System-level Simulation Model Research Articles

Ocean wave energy harvesting: Utilizing buoy float to induce dielectric elastomer deformation and electret vibration for power generation

The dielectric elastomeric polymer material, characterized by its high energy output, resilience, mechanical compliance, lightweight, damage tolerance, and low cost, demonstrates significant potential as an innovative sustainable energy converter. It seamlessly adapts to the ever-changing climatic conditions of the ocean, converting the violent impacts of wave kinetics into electrical energy. This paper proposed a viable electret and dielectric elastomer wave energy harvester to convert ocean wave energy into electricity and aims to achieve self-priming operation in the conjugate components. The output voltage from the electret also functions as the bias voltage for the dielectric elastomer, based on the intrinsic variable capacitance electric translation principle. The dielectric elastomer's deformation, equivalent to variable capacitance, successfully converted the mechanical energy from the ocean waves into electrical energy. The ocean wave energy conversion is evaluated using a system-level approach, incorporating theoretical, simulation, and experimental models. In addition, electric power generation is assessed with parameters such as output voltage, electret surface potential, and bias voltage. Essentially, the electric energy produced by the electret generator can serve as the bias voltage source for the dielectric elastomer generator, providing a self-sustaining solution for ocean wave energy harvesting. The innovative power device envisions various potential configurations for ocean-based power generation.

A system-level CFD simulation model for investigating the energy dissipation mechanism of seawater pump and rotary energy recovery device in SWRO desalination system

Seawater reverse osmosis (SWRO) technology has been universally adopted because of its high efficiency, economic benefits, easy maintenance, and high-pressure seawater pump (HPSP) and energy recovery device (ERD) are essential components, which determine the specific energy consumption of SWRO system. However, it is still unclear about energy dissipation mechanism and mixing characteristics from the perspective of system. For that, this thesis proposes a novel system-level Computational Fluid Dynamics (CFD) model considering all interfaces in HPSP and integrated energy recovery and pressure boost device (IERPBD). To profoundly investigate the system performance under various operating conditions, the pressure and composition distribution, power loss of each interface and mixing rate are numerically calculated and analyzed. Additionally, experiment of the effect of temperature on SWRO system performance is conducted to practically verify the proposed model, which indicates that the presented model could precisely reflect the energy dissipation and mixing characteristics. Besides, it is advised that the rotating speed of HPSP and IERPBD should not be set too high which could increase the mixing rate and energy consumption, and higher temperature might lower the quality of produced freshwater. This study offers a feasible way to reveal the energy dissipation mechanism of SWRO desalination system.

A Novel Optimal Sensor Placement Method for Optimizing the Diagnosability of Liquid Rocket Engine

There are hundreds of various sensors used for online Prognosis and Health Management (PHM) of LREs. Inspired by the fact that a limited number of key sensors are selected for inflight control purposes in LRE, it is practical to optimal placement of redundant sensors for improving the diagnosability and economics of PHM systems. To strike a balance between sensor cost, real-time performance and diagnosability of the fault diagnosis algorithm in LRE, this paper proposes a novel Optimal Sensor Placement (OSP) method. Firstly, a Kernel Extreme Learning Machine-based (KELM) two-stage diagnosis algorithm is developed based on a system-level failure simulation model of LRE. Secondly, hierarchical diagnosability metrics are constructed to formulate the OSP problem in this paper. Thirdly, a Hierarchy Ranking Evolutionary Algorithm-based (HREA) two-stage OSP method is developed, achieving further optimization of Pareto solutions by the improved hypervolume indicator. Finally, the proposed method is validated using failure simulation datasets and hot-fire test-run experiment datasets. Additionally, four classical binary multi-objective optimization algorithms are introduced for comparison. The testing results demonstrate that the HREA-based OSP method outperforms other classical methods in effectively balancing the sensor cost, real-time performance and diagnosability of the diagnosis algorithm. The proposed method in this paper implements system-level OSP for LRE fault diagnosis and exhibits the potential for application in the development of reusable LREs.

Model-Based Digital Overall Integrated Design Method of AUVs

Autonomous underwater vehicles (AUVs) have the characteristics of a high performance, a complex coupling mechanism, a compact, complex system composition, as well as high requirements for design constraints, quality, and reliability. In the traditional overall design process, numerous design tools and software programs are used, which results in poor model data sharing, a lack of uniqueness and synchronization between system levels, and difficulty in process tracing. Moreover, it is challenging to meet the technical requirements for close collaboration and rapid iteration of multiple positions. To address the aforementioned limitations, this study proposes a digital overall integrated design method for the design and simulation integration of AUVs and defines a unified architecture and interface for system-level design simulation models, thus solving the interoperability and consistency problems in multiple tools and models. In addition, a model-based AUV system integration design verification method that combines different processes, specifications, and models is designed, and software similar to Cameo, which can provide technical means for system-level integrated design and achieve rapid modeling and simulation verification based on system design solutions, is developed. Finally, a practical system design is conducted by taking specific AUV equipment as a research object, and the proposed methods are compared with traditional methods to prove the improvement effect of the technical route on the equipment and development efficiency.

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)).

An Interface ASIC Design of MEMS Gyroscope with Analog Closed Loop Driving.

This paper introduces a digital interface application-specific integrated circuit (ASIC) for a micro-electromechanical systems (MEMS) vibratory gyroscope. The driving circuit of the interface ASIC uses an automatic gain circuit (AGC) module instead of a phase-locked loop to realize a self-excited vibration, which gives the gyroscope system good robustness. In order to realize the co-simulation of the mechanically sensitive structure and interface circuit of the gyroscope, the equivalent electrical model analysis and modeling of the mechanically sensitive structure of the gyro are carried out by Verilog-A. According to the design scheme of the MEMS gyroscope interface circuit, a system-level simulation model including mechanically sensitive structure and measurement and control circuit is established by SIMULINK. A digital-to-analog converter (ADC) is designed for the digital processing and temperature compensation of the angular velocity in the MEMS gyroscope digital circuit system. Using the positive and negative diode temperature characteristics, the function of the on-chip temperature sensor is realized, and the temperature compensation and zero bias correction are carried out simultaneously. The MEMS interface ASIC is designed using a standard 0.18 μM CMOS BCD process. The experimental results show that the signal-to-noise ratio (SNR) of sigma-delta (ΣΔ) ADC is 111.56 dB. The nonlinearity of the MEMS gyroscope system is 0.03% over the full-scale range.

Numerical Study on Pipeline Pressure Surge of the Large Aircraft Fuel System

The sudden closure of the refueling valve during the refueling process will cause the water hammer phenomenon in the pipeline of the large aircraft fuel system and produce pressure waves propagating along the pipeline. In serious cases, it will cause severe damage to the pipeline. The pressure surge in the pipeline can be affected by many design factors. In this study, the numerical modeling method of the large aircraft fuel system is studied using the Flowmaster program, and the accuracy of steady and transient state analysis of the simulation method is verified by experimental data. Based on this numerical method, a complete system-level simulation model of the large aircraft fuel system was established. Using this model, the effects of valve closure speed, diameter of the refueling main pipe, and refueling volume flow rate on pipeline pressure surge during the refueling process are investigated. The results indicate that all three factors have a significant impact on the pipeline pressure surge of the fuel system. The effect of the valve closing speed and the pipe diameter on the pressure surge of the pipeline is nonlinear and gradually weakened with the decrease of valve speed and the increase of pipe diameter, while the effect of refueling volume flow rate on the pipeline pressure surge is approximately linear.

Performance Assessment of Seawater, Wet and Dry Cooling in a 50-MW Parabolic Trough Collectors Concentrated Solar Power Plant in Kuwait

Abstract Kuwait is a country with great potential for concentrated solar power (CSP) due to its high solar resource. The current work analyzes the potential of the application of CSP technology in the country and its particularities. Specifically, the current work examines a CSP plant with parabolic trough collector (PTC) technology and how this technology is affected in its performance depending on the location (inland or coastal) and the refrigeration system (wet, dry, or seawater cooled). The modeling methodology is based on a two-step approach: first, the Rankine steam power cycle is modeled in detail in a state-of-the-art steady-state simulation environment, obtaining the performance of the power cycle for each cooling technology; second, the power cycle performance maps are integrated into a detailed transient system-level simulation model of the complete CSP plant in order to perform annual yield simulations for the different representative locations of the climate of Kuwait. These results provide valuable information on both the potential of this technology for its more immediate application such as electricity generation and other future applications such as the desalination of seawater where the location must necessarily be coastal.

Enhancement of risk informed validation framework for external hazard scenario

In recent years, the U.S. Nuclear Regulatory Commission (USNRC) and the International Atomic Energy Agency (IAEA) have developed methodologies to assess the vulnerabilities of nuclear plants against site specific extreme hazards. In many cases, advanced simulation tools are being considered to simulate multi-physics, multi-scale phenomena and to evaluate vulnerability of nuclear facilities. The credibility of advanced simulation tools is assessed based on a formal verification, validation, and uncertainty quantification procedure. One of the key limitations in validation is the lack of relevant experimental data at system-level. This limitation leads to a decrease in the confidence of system-level risk predictions. Therefore, a robust validation framework is needed to formalize the confidence in predictive capability of advanced simulation results. This study enhances the existing risk informed validation methodology, originally proposed by Kwag et al. [1] and Bodda et al. [2], by developing additional attributes and a new set of validation indicies for a complete and wider applicability of the framework. In this manuscript, the methodology to identify the critical path that leads to the system-level failure is illustrated. The overall validation is checked for completeness and consistency by comparing the critical path for both the system-level simulation and experimental models. The applicability of the code for an intended application is represented in terms of various maturity levels and helps in the process of decision making.

System Level Modelling of Batteries in Spacecraft Power System in Multiple Source and Multiple Load Configuration

AbstractIn present day spacecraft applications, power system uses solar arrays as the primary source of power generation and rechargeable Lithium ion batteries as secondary source of power. In normal orbits, during sunlit period, solar arrays support the power requirement from all the subsystems and payloads along with the charge power requirement of batteries. During eclipse period, entire load should be supported by batteries. In addition to the eclipse support, starting from launch pad to till deployment of solar panels, all loads will be on batteries. Contingency loads should also be taken care by batteries. So, battery sizing is very critical part in designing the power system of spacecraft. In multiple source and multiple load configuration where two or more batteries are connected to same Spacecraft power bus, current sharing between the batteries is expected, which needs to be considered for optimized sizing and designing of batteries. The scenario becomes complex with additional constraints namely some loads can come on one battery and not on others or vice versa. Even in a configuration where potential difference exists between batteries, current sharing will start as soon as this difference vanishes. A system level simulation model is developed, using network equations, to analyze in‐circuit performance of batteries in multiple source and multiple load power system. The simulation model uses actual current sharing and predicts State of Charge (SOC) of each battery from which Open Circuit Voltage (OCV) is derived. This OCV of batteries is used periodically for finding actual current sharing which runs in a loop for analyzing battery performance in multisource system. Currently a configuration in which two batteries are connected to two buses, which are paralleled and having different loads, is simulated. Optimized battery sizing, actual current sharing and SOC of each battery are derived. This model can also be extended to a system where more than two batteries are present. Two different approaches are used for simulation and results are compared. The developed generic model has features to use in multiple battery configuration.

Impact of Increasing Wait Times on Overall Mortality of Chimeric Antigen Receptor T-Cell Therapy in Large B-Cell Lymphoma: A Discrete Event Simulation Model.

The development of chimeric antigen receptor (CAR) T cells has transformed oncology treatment, with the potential to cure certain cancers. Although shown to be effective in selected populations and studies, CAR T-cell technology requires considerable health care resources, which may lead to additional wait times to access this type of treatment in future. The objective of our study was to estimate the potential impact of increasing wait times on CAR T-cell therapy effectiveness compared with standard chemotherapy for patients with relapsed/refractory diffuse large B-cell lymphoma. A health system-level discrete event simulation model was developed to project the potential impact of wait times on CAR T-cell therapy for patients with relapsed/refractory diffuse large B-cell lymphoma. Waiting queues and health states related to treatment and clinical progression were implemented. Using data from the literature, we evaluated nine scenarios of using CAR T-cell therapy with wait times ranging from 1 to 9 months. The outcome of interest was 1-year all-cause mortality. Increasing the wait time of receiving CAR T-cell therapy from 1 to 9 months increased the predicted 1-year mortality rate from 36.1% to 76.3%. Baseline 1-year mortality was 34.0% in patients receiving CAR T-cell therapy with no wait times and 75.1% in patients treated with chemotherapy. This resulted in an increased relative mortality rate of 6.2% to 124.5% over a 1- to 9-month wait time compared with no wait time. We found that modest delays in CAR T-cell therapy significantly hinder its effectiveness. Because CAR T-cell therapy offers a potential cure, it is expected that the uptake rate will be substantially increased once the therapy is regularly funded by a health care system. Wait times may be prolonged if system resource availability does not match the demand. Strategies must be developed to minimize the impact of delays and reduce complications during waiting.

A New Control Architecture With Spatial Comb Filter and Spatial Repetitive Controller for Circulating Current Harmonics Elimination in a Droop-Regulated Modular Multilevel Converter for Wind Farm Application

Circulating current control is one of the critical issues in modular multilevel converters (MMCs). When a frequency-droop-regulated MMC is used to integrate an offshore wind farm into an high-voltage dc transmission system, the variation in its operating ac line frequency induces a change in circulating current harmonic frequencies. Hence, the conventional circulating current controllers, such as proportional-resonant or repetitive controller, which are tuned to a specific frequency, fail to alleviate the circulating current harmonics. In this paper, a new control architecture comprising of a spatial comb filter (SCF) and a spatial repetitive controller (SRC) is proposed to effectively attenuate the even-order harmonics in the circulating current independent of the operating ac line frequency of the MMC. The proposed controller incorporates the phase sampling technique to achieve the dynamic change in the sampling frequency, which is the key to strong periodic disturbance rejection capability of the SCF and SRC even under variable frequency operation. A system level simulation model has been developed on PLECS simulation software to demonstrate the performance of the proposed control architecture. In addition, a scaled-down laboratory prototype of a 1-kW, 400-V, five-level single-phase MMC is developed and the experimental results are presented to substantiate the performance of the proposed control scheme.

Magnetic Frequency Tuning of a Multimodal Vibration Energy Harvester.

In this paper, we present a novel vibration-based piezoelectric energy harvester, capable of collecting power at multiple operating frequencies and autonomously adapting itself to the dominant ambient frequencies. It consists of a compact dual-frequency resonator designed such that the first two fundamental natural frequencies are in the range of [50, 100] Hz, which is a typical frequency range for ambient vibrations in industrial environments. A magnetic frequency-tuning scheme is incorporated into the structure, which enables the frequency agility of the system. In contrast to single frequency harvesters, the presented approach combines multi-resonance and frequency tunability of both modes enabling a larger operative bandwidth. We experimentally demonstrate independent bi-directional tunability of our dual-frequency design. Furthermore, a control algorithm based on maximum amplitude tracking has been implemented for self-adaption of the system. The latter has been demonstrated in a system-level simulation model, which integrates the dual-frequency resonator, the magnetic tuning, and the control algorithm.

Evaluation of operational and environmental sustainability tradeoffs in multimodal freight transportation planning

Transportation planners often need to justify transportation related investments to public officials. Besides efficiency measures, the environment protection and sustainability are gaining more and more importance. In order to improve freight flow efficiency in a sustainable way, it is necessary to have a systematic tool to study the freight flow over all three major surface modes and their connections and, in turn, to help public officials identify the best way to improve freight transportation. We built a system-level intermodal simulation model that includes highways, railways, and waterways because all three modes, working together, play significant roles in freight flows. We evaluated the performance of the Louisiana freight network under different scenarios and measured the benefits of mode changes evaluating the tradeoff between environmental goals and other performance measures.

DESIGN OF AN ACTIVE LOW FREQUENCY VIBRATION ISOLATION SYSTEM FOR ATOM INTERFEROMETRY BY USING SLIDING MODE CONTROL

Active vibration isolation is gaining increased attention in the ultra-high precision application of atom interferometry to effectively treat the unavoidable ground vibration. In this system, a digital control subsystem is used to process and feedback the vibration measured by a seismometer. A voice coil actuator is used to control and cancel the motion of a commercial passive vibration isolation platform. The system level simulation model is established by Simulink software, The simulation results demonstrate the asymptotic stability of the system and the robustness of the control algorithm. Compared with the conventional lead–lag compensation type controller, the algorithm adopted uses sliding mode control, taking advantage of its easy computer implementation and its robust high performance properties. With the feedback path closed, the system acts like a spring system with a natural resonance frequency of 0.02 Hz. The vibration noise in the vertical direction is about 20 times reduced during 0.1 and 2 Hz, The experimental results verify that the isolator has significant vibration isolation performance, and it is very suitable for applications in high precision gravity measurement.

Modelling and Simulation on Multibody Dynamics for Vehicular Cold Launch Systems Based on Subsystem Synthesis Method

The fast simulation of the vehicular cold launch system (VCLS) in the launch process is an essential requirement for practical engineering applications. In particular, a general and fast simulation model of the VCLS will help the designer to obtain the optimum scheme in the initial design phase. For these purposes, a system-level fast simulation model was established for the VCLS based on the subsystem synthesis method. Moreover, a comparison of the load of a seven-axis VCLS on the rigid ground through both theoretical calculations and experiments was carried out. It was found that the error of the load of the rear left outrigger is less than 7.1%, and the error of the total load of all the outriggers is less than 2.8%. Moreover, time taken for completion of the simulation model is only 9.5 min, which is 5% of the time taken by conventional algorithms.

Diesel and Spark Ignition Engines Emissions and After-Treatment Control: Research and Advancements

One of the major risks mankind has encountered during recent years is, without a doubt, the anthropogenic contribution to environmental pollution [...]

Innovative Calibration Method for System Level Simulation Models of Internal Combustion Engines

The paper outlines a procedure for the computer-controlled calibration of the combined zero-dimensional (0D) and one-dimensional (1D) thermodynamic simulation model of a turbocharged internal combustion engine (ICE). The main purpose of the calibration is to determine input parameters of the simulation model in such a way as to achieve the smallest difference between the results of the measurements and the results of the numerical simulations with minimum consumption of the computing time. An innovative calibration methodology is based on a novel interaction between optimization methods and physically based methods of the selected ICE sub-systems. Therein physically based methods were used for steering the division of the integral ICE to several sub-models and for determining parameters of selected components considering their governing equations. Innovative multistage interaction between optimization methods and physically based methods allows, unlike the use of well-established methods that rely only on the optimization techniques, for successful calibration of a large number of input parameters with low time consumption. Therefore, the proposed method is suitable for efficient calibration of simulation models of advanced ICEs.

Efficiency Analysis of Gas Turbine Combined-Cycle Fed with Synthetic Natural Gas (SNG) and Mixture of Syngas and SNG

The effect of synthetic natural gas (SNG) and mixture of syngas and SNG fed to Natural Gas Combined-Cycle (NGCC) plants is presented in this study via a system-level simulation model. The commercial chemical process simulator, Pro/II® V8.1.1, was used in the study to build the analysis model. The NGCC plant consists of gas turbine (GT), heat recovery steam generator (HRSG) and steam turbine (ST). The study envisages two analyses as the basic and feasibility cases. The former is the benchmark case which is verified by the reference data with the GE 7FB gas turbine. According to vendor’s specification, the typical net plant efficiency of GE 7FB NGCC with two gas turbines to one steam turbine is 57.5% (LHV), and the efficiency is the benchmark in the simulation model built in the study. The latter introduces a feasibility study with actual parameters in Taiwan. The SNG-fed GE 7FB based combined-cycle is evaluated, and the mixture of SNG and syngas is also evaluated to compare the difference of overall performance between the two cases. The maximum ratio of syngas to SNG is 0.14 due to the constraint for keeping the composition of methane at a value of 80 mol%, to meet the minimum requirement of NG in Taiwan. The results show that the efficiency in either case of SNG or mixture of SNG and syngas is slightly lower than the counterpart in the benchmark one. Because the price of natural gas is much higher than that of coal, it results in higher idle capacity of NGCC. The advantage of adopting SNG in Taiwan is that it could increase the capacity factor of combined-cycles in Taiwan. The study shows a possible way to use coal and reduce the CO2 emission, since coal provides nearly half of the electricity generation in Taiwan in recent years.

Thermal management of software changes in product lifecycle of consumer electronics

The power consumption of consumer electronic products varies with processor execution, which itself depends on software. Therefore, software changes, such as software updates and new software installations, increase the thermal risk, even when the hardware development is complete. In this paper, we first introduce a typical system-level thermal simulation model, coupling the activities within modules related to software, electrical parts, and mechanical structures. Through a case study, we then investigate thermal management in both the development and maintenance phases of the product lifecycle. The simulation model efficiently evaluates the thermal risk under a number of variations caused by software changes.