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Designing Unmanned Aircraft Systems (UASs) for optimal autonomy while meeting user requirements is quite challenging. Researchers have focused on improving autonomy algorithms and verification methods to ensure safe and reliable autonomous behavior in UASs, but little research has been conducted on requirements engineering for UASs to answer design questions and explore the trade space for using autonomy to satisfy user requirements. This paper introduces a method to determine an optimal set of autonomous capabilities that satisfies UAS user requirements in the early stages of conceptual design. The method uses a modified Autonomy Requirements Engineering (ARE) process that applies quantitative measures and statistical analysis to Goal-Oriented Requirements Engineering (GORE). We demonstrate this method in a case study of a “disaster robot,” i.e., a hazard response UAS for which the autonomy requirements were optimized using a goal model developed in the Goal-oriented Requirement Language (GRL), as implemented in the modeling tool jUCMNav. The high-level goals of the hazard response UAS—system performance, cost, and safety—were evaluated using the formula-based GRL strategy evaluation algorithm resident in jUCMNav version 6.0. An autonomy trade space study was conducted through a Design and Analysis of Simulation Experiments (DASE). Our designed simulation experiment inserted the number of trials (evaluation strategies) and inputs into the goal model, and evaluation data were analyzed to optimize design factors based on user weightings of the response variables. This paper presents a structured method of ARE for UASs, which could be adopted more broadly across other domains, demonstrating how to optimize autonomous capabilities for different design conditions. [ABSTRACT FROM AUTHOR]

In this paper, the authors present the development of an optimisation suite and its implementation. This paper is part of an ongoing project that aims at developing a hybrid metaheuristic optimisation suite to solve multi-objective simulation optimisation problems. The suite is developed as a third-party library to solve discrete-event, stochastic simulation optimisation (SO) problems with multi-objectives, and is integrated with Tecnomatix Plant Simulation, a simulation software package developed by Siemens. Two real-life multi-objective SO problems are selected to test the suite's performance, and the test results are discussed. [ABSTRACT FROM AUTHOR]

This paper considers the scheduling of stochastic customer orders to minimize expected cycle time. Customer orders dynamically arrive at a machine station, and each order consists of multiple product types. Random workloads are required by each product type, and the workloads are assigned to a set of unrelated parallel machines in the station to be processed. The objective is to obtain the minimal long-run expected order cycle time through proper workload assignments. In view of the difficulty in evaluating the objective function, this paper models the targeted problem as a simulation optimization problem and proposes to solve it under the multifidelity model framework. To improve the efficiency in evaluating candidate solutions, a low-fidelity model is constructed to select solutions with better performances for high-fidelity simulations. The effectiveness of this low-fidelity model is demonstrated through a series of theoretical evidences. A simulation optimization algorithm, named Bound-Multi-fidelity Optimization with Ordinal Transformation and Optimal Sampling Bound-(MO2TOS), is developed by taking advantage of the properties of the low-fidelity model. Numerical experiments are conducted to evaluate the performance of the proposed algorithm against three other well-known simulation optimization algorithms in the literature. Results indicate that the Bound-MO2TOS outperforms all the other tested algorithms, and its performance is robust against changes in problem scale. Note to Practitioners—Customer order scheduling models have wide applications in industries where every single order may contain multiple product types and the entire order requires one shipment delivery. In many applications, such as pigments dyes manufacturing, auto repair, and grocery, consideration of customer orders rather than individual jobs is often preferred. Given the stochastic nature and the synchronization constraints of the problem, a multifidelity simulation algorithm named Bound-Multi-fidelity Optimization with Ordinal Transformation and Optimal Sampling Bound-(MO2TOS) is proposed. Experimental results suggest that the proposed algorithm outperforms three other popular simulation optimization algorithms under a variety of scenarios. It is admitted that further improvement can be made in refining the computation resource distribution process of Bound-MO2TOS. In the future research, such an improvement will be more thoroughly elaborated so that practitioners can utilize it to coordinate their productions better. [ABSTRACT FROM AUTHOR]

Aero-servo-elastic analysis of a complex hypersonic aircraft is presented in this paper. A structure geometry was designed and built based on the X-43A vehicle. First, a three-dimensional structural finite element model was proposed with effective two-dimensional elements, which can obtain effective modal analysis results without useless local modes. Second, computational fluid dynamic (CFD) simulation was adopted to find aero-heating distribution of thermal mode via this structure. Aero-heating effect was included to study thermal-modal characteristics of the present structure. Influence due to material characteristic change and thermal stress was studied. After structural finite element analysis was completed, flutter of the present vehicle was investigated. Aero-servo-elastic analysis was then started from the definition of an aero-servo-elastic closed-loop system. In this system, the present aircraft is treated as flexible structure, in which the control sensor on the aircraft received not only rigid motion signal but also elastic vibration signal, and this signal can translate into the deflection signal to form aerodynamic control force through this aero-servo control system, and this force can continually influence aerodynamic force. One of the most important steps for this analysis was computation of unsteady aerodynamic force of the present structure, and the related process was developed based on an effective fitting method. Finally, bode diagrams of pitching, rolling and yawing were investigated, form which the law of aero-servo stability of the X-43A vehicle can be observed and analyzed. It can be found from the results of this paper that effective investigation of aero-servo-elastic characteristics of a complex hypersonic aircraft should be based on accurate structural finite element modeling, modal analysis and flutter analysis. The proposed method in this paper can provide effective analysis process for the design of controller for hypersonic aircraft. [ABSTRACT FROM AUTHOR]

• The extremal ellipsoid surface reflecting the dynamic mechanism of the gyrostat system is derived. • The bifurcation of the Casimir power and energy leaps are found to be the indicators of different definitive dynamics. • The state changes of the displacement orbit of the gyrostat are simulated by the COMSOL finite element platform. Most of the existing research on gyrostat systems uses the Melnikov method to analyze chaotic dynamic characteristics. The mechanism of chaotic motion from the energy perspective of gyrostat systems has rarely been analyzed. The gyrostat system with positive damping disturbance is modeled in this paper. Casimir energy and power are given. The mechanism of the orbital expansion and contraction of the gyrostat is revealed through the sign change of Casimir power and the ellipsoid of Casimir energy. The bifurcations of the Casimir power corresponding to the state bifurcation and Lyapunov exponent spectrum reflect the evolution and transition of gyrostat's dynamics. The energy-level leap expressed by the variance of Casimir energy is found to determine the bifurcation of dynamics for the first time. The coexistence of the gyrostat is explained using Casimir power and local stability of equilibrium point. The COMSOL finite element simulation platform is built to study the state changes of the displacement orbit of the frame gyrostat model. A comparison is performed for the displacement results conducted by the COMSOL and the numerical simulation for the gyrostat system kinematic model. The different displacement states of the gyrostat system under free motion and in the presence of damping disturbance and external torques are obtained. [ABSTRACT FROM AUTHOR]

This paper studies a class of fractional-order systems (FOSs) and proposes control laws based on physical significance variables. Lyapunov techniques and the methods that derive from Yakubovici–Kalman–Popov Lemma are used, and the frequency criterions that ensure asymptotic stability of the physical significance variable closed-loop system are inferred. The asymptotic stability of the observer system is studied for a sector control law where the output is defined by the physical significance variables. Frequency criterions and conditions for asymptotic stability are determined. The control techniques are extended to a class of linear delay fractional-order systems and nonlinear FOS. Numerical simulations of a class of systems described by fractional-order models show the method efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the problem of adaptive observer design for a class of nonlinear systems subject to unknown parameters and such that the classical observer matching assumption is not satisfied. We adopt the idea of generating auxiliary outputs based on a high-gain observer. The estimated auxiliary outputs are then employed by an adaptive observer to reconstruct both states and unknown parameters. The stability analysis is established based on Lyapunov theory. It is shown that the state estimation error and the adaptation error are uniformly bounded and converge to a compact set that may be reduced by an appropriate choice of the design parameters. In order to improve the robustness of our approach against disturbances, the proposed observer is appropriately modified based on sliding modes theory. Theoretical results are illustrated and validated for the twin-rotor MIMO system with numerical simulations. [ABSTRACT FROM AUTHOR]

This paper presents an extensive examination of the wake characteristics and hydrodynamic performance of a 1:60 scale horizontal axis tidal stream turbine under yawed inflow conditions. Experimental investigations were conducted in a laboratory flume, while numerical simulations utilized the actuator line method and large-eddy simulation technique. The turbine was subjected to an inflow turbulence intensity of 6% and was tested at five different yaw angles (5°, 10°, 15°, 20°, and 30°). The findings demonstrate a substantial reduction in the power coefficient as the yaw angle increases, with a notable drop of 47.1% recorded at a yaw angle of 30°. Furthermore, numerical simulations of wake characteristics, including mean velocity and turbulence intensity, were examined and compared with measurements, yielding satisfactory agreement. The yawed wake flow exhibited asymmetrical distributions of mean velocity and deviations from the centerline. Additionally, distinct deformations of the yawed wake in the y - z cross sections were observed, indicating a discernible curled kidney shape that intensified with larger yaw angles. Moreover, interactions between the turbine wake and support structures affected the width and turbulence intensity of the near wake, introducing additional unsteadiness that accelerated wake recovery. • The impact of yaw on tidal turbine performance and wake behavior has been studied through water flume experiments and numerical simulations. • Power loss is observed under yawed inflow, with the maxiamun reduction of 47.1% at yaw angle of 30°. • The aggravation of wake deflection and the acceleration of velocity recovery are observed as yaw angle increases. • Yaw misalignment causes a curled kidney shaped profile in wake cross sections. • Blade tip vortices, nacelle wake, stanchion wake and their interactions severely affect the near wake characteristics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lattice beam model extended to self-healing in cementitious materials. • A new rate dependent discrete damage-healing model is presented. • Healing response derived from healing-agent chemo-physical properties. • Detailed information is provided on the size and disposition of cracking and healing zones throughout a transient analysis. • The model provides valuable information required for designing a self-healing system. • Model validated using experiments with healing under fixed and moving crack conditions. • Nature and extent of damage-healing zones determined numerically. This paper describes the development of a discrete lattice model for simulating structures formed from self-healing cementitious materials. In particular, a new approach is presented for simulating time dependent mechanical healing in lattice elements. The proposed formulation is designed to simulate the transient damage and healing behaviour of structures under a range of loading conditions. In addition, multiple and overlapping damage and healing events are considered. An illustrative example demonstrates the effects of varying the healing agent curing parameters on the computed mechanical response. The model is successfully validated using published experimental data from two series of tests on structural elements with an embedded autonomic self-healing system. The meso -scale model gives detailed information on the size and disposition of cracking and healing zones throughout an analysis time history. The model also provides an accurate means of determining the volume of healing agent required to achieve healing for all locations within a structural element. The importance of the information provided by the model for the design of self-healing cementitious material elements is highlighted. [ABSTRACT FROM AUTHOR]

A continuous flow model to simulate the horizontal centrifugal casting was built based on the numerical simulation technique of filling and solidification processes, which realized the continuous simulation of the metallic melt from the pouring gate to the mold filling in the cavity of the steel back. The effects of different rotate speeds, pouring rates and cooling methods on the filling process and the solidification temperature field of centrifugal casting Babbitt lining were studied. The results show that the rotate speed and the pouring rate mainly influenced the flow states of the molten metal in the filling process. The cooling method decided the solidification rate and then affected the microstructure of the casting. The defects of the Babbitt lining manufactured by horizontal centrifugal casting machine were found to occur in the final solidified region of the simulation model. The simulation model built in this paper is designed to guide the improvement in the actual process. [ABSTRACT FROM AUTHOR]

This paper analyzes the stability and passivity problems for a class of memristor-based fractional-order competitive neural networks (MBFOCNNs) by using Caputo's fractional derivation. Firstly, impulsive effects are taken well into account and effective analysis techniques are used to reflect the system's practically dynamic behavior. Secondly, by using the Lyapunov technique, some sufficient conditions are obtained by linear matrix inequalities (LMIs) to ensure the stability and passivity of the MBFOCNNs, which can be effectively solved by the LMI computational tool in MATLAB. Finally, two numerical models and their simulation results are given to illustrate the effectiveness of the proposed results. [ABSTRACT FROM AUTHOR]

Double-layered shaped charge (DLSC) is a special type of shaped charge which has been recently attracted to enhance the penetration performance. The DLSC consists of a co-axial double-layered charge composed of outer high-velocity explosive and inner low-velocity explosive. In this paper, numerical simulations and experiments are carried out to investigate the usefulness of the DLSC compare to an ordinary shaped charge (OSC) at different stand-off distances. Jet properties of shaped charges are measured by simulation models and compared with the experimental penetration depths. It was found that the penetration performance strongly depends on the existence of jet breakup and the DLSCs performed better than the OSC only when no jet breakup occurs before reaching the target. The comparison study between the simulations and experiments also revealed that the jet properties such as kinetic energy, cumulative jet mass, and the initial jet breakup distance are highly related to the penetration performance. [ABSTRACT FROM AUTHOR]

In this paper we investigate the adsorption of various probe molecules in order to characterize the porous structure of a series of pillared interlayered clays (PILC). To that aim, volumetric and microcalorimetric adsorption experiments were performed on various Zr PILC samples using nitrogen, toluene, and mesitylene as probe molecules. For one of the samples, neutron scattering experiments were also performed using toluene as adsorbate. Various structural models are proposed and tested by means of a comprehensive computer simulation study, using both geometric and percolation analysis in combination with Grand Canonical Monte Carlo simulations in order to model the volumetric and microcalorimetric isotherms. On the basis of this analysis, we propose a series of structural models that aim at accounting for the adsorption experimental behavior, and make possible a microscopic interpretation of the role played by the different interactions and steric effects in the adsorption processes in these rather complex disordered microporous systems. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid optimization technique based on particle swarm optimization (PSO) and artificial bee colony (ABC) algorithm is presented for the optimal design of infinite impulse response (IIR) filter with low quantization effect. In this method, different variants of PSO have been exhaustively tested, and the time varying coefficients-PSO (TVC-PSO) is used to formulate a new hybrid technique for better exploitation and exploration, which is further modified by sorting and replacement mechanism of Scout Bee from ABC algorithm. For designing IIR filter, an objective function is constructed that satisfies the absolute error including peak ripples in passband and stopband regions in frequency domain, while stability of designed filter is confirmed by exploiting the lattice form structure during iterative computation that also reduces computation complexity. Several attributes such as passband error (ep), stopband error (es), and stopband attenuation (As) are used to measure the performance of proposed algorithm. The simulation results presented in this paper evidence that this technique can be effectively used for designing digital IIR filter with higher filter taps, and low quantization effect for fixed number of bits. [ABSTRACT FROM AUTHOR]

Road network microsimulation is computationally expensive, and existing state of the art commercial tools use task parallelism and coarse-grained data-parallelism for multi-core processors to achieve improved levels of performance. An alternative is to use Graphics Processing Units (GPUs) and fine-grained data parallelism. This paper describes a GPU accelerated agent based microsimulation model of a road network transport system. The performance for a procedurally generated grid network is evaluated against that of an equivalent multi-core CPU simulation. In order to utilise GPU architectures effectively the paper describes an approach for graph traversal of neighbouring information which is vital to providing high levels of computational performance. The graph traversal approach has been integrated within a GPU agent based simulation framework as a generalised message traversal technique for graph-based communication. Speed-ups of up to 43 ×  are demonstrated with increased performance scaling behaviour. Simulation of over half a million vehicles and nearly two million detectors at a rate of 25 ×  faster than real-time is obtained on a single GPU. [ABSTRACT FROM AUTHOR]

The existing experimental methods and numerical models were difficult to get accurate aerodynamic characteristics of the anti-torque system of a NOTAR under rotor wake. To solve this problem, a new three-dimensional aerodynamic model with momentum source based on finite volume method was proposed in this paper. By means of time domain equalization and spatial interpolation, the complicated dynamic meshes on blade were replaced by the nonblade fixed rotor domain with momentum source. And the model was calculated by steady, compressible and three-dimensional Reynolds averaged N-S equation. In this paper, a typical NOTAR was took for research, the aerodynamic characteristics including flow field and variation regularity of lateral force with momentum coefficient of anti-torque system during hover condition was obtained by applying the above computational model, and the accuracy of which was verified by corresponding experimental data. In addition, the model was also used to analyze the key factors that influence working condition of the tail boom, including length of tail boom, area of nozzle and fan pressurization. And the curves of variation regularity were given. The model and work in this paper could provide reference for further research and design on anti-torque system for NOTAR. [ABSTRACT FROM AUTHOR]

SUMMARY Although computer simulation is certainly a powerful tool for power system stability assessment, manual analysis is more helpful for understanding mechanism of unstable phenomena. Among unstable phenomena, oscillatory stability must be the most complex one. The paper analyzes the impact of recently developed Japanese RE's standard active anti-islanding function named 'frequency feedback with step injection' on power system oscillatory stability. Since active anti-islanding makes islanded system unstable, it also makes stability of large interconnection worse. The question is how serious is the impact and how the impact can be mitigated. The paper presents a method for oscillatory stability analysis considering induction motor load, RE, and anti-islanding function on RE so minutely as readers can reproduce. Analyses are performed as case studies on aggregated power sending and receiving systems in existing interconnection of Japan. The analyses results are verified by simulation results on the same case studies. [ABSTRACT FROM AUTHOR]

This paper presents an optimal design of low noise amplifier (LNA) using an efficient swarm-based optimizer called firefly algorithm (FA). Many researchers have used firefly algorithm to solve various nonlinear engineering problems and reported outstanding results. In view of this, FA is implemented for the first time in this paper to optimize the parameters of LNA like gain and noise figure (NF). Two case studies have been performed which includes the minimization of NF and maximization of gain. Optimization of these two parameters has been carried out by considering each parameter as a single objective function. Penalty factor method is considered for handling the constraints. Other parameters of LNA like power consumption, linearity, and stability are also discussed for both the cases. The designed LNA has a cascode structure with inductive source degeneration topology and is implemented in UMC 0.18-μm CMOS technology using CADENCE software. LNA is designed for 5.5-GHz frequency. The performance of FA in optimizing the parameters of LNA is also compared with the performance of other similar contemporary algorithms like particle swarm optimization (PSO), human behavior PSO (HB-PSO), backtracking search algorithm, and cuckoo search algorithm (CSA). The optimized value of LNA parameter using FA and other algorithms when simulated in MATLAB environment is compared with the simulated result of CADENCE. Statistical analysis is also performed for each case study, and the results are compared with the above-mentioned optimization algorithms. Simulation results, comparative study, and statistical analysis confirm the superiority of FA over other methods in terms of its computational efficiency, consistency, and robustness. [ABSTRACT FROM AUTHOR]

In this paper, we study the use of virtual element method (VEM) for geomechanics. Our emphasis is on applications to reservoir simulations. The physical processes behind the formation of the reservoirs, such as sedimentation, erosion, and faulting, lead to complex geometrical structures. A minimal representation, with respect to the physical parameters of the system, then naturally leads to general polyhedral grids. Numerical methods which can directly handle this representation will be highly favorable, in particular in the setting of advanced work-flows. The virtual element method is a promising candidate to solve the linear elasticity equations on such models. In this paper, we investigate some of the limits of the VEM method when used on reservoir models. First, we demonstrate that care must be taken to make the method robust for highly elongated cells, which is common in these applications, and show the importance of calculating forces in terms of traction on the boundary of the elements for elongated distorted cells. Second, we study the effect of triangulations on the surfaces of curved faces, which also naturally occur in subsurface models. We also demonstrate how a more stable stabilization term for reservoir application can be derived. [ABSTRACT FROM AUTHOR]

This paper conducted a parametric modeling for air knife structure in a printing factory, used HYPERMESH software to divide the meshes of air model and combined with actual conditions to define various boundary conditions in the inner flow field of air knife. Meanwhile, this paper adopted fluid dynamics software Fluent to conduct numerical simulation for the internal airflow of air knife, obtained the distribution regulation of flow field, conducted a parametric modeling for air knife structure under many internal structural proposals through ANSYS design module based on the simulation computational result, conducted optimization design for the position of guide plates, the number of outlets and the size of return air tank in the detailed structure in the air knife in order to determine specific dimension parameters and optimal proposals. Based on the computational results of simulation, this paper found that the original air knife structure had a non-uniform flow field and low velocity at the inlet and outlets. With the increase of length of air knife, the velocity of the middle outlet reduced to zero and did not have obvious effects any more. Guide plates in the air knife had a great influence on the inner flow field of air knife. Through optimization design, the inner flow field of air knife became uniform when there was only one guide plate. When the guide plate was close to the front end of the air knife, the inner flow field of air knife was relatively uniform and velocity at the inlet and outlets was relatively high. This paper conducted a model design for air knives with different structural types and determined proposal 4 as the optimal design through repeated analysis. The design method in this paper could provide guidance for studying and designing air knife structures in the aspect of technological approach and theory [ABSTRACT FROM AUTHOR]

The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial timescales. This paper describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents orbital, solar, volcanic, and land use/land cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the Tier 1 (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated Tier 2 simulations. Additional experiments (Tier 3) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This paper outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data). [ABSTRACT FROM AUTHOR]

This paper describes a method for determining the strain state of a thin anisotropic plate with elastic arbitrarily arranged elliptical inclusions. Complex potentials are used to reduce the problem to determining functions of generalized complex variables, which, in turn, comes down to an overdetermined system of linear algebraic equations, solved by singular expansions. This paper presents the results of numerical calculations that helped establish the influence of rigidity of elastic inclusions, distances between inclusions, and their geometric characteristics on the bending moments occurring in the plate. It is found that the specific properties of distribution of moments near the apexes of linear elastic inclusions, characterized by moment intensity coefficients, occur only in the case of sufficiently rigid and elastic inclusions. [ABSTRACT FROM AUTHOR]

The objective of this paper is to study the dynamical properties of a discrete-time prey–predator model under imprecise biological parameters. We consider refuge for prey species as a constant number. The equilibria of the model are obtained, and the dynamic behaviors of the proposed system are examined for the interval biological parameters. Simulations of the model are performed for different parameters of the model. Numerical simulations demonstrate that the proposed discrete model exhibits rich dynamics of a chaotic and complex nature. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the equivalent small parameter method (ESPM) is used to establish the nonlinear mathematical model of the fractional‐order buck–boost converter in continuous current mode (CCM), and the analytical expression of approximate steady‐state period of converter state variable is obtained by using equivalent small parameter method and combining with harmonic balance principle. The Matlab/Simulink is used to construct the fractional‐order capacitance and inductance and to build the circuit model as well as the simulation model of fractional‐order buck–boost converter. Moreover, the simulation results of Oustaloup circuit model and numerical simulation model are compared with those of ESPM model to verify the validity and accuracy of the ESPM. The model is simulated by changing the orders of the capacitor and inductor to obtain the influence rule of the order of fractional element on harmonic characteristics of the state variables. [ABSTRACT FROM AUTHOR]

In this paper, the influence of vibration parameters on twin-roll strip vibration cast-rolling is studied. Through a comparison of vibration and nonvibration cast-rolling experiments with a 7075 aluminum alloy, it is found that the mechanical vibration introduced during the cast-rolling process can refine the grains and inhibit segregation. A thermal-flow-coupled numerical simulation model of the actual twin-roll strip vibration cast-rolling process is constructed to study the time-domain characteristics and frequency-domain characteristics of the flow field and temperature field in the molten pool, and the model is verified by experiments. The simulation results show that the disturbing effect of vibrations on the flow field in the molten pool can increase the nucleation rate by promoting dendrite fusing and inhibit the segregation of alloying elements. The vibration also affects the temperature field. During vibration cast-rolling, the height of the kiss point changes sinusoidally with time. Based on an analysis of the influence of the amplitude and vibration frequency on the temperature field and flow field, the optimal vibration parameters of the vibration cast-rolling process are determined and provide a foundation for the promotion and application of the new technology of vibration cast-rolling. [ABSTRACT FROM AUTHOR]

Computer simulation modeling approach has been used for the last decades to address the growing need for estimation, analysis and improvement of project performance indicators. In this research, a dynamic simulation model is developed capturing both hierarchical and dynamic complexities of projects. This paper discusses how changes in dynamics can influence the critical performance indicators of a project throughout its lifecycle. The designed simulation model is capable of assessing the robustness and suitability of the scope and change management policies. The validity of the model was tested by a real-world project in the petrochemical industry. The significant factors influencing a project's performance are investigated in the case study. The simulation results indicate that resource allocation decisions could be optimized to improve project performance indicators. The developed decision model can be regarded as a flexible and predictive tool in the construction industry with the purpose of explaining the dynamic behavior of a project. SD: System Dynamics [ABSTRACT FROM AUTHOR]

In this paper, we analyze the dynamics and formation mechanisms of bound states (BSs) of light bullets in the output of a laser coupled to a distant saturable absorber. First, we approximate the full three-dimensional set of Haus master equations by a reduced equation governing the dynamics of the transverse profile. This effective theory allows us to perform a detailed multiparameter bifurcation study and to identify the different mechanisms of instability of BSs. In addition, our analysis reveals a non-intuitive dependence of the stability region as a function of the linewidth enhancement factors and the field diffusion. Our results are confirmed by direct numerical simulations of the full system. [ABSTRACT FROM AUTHOR]

This paper takes the risk management and countering strategies of a project as the basis of theoretical knowledge, IT modeling and simulation technology. By combining this approach with the processes of large international construction projects, we specifically research the political risk, natural risk, economic risk, design risk and risk of construction preparation in the project approval and early preparation stages. We also emphasize the risk identification, risk estimation, risk evaluation, risk response, risk monitoring and risk management decisions for the importance of the practice of large international projects and subsequently indicate the primary issues and countering strategies in international project risk management that should receive attention during a construction project. [ABSTRACT FROM AUTHOR]

Summary: Identification of nonlinear hysteretic systems has practical significance for the prediction of structural response. This paper develops a novel parameter identification method for nonlinear hysteretic systems. The Bouc–Wen model and its improved models are used to parametrically characterize the structural systems. Model parameters are identified using a given load‐displacement trajectory. The proposed method is developed under the framework of the sequence model optimization, which provides a broader search domain and needs fewer iterations. Firstly, a series of sensitivity analyses were conducted to investigate the effects of the Bouc–Wen parameters on the hysteresis behavior and to guide the identification process. Subsequently, based on the framework of the sequence model optimization, a novel strategy for identifying the model parameters of the nonlinear hysteresis system was proposed. Finally, the effectiveness and accuracy of the proposed algorithm were verified by the experimental data and numerical simulation results. The results indicate that the identified numerical model can accurately capture the strength and stiffness degradation and the pinching effect of the structural system. As a result, the predicted hysteretic trajectories are well agreed with the actual structural responses. The case studies demonstrate that the proposed method is sufficiently accurate and computationally efficient for the nonlinear hysteretic systems. [ABSTRACT FROM AUTHOR]

The author's experiences over a span of more than 50 years are characterised as a journey. Early interests in computer system performance modelling, information storage and retrieval, and computer networks become secondary to research topics in computer simulation. Organisations, events, and, most important, people define the paths, waysides, excursions, side roads, and major stops along the way. Editorial positions constitute an enduring thread throughout the journey. Capturing and preserving the history of the modelling and simulation discipline, frequently a topical sojourn, emerges as a dominant activity in the latter years. Two evocative questions, based on the prediction of a prominent computing pioneer, conclude the paper. 1955 Oldsmobile Starfire (98 Convertible) [ABSTRACT FROM AUTHOR]

The system dynamic model (SD model) can simulate the dynamic change of the system from the overall perspective and carry out dynamic analysis of the structure, behavior and causality of the system by computer simulation under different assumptions. Therefore, to solve the problem of tripartite game between the government, private sector and owners which caused by the application of PPP model in the old community renovation, this paper establishes a three-party game model based on the evolutionary game theory and simulates the evolvement path of each participant by establishing SD Model with relevant computer Software. The research finds that: (1) the government, the community owners and the private sectors will eventually reach a stable and balanced state (supervision, participation, effort); (2) the government is dominant in the renovation, and the strategic choice of the private sectors and the community owners depends on the government's strategy, the variables determined by the government and the relationship between these exogenous variables; (3) although a single variable could influence the strategic choice of each party, the formation of the final stable state depends on the interaction of multiple variables, and the government should handle the relationship between each stakeholders. [ABSTRACT FROM AUTHOR]

Optimizing the dynamic responses of a slab track system is a key aspect to improve the quality of a railway track structure. In this paper, numerical modelling and simulation of vertical dynamics of the railway track structure engaging the asphalt concrete in substructures were carried out. Thus, a 3D finite element (FE) model was developed. The developed model was validated by comparing its outputs, that is, acceleration with the measured ones from realistic experimental data. The good agreement between the simulated and measured data which resulted from the validation confirmed that the proposed model has a capability of simulating the complex dynamic performances of the train-track-ground system under different loading conditions. Analyses of the determined results from the simulation model performances revealed that three specific factors, which were the speed of the train, the temperature, and thickness of the asphalt concrete trackbed, mainly influenced the dynamic behavior of the railway structure. Thereby, those factors were taken into consideration while evaluating the dynamic responses and designing the asphalt concrete trackbed in railway substructures. [ABSTRACT FROM AUTHOR]

The advancement of computing technology makes it possible to build extremely accurate digital reconstructions of brain circuits. Are such unprecedented levels of biological accuracy essential for brain simulations to play the roles they are expected to play in neuroscientific research? The main goal of this paper is to clarify this question by distinguishing between various roles played by large-scale simulations in contemporary neuroscience, and by reflecting about what makes a simulation biologically accurate. It is argued that large-scale simulations may play model-oriented and prediction-oriented roles in brain research, and that the concept of biological accuracy can be interpreted as related to the plausibility of the theoretical model implemented in the simulation system, to the accuracy of the computer implementation, and to the level of details of the implemented model. Building on these observations and distinctions, it is argued that biological accuracy is not essential for a computer simulation to play the epistemic roles it is expected to play in brain research. [ABSTRACT FROM AUTHOR]

Context. Fewer than 1% of all exoplanets detected to date have been characterized on the basis of spectroscopic observations of their atmosphere. Unlike indirect methods, high-contrast imaging offers access to atmospheric signatures by separating the light of a faint off-axis source from that of its parent star. Forthcoming space facilities, such as WFIRST/LUVOIR/HabEX, are expected to use coronagraphic instruments capable of imaging and spectroscopy in order to understand the physical properties of remote worlds. The primary technological challenge that drives the design of these instruments involves the precision control of wavefront phase and amplitude errors. To suppress the stellar intensity to acceptable levels, it is necessary to reduce phase aberrations to less than several picometers across the pupil of the telescope. Aims. Several focal plane wavefront sensing and control techniques have been proposed and demonstrated in laboratory to achieve the required accuracy. However, these techniques have never been tested and compared under the same laboratory conditions. This paper compares two of these techniques in a closed loop in visible light: the pair-wise (PW) associated with electric field conjugation (EFC) and self-coherent camera (SCC). Methods. We first ran numerical simulations to optimize PW wavefront sensing and to predict the performance of a coronagraphic instrument with PW associated to EFC wavefront control, assuming modeling errors for both PW and EFC. Then we implemented the techniques on a laboratory testbed. We introduced known aberrations into the system and compared the wavefront sensing using both PW and SCC. The speckle intensity in the coronagraphic image was then minimized using PW+EFC and SCC independently. Results. We demonstrate that both techniques - SCC, based on spatial modulation of the speckle intensity using an empirical model of the instrument, and PW, based on temporal modulation using a synthetic model - can estimate the wavefront errors with the same precision. We also demonstrate that both SCC and PW+EFC can generate a dark hole in space-like conditions in a few iterations. Both techniques reach the current limitation of our laboratory bench and provide coronagraphic contrast levels of 5 e 10-9 in a narrow spectral band (<0:25% bandwidth). Conclusions. Our results indicate that both techniques are mature enough to be implemented in future space telescopes equipped with deformable mirrors for high-contrast imaging of exoplanets. [ABSTRACT FROM AUTHOR]

The current practice and the requirements of industrial enterprises in all industrial areas require a detailed display of manufacturing systems course of events. In this paper, we studied the effects and impacts of computer simulation to improve the actual industrial production. We also verified whether the proposed simulation model and its intervention in the logistics of concrete production in a concrete manufacturing enterprise will correspond to reality. The EXTENDSIM simulation software was used. The simulation results utilization in practice has increased the actual production several times. The simulation results indicated that it is necessary to double the intensity of company supply, i.e. a frequency of entry set to 0.15 days for each timber type. This adjustment increased the performance of unutilized devices and the whole manufacturing system several times, up to 54,475 produced building timber elements, which represents an increase of production by about 199.6% while maintaining company flexibility. [ABSTRACT FROM AUTHOR]

Bénard-Marangoni convection can be used to self-organize hexagonal convective cells, but defects easily emerge in the hexagonal pattern, which hinders its application in industry. The dynamics of front propagation and defect generation are studied in this paper. We focus especially on the onset process of a local disturbance of a hexagonal pattern, named the "nucleus." The front propagation of the nucleus has been researched through numerical simulations of a model equation and experiments. In the numerical simulations, a single nucleus can evolve into a perfect hexagon pattern under critical or subcritical conditions, and a random disturbance can generate multiple nuclei which evolve into grain boundaries. In addition, under supercritical conditions, defects also emerge as a single nucleus grows. The instability of front propagation is considered to be the mechanism for the generation of irregular patterns. The curvature effect makes the protrusion of the front have a larger velocity in supercriticality, which results in a wavy front, and defects are generated in the concave portion of the front. Also, because of the curvature effect, the front of an irregular pattern has a larger velocity than that of the regular pattern since the protrusion of the front in the irregular pattern increases the average velocity. Experiments have also been carried out by using an infrared camera to analyze front propagation. The results are qualitatively in agreement with the results of numerical simulations. Through the study of defect generation in front propagation, we put forward a method for generating a hexagon pattern which greatly reduces the number of defects. [ABSTRACT FROM AUTHOR]

Tunnel excavation in squeezing ground exhibits large time-dependent and often anisotropic deformation. Within the context of the Fréjus road tunnel and its safety gallery excavated under the Alps between France and Italy, an interesting configuration of two parallel tunnels under squeezing ground conditions is observed. The special feature of this case study lies in the fact that both tunnels have been excavated in similar geotechnical conditions but with different excavation techniques. The road tunnel was excavated with conventional drill and blast methods in the 70s, whereas the safety gallery was excavated between 2009 and 2016 with a single-shield tunnel boring machine (TBM). This paper presents monitoring data processing and numerical simulations of both tunnels with the aim of studying the influence of the excavation method on the time-dependent tunnel response. A calibration of a visco-elasto-plastic anisotropic constitutive model based on the back-analysis of convergence measurements retrieved during the excavation of the Fréjus road tunnel is carried out. The identified ground behavior can be extrapolated to the parallel zones of the safety gallery. In particular, we are interested in the prediction of the stress state in the segmental lining of the gallery during its excavation and the comparison with in situ measurements. It is shown that the time-dependent behavior of the ground is affected by the excavation technique. Finally, an attempt to predict the long-term response of both tunnels is proposed. [ABSTRACT FROM AUTHOR]

In this paper we present an analytical and numerical modeling of a general polymerization process with possible lengthening by an agglomeration mechanism. The proposed model takes into account the 2D spatial diffusion of the monomers for the mass transfer between monomers and polymers. We investigate the well-posedness of this general polymerization model and propose an adequate numerical scheme based on a generalization of the anti-dissipative method developed in Goudon (Math. Models Methods Appl. Sci. 23:1177–1215, 2013). [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the numerical implementation of the field dislocation mechanics (FDM) theory for the simulation of dislocation-mediated plasticity. First, the mesoscale FDM theory of Acharya and Roy (2006 J. Mech. Phys. Solids 54 1687–710) is recalled which permits to express the set of equations under the form of a static problem, corresponding to the determination of the local stress field for a given dislocation density distribution, complemented by an evolution problem, corresponding to the transport of the dislocation density. The static problem is solved using FFT-based techniques (Brenner et al 2014 Phil. Mag. 94 1764–87). The main contribution of the present study is an efficient numerical scheme based on high resolution Godunov-type solvers to solve the evolution problem. Model problems of dislocation-mediated plasticity are finally considered in a simplified layer case. First, uncoupled problems with uniform velocity are considered, which permits to reproduce annihilation of dislocations and expansion of dislocation loops. Then, the FDM theory is applied to several problems of dislocation microstructures subjected to a mechanical loading. [ABSTRACT FROM AUTHOR]

Purpose: The internal force is more complicated in a combined load case than in a single load case, and the influence of the combined load on the stress cannot be neglected. The purpose of this paper is to study the mechanical behavior of the flexible riser under combined load conditions of tension and internal pressure or external pressure. Design/methodology/approach: The mechanical behavior of the flexible riser under combined load conditions is studied by numerical simulation with a nine-layer detailed finite element model. The layers of flexible riser are modeled separately, and the interactions between layers have been taken into consideration in numerical simulation. Findings: Under tension and internal pressure or external pressure, the pressure armor will bear extra external pressure because of the squeezing actions between layers caused by tension, and the extra external pressure will increase proportionately with the increase of the tension. Under internal pressure and tension, the internal stress for tension armor was nearly unchanged compared to that under unique tension load, whereas under external pressure and tension, the change of internal stress for tension armor was significant. Prediction methods of internal force for pressure armor and tension armor under pressure and tension are given, and the result from the formula agrees well with the simulation results. Originality/value: The prediction methods on the internal force of flexible riser proposed in this study are proven accurate, with numerical simulation results, and the prediction methods are convenient for engineering applications. [ABSTRACT FROM AUTHOR]

A new attack against the Kirchhoff-Law-Johnson-Noise (KLJN) secure key distribution system is studied with unknown parasitic DC-voltage sources at both Alice's and Bob's ends. This paper is the generalization of our earlier investigation with a single-end parasitic source. Under the assumption that Eve does not know the values of the parasitic sources, a new attack, utilizing the current generated by the parasitic dc-voltage sources, is introduced. The attack is mathematically analyzed and demonstrated by computer simulations. Simple defense methods against the attack are shown. The earlier defense method based solely on the comparison of current/voltage data at Alice's and Bob's terminals is useless here since the wire currents and voltages are equal at both ends. However, the more expensive version of the earlier defense method, which is based on in-situ system simulation and comparison with measurements, works efficiently. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present the procedure test for calibration and validation of the numerical model for X22CrMoV12-1 steel multilayer welding. On the real multilayer weld was described how to arrange the whole experiment in order to obtain not only relevant input data but also verification data. Tests on a specially prepared specimen, welded with 8 beads in 4 layers, allows to determine the actual geometry of the single welded beads, registration of welding thermal cycles and the hardness distribution in successively deposited beads together with determining the heat influence of subsequent layers. The results of the real welding tests were compared with the results obtained from the numerical simulations and extended by the calculated stresses and distortions distributions of the tested specimen. A new, improved hardness prediction algorithm for high-alloy martensitic and bainitic steels was also proposed. [ABSTRACT FROM AUTHOR]

The changes in the maritime service market have brought unprecedented challenges to maritime service enterprises. This paper uses the method of system dynamics to study the causal relationship of the core competence of maritime logistics enterprises from the perspective of service innovation by analyzing its influencing factors and evolution process, thus constructs the system dynamics model of the evolution of core competence of maritime logistics enterprises, and then uses Vensim PLE to simulate the model. Through the verification and analysis of the validity and sensitivity of the simulation model, it shows that the model can fit the evolution process of the core competence of the maritime logistics enterprise, reveal the process and mechanism of it, and provide management strategy for the competence's upgrading. So it can improve the overall efficiency of maritime logistics enterprises, guide them to take competitive advantages in the fast and changing market. The construction and operation of computer simulation model provides an effective research method and way for the evolution of core competence of maritime logistics enterprises. [ABSTRACT FROM AUTHOR]

This research is based on the Derivative/Integration of the Power Spectrum for the reduction of noise in a periodic signal. The performed procedure, joined to a convolution process, results in the detection of the original values of amplitude, phase and frequency of the spectral components of the periodic signal. In this paper, second-order statistics foundations are presented and the validation of the proposed algorithm is exposed in both theoretical and practical sense. [ABSTRACT FROM AUTHOR]

In this paper, it is shown that when a flow undergoes a steady bifurcation breaking one reflection symmetry, the mean flow obtained by averaging the two possible asymmetric flow fields resulting from the instability remains marginally stable in the postcritical regime. This property is demonstrated rigorously through an asymptotic analysis which closely follows that proposed in Sipp and Lebedev (J Fluid Mech 792:620–657, 2007) for a Hopf bifurcation with focus on wakes. In the case of wakes, the marginal stability of the mean flow is well known and had several consequences documented in the literature. To the authors' knowledge, the marginal stability of mean flows after a symmetry-breaking pitchfork bifurcation is demonstrated here for the first time. As an example of possible consequences of marginal stability, the self-consistent model proposed for wakes in Mantič-Lugo et al. (Phys Rev Lett 113:084501, 2014) and relying on marginal stability is also applied here to the symmetry-breaking instability of the flow in a channel with a sudden expansion. For this specific case, the marginal stability of the mean flow is first demonstrated by dedicated direct numerical simulations; successively, it is shown that the resulting self-consistent model predicts the nonlinear saturation of the instability with remarkable accuracy. [ABSTRACT FROM AUTHOR]

This paper presents the formulation of a new methodology to design adaptive structures. This design method synthesises structural configurations that are optimum hybrids between a passive and an active structure. An optimisation scheme searches for an optimal material distribution and actuation layout to minimise the structure whole-life energy which consists of an embodied part in the material and an operational part for structural adaptation. Instead of using more material to cope with the effect of loads, here, strategically located active elements redirect the internal load path to homogenise the stresses and change the shape of the structure to keep deflections within required limits. To ensure the embodied energy saved this way is not used up to by actuation, the adaptive solution is designed to cope with ordinary loading events using only passive load-bearing capacity whilst relying on active control to deal with larger events that have a smaller probability of occurrence. The design methodology has been implemented for statically determinate and indeterminate reticular structures. However, the formulation is general and could be implemented to other structural types. Numerical simulations on a truss system case study confirm that substantial savings up to 50% of the whole-life energy can be achieved by the adaptive solution compared to a passive solution designed using state of the art optimisation methods. [ABSTRACT FROM AUTHOR]