Lumped Parameter Research Articles

Lumped Parameter Analysis of Autogenous Propellant Pressurization System for Nuclear Thermal Rocket

This work proposes a new propellant management configuration for an ammonia-fueled nuclear thermal propulsion system. The suggested configuration maximizes the advantage deriving from the autogenous pressurization of ammonia by exploiting the thermal power lost by the nuclear reactor toward the vacuum space due to leaking radiation. In this layout, a tank containing ammonia in saturated conditions is placed near the nuclear reactor and receives an input thermal power proportional to the dose of gamma rays and neutrons absorbed by the tank walls and the ammonia itself. Such a thermal power accelerates the vaporization process of the saturated ammonia, thus increasing the pressure in the tank. A pressure regulator valve exploits this overpressure to pressurize the ammonia propellant contained in a run tank to the level required by the mission by connecting the two ammonia volumes. The pressure achieved inside the run tank pushes the propellant with an adequate mass flow rate inside the nuclear reactor. The developed lumped parameter analysis shows how this propellant management system can provide a constant mass flow to the nuclear reactor without using a turbopump assembly. Moreover, it is shown how the proposed concept allows for a reduction in the radiation shield mass.

Dynamic simulation and control strategy development of molten salt steam generation system for coal-fired power plant flexible retrofit

The coal-fired power plant (CFPP) coupled with the molten salt thermal energy storage system is a potential way to improve its flexibility and peak-shaving ability. The steam generation system (SGS) is a suitable choice to convert the feed water into hot steam by using the heat from the molten salt. In this paper, the schematic of an SGS coupled with the CFPP is presented. A dynamic model of the SGS basing lump parameter method is established and validated to investigate its dynamic response characteristics. Five different disturbance experiments including feed water inlet parameters, molten salt inlet parameters and medium pressure steam valve, are conducted and analyzed. The dynamic response curves of molten salt and steam are obtained. Moreover, the load adjustment process of SGS with three different load changing rates (3 %, 6 %, 10 % Pe/min) under the rated conditions is compared and its influence on the SGS is analyzed. The temperature changing rates in the thick-wall components of SGS are within 2 °C/min which meets the safe operating standard. Based on the above results, the three elements control strategy with excellent robustness for the SGS safety operation is proposed and demonstrated. The results show that the response time for the SGS load regulation process and the water level fluctuation have been significantly improved as the three elements control strategy is imposed. The water level can be stabilized in 200 s with tiny fluctuation when the SGS loads down 10 % thermal load with 10 % Pe/min load changing rate. These results could provide useful references for the design and control strategy making of the CFPP coupled with the molten salt thermal energy storage system.

Conductive paths generation using topology optimization for worst-case thermal design in space systems

Designing thermal systems for space platforms is a challenging task due to the wide variability in thermal conditions during the orbit and the strict constraints imposed by other subsystems. Several strategies have been developed to address these challenges while minimizing the thermal control subsystem’s signature, encompassing different algorithms optimize components positions in the platform. When relocation is not possible, thermal couplings between components can be modified to enhance heat transfer and achieve more uniform temperature distribution. To design optimal thermal paths in 2D space structures, in this paper a topology optimization framework based on the Heaviside Projection Method is introduced, using the Lumped Parameter Method (LPM) and taking the radiation heat transfer into account. The algorithm’s performance is tested on a Printed Circuit Board (PCB) by designing an optimal copper layer to meet specific thermal requirements under both extreme hot and cold conditions. Results show a significant improvement in thermal compliance for all components with the addition of this high-conductivity layer. Additionally, a reduction method is introduced to transfer the material distribution from the optimization to a coarser mesh of any size, which is useful to facilitate its implementation in existing software, where a large number of degrees of freedom can be a limitation.

Continuous Control Set Predictive Control with Affine Registration Technique for Permanent Magnet Synchronous Motor Drive

This article introduces an affine registration (AR) algorithm to improve the performance of ultra-local (UL) model-free predictive control (MFPC) methods. The UL model is extensively utilized in continuous control set (CCS)-MFPC to estimate lumped parameters. However, in these cases, variations in inductance during operation can significantly impact the input gain coefficient of the UL model. Little work has focused on this aspect, which makes the motivation and novelty of this paper. The AR technique, derived from image processing methodologies, is employed to establish a mapping between predicted states and actual states during the commissioning process. Subsequently, during actual operation, the resolved voltage reference is modified based on the AR matrix to compensate for errors in the UL model. The theoretical control model is rigorously derived, and experimental results are presented to validate the superior performance of the proposed method.

Quantitative evaluation of the effect of Circle of Willis structures on cerebral hyperperfusion: A multi-scale model analysis

Cerebral hyperperfusion occurs in some patients after superficial temporal artery–middle cerebral artery bypass surgery. However, there is uncertainty about cerebral hyperperfusion after bypass for patients with different Circle of Willis (CoW) structures.This study established a lumped–parameter model coupled with one–dimensional model (0–1D), whilst a deep learning model for predicting pressure drop (DLM–PD) caused by stenosis and a cerebral autoregulation model (CAM) were introduced into the model. Based on this model, 9 CoW structural models before and after bypass were constructed, to investigate the effects of different CoW structures on cerebral hyperperfusion after bypass. The model and the results were further validated by clinical data.The MSE of mean flow rates from 0–1D model calculation and from clinical measurement was 1.4%. The patients exhibited hyperperfusion in three CoW structures after bypass: missing right anterior segment of the anterior cerebral artery (mRACA1) (13.96% hyperperfusion); mRACA1 and foetal–type right anterior segment of posterior cerebral artery (12.81%), and missing anterior communicating artery and missing left posterior communicating artery (112.41%). The error between the average flow ratio from the model calculations and from clinical measurements was less than 5%.This study demonstrated that the CoW structure had a significant impact on hyperperfusion after bypass. The general 0–1D model coupled with DLM–PD and CAM proposed in this study, could accurately simulate the hemodynamic environment of different CoW structures before and after bypass, which might help physicians identify high–risk patients with hyperperfusion before surgery, and promote the development of non–invasive diagnosis and treatment of cerebrovascular diseases.

Effect of upper body venoarterial ECMO on systemic hemodynamics and oxygenation: A computational study

BackgroundThis study seeks to quantify the effects of upper body veno-arterial extracorporeal membrane oxygenation (VA ECMO) on the anatomical distribution of oxygen delivery in the setting of hypoxic respiratory failure and provide new insights that will guide clinical use of this support strategy to bridge patients to lung transplant. MethodsEmploying a patient-specific vascular geometry and a quantitative model of oxygen transport, computational simulations were performed to determine hemodynamics and oxygen delivery in the ascending and descending aorta, left and right coronary arteries, and great vessels during upper body VA ECMO support. Oxygen content in ECMO circuit blood flow was varied while considering different degrees of lung failure severity. Using lumped parameter models to dynamically apply perfusion boundary conditions, hemodynamic parameters and oxygen content were analyzed to assess the effect of ECMO supply titration. ResultsThe results emphasize the importance of anatomical distribution for tissue oxygen delivery in severe lung failure, with ECMO-derived flow primarily augmenting oxygen content in specific vascular beds. They also demonstrate that although cannulating the subclavian artery can enhance cerebral oxygen delivery, its ability to ensure sufficient oxygen delivery to the coronary circulation seems to be comparatively restricted. ConclusionsThe oxygen delivery to a specific vascular area is primarily determined by the oxygen content in the source of perfusion. Caution is advised with upper body VA ECMO for patients with hypoxic respiratory failure and right ventricle dysfunction, due to potential coronary ischemia. Management of these patients is challenging due to disease progression and organ availability uncertainties.

A methodology for predicting and optimizing the lubrication of an off-road machine transmission

This article presents an analysis method based on lumped-parameters (LP) and computational fluid dynamics (CFD) to evaluate the behavior and calibrate the lubrication (LUB) circuit in an agricultural dual-clutch transmission. Gearbox LUB is crucial because it affects reliability, life, and transmission efficiency. The transmission’s hydraulic circuit consists of the higher pressure power transmission control and actuation circuit and the low pressure LUB circuit. The former was analyzed with LP approach, instead the latter was modeled with CFD approach due to its geometric complexity. The results will be contextualized by commenting on the advantages and limitations of LP and CFD analysis, finally outlining a mixed analysis methodology. The simulations are solved for different engine speed. The results are used to calibrate a comprehensive LP model (model) and to optimize the LUB circuit by adjusting some critical design parameters. As an experimental approach, simplified tests are usually performed ignoring the action of the centrifugal force, which has a great impact on the flow regime inside the LUB ducts. This work aims to develop a methodology for analyzing LUB in all parts of the gearbox, which can help designers test various combinations within industrial timeframes and obtain reliable and the most efficient configuration.

Evaluating the thermal stability of an interior permanent magnet synchronous machine through iterative multi‐physics simulation

AbstractThis paper investigates the thermal operating capability of an interior permanent magnet synchronous machine. An iterative workflow is presented, combining electromagnetic modeling, control, power‐loss modeling, and thermal modeling to identify maximum thermal stable operating points. Special attention is given to the critical temperatures of winding and permanent magnets. A nonlinear reduced order model based on finite element method model was used to simulate the system, including an inverter model with space vector pulse width modulation in combination with field‐oriented control. Furthermore, an advanced iron core loss model and thermal lumped parameter model were employed. The presented approach allows for evaluating losses and their impact on steady‐state temperatures. The obtained results highlight the significant influence of space vector pulse width modulation on iron core losses and the importance of considering both advanced power‐loss models and adequate thermal models when analyzing the machine's thermal state. This research emphasizes the concept of a thermally stable envelope, providing a comprehensive understanding of the thermal boundaries under various operating conditions.

Numerical Analysis of the Effect of the Non-phase-change Gas on the Atmospheric CO<sub>2</sub> Decompression Capture Characteristics by Cryogenic Heat (Formulation Based on Unsteady Lumped Parameter System Analytical Model and Temporal Change of Various Quantities under Reference Analytical Conditions)

Numerical Analysis of the Effect of the Non-phase-change Gas on the Atmospheric CO<sub>2</sub> Decompression Capture Characteristics by Cryogenic Heat (Formulation Based on Unsteady Lumped Parameter System Analytical Model and Temporal Change of Various Quantities under Reference Analytical Conditions)

Improved compensation networks for dynamic wireless power transfer in a multi-inductor track

PurposeThe purpose of the study is to design the compensation network of a dynamic wireless power transfer system, considering the movement of the receiving coil along an electrified track with a large number of inductors buried on the road.Design/methodology/approachA finite element model has been developed to calculate the self-inductances of transmitting and receiving coils as well as the mutual inductances between the receiving coil and the transmitting ones in the nearby and for various relative positions. The calculated lumped parameters, self-inductances and mutual inductances depending on the relative positions between the coils, have been considered to design the compensation network of the active coils, which is composed of three capacitive or inductive reactances connected in the T form. The optimal values of the six reactances, three for the transmitting coils and three for the receiving one, have been calculated by resorting to the Genetic Algorithm NSGA-II.FindingsIn this paper, the results obtained by means of the optimizations have broadly discussed. The optimal values of the reactances of the compensation networks show a clear trend in the receiving part of the circuit. On the other hand, the problem seems very sensitive to the values of the reactances in the transmitting circuit.Originality/valueDynamic wireless power transfer system is one of the newest ways of recharging electric vehicles. Hence, the design of compensation networks for this kind of systems is a new topic, and there is the need to investigate possible solutions to obtain a good performance of the recharging system.

Frequency Domain Thermal Analysis of Future Spacecraft and Systems

Future space telescopes require tight thermomechanical stability. The thermal analysis may be based on a nonlinear steady solution with a superimposed linear transient perturbation. This linearity allows frequency domain (FD) thermal solutions that retain high resolution when scaled. Linearity allows generality through superposition. Linear superelements can represent subsystems and thereby simplify interfaces. The (rare) prior spacecraft FD thermal analyses have been with N×N system matrices, converting lumped parameter (LP) time domain models to FD. This paper includes continuously distributed resistance and capacitance elements. Exact distributed element results differ greatly from LP renditions at higher frequency. Two FD methods are used together: a 2×2 matrix method with a bridge to an N×N matrix method. The 2×2 method allows the combination of elements in series/parallel configurations into overall elements. The 2×2 matrices can then be used in an N×N system matrix formulation. This paper includes FD analysis and programming methods, FD testing methods, and model to data comparisons. A thermal signal generator was developed for FD testing.

Correlation of the properties of quasi-ternary Ni-based superalloys computed from DFT to elemental properties enabling predictions on the behavior of metallic alloying elements

Research on multicomponent superalloys derived from Ni3Al shows that certain elemental additions congregate at the boundary of the γ/γ′ interface while certain others partition into either the γ or the γ′ phases. Such microstructural features have a strong bearing on the performance of the superalloy. However, no established correlations exist as of now, that can help predict such a behavior. The present work addresses this issue by examining the properties of the quasi-ternary alloys of Ni3Al and brings out correlations to selected lumped parameters related to the elemental properties. Computation of thermodynamic properties of 11 alloys of quasi-ternary Ni24Al7X system was carried out from first principles using Wien 2k and Gibbs2 code on a supercell constructed with 32 atoms. Elements X substituted at the Al site are selected from the information derived from the literature. Systematic variations are shown to occur in compressibility and heat of formation ΔH of the alloys with average electron concentration, elemental radii and/or electronegativity of the constituent elements in the alloys. Analysis of the data computed for a supercell on ΔH of quasi-ternary Ni31X alloys of Ni (the γ phase) and the ΔH of Ni24Al7X alloys (the γ′ phase) explains the possible reason for the enrichment of elements like Re and W at the γ/ γ′ interface. Trends in the observed correlations correctly predict the experimental observations on alloying effects reported from spectroscopic studies on quasi-ternary alloys of Ni3Al. The scope of predicting alloying behavior based on basic elemental properties gains significance in the design of superalloys.

Study of operation mode and breakdown characteristics for multi-stage gas switch

Multi-stage gas switches (MSGSs) are widely used in megavolt pulsed power systems due to their advantages of high withstand voltage, fast establishing time and relatively high operating frequency. Multiple operation modes, which are induced by the different breakdown sequences at each stage, are found to affect the breakdown characteristics of the gas switch. Based on the theoretical analysis of the working principle, the classification of the operation mode and the factors determining the operation mode of the MSGS are proposed. Methods for investigating the output waveform for MSGS are established by simulating lumped parameters and studying the breakdown time sequence of individual stages. In comparison with the intended mode of operation, the disadvantages of the unintended modes of operation for MSGS, including error-breakdown and non-triggering mode, are revealed. For unintended modes, the distortion of the output waveform, which determines the efficiency of energy transmission through the switch and the increased delay time jitter, which determines the synchronization of the gas switch, are further investigated. The possibility of non-triggering and its mechanism on surface flashovers induced by drifting electrons are also analyzed. Based on this study, design principles and methods are proposed to ensure the intended operation of the MSGS.

Stable and Radio-Isotopic tools to understand the groundwater recharge and dynamics of CHASHMA-Mianwali area, Pakistan

The study conducted on “Chashma-Mianwali” area to investigate the impact of canals, lake and rivers flowing through the area on groundwater recharge and dynamics of the area. Isotopic and noble gases data suggested localize impacts of canals, lake and river on groundwater recharge. Groundwater residence time using Tracer Lump Parameter Model (LPM), and Chloroflourocarbons (CFCs) data suggest a very young water in the range of 14–59 years. The real and filtration velocities of groundwater were found to be 22.2 cm/day and 10.94 cm/day, respectively, in south-west direction and in-situ effective porosity of the aquifer was 49.3 %. The hydraulic conductivity of the aquifer was estimated with average value of 143 m/day with Transmissivity (T) of 43,127 m2/day.

Evaluating head impact intensities and accelerations using flexible wearable sensors for traumatic brain injury assessment

In response to the significant health threat posed by Traumatic Brain Injury (TBI) resulting from sudden collisions on the head, there is an urgent need for timely assessment and evaluation. With the wide applications of wearable devices in health monitoring, here we report a flexible and wearable smart headband based on a polyvinylidene fluoride (PVDF) sensor to evaluate the impact force and acceleration for TBI assessment. Based on the electromechanical coupling characteristics of PVDF, a lumped parameters model of an equivalent circuit was obtained by a system identification method, which accurately transforms the output signal of the PVDF sensor to the impact force for TBI assessment of focal brain damage. Besides, a drop tower was used to impose different impact intensity levels on a dummy head wearing the smart headband; the results (MSE< 0.018) of transformed impact force show the universal applicability of the model. Moreover, the correlation analysis results show that the impact force has a positive correlation (R>85 %) with impact acceleration at the head center of gravity, which enables the TBI assessment of diffuse brain damage. This smart headband can be used for real-time monitoring of human head impact and has excellent potential for application in medical and sports devices.

Trenched microwave resonator integrated with porous PDMS for detection and classification of VOCs with enhanced performance

Microwave resonators combined with polymer absorption layers are widely used in volatile organic compound (VOC) detection based on their variable resonant frequencies. However, the response time is limited due to the polymer’s slow volumetric absorption of VOC molecules. By constructing a porous structure in Polydimethylsiloxane (PDMS), resulting in reduced the response time to as short as 71.1%. To mitigate the sensitivity decline caused by the porous PDMS, a trenched-substrate complementary split-ring resonator (CSRR) is proposed for enhancing the interaction between the electromagnetic fields (EMFs) and the porous PDMS with VOCs. The removal of the substrate beneath CSRR’s sensing region enhances the effective EMF, increasing frequency and amplitude sensitivities up to 175.5% and 137.8%, respectively. Responses to four common VOCs by the sensor show a maximum sensitivity of 217 Hz/ppm and a minimum limit of detection of 295 ppm. Additionally, resonant parameters and extracted lumped parameters are utilized to establish two decision-tree-based VOC classification models, achieving high accuracies of 98.71% and 99.59%, respectively. And the latter one fully utilizing responses throughout the swept band, proves superior in identifying similar substances. This sensor technology helps promote the sensitive detection and accurate classification of diverse VOCs.

Lumped parameters models for the stability analysis of rotors supported on gas bearings

In this paper different lumped parameters models are presented for the stability analysis of rotors supported on gas bearings. The analysis is carried out taking into account the damping and stiffness coefficients of journal bearings, calculated with the perturbation method. Lumped parameters models of different complexity are discussed for the description of the main rigid modes of the spindle. In case of symmetric systems, it is shown that the complexity of the model can be reduced by halving the number of the degrees of freedom. The analogy with the single mass approach is demonstrated. The considerations discussed in the paper are preliminary for the stability analysis of more complex systems, such as the ones with non-fixed bushes.

Vibration Characteristics Investigation of Hard-Coated Mistuned Blisk With Multipackets by Lumped Parameter Model

Abstract To improve the performance and reduce the vibration of the mistuned blisk, a novel approach combining hard-coating and multipackets is presented. First, the dynamical models of the blisk without hard-coating and multipackets, the hard-coated mistuned blisk without multipackets, and the hard-coated mistuned blisk with multipackets are established based on the lumped parameter model (LPM). Then, the solved results are compared with those previous literature to validate the feasibility and correctness of the proposed models. Furthermore, the characteristics of the natural frequencies and the vibration responses for the mistuned blisk is investigated by proposed LPMs. Finally, the effect of the hard-coating and multipackets on the vibration characteristics for the mistuned blisk are discussed. The obtained results manifest that the vibration response of the mistuned blisk can be further suppressed when the hard-coating and the multipackets are considered simultaneously compared with only the hard-coating or multipackets considered, which provides useful guidance on the vibration reduction for the mistuned blisk.

Research on modified lumped parameter method in torsional vibration analysis of reciprocating compressor shaft

Abnormal vibrations often occur during the operation of reciprocating compressors under different load conditions. To efficiently and accurately calculate the torsional vibration response of the shafting under various working conditions, a modified lumped parameter method (MLPM) based on finite element mode modification is proposed. MLPM is derived from the lumped parameter method (LPM) and incorporates corrections to the stiffness matrix based on the multi-degree-of-freedom modal calculation using a finite element model. This allows MLPM to combine the high accuracy of finite element method (FEM) with the fast computing speed of LPM. To demonstrate the effectiveness of MLPM, an abnormal vibration compressor equipped with a stepless capacity control system is considered. MLPM is utilized to calculate the torsional natural frequency (TNF) and torsional torque response of the compressor’s shafting. The computed 1st-order TNF error between MLPM and FEM is only 0.20%. In the time domain, the torque response error of MLPM is less than 3.07%, while in the frequency domain, it is less than 0.57%. Moreover, MLPM exhibits a significantly increased calculation speed of more than 95% compared to FEM. By comparing MLPM results with torsional vibration test data, the 1st-order TNF error is found to be less than 0.50%, and the frequency-domain torque response error is no more than 8.91%. Furthermore, MLPM is effectively applied to solve the abnormal vibration problem of the compressor. It proposes a modification plan for the shafting, which successfully avoids torsional resonance and reduces the peak value of the torque response by 54.77%. These results demonstrate that MLPM is highly suitable for practical engineering applications due to its combination of high accuracy and fast computing speed.

Analysis of Centrifugal Machine Load on Block Foundation

In addition to having static load machine foundations receive dynamic load from engine vibrations. Their structure must be able to withstand both loads without failures. This study aims to discuss loads on the machine foundation of a block type machine having a high frequency. The analysis method used lumped parameter system and the foundation dimensions were 6 x 4 x 1 m with a depth of 1 m, with engine frequencies of 1800 and 3000 rpm. The results of this analysis show that the higher the machine foundation was, the smaller the vertical and horizontal amplitude, and rocking amplitude amplitude would be. The value of the natural frequencies of the machine foundation of vertical and horizontal amplitudes got smaller, while the rocking amplitude became bigger. So, the amplitude clearance value of the frequency of 1800 rpm and 3000 rpm met the safety requirements of the machine foundation, namely the maximum vertical amplitude requirement is troublesome to persons, with high frequency machines vertical vibration is 0.002-0.003 and horizontal vibration was 0.004-0.005. Keywords: Machine foundations, amplitude, damping, static load, dynamic load