System-level Model Research Articles

A System-Level Modeling of PEMFC Considering Degradation Aspect towards a Diagnosis Process

This paper proposes a modular modeling towards a health system integration of fuel cells by considering not only the dynamics of the gases but also fault models that affect the PEMFC performances. The main goal is to simulate the faulty state in order to overcome data scarcity, since running a fuel cell to generate a database under faulty conditions is a costly process in time and resources. The degradation processes detailed in this paper allow to introduce a classification of faults that can occur, giving a better understanding of the performance losses necessary to simulate them. The faults that are detailed and modeled are the flooding, drying and aging processes. This modeling is based on a system approach, so it runs faster than real-time degradation tests, allowing the training and validation of online supervisors, such as the energy management strategy (EMS) method or diagnosis. The faults are reproduced according to the study requirements to be a very effective support tool to help design engineers to include faulty conditions in early design stages toward a diagnosis process and health-conscious energy management strategies.

A Multi-Box Behavioural Nonlinear Mixer Model

ABSTRACT This paper presents a new behavioural mixer model in a multi-box structure. In the proposed model, as well as amplitude and phase nonlinearity, the memory effect is also modelled. The multi-box structure is constructed in line with the Hammerstein model to characterise both fundamental signals, intermodulation distortion (IMD) and harmonic distortion (HD) for mixers in particular and all frequency translating devices in general. A testbed is constructed to measure both amplitude and phase characteristics. A good match between the measured and the calculated results is obtained using curve fitting and optimisation algorithms. In order to model the memory effect, a finite impulse response (FIR) filter is used. The measured IM3 imbalance is successfully modelled with this filter. For fundamental components, amplitude and phase errors are less than 0.1 dB and 1 degree, respectively. For IM3 components, amplitude and phase errors are less than 4 dB and 10 degrees, respectively. For the overall accuracy of the model, measurements are conducted with two-tone and modulated signals, and normalised mean square error (NMSE) values are calculated as −31.5 dB and −29.3 dB, respectively. The results are obtained for a wide range of input power span, including the compression region where nonlinearity is strongly pronounced. The proposed model is capable of accurately representing nonlinearity and memory effect for mixers and frequency translating devices in general and thus may be used for system-level modelling and linearisation applications.

Co-optimisation of the heliostat field and receiver for concentrated solar power plants

In a concentrated solar power (CSP) tower plant, it is essential to understand the performance of the subsystem formed by the heliostat field and the receiver, operated with an optimal aiming strategy that guarantees the safety and lifetime of the receiver while maximising performance. State-of-the-art studies optimise the heliostat field, aiming strategy and the receiver independently. However, the field and the receiver are interdependent and co-optimisation of the field-receiver subsystem is necessary to obtain the optimal configuration. Fast and accurate annual performance assessments of the subsystem are needed to calculate the annual energy output and the Levelised Cost of Energy (LCOE) of the full CSP system. In this study, a co-optimisation method is proposed based on coupled instantaneous optical, thermal and mechanical models integrated into a system-level model for annual simulation of full system and economics. The resulting system-model is then used for design optimisation based on a genetic algorithm. Several techniques are implemented to make this complex and computationally expensive problem tractable. The proposed method is used to optimise the design of two systems composed of a surround field and a liquid sodium-cooled cylindrical external receiver for first the annual performance and then the LCOE. The good behaviour of the method is confirmed by a sensitivity study. The LCOE-based optimisation leads to a less efficient system than the efficiency-based optimisation but a higher capacity factor. The methods presented are applicable to other CSP plant configurations, including state-of-art molten salt power tower plants.

A Hybrid Health Monitoring Approach for Aircraft Flight Control Systems With System-Level Degradation

This paper proposes a novel hybrid health monitoring approach to monitor the system-level degradation of aircraft flight control systems (FCSs). The idea derives from observing the nonlinear hysteresis phenomenon in FCS. First, a health FCS model is developed to implement the nonlinear degradation signal extraction of FCS by building an adaptive-network-based fuzzy inference system, a data-driven method. Subsequently, the Jump Markov autoregressive exogenous (JMARX) system with time delays is adopted to establish the FCS system-level degradation model. An expectation maximum-convex optimization algorithm is innovatively proposed to identify the model parameters. After that, three health indicators associated with the degradation model parameters are utilized for FCS system-level health monitoring. Finally, a practical flight experiment is conducted by a civil aircraft. The obtained experimental data is used to validate the effectiveness of the proposed FCS monitoring approach. The model of the time-delay JMARX system gets good modeling evaluation results on mean absolute error, standard deviation, etc. Besides, each of the three health indicators shows a clear FCS degradation tendency, which indicates that the proposed method successfully extracts the degradation information and monitors the health states of FCS. This approach is potential for practical and effective engineering applications in the aviation industry.

A comprehensive system-level model for performance evaluation of proton exchange membrane fuel cell system with dead-ended anode mode

In this study, a comprehensive system-level model was developed for a proton exchange membrane fuel cell (PEMFC) system with a dead-ended anode (DEA) mode. The global system model consisted of a series of local component models, including PEMFC stack, manifolds, air compressor, humidifier and valves. Membrane water conversion and N2 crossover were simultaneously considered in the stack component model. Based on the system-level model, the output voltage and water content of the PEMFC and the compressor power consumption at various currents and ambient pressures were investigated. Additionally, the dynamic behaviors of the cell voltage, its water content, and system hydrogen utilization rate were predicted for two legislated driving cycles—the New European Driving Cycle (NEDC) and the Worldwide Harmonized Light Vehicle Test Procedure (WLTP). The fuel cell voltage fluctuation owing to the anode purge occurred with an increase in the load current. Increasing the ambient pressure increased decay rate and recovery rate of the cell voltage, improved membrane hydration, and lowered the compressor power consumption. For the variable loads of the NEDC and WLTP, the fuel cell voltage and power fluctuated significantly. The membrane water content was controlled by the current in the low-current zone (i < 0.5 A cm−2) and was dominated by the high airflow in the high-current zone (i > 0.9 A cm−2). In the medium-current zone (0.5 A cm−2 ≤ i ≤ 0.9 A cm−2), the membrane water was saturated. The water vapor exhibited a dynamic behavior similar to that of the membrane water; the behavior fluctuated in low and high current zones and stabilized in the medium current zone. The liquid water fluctuated significantly in each current zone of the NEDC and WLTP. Additionally, the H2 utilization rates under NEDC and WLTP were greater than 99%. The developed global system model helps to understand the transient behaviors of a DEA-mode PEMFC system and improves the system responsibility for fuel cell system design and development.

A Low-Noise Interface ASIC for MEMS Disk Resonator Gyroscope.

This paper proposes a low-noise interface application-specific integrated circuit (ASIC) for a microelectromechanical systems (MEMS) disk resonator gyroscope (DRG) which operates in force-to-rebalance (FTR) mode. The ASIC employs an analog closed-loop control scheme which incorporates a self-excited drive loop, a rate loop and a quadrature loop. A ΣΔ modulator and a digital filter are also contained in the design to digitize the analog output besides the control loops. The clocks for the modulator and digital circuits are both generated by the self-clocking circuit, which avoids the requirement of additional quartz crystal. A system-level noise model is established to determine the contribution of each noise source in order to reduce the noise at the output. A noise optimization solution suitable for chip integration is proposed based on system-level analysis, which can effectively avoid the effects of the 1/f noise of the PI amplifier and the white noise of the feedback element. A performance of 0.0075°/√h angle random walk (ARW) and 0.038°/h bias instability (BI) is achieved using the proposed noise optimization method. The ASIC is fabricated in a 0.35 μm process with a die area of 4.4 mm × 4.5 mm and power consumption of 50 mW.

A System-Level Harmonic Control Method Based on Multibus Voltage Detected APF Without Exact Phase Synchronization

The decentralized distribution of nonlinear harmonic loads drives the trend of harmonic control from local compensation to system-level mitigation. Based on the active power filter (APF) with multi-bus harmonic detections, comprehensive control of harmonic distortions in multiple buses achieves, which is so-called system-level harmonic mitigation. However, existing system-level harmonic mitigation methods require high-speed data exchange for real-time phase synchronization among multiple buses, which reduces the feasibility of the methods. To reduce the burden of communication, a system-level harmonic mitigation method without inter-bus phase synchronization is proposed in this paper. Firstly, the phase synchronization problem is analyzed, and control system of multi-bus detected APF is proposed, in which the reference phase of each detector could be set locally. Then, a new online system-level harmonic mitigation model is introduced and solved to obtain the optimal APF current reference. Subsequently, the closed-loop control strategy of multi-bus detected APF is raised and four control stages are designed to cope with different situations. Finally, an eight-bus network with dynamic harmonic loads is designed in simulation and experiment. According to the results, multi-bus harmonic voltage distortions in the network could meet the standard. The proposed method contributes to achieving good harmonic compensation performance without multi-bus phase-synchronization.

Benchmarking and Simulation of Solid-Oxide Steam Electrolysis for Propellant Production in a Vacuum Chamber-Simulated Lunar Environment

Federal space agencies across the globe have prioritized development of in-situ resource utilization (ISRU) technology, such as propellants from lunar ice, to support space activities. High-temperature, solid oxide electrolysis cell (SOEC) systems integrated with an efficient balance-of-plant (BOP) have the potential to produce H2 and O2 at specific energy (kWhelec/kgH2) lower than conventional liquid-phase alkaline and PEM electrolysis systems, due to lower voltages for steam electrolysis (vs. liquid H2O). This NASA-sponsored collaboration explored the feasibility of achieving such low specific energy in a high-temperature SOEC system operating in a cryo-vacuum characteristic of permanently shadowed craters on the lunar surface where H2O ice can be found. A lab-scale »2.5-kWelec SOEC stack and BOP achieved a specific energy < 50 kWhelec/kgH2 at a production rate of > 0.075 kgH2/h operating in a cryo-vacuum chamber. System-level simulation models of the lab-scale SOEC stack were benchmarked with experimental tests and used to explore scaling of a system for lunar deployment. The lab-scale tests and scale-up modeling suggest a pathway to a MW-scale SOEC system that can achieve < 46 kWhelec/kgH2 with relatively low specific mass (kgsystem/(kgH2/h)).

Theories for interventions to reduce physical and verbal abuse: A mixed methods review of the health and social care literature to inform future maternity care.

Despite global attention, physical and verbal abuse remains prevalent in maternity and newborn healthcare. We aimed to establish theoretical principles for interventions to reduce such abuse. We undertook a mixed methods systematic review of health and social care literature (MEDLINE, SocINDEX, Global Index Medicus, CINAHL, Cochrane Library, Sept 29th 2020 and March 22nd 2022: no date or language restrictions). Papers that included theory were analysed narratively. Those with suitable outcome measures were meta-analysed. We used convergence results synthesis to integrate findings. In September 2020, 193 papers were retained (17,628 hits). 154 provided theoretical explanations; 38 were controlled studies. The update generated 39 studies (2695 hits), plus five from reference lists (12 controlled studies). A wide range of explicit and implicit theories were proposed. Eleven non-maternity controlled studies could be meta-analysed, but only for physical restraint, showing little intervention effect. Most interventions were multi-component. Synthesis suggests that a combination of systems level and behavioural change models might be effective. The maternity intervention studies could all be mapped to this approach. Two particular adverse contexts emerged; social normalisation of violence across the socio-ecological system, especially for 'othered' groups; and the belief that mistreatment is necessary to minimise clinical harm. The ethos and therefore the expression of mistreatment at each level of the system is moderated by the individuals who enact the system, through what they feel they can control, what is socially normal, and what benefits them in that context. Interventions to reduce verbal and physical abuse in maternity care should be locally tailored, and informed by theories encompassing all socio-ecological levels, and the psychological and emotional responses of individuals working within them. Attention should be paid to social normalisation of violence against 'othered' groups, and to the belief that intrapartum maternal mistreatment can optimise safe outcomes.

Modeling of Iodine Feeding System to Achieve Flow Control under the Coupling of Multiple Conditions

The design of an iodine working medium storage and supply system is one of the key technologies for the electrical propulsion of iodine working medium. Solid iodine sublimates into a gaseous state in the storage tank, and is transported to the thruster through flow control through components such as a proportional valve or throttle tube. However, iodine working medium has corrosive properties and poor thermal conductivity, which can easily cause condensation in the throttle tube and throttle valve, affecting the accuracy of experimental results or blocking the pipeline, leading to the suspension of the experiment. Based on the system level modeling of the iodine working medium electric propulsion storage and supply system, and taking into account the impact of the coupling effects of various conditions such as the physical parameters of iodine vapor, storage tanks, pipelines, outlet conditions, and proportional valves on the outlet mass flow rate of the iodine storage and supply system, the control of the outlet mass flow rate is achieved by adjusting the valve opening of a comparative example, providing a reference for the selection of the size of the throttle tube in future ground experiments or the control of the proportional valve opening.

Multi-fidelity modeling and analysis of a pressurized vessel-pipe-safety valve system based on MOC and surrogate modeling methods

A pressurized vessel-pipe-safety valve (PVPSV) combination is a commonly used configuration in nuclear power plants, and a good numerical model is essential for the system design, sizing and performance optimization. However, owing to the large-scale and cross-scale features, it is still a challenge to build a system level numerical model with both high accuracy and efficiency. To overcome this, a novel system level modeling method which can synthesize the advantages of various models is proposed in this paper. For system modeling, the analytical approach, the method of characteristics (MOC) and the surrogate model approach are respectively adopted to predict the dynamics of the pressure vessel, the connecting pipe and the safety valve, and different models are connected through data interfaces. With this system model, dynamic simulations were carried out and both the stable and the unstable system responses were obtained. For the model verification purpose, the simulation results were compared with those obtained from experiments and full CFD simulations. A good agreement and a better efficiency were obtained, verifying the ability of the model and the feasibility of the modeling method proposed in this paper.

Multi-harvesting smart solution for self-powered wearable objects: System-level model and transistor-level design

Internet of Things and growing popularity of connected devices are increasing the demand for wearables applications, which is driving the development of ultra-low power secure systems. Thus, having a system running at low voltage with low power consumption introduces the use of ambient energy harvesting. Besides, batteries have several limitations reducing their compatibility with wearables, including periodical need for recharge, limited life-time, heavy and large form factor and non-eco-friendly life-cycle. Therefore ambient energy harvesting technology gives a promising alternative for self-powered wearables. The integration of these solutions on the same silicon support is a real technological challenge. This paper proposes a multi-harvesting fully-integrated system architecture combining AC and DC sources. Based on a MATLAB/Simulink model, the proposed system allows the calibration of an optimal solution. It is designed and simulated in 40 nm CMOS process, demonstrating the use of an AC source as secondary input to start a harvesting system with very low DC source as main source.

Effects of crack and structural flexibility on planetary gear system fault feature considering ring gear boundary condition

The crack will inevitably aggravate the transmission system vibration. In addition, the structure of planetary gear train is much more complex, and due to the installation conditions and other factors, the boundary conditions of ring gear are also different (including the pin support constraint and outer rim constraint). In view of the deficiencies of the existing research on the planetary gear train crack morphology, which are mostly based on simple assumptions and lack of experimental verification, the crack growth test is carried out and the theoretical crack morphology is verified. Then, the vibration feature is analyzed based on the obtained crack morphology and the established system-level dynamic model of the planetary gear train (composed of housing, carrier, gear and shaft, etc.). The studies reveal that the fault feature is more obvious when the initial crack location is far away from the tooth root. Under the boundary condition of outer rim constraint, the thinner ring gear can decrease the dynamic response and crack impact, but when restraining the pin support, the observed phenomenon is opposite. After considering the housing flexibility, the vibration is reduced, however, the increasing flexibility weakens the crack fault feature of the planetary gear train.

Investigations on MBSE modelling and dynamic performance assessment of an electrical trimmable horizontal stabilizer actuator

With the development of power-by-wire technology for more electric aircraft, the electro-mechanical actuator (EMA) has the advantages to replace the conventional hydraulic servo actuator in some aerospace flight controls. Conventional hydraulically powered trimmable horizontal stabilizer actuation (THSA) system is nowadays developed to be electrically supplied. Given their safety-criticality, no-back mechanism and redundant load paths are utilized to meet the flight control requirements. However, rare literatures have introduced these functions and addressed the virtual prototyping activities from system-level point of view. This paper proposed such a model of a THSA system with dual electric power sources and fault-tolerant mechanical load paths. The nonlinear effects of components are considered with realism, and system-level simulation test is conducted to support the model-based system engineering (MBSE) approach. The models are developed with a power view instead of a pure signal view. Focusing on the friction effect and compliance effect with backlash or preload, some improved and novel approaches are adopted for these crucial components and validated via experimental results. Meanwhile, the implemented system-level model enables injection of crucial faults. Finally, the simulation of the proposed model shows that it is an efficient resource to investigate the actuator’s dynamic performance, to virtually prove that the actuator meets the fail/safe constraint, and to demonstrate the soundness of the fault monitoring functions.

Finnish emergency medical services managers’ and medical directors’ perceptions of collaborating with patients concerning patient safety issues: a qualitative study

ObjectivesThis study aimed to describe emergency medical services (EMS) managers’ and medical directors’ perceptions of collaborating with patients concerning patient safety issues in the EMS.DesignThe study used a descriptive qualitative...

Open drug discovery in Alzheimer's disease.

Alzheimer's disease (AD) drug discovery has focused on a set of highly studied therapeutic hypotheses, with limited success. The heterogeneous nature of AD processes suggests that a more diverse, systems-integrated strategy may identify new therapeutic hypotheses. Although many target hypotheses have arisen from systems-level modeling of human disease, in practice and for many reasons, it has proven challenging to translate them into drug discovery pipelines. First, many hypotheses implicate protein targets and/or biological mechanisms that are under-studied, meaning there is a paucity of evidence to inform experimental strategies as well as high-quality reagents to perform them. Second, systems-level targets are predicted to act in concert, requiring adaptations in how we characterize new drug targets. Here we posit that the development and open distribution of high-quality experimental reagents and informatic outputs-termed target enabling packages (TEPs)-will catalyze rapid evaluation of emerging systems-integrated targets in AD by enabling parallel, independent, and unencumbered research.

Neural simulation pipeline: Enabling container-based simulations on-premise and in public clouds.

In this study, we explore the simulation setup in computational neuroscience. We use GENESIS, a general purpose simulation engine for sub-cellular components and biochemical reactions, realistic neuron models, large neural networks, and system-level models. GENESIS supports developing and running computer simulations but leaves a gap for setting up today's larger and more complex models. The field of realistic models of brain networks has overgrown the simplicity of earliest models. The challenges include managing the complexity of software dependencies and various models, setting up model parameter values, storing the input parameters alongside the results, and providing execution statistics. Moreover, in the high performance computing (HPC) context, public cloud resources are becoming an alternative to the expensive on-premises clusters. We present Neural Simulation Pipeline (NSP), which facilitates the large-scale computer simulations and their deployment to multiple computing infrastructures using the infrastructure as the code (IaC) containerization approach. The authors demonstrate the effectiveness of NSP in a pattern recognition task programmed with GENESIS, through a custom-built visual system, called RetNet(8 × 5,1) that uses biologically plausible Hodgkin-Huxley spiking neurons. We evaluate the pipeline by performing 54 simulations executed on-premise, at the Hasso Plattner Institute's (HPI) Future Service-Oriented Computing (SOC) Lab, and through the Amazon Web Services (AWS), the biggest public cloud service provider in the world. We report on the non-containerized and containerized execution with Docker, as well as present the cost per simulation in AWS. The results show that our neural simulation pipeline can reduce entry barriers to neural simulations, making them more practical and cost-effective.

Model organism life extending therapeutics modulate diverse nodes in the drug-gene-microbe tripartite human longevity interactome

Advances in antiaging drug/lead discovery in animal models constitute a large body of literature on novel senotherapeutics and geroprotectives. However, with little direct evidence or mechanism of action in humans—these drugs are utilized as nutraceuticals or repurposed supplements without proper testing directions, appropriate biomarkers, or consistent in-vivo models. In this study, we take previously identified drug candidates that have significant evidence of prolonging lifespan and promoting healthy aging in model organisms, and simulate them in human metabolic interactome networks. Screening for drug-likeness, toxicity, and KEGG network correlation scores, we generated a library of 285 safe and bioavailable compounds. We interrogated this library to present computational modeling-derived estimations of a tripartite interaction map of animal geroprotective compounds in the human molecular interactome extracted from longevity, senescence, and dietary restriction-associated genes. Our findings reflect previous studies in aging-associated metabolic disorders, and predict 25 best-connected drug interactors including Resveratrol, EGCG, Metformin, Trichostatin A, Caffeic Acid and Quercetin as direct modulators of lifespan and healthspan-associated pathways. We further clustered these compounds and the functionally enriched subnetworks therewith to identify longevity-exclusive, senescence-exclusive, pseudo-omniregulators and omniregulators within the set of interactome hub genes. Additionally, serum markers for drug-interactions, and interactions with potentially geroprotective gut microbial species distinguish the current study and present a holistic depiction of optimum gut microbial alteration by candidate drugs. These findings provide a systems level model of animal life-extending therapeutics in human systems, and act as precursors for expediting the ongoing global effort to find effective antiaging pharmacological interventions. Communicated by Ramaswamy H. Sarma

Output power regulation system for portable micro fuel cell systems

This article presents an output power regulation system for micro fuel cells to help enhance the stability of the fuel cell in a portable micro power system. The structure of an MCU-controlled DC-DC converter is proposed. Then, the output characteristics of a selected fuel cell stack and the DC-DC converter’s power control functions are estimated by a system-level model. Based on the simulation results, the model provides a power regulation system which is implemented, and the test shows that it fulfills its intended function and the output power is regulated to a fixed level of 5 W–40 W with good efficiency.

An improved Closed-Circuit RO (CCRO) system: Design and cyclic simulation

A volume-varying stirred tank with a free-piston are placed in front of DuPont's Closed-Circuit RO (CCRO) system to achieve improved energetics. Valves are used to direct fluid flow and piston motion to enable cyclic operations consisting of CC filtration and flushing steps. Similar to CCRO, overall system recovery in the proposed system is controlled by the CC/flushing time ratio, and uninterrupted permeate production is possible if the flushing is done at high pressures. Spatiotemporal system-level models are developed and formulated as a set of coupled partial differential equations (PDEs) and ordinary differential equations (ODEs). Detailed numerical simulations and parametric studies are carried out to explore the flow and mass transfer characteristics and to compare its performance at the cyclic steady-state (CSS) with the original CCRO and the conventional steady-state RO.