Coupling Of Subsystems Research Articles

MnSnTeO6: A Chiral Antiferromagnet Prepared by a Two-Step Topotactic Transformation.

MnSnTeO6, a new chiral antiferromagnet, was prepared both by topotactic transformation of the metastable rosiaite-type polymorph and by direct synthesis from coprecipitated hydroxides. Its structure and its static and dynamic magnetic properties were studied comprehensively both experimentally (through X-ray and neutron powder diffraction, magnetization, specific heat, dielectric permittivity, and ESR techniques) and theoretically (by means of ab initio density functional theory (DFT) calculations within the spin-polarized generalized gradient approximation). MnSnTeO6 is isostructural with MnSb2O6 (space group P321) and does not show any structural transition between 3 and 300 K. The magnetic susceptibility and specific heat exhibit an antiferromagnetic ordering at TN ≈ 9.8 K, which is confirmed by low-temperature neutron data. At the same time, the thermodynamic parameters demonstrate an additional anomaly on the temperature dependences of magnetic susceptibility χ(T), specific heat Cp(T) and dielectric permittivity ε(T) at T* ≈ 4.9 K, which is characterized by significant temperature hysteresis. Clear enhancement of the dielectric permittivity at T* is most likely to reflect the coupling of dielectric and magnetic subsystems leading to development of electric polarization. It was established that the ground state of MnSnTeO6 is stabilized by seven exchange parameters, and neutron diffraction revealed incommensurate magnetic structure with propagation vector k = (0, 0, 0.183) analogous to that of MnSb2O6. Ab initio DFT calculations demonstrate that the strongest exchange coupling occurs between planes along diagonals. All exchange parameters are antiferromagnetic and reveal moderate frustration.

Особенности релаксации остаточной намагниченности антиферромагнитных наночастиц на примере ферригидрита

In this work, we studied the relaxation of the remanent magnetization of antiferromagnetically ordered ferrihydrite nanoparticles under the conditions of realization of the exchange bias effect for these systems. Magnetization relaxation is characterized by a logarithmic dependence on time, which is typical for thermo-activation processes of the hopping of the magnetic moment of particles through potential barriers caused by magnetic anisotropy. The energy of the barriers obtained from processing the data on relaxation of the remanent magnetization (under the conditions of field cooling) significantly exceeds that for ordinary conditions (zero field cooling). The observed difference indicates the possibility of using the residual magnetization relaxation process to analyze the mechanisms responsible for the effect of exchange bias in antiferromagnetic nanoparticles and obtain the parameters characterizing the exchange coupling of magnetic subsystems in such objects.

Effect of Hot Water Setting Temperature on Performance of Solar Absorption-Subcooled Compression Hybrid Cooling Systems

The solar absorption-subcooled compression hybrid cooling system (SASCHCS) displays outstanding advantages in high-rise buildings. Since the performance coupling of collectors and absorption subsystems is stronger due to the absence of backup heat and the effect of generator setting temperature has not been realized adequately, it is highly important to study the relationship of SASCHCS operation and the set point temperature of hot water to prevent performance deterioration by inappropriate settings. Therefore, the paper mainly deals with the effect of collector and generator setting temperature. The investigation was based on the entire cooling period of a typical high-rise office building in subtropical Guangzhou. The off-design model of hybrid systems was built at first. Subsequently, the impact mechanism of setting temperature in two hot water cycles on facility operation was analyzed. It was found that the excessive rise of collector setting temperature deteriorated the energy saving, while the appropriate improvement of generator set point temperature was beneficial for the solar cooling. Besides, global optimization by the genetic algorithm displayed that 71.6 °C for the collector setting temperature with 64.5 °C for the generator was optimal for annual operation. The paper is helpful in enhancing the operation performance of SASCHCS.

A receptance-based method for frequency assignment via coupling of subsystems

This paper presents a theoretical study of the frequency assignment problem of a coupled system via structural modification of one of its subsystems. It deals with the issue in which the available modifications are not simple; for example, they are not point masses, grounded springs, or spring-mass oscillators. The proposed technique is derived based on receptance coupling technique and formulated as an optimization problem. Only a few receptances at the connection ends of each subsystem are required in the structural modification process. The applicability of the technique is demonstrated on a simulated rotor system. The results show that both bending natural frequencies and torsional natural frequencies can be assigned using a modifiable joint, either separately or simultaneously. In addition, an extension is made on a previously proposed torsional receptance measurement technique to estimate the rotational receptance in bending. Numerical simulations suggest that the extended technique is able to produce accurate estimations and thus is appropriate for this frequency assignment problem of concern.

Research Platform: Decentralized Energy System for Sector Coupling

AbstractIndustrial facilities usually need multiple energy subsystems, e.g., for heat, cold, and electric power supply. Normally, these energy subsystems are controlled locally and independent of each other. Coupling of the different subsystems can open up additional potential. Fraunhofer IISB has developed a demonstration and research platform for investigating the benefits of such sector coupling. A major precondition is to understand the energy flows in the system and establish an overall and flexible system control to realize the required algorithms for setting up an intelligent decentralized energy system. Major components of the overall system are various storages, which extend the degree of freedom for sector coupling and increase the effectiveness of the different subsystems.

Fault-tolerant control for a class of linear interconnected hyperbolic systems by boundary feedback

This paper considers a fault-tolerant control problem for a class of interconnected linear hyperbolic partial differential equation systems. Both subsystem faults and coupling faults are considered. Firstly, the well-posedness of the faulty system is analyzed by using semigroup theory. Secondly, for the fault-free case, a stabilizing boundary feedback control based on small-gain theorem is proposed. Consequently, in the presence of faults, fault recoverability conditions are established that maintain the stability of the faulty systems. The fault-tolerant control strategies are also provided. A heat exchanger example is taken to illustrate the effectiveness and practicality of the proposed methods.

Gauging the boundary in field-space

Local gauge theories are in a complicated relationship with boundaries. Whereas fixing the gauge can often shave off unwanted redundancies, the coupling of different bounded regions requires the use of gauge-variant elements. Therefore, coupling is inimical to gauge-fixing, as usually understood. This resistance to gauge-fixing has led some to declare the coupling of subsystems to be the raison d’être of gauge (Rovelli, 2014).Indeed, while gauge-fixing is entirely unproblematic for a single region without boundary, it introduces arbitrary boundary conditions on the gauge degrees of freedom themselves—these conditions lack a physical interpretation when they are not functionals of the original fields. Such arbitrary boundary choices creep into the calculation of charges through Noether's second theorem (Noether, 1971), muddling the assignment of physical charges to local gauge symmetries. The confusion brewn by gauge at boundaries is well-known, and must be contended with both conceptually and technically.It may seem natural to replace the arbitrary boundary choice with new degrees of freedom, for using such a device we resolve some of these confusions while leaving no gauge-dependence on the computation of Noether charges (Donnelly & Freidel, 2016). But, concretely, such boundary degrees of freedom are rather arbitrary—they have no relation to the original field-content of the field theory. How should we conceive of them?Here I will explicate the problems mentioned above and illustrate a possible resolution: in a recent series of papers (Gomes, Hopfmller,& Riello, 2018; Gomes & Riello, 2017, 2018) the notion of a connection-form was put forward and implemented in the field-space of gauge theories. Using this tool, a modified version of symplectic geometry—here called ‘horizontal’—is possible. Independently of boundary conditions, this formalism bestows to each region a physically salient, relational notion of charge: the horizontal Noether charge. Meanwhile, as required, the connection-form mediates a composition of regions, one compatible with the attribution of horizontal Noether charges to each region. The aims of this paper are to highlight the boundary issues in the treatment of gauge, and to discuss how gauge theory may be conceptually clarified in light of a resolution to these issues.

Modeling and Simulation of Satellite Attitude Dynamics and Control System using Modelica

The control of attitude of a satellite is difficult to verify since several subsystems of different disciplines, e.g., flexible multibody dynamics, machines, electronics and control, are involved and strongly coupled. A traditional method is to model each single discipline subsystem with a domain specific software, and combine them through interfaces. However, the problems are that lots of interfaces between software have to be developed, and manual decoupling of systems should be considered during modelling process. In this Paper, models of the dynamics and the control system are established in a unified modelling software, MWorks, which is an Integrated Development Environment of Modelica. The model can be used to verify the satellite control strategy, and also provide an effective means for satellite attitude control system design. Moreover, on this basis, the whole satellite was modelled to access state parameters changes under the coupling of the dynamic subsystem, the attitude control subsystem, the power supply subsystem, the propulsion subsystem and the integrated electronic subsystem can be synthetically considered.

Multi-disciplinary design optimization with variable complexity modeling for a stratosphere airship

This paper proposes a hybrid architecture based on Multi-disciplinary Design Optimization (MDO) with the Variable Complexity Modeling (VCM) method, to solve the problem of general design optimization for a stratosphere airship. Firstly, MDO based on the Concurrent SubSpace Optimization (CSSO) strategy is improved for handling the subsystem coupling problem in stratosphere airship design which contains aerodynamics, structure, and energy. Secondly, the VCM method based on the surrogate model is presented for reducing the computational complexity in high-fidelity modeling without loss of accuracy. Moreover, the global-to-local optimization strategy is added to the architecture to enhance the process. Finally, the result gives a prominent stratosphere airship general solution that validates the feasibility and efficiency of the optimization architecture. Besides, a sensitivity analysis is conducted to outline the critical impact upon stratosphere airship design.

The spatial and temporal evolution of coordinated ecological and socioeconomic development in the provinces along the Silk Road Economic Belt in China

The ecological and socioeconomic conditions of the provinces along the Silk Road Economic Belt (SREB) in China are quite different. Current research lacks a scientific analysis of the spatial and temporal evolution of the coordinated ecological and socioeconomic development in this region. Based on the ecological footprint and the Comprehensive Development Index (CDI), an evaluation indicator system for coordinated ecological and socioeconomic development was constructed. The weights of the indicators were determined by the entropy method. Using data from 2005 to 2016, the coupling coordination degree model was used to evaluate the coordination level between the ecological and socioeconomic subsystems. The results showed a decreasing trend in the comprehensive evaluation function score of the ecological subsystem. The socioeconomic subsystem scores and coupling coordination degree fluctuated slightly in 2014 and 2015, but they increased in general. The coordinated development improved, and the spatial differences were obvious. Ecological degradation gradually exhibits a restrictive effect on socioeconomic subsystem, further restricting the improvement of the coordinated development. This study can provide a basis for scientific evaluation of the coordinated development level of ecological and socioeconomic conditions, and is conducive to improving the regional cooperation mechanism.

Evaluating National Multi-energy System Based on General Modeling Method

This paper uses an integrated evaluation framework to evaluate the possible national multi-energy flow in China in a near future. The framework includes an integrated modeling for national multi-energy system in China. These key and bone national energy facilities are all modeled in a generalized network flow formulation. The modeling considers the regional energy system, inter-regional power and natural gas transmission system and the district supply heat model. Specific modeling method is abstracted as some general modeling rules to tackle the difficulty of modeling so many different energy facilities through focus on the input energy flow and output energy flow of them. In addition, it also contains a short-term or mid-term (1~3 years) operation evaluation model based on the least socio-economic cost or national energy resource adequacy. The model is proposed to find the potential of Chinese bone national energy system in an integrated multi-energy perspective and to evaluate the impact of a short-term or mid-term national energy policy in technical way considering the coupling of different energy sub-systems. Although it is difficult to verify the national energy model, the open and known energy data of China in 2016 is used to verify the model. Then this model is employed to evaluate the China multi-energy system in 2020 to give some suggestions on the optimization of energy flow at the national scale and supply heat transition.

Concept of Modal Repulsion for Examining the Subsynchronous Oscillations Caused by Wind Farms in Power Systems

This paper investigates the torsional subsynchronous oscillations (SSOs) of synchronous generators caused by the grid-connected wind farms. The investigation does not rely on the representation of a wind farm by an aggregated wind generator and is based on a multi-input and multi-output closed-loop model. The model is comprised of the wind farm subsystem, which includes all the wind farms, and the subsystem of rest of power system (ROPS). Theoretical analysis proves that the open-loop SSO modal coupling of wind farm subsystem and ROPS subsystem results in the closed-loop SSO modal repulsion on the complex plane. Subsequently, damping of torsional SSOs decreases and growing SSOs may occur when the closed-loop modal repulsion is strong. Hence, closed-loop modal repulsion explains and reveals the mechanism about why the wind farms may cause the torsional SSOs in the power system. In addition, a method of open-loop modal analysis is proposed to detect the SSO instability risk brought about by the wind farms. The detection is based on the estimation of degree of closed-loop modal repulsion and only needs the modal information of open-loop subsystems. An example power system with wind farms is presented to demonstrate analysis and conclusions made in the paper.

Energy-leak monitoring and correction to enhance stability in the co-simulation of mechanical systems

Non-iterative co-simulation is an increasingly important technique for the simulation of complex mechanical systems. Adopting co-simulation schemes enables the simultaneous use of computational resources and makes it possible to select the most appropriate modelling techniques and algorithms to describe and solve the dynamics of each system component. However, it inherently requires the coupling of different subsystems at discrete communication times, which may compromise the stability of the overall integration process. One of the negative effects of discrete-time communication is the introduction of artificial energy in the system dynamics, which can render the simulation unstable if it accumulates over time. Excess energy can be dissipated introducing virtual damping elements in the subsystem models. The actual amount of damping must be adjusted as the simulation progresses to ensure that all the artificially generated energy is removed from the system while keeping the dynamics realistic. In this paper, we introduce a monitoring framework to keep track of this excess energy, and put forward a dissipation methodology to eliminate it. The ability of this framework to achieve stable non-iterative co-simulation was tested with several mechanical system examples.

The MEOW lunar project for education and science based on concurrent engineering approach

The use of concurrent engineering in the design of space missions allows to take into account in an interrelated methodology the high level of coupling and iteration of mission subsystems in the preliminary conceptual phase. This work presents the result of applying concurrent engineering in a short time lapse to design the main elements of the preliminary design for a lunar exploration mission, developed within ESA Academy Concurrent Engineering Challenge 2017. During this program, students of the Master in Space Systems at Technical University of Madrid designed a low cost satellite to find water on the Moon south pole as prospect of a future human lunar base. The resulting mission, The Moon Explorer And Observer of Water/Ice (MEOW) compromises a 262 kg spacecraft to be launched into a Geostationary Transfer Orbit as a secondary payload in the 2023/2025 time frame. A three months Weak Stability Boundary transfer via the Sun-Earth L1 Lagrange point allows for a high launch timeframe flexibility. The different aspects of the mission (orbit analysis, spacecraft design and payload) and possibilities of concurrent engineering are described.

Diagnosis of Interconnected Systems via well tuned Model-Based Coupling Algorithms

This paper presents a heuristic tuning method for a recently proposed model-based coupling algorithm. The purpose of the coupling algorithm is to mitigate effects caused by non ideal coupling of different subsystems where coupling imperfections like time delays, data losses or noisy measurements degrade the overall system performance. If the coupling algorithm is well tuned, a consistency criterion can be used for online closed-loop diagnosis. The simplicity and effectiveness of the proposed tuning and diagnosis approach is demonstrated via a laboratory experiment.

Modal Analysis of Lightweight Racing Car

The article deals with modal analysis of light racing car. The objective of the modal analysis was to obtain a mathematical model of the structure that matches as closely as possible to the experimental results achieved in the tests. The post-processing stage encompasses the use of the results to update theoretical predictions, optimization via structural modification, subsystem coupling, calculation of real modes from complex modes, etc. So, modal analysis has been used as a simple way to calculate the natural frequencies of the system and as the technique for finding out, which frequencies can be destructive and dangerous for it. Within the article, the verification of boundary conditions of virtual FEM analysis was done using the experimental modal analysis. It was performed on a simple fixed beam. After the results comparison, it could be stated that the values of natural frequencies correspond each other, so the virtual lightweight racing car could be analyzed in software Autodesk Inventor Professional. The analysis has helped to improve the stiffness of the car to be more stable on the wavy surface of the racing road.

Coupled electronic and atomic effects on defect evolution in silicon carbide under ion irradiation

Understanding energy dissipation processes in electronic/atomic subsystems and subsequent non-equilibrium defect evolution is a long-standing challenge in materials science. In the intermediate energy regime, energetic particles simultaneously deposit a significant amount of energy to both electronic and atomic subsystems of silicon carbide (SiC). Here we show that defect evolution in SiC closely depends on the electronic-to-nuclear energy loss ratio (Se/Sn), nuclear stopping powers (dE/dxnucl), electronic stopping powers (dE/dxele), and the temporal and spatial coupling of electronic and atomic subsystem for energy dissipation. The integrated experiments and simulations reveal that: (1) increasing Se/Sn slows damage accumulation; (2) the transient temperatures during the ionization-induced thermal spike increase with dE/dxele, which causes efficient damage annealing along the ion trajectory; and (3) for more condensed displacement damage within the thermal spike, damage production is suppressed due to the coupled electronic and atomic dynamics. Ionization effects are expected to be more significant in materials with covalent/ionic bonding involving predominantly well-localized electrons. Insights into the complex electronic and atomic correlations may pave the way to better control and predict SiC response to extreme energy deposition.

Effector-Triggered Self-Replication in Coupled Subsystems.

In living systems processes like genome duplication and cell division are carefully synchronized through subsystem coupling. If we are to create life de novo, similar control over essential processes such as self-replication need to be developed. Here we report that coupling two dynamic combinatorial subsystems, featuring two separate building blocks, enables effector-mediated control over self-replication. The subsystem based on the first building block shows only self-replication, whereas that based on the second one is solely responsive toward a specific external effector molecule. Mixing the subsystems arrests replication until the effector molecule is added, resulting in the formation of a host-effector complex and the liberation of the building block that subsequently engages in self-replication. The onset, rate and extent of self-replication is controlled by the amount of effector present.

Effector‐Triggered Self‐Replication in Coupled Subsystems

AbstractIn living systems processes like genome duplication and cell division are carefully synchronized through subsystem coupling. If we are to create life de novo, similar control over essential processes such as self‐replication need to be developed. Here we report that coupling two dynamic combinatorial subsystems, featuring two separate building blocks, enables effector‐mediated control over self‐replication. The subsystem based on the first building block shows only self‐replication, whereas that based on the second one is solely responsive toward a specific external effector molecule. Mixing the subsystems arrests replication until the effector molecule is added, resulting in the formation of a host–effector complex and the liberation of the building block that subsequently engages in self‐replication. The onset, rate and extent of self‐replication is controlled by the amount of effector present.

Robust Distributed Predictive Control of Waterborne AGVs-A Cooperative and Cost-Effective Approach.

Waterborne autonomous guided vessels (waterborne AGVs) moving over open waters experience environmental uncertainties. This paper proposes a novel cost-effective robust distributed control approach for waterborne AGVs. The overall system is uncertain and has independent subsystem dynamics but coupling objectives and state constraints. Waterborne AGVs determine their actions in a parallel way, while still minimizing an overall cost function and respecting coupling constraints robustly by communicating within a neighborhood. Our first contribution is the proposal of the system robustness level for the cost-effective robust distributed model predictive control (RDMPC) for waterborne AGVs. Cost-effective RDMPC models the price of robustness by explicitly considering uncertainty and system characteristics in a tube-based robust control framework. The second contribution is an efficient integrated branch & bound (B&B) and the alternating direction method of multipliers (ADMMs) algorithm for solving the cost-effective RDMPC problem. The algorithm exploits special ordered variable sets and combining branching criteria with intermediate ADMM results conducting smart search in B&B. Simulation results demonstrate the effectiveness of the proposed approach for cooperative distributed waterborne AGVs with cost-effective robustness.