Lumped Parameter Approach Research Articles

Development of a PWR-W GOTHIC 3D model for containment accident analysis

The confinement of radioactive material in a nuclear power plant, including the discharge control and the release minimization, is a fundamental safety function to be ensured in a design basis accident (DBA).For plant licensing analysis, the containment is usually modeled with a lumped parameter approach. Inherent to the lumped parameter approach is the assumption that within each region the fluid is well mixed. However, the containment is a large building with a complex configuration and it is distributed in several compartments that avoid the well mixing of the fluid and could have three-dimensional effects that affect the thermal–hydraulic behavior. Therefore, the commonly used lumped parameter approach may not be enough to capture these effects.In order to study these assumptions, four generic PWR containment models have been developed for Mass and Energy (M&E) release analysis with GOTHIC 8.0 (QA) code, three of them being subdivided and the fourth one is a lumped parameter model. A Large Break LOCA is simulated in order to compare the thermal–hydraulic behavior of the different models. The results show a high dependence on the three-dimensional phenomena, especially the temperature and velocity distribution. In contrast, the pressure evolution is qualitatively similar in all models with small quantitative differences.

Fluid dynamics of heart valves during atrial fibrillation: a lumped parameter-based approach

Atrial fibrillation (AF) consequences on the heart valve dynamics are usually studied along with a valvular disfunction or disease, since in medical monitoring, the two pathologies are often concomitant. Aim of the present work is to study, through a stochastic lumped-parameter approach, the basic fluid dynamics variations of heart valves, when only paroxysmal AF is present with respect to the normal sinus rhythm in absence of any valvular pathology. Among the most common parameters interpreting the valvular function, the most useful turns out to be the regurgitant volume. During AF, both atrial valves do not seem to worsen their performance, while the ventricular efficiency is remarkably reduced.

Dynamic Analysis of Offset Printing Press Gear-Cylinder-Bearing System under Time-Varying Meshing Stiffness Effect

This study propose a new nonlinear model for offset printing press gear-cylinder-bearing system by the lumped parameter approach. The multi-DOF model consists of helical gear pairs and spur gear pairs with time-varying meshing stiffness. Bearing and shaft flexibilities are include in the model as well. The equations of motion are obtained by Darren Bell principle and Runge-Kutta numerical method is used to slove the equations of motion. The results show that meshing stiffness and bearing stiffness significantly affect critical speed, vibration acceleration and meshing force. Multi-body dynamics software are applied to compare with lumped parameter model. The results show that there are many similarities in different aspects. Results of experimental study on offset printing press are also presented for validation of different models. After Discrete Fourier Transform, the graphics display that acceleration peaks frequencies are an integer multiple of the gear mesh frequency. It demonstrate that mechanical vibration is mainly from gear transmission system at high printing speed and gear transmission system lead to nonlinear vibration. This work provide a foundation for further improvement of the dynamics of gear system.

Evaluation of passive autocatalytic recombiners operation efficiency by means of the lumped parameter approach*

Abstract The problem of hydrogen behavior in containment buildings of nuclear reactors belongs to thermal-hydraulic area. Taking into account the size of systems under consideration and, first of all, safety issues, such type of analyses cannot be done by means of full-scale experiments. Therefore, mathematical modeling and numerical simulations are widely used for these purposes. A lumped parameter approach based code HEPCAL has been elaborated in the Institute of Thermal Technology of the Silesian University of Technology for simulations of pressurized water reactor containment transient response. The VVER-440/213 and European pressurised water reactor (EPR) reactors containments are the subjects of analysis within the framework of this paper. Simulations have been realized for the loss-of-coolant accident scenarios with emergency core cooling system failure. These scenarios include core overheating and hydrogen generation. Passive autocatalytic recombiners installed for removal of hydrogen has been taken into account. The operational efficiency of the hydrogen removal system has been evaluated by comparing with an actual hydrogen concentration and flammability limit. This limit has been determined for the three-component mixture of air, steam and hydrogen. Some problems related to the lumped parameter approach application have been also identified.

A dynamic model of a passively cooled small modular reactor for controller design purposes

An analytical dynamic model for a passively cooled small modular reactor (SMR) is developed using a state-variable lumped parameter approach. Reactor power is represented by the generation time formulation of the point kinetics equations with a single combined neutron precursor group. The heat transfer process in the core is described via an overall heat transfer coefficient by defining two coolant lumps paired to a single fuel lump. In addition, a thermal–hydraulics model for single-phase natural circulation is incorporated. For the helical-coil steam generator, a moving-boundary model including subcooled, two-phase, and superheated regions is utilized. Finally, the hot leg riser and downcomer regions are expressed by first-order lags. The performance of the overall system described by ordinary differential equations (ODEs) is evaluated by the Simulink dynamic environment and directly using a MATLAB ODE solver recommended for stiff systems. Simulation results based on NuScale SMR design data show that the initial steady-state values for 100% power are within range of the design data and the model can predict the system dynamics due to typical perturbations, e.g., control rod movement and change in feedwater mass flow rate and temperature. The model developed in this work can be utilized as a foundation for designing and testing a suitable control algorithm for reactor thermal power.

Power-frequency control of hydropower plants with long penstocks in isolated systems with wind generation

In this paper the power-frequency control of hydropower plants with long penstocks is addressed. In such configuration the effects of pressure waves cannot be neglected and therefore commonly used criteria for adjustment of PID governors would not be appropriate. A second-order Π model of the turbine-penstock based on a lumped parameter approach is considered. A correction factor is introduced in order to approximate the model frequency response to the continuous case in the frequency interval of interest. Using this model, several criteria are analysed for adjusting the PI governor of a hydropower plant operating in an isolated system. Practical criteria for adjusting the PI governor are given. The results are applied to a real case of a small island where the objective is to achieve a generation 100% renewable (wind and hydro). Frequency control is supposed to be provided exclusively by the hydropower plant. It is verified that the usual criterion for tuning the PI controller of isolated hydro plants gives poor results. However, with the new proposed adjustment, the time response is considerably improved.

Fully Coupled Dynamic Model of Thomson’s Levitating Ring

The complete electromagnetic-mechanical-thermal modeling approach is demonstrated on the Thomson’s levitating ring experiment. This problem, but with a different set of parameters, was also described by Laithwaite and defined by Freeman and Lowther as TEAM17 problem. This paper presents its most complete solution. The factors for determining the vertical displacements and influence of the height of the ring are explained. The whole apparatus is explained in detail so that an accurate computer model can be made. The model introduced is validated against measurements and transient finite- element method (FEM) solvers. All the results prove the applicability of using steady-state FEM analysis with lumped parameter approach for a fast and effective fully coupled modeling.

A non-continuum lumped-parameter dynamic model applied to Indian traffic

Dynamic traffic flow models are essential for obtaining information about the time evolution of variables describing the traffic flow phenomena and have a critical role in the development and implementation of real-time applications such as Intelligent Transportation Systems. Macroscopic traffic flow models that treat the traffic as a continuum are preferred for such applications. But, existing macroscopic models characterize homogeneous traffic, and may not be directly applicable to capture the vehicle heterogeneity seen on Indian roads. To address this issue, a non-continuum macroscopic dynamic traffic flow model based on the lumped-parameter approach was developed in this study. The model was developed based on the conservation of vehicles equation and a dynamic speed equation, incorporating an empirically developed traffic stream model, which is an important contribution of this study. Using this model, an estimation scheme has been developed based on the Kalman filtering technique to estimate traffic states in real time. The proposed scheme was implemented and corroborated for the heterogeneous traffic conditions existing in India. The performance of this scheme has been evaluated and the results obtained have been found to be promising.

Nonlinear dynamic properties of hydraulic suspension bushing with emphasis on the flow passage characteristics

Hydraulic bushings, which are often employed in vehicle suspension systems, exhibit significant excitation-dependent properties. However, previous analyses were mainly based on the linear system theory. To overcome this void, nonlinear characteristics of common hydraulic bushing configurations are examined in this article, with focus on the component properties as excited by sinusoidal or step displacements of various amplitudes. First, a nonlinear model for a laboratory prototype with a long passage and a short passage (in parallel) is developed using a lumped-parameter approach. Then the system parameters and nonlinearities are identified using experimental and computational methods, with an emphasis on characterization of the flow passage resistances. Steady-state harmonic and transient step experiments are conducted on the prototype, and the dynamic pressures inside two fluid chambers and the force transmitted to the base are measured. Numerical solution of the nonlinear model shows that the proposed model predicts both steady-state sinusoidal responses and transient responses well for single-passage and dual-passage configurations; significant improvement over a corresponding linear model is observed. Finally, approximate analytical and semi-analytical solutions of the nonlinear model are obtained by using the harmonic balance method.

Tilting-Pad Journal Bearings With Active Lubrication Applied as Calibrated Shakers: Theory and Experiment

In recent years, a continuous research effort has transformed the conventional tilting-pad journal bearing (TPJB) into a mechatronic machine element. The addition of electromechanical elements provides the possibility of generating controllable forces over the rotor as a function of a suitable control signal. Such forces can be applied in order to perform parameter identification procedures “in situ,” which enables evaluation of the mechanical condition of the machine in a noninvasive way. The usage of a controllable bearing as a calibrated shaker requires obtaining the bearing specific frequency dependent calibration function, i.e., the transfer function between control signal and force over the rotor. This work presents a theoretical model of the calibration function for a TPJB with active lubrication. The bearing generates controllable forces by injecting pressurized oil directly into the bearing clearance. The injected flow is controlled by means of a servovalve. The theoretical model includes the dynamics of the hydraulic system using a lumped parameter approach, which is coupled with the bearing oil film using a modified form of the Reynolds equation. The oil film model is formulated considering an elastothermohydrodynamic lubrication regime. New contributions to the mathematical modeling are presented, such as the inclusion of the dynamics of the hydraulic pipelines and the obtention of the bearing calibration function by means of harmonic analysis of a linearized form of the controllable bearing constitutive equations. The mathematical model is used to study the relevance and effects of different parameters on the calibration function, aiming at providing general guidelines for the active bearing design. Finally, experimental results regarding the calibration function and the usage of the studied bearing as a calibrated shaker provide insight into the possibilities of application of this technology.

Impact of atrial fibrillation on the cardiovascular system through a lumped-parameter approach.

Atrial fibrillation (AF) is the most common arrhythmia affecting millions of people in the Western countries and, due to the widespread impact on the population and its medical relevance, is largely investigated in both clinical and bioengineering sciences. However, some important feedback mechanisms are still not clearly established. The present study aims at understanding the global response of the cardiovascular system during paroxysmal AF through a lumped-parameter approach, which is here performed paying particular attention to the stochastic modeling of the irregular heartbeats and the reduced contractility of the heart. AF can be here analyzed by means of a wide number of hemodynamic parameters and avoiding the presence of other pathologies, which usually accompany AF. Reduced cardiac output with correlated drop of ejection fraction and decreased amount of energy converted to work by the heart during blood pumping, as well as higher left atrial volumes and pressures are some of the most representative results aligned with the existing clinical literature and here emerging during acute AF. The present modeling, providing new insights on cardiovascular variables which are difficult to measure and rarely reported in literature, turns out to be an efficient and powerful tool for a deeper comprehension and prediction of the arrythmia impact on the whole cardiovascular system.

Study on dynamic characteristics and load sharing of a herringbone planetary gear with manufacturing errors

In this paper, a new and generalized dynamic model for a herringbone planetary gear train (HPGT) is proposed to investigate the free and forced vibration characteristics, as well as load sharing characteristics by employing the lumped-parameter approach. The proposed model takes into account manufacturing eccentric errors of the components and tooth profile errors of all gears. The model can be used for the vibration performance and dynamic load sharing analysis of the HPGT with different types of manufacturing errors and arbitrary number of planets. The free and forced vibration, as well as the load sharing of an HPGT with three planets are numerically computed with the model presented, and these are analyzed respectively in time domain and frequency domain. The effects of the manufacturing eccentric error and tooth profile error as well as component float on load sharing are discussed respectively. Results indicate that manufacturing errors have an impact on dynamic characteristics and load sharing. The float can significantly reduce the load sharing coefficient of the system.

Validation of special nodalisation features for lumped-parameter injection modelling based on MISTRA facility tests from ISP-47 and SARNET

This paper is a continuation of a previously published work regarding application of lumped-parameter code COCOSYS to the containment atmosphere mixing in the presence of jet/plume gas injection. The aim of the previous study was to develop a nodalisation scheme for satisfactory simulation of MISTRA M5 experiment. For this paper the aim was expanded to include the demonstration of nodalisation applicability to different experimental sequence. The task was defied to simulate additional MISTRA facility experiment using the same (except the differences caused by different experimental conditions, e.g., injection diameter) nodalisation scheme.The paper presents results of the simulation of two MISTRA facility experiments – M5 from the SARNET spray benchmark and one test from the International Standard Problem No. 47. Presented simulations were performed using lumped-parameter code COCOSYS with the same enhanced nodalisation scheme. Lumped-parameter code provided reasonable results in both cases. Nodalisational features employed to enhance plume injection simulation in lumped-parameter approach successfully mitigated inherent limitations of this approach in gas mixing modelling.

Effects of refrigerant charge and structural parameters on the performance of a direct-expansion solar-assisted heat pump system

The direct-expansion solar-assisted heat pump (DX-SAHP) is widely studied as a refrigeration system, which can supply hot water for domestic use during the whole year. The system refrigerant charge and structure parameters are believed to have a great effect on the cycling thermal performance. The refrigerant mass charge including two-phase and single-phase in heat exchangers and pipes is calculated with distributed and lumped parameter approach mathematical models, respectively. Based on the system simulation program, the refrigerant distribution characteristics and system performance under varied structural parameters are obtained. The mathematical calculation results show that the 70%–80% refrigerant charge exists in the condenser and collector; the optimum refrigerant charge, solar collector area, condenser pipe length and condenser internal diameter for the system are 1.65–1.75 kg, 6.0 m2, 70 m and 9 mm, respectively. In the optimum parameters, the better system performance and feasible cost can be achieved.

Transit time determination for a riverbank filtration system using oxygen isotope data and the lumped-parameter model

The mathematical description of the lumped-parameter Dispersion Model is presented, and its use for estimating transit time and proportion of river water in a riverbank filtration system on Szentendre Island (in the Danube River, Hungary) is assessed by applying stable oxygen isotope data. The modelling approach could only be used to analyse single oxygen-isotope peaks observed during a 6-month-long time series, because the mean input (Danube) concentration was very close to the output (well) concentration. The water level in the Danube varied, but the lumped-parameter approach is only applicable for steady-state conditions. Isotope data observed during quasi steady-state hydraulic conditions selected at medium and higher water levels were modelled. At low water levels the method could not be used because the 18O content of the Danube water and of collector wells was similar.Editor D. Koutsoyiannis; Associate editor M.D. FidelibusCitation Kármán, K., Maloszewski, P., Deák, J., Fórizs, I. and Szabó, C., 2014. Transit time determination for a riverbank filtration system using oxygen isotope data and the lumped-parameter model. Hydrological Sciences Journal, 59 (6), 1109–1116. http://dx.doi.org/10.1080/02626667.2013.808345

SIGNIFICANCE OF INCORPORATING HETEROGENEITY IN A NON-CONTINUUM MACROSCOPIC MODEL FOR DENSITY ESTIMATION

The heterogeneity of traffic and the lack of lane discipline on the roads in India and other developing countries add complexity to the analysis and modeling of traffic. It is generally believed that it is important to take heterogeneity into account in traffic modeling. The aim of the present study is to check the validity of this assumption by analyzing the effect of incorporating heterogeneity in a macroscopic level traffic flow analysis. The application considered is real-time congestion analysis on Indian roads. Traffic density is considered as the congestion indicator. The measurement of density is difficult since it is a spatial parameter. It is usually estimated from other traffic parameters that can be readily measured using available sensors. A model-based estimation scheme using Kalman filtering has been employed to estimate traffic density. A non-continuum macroscopic model was attempted based on the lumped parameter approach. All the traffic variables were quantified without considering traffic lanes in order to take into account the lack of lane discipline. The effect of heterogeneity has been studied by incorporating static values of Passenger Car Units (PCU), dynamic values of Two Wheeler Units (TWU) and considering different classes of vehicles explicitly in the modeling process. The proposed estimation schemes without and with heterogeneity have been compared. The results have been corroborated using data collected from a road stretch in Chennai, India. The study shows that the significance of incorporating heterogeneity into the modeling of mixed traffic at the macroscopic level was not very significant.

A Model for the Prediction of Thermal Response of Bone in Surgical Drilling

This paper develops a mathematical model for predicting the thermal response in the surgical drilling of bone. The model accounts for the bone, chip, and drill bit interactions by providing a detailed account of events within a cylindrical control volume enveloping the drill, the cut bone chip within the drill bit flute, and the solid bone. Lumped parameter approach divides the control volume into a number of cells, and cells within the subvolumes representing the drill solid, the bone chip, and the bone solid are allowed to interact. The contact mechanics of rough surfaces is used to model chip–flute and chip–bone frictional interaction. In this way, not only the quantification of friction due to sliding contact of chip–flute and chip–bone rough surface contact is treated but also the contact thermal resistances between the rubbing surfaces are included in the model. A mixed combination of constant and adaptive mesh is employed to permit the simulation of the heat transfer as the drill bit penetrates deeper into the bone during a drilling process. Using the model, the effect of various parameters on the temperature rise in bone, drill, and the chip is investigated. It is found that maximum temperature within the bone occurs at the location adjacent to the corner of the drill-tip and drill body. The results of the model are found to agree favorably with the experimental measurements reported within the existing literature on surgical drilling.

A novel approach for predicting the operation of external gear pumps under cavitating conditions

This paper addresses the problem of predicting the effects of gas cavitation in fluid power components, accounting for the dynamic features of gas (including free air and vapour) release and adsorption. Several approaches to evaluate fluid properties under cavitating conditions have been proposed in the past, but those suitable to model hydraulic components with the classic lumped parameter approach do not consider the dynamic nature of the gas cavitation process. Cavitation can have a relevant impact on component operation, particularly for positive displacement machines directly connected to the oil reservoir. With the goal of studying the cavitation effects in hydrostatic units, in this paper a novel model to describe fluid properties – which utilizes a simplified formulation of the Full Cavitation Model – was integrated in an existing lumped parameter model for external gear machines previously developed by the authors’ research team. While the basic formulation of the new fluid model was previously validated for a single closed fluid chamber, the present study extends its formulation for the case of complete systems in which multiple chambers with variable volume are connected to each other. A proper experimental set-up was developed to permit the validation of the proposed model for the case of external gear pumps. Comparisons between measured and simulated instantaneous internal tooth space pressures as well as the outlet flow rates are presented. The significance of the proposed model is highlighted by comparing its predictions with those obtained using classic models of fluid properties, which cannot predict with accuracy the effects of cavitation.

A multiscale 0-D/3-D approach to patient-specific adaptation of a cerebral autoregulation model for computational fluid dynamics studies of cardiopulmonary bypass

Neurological complication often occurs during cardiopulmonary bypass (CPB). One of the main causes is hypoperfusion of the cerebral tissue affected by the position of the cannula tip and diminished cerebral autoregulation (CA). Recently, a lumped parameter approach could describe the baroreflex, one of the main mechanisms of cerebral autoregulation, in a computational fluid dynamics (CFD) study of CPB. However, the cerebral blood flow (CBF) was overestimated and the physiological meaning of the variables and their impact on the model was unknown. In this study, we use a 0-D control circuit representation of the Baroreflex mechanism, to assess the parameters with respect to their physiological meaning and their influence on CBF. Afterwards the parameters are transferred to 3D-CFD and the static and dynamic behavior of cerebral autoregulation is investigated.The parameters of the baroreflex mechanism can reproduce normotensive, hypertensive and impaired autoregulation behavior. Further on, the proposed model can mimic the effects of anesthetic agents and other factors controlling dynamic CA. The CFD simulations deliver similar results of static and dynamic CBF as the 0-D control circuit. This study shows the feasibility of a multiscale 0-D/3-D approach to include patient-specific cerebral autoregulation into CFD studies.

A modeling approach for robotic catheters: effects of nonlinear internal device friction

Recently, robotic surgery systems using passive flexible catheters have been developed for minimally invasive surgical applications – such as in the treatment of atrial fibrillation – where catheter control in the open chamber of the heart is required. The soft, atraumatic construction of these devices help reduce injury to delicate cardiac structures while providing a means of tool placement and control. To provide kinematic and control relationships, various models of continuous catheters have been developed. However, these approaches cannot explain the nonlinear behavior of the catheter when the effect of internal friction is considered. In this paper, we describe a lumped-parameter modeling approach which directly accounts for the effects of internal device friction. The nonlinear model is validated against experimental results from a prototype robotic catheter and is shown to correctly predict the variations in curvature and path-dependent instantaneous behavior observed. Finally, the validated model is used to investigate and describe a set of non-ideal catheter motions observed in practice.