ALBERT

Description: A novel composite adaptive antidisturbance controller is developed for a class of discrete-time switched system. First, two composite adaptive observers are proposed to estimate the external disturbances and unknown parameters, respectively. Then, based on the estimation values, a composite adaptive antidisturbance controller is constructed, which can guarantee system has a good antidisturbance performance. A solvable sufficient condition is presented by using linear matrix inequalities (LMIs). Finally, a numerical example is shown to demonstrate the effectiveness of the proposed control approach.

Description: The dam reliability study is essential for dam operation safety, regarding the complexity in dam failure causes. The assessment of the dam reliability is now mainly probabilistic or nonprobabilistic. The probabilistic method is usually applied to the cases with sufficient knowledge on dam parameters, while the nonprobabilistic method is suitable for the cases with insufficient knowledge on dam parameters. Since a dam can contain multiple parameters, information abundancy can vary among those parameters, and neither the probabilistic method nor the nonprobabilistic method alone is enough for dam reliability assessment. In this paper, the probabilistic method and nonprobabilistic method are modified based on the adjusted first-order second-moment method and the interval analysis method to suit the dam reliability assessment. Based on characterization on these two methods and the research of the fusion method, the secondary performance function of the dam is constructed, and the construction method of the risk assessment model for dam is proposed. Combined with a case study, this paper contributes to the safe operation of the dam.

Description: When evaluating the ship’s underwater electric field stealth, the underwater electric potential or the underwater electric field is often used, but it is easily affected by the environment conditions. As a result, the evaluating accuracy is not high. To solve this problem, the equivalent electric dipole moment is used as the evaluating factor in this paper. Firstly, the method of inverting the equivalent electric dipole moment in the frequency domain is proposed. However, the limited measuring range will also lead to some errors based on the proposed method. As a result, we improve the proposed method by applying an integral correction which uses a standard dipole source. To test the effectiveness of this method, a simulation experiment is carried out, and the results show that the method has high inversion accuracy even in a low signal-to-noise ratio (SNR) environment. This method has provided a new technological approach for evaluating the ship’s corrosion-related static electric field.

Description: This paper takes the double predriven recovery rooms (DPRR) of 31109 panel of a coal mine in Inner Mongolia as a case study. DPRRs are used to withdraw mining equipment, which play a significant role in safe and efficient production in the final longwall mining stage. Theoretical analysis and numerical simulation were carried out to study the reasonable size of the front abutment pillar between DPRR (inter-DPRR pillar) and the damage depth of the DPRR floor. The results show that (1) the stress distribution of the fender (the remnant longwall panel) can be approximately divided into three stages with the advance of the working face: stress redistribution (the first) stage, stress superimposed growth (the second) stage, and stress transfer (the third) stage. (2) According to stress distribution and the corresponding failure mode of the fender, the calculation model of the slippage damage of the DPRR floor is rectified, and the damage range of the floor is rezoned to make it more suitable for the damage depth of the room. (3) The zone of influence of the front abutment pressure is 40–50 m, and the stress around the DPRR increases significantly in the final mining stage. When the size of the inter-DPRR pillar is greater than 15 m, the effect of increasing the coal pillar size on lowering the peak stress of the main predriven recovery room is limited. (4) Floor heave tends to increase at first and then decrease with depth and reaches the maximum in the depth of 5 m in the final mining stage, indicating that 5 m is the starting point for the initial depth of the floor heave. (5) The theoretical calculation shows that the reasonable size of the inter-DPRR pillar is 20 m, and the critical width of the fender is 18.48 m, which can guide the secondary support to prevent dynamic disasters. Floor grouting and constructing concrete floor are effective and economic ways to control the floor heave.

Description: The homogeneous-heterogeneous reaction in the boundary layer flow of a water-based nanofluid in the stagnation-point region of a plane surface is investigated. The type of small particles explored here is the single-walled carbon nanotubes. The homogeneous nanofluid model is employed for description of behaviours of nanofluids. Here, the homogeneous (bulk) reaction is isothermal cubic autocatalytic, while the heterogeneous (surface) reaction is single, isothermal, and first order. The steady state of this system is analysed in detail, with equal diffusion coefficients being considered for both reactants and autocatalysts. Multiple solutions of the reduced system are captured for some particular sets of physical parameters, which seem to be overlooked in all previous published works with regard to studies of homogeneous-heterogeneous reactions modeled by homogeneous nanofluid models. Besides, we discover the significant limitation of previous conclusion about that the solutions by homogeneous nanofluid flow models can be recovered from those by regular fluids.

Description: Accurate simulation of cavitating flows in pipeline systems is important for cost-effective surge protection. However, this is still a challenge due to the complex nature of the problem. This paper presents a numerical model that combines the discrete vapor cavity model (DVCM) with the quasi-two-dimensional (quasi-2D) friction model to simulate transient cavitating flows in pipeline systems. The proposed model is solved by the method of characteristics (MOC), and the performance is investigated through a numerical case study formulated based on a laboratory pipeline reported in the literature. The results obtained by the proposed model are compared with those calculated by the classic one-dimensional (1D) friction model with the DVCM and the corresponding experimental results provided by the literature, respectively. The comparison shows that the pressure peak, waveform, and phase of pressure pulsations predicted by the proposed model are closer to the experimental results than those obtained by the classic 1D model. This demonstrates that the proposed model that combines the quasi-2D friction model with the DVCM has provided a solution to more accurately simulate transient cavitating flows in pipeline systems.

Description: A generalized base station-relay-user equipment (BS-Relay-UE) beamforming design is investigated for a cooperative multiple-input multiple-output (MIMO) multirelay networks with imperfect channel state information (CSI). In order to minimize the worst-case mean square error (MSE) which is subject to a semi-infinite (SI) relay power constraints, a generalized optimal beamforming structure for the relay amplifying matrix is effectively proposed, and then the SI relay power constraints are converted into linear matrix inequalities (LMIs) version. In such conversion, the objective problem recasts as a decoupled biconvex semidefinite programming (SDP) one which can be efficiently solved by the proposed alternating algorithm. The system performance has been verified in terms of worst-case MSE using a set of qualitative analyses. The results show us that the proposed beamforming method outperforms the conventional schemes and can also effectively reduce the computational complexity when it is compared to the cutting-set schemes and also to the nonrobust ones.

Description: We focus on the power consumption problem for a downlink multiuser small-cell network (SCN) considering both the quality of service (QoS) and power constraints. First based on a practical power consumption model taking into account both the dynamic transmit power and static circuit power, we formulate and then transform the power consumption optimization problem into a convex problem by using semidefinite relaxation (SDR) technique and obtain the optimal solution by the CVX tool. We further note that the SDR-based solution becomes infeasible for realistic implementation due to its heavy backhaul burden and computational complexity. To this end, we propose an alternative suboptimal algorithm which has low implementation overhead and complexity, based on minimum mean square error (MMSE) precoding. Furthermore, we propose a distributed correlation-based antenna selection (DCAS) algorithm combining with our optimization algorithms to reduce the static circuit power consumption for the SCN. Finally, simulation results demonstrate that our proposed suboptimal algorithm is very effective on power consumption minimization, with significantly reduced backhaul burden and computational complexity. Moreover, we show that our optimization algorithms with DCAS have less power consumption than the other benchmark algorithms.

Description: The TTS iterative method is proposed to solve non-Hermitian positive definite linear systems and some convergence conditions are presented. Subsequently, these convergence conditions are applied to the ALUS method proposed by Xiang et al. in 2012 and comparison of some convergence theorems is made. Furthermore, an example is given to demonstrate the results obtained in this paper.

Description: The flow characteristics of raw sewage directly affect the technical and economic performance of sewage-source heat pump systems. The purpose of this research is to characterize the flow characteristics of sewage by experimental means. A sophisticated and flexible experimental apparatus was designed and constructed. Then the flow characteristics of the raw sewage were studied through laboratorial testing and theoretical analyses. Results indicated that raw sewage could be characterized as a power-law fluid with the rheological exponentnbeing 0.891 and the rheological coefficientkbeing 0.00175. In addition, the frictional loss factor formula in laminar flow for raw sewage was deduced by theoretical analysis of the power-law fluid. Furthermore, an explicit empirical formula for the frictional loss factor in turbulent flow was obtained through curve fitting of the experimental data. Finally, the equivalent viscosity of the raw sewage is defined in order to calculate the Reynolds number in turbulent flow regions; it was found that sewage had two to three times the viscosity of water at the same temperature. These results contributed to appropriate parameters of fluid properties when designing and operating sewage-source heat pump systems.