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This article is concerned with the stabilization problem for a class of networked systems subject to successive packet losses. Different from the input delay approach used in some existing literature, the continuous‐time system under consideration is first converted into a discrete‐time stochastic system with system matrices subject to stochastic characteristic. In order to deal with the difficulties in the calculations of mathematical expectations of both matrix exponential and integral of matrix exponential function, the upper bound of successive packet losses and packet drop rate are assumed to be known and then the probabilities of the number of successive packet losses taking each value in a bounded set are calculated. Based on this, stability criteria are derived by recurring to the law of total expectation, which guarantee the exponential mean‐square stability of resulting closed‐loop discrete‐time stochastic system with a prescribed H∞ performance. Moreover, a controller design procedure is then proposed. Finally, to verify the analysis results and testify the effectiveness and applicability of the designed algorithm, a numerical simulation example is given. [ABSTRACT FROM AUTHOR]

Event-triggered schemes are characterized in less communication traffic while maintaining the resulting controlled plant’s desired stability and performance criteria. In the presence of packet dropouts, this paper is concerned with the modeling and control problems for a class of discrete-time stochastic systems with event-triggered schemes. Two different mathematical analysis methods are proposed to model the packet loss when an event-triggered scheme is subject to packet loss. First, a stochastic distributed sequence satisfying the Bernoulli process is utilized to model the triggered packets transmitted in the communication networks. Considering the difference between time-triggered and event-triggered schemes, an equivalent model with a random sequence not satisfying a Bernoulli distribution process is also analyzed, which is not the same as some existing results in the literature. Then, the mean-square exponential stability of resulting augmented system is guaranteed and the prescribed ${H}_{\infty }$ performance level is achieved by solving resulting discrete ${P}$ -problem. Two examples with simulations are provided to validate the analytical results and demonstrate the effectiveness of the proposed co-design techniques. [ABSTRACT FROM AUTHOR]

Innovative fin arrangements were proposed to enhance the thermal performance of latent heat storage units. The enthalpy-porosity approach was employed to optimize the fin distribution and predict the transient melting behaviors of N-octadecane. The unit with horizontal fins of uniform length was set as the base condition for comparison. It was found that the dead space of heat transfer and melting due to natural convection was not effectively eliminated by the conventional fin set. The region persisted at the bottom of the unit until the end of the melting process. In light of these observations, the fins were repositioned and resized. Three alternative fin configurations were proposed and evaluated: angled fins, asymmetrically located fins, and stepped fins. Results illustrated that fin structures significantly influenced the heat transfer characteristics and melting behaviors of latent heat storage units. Generally, greater enhancements were attained with downward angles and downward offset distances. The downward angle −20°led to an accelerated melting rate of 18.3 % compared to the base condition. In case 9, where the fins were moved down by 12 mm, the heat transfer enhancement ratio reached 32.5 %. However, introducing inhomogeneity in the fin length had only a minimal impact on the melting process. • Non-uniformity in heat transfer due to natural convection decreases the overall PCM melting. • Novel fin arrangements are employed in this paper to improve the PCM melting as well as heat transfer. • Fins with downward angle and downward offset can substantially increase the thermal energy storage rate. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the modeling and stabilization problems for a class of discrete-time stochastic networked systems (DSNSs) subject to successive packet losses. The system under consideration is transformed into a stochastic one with bounded stochastic delay. Considering that the stochastic delay is characterized by nonuniform distribution, a new equivalent model is then constructed that enables the DSNS’s controller design to benefit from knowing the probability characteristic of packet losses. Specially, to verify this feature, the probabilities of the delay can be explicitly obtained by utilizing the formula of total probability, which is critical to model transformation and analyze practical problems that exist in DSNSs. Based on the proposed model, sufficient conditions are established under which the globally mean-square asymptotic stability of resulting stochastic delay closed-loop system is guaranteed, and a delay-distribution-dependent design procedure is then proposed. A numerical example with simulation is provided to validate the analytical results and demonstrate the effectiveness of the design procedure. [ABSTRACT FROM AUTHOR]

In this paper, the H∞$$ {H}_{\infty } $$ saturated control problems of networked systems with random sampling periods and stochastic transmission delays are investigated. The main issue is to design an H∞$$ {H}_{\infty } $$ saturated controller such that the controlled close‐loop system is exponentially mean‐square stable with a desired H∞$$ {H}_{\infty } $$ performance. A matrix exponential which is different from some existing literature is used to reconstruct the discrete‐time stochastic system to an equivalent yet tractable augmented model without any additional conditional constraint. In virtue of reduced‐order confluent Vandermonde matrix approach and Kronecker product operation, the stability condition in terms of linear matrix inequality is derived and then the desired H∞$$ {H}_{\infty } $$ saturated controller is designed. It should be emphasized that the improved method can also be used for the stability analysis and controller design when the system matrix contains complex roots. Finally, two numerical examples and a three‐axis milling machine system are utilized to manifest the reliability and practicality of the designed strategy. [ABSTRACT FROM AUTHOR]

Summary: This paper is concerned with the problem of delay‐distribution–dependent robust exponential stability for uncertain stochastic systems with probabilistic time‐varying delays. Firstly, inspired by a class of networked systems with quantization and packet losses, we study the stabilization problem for a class of network‐based uncertain stochastic systems with probabilistic time‐varying delays. Secondly, an equivalent model of the resulting closed‐loop network‐based uncertain stochastic system is constructed. Different from the previous works, the proposed equivalent system model enables the controller design of the network‐based uncertain stochastic systems to enjoy the advantage of probability distribution characteristic of packet losses. Thirdly, by applying the Lyapunov‐Krasovskii functional approach and the stochastic stability theory, delay‐distribution–dependent robust exponential mean‐square stability criteria are derived, and the sufficient conditions for the design of the delay‐distribution–dependent controller are then proposed to guarantee the stability of the resulting system. Finally, a case study is given to show the effectiveness of the results derived. Moreover, the allowable upper bound of consecutive packet losses will be larger in the case that the probability distribution characteristic of packet losses is taken into consideration. [ABSTRACT FROM AUTHOR]

In this paper, the stabilization problem of networked systems with communication constraints is studied, where the random sampling periods, deception attacks and packet losses are considered simultaneously. Different from the existing literature, the actual sampling periods are subject to undesirable physical constraints and fluctuate around an ideal sampling period with certain probability distribution. First, a closed-loop discrete-time stochastic system is constructed by considering the random sampling periods, deception attacks and packet losses in a unified framework. Second, an equivalent yet tractable stochastic model is established with the aid of matrix exponential computation. By reduced-order confluent Vandermonde matrix approach, law of total expectation, convolution formula and Kronecker product operation, a controller is designed such that the exponential stability in the mean-square sense of closed-loop stochastic system is guaranteed. Subsequently, a special model is discussed where no deception attack occurs and then the corresponding controller is designed. Finally, an illustrative example is given to show the effectiveness of the designed approach. [ABSTRACT FROM AUTHOR]

This paper is concerned with the H ∞ performance analysis for networked control systems with transmission delays and successive packet dropouts under stochastic sampling. The parameter uncertainties are time-varying norm-bounded and appear in both the state and input matrices. If packet loss is considered the same as time delay, when models the networked control systems with successive packet dropouts and delays as ordinary linear system with input-delay approach, due to sampling period is stochastic, then the delay caused by packet losses is a stochastic variable, which leads to difficulties in the stability analysis of the considered system. However, if we can transform the system with stochastic delay into a continuous system with stochastic parameter, we can solve the problem. In this paper, by assuming that the network packet loss rate and employing the information of probabilistic distribution of the time delays, the stochastic sampling system is transformed into a continuous-time model with stochastic variable, which satisfies a Bernoulli distribution. By linear matrix inequality approach, sufficient conditions are obtained, which guarantee the robust mean-square exponential stability of the system with an H ∞ performance. What's more, an H ∞ controller design procedure is then proposed, and a less conservative result is obtained by taking the probability into consideration. Finally, a numerical simulation example is employed to show the effectiveness of the obtained results. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Efficient and rational use of thermal energy requires the design and development of suitable and cost-effective latent heat storage systems. In this study, a novel curved thermal storage unit is put forward and its thermal behavior has been numerically compared with the traditional rectangular PCM-based thermal storage unit. The solid-liquid interface evolution, liquid flow pattern and temperature distribution are presented. Transient Nu at the heating wall and full melting time are also calculated. The numerical results show the high impact of the enclosure geometry on melting and nature convection. A reduction of 30.6 % in thermal storage time has been achieved by changing the unit from rectangular to curve. Moreover, parametric studies are conducted to assess how thermal performance of the units is affected by the heating wall temperature and PCM thermal conductivity. Correlations encompassing a wide range of parameters are developed in terms of full melting time. Results indicate that proportion of full melting time reduced for the curved unit is almost a constant value and does not vary significantly with these factors. All these may be very helpful for the design of more efficient thermal storage units. [ABSTRACT FROM AUTHOR]

Thermal energy storage plays an important role in correcting the disparity between energy supply and demand as well as improving the energy efficiency. The present work numerically investigates the conjugate heat transfer between PCM and heat transfer fluid within the novel and efficient frustum-shaped thermal storage units. A two-dimensional control volume-based numerical model is developed employing the CFD software Fluent. Five units of equal volume but different dimensions are compared to illustrate impacts of geometry on melting, and the optimal geometric design is determined. Then, the multiple PCMs technology is employed to the optimal unit to further enhance the melting heat transfer. Effects of the multiple PCMs arrangement, multiple PCMs' melting temperature distribution, and type on the melting behavior and heat transfer are investigated. Compared with the frustum-shaped and traditional shell-and-tube unit with a single PCM, predicted results indicate that the five PCMs arrangement in frustum-shaped unit can make the thermal storage time reduced by 21.5 % and 47.5 %, respectively. The great improvement may be of great significance to the optimal design of latent heat storage. [ABSTRACT FROM AUTHOR]

In this paper, a fundamental practical unit, namely the wedge-shaped enclosure, is proposed as a novel and efficient latent heat storage unit for thermal energy storage. The enthalpy-porosity method that treats the solid and liquid zones as a single domain is employed. Effect of the mushy zone constant C on melting is analyzed and a suitable value is obtained by comparing the numerical results with experimental data in the literature. A series of simulations are conducted to analyze the transient melting coupled with natural convection as well as the heat transfer process. Fourteen units those have different length ratios between top and bottom of the enclosures are investigated and compared by the analysis of transient temperature fields, vertical velocity distributions, and evolution of the melting fronts. It is found that the length ratio n dramatically affects the full melting time and heat transfer intensity. An enclosure of n = 5.5, which has the shortest completion time and the highest heat transfer intensity, is determined as the optimal unit. Compared with the base geometry ( n = 1), charging time of the optimal unit ( n = 5.5) decreased by 32.8 %, while the heat transfer intensity increased by 45.7 %. This is a significant improvement in the field of latent heat storage. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a systematic framework for stability and guaranteed cost control of linear impulsive systems subject to random time‐ and event‐triggering impulses. Moment stability criteria and design methods of time‐ and event‐triggered controllers with guaranteed quadratic performance for the impulsive system are established. It shows that the proposed event‐triggered controller in the sense that it guarantees at least the same quadratic performance function bound as the designed time‐triggered guaranteed cost controller, however, with a larger, or at most equal, average inter‐transmission time. Based on the proposed framework of random‐impulses systems, a stochastic dynamic event‐triggered control strategy is proposed to solve sampled‐data control systems in the presents of sporadic measurements or stochastic sampling. Numerical simulations illustrate the effectiveness of the proposed theoretical results. [ABSTRACT FROM AUTHOR]

This paper considers the sample-data-based consensus problem of multiagent systems with time-varying delay and packet losses. To distinguish the time delays caused by network-induced time-delay and packet losses, the switched system is utilized. A lower gain controller is designed based on the solution of a parametric algebraic Riccati equation. The Lyapunov stability theory is utilized to obtain the limitations on the frequency and the duration of packet losses which guarantees the consensus of multiagent systems. On the other hand, we theoretically prove that refined time-delay function can reduce the conservatism. A simulation example is given to illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Phase change material (PCM) can effectively reduce temperature fluctuations in greenhouses and increase crop yields. Plastic greenhouses are a major form of facility agriculture in southern China, and there are no walls in it. Therefore, how to combine plastic greenhouses with PCM has become research hotspot. A new type of high absorption latent heat storage plate (LHSP) was proposed. That is to lay PCM plates on the north side of the plastic greenhouse vertically. To enhance solar energy utilization and reduce heat loss, solar high absorption and thermal insulation layer were respectively placed on the sunny side and shady side. Two greenhouses were constructed and LHSP was placed in one greenhouse as Case 1. After that, a solar high absorption film and thermal insulation layer were attached to the sunny side and the shady side as Case 2 and Case 3. The average air temperature of two greenhouses and the thermal performance of LHSP were compared under three cases. Results showed that, in Case 1, the LHSP can raise the average air temperature inside the greenhouse by 1.8–2.9 °C during the night. in Case 2 and 3, the average air temperature had a stable improvement of 1.6–2.2 °C and 1.8–2.1 °C respectively at night. Besides, in Case 2, the heat storage of LHSP on sunny side had increased by 26.2%. In Case 3, the total average heat loss of LHSP was reduced by 21.5% and the average heat release from sunny side had risen by up to 39.7%. The high absorption latent heat storage plate showed excellent thermal performance. [ABSTRACT FROM AUTHOR]

The use of the electro-Fenton process to continuously generate H 2 O 2 and efficiently degrade organic pollutants is considered a promising technology. The ratio of generation of H 2 O 2 is usually regarded as the critical step; however, how the H 2 O 2 is utilized is also of particular importance. Herein, activated carbon was activated at different temperatures and used to explore the effect of nitrogen doping on the production and utilization of H 2 O 2 in the electro-Fenton-based degradation of organic pollutants. The experimental results indicate that nitrogen-doped activated carbon simultaneously promotes the generation and utilization of H 2 O 2 , which is attributed to the regulation of the competition between phenol and O 2 adsorption by the doped nitrogen. Nitrogen doping not only improves 2e−ORR selectivity but also aggregates phenol near the cathode to balance the concentrations of phenol and ·OH. Density functional theory (DFT) calculations further confirmed that pyrrole-N as a dopant promoted the adsorption of phenol, while pyridine-N was more favorable for O 2 adsorption. The unique balance of nitrogen types possessed by modified activated carbon NAC-750 permits the efficient synergistic generation and utilization of H 2 O 2 in a balanced manner during the degradation of phenol. This work provides a new direction for the rational nitrogen-doping modification of activated carbon for the electro-Fenton-based degradation of organic pollutants. [Display omitted] • The adsorption of phenol affects the adsorption of O 2 and the generation of H 2 O 2. • Graphite-N is the main site for the competitive adsorption of phenol and O 2. • Competition can be effectively regulated by regulating nitrogen doping types. • Reasonable nitrogen doping can promote the generation and utilization of H 2 O 2. [ABSTRACT FROM AUTHOR]

Experiment and numerical simulation were performed to research the possibility of adopting different ventilation modes for smoke confinement in a subway station fire accident. Bench scale experiments were conducted in a 1:50 scale model of a subway station. Fire Dynamics Simulator software (FDS) was utilized to carry out numerical simulations, which conducted in a full scale subway station. Experiment result agreed well with simulation result and the research showed that the different ventilation mode had different efficacy of smoke confinement released by the fire in basement 2. In addition, when the USME ventilation mode was adopted and there were smoke exhausted from basement 2 and air supplied into the basement 1, the efficacy of smoke confinement was the best. According to these cases conducted in this paper, the layouts of the ventilation vents had little influence on the efficacy of smoke confinement. Once the HRR was too big, the concentration would pass 50 PPM and the amount of exhausted smoke should be increased. [ABSTRACT FROM AUTHOR]

Smoke is the element of a fire that causes the greatest loss of life. The importance of eliminating smoke is underscored in the fire safety engineering of underground subway stations. In this study, an experiment and a numerical simulation were performed to determine the efficacy of different ventilation modes. The experiment was conducted on a 1:50 scale model of a subway station and a complementary Fire Dynamics Simulator (FDS) simulation was performed on a full scale station. The influences of natural ventilation, mechanical ventilation and hybrid ventilation were examined. The results indicated that natural ventilation was good for smoke elimination when the fire source was under the dome, and the gas temperature measured in the middle of the basement 1 decreased significantly as the size of the vent increased. Smoke was exhausted from the basement 1 and fresh air supplied into the basements 2 and 3, which had the best efficacy when managing the smoke diffusion. No matter that the fire source was under the dome or out of the atrium, the carbon monoxide (CO) concentration was the smallest when the modified hybrid ventilation system was in operation. At the same time, changes in the natural ventilation vent had an influence on smoke elimination and the efficacy of smoke elimination became better with the increasing of the dimension of the vent when the fire location was under the dome. [ABSTRACT FROM AUTHOR]

This paper presents two novel Lyapunov methodologies for almost sure stability of hybrid stochastic systems under asynchronous Markovian switching. One is established by a concave composite Lyapunov function with exponential martingale inequality. The other is derived by the strong law of large numbers, which can explore the coupling between the drift part and diffusion part of the systems, thus fully capturing the stabilizing effect of the stochastic noise. Both of these stability conditions give a quantitative relationship between the size of the detected delay of switching signal, the stationary distribution and the generator of Markov chain. As applications, easy-to-check stability and stabilization criteria are further provided for one-sided growth nonlinear systems and linear systems. Numerical examples illustrate the proposed theoretical results. [ABSTRACT FROM AUTHOR]