Conventional Steady-state Model Research Articles

Hybrid-timescale dispatch of heat and electricity integrated system considering dynamic heat flow

In the electricity and heat integrated energy system, the transmission speed of heat energy is much slower than that of electricity. While the ignorance of the dynamic characteristic of heat system during the dispatch process often fails to satisfy the heat load. To address this issue and further improve the flexibility of the system, a dynamic linear model of heat pipeline is proposed, and a hybrid-timescale optimal dispatch strategy is established in this paper. Firstly, based on the finite difference method, the partial differential equation of heat pipeline is converted into a linear equality constraint. Then, a hybrid-timescale optimal dispatch model is established. By considering different dynamic characteristics of heat and power system, the calculation of dynamic linear model and dispatching of devices of power and heat system are realized under three different timescales. Finally, by using MATLAB, the effectiveness of the proposed dynamic model is validated compared with the conventional steady-state model and measured data. A series of simulation results verify that the proposed hybrid-timescale optimal dispatch strategy considering dynamic model helps the system to increase the supply rate of the heat load by 100% and decrease the economic cost,CO2andNOxemission by 0.79%, 0.2%, and 18.9%, respectively.

Dynamic Simulation of Three Phase Induction Machines Based on Reduced Order Model for Power Systems Analysis

Induction machines are a crucial type of electrical equipment utilized as motors in various industries and single-phase forms in household applications. They make up more than 80% of the industrial motors used today. This paper presents a dynamic simulation of three-phase induction machines based on the (d-q) model, providing a clear and easy-to-understand explanation of the behavior of the induction motor in the synchronous reference frame. The simulation is implemented using SIMULINK/MATLAB software, and full-order model analysis is conducted for transient analysis. However, modeling induction machines as part of power system analysis can be done with a less detailed model than the full-order one. In this paper, a reduced-order model is employed to simulate the induction motor using MATLAB/SIMULINK. The results of the reduced-order system and the full-order framework are compared to investigate the model's limits, and the computational benefits of saving time during large power system simulations justify the relative decrease in accuracy. The use of a reduced-order model results in a significant reduction in computation time when simulating large and very large-scale power systems, with a much higher accuracy in transient analysis than the conventional steady-state model.

A Coordination Scheme for a Combined Protection System Considering Dynamic Behavior and Wind DGs Fault Ride-Through Constraints

• A proposed design of a hierarchical protection scheme is presented. • Protective devices are optimally coordinated based on fault current transients. • Hybrid superconducting fault current limiters are optimally allocated to keep coordination under synchronous and inverter-based wind DGs. • Ride-through capability of wind DGs is integrated into the fault current limiter sizing problem. • Changes of network topology and variation of detected fault current are considered. A combined protection system has multiple types of devices such as directional overcurrent relays, reclosers, and fuses to protect distinct areas in a DG-incorporated network. An approach for setting all protective devices to realize complete coordination of adjacent ones taking transient responses into account is presented. The participation of synchronous generator-based and/or inverter-based wind DGs can degrade protection coordination. So, a scheme for sustaining coordination by optimal hybrid superconducting fault current limiters is proposed. The scheme can cope with variation of network topology; and handles the change of fault current level perceived by the protection device under a given topology. Moreover, instead of the conventional steady-state models, more realistic dynamic models of relays, reclosers, DGs, and fault current limiter are used. As a serious operation problem, undesired tripping of wind DGs under fault condition can occur due to the sag of terminal voltage below certain limits defined by national and international standards. Therefore, the proposed scheme prevents this undesired tripping of wind DGs by integrating its ride-through capability constraints into the fault current limiter allocation problem. The proposed approach is applied to the IEEE 9-bus and 30-bus systems. Results confirm the efficacy of the proposed method.

Kinetic Modeling of Time-Dependent Enzyme Inhibition by Pre-Steady-State Analysis of Progress Curves: The Case Study of the Anti-Alzheimer's Drug Galantamine.

The Michaelis–Menten model of enzyme kinetic assumes the free ligand approximation, the steady-state approximation and the rapid equilibrium approximation. Analytical methods to model slow-binding inhibitors by the analysis of initial velocities have been developed but, due to their inherent complexity, they are seldom employed. In order to circumvent the complications that arise from the violation of the rapid equilibrium assumption, inhibition is commonly evaluated by pre-incubating the enzyme and the inhibitors so that, even for slow inhibitors, the binding equilibrium is established before the reaction is started. Here, we show that for long drug-target residence time inhibitors, the conventional analysis of initial velocities by the linear regression of double-reciprocal plots fails to provide a correct description of the inhibition mechanism. As a case study, the inhibition of acetylcholinesterase by galantamine, a drug approved for the symptomatic treatment of Alzheimer’s disease, is reported. For over 50 years, analysis based on the conventional steady-state model has overlooked the time-dependent nature of galantamine inhibition, leading to an erroneous assessment of the drug potency and, hence, to discrepancies between biochemical data and the pharmacological evidence. Re-examination of acetylcholinesterase inhibition by pre-steady state analysis of the reaction progress curves showed that the potency of galantamine has indeed been underestimated by a factor of ~100.

Dynamic performance of an organic Rankine cycle system with a dynamic turbine model: A comparison study

Particular interest has been shown in the dynamic modeling and the operation of organic Rankine cycle (ORC) systems, which have emerged to harvest energy from low-grade heat sources. In conventional studies corresponding to ORC dynamics, the turbine is generally modeled as a steady-state component, and the efficiency, mass flow rate, and rotational speed of the turbine are less concerned, which may lead to inaccuracy of the system performance during dynamic operations. In this paper, the dynamic model of an ORC system is established, and a comprehensive dynamic turbine model is considered for the first time in such studies. The turbine 1D design and off-design is performed, and the mass inertia and the rotational inertia are also considered in the turbine model. In two operation modes, the dynamic responses of the ORC system to severe disturbance of the heat source parameters are investigated and compared with systems applying conventional steady-state models. Considerable differences have been shown in terms of turbine efficiency (with a maximum relative error of 12.9%), mass flow rate (with a maximum relative error of 8.3%), and net power output of the ORC systems using different turbine models. Furthermore, the use of the dynamic turbine model has extended the settling time and undershoot of the controlled parameter. This study reveals that the dynamic turbine model should be carefully considered in investigations related to ORC dynamics.

A solvable thermal circuit for modelling PVT air collectors

The steady state thermal analysis of a photovoltaic thermal (PVT) air collector typically involves solving energy balance equations to determine temperatures as a function of distance along the collector and to calculate the thermal energy output. While this approach is appropriate for a simple PVT air collector model, for more detailed models the resulting energy balance equations increase significantly in complexity. In this paper it is demonstrated how an RC circuit can be used to model a PVT air collector under steady state conditions to determine the thermal parameters of the collector. This is achieved by utilising a capacitor in the circuit, which acts as an analog integrator. Simulation of the circuit is used to illustrate the equivalence of this approach with conventional steady state models. The advantage of using a solvable circuit is that models of PVT air collectors of increasing complexity can be quickly and easily analysed by simply adding additional components to the circuit.

Reconstructing relative humidity from plant delta18O and deltaD as deuterium deviations from the global meteoric water line.

Cellulose delta18O and deltaD can provide insights on climates and hydrological cycling in the distant past and how these factors differ spatially. However, most studies of plant cellulose have used only one isotope, most commonly delta18O, resulting in difficulties partitioning variation in delta18O of precipitation vs. evaporative conditions that affect leaf water isotopic enrichment. Moreover, observations of pronounced diurnal differences from conventional steady-state model predictions of leaf water isotopic fractionation have cast some doubt on single isotope modeling approaches for separating precipitation and evaporation drivers of cellulose delta18O or deltaD. We explore a dual isotope approach akin to the concept of deuterium-excess (d), to establish deuterium deviations from the global meteoric water line in leaf water (deltad(l)) as driven by relative humidity (RH). To demonstrate this concept, we survey studies of leaf water delta18O and deltaD in hardwood vs. conifer trees. We then apply the concept to cellulose delta18O and deltaD using a mechanistic model of cellulose delta18O and deltaD to reconstruct deuterium deviations from the global meteoric water line (deltad(c)) in Quercus macrocarpa, Q. robur, and Pseudotsuga menziesii. For each species, deltad(c) showed strong correlations with RH across sites. deltad(c) agreed well with steady-state predictions for Q. macrocarpa, while for Q. robur, the relationship with RH was steeper than expected. The slope of deltad(c) vs. RH of P. menziesii was also close to steady-state predictions, but deltad(c) were more enriched than predicted. This is in agreement with our leaf water survey showing conifer deltad(l) was more enriched than predicted. Our data reveal that applications of this method should be appropriate for reconstructing RH from cellulose delta18O and deltaD after accounting for differences between hardwoods and conifers. Hence, deltad(c) should be useful for understanding variability in RH associated with past climatic cycles, across regional climates, or across complex terrain where climate modeling is challenging. Furthermore, deltad(c) and inferred RH values should help in constraining variation in source water delta18O.

Galactic scale star formation: Interplay between stellar spirals and the ISM

AbstractSpiral structures in the disk galaxies have been extensively studied by many theoretical papers, but conventional steady-state models are not consistent with what we observe in time-dependent, multi-dimensional numerical simulations and also in real galaxies. Here we review recent progress in numerical modeling of stellar and gas spirals in disk galaxies. The spiral arms excited in a stellar disk can last for 10 Gyrs without the ISM, but each spiral arm is short-lived and is recurrently formed. The stellar spirals are not waves propagating with a single pattern speed. The ISM is concentrated in local potential minima, which roughly follow the galactic rotation together with the stellar arms, therefore galactic dust lanes are not the classic ‘galactic shocks’.

Pressure Drop in a Packed Bed under Nonadsorbing and Adsorbing Conditions

Simulation of cyclic adsorption processes for gas separations relies on accurate models of the bed pressure drop during dynamic pressurization, depressurization, and breakthrough steps. This is especially true for rapid pressure swing adsorption (RPSA), where large gas flows can cause significant changes in the axial pressure gradient through the bed, influencing process performance. Under these conditions, there is some question as to the validity of conventional steady-state models used to represent the dynamic, rapidly changing pressures. In this study, the ability of the steady-state Ergun equation to represent pressure drop under dynamic adsorbing and nonadsorbing conditions was tested. The Ergun equation accurately reproduced dynamic depressurization and breakthrough pressure profiles using values of κviscous and κkinetic (the two Ergun parameters) determined experimentally from the steady-state flow of a variety of gases through a packed bed of LiLSX pellets. The full momentum equation was also tested, and errors of <0.1% were observed between the Ergun equation and the full momentum balance under dynamic conditions for a nonadsorbing packed bed. These observations and simulations suggest the Ergun equation can be reliably used to reproduce experimental profiles under dynamic adsorbing conditions where high gas flows result.

Application of Compartmental Modeling to Determination of Trace Element Requirements in Humans

The potential of compartmental modeling for determining dietary requirements of the trace elements is explored. Transport kinetics of tracee and tracer within a physiologically meaningful arrangement of compartments were simulated by using whole body copper (Cu) metabolism in adult humans as an example. The simulation was based on known, quantitative Cu metabolism, and required a non-steady-state model rather than a more conventional steady-state model. The simulation indicated that a reduction in dietary Cu intake could result in (1) loss of Cu from storage compartments, (2) maintenance of homeostasis by adaptive changes in dietary Cu absorption and endogenous excretion, or (3) a response intermediate between the two. By performing tracer experiments, it should be possible to determine the relative significance of mechanisms 1 and 2 in response to progressively smaller dietary intakes of Cu. Whether the body conserves Cu by adapting metabolically to low Cu intake or, alternatively, undergoes significant Cu loss because of an inability to adapt, may be an important factor in recommending a dietary requirement. The basic structure of the whole-body model of Cu metabolism used in this study has features consistent with the metabolism of other trace elements. Thus, the present example may also provide an approach to the study of dietary requirements of other elements.

RESPONSE CHARACTERISTICS OF THE DIFFUSIVE SAMPLER AT FLUCTUATING VAPOR CONCENTRATIONS

An unsteady state model for calculating the collecting characteristics of organic vapors in the diffusive sampler is proposed using Fick's law and a mass balance equation. The results of a theoretical model suggest that when the vapor concentration in the ambient air rises suddenly from zero to a certain concentration, C0, a larger mass of the vapors should move into the sampler than will move under the steady state conditions because a greater vapor concentration gradient is formed in the sampler. On the other hand, when the vapor concentration changes from C0 to zero, the concentration profile becomes convex and the vapors that exist near the entrance move out of the sampler. When the above two phenomena occur consequently, that is, the vapor concentration changes rectangularly, the collected amount of the vapor becomes equal to that of the steady state condition. In the case of sinusoidal and triangular vapor concentration changes, the collected amount of the vapor also becomes the same as that of the steady state when the time passes 1.4tR (tR: average residence time at the steady state) after the end of the sampling. This theoretical result is supported by an experimental study. There are no significant differences observed between the measured collected amount of vapor at intermittent loading and the calculated one using a conventional steady state model although the collected amount at continuous loading is lower.

Response Characteristics of the Diffusive Sampler at Fluctuating Vapor Concentrations

An unsteady state model for calculating the collecting characteristics of organic vapors in the diffusive sampler is proposed using Fick's law and a mass balance equation. The results of a theoretical model suggest that when the vapor concentration in the ambient air rises suddenly from zero to a certain concentration, C0, a larger mass of the vapors should move into the sampler than will move under the steady state conditions because a greater vapor concentration gradient is formed in the sampler. On the other hand, when the vapor concentration changes from C0 to zero, the concentration profile becomes convex and the vapors that exist near the entrance move out of the sampler. When the above two phenomena occur consequently, that is, the vapor concentration changes rectangularly, the collected amount of the vapor becomes equal to that of the steady state condition. In the case of sinusoidal and triangular vapor concentration changes, the collected amount of the vapor also becomes the same as that of the steady state when the time passes 1.4tR (tR: average residence time at the steady state) after the end of the sampling. This theoretical result is supported by an experimental study. There are no significant differences observed between the measured collected amount of vapor at intermittent loading and the calculated one using a conventional steady state model although the collected amount at continuous loading is lower.

Dopant Segregation in Earth- and Space-Grown InP Crystals

Macro- and microsegregation of sulphur in InP crystals grown from In solution by the travelling heater method under microgravity and normal gravity are analyzed using spatially resolved photoluminescence. Whereas the macrosegregation in earth- as well as space-grown crystals is explained by conventional steady-state models based on the theory of Burton, Prim and Slichter (BPS), the microsegregation can only be understood in terms of the non-steady-state step exchange model.