Abstract:In an effort to improve the calibration accuracy and ensure the rate sensing performance of gyrowheel, a suitable signal denoising method to extract the useful information from the complicated noise is essential. First, according to the causes of noise, the noise characteristics of gyrowheel were analyzed. Second, the traditional low-pass filter (LPF) was introduced to attenuate the high-frequency periodic noises without influencing the useful low-frequency characteristics. Then the empirical mode decomposition (EMD) method was applied to the filtered signal, and a criterion for selecting relevant intrinsic mode functions (IMF) was presented by using the similarity measurement between probability density functions of IMFs. Combining with the existing thresholding-based denoising technique, a hybrid EMD/LPF denoising strategy was proposed. Simulation results show that the proposed criterion for selecting relevant IMFs was always effective under different SNR conditions. Meanwhile, the proposed method was applied to standard test signals and real signals, and results show the effectiveness and superiority of the hybrid denoising method.

Abstract:To solve the tracking problems of communication delay and parameter uncertainty in spacecraft formation flying system and realize the control objective of collision avoidance, this study investigated the adaptive cooperative control of spacecraft formation flying system with collision avoidance based on the relative motion nonlinear dynamic model and the potential function method. First, an adaptive cooperative collision avoidance control law with full state feedback was proposed, which has the robustness to communication delays and parameter uncertainties. Then, considering the situation of unmeasurable velocity, a control law without velocity measurement was proposed by introducing a new type of filter, which can enable the formation spacecraft to track the desired trajectory and fly in the safe regions without collision. Finally, the Lyapunov stability of the spacecraft formation flying closed-loop system was analyzed for the cases of full state feedback and without velocity measurement feedback, and it was found that the robustness of the closed-loop system to communication delay and parameter uncertainty was significantly improved. Simulation results show that the proposed two adaptive cooperative control laws could guarantee that the formation spacecraft tracks the desired trajectory effectively and achieves the formation flying mission with collision avoidance.

Abstract:Due to the complex disturbances and uncertainties in return process, the attitude system of vertical takeoff vertical landing (VTVL)-reusable launch vehicle (RLV) is nonlinear and high dynamic. To solve the nonlinear attitude tracking control problem with complex disturbances in the return process of VTVL-RLV, a composite fast attitude tracking control method consisting of double-order power fixed-time convergence sliding mode surface and fixed-time convergence disturbance observer (FxTDO) was proposed. The FxTDO was introduced to obtain high precision approximation of the bounded matched disturbance and avoid the influence of the observer on the performance of the control system. In order to achieve fixed-time convergence of attitude tracking controller, the double-order power fixed-time convergent sliding mode surface was given based on double-power correction terms. By introducing the disturbance approximation to directly compensate the matched lumped disturbance in double-order power fixed-time convergence sliding mode control law, the discontinuous control term was removed to reduce the chattering phenomenon at permissible loss of convergence accuracy. Simulation results of the aerodynamic deceleration flight phase revealed the effectiveness of the FxTDO and the proposed FxTDO-based fixed-time convergence sliding mode tracking control method.

Abstract:To solve the stability and fast deployment problems of tethered satellite system (TSS) in elliptical orbits, a novel backstepping-like nonlinear control algorithm was proposed based on the traditional backstepping control method. Different from the traditional backstepping method which is only suitable for strict feedback systems, the proposed backstepping-like nonlinear control has a wider range of application that it can be applied to the control of non-strict feedback systems and can improve the control performance with effective use of the nonlinear model. First, the nonlinear dynamic model for the deployment of TSS in elliptical orbit was established based on the Lagrangian mechanics, and the dimensionless system model was further simplified with a new dimensionless transformation. Then, by utilizing the simplified model, a backstepping-like nonlinear control method was proposed to deal with the coupling characteristics of the system model, and the Lyapunov function was adopted to verify the asymptotic stability of the system states. Finally, simulation experiments of non-linear control and PID control for the deployment of TSS in elliptical orbit were carried out, and the effectiveness of the proposed backstepping-like nonlinear control was verified by comparison. Simulation results show that the proposed method deployed the tether satellite effectively and stably and achieved better performance than the classical PID controller.

Abstract:To achieve highly parallel data transmission and computation of convolutional neural network acceleration and generate efficient hardware accelerator design, a hardware design and exploration method based on data-alignment and multi-filter parallel computing was proposed. In order to improve the data transmission and computation speed and adapt to various input image sizes, the method first aligned the data according to the input image size to achieve highly parallel transmission and computation at the data level. The method also used the multi-filter parallel computing method so that different filters can simultaneously convolve the input image to achieve parallel computing at the filters level. Based on this method, mathematical models of hardware resources and performance were formulated and numerically solved to obtain the performance and resource co-optimized neural network hardware architecture. The proposed design method was applied to the single shot multibox detector (SSD) network, and results show that the accelerator on Xilinx Zynq XC7Z045 at 175 MHz clock frequency could achieve the throughput of 44.59 FPS, power consumption of 9.72 W, and power efficiency of 31.54 GOP/(s·W). The accelerator consumed 85.1% and 93.9% less power than the central processing unit (CPU) and graphics processing unit (GPU) implementations respectively. Compared with the exiting designs, the power efficiency of the proposed design increased 20%~60%. Therefore, the design method is more suitable for embedded applications with low power requirements.

Abstract:To improve the performance of belief propagation multi-target tracking under dense clutter interference, an amplitude clutter suppression-based Gaussian mixture belief propagation (GMBP-AC) multi-target tracking method was proposed. First, based on the classical Rayleigh distribution model, the initial signal-to-noise ratio (SNR) of target was estimated by the maximum likelihood estimation. The truncated normal distribution model for the SNR of target was constructed with the combination of prior information and then marginalized. Next, based on the amplitude information, the amplitude likelihood ratio (ALR) of each measurement was calculated before belief propagation and introduced into the measurement information function, which improved the association accuracy between targets and measurements. Finally, the measurement information admission rate was set to get the lower limit of ALR, and the measurements of all the sensors were selected to complete the target initiation efficiently. The research shows that under different SNR and clutter densities, compared with GMPHD, GMBP, and GMBP-AK, the proposed GMBP-AC has higher computational efficiency. The method can respond to the changes of target numbers more accurately and quickly in various time periods, and meanwhile reduce the OSPA error greatly. It further proves that under dense clutter interference, the proposed method has high efficiency of clutter suppression, and can improve the target numbers estimation performance and multi-target tracking accuracy.

Abstract:Channel prediction algorithm based on high order singular value decomposition (HOSVD) denoising is sensitive to the small number of antennas and cannot cope with the maximum Doppler shift, which may result in a sharp drop in the channel estimation and prediction performance and the loss of channel capacity. To solve this problem, this paper proposes an improved channel prediction algorithm based on HOSVD denoising. The proposed algorithm first smoothes the sampled channel state information (CSI) by using the space-time correlation inherent in the multiple-input multiple-output channel, and then uses HOSVD to reduce the influence of noise and reconstruct the channel matrix based on the multi-dimensional structure characteristics of the channel. Finally, the recursive least squares filter is used to predict future CSI. Simulation results show that the channel estimation error and the prediction error of the proposed algorithm were better than those of the comparison algorithm. This is because the proposed algorithm uses matrix rearrangement and space-time smoothing to increase the number of antennas virtually, which can effectively reduce the influence of the Doppler shift factor and the rank missing problem caused by the small number of antennas on the prediction accuracy, thus compensating the loss of channel capacity. At the same time, by comparing the influence of antenna number and the Doppler frequency shift on the performance of different algorithms, it can be found that the proposed algorithm could provide better prediction performance and channel capacity under unfavorable conditions such as Doppler frequency shift and few antennas, which has certain advantages.

Abstract:To solve the problems existing in the observable degree analysis method based on the SVD of the observable matrix of linear time-varying systems, such as the inconsistency of state dimensions and the nonuniqueness of singular value reference, an improved method was proposed. First, the relationship between linear time-varying system and piecewise linear constant system (PWCS) was expounded, and the PWCS observability analysis theory was introduced. Under the condition of satisfying the theorem, the complexity of the analytical calculation could be effectively reduced by the stripped observability matrix (SOM) instead of the total observability matrix (TOM). Then, the SVD of SOM and its singular value as well as the corresponding singular vector were extracted by the system. Next, the observation equation of the system was deduced, and the observability index of each state of the system was obtained according to the longitudinal comparison of the observation degree of the same state under different maneuver conditions of the carrier. Finally, the SINS/DVL integrated navigation system was used for simulation verification. Simulation results show that the observability index calculated by this method was consistent with the Kalman filter state estimation error characteristics, which proves that the improved method can predict and accurately describe the state estimation effect. Meanwhile, the system adaptive feedback correction was performed according to the calculated state observability, which could effectively improve the navigation precision.

Abstract:To restrain the accumulated navigation error of shipborne grid inertial navigation system (INS), the paper proposed a comprehensive calibration method based on grid frame to estimate and compensate the gyroscope constant drift. First, the P equation was derived based on grid frame, and the P equation established the relationship among the position errors, the grid yaw error, and the platform drift angles ψ. Then the ψ equation was derived to establish the relationship between the gyroscope constant drifts and the platform drift angles ψ. Finally, on the basis of P equation and ψ equation, a two-point comprehensive calibration scheme was designed, and the gyroscope constant drifts in body frame were estimated and compensated by establishing the relationship between the gyroscope constant drifts and observation errors. Under external level damping state, the gyroscope constant drifts were estimated after obtaining two intermittent external position and azimuth information, then the comprehensive calibration of shipborne grid INS was realized by resetting the position errors and grid yaw error and compensating the gyroscope constant drifts. Simulation results demonstrate that with the aid of two intermittent external position and yaw information, the proposed two-point comprehensive calibration method can estimate the gyroscope constant drifts accurately. Conducting the gyroscope error compensation and the system reset can efficiently restrain the accumulated errors of shipborne grid INS, thus significantly improve the navigation accuracy of ships navigating in polar regions.

Abstract:To prevent the occurrence of danger or accident during the correction process of all-electric differential braking, the safety problem was regarded as a control problem, and the safety analysis based on STAMP/STPA was carried out from the control point of view. First, based on the system-theoretic accident model and process (STAMP), the STAMP model of the aircraft all-electric differential braking system considering human-machine coordination was established to determine the control feedback relationship of the entire differential braking system. Then, the system theoretic process analysis (STPA) method was used to analyze the safety of the differential braking correction process, determine system-level accidents and hazards, identify potential risks and unsafe control actions (UCA), and conduct qualitative analysis of UCA from the aspects of control, feedback, and coordination. Finally, an airplane ground sliding model was established to simulate and analyze some unsafe control behaviors (UCA1, UCA2, and UCA5) that occurred during the correction process. Simulation results show that the differential braking action was not provided in the case of 1° initial yaw angle or 1 m/s continuous crosswind, and the aircraft was out of the runway after 5 s; the differential braking action delay occurred at 1° initial yaw angle (with no crosswind), and the aircraft was out of the runway when the delay was greater than 5 s. From the quantitative point of view, the safety constraints of the aircraft all-electric differential braking correction process were proposed, and the effectiveness of the STAMP/STPA method was verified.

Abstract:Aiming at the problem of cooperative collision detection and resolution of multi-UAVs by heading control, this paper proposes a local centralized two-layer optimization method. First, the practical conflict constraints and the potential conflict constraints are regarded as the same type of constraints to ensure that the multi-UAV conflict problem can be solved in great degree. The method of conflict detection based on sampling is designed, and the number of searching feasible regions is reduced by rotating local coordinate system, and two kinds of constraint conditions, including the terminal point constraint and the tangential constraint, are analyzed. Then, the conflict relation of multi-UAV conflict problem is divided by graph theory, and the additional flight distance caused by maneuver is taken as the cost of resolution to design the maneuver cost function. In order to solve the non-linear optimization problem of the designed maneuvering cost function, a two-layer optimization strategy is proposed. The initial feasible solution is firstly searched by Stochastic Parallel Gradient Descent (SPGD), and then the optimal solution is obtained by using Sequential Quadratic Programming (SQP). Finally, Monte Carlo method is used to evaluate the reliability of the algorithm. The simulation results show that this method can satisfy the need of online planning and can achieve 100% conflict resolution under the condition of conflict start distance D_avo=τ×v_i(τ=25 s). This method can reduce the maneuvering consumption on the basis of ensuring the security of multi-UAV conflict resolution.

Abstract:For the attitude control of diamond joined-wing unmanned aerial vehicle (UAV) with unknown external disturbances, the system has the characteristics of strong coupling, non-linearity, multi-input, and multi-output. Combining with sliding mode variable structure control theory, fractional calculus theory, adaptive control theory, new reaching law based on Fal function, and extended state disturbance observer, an adaptive fractional sliding mode control method was proposed. First, by introducing the fractional calculus theory and utilizing the genetic and memory characteristics of fractional calculus operators, the sliding surface of fractional calculus was designed to soften the controller output and control the overshoot of the controller. Then, in order to improve the weaknesses of traditional reaching law such as long convergence time and serious chattering, a new reaching law was proposed based on the Fal function, which could realize fast convergence without chattering. Finally, since there were modeling errors and external disturbances in the control system, the extended state observer was used to estimate and compensate the combined disturbance online. Simulation results show that the proposed control method had strong robustness and achieved ideal control effect.

Abstract:To alleviate the sensitivity of homing guidance with respect to initial state errors and enhance the anti-disturbance capability of missile at the final time, this paper presents an optimal guidance law with impact angle constraint based on a class of hyperbolic tangent weighting function using the indirect Gauss pseudospectral method. First, an impact angle coordinate system was established based on the desired impact angle and the position of the target, in which the motion kinetics for the engagement was constructed and the homing guidance model with impact angle constraint was obtained. Second, the two-point boundary problem was derived by utilizing the minimum principle, which was then discretized into a set of algebraic equations by employing the Gauss pseudospectral method. Finally, the optimal guidance law was easily obtained via explicitly solving the algebraic equations. This approach does not need to solve the Riccati differential equations and avoids cumbersome integral operations, which leads to a low computational load. The derivation of the proposed guidance law does not rely on the concrete form of weighting functions, and it can handle complex weighting functions. Simulation results demonstrate the performance of the proposed guidance law and show that the trajectory and acceleration command of missile could be shaped as desired by employing different types of weighting functions. The proposed algorithm could effectively reduce the sensitivity of homing guidance with respect to initial state errors and ensure the operational margin to cope with external disturbances at the end of the homing phase, provides more degrees of freedom in the guidance law design to accomplish specified guidance objectives.

Abstract:Electronic images are easily contaminated and blurred during the processes of acquisition, transmission, and storage, and the fidelity of the original images are degraded. To address this issue, a hybrid denoising method based upon variational mode decomposition (VMD) and Stein unbiased risk estimator (SURE) was proposed, taking the electron backscatter diffraction (EBSD) images of Aluminum alloy, dual-phase steel, and Ti6Al4V as examples. To begin with, the clean EBSD images were contaminated by adding Gaussian noise and speckle patterns noise. Then, the noisy image was decomposed into characteristic information component and high-frequency noise components using the Bi-variational mode decomposition (BVMD) algorithm. Next, the generated inherent characteristic component was fed into the Haar wavelet redundant dictionary (HWRD) for sparse representation. Meanwhile, the optimal objective shrinkage function was derived with the function of one-order differentiable shrinkage. Finally, the adaptive threshold was obtained via golden section search (GSS) method. Experimental results show that the proposed method could effectively remove the external interference noise and improve the peak signal-to-noise ratio (PSNR) of the image. Specifically, taking the EBSD image of Aluminum alloy as an example, when the noise standard deviation was 30, the proposed method exceeded the maximum point of single sparse SURE method in terms of PSNR value, which also outperformed the Neigh-Shrink method by 0.39 dB, the K-singular value decomposition (KSVD) method by 2.895 dB, and the soft-wavelet threshold denoising (SWTD) by 3.07 dB.

Abstract:To obtain bandgap reference voltage with high PSRR, high precision, and low temperature coefficient and meanwhile reduce the influence of non-ideal factors in the process, a piecewise curvature compensated bandgap reference circuit with a trimming procedure was proposed. The current with positive and negative temperature coefficients was generated by utilizing the resistor divider and the electrical characteristics of the MOSFET operating in the subthreshold region. The bandgap reference voltage was compensated at high temperature and low temperature respectively. A new chip-level trimming method including temperature coefficient trimming and voltage amplitude trimming for rapidly optimizing the reference voltage temperature coefficient, which can quickly acquire the code value of the lowest temperature coefficient curve and improve work efficiency. Based on 0.35 μm Bipolar-CMOS-DMOS (BCD) process, the chip was taped out to verify the feasibility of the trimming scheme. Simulation and test results show that: from -40℃ to 125℃, the lowest simulated reference voltage temperature coefficiency was 0.84×10^-6/℃, the lowest measured temperature coefficiency was 5.33×10^-6/℃, and the average temperature coefficiency was 7.47×10^-6/℃ according to ramdom sampling. The average trimming times for ten chips was 3.5 by using the method based on calculating the slope. The efficiency was improved by 59.8％ compared with the method of successive approximation. The bandgap reference voltage with low temperature coefficient is helpful to improve the accuracy of the battery management chip in estimating battery residual power. This circuit has been successfully applied to high precision analog-to-digital converter in battery management chips.

Abstract:As an emerging unmanned combat force and indispensable civilian equipment, unmanned aerial vehicles (UAVs) have gradually been integrated into all aspects of national security and social development. Path planning is the core link to ensure that UAVs successfully complete the established task. In order to solve the problem of real-time path planning with many static and dynamic threats in the planning space, a method of autonomous obstacle avoidance path planning with receding horizon is proposed. Firstly, the path planning model was constructed as a single objective function optimization problem. According to the simplified kinematic model and constraints of the UAV, the receding horizon optimization strategy was used to generate the optimal path sequence. Then, the receding horizon optimization strategy was also used to generate sub-sequences for the trajectories between the optimal path sequences. Considering the threat and flight constraints, the negative gradient descent method was used to search the waypoint, and the genetic algorithm was used to plan the sub-sequences. Finally, the approximate global optimal path was obtained by repeated receding iterative optimization, and the trajectory was processed by bezier curve to represent the actual flight path. The experimental simulation results show that the model is reasonable and the method is effective. Meanwhile, it also has good threat avoidance ability and can plan a smooth path. Compared with the global planning method, the proposed method reduces the convergence time, has stronger real-time performance, and can converge to the approximate global optimal solution quickly and robustly.

Abstract:When designing a scientific super-pressure balloon, the capability of a balloon to withstand pressure can be effectively improved by arranging tendons on the surface of the balloon. To solve the problem of the large difference of longitudinal strain between the balloons membrane and tendons at the high “latitude” position, a design scheme of a sliding cable membrane structure was propased. First, the sliding cables on the balloon was used to replace the tendons sealed to the menbrane, which is more advantageous for the stress transmission on membrane. Then, in order to make the stress on the membrane evenly distributed in the circumferential direction, the equilibrium shape analysis of the membrane of the cable membrane structure was carried out. According to the relationship between the radius of the meridional and the latitudinal curvature of the balloon membrane and the capability of the balloon to withstand pressure, an elliptical correction method was adopted to design a super-pressure balloon with sliding cable membrane structure to make the membrane stress more evenly distributed along the circumferential direction, thus further improving its capability to withstand pressure. Finally, taking a super-pressure balloon with sixteen bulges as an example, whose original shape is spherical with a diameter of four meters, the finite element model of the floating state super-pressure balloon was established by the software Abaqus for numerical simulation. Numerical results show that the pressure bearing capacity of the balloon increased with increasing radial tightening amount dl of the equatorial section rope, the modified super-pressure balloon could withstand higher pressure, and the stress distribution was more uniform on membrane. When the cable and the film were relatively smooth, the reduction of the friction coefficient could reduce the rope stress.

Abstract:The drilling process of a bored pile can cause radial unloading-induced borehole contraction. In this study, the stress-displacement solution for a borehole under radial unloading in cohesiveless soil was derived based on the SMP yield criterion and the non-associated flow rule. By combining with earth pressure formulas derived from cavity wall formula and Berezantsev’s formula, the variation curves of borehole wall displacement with borehole depth were obtained, which were compared the results of the case with elastic deformation ignored in plastic zone. Parameters study shows that the unloading factor n, borehole radius a₀, and internal friction angle  had obvious influences on borehole wall displacement, and the effects of n and  had a critical value where the borehole wall displacement was significantly increased when n and  were less than the value. However, the influence of dilatancy angle ψ on borehole wall displacement was limited and could be ignored. In addition, n was a function only related to , while r_p/a was a constant value only related to n and  and had no relation with depth, which suggests that the self-supported depth of vertical drilling in cohesiveless soil was zero. Moreover, it can be found that the wall displacement was smaller and the plastic zone radius was larger when elastic deformation was ignored in plastic zone, which indicates that the solution of ignoring elastic deformation in plastic zone is not conservative in engineering applications. Lastly, the value of borehole wall displacement with different earth pressures along depth was quite different, which shows that the selection of earth pressure in vertical drilling should be combined with real field measurement.

Abstract:In order to guide the production of block caving method with high horizontal in situ stress, the stress evolution law of the extraction level excavations during the process of undercutting with high horizontal in situ stress was studied, and the occurrence mechanism of specific characteristics of ground pressure disaster in the extraction level excavations was revealed. According to the actual engineering and physical parameters of the mine, a numerical simulation model was established by using finite difference software FLAC3D, and Mohr-Coulomb failure criterion was adopted in calculation. In the simulation process, the extraction level excavations were excavated firstly according to the backward undercutting method. The process of the undercutting was divided into three steps, and the stress states of extraction level excavations after each step were monitored and analyzed respectively, which were compared with the actual situation of ground pressure disaster on site. The results are consistent with the evolution law of ground pressure disaster on site, showing that with the development of undercut blasting, compressive stress concentration gradually occurred in the extraction level excavations in the vicinity of the undercut front. Ground pressure disasters occurred when the compressive stress increased beyond the shear failure condition of rock mass. Tensile stress concentration appeared in the extraction level excavations below the undercut layer, and ground pressure disasters occurred again when the tensile stress increased beyond the tensile failure condition of rock mass. Under high horizontal in situ stress, the extraction level excavations of block caving method presented the stress law of "compressive stress concentration followed by tensile stress concentration". With the increase of undercut area, the extent of compressive stress and tensile stress concentration became increasingly obvious, thus ground pressure disasters occurred repeatedly in the extraction level excavations in actual production.

Abstract:In view of crushing magnetite ore in metal mining enterprises, engineering problems exist such as huge energy consumption and low energy utilization ratio. Split Hopkinson pressure bar device and high-speed photography technology were utilized in this study. First, the pattern and mechanism of energy migration and transformation of magnetite ore under impact load were studied. Second, the standard square hole sand and stone sieve and the GZS-1 high frequency vibrating sieve were adopted to investigate the fragmentation distribution of magnetite ore, the variation of the average particle size, and the transformation process of ore impact crushing mode under different dissipation energy. Then, the correlation problem between ore energy dissipation rate and crushing degree was analyzed with the increase of strain rate. Finally, combining with the basic factors that affect ore fragmentation distribution, the prediction model expression of the average particle size of magnetite ore was derived. The research shows that with the increase of incident energy, the decrease of ore wave impedance changed the transmission coefficient and the reflection coefficient between ore and pressure bar, and affected the distribution of each energy in incident energy. It means that the energy dissipation rate and the energy reflectance increased, but the energy transmittance decreased. The higher the dissipated energy was, the severer the degree of ore broken was. When ore dissipated energy is increased from 14.79 J to 121.18 J, the main distribution region of ore fragment size moved from the coarse-grained end (26.5 mm, 37.5 mm) to the fine-grained end (4 mm, 16 mm). There was a subtractive logarithmic relation between dissipated energy and average particle size (d_s), and d_s reduced by nearly 56.04 %. There was a critical value in d_s. When d_s was greater than this value, there was a positive correlation between energy dissipatation rate and crushing degree. Conversely, there was a negative correlation between them. At this value, the magnetite ore could be broken optimally. The results have certain reference value for the control of energy consumption in the crushing process of magnetite ore.

Abstract:To investigate the relation of crushing effect of magnetite and energy under mechanical impact, the drop weight impact experiments, electron microscope observation test, and atomic absorption spectrometric analysis tests were carried out. The fragmentation characteristics and the separate mechanism of mineral particles of banded magnetite-quartzite under impact were analyzed, and the theoretical relations between energy density and size fractal dimension of fragments, average fragment size, and mineral particle separation efficiency were obtained. The study found that there were fractal characteristics in size distribution fragments, and the breakage extent of magnetite-quartzite under impact could be described more comprehensively with size fractal dimension and average fragment size. The fragment size under the separation of mineral particles was consistent with size of minerals, and the smaller the fragment size, the more remarkable the mineral separation is. The morphology and optical characteristics of separated particles after the impact crushing were closer to the mineralogical characteristics of the ore in comparison with the products of the second stage grinding, and the total iron grade of separated magnetite particles produced from impact crushing met the requirement of beneficiation for it was higher than that produced from the second stage grinding. The results showed that the average particle size decreased by cubic polynomial with the increase in energy density. The fractal dimension increased exponentially, and the separation efficiency of mineral particles increased by cubic polynomial. The specific energy consumed in magnetite ore processing could be reduced by increasing the breakage extent of magnetite-quartzite, the mass ratio of mineral particles, and energy density during crushing, and directly conducting magnetic separation after sieving mineral particles.

Abstract:To study the influence mechanism of calcite surface structure on water adsorption, molecular dynamic simulation was firstly employed to investigate the adsorption characteristics of water on various calcite surface structure with different types and scales. Then, the water adsorption characteristics in nano-slit with surface defects were investigated, which was used to decipher the formation mechanism of water blocking. Finally, the dangling bond characteristics and surface energy results were combined to explain the differential adsorption mechanisms. Results showed that calcite surface structure had great influence on water adsorption. Water was preferentially adsorbed and aggregated around the surface structure, and the adsorption strength and density were much higher than those on the ideal calcite surface. Size of surface structure also presented a great influence on water adsorption. The larger the structure, the stronger the water adsorption. Water in the nano-slits rapidly aggregated around the surface structure and formed obvious adsorption protrusions. Then the adsorption protrusions combined into a water film and blocked the flow space. The water blocking effect appeared. The dangling bond density and surface energy of the vacant surface, protrude surface, and ideal surface were 7.275 nm^-2 and 0.734 J/m², 6.716 m^-2 and 0.721 J/m², 5.098 nm^-2 and 0.581 J/m², respectively. There were more active sites with stronger reactivity on the vacant and protrude surface. Therefore, water was preferentially adsorbed on them.

Abstract:To investigate the impact of climate difference on the energy performance of office buildings in cold regions of China, Morris method was adopted to conduct a sensitivity analysis on the influence parameters of building indoor environmental construction loads in Beijing, Lanzhou, Kashgar, and Lhasa. Loads distribution was obtained to reflect the load differences among the four cities, and sensitivity and correlation were adopted to describe the regional differences in the influence of parameters on load so as to optimize the building load according to the correlation determination. Results show that the load level in Lhasa was lower than others, and was significantly affected by radiation-related parameters, where the sensitivity of solar absorptance of external wall and roof structures could be close to the average heat conductivity of corresponding structures. High sensitivity ranking parameters (internal loads and set-point temperatures) and some low ranking parameters (structure parameters dominated by heat conduction) had the same optimal value in different regions, while the optimal values of SHGC and WWR generally showed regional difference, orientation difference, and uncertainty. Only Lhasa and Kashgar had the same optimal value for SHGC (0.52) and WWR (0.25) in all orientations. In addition, compared with the optimization solution of NSGA-Ⅱ (200 generations, 10 populations/generation), the optimizagtion of building load based on Morris sensitivity analysis was not only slightly better but could save at least 1/3 of total time consumption. This study reveals that the local climate difference in cold regions has a significant impact on building loads, while Morris sensitivity analysis can analyze this difference and quickly optimize the building energy consumption performance in design stage.

Abstract:The study is aimed to develop an ideal method to estimate empirical coefficient of diffuse solar radiation model in the Chinese cities where there is no record of solar radiation data. The ground meteorological and solar radiation data from China Meteorological Data Service Center and the method of regression analysis were used to develop and verify the model. The sunshine duration, global solar radiation and diffuse solar radiation from 2000 to 2017 of 17 stations were selected. 12 individual models based on sunshine duration ratio and clearness index and 3 modified models based on geographical parameters (longitude, latitude, and altitude) were built using the data of the first ten years of each station. The data of the last four years of each station were used to evaluate the accuracy of the models. The models were evaluated using coefficient of determination (R²), mean absolute percentage bias error (MAE), and root mean percentage squared error (RMSE). Results show that the form of the model had a great influence on accuracy. The accuracy of the polynomial model was higher than that of the logarithmic and exponential forms, and the accuracy of the primary function was lower than that of the quadratic and cubic functions. Besides, the model using clearness index and sunshine duration ratio as its input parameters was the most accurate among individual models, and the model based on clearness index was the most accurate among modified models. For unobserved stations, the diffuse solar radiation can be estimated by the proposed model based on latitude, longitude, altitude, and clearness index.

Abstract:Due to the adverse effects of traffic noise on human hearing, blood pressure, and cardiovascular system, reducing traffic noise interference and realizing indoor natural ventilation have become the key technical problems of street-facing buildings. To effectively solve this problem, a new sound insulation ventilation device was designed, and a corresponoling sound insulation ventilation model as well as a calculation model of fresh air volume was established. According to the simplified model of sound insulation ventilation, a Simulink simulation model was constructed. Effects of ambient noise and frequency on the sound insulation performance of the device were analyzed through experiments. The ventilation experimental data were compared with the simulation results to verify the accuracy of the Simulink simulation model. Influence of ventilation volume and ventilation chamber volume on the ventilation effect of the device was studied by Simulink simulation model. Then an optimization scheme was put forward, and the ventilation effect of the optimized device was simulated. Experiment results show that the indoor noise of running device was approximately the same as that when the window was closed. The sound insulation effect of the device was more ideal for medium and high frequency ambient noise. The Simulink simulation model could reflect the ventilation effect well. When the ventilation chamber volume was matched with the economic ventilation volume, the economic efficiency was the best. By adopting the further optimized device, the fresh air volume of single bedroom could reach 35.16 m³/h and the CO₂ volume fraction could be controlled within 1 030×10^-6, which meets the requirements of indoor air quality.