Search

In this work, an analytical model describing liquid wicking phenomenon in porous media was constructed, based on the statistical geometry theory and the fractal theory. In the model, a new structure-property relationship, depicted by specific surface, porosity, tortuosity, pore fractal dimension, maximum pore size of the porous media, was introduced into the energy conservation equation. According to the theoretical model, the accumulated imbibition weight in porous media was achieved, and the predictions were verified by available experimental data published in different literatures. Besides, structure parameters influencing the imbibition process upon approaching equilibrium height were discussed. The model and results in this work are useful for the application of porous media in scientific research and industry.

This study has provided quantitative information on the in vitro release and digestion of DHA microcapsules as influenced by the wall protein and DHA source.

As the basis for the static security of the power grid, power load forecasting directly affects the safety of grid operation, the rationality of grid planning, and the economy of supply-demand balance. However, various factors lead to drastic changes in short-term power consumption, making the data more complex and thus more difficult to forecast. In response to this problem, a new hybrid model based on Vari-ational mode decomposition (VMD) and Long Short-Term Memory (LSTM) with seasonal factors elimination and error correction is proposed in this paper. Comprehensive case studies on four real-world load datasets from Singapore and the United States are employed to demonstrate the effectiveness and practicality of the proposed hybrid model. The experimental results show that the prediction accuracy of the proposed model is significantly higher than that of the contrast models. Index Terms-Power grid security, short-term load forecasting , seasonal factors elimination, error correction.

Based on the statistical geometry theory and the fractal theory, a theoretical model to predict the pressure drop of fluid flowing through porous media has been derived in this work. This model is expressed as a function of specific surface, porosity, tortuosity, the pore fractal dimension, maximum pore size, which have clear physical meaning. To verify this model, experiments have been carried out with air using glass beads of three samples. For each sample, the present model fits the experimental data well. Besides, a comparison between the Ergun equation and present model has been made, the result shows that the present model fits the experimental data much better than the Ergun equation and has good accuracy in the range of [Formula: see text].

This paper is concerned with the forced flow through curved open capillary channels under microgravity conditions. A maximum flow rate in the open capillary channel achieves when the flow rate exceeds a certain value and the free surface collapses leading to the gas ingestion. The gas ingestion is not desired for most of the applications. In order to prevent it and enable an optimal performance, it is vital to understand the influences of the channel geometry parameters and liquid properties on the maximum flow rate. In this paper, the one-dimensional theoretical model successfully applied to the straight open capillary channel is extended to the curved open capillary channel. The result shows that under the same boundary conditions, the maximum flow rate in the curved open channel is smaller than that in the straight open channel. The maximum flow rate decreases with the curvature of open channel increasing. By analysis, the pressure loss and the centrifugal force effect due to the curve motion in a curved path are considered to be the cause of the maximum flow rate difference between the curved channel and the straight channel. It is found that the centrifugal force effects weaken the pressure difference balance ability of the free surface and the pressure loss in the curved open channel is greater than that in the straight open channel. By comparison, the one-dimensional theoretical results agree well with CFD simulations and the average relative error is only 1.51%. Furthermore, the parametric study of flow in the curved open capillary channel depicts that the maximum flow rate increases with the channel curvature or aspect ratio increasing, and decreases with the open channel length, contact angle or Ohnesorge number increasing. This conclusion can be utilized to design the open channel in space liquid management system.

In the absence of gravity, spontaneous capillary flow along an interior corner is a significant portion of liquid behavior in spacecraft. To effectively control the space liquid, the design of fluids management processes in the low-gravity environment of space requires a rapid and accurate prediction of capillary flow in interior corners. So far, the previous studies have been focused on the capillary flow along the straight interior corner. However, the curved interior corner is far more common. A comprehensive theoretical model is established to study the curved corner effects based on previous studies. By analysis, the centrifugal force caused by the curve motion is the decisive factor which makes the capillary flow in curved interior corners different from that in straight interior corners. The influences of centrifugal force on the free surface and friction factor are discussed, and high-precision approximation modeling method is used in free surface modeling to speed up the solving process. To validate the theoretical model, a series of microgravity drop tower experiments are conducted. By comparison, the theoretical results agree well with the experimental results. The results show that the liquid rises faster as the channel curvature increases. This feature can be used to transport and manage liquid better in spacecraft. A modified Suratman number Su is introduced to judge the curved corner effects. When S u = 3 , the relative error e caused by neglecting the curved corner effects is up to 36% which means the curved corner effects have a great influence on the capillary flow. When Su ≪ 1, the relative error e is close to 0 which means the curved corner effects can be neglected.

In recent years the advent of on-orbital refueling technology and the accompanying interest in liquid management in space have rekindled attention to the study of the liquid-gas interface determination. So far, a series of numerical methods, such as the Shooting method, are used to calculate the mathematical model of liquid-gas interface. However, these methods have some drawbacks in common, such as poor convergence, dependence on initial value and instability. As a result, long calculation time and sudden calculation interruption are inevitable. Although satisfactory results can be achieved, it requires human intervention. As an important intermediary of capillary flow and liquid management device design, liquid-gas interface calculations need to be done thousands of times. Therefore, the quickness and robustness of liquid-gas interface calculations are needed. Surrogate modeling method arising with the development of aerospace technology in recent years provides a new way to solve this problem. Combining with the characteristics of liquid-gas interface calculation, a double-layer radial basis function surrogate model is proposed to approximate the mathematical model of liquid-gas interface. This surrogate model is approximately equivalent to the mathematical model of liquid-gas interface but is much easier to solve. Compared with the Shooting method, the efficiency of the surrogate model is improved by 99.46%, and the success rate is increased to 100% from 35%.

Due to the increasing complexity of dynamic systems, it is increasingly difficult for traditional mathematical methods to meet the modeling requirements of complex dynamic systems. With the continuous innovation of computer and big data technologies, massive data can be easily obtained and stored. Therefore, studies of dynamic system modeling through data-driven approaches have attracted more and more researchers’ attention. This paper compares the dynamic mode decomposition method and dynamic equation reconstruction. Taking Lorenz and nonlinear Helmholtz resonant systems as examples, the two methods show the ability to reconstruct and describe the evolution characteristics of the dynamic system. Specifically, the dynamic mode decomposition method can describe the characteristics of the dynamic system more intuitively; however, it cannot provide physical insights. On the other hand, the discovery of dynamic equations from data can more accurately express the physical evolution characteristics of the dynamic system; however, it is easily affected by random noise. Because the dynamic mode decomposition method can obtain a reduced-order model, which can not only retain useful information of the original data but also reduce the noise disturbances, it can effectively improve the noise attenuation and finally reconstructions of differential dynamical equations.