in the initial void ratio. [ABSTRACT FROM AUTHOR]

The critical state line of Tacheng rockfill material (TRM) was described by a pressure-power function. A simple bounding-surface plasticity model, combining the dilatancy stress ratio and peak-failure stress ratio pertaining to the state pressure index, was developed for TRM within the framework of critical-state soil mechanics and the bounding surface plasticity. Detailed investigations of influences of design parameters on the model predictions were carried out. The developed model, using a set of model constants, captured well behaviors such as strain hardening and volumetric contraction for TRM in a loose state (e.g., at a large initial void ratio or a high initial confining pressure) and strain softening and volumetric expansion in a dense state (e.g., at a small initial void ratio or a low initial confining pressure). [ABSTRACT FROM AUTHOR]

The particle breakage during specimen compaction had more significant influence on the position of the breakage critical-state line (BCSL) of Tacheng rockfill material (TRM) in the e-ln p′ plane than the particle breakage during shearing, based on the large-scale triaxial compression tests on TRM in a wide range of densities and pressures. The state-dependent dilatancy and the plastic modulus were correlated to the breakage index, based on the formulations of the BCSL of TRM in the e-ln p′ plane. The state-dependent model considering particle breakage was proposed for TRM within the framework of the generalized plasticity theory. The proposed model contained fourteen material constants. The test data of TRM from Group A were adopted to determine these material constants, while the test data from Group B were used independently to validate the model predictive capacity. The comparisons between model simulations and test data illustrated that the model with consideration of particle breakage could well represent the stress-strain behaviors of TRM, e.g., the strain hardening and volumetric contraction behaviors at a loose state and the strain softening and volumetric expansion behaviors at a dense state, and also the particle breakage behaviors of TRM. [ABSTRACT FROM AUTHOR]

Surface temperature profile is an important parameter in lunar microwave remote sensing. Based on the analysis of physical properties of the lunar samples brought back by the Apollo and Luna missions, we modeled temporal and spatial variation of lunar surface temperature with the heat conduction equation, and produced temperature distribution in top 6.0 m of lunar regolith of the whole Moon surface. Our simulation results show that the profile of lunar surface temperature varies mainly within the top 20 cm, except at the lunar polar regions where the changes can reach to about 1.0 m depth. The temperature is stable beyond that depth. The variations of lunar surface temperature lead to main changes in brightness temperature ( T ) at different channels of the lunar microwave sounder (CELMS) on Chang'E-1 (CE-1). The results of this paper show that the temperature profile influenced CELMS T , which provides strong validation on the CELMS data, and lays a solid basis for future interpretation and utilization of the CELMS data. [ABSTRACT FROM AUTHOR]

Lunar regolith parameters, such as physical temperature, thickness and dielectric constant, are important in studying regolith features, distribution of lunar resources and evolution of the Moon. There had been no measurement obtained by lunar-orbit-borne microwave radiometer applied to evaluate the properties of lunar regolith before CE-1 Lunar Microwave Sounder (CELMS) being launched. CEMLS is the first passive microwave radiometer in the world to sound the surface of the Moon. The brightness temperatures ( T ) sensed by CELMS include complicated information on the above geophysical parameters. In this paper, algorithms of retrieving dielectric constant, regolith thickness, and He content from CELMS brightness temperatures are developed, and the results are compared with those from literature. The results show that the regolith thicknesses are mostly in the range of 4.0-6.0 m, and 43% of them are bigger than 5.0 m. The content of He evaluated by retrieved regolith thickness is about 1.03 million tons. [ABSTRACT FROM AUTHOR]

Investigation on Lunar polar area is almost every lunar mission’s primary objective in recent years. The rationale behind it is that illumination and ice resources in this area can be potentially very helpful for constructing lunar human base. In this paper, we analyze microwave radiometric characteristics of the Moon by using the newly acquired Chang’E-1 Lunar Microwave Sounder (CELMS) data. Microwave brightness temperature at Lunar South Pole (LSP) is distributed regularly with a style of “ring-in-ring”, decreasing from equator to pole. Regolith temperature gradient is bigger at lunar equator than at polar area. Brightness temperature diurnal difference decreases with observation frequency. Microwave brightness temperature distribution maps at LSP and Lunar North Pole (LNP) have been made based on the analysis. It is found that microwave brightness temperature becomes to synchronize with elevation beyond −85° latitude. This phenomenon is related to lightening condition and indicates temperaturedistribution at LSP. The brightness temperature anomaly cold points are potentially cold trap areas for water or ice while hot points imply plenty of illumination resources there. [ABSTRACT FROM AUTHOR]

To support the microwave brightness data retrieval of future China space-borne lunar exploration microwave radiometer, based on the collection of plentiful terrestrial basalts and anorthosites and their chemical compositions got by X-ray fluorescence, nine lunar soil simulators were prepared and made respectively into 0.8, 1.0, 1.2, 1.4 and 1.6 g/cm³ five densities each. We measured their relative dielectric constants over the range of 0.5–20 GHz with open-ended coaxial line model on the HP8722C Network Analyzer and then processed and analyzed the measurement data. This study shows that among the three parameters of density, frequency and composition, density has the strongest effect on the relative dielectric constants, frequency comes second, composition the least. The three parameters account for 45%, 33% and 22% respectively of the changed real part of a relative dielectric constant, and 55%, 27% and 19% respectively of the changed imaginary part. The real parts of the relative dielectric constants are linearly linearly correlated with density or frequency, and the imaginary parts have a linear relation with both approximately over the range of 0.5–10 GHz and tend to be poorly correlated with them in 10–20 GHz. The effect of composition on a relative dielectric constant seems very complicated, both probably do not follow a simple function relation, with the least correlation. Multiple regression analysis indicates that major element oxides SiO2, Al2O3, CaO, MgO, TiO2 and ΔFe are correspondent to a one-order polynomial, and TiO2 or ΔFe or TiO2+ΔFe has not been proven to be the indicators in the contribution to the relative dielectric constants. [ABSTRACT FROM AUTHOR]