Steady-state Criteria Research Articles

Static voltage stability analysis of integrated smart energy systems

The analysis of multi-energy flows forms the cornerstone for the study of state estimation, safety assessment, and optimization in integrated smart energy systems (ISES). The interactions between various energy flows and the inherent variability of renewable energy sources often lead to significant challenges to the static stability of ISES. This paper investigates the static voltage stability of ISES under multi-energy coupling conditions through multi-energy flow analysis in electric-gas-thermal energy systems. First, a steady-state model of the ISES is constructed by representing the interconnected energy subsystems as equivalent sources and loads in the power grid. Subsequently, through the coupling elements of ISES, the power flows of the natural gas system (NGS) and the district heating system (DHS) are converted into active power in the electrical power system (EPS), resulting in an equivalent power flow equation for the ISES. Then, using Brouwer’s fixed-point theorem, the analytical sufficient conditions for solving the equivalent power flow equation are derived. Finally, a simulation model based on MATLAB/Simulink is established. The steady-state criterion for ISES is obtained in this paper, and the correctness and effectiveness of the proposed conclusions are verified by the simulation results.

Variant slip effects, aspect ratios and steady-state criteria in unsteady cavities with direct PDE simulation of eddies

Variant slip effects, aspect ratios and steady-state criteria in unsteady cavities with direct PDE simulation of eddies

Influence of reinforcement and its omission on trial-by-trial changes of response bias in perceptual decision making.

Discrimination performance in perceptual choice tasks is known to reflect both sensory discriminability and nonsensory response bias. In the framework of signal detection theory, these aspects of discrimination performance are quantified through separate measures, sensitivity (d') for sensory discriminability and decision criterion (c) for response bias. However, it is unknown how response bias (i.e., criterion) changes at the single-trial level as a consequence of reinforcement history. We subjected rats to a two-stimulus two-response conditional discrimination task with auditory stimuli and induced response bias through unequal reinforcement probabilities for the two responses. We compared three signal-detection-theory-based criterion learning models with respect to their ability to fit experimentally observed fluctuations of response bias on a trial-by-trial level. These models shift the criterion by a fixed step (1) after each reinforced response or (2) after each nonreinforced response or (3) after both. We find that all three models fail to capture essential aspects of the data. Prompted by the observation that steady-state criterion values conformed well to a behavioral model of signal detection based on the generalized matching law, we constructed a trial-based version of this model and find that it provides a superior account of response bias fluctuations under changing reinforcement contingencies.

Note on particle balance in particle-in-cell/Monte Carlo model and its implications on the steady-state simulation

The steady-state criterion for plasma numerical simulations can be determined by the particle balance relation. In this study, we utilized a one-dimensional (1D) particle-in-cell/Monte Carlo model to investigate particle transport in a capacitively coupled plasma discharge, including particle density change, flow, generation, and loss. Our analysis revealed that the generation rate and loss rate are equivalent in both time and space, indicating a fine balance in the steady state of the discharge system. Additionally, we presented the spatio-temporal distribution and time-averaged particle transport term for electrons and ions to demonstrate how particles attain equilibrium at varying pressures. This validation method can be particularly useful in numerical simulations where determining steady state can be challenging. Our findings establish the correctness and reliability of the method.

DYNAMIC CONDITIONS OF COMPENSATED SYNCHRONOUS MACHINE

The dynamic behavior of synchronous machine with longitudinal-transverse excitement by maintenance of the rotor overhang corner as equal zero are considered. The given condition is named as compensated and correspond with full compensation of transverse armature reaction by magnetizing force of transverse excitement winding. In such machine is absented the limit of steady-state overload, but active and reactive components of load current are concurrent as projections of load current image vector on orthogonal axes of machine inductor. The research aim is a determination of steady-state stability criterion of compensated synchronous machine working on powerful electrical system. The researches are organized in assumption of inductor current invariance and at neglect of stator windings time constant. The electromagnetic moment expression of longitudinal-transverse excitement synchronous machine in compensated work condition is received as a result of analysis of the spatial vector diagrams and equations. The expression analysis has allowed to find the criterion of rotor creepage stability and to examine the steady-state stability of the machine in different work conditions. It is shown that machines stability factor is defined by not only the reactive power of machine short circuit, but also associated reactive power.

Find_tfSBP: find thermodynamics-feasible and smallest balanced pathways with high yield from large-scale metabolic networks

Biologically meaningful metabolic pathways are important references in the design of industrial bacterium. At present, constraint-based method is the only way to model and simulate a genome-scale metabolic network under steady-state criteria. Due to the inadequate assumption of the relationship in gene-enzyme-reaction as one-to-one unique association, computational difficulty or ignoring the yield from substrate to product, previous pathway finding approaches can’t be effectively applied to find out the high yield pathways that are mass balanced in stoichiometry. In addition, the shortest pathways may not be the pathways with high yield. At the same time, a pathway, which exists in stoichiometry, may not be feasible in thermodynamics. By using mixed integer programming strategy, we put forward an algorithm to identify all the smallest balanced pathways which convert the source compound to the target compound in large-scale metabolic networks. The resulting pathways by our method can finely satisfy the stoichiometric constraints and non-decomposability condition. Especially, the functions of high yield and thermodynamics feasibility have been considered in our approach. This tool is tailored to direct the metabolic engineering practice to enlarge the metabolic potentials of industrial strains by integrating the extensive metabolic network information built from systems biology dataset.

Evaluation of a short protocol for indirect calorimetry in females with eating disorders and healthy controls

To enable clinicians to identify the clinical picture and treatment progress and to adjust eating plans according to personal energy needs, it is important to know the patient's correct resting metabolic rate (RMR). Indirect calorimetry (IC) is the preferred method for assessment of RMR, but long duration of measurement increases the load on the patients, and reduces the effectiveness in clinical and scientific settings. Further; not all patients reach a valid RMR according to the suggested best practice protocol, with 5min of steady state (SS) where respiratory gas volume exchange varies less than 10%. The aim of this study was to evaluate the possibility for an abbreviated RMR protocol and SS criterion. Forty two women diagnosed with bulimia nervosa or binge eating disorder (eating disorder group, ED), originally recruited for an outpatient treatment study, and 26 age and gender matched healthy controls (HC) were studied during a single, prolonged IC measurement. Participants rested for 10min in supine position wearing a two-way breathing facemask, before a continuous measurement period of 20min. Results from a standard 5min SS criterion was compared to an abbreviated 3min SS criterion. Both SS-criteria were evaluated through three different SS protocols (<10% variation in respiratory gas exchange), being: 1) measurement during the first 3 or 5min, 2) measurement after discarding the first 5min, and 3) the lowest identified RMR during the 20min of measurement. About 50% of the participants reached an early SS in both the defined SS minute criteria. Participants reaching a valid SS throughout the 20min of measurement increased from ∼90% to 100% with an abbreviated 3min SS. With a 5min SS criterion, the median (range) RMR for the 3 protocols were 1639.9 (1239.2), 1508.8 (1457.6) and 1500.6 (1328.8) respectively for the ED group, and 1702.2 (1239.4), 1608.4 (1076.4) and 1594.8 (1029.2) respectively for the HC group, (p>0.05 for all between-group analysis). With a 3min SS criterion, the median (range) RMR were 1533.6 (1298.2), 1461.2 (1406.1), and 1395.8 (1447.3) respectively for the ED group and 1681.7 (1332.4), 1613.7 (1266.0) and 1523.1 (1050.3), respectively for the HC group, (p>0.05 for all between-group analysis). Lowest measured RMR was different compared to the other two SS protocols in both the ED- and the HC group, and for both the 5min- and the 3min SS criteria, respectively (p<0.04). Furthermore, a SS of 3min resulted in lower RMR compared to 5min SS (p<0.00) and an increased number of participants classified as hypo-metabolic (RMRmeasured/RMRcalculated<0.9). An abbreviated measurement protocol to identify the lowest RMR using IC was not successful. Abbreviating the SS criteria from 5 to 3min, resulted in a lower RMR, hence encouraging further examination of the validity of shorter SS criterion than practiced today. Registered in Clinical Trials by id-number NCT02079935, and approved by the Norwegian Regional Committee for Medical and Health Research Ethics with id-number 2013/1871. The trial in which control persons were recruited, is approved by the Norwegian Regional Committees for Medical and Health Research Ethics with the id-number 2016/1718, and prospectively registered in Clinical Trials with the id-number NCT03007459.

Approximate Time to Steady-state Resting Energy Expenditure Using Indirect Calorimetry in Young, Healthy Adults.

Indirect calorimetry (IC) measurements to estimate resting energy expenditure (REE) necessitate a stable measurement period or steady state (SS). There is limited evidence when assessing the time to reach SS in young, healthy adults. The aims of this prospective study are to determine the approximate time to necessary reach SS using open-circuit IC and to establish the appropriate duration of SS needed to estimate REE. One hundred young, healthy participants (54 males and 46 females; age = 20.6 ± 2.1 years; body weight = 73.6 ± 16.3 kg; height 172.5 ± 9.3 cm; BMI = 24.5 ± 3.8 kg/m2) completed IC measurement for approximately 30 min while the volume of oxygen (VO2) and volume of carbon dioxide (VCO2) were collected. SS was defined by variations in the VO2 and VCO2 of ≤10% coefficient of variation (%CV) over a period of five consecutive minutes. The 30-min IC measurement was divided into six 5-min segments, such as S1, S2, S3, S4, S5, and S6. The results show that SS was achieved during S2 (%CV = 6.81 ± 3.2%), and the %CV continued to met the SS criteria for the duration of the IC measurement (S3 = 8.07 ± 4.4%, S4 = 7.93 ± 3.7%, S5 = 7.75 ± 4.1%, and S6 = 8.60 ± 4.6%). The current study found that in a population of young, healthy adults the duration of the IC measurement period could be a minimum of 10 min. The first 5-min segment was discarded, while SS occurred by the second 5-min segment.

Feasibility and Acceptability of Implementing Indirect Calorimetry Into Routine Clinical Care of Patients With Spinal Cord Injury.

Background: In the absence of reliable predictive equations, indirect calorimetry (IC) remains the gold standard for assessing energy requirements after spinal cord injury (SCI), but it is typically confined to a research setting. The purpose of this study is to assess the feasibility and acceptability of implementing IC into routine clinical care in an Australian SCI rehabilitation facility. Methods: Bedside IC (canopy hood) was performed, and patients completed an IC acceptability questionnaire (open-ended; yes/no; 5-point Likert scale). Fasted resting energy expenditure (REE) steady-state criteria were applied to assess data quality, and adherence to a test ≥20 minutes was recorded. Staff were surveyed to assess impact of IC on usual care. Results: Of 35 eligible patients, 9 declined (7 reported claustrophobia). One patient could not be tested before discharge and 25 underwent IC (84% male, injury level C2-L2, AIS A-D). Anxiety prevented one patient from completing IC, while another failed to fast. The remaining 23 patients achieved a steady-state REE (≥5 consecutive minutes with ≤10% coefficient of variation for VO2 and VCO2). Test-retest (n = 5) showed <10% variation in REE. Patients deemed the procedure acceptable, with 88% reporting a willingness to repeat IC. Eighty percent of patients and 90% of staff agreed it was acceptable for IC to be integrated into usual care. Conclusion: This study found that IC is a feasible and acceptable addition to the routine clinical care of patients recovering from SCI and may serve to improve accuracy of nutrition interventions for this patient population.

Integral Sliding Manifold Design for Linear Systems With Additive Unmatched Disturbances

This note offers an integral sliding manifold design method for linear systems that minimizes the impact of unmatched constant external disturbances. System sensitivity upon an unmatched disturbance vector is assessed by the steady-state dependent criterion function. The derived procedure easily finds a unique integral sliding manifold that minimizes a quadratic optimization criterion. Applicability of this method in case of slowly-varying disturbances is supported by determining disturbance frequency limit that guarantees satisfactory performance. The proposed approach has been demonstrated on a numerical example and verified by simulations.

Dryout Methodology with New Steady-State Criterion and More-Accurate Statistical Treatment of Channel Bow

An overview is given of existing design criteria to prevent fuel cladding dryout and the methods used in boiling water reactor reload analysis to evaluate the impact of channel bow on margins in the critical power ratio (CPR). Potential weaknesses in today’s methodologies are discussed. Westinghouse in collaboration with KKL and Axpo - operator and owner of the Leibstadt NPP - has developed an enhanced CPR methodology based on a new criterion to protect against dryout during normal operation and with a more rigorous treatment of channel bow. The new steady-state criterion is expressed in terms of an upper limit of 0.01 for the dryout failure probability per year. This is considered a meaningful and appropriate criterion that can be directly related to the probabilistic criteria setup for the analyses of anticipated operation occurrences and accidents.In the Monte Carlo approach, a statistical modeling of channel bow and an accurate evaluation of CPR response functions allow the associated CPR penalties to be included directly in the plant safety limit minimum CPR and operating limit minimum CPR in a best-estimate manner. In this way, the treatment of channel bow is equivalent to all other uncertainties affecting CPR. Emphasis is put on quantifying the statistical distribution of channel bow throughout the core using measurement data.The enhanced CPR methodology has been implemented in the Westinghouse Monte Carlo code McSLAP. The methodology improves the quality of dryout safety assessments by supplying more-valuable information and better control of conservatisms in establishing operational limits for CPR.The methodology is demonstrated with application examples from the introduction at KKL.

Accuracy of Abbreviated Indirect Calorimetry Protocols for Energy Expenditure Measurement in Critically Ill Children

Accurate measurement of resting energy expenditure (REE) using indirect calorimetry (IC) facilitates optimal energy prescription. Steady-state (SS) REE obtained using a 5-minute protocol (SS5) has been used as a surrogate for 24-hour REE measurement. However, SS5 conditions are difficult to achieve in critically ill children on mechanical ventilatory support. The authors prospectively examined factors associated with successful IC testing using the standard SS5 protocol in mechanically ventilated children. They examined the agreement of REE between SS5 and 2 abbreviated SS protocols: 4-minute (SS4) and 3-minute (SS3) protocols as well as the Schofield prediction equation, using Bland-Altman analysis. IC testing (n = 45) was completed in 34 children. SS was achieved during 25 (56%), 31 (69%), and 42 (93%) tests, using the SS5, SS4, and SS3 protocols, respectively. Intratest variability in respiratory rate, endotracheal tube leak, and inspiratory time was associated with failed IC by the SS5 protocol. The mean bias (limits of agreement) for REE was 2.8 (-47 to 65), 5.8 (-71 to 72), and -127 (-418 to 1176) kcal/d using SS4, SS3, and Schofield, respectively. A stronger agreement was observed when means of all abbreviated SS REE values during a 30-minute test were used. In mechanically ventilated children, 4-minute and 3-minute SS protocols allowed REE measurements to be obtained in most patients with reasonable accuracy. Abbreviated protocols may decrease the need to rely on inaccurate equations when assessing energy expenditure in children who fail IC testing by standard SS criteria.

EFFECT OF ASYMMETRY AND ROUGHNESS OF STENOSIS ON NON-NEWTONIAN FLOW PAST AN ARTERIAL SEGMENT

Numerical investigations of non-Newtonian blood flow are carried out through an asymmetric arterial constriction (stenosis) obtained from casting of mildly stenosed artery [Back et al. [1984] Effect of mild atherosclerosis on flow resistance in a coronary artery casting by man, J. Biomech. Eng., Trans. ASME106, 48]. The Marker and Cell method, for governing equations of motion for the flow in primitive variables formulations is developed in a staggered grid to discretize the momentum equations representing the non-Newtonian viscous incompressible flow characterized by the generalized Power-law model in cylindrical coordinates system under axial symmetric conditions so that the problem effectively becomes two-dimensional. The modified pressure equation has been solved by Successive-Over-Relaxation method and the pressure–velocity correction formulae have been derived. Satisfactory level of convergence namely, the mass conservation of the order of 0.5 × 10-12 and consequently the steady-state criteria have been achieved. The separation points, reattachment points, pressure drop, and the wall shear stress distribution resulting from the present simulation agree well with the available numerical and experimental results. Secondary separation has also been predicted at higher Reynolds numbers. Further, in-depth study of the flow patterns reveals that shear-thickening model of generalized Power-law fluid experiences excess pressure drop more than that of shear-thinning model as in the case of flow past through cosine and smooth-shaped constrictions than irregular ones. The efficiency of the numerical code is illustrated by applying it to a test problem in order to validate the applicability of the technique as well as the simulation under consideration.

A Reduced Abbreviated Indirect Calorimetry Protocol Is Clinically Acceptable for Use in Spontaneously Breathing Patients With Traumatic Brain Injury

A steady state should be established when using indirect calorimetry to assess resting energy expenditure, reduce error, and improve the validity of the measurement. Steady-state criteria are often rigorous and difficult to achieve in hospitalized patients, particularly in patients recovering from traumatic brain injury. This study aimed to assess whether reducing the timeframe for steady-state conditions to 2, 3, or 4 minutes when using indirect calorimetry was significantly different from the widely accepted 5-minute steady-state protocol in patients recovering from traumatic brain injury. Indirect calorimetry using an open-circuit calorimeter was used to measure resting energy expenditure in 20 spontaneously breathing patients with traumatic brain injury. Each patient underwent repeated measurements once per day at various stages of his or her recovery. Bland-Altman methods comparison was used for statistical analysis. In total, 124 measurements were recorded, of which 59% met 5-minute, 70% met 4-minute, 76% met 3-minute, and 84% met 2-minute steady-state conditions. Mean within-patient coefficient of variation was 13% (range, 0%-35%). Agreement at the +/-10% level using Bland-Altman plots was 100% for a 4-minute steady-state protocol, 96% for a 3-minute protocol, and 90% using a 2-minute protocol. A 4-minute or 3-minute abbreviated steady-state indirect calorimetry protocol is clinically acceptable to measure resting energy expenditure in spontaneously breathing patients with a traumatic brain injury.

Modeling hybrid network dynamics under random perturbations

We define stochastic network models based on internal structural dynamics of individual nodes which undergo Markovian switching subject to noise and external shocks. Steady-state stability and reliability criteria are established in closed form and show explicit dependence on system parameters.

Dynamic Redesign of a Flow Control Servovalve Using a Pressure Control Pilot1

In this paper, the dynamic performance of an unconventional two-spool flow control servovalve using a pressure control pilot is analyzed. Such valves are less expensive than typical servovalves but also tend to be limited in their dynamic performance. Based on a previously developed eight state nonlinear model, we develop a simplified linear model which is able to capture the essential dynamics of the valve. Using root locus analysis method, the limitation in dynamic performance is shown to be due to a “zero” introduced by the structure of the interconnection of the subsystems. Design parameters that move the zero further to the left half plane, and do not adversely affect other steady-state criteria are identified. The effectiveness of these parameters to improve the dynamic performance is demonstrated. This analysis demonstrates how the structure of the interactions between subsystems in a dynamic component, such as a hydraulic valve, can critically limit the dynamic performance of the component.

A Dynamic Study of Two One-State-Variable, Rate-Dependent, and State-Dependent Friction Laws

I compare two one-state-variable, rate-dependent, and state-dependent friction laws, that is, the slip law and slowness law, through the analyses of stability conditions based on a dynamic one-degree-of-freedom spring-slider model, subjected to such two kinds of friction. Results show that at low velocities, the stability criteria for the two laws are equal and similar to the steady-state criteria deduced by Ruina (1983). On the other hand, at higher velocities, the stability criterion for the slip law depends not only on the parameters of the friction law, but also on the sliding velocity and state variable of the system, whereas the stability criterion for the slowness law is the same as that at low velocities.

Free [ADP] and Aerobic Muscle Work Follow at Least Second Order Kinetics in Rat Gastrocnemius in Vivo

The relationship between free cytosolic [ADP] (and [P(i)]) and steady-state aerobic muscle work in rat gastrocnemius muscle in vivo using (31)P NMR was investigated. Anesthetized rats were ventilated and placed in a custom-built cradle fitted with a force transducer that could be placed into a 7-tesla NMR magnet. Muscle work was induced by supramaximal sciatic nerve stimulation that activated all fibers. Muscles were stimulated at 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 1.0, and 2.0 Hz until twitch force, phosphocreatine, and P(i) were unchanged between two consecutive spectra acquired in 4-min blocks (8-12 min). Parallel bench experiments were performed to measure total tissue glycogen, lactate, total creatine, and pyruvate in freeze-clamped muscles after 10 min of stimulation at each frequency. Up to 0.5 Hz, there was no significant change in muscle glycogen, lactate, and the lactate/pyruvate ratios between 8-12 min. At 0.8 Hz, there was a 17% fall in glycogen and a 65% rise in the muscle lactate with a concomitant fall in pH. Above this frequency, glycogen fell rapidly, lactate continued to rise, and ATP and pH declined. On the basis of these force and metabolic measurements, we estimated the maximal mitochondrial capacity (V(max)) to be 0.8 Hz. Free [ADP] was then calculated at each submaximal workload from measuring all the reactants of the creatine kinase equilibrium after adjusting the K'(CK) to the muscle temp (30 degrees C), pH, and pMg. We show that ADP (and P(i)) and tension-time integral follow a Hill relationship with at least a second order function. The K(0.5) values for free [ADP] and [P(i)] were 48 microM and 9 mM, respectively. Our data did not fit any form of the Michaelis-Menten equation. We therefore conclude that free cytosolic [ADP] and [P(i)] could potentially control steady-state oxidative phosphorylation in skeletal muscle in vivo.

Simultaneous steady state and dynamic design of process systems using structural indicators

The simultaneous design of the steady-state and dynamic performance of a process has the ability to satisfy much more demanding dynamic performance criteria than the design of dynamics only by the connection of a control system. A method for designing process dynamics based on the use of a linearised systems' eigenvalues has been developed. The eigenvalues are associated with system states using the unit perturbation spectral resolution (UPSR), characterising the dynamics of each state. The design method uses a homotopy approach to determine a final design which satisfies both steady-state and dynamic performance criteria. A highly interacting single stage forced circulation evaporator system, including control loops, was designed by this method with the goal of reducing the time taken for the liquid composition to reach steady-state. Initially the system was successfully redesigned to speed up the eigenvalue associated with the liquid composition state, but this did not result in an improved startup performance. Further analysis showed that the integral action of the composition controller was the source of the limiting eigenvalue. Design changes made to speed up this eigenvalue did result in an improved startup performance. The proposed approach provides a structured way to address the design-control interface, giving significant insight into the dynamic behaviour of the system such that a systematic design or redesign of an existing system can be undertaken with confidence.

Performance evaluation of a job-shop-like flexible manufacturing system with transfer blocking using a Markovian queuing network model

An industrial flexible manufacturing system (FMS) is investigated with Markovian analysis in order to estimate the steady-state performance criteria. The system includes flexible machines, fixed storage areas, a fixed number of pallets and an automated material handling device. A procedure is developed to aggregate part-type dependent data so that a single class of parts is obtained and the number of states of the underlying Markov chain is significantly reduced. Problems encountered when implementing Markovian approaches are dealt with by using the QNAP2 software package. Results based on a real workload are given for several transport durations and are very satisfactory when compared with those of simulation experiments. The overall approach exhibits a great flexibility, which is highly desirable for the systems studied.