基于双态混沌PSO的机载激光通信视轴稳定控制

机载空间激光通信视轴稳定是激光通信链路建立的前提。在视轴稳定平台中应用自抗扰控制方法取得了良好的控制效果,但自抗扰控制需调整参数众多且缺乏规范的调整手段。针对自抗扰控制调参难的问题,本文提出了一种利用双态混沌粒子群算法优化自抗扰控制参数的方法。仿真结果表明,与PSO-PID控制方法相比,该方法具有更快的响应速度,更强的抗干扰能力和更好的鲁棒性。     

Real-Time Monitoring of Gas–Solid Fluidized-Bed Granulation and Coating Process: Evolution of Particle Size,Fluidization Regime Transitions,and Psychometric Parameters

Moisture content and particle size are critical parameters in fluidized-bed granulation and coating. In this study, microcrystalline cellulose was granulated and coated. The particle size was monitored in real time by a Parsum IPP70 probe. The fluidization regime was assessed by Gaussian spectral analysis. The bed temperature and gas humidity profile were monitored to evaluate the drying efficiency. The defluidization phase was detected in the early stages with frequencies below 6.0 Hz. The Parsum probe showed the growth of the particles due to agglomeration. The psychometric parameters indicated the lower potential energy for drying. Therefore, monitoring in real time is important to detect failures.     

A novel approach to fuzzy wavelet neural network modeling and optimization

In this paper, an efficient approach of combining Takagi–Sugeno–Kang fuzzy system with wavelet based neural network is presented. The model replaces the constant or a linear function of inputs in conclusion part of traditional TSK fuzzy model with wavelet neural network (WNN), thus each rule uses fuzzy set to separate the input space into subspaces spanned by different wavelet functions. For finding the optimal values for parameters of our proposed fuzzy wavelet neural network (proposed-FWNN), a hybrid learning algorithm integrating an improved particle swarm optimization (PSO) and gradient descent algorithm is employed. The two-layer inline-PSO process is proposed in this paper, whose adjustment scheme is more fitting the consequent pattern learning based gradient descent optimization and will locate a good region in the search space. Simulation examples are given to test the efficiency of proposed-FWNN model for identification of the dynamic plants. It is seen that our modeling and optimization approach results in a better performance.     

A contact model for rough crushable sand

Sand roughness is now accessible to measurement. Incorporating this parameter into sand models using the discrete element method (DEM) is known to improve bulk small strain response. In this work we explore the effect on problems where particle crushing takes place. A well-established DEM particle crushing model and a rough Hertzian contact model are here combined to incorporate both effects in a single contact model. Including contact roughness results in stronger particles whilst all other material parameters being equal. The model is then used to simulate high pressure oedometric compression tests on a strong silica sand. It is shown that including realistic values of surface roughness enables to correctly capture both load-unload behaviour and particle size distribution evolution while using realistic values of elastic bulk properties for the sand grains. Roughness is then a model refinement that may result in simpler, more objective DEM calibrations.     

Investigation of the ultimate particle size distribution of a carbonate sand

A series of ring shear tests were conducted to investigate the ultimate particle size distribution of a carbonate sand. The tests were carried out under different stress levels, on three types of specimens: 1) uniformly graded specimens made of dry natural sand 2) remoulded specimens of the crushed sand after first shearing to large strains 3) specimens made of natural sand grains but with the same grading as in (2). The first series of tests on type (1), carried out to very large strains, led to apparently stable gradings, distinct for each stress level. Only limited additional particle breakage could be induced by remoulding the specimens after shearing (type (2)) and subjecting them to more shearing. Tests on specimens created at the apparently stable gradings (type (3)) but from the intact sand particles however led to significantly greater breakage. For the three types a stable, fractal grading was achieved. Analyses of the soil particles’ shape showed that the aspect ratio, sphericity and circularity reach a steady value at large strains, in parallel to reaching a stable grading. The mobilized angle of shearing resistance however was not significantly different in the different types of samples, suggesting the final grading dominates the behaviour.     

Effect of lognormal particle size distributions on particle spreading in additive manufacturing

Additive manufacturing (AM) has attracted much attention worldwide in various applications due to its convenience and flexibility to rapidly fabricate products, which is a key advantage compared to the traditional subtractive manufacturing. This discrete element method (DEM) study focusses on the impact of particle polydispersity during the particle spreading process on parameters that affect the quality of the final product, like packing and bed surface roughness. The particle systems include four lognormal particle size distribution (PSD) widths, which are benchmarked against the monodisperse system with the same mean particle diameter. The results reveal that: (i) the solid volume fraction of the initial packed particle bed in the delivery chamber increases then plateaus as the PSD width increases; (ii) regardless of PSD width, the solid volume fraction of the particle bed increases with spreading layer height before compression, but decreases with layer height after compression; (iii) the bed surface roughness increases with PSD width or layer height both before and after the compression of the spreading layer; (iv) the extent of increase in solid volume fraction during compression is correlated with the extent of decrease in bed surface roughness; and (v) the broader PSDs exhibit larger fluctuations of solid volume fraction of the particle bed and bed surface roughness due to greater variability in the arrangement of particles of different sizes. The results here have important implications on the design and operation of particle-based AM systems.     

Understanding the need for pre-injection from permeability measurements: What is the connection?

Pre-grouting ahead of tunnels has three main functions: to control water inflow into the tunnel, to limit groundwater drawdown above the tunnel, and to make tunnelling progress more predictable since rock mass quality is effectively improved. It helps to avoid settlement damage caused by consolidation of clay deposits beneath built-up areas, since towns tend to be built where terrain is more flat, due to the clay deposits. There are so many instances of settlement damage that the profession needs to take note of the need for high-pressure pre-grouting, to use micro-cements and micro-silica additives. The use of highpressure injection may cause joint jacking, but this is local in extent when the rapid pressure decay away from an injection hole is understood. This effect is variable and depends on the geometrical parameters of the joints. This pressure-decay advantage must not be violated by maintaining high pressure when grout flow from the injection hole has ceased. The latter can cause damage to the grouting already achieved. Simplified methods of estimating mean hydraulic apertures(e) from Lugeon testing are described, and from more sophisticated three-dimensional(3 D) permeability measurement. The estimation of the larger mean physical joint apertures(E) is based on the joint roughness coefficient(JRC).Comparison is then made with the empirical aperture-particle size criterion E 4 d95, where d95 represents almost the largest cement particle size. Depending on joint set orientations and on the available micro-cements, the decision must be made of which range of pre-injection pressure should be aimed for,using successive reductions of the water-cement ratio w/c. More simple estimation of permeability, also with depth dependence, can be made with the empirical link between a modified rock mass quality Q and permeability, which is termed QH2 O. The value of this parameter can be based on core-logging or intunnel face logging. The 3 D before-and-after-grouting permeability measurements have been used to justify the quantification of rock mass quality Q-parameter improvement, and the consequent increases in expected P-wave velocity and deformation modulus, for application in dam foundation treatment and its monitoring.     

考虑布线资源松弛的X结构Steiner最小树算法

为了进一步考虑X结构,并充分利用障碍内可用布线资源,文中提出考虑布线资源松弛的X结构Steiner最小树算法.为了能够求解离散问题,在粒子的更新操作中引入交叉算子和变异算子.通过构建查找表,为整个算法流程提供快速的信息查询.提出角点选取策略,通过引入一些障碍角点,使粒子满足约束.最后构建精炼策略,进一步提高最终布线树的质量.实验表明,文中算法充分利用障碍内可用布线资源,有效缩短总布线长度,取得较佳的总布线长度.     

Milling of pharmaceutical powder carrier excipients: Application of central composite design

Pharmaceutical powder carriers are often used to prevent agglomeration of a micronized drug in the co-milling process. Twenty-four pharmaceutical excipients were subjected to preliminary mild milling conditions in this work. Ten of them showed acceptable milling properties with alginic acid, calcium alginate, microcrystalline cellulose (Avicel® 200), carrageenan, and hypromellose having the best particle size reduction without any aggregation while maintaining a narrow span. For the latter five substances, circumscribed central composite design (CCD) evaluating the effect of the factors milling speed and timeon the responses (particle size, particle size distribution) for three milling ball sizes was used to establish optimal milling conditions. For all ten possible factor combinations and each ball size, a quadratic response surface model was used to predict the response variable. For three substances out of five, the best results were achieved using 5-mm balls. Thermal characteristics showed the good stability of excipients under optimized milling conditions.