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Ningbo's seaport hydrogen refueling station was used as the research object. The effects of different leakage angles, wind direction, roof shape, leakage hole diameters, temperature, and humidity on the diffusion of hydrogen leakage were studied by numerical simulation. The influence of leakage angle on hydrogen leakage is mainly reflected in the presence or absence of obstacles. The volume of the flammable hydrogen cloud was reduced by 31.16%, and the volume of the hazardous hydrogen cloud was reduced by 63.22% when there was no obstacle. The wind direction can significantly impact hydrogen leakage, with downwind and sidewind accelerating hydrogen discharge and reducing the risk. At the same time, headwind significantly increases the volume of the flammable hydrogen cloud. Compared with no wind, the volume of the flammable hydrogen cloud increased by 71.73% when headwind, but the volume of the hazardous hydrogen cloud decreased by 24.00%. If hydrogen shows signs of accumulation under the roof, the sloping roof can effectively reduce the hydrogen concentration under the roof and accelerate the hydrogen discharge. When the leakage angle θ = 90°, the sloping roof reduced the volume of the flammable hydrogen cloud by 11.74%. The leakage process was similar for different leak hole diameters in the no wind condition. The inverse of the molar fraction of hydrogen on the jet centerline was linearly related to the dimensionless axial distance of the jet in different cases. Using a least squares fit, the decay rate was obtained as 0.0039. In contrast, temperature and humidity have almost no effect on hydrogen diffusion. Hydrogen tends to accumulate on the lower surface of the roof, near the roof pillars and the hydrogen dispenser. In this paper, a set of hydrogen detector layout schemes was developed, and the alarm success rate was verified to be 83.33%. •CFD numerical model for hydrogen refueling station at seaport is developed. •Pseudo-diameter model is used to describe simplified high-pressure hydrogen jet. •Effects of roof, leakage angles and wind on hydrogen diffusion are studied. •Recommendations on hydrogen detector layout are given based on parametric study. [ABSTRACT FROM AUTHOR]

• Dynamic stability of MDOF systems under parametric excitation was numerically simulated. • Responses of MDOF Mathieu-Hill equations were simultaneously obtained. • The conventional Hill ID method was numerically calibrated. • No resonances, simple resonances, combination additive and differential resonances were simultaneously determined. The stability and responses of dynamic systems under parametric excitation are often encountered in many fields of science and engineering, such as slender columns and thin plates under axial loadings. This paper proposes a novel numerical simulation method to simultaneously construct stability diagrams and predict the responses of multiple degree-of-freedom (DOF) dynamic systems under arbitrary parametric loadings. The method divides an arbitrary load into discrete segments to approximate the variable excitation function by a step function and then accumulates the system responses of each segment using a matrix method. Dynamic stability and response analysis of undamped and damped 1DOF, 2DOF, 3DOF, and multiple DOF systems are conducted, and numerical examples are compared to conventional methods to show the accuracy and advantage of the proposed numerical simulation method. The instability diagrams are also substantiated by vibration response curves obtained from the same method. The method is applied to calibrate the validity and ranges of applicability of the Hill infinite determinants in the Floquet theory of 1DOF Mathieu-Hill equations. The second order approximation of the first instability region from the Hill determinant is acceptable. However, the fourth order approximation of the second instability region must be used to obtain a relatively accurate result. For 2DOF, 3DOF, and multi-parameter linear periodic systems, the method can simultaneously render four types of instability regions in a single procedure: no resonances, simple parametric resonances, combination additive resonances, and combination differential resonances. These results could provide a better understanding of stability and responses of dynamic systems under parametric excitation. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the stability of hydro-turbine governing system (HTGS) with sloping ceiling tailrace tunnel (SCTT) and upstream surge tank (UST) considering nonlinear hydro-turbine characteristics (NHTCs). Firstly, the mathematical model of HTGS is presented based on nonlinear seventh-order state equation, which is verified by example analysis so as to study the stability of HTGS. Subsequently, the effect of HTGS parameters on the stability of the system is investigated with numerical simulation. Finally, the coupling effect mechanism of SCTT and UST on stability under the effect of NHTCs is revealed by using contrastive analysis. The results are summarized as follows: (1) T a , K d and T wt perform larger effect on the stability of HTGS, while the influence of F and T wy is mild; (2) the NHTCs are beneficial under negative load disturbance and unfavorable under positive load disturbance for the stability and dynamic performance of HTGS; (3) the coupling effect of SCTT and UST outperforms the results of SCTT or UST alone under all load disturbances; (4) the incorporation of UST to the established model plays a certain role in stability compensation, while the introduction of SCTT not only improves the stability but also achieves smaller amplitude and lower frequency. [ABSTRACT FROM AUTHOR]

The escape rate of hydrogen in photobiological hydrogen production plays an important role in the biochemical reaction process, and the interaction of hydrogen bubbles in bio-hydrogen production material liquid affects the escape rate of hydrogen. In this paper, the Eulerian-Eulerian-Multifluid VOF method is used to simulate the interactions of three types of hydrogen bubbles: coalescence of equal-sized inline hydrogen bubbles, a small leading hydrogen bubble is chased by a large trailing hydrogen bubble and a large leading hydrogen bubble is chased by a small trailing hydrogen bubble. The results show that the interaction strength between hydrogen bubbles is influenced by the initial interval and initial diameter of the hydrogen bubbles and the flow index of the hydrogen-producing material liquid. The hydrogen bubbles exhibit three types of aggregation. In the pre-merger period, the velocity of the trailing hydrogen bubble also shows four stage changes, which are acceleration to the maximum velocity - deceleration - small increase in velocity - deceleration to the merging velocity. There is also a brief acceleration of the leading hydrogen bubble. For the interaction between Type II and Type III hydrogen bubbles of the same size, there is no significant difference in the rise rate of large hydrogen bubbles after the coalescence. • Two inline hydrogen bubbles exhibit three types of aggregation. • The velocity of trailing bubble before aggregation shows four stages of variation. • When trailing bubble approaches leading bubble, it undergoes a lateral migration. • Before aggregation, the larger bubble always strongly influences the smaller bubble. [ABSTRACT FROM AUTHOR]

Magnetic torquers are attitude control devices used in spacecraft systems, and extensive research has been conducted on the attitude control of such spacecraft systems equipped with magnetic torquers. In this paper, a control law for spin spacecraft systems is proposed. Unlike existing control laws that switch between the spin rate and spin axis orientation control, the proposed angular momentum control law (AMCL) simultaneously provides feedback control for the spin rate and spin axis orientation based on the angular momentum error from the target. The steady-state and asymptotic behaviors of the angular momentum error are analyzed. In the analysis, both the saturated and unsaturated magnetic moments are considered. A testbed with magnetic torquers and a geomagnetic field simulator are developed to experimentally evaluate the performance of the AMCL. The geomagnetic field simulator is constructed using three Helmholtz coils to generate a time-variant magnetic field similar to that in orbit. The AMCL is used to conduct two ground experiments on the spin rate and spin axis orientation control. The effectiveness of the AMCL and behavior of the testbed are experimentally evaluated by comparing and analyzing the experimental and numerical simulation results. Consequently, the AMCL is found to achieve the required states in the experiments, and the asymptotic and steady-state behaviors appear to be consistent with the estimations made by numerical simulations. In conclusion, the proposed AMCL can appropriately control the spin motion of a spacecraft. [ABSTRACT FROM AUTHOR]

• The global uniform exponential stability is established for zero-order delayed systems. • The stability results for impulsive dynamical networks are obtained. • The event-triggered impulsive control (ETIC) is designed to stabilize dynamical networks. • ETIC has lower impulse frequency and control cost than the classic impulsive control. • A non-instantaneous ETIC is proposed to improve the instantanity and discontinuity of ETIC. This paper studies the stability for impulsive dynamical networks (IDN) where different nodes may have different impulse time sequences. By deriving the conditions of global uniform exponential stability for zero-order delayed systems, the criteria of stability for IDN are established. The stability results for IDN are then used to design event-triggered impulsive control (ETIC) for stabilization of continuous-time dynamical networks (CDN). In every node of CDN, three levels of event-triggering conditions are set for ETIC. The exponential stabilization of CDN is shown to be achieved by the designed ETIC and it also shows that the ETIC is robust w.r.t. time-delays. Moreover, a non-instantaneous ETIC (NI-ETIC) is proposed for the stabilization of CDN. Three examples with numerical simulations are given to show that the designed ETIC has lower impulse frequency and cost of control than the classic time-triggered impulsive control. It is also shown that the discontinuity and the instantanity of ETIC are improved by the NI-ETIC. [ABSTRACT FROM AUTHOR]

In this study, the fixed-time synchronization (FXTS) of delayed memristive neural networks (MNNs) with hybrid impulsive effects is explored. To investigate the FXTS mechanism, we first propose a novel theorem about the fixed-time stability (FTS) of impulsive dynamical systems, where the coefficients are extended to functions and the derivatives of Lyapunov function (LF) are allowed to be indefinite. After that, we obtain some new sufficient conditions for achieving FXTS of the system within a settling-time using three different controllers. At last, to verify the correctness and effectiveness of our results, a numerical simulation was conducted. Significantly, the impulse strength studied in this paper can take different values at different points, so it can be regarded as a time-varying function, unlike those in previous studies (the impulse strength takes the same value at different points). Hence, the mechanisms in this article are of more practical applicability. • Novel fixed-time stability theorem with indefinite derivative of Lyapunov function. • Impulse strength can take different values at different impulse points. • New fixed-time synchronization mechanisms via three different controllers. • Settling time is related to the selection of the impulse points and the impulse strength. [ABSTRACT FROM AUTHOR]

• A novel structure for the active pressure management of a storage tank is proposed. • The evolutions of temperature and flow during the whole process are illustrated. • A heat-pipe-like and a redistributor work mode are uncovered in different zones. Inevitable evaporation process occurring in liquid hydrogen storage may bring about safety risks associated with over-pressure and hydrogen discharge. Using a cryogenic refrigerator to compensate for the heat leakage is expected to eliminate the risk of hydrogen vent, realizing long-term lossless storage. Presently, active lossless storage technology applied on civil fields has rarely been studied. This paper presents a numerical study on the dynamic evolution process within an active cooling system of a liquid hydrogen tank. The accuracy of the model is validated with an average deviation of 0.47%. During the self-pressurized process, the maximum temperature difference is more than 26 K in the ullage zone. After cooling capacity being introduced, a three-stage depressurization process appears. Minor cooling capacity that is less than heat leakage can still realize pressure management. Further analyses show two operating modes similar to gravity heat pipes and thermal redistributors occurring in the ullage and the liquid zone, respectively. This work suggests the effectiveness of active cooling on controlling the ullage pressure, which may be applicable to future hydrogen refueling stations and intercity hydrogen transportation. [ABSTRACT FROM AUTHOR]

In this paper, computational fluid dynamics (CFD) numerical simulation is used to analyze and discuss the horizontal propagation process of premixed hydrogen flame with obstacles. A total of three different obstacle channel arrangements at the blocking ratio of 0.5, which will affect the explosion flame and pressure development. The results show that the premixed flame is affected by flow instabilities and vortices when propagating through the obstacle channel, thereby distorting the flame. The vortices outside the flame boundary are more conducive to the acceleration of the flame. The continuous acceleration and synergistic promotion of the flame is more prominent due to the existence of the channel in the central axis of flame propagation, and the maximum velocity even achieved 307.91 m/s. The degree of the wrinkle of flame increases with the number of obstacle channels. The flame propagation process is always accompanied by pressure variations, and the dynamic pressure builds up at the flame front and intensifies periodically. But the downstream pressure gradually increases as the number of obstacle channels increases. CFD simulation of the explosion process clearly reveals the changing trends and interactions of explosion characteristic factors. • The vortex outside the flame boundary is more beneficial for flame acceleration. • Arrangement of obstacle channels effects the trend of flame front motion. • Pressure oscillation and magnitude can be changed by the obstacle arrangement. [ABSTRACT FROM AUTHOR]

This paper focuses on the problem of stochastic mixed impulsive control and stability for stochastic functional differential systems with semi-Markov jump. A new definition of average stochastic impulsive gain is formulated to estimate the stochastic mixed impulsive intensity. Functional systems states are referred to the historical system states in the past time interval rather than in the past time instant of the current time instant. The stability analysis is carried out based on the constructed appropriate Lyapunov functional, Dupire functional Itô's formula, stochastic analysis theory and graph theory techniques. Moreover, we provide some exponential stability criteria for the investigated systems, which have close relation to not only the topological structures and semi-Markov jump of the functional systems but also average stochastic impulsive gain and stochastic disturbance intensity. Further we put it into practice of a new class of stochastic oscillators systems with semi-Markov jump and the corresponding numerical simulations results are on show to demonstrate the validity of the derived theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, a fractional nonlinear control strategy based on the nested saturations technique and the Caputo-Fabrizio derivative for a quadrotor aircraft, to maintain desired position and orientation in stationary flight and trajectory tracking tasks, is proposed and developed. In addition, the dynamic model is obtained by using the Euler–Lagrange formulation, and then it is generalized to an arbitrary order through the Caputo-Fabrizio derivative. The traditional nonlinear control based on the nested saturation technique is also developed and implemented on the quadrotor for comparison purposes between both control schemes. Numerical simulations demonstrated the superiority of the proposed control strategy for stabilizing the quadrotor at hover and reaching the desired position and orientation, over its integer-order counterpart. In addition, three additional desired trajectories are considered, keeping the same gains and orders, to demonstrate the robustness of the proposed control scheme under different operating conditions. In this sense, our controller presents significant performance improvements, which were validated through system simulations. Our proposed control system and its traditional counterpart were tuned experimentally using the response of the system to a desired trajectory. [ABSTRACT FROM AUTHOR]

This paper investigates global synchronization of complex-valued neural networks (CVNNs) with unbounded time-varying delays. By applying analytical method and inequality techniques, an algebraic criterion is established to ensure global synchronization of the CVNNs via a devised feedback controller, which generalizes some existing outcomes. Finally, two numerical simulations and one application in image encryption are provided to verify the effectiveness of the theoretical results. [ABSTRACT FROM AUTHOR]

The global exponential synchronization issue of coupled neural networks with time-delayed impulses is investigated in this paper. On the basis of the characteristics of coupled neural networks and theorems, we have built a novel coupled systems model. In order to fit the real situation, the impulses are flexible and it can beyond the impulsive interval under certain conditions in this paper. Therefore, our results are less restrictive and more practical compared to existing research. Besides, by using average impulsive delay (AID) and average impulsive interval (AII), we investigate two different effects of impulses on synchronization respectively and get a few adequate conditions for different types of synchronization. Finally, there are two examples of numerical simulations presented to illustrate the efficiency of the conclusions. [ABSTRACT FROM AUTHOR]

Abstract: In the present work a number of configurations and difficulties of MEE system such as condensate flashing, vapor bleeding, steam splitting, preheating of liquor using condensate, variable physical properties and boiling point rise are taken into consideration to analyze the evaporation system. For this purpose seven effect evaporator system of a typical Indian pulp and paper industry is considered. The model developed is a set of nonlinear algebraic equations that include total and solute mass balances, energy balances, heat transfer rate equations, and the composition and temperature dependence of thermodynamic properties such as vapor pressures and enthalpies. The model is solved using nonlinear equation solver. Economic evaluation to optimize the number of flash tanks is carried out for seven effect evaporator system. The two different types of configurations of vapor bleeding are considered and compared. Considering optimum number of flash tanks and best configuration of vapor bleeding, a system is designed. Further, a modified system is found considering optimum number of flash tanks and preheating of liquor using condensate. This modified design enhances the steam economy by 23.77% and reduces the steam consumption by 36.76% in comparison to base case and thus, it is selected as optimum design. Finally, Pinch analysis of the MEE network has also been carried out and it is found that predicted results are compared well with base case. [Copyright &y& Elsevier]

We suggest a method to identify the suitability of a chosen indoor environment for paper material conservation in historical libraries. Our approach is based on two steps: numerical simulation for solving the air velocity, moisture and temperature fields, and then post-processing indexes evaluation to assess how the indoor microclimatic conditions can be favourable or not to the growth and development of microorganisms responsible for paper deterioration. A real case study was analysed in two different conditions: one the present situation and the other proposed by the authors with a HVAC system assuring controlled air temperature and RH levels. Numerical models, validated by experimental data published in previous works, were used to carry out microclimatic results. Starting from these results, some indexes suggested by the scientific literature were computed to check the suitability of the indoor environment for preserving a library heritage. Boolean parameters were also deduced from the combination of microclimatic factors favouring the growth of microorganisms responsible for paper material deterioration. Our research can provide a methodological approach that predictively allows one to know when, where and how the processes responsible for indoor microorganism activity can find the microclimatic conditions for their kick-off and triggering, and then their areas of potential growth. The proposed method highlights the main causes of the deterioration processes connected to building thermo-physics. Simulation results turned out to be a fundamental approach to identify the risky zones and potential areas of triggering deterioration processes of all the materials present. [ABSTRACT FROM AUTHOR]

• Heterogeneous networks with both heterogeneous coefficients and heterogeneous nonlinear functions are investigated. • A generalized impulsive controller is designed. • Parameter uncertainties of both linear and nonlinear dynamics are considered. • The sufficient criteria of quasi-synchronization are derived for the heterogeneous networks. The target of this paper is studying the problem of quasi-synchronization of heterogeneous Lur'e networks with uncertain parameters and impulsive effect. Considering the heterogeneity of Lur'e networks, quasi-synchronization instead of synchronization is discussed. Noting that the uncertain factors exist extensively in reality, uncertain parameters are introduced to the system in this paper. By using the Schur complement lemma, stability theory and the principle of comparison, the sufficient criteria for the heterogeneous networks to achieve quasi-synchronization are derived, and the upper bound of exponential quasi-synchronization errors is calculated. In addition, two corollaries are presented in consideration of homogeneous systems and weighted undirected graphs. Finally, three numerical simulations are given to illustrate the effectiveness of the control protocol and theoretical results. [ABSTRACT FROM AUTHOR]

Chemical ablation and mechanical erosion of hybrid rocket nozzles can cause loss of nozzle thermal protection material, resulting thrust reduction. In this paper, the chemical ablation and mechanical erosion mechanisms of nozzle thermal protection materials are studied through numerical simulation. For chemical ablation, a coupled thermal-mechanical-chemical model is established, considering three mechanisms: wall regression caused by non-homogeneous chemical reactions at the wall, convective heat transfer and fluid-structure interaction. For mechanical erosion, a Fluent DPM model and an Abaqus DEM model are established, which are investigated from the perspectives of empirical formula and solid mechanics mechanisms respectively, and validated against each other. The comprehensive effect of chemical ablation and mechanical erosion on the morphology of the nozzle is considered. The results show that both chemical ablation and mechanical erosion dominate the wall regression rate at the downstream of the converging section and upstream of the throat while the other location is only dominate by chemical ablation. After 5s of operation, thrust of rocket engine decreases by 5.8%. The Abaqus DEM model presented by this paper breaks the limitations of the empirical formulae due to the introduction of the material constitutive model and the failure criterion. • A coupled thermal-mechanical-chemical model is established. • Mechanical erosion is studied from perspective of empirical formula and the solid mechanics mechanism. • Comprehensive effect of chemical ablation and mechanical erosion on nozzle inner wall morphology is studied. [ABSTRACT FROM AUTHOR]

• A novel tether-net release mechanism was proposed to improve the capture of space debris. • Vibration tests were conducted to verify the materials' toughness and mechanisms. • The net release mechanism of the fabricated model was experimentally verified. • The best combination of net size and spring constant was selected. This paper presents the general concept, mechanism, and components of a novel net-launching device for capturing space objects. The novelty of the solution and its distinct features, which ensure safer and more sustainable in-space performance as compared with the known previous solutions, are also described. Furthermore, issues related to the design parameters of the device and its parts are highlighted, and detailed calculations and analyses are presented. Examples of design solutions for real-scale applications involving the removal of space debris and a miniaturized mechanism (as a case study) are presented. The features of the proposed device are highlighted, and its efficacy and potential are demonstrated using numerical simulations and field experiments. [ABSTRACT FROM AUTHOR]

In this paper, an efficient dimension splitting method is applied to the two-dimensional (2D) and three-dimensional (3D) Cahn-Hilliard type equations with significant applications in physical, biological and computer science. The proposed method can greatly reduce the storage requirements and computational complexity in two and three dimensions, and preserve the high precision and mass conservation. The dimension splitting method is based on auxiliary variables for spatial derivative terms and the operator splitting approach. It converts the 2D or 3D problem into a series of one-dimensional (1D) problems which can be solved by using multi-thread. The stability and accuracy of the proposed method are improved by a local stabilizing approach and extrapolation. The analyses of discrete energy and discrete mass conservation property are shown. Numerical examples confirm the advantages of proposed method. And a variety of simulations, such as the phase separations, curvature driven flows, diblock copolymers, tumor growth and volume restoration, are performed with respect to practical applications. • Dimension splitting method for Cahn-Hilliard type equations. • The global stability is achieved by the local stability of solving each sub-problem. • Fourth-order mass conservative scheme based on the compact differencing and extrapolation. • A large number of numerical examples for practical applications. [ABSTRACT FROM AUTHOR]

Industrial processes are subject to various noise disturbances that lead to the stochastic nature of the modeled system and the uncertainty of the model parameters. In this paper, a variational Bayesian State Space Model (VBSSM) model is developed for dynamic process monitoring, allowing the uncertainty of parameters to be described by probabilities. The conjugate prior allows the posterior distribution of the parameters to be estimated iteratively through the Rauch Tung Striebel (RTS) smoothing estimation with the VB framework. The next state can be better predicted even in the presence of noisy perturbations, and imperceptible correlations among multiple variables can be found. By maximizing the lower bound of the objective function to approximate the true posterior distribution of the parameters, the fault detection index is constructed by the corresponding residual. Finally, the effectiveness and superiority of the proposed method is verified by numerical simulations, Tennessee Eastman process and hot rolling industry examples. • This work develops variational Bayesian state space model (VBSSM) based on variational Bayes, where the dynamic properties of the data are described directly through the SSM. • The increased dimensionality of the state space due to the Cholesky decomposition is avoided. • The developed VBSSM method describes the parameter uncertainty probabilistically instead of point estimation and therefore avoids overfitting. [ABSTRACT FROM AUTHOR]

In this paper, we study the global stability of delayed genetic regulatory networks (DGRNs) with Hill-type activation (or inhibition) functions based on the mixing monotone semiflows approach, where Hill coefficients can be arbitrary positive real number. A new result on the global stability of DGRN is given in the case that all Hill coefficients are less than or equal to 1. In addition, for all Hill coefficients greater than 1, a new sufficient condition for global convergence of DGRN is given, which is less conservative than the condition of the existing correlation results. Finally, two numerical examples and simulations are given to explain the effect of obtained results. [ABSTRACT FROM AUTHOR]

This paper presents an approach to ensuring the safety of a landing module on a threat during its splashdown in the World Ocean. We propose mathematical methods and software to predict the main hydrophysical disturbances from underwater vehicles, which are necessary to estimate artificial anomalies on the sea surface. • Detection of underwater objects ensures safety of the spacecraft splashdown. • Underwater object creates identifiable hydrophysical anomalies. • Computer technologies can predict hydrophysical anomalies. • Analysis of radar images of anomalies allows to detect an underwater object. [ABSTRACT FROM AUTHOR]

Various celestial bodies contain cracks. Also, cracks can be in the skin of aircraft, while their growth is one of the main mechanisms for the breakup of structures. This paper presents a study of one and two rectangular cracks. The influence coefficient (the ratio of the stress intensity factors for the fracture system to the corresponding value for a single crack of the same size) was chosen as the quantity under investigation. The final shape of the crack in the case of its growth is also studied. The following methods were used to model this process: the three-dimensional boundary elements method of discontinuous displacements, in which stress and displacement field is a finite series of expansions of analytically found functions, as well as the two-dimensional boundary elements method of discontinuous displacements, which takes into account the twisting of a growing crack along the stress field at the tip. • Single rectangular crack and system of two parallel cracks were investigated. • For rectangular crack growth is likely to happen from the centers of the sides. • The danger of two parallel cracks depends significantly on their relative position. • Pair of uniaxial cracks is less dangerous then a single crack of the same size. • Non-overlapping cracks in close planes are the most dangerous. [ABSTRACT FROM AUTHOR]

• The coupled characteristics of compressor and expander are investigated. • Model of the whole air refrigerator is established by the coupled characteristics. • Effects of turboexpander inlet temperature and first stage compression ratio. • Characteristics of the air refrigerator under variable cooling capacity. Reverse Brayton air refrigerators are environmentally friendly and have broad application prospects, which can work under various conditions. In this paper, the characteristics of a open-loop air cycle for room temperature applications were investigated. The compressor and turboexpander in the cycle were modeled by numerical simulation. Based on coupled characteristics of the compressor and expander, a system model was established. The effects of the first stage compression ratio and the expander inlet temperature on the refrigerator performance were studied by experiments. The accuracy of the system model is verified by comparing with the experiments, and the maximum deviations of expander rotating speed and supplied mass flow are 3.1% and 4.83%, respectively. With the increase of the first-stage compression ratio and the decrease of expander inlet temperature, the mass flow rate of supplied air and cooling capacity of the cycle increase. The expander efficiency can be maintained near the optimal value. At the expander inlet temperature of 313.2 K, COP drops by 31.7 % when the cooling capacity is reduced from 3.34 kW to 0.74 kW. [ABSTRACT FROM AUTHOR]

Hydrogen energy can be produced by the decomposition of hydrogen and carbon compounds. A numerical analysis method of accuracy and efficiency provides important reference value for optimizing development plans and predicting production performance of hydrogen and carbon compounds. In this work, embedded discrete fracture model (EDFM) is used to study the production performance of hydrogen and carbon compounds under non-liner seepage under the threshold pressure gradient and complex fracture systems consist of the hydraulic fractures, secondary fractures, natural fractures. A dual-permeability model of the same case is also constructed as a comparison study to analyze the development of hydrogen and carbon compounds. On this basis, the influence of threshold pressure gradient on production of hydrogen and carbon compounds is quantitatively evaluated in this paper to modify the numerical model and a novel method for the simulation of fractured hydrogen and carbon compounds reservoirs is provided. Through model comparison, the impact of fractures in the reservoir on production can reach 289.1%. A dual-permeability model of the same case is also constructed as a comparison study to analyze the development of the reservoir and the result shows a 7.9% distinction on the cumulative production. It is analyzed that when the threshold pressure gradient is increased from 0.1 MPa/m to 0.6 MPa/m, the output decline of different models ranges from 6% to 15% and a novel method improving model fidelity for the simulation of fracture reservoirs is provided. • A new numerical simulator was presented to study production performance in shale reservoirs. • Both embedded discrete fractures and the threshold pressure gradient were considered into model. • The method provides a new idea and reference for future horizontal well fracturing model. [ABSTRACT FROM AUTHOR]

• We consider competition between sensitive and resistant subpopulations as an optimal control problem. • Bespoke objective functional directly penalizing domination of resistant subpopulation is analyzed. • Properties of singular arc appearing in this optimal control problem are studied. • Penalizing chemoresistance gives rise to singular arcs in the optimal control. • Numerical simulations show that non-trivial competition has a major impact on the structure of optimal control. Emergence of pesticide-resistant strains of pests, antibiotic-resistant bacteria or chemotherapy-resistant tumor cells is a major obstacle standing in the way of effective external control of undesirable growth of these populations. Once the resistant subpopulation becomes dominant the means to control the population are effectively lost. Prevention of resistance may be therefore considered one of the optimal control goals to ensure long-term controllability. In this paper we formulate nonlinear optimal control problem motivated by the question of controlling the growth of two coexisting subpopulations representing two phenotypes of the same species. However, the model we consider is a standard competition model with populations following logistic growth, and therefore it is more general and can be used also when two competing populations are taken into account. We consider a situation when the control (e.g. pesticide or drug) has effect only on the specimen belonging to one (sensitive) population while having no effect on the other (resistant) population. We use a non-standard, nonlinear objective functional in which, aside from penalizing the overall size of both populations, we include an additional, nonlinear term to ensure that the control-sensitive population remains the dominant one. It is shown how the resistance penalty gives rise to locally-optimal singular controls which are key to achieving the balance between resistant and sensitive populations whenever the subpopulations are similar in terms of the model parameters. Analytic properties of the singular arcs and the structure of optimal control are investigated. Both theoretical and numerical results strongly suggest that the optimal control contains a singular interval. [ABSTRACT FROM AUTHOR]

Understanding the formation of impact craters on planetary surfaces has fundamental importance in geology, impact dynamics, and planetary sciences. The finite element-smoothed particle hydrodynamics (FE-SPH) adaptive method combines the advantages of smoothed particle hydrodynamics (SPH) and finite element method (FEM) in solving hypervelocity impact (HVI) problems. Employing FE-SPH adaptive method is a new idea for the analysis of planetary impact cratering which is different from impact-simplified arbitrary Lagrangian Eulerian (iSALE). In this paper, we establish a complete numerical model of planetary impact cratering through the FE-SPH method, including material failure criterion, thermodynamic analysis, gravity preloading, etc. We reproduce the numerical results by Collins et al. (2012) and highly consistent results are obtained through comparative analysis. This study simulates the formation process of simple and complex impact craters, and the temperature, pressure, density, and geometric shape of the impact zone can be quantitatively obtained. We further analyze the distribution of polymorphs and rock fragmentations in the impact zone based on the theories of shock metamorphism. The proposed analysis method may assist geologists in conducting geological studies. • We establish a complete numerical model of planetary impact cratering different from iSALE. • We analyze the distribution of high-pressure polymorphs based on shock metamorphism. • The FE-SPH model has higher numerical precision for planetary cratering impacts. [ABSTRACT FROM AUTHOR]

This paper presents a systematic methodology, called the MBP-preserving iteration technique, to develop the maximum bound principle (MBP) preserving numerical algorithms for a class of semilinear parabolic equations. Two types of MBP-preserving iterations are suggested to solve two well-known θ -weighted schemes, respectively. Within some mild time-step constraints, the corresponding iteration solutions are proved to preserve the MBP property at each iteration step so that the numerical scheme has a uniquely MBP-preserving solution. In addition, concise error estimates in the maximum norm are established on nonuniform time meshes. Several numerical examples coupled with an adaptive time-stepping strategy are implemented for the Allen-Cahn model to confirm the theoretical findings and demonstrate their effectiveness for long-time numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, we study the asymptotic stability of a particular class of linear 2D discrete Fornasini-Marchesini models. The solutions of the model can be expressed in terms of doubly indexed sequences in a simple way only when the matrices describing the model commute. In this situation, we are able to analyse directly the limit of all the trajectories. By doing so, we propose the first necessary and sufficient condition for asymptotic stability of Fornasini-Marchesini matrix models. This condition is not computationally challenging as it is ultimately based on the eigenvalues of the matrices describing the model. We support our result with numerical simulations. [ABSTRACT FROM AUTHOR]

• A novel discontinuous similar material for physical model experiments has been developed. • The bulking characteristics of the broken goaf roof under different roof cutting conditions have been revealed. • The protection effect of the roof cutting technology for the gob-side roadway has been obtained. • The excavation compensation effect of the bulking roof rock after failure by roof cutting has been proposed. The stability control of gob-side entry retaining (GSER) has consistently been an important topic of interest within the field of no-pillar mining. This paper presents a novel discontinuous similar material for conducting physical model experiments, in conjunction with discrete element numerical simulation, to investigate the goaf roof failure and bulking characteristics based on gob-side entry retaining by roof cutting. The results indicate that the application of roof cutting technology (RCT) can significantly expand the failure range of the goaf roof vicinity to the roof cutting line. This expansion leads to a 20% increase in the volume of broken roof rock, which in turn facilitates the formation of effective support and stress compensation for the overlying strata, and the possibility of failure and displacement in the overlying strata is reduced. RCT can decrease the length of the cantilever beam located on the gob-side roadway, which is beneficial for maintaining the stability of the roadway. This paper presents a rational approach for determining an appropriate roof cutting height and angle. The in-situ application results show that the deformation of the surrounding rock of GSER by RCT is small, indicating a high level of integrity, fully meeting the requirements of serving the production of the subsequent working face. This paper serves as a reference for future research on the stability control of gob-side roadways based on GSER approach. [ABSTRACT FROM AUTHOR]