Basic Time Step Research Articles

Rule Based Coordinated Control of Domestic Combined Micro-CHP and Energy Storage System for Optimal Daily Cost

This paper presents a novel control algorithm for optimising operational costs of a combined domestic micro-CHP (combined heat and power), battery and heat storage system. Using a minute by minute basic time-step, this work proposes a simple and computationally efficient rule based whole-system management, developed from empirical study of realistic simulated domestic electricity and heat loads. The CHP availability is considered in two binary states which, together with leveraging storage effectively, maximises CHP efficiency, and gives the algorithm increased real world feasibility. In addition, a novel application of a dual battery system is proposed to support the micro-CHP with each battery supplying just one of the distinctive morning and evening electrical load peaks, and thus inherently improving overall battery system lifetime. A case study is presented where the algorithm is shown to yield approximately 23% energy cost savings above the base case, almost 3% higher savings than that of the closest previous work, and 96.8% of the theoretical minimum cost. In general, the algorithm is shown to always yield better than 88% of the theoretical minimum cost, a ratio that will be considerably higher when real-world CHP limitations are factored into the theoretical minimum calculation.

Efficient high-order structure-preserving methods for the generalized Rosenau-type equation with power law nonlinearity

Based on the multi-symplectic Hamiltonian formula of the generalized Rosenau-type equation, a multi-symplectic scheme and an energy-preserving scheme are proposed. To improve the accuracy of the solution, we apply the composition technique to the obtained schemes to develop high-order schemes which are also multi-symplectic and energy-preserving respectively. Discrete fast Fourier transform makes a significant improvement to the computational efficiency of schemes. Numerical results verify that all the proposed schemes have satisfactory performance in providing accurate solution and preserving the discrete mass and energy invariants. Numerical results also show that although each basic time step is divided into several composition steps, the computational efficiency of the composition schemes is much higher than that of the non-composite schemes.

Short-time fluctuations and their impact on waste-to-energy conceptual design optimized by multi-stage stochastic model

The paper focuses on the development of a computational tool for effective investment planning in the field of waste-to-energy. The expected return on investment is only achieved if the plant operates successfully in the future. Generally, the operation of any plant can be analysed at various levels of detail, which differ in the basic time step. We may distinguish short-term, mid-term and long-term operation planning. The construction period of any waste-to-energy plant, including legislative processes usually lasts 5 to 10 y. The following operation is planned for next 20 - 30 y. Such a long project duration requires a robust design with low sensitivity to future changes in the key parameters. So here, multi-stage optimization model, which proposes a conceptual design of the plant based on plant’s performance under different future scenarios can serve as an effective support tool. So future operation modelling represents an integral part of such a tool. The objective of the paper is to discuss a proper time interval in the context of the complex multi-stage model and the influence of different time steps. The proper length of the time step varies depending on the required accuracy of the model. This paper aims to determine the susceptibility of different models depending on the time step. Correction coefficients for a more accurate model, which take into account the fluctuation of the data on the shorter time intervals, are proposed. The paper reviews aspects, which substantially fluctuate and vary with time and thus their prediction for long periods of time is very difficult, e.g. heat demand or waste supply. They are described and classified and their influence on the future economy of the plant is analysed. Data analysis of these parameters over shorter periods of time can also help to include auxiliary equipment such as heat accumulators or reserve gas or coal- fired boilers into the investment planning phase. Given the scope of the model is to design a new project, which uses data on an annual basis. For a more realistic model outputs, daily fluctuations in many parameters should be mentioned as well. For this purpose system of correction coefficients is proposed where applicable.

System Dynamics Simulation Modelling of Managing a Maritime Shipping Organization

This paper is a result of the research team at the University of Split, Faculty of Maritime Studies in dynamics of conduct maritime transport organizations. Results of the paper are shown in paper [8], and wish of the authors is to present a model to wider audience. What is new in this paper are Subsystem of debts, Subsystem of credits, Subsystem of loans and Subsystem of commercial department. System dynamics simulation modelling is one of the most suitable and most successful scientific methods of modelling of dynamics of complex, non-linear, natural, technical and organizational systems. System dynamics models are basically continuous models, as the subjects are presented by a set of non-linear differential equations, i.e. “equations of state”. However, they are also discrete, as their basic time step, i.e. sampling “DT” is defined in full accordance with the Sampling Theorem (Shannon, Nyquist and Koteljnikov). Such selection of the basic time step of DT enables computer modelling of continuous simulation models in digital computer, which is very suitable for training students at maritime faculty, engineering and electro technical faculties, and for theoretical and practical training of engineers of ship processes, as it enables them, by applying system dynamics approach, to acquire new information and skills about the complex dynamics of performance of maritime systems and processes. In a system dynamics model a shipping company is an integrated part of the surroundings and cannot be observed separately, without mutual interference.

Simulation Modelling of Managing a Maritime Shipping Organisation Using System Dynamics

This paper is a result of the research team at the University of Split, Faculty of Maritime Studies in dynamics of conduct maritime transport organizations. Results of the paper are shown in paper [8], and wish of the authors is to present a model to wider audience. What is new in this paper are Subsystem of debts, Subsystem of credits, Subsystem of loans and Subsystem of commercial department. System dynamics simulation modelling is one of the most suitable and most successful scientific methods of modelling of dynamics of complex, non-linear, natural, technical and organisational systems. System dynamics models are basically continuous models, as the subjects are presented by a set of non-linear differential equations, i.e. “equations of state”. However, they are also discrete, as their basic time step, i.e. sampling “DT” is defined in full accordance with the Sampling Theorem (Shannon, Nyquist and Koteljnikov). Such selection of the basic time step of DT enables computer modelling of continuous simulation models in digital computer, which is very suitable for training students at maritime faculty, engineering and electro technical faculties, and for theoretical and practical training of engineers of ship processes, as it enables them, by applying system dynamics approach, to acquire new information and skills about the complex dynamics of performance of maritime systems and processes. In a system dynamics model a shipping company is an integrated part of the surroundings and cannot be observed separately, without mutual interference.

Implementation of a symplectic multiple-time-step molecular dynamics algorithm, based on the united-residue mesoscopic potential energy function

A symplectic multiple-time-step (MTS) algorithm has been developed for the united-residue (UNRES) force field. In this algorithm, the slow-varying forces (which contain most of the long-range interactions and are, therefore, expensive to compute) are integrated with a larger time step, termed the basic time step, and the fast-varying forces are integrated with a shorter time step, which is an integral fraction of the basic time step. Based on the split operator formalism, the equations of motion were derived. Separation of the fast- and slow-varying forces leads to stable molecular dynamics with longer time steps. The algorithms were tested with the Ala(10) polypeptide chain and two versions of the UNRES force field: the current one in which the energy components accounting for the energetics of side-chain rotamers (U(rot)) can lead to numerically unstable forces and a modified one in which the the present U(rot) was replaced by a numerically stable expression which, at present, is parametrized only for polyalanine chains. With the modified UNRES potential, stable trajectories were obtained even when extending the basic time step to 15 fs and, with the original UNRES potentials, the basic time step is 1 fs. An adaptive multiple-time-step (A-MTS) algorithm is proposed to handle instabilities in the forces; in this method, the number of substeps in the basic time step varies depending on the change of the magnitude of the acceleration. With this algorithm, the basic time step is 1 fs but the number of substeps and, consequently, the computational cost are reduced with respect to the MTS algorithm. The use of the UNRES mesoscopic energy function and the algorithms derived in this work enables one to increase the simulation time period by several orders of magnitude compared to conventional atomic-resolution molecular dynamics approaches and, consequently, such an approach appears applicable to simulating protein-folding pathways, protein functional dynamics in a real molecular environment, and dynamical molecular recognition processes.

A comprehensive Eulerian modelling framework for airborne mercury species: model development and applications in Europe

A comprehensive mercury model system using the Eulerian reference frame of the Acid Deposition and Oxidant Model (ADOM) has been developed under the Canada–Germany Science & Technology Co-operation Agreement and applied within the European Union MArine Science and Technology–BAltic Sea SYstem Study (MAST-III-BASYS) and the Environment & Climate project Mercury Species over Europe (MOE), to study the regional transport and deposition fluxes of atmospheric mercury species. The model is able to simulate long-range transport of mercury over the entire depth of the troposphere with a basic time step of 1 h and incorporates current knowledge of physico-chemical forms and transformation reactions of atmospheric mercury species. Model predicted concentration and deposition pattern of mercury species over Europe are presented and concentrations of total gaseous mercury in ambient air and total mercury in precipitation calculated by the model are compared with observed values from a BASYS monitoring network study in February/March 1998. Concentrations in air agree within a factor of about 2 with observed values, thus indicating that the model is capable of reproducing observations satisfactorily even on an hourly basis. Observed monthly average concentrations in precipitation at four monitoring stations at the Baltic Sea coast are reproduced by the model within a factor of 1.3 suggesting that the chemical scheme in the model is based on an adequate parameterisation of aqueous phase chemistry.

An explicit conditionally stable finite difference equation for‐heat conduction problems

AbstractThis paper reports a new explicit and conditionally stable finite difference equation for heat conduction. It predicts results with an accuracy comparable with or better than that obtainable by other methods. Stability of operation can be extended to any desired degree by subdividing the basic time step and increasing the number of nodes. Some existing difference equations are special cases of the new equation reported in this paper. The new solution has been tested by calculating the response of a slab to transient and progressive waves whose analytical solutions are known.

A Hierarchical Model of Lotic Ecosystems

This paper presents the structure and properties of a total stream model that simulates the dynamics of small, flowing—water ecosystems in the northwestern United States. Conceptually, the model is hierarchically structured, consisting of 7 basic processes: periphyton dynamics, grazing, shredding, collecting, invertebrate predation, vertebrate predation, and detrital conditioning. These processes are subprocesses of 3 echelons of higher level processes: detritivory; herbivory; primary consumption; predation; and the total ecosystem. The model has 14 state variables in the 7 basic processes, and is conceptualized in discrete time with a basic time step corresponding to 1 day. Behavior of the stream model relative to different schedules of energy inputs and to the practice of clear—cut logging was investigated and related to contemporary theory of lotic ecosystems. In general, model behavior indicated that the regulation of biological processes in streams is complex, the mechanisms of which vary seasonally and from process to process. If a process is regulated by food supply, its annual production tends to increase as predation increases, while mean biomass may or may not be affected appreciably. In contrast, an increase in predation tends to decrease both mean biomass and annual production in processes regulated primarily by predation and such life history phenomena as insects emergence. The stream model provided the stimulus that led to a mathematical expression for the rate of production at the level of the entire ecosystem, and model behavior suggests that this rate tends to remain constant along a continuum from small, first—order streams with no tributaries to larger rivers which eventually drain into the sea.