Lumped Model Research Articles

Numerical simulation of the general rate model of chromatography using orthogonal collocation

Process chromatography is a critical manufacturing step in the purification of biopharmaceutical therapeutics and monoclonal Antibody (mAb) capture using Protein A-chromatography is the most expensive step in the entire production chain. Protein A-chromatography performance is hard to predict due to variations in chromatography column characteristics causing wastage and reduced efficiency. Additionally, it is not yet established how to use Protein A-chromatography optimally in continuous manufacturing. Mechanistic modeling of the chromatography process enables simulation-based optimization of operations to both reduce waste and increase productivity in continuous manufacturing. We present an easy-to-use, yet computationally efficient Python package called Simulation Testbed for Liquid Chromatography (STLC). STLC is a chromatography simulator implementing a solver for the General rate model, a comprehensive mathematical model in the field, and the simplified Lumped kinetic model. STLC uses orthogonal collocation to discretize the spatial domain turning the equations into an algebraic system of ordinary differential equations. The equations are integrated in time with a fixed step length backward Euler method. We evaluate STLC in numerical trials and benchmark against high-resolution references showing high-order convergence. This allows for reduced computation system size making the package a good choice for use in the rapid prototyping of simulated chromatography processes.

A prescribed time attitude control method based on thrust vector control (TVC) nozzle for solid propulsion satellite

With the development of on-orbit missions, solid propulsion technology is applied to the rapid orbital maneuver of satellites. During solid propulsion maneuver, the position change of the mass center caused by the fuel consumption and the installation error of thruster have brought serious attitude disturbances. For this problem, a novel prescribed time attitude control method is proposed in this paper. Firstly, a dynamics model of the solid propulsion micro-satellite is established, while the thrust direction is adjusted by the thrust vector control (TVC) nozzle. Then, a constraint boundary function is constructed to characterize the strict fixation of the thruster operating time and an adaptive fuzzy observer is developed to quickly estimate the lumped model uncertainties. Using the backstepping method, a novel prescribed time attitude control strategy regardless of initial conditions is designed. Simulation results show that the designed controller can achieve the prescribed time convergence of satellite attitude during solid propulsion orbital maneuver, effectively.

A Review on Lumped-Kinetic Modelling Methodologies for an industrial FCCU - riser reactor for catalytic cracking

A comprehensive review of scientific literature on various lumped kinetic models used in modelling FluidisedCatalytic Cracking Units (FCCU) used in the petrochemical industry has been done, along with a brief introductionto the working of FCCU. The most popular four lumped kinetic model has been discussed in detail along with themathematical model and then solved using MATLAB. The modified form of the model that considers axialdispersion has also been discussed. The results of the simulation have been plotted and analysed. A brief overviewof three, five, six, seven, nine, and twelve lumped kinetic models has also been discussed.

Comparative analysis of insulated floating cover of water pit thermal energy storage

Water pit thermal energy storage (PTES) as a sensible heat storage technology has been applied in many places with significant success. The insulated floating cover (IFC) of water pit is the key component of the PTES thermal storage efficiency and accounts for more than half of the total cost of the entire water pit. In this paper, a one-dimensional finite element model (1D FEM) and a zero-dimensional lumped thermal system model (0D LTSM) are established for the composite IFC of PTES, and their respective results are compared with experiments respectively. LTSM results match the FEM resolution results if the LTSM is sufficiently refined by discretized each layer into several sub-systems with their own mass and thermal resistance. In this LTSM, 5 sub-systems are used in the thermal insulation layer, and 2 sub-systems are used in the upper and lower impervious barrier respectively. The results show that the LTSM can accurately describe the transient heat transfer process of the composite IFC. The results of LTSM and FEM are in good agreement with 99.2%, which is about 2.6% different from the experimental results.

Effect of Inadequate Lap Splice Length on the Collapse Probability of Concrete wall Buildings in Malaysia

Background: In recent decades, Malaysia has shown a significant increase in the number of constructed high-rise buildings due to rapid urbanization and an increase in its population. However, due to the country's low seismicity, the majority of such tall buildings and infrastructures have not been designed against seismic actions. Therefore, they do not comply with the required seismic detailing and often suffer from inadequate lap splice length. After the 2015 Sabah earthquake that imposed significant damage to public buildings, the seismic vulnerability of buildings in Malaysia received increasing attention. As a result, researchers have tried to quantify the seismic vulnerability of buildings in Malaysia through the development of fragility curves. Objectives: In Malaysia, most developed seismic fragility curves for buildings have not taken into account the effect of inadequate lap splice length. Therefore, this study investigates to what extent an inadequate lap splice length can alter the concrete wall buildings’ probability of collapse. Methods: Two 25-story concrete wall buildings with an identical plan but different parking levels were selected. Fifteen natural far-field earthquake records were used in the incremental dynamic analysis to calculate the inter-story drift demand and capacities. The inelastic response of beams and columns was simulated through the lumped plasticity model, and that of concrete walls and slabs was taken into account through the fiber-based distributed plasticity model. The effect of inadequate lap splice length in columns was simulated in the finite element models using the proposed method in ASCE/SEI 41-17 code. The developed fragility curves were compared with those established by other researchers for the same buildings. Results: It was observed that seismic-induced damage mostly concentrated on the columns of parking levels while the concrete walls remained in the elastic region. The obtained inter-story drift capacities were all less than 2%. Besides, the inter-story drift capacities of interior frames were less than half of exterior frames. The exterior frame of the building with three parking levels exhibited a larger probability of exceeding the CP limit state than the interior frame. A similar observation was made for the building with five parking levels when the PGA was more than 0.25g. Moreover, the probability of exceeding the CP limit state of the exterior frame with three parking levels was significantly more than that of the exterior frame with five parking levels. A similar observation was made for the interior frames when the PGA was larger than 0.2g. Furthermore, the conducted comparison showed that an inadequate lap splice length could increase the concrete wall buildings’ probability of collapse between 38 to 89%. The increase in the collapse probability of the interior frame with five parking levels was almost twice that of the exterior frame. Conclusion: It was concluded that the inadequate lap splice length could significantly reduce columns’ rotational capacity and result in brittle failure mode and limited residual strength. Besides, the inadequate lap splice length of columns reduced the inter-story drift capacity of investigated buildings and significantly increased their probability of collapse. Therefore, it was strongly suggested to include the effect of inadequate lap splice length in the finite element models when conducting seismic vulnerability studies.

The essential spectrum of periodically stationary pulses in lumped models of short‐pulse fiber lasers

AbstractIn modern short‐pulse fiber lasers, there is significant pulse breathing over each round trip of the laser loop. Consequently, averaged models cannot be used for quantitative modeling and design. Instead, lumped models, which are obtained by concatenating models for the various components of the laser, are required. As the pulses in lumped models are periodic rather than stationary, their linear stability is evaluated with the aid of the monodromy operator obtained by linearizing the round‐trip operator about the periodic pulse. Conditions are given on the smoothness and decay of the periodic pulse that ensure that the monodromy operator exists on an appropriate Lebesgue function space. A formula for the essential spectrum of the monodromy operator is given, which can be used to quantify the growth rate of continuous wave perturbations. This formula is established by showing that the essential spectrum of the monodromy operator equals that of an associated asymptotic operator. Since the asymptotic monodromy operator acts as a multiplication operator in the Fourier domain, it is possible to derive a formula for its spectrum. Although the main results are stated for a particular experimental stretched pulse laser, the analysis shows that they can be readily adapted to a wide range of lumped laser models.

Iterative learning control of a pneumatically actuated lung tumour mimic model for an improvement of PET/CT-imaging

In this paper, a model-based tracking control is proposed for a mechanism dedicated to accurately reproduce the breathing-induced motion of a human lung tumour. In former work, a 3-dimensional mechanism equipped with three pneumatically driven axes has been developed and constructed for this purpose. The overall control structure consists of decentralised axis controller for each pneumatic cylinder with a cascaded structure: A fast inner control loop governs the pressure induced drive force using backstepping techniques, whereas the outer control loop is related to an optimal, robust position control of the cylinder. Additionally, discrete-time iterative learning controllers are utilised to compensate lumped disturbance forces and model uncertainties. The suggested overall control structure has been implemented on the innovative test rig and successfully validated in a clinical framework. The given work represents the basis for future improvements of algorithms regarding PET/CT-imaging as well as radiotherapy.

An experimentally-verified approach for enhancing fluid drag force simulation in vertical oilwell drill strings

ABSTRACT The oilwell drilling fluid flows cause viscous and hydrodynamic forces on drill strings. This effect is ignored or treated as a constant in most drill string models. The present study introduces mathematical models for lateral vibration damping and axial drag forces that are employable in lumped segment drill string models. First, the variables to which drilling fluid-generated forces are most sensitive were identified and the Response Surface Method was applied to design the experiment matrix. The lateral vibration-damping experiments, which were validated using a scaled-down physical model, and the axial drag experiments were done using Fluid-Structure Interaction simulations. The results were statistically analysed to acquire the models and were implemented in a 3D lumped segment bond graph developed using the Newton-Euler formulation and body-fixed coordinates. The results indicate a considerable effect of the extended treatment of damping and axial drag on bending moment fluctuation, wellbore interactions, and weight on bit.

Numerical evaluation of the coupled/uncoupled effects of lower marine riser package and/or blowout preventer with a lower flex joint in a hang-off drilling riser

Lower marine riser package and/or blowout preventer (LMRP/BOP) are key marine riser components. However, they are often oversimplified or ignored in traditional studies, which inevitably causes certain calculation deviations, especially when the risers are in hang-off modes. Considering the full size of LMRP/BOP and rotational stiffness of the lower flex joint (LFJ), a fully coupled multibody model compared with the traditional single lumped mass model, is developed using the self-made finite element method program. Different numerical methods and the results in the literature verify this model's accuracy. The coupled and decoupled effects of the LFJ and the LMRP/BOP in the two numerical models versus LMRP/BOP weight, LFJ rotational stiffness, pipe wall thickness, riser suspension length, and ship heave motion in different running stages are comprehensively studied. Significant differences in the inherent vibration and time-domain characteristics between the two models indicate the coupled effects of the large-diameter LMRP/BOP and the rotational stiffness of LFJ of a hang-off drilling riser during running and installation procedures should not be oversimplified but should be well equivalent and considered for accurate evaluations in ocean engineering.

Study on torsional vibration characteristics and suppression of electric vehicles with dual-motor drive system

The battery electric vehicles with dual-motor coupling drive system have serious torsional vibration problems when the driving torque changes rapidly. This paper targets at reducing the negative effect of the torsional vibration with an active control strategy. The torsional vibration model of the dual-motor coupling drive system is established through the lumped mass method. A four-inertia modeling method which can reflect the powertrain configuration characteristics is proposed, by simplifying the traditional lumped mass model, and the feasibility is verified based on the error comparing of the torsional vibration characteristics between the two models. Combined Kalman filter theory, PID control theory and fuzzy control theory, a real-time self-tuning active control strategy is proposed to compensate motor torque by considering vehicle acceleration as the control input. Finally, the four-inertia model with the control strategy is simulated under such conditions as the torque abrupt change and the C-WTVC driving cycle. The simulation results indicated that the proposed active control strategy performs well in the torsional vibration suppression and the control effect is robust to the different structural parameters.

New Insights for Parasitic Effects of Label-Free Biosensors Based on Capacitive Micromachined Ultrasonic Transducers

Capacitive micromachined ultrasonic transducers (CMUTs) are regarded as an attractive candidate in bio-applications such as imaging and molecule monitoring. However, the previous researches on biochemical sensing are mostly air-coupled application based on a CMUTs array because cell-to-cell mutual radiation and large motional loss in liquid environment are able to produce nonignorable noise. For a CMUTs cell, its characteristics (e.g., electrical, mechanical, and acoustic) are susceptible to parasitic effects owning to the physically capacitive dielectric dispersion, motional damping, and connection loss. Neglecting the parasitic effects on multidomain characteristics of CMUTs leads to significant robustness errors. Furthermore, finite element method (FEM) is not sufficient enough to model such parasitic effects when considering an integrated circuit interface and the evaluation of system responses. This article highlights a lumped element model (LEM) to analyze the behaviors of a label-free biosensor based on a single CMUTs cell directly operating in liquid. We successfully explore the performance of the biosensor with different types of parasitic effects in transient and frequency domains through LEM and FEM. The parasitic effects on mass loading of sensing layer and biomolecule such as deoxyribonucleic acid (DNA) and Immunoglobulin G (IgG) probes are predicted by LEM based on their surface mass densities. The proposed approach is capable of analyzing the variation’s margin of CMUTs-based biosensors to improve robustness for parasitic extraction in liquid.

Effect of Uniformly Distributed Parameter Line Models on the Evaluation of PV Curves and of the Maximum Loading Condition

PV curves are generally obtained by considering lumped models of transmission lines. This approximated model can yield an inaccurate estimation of the maximum loading condition of the system. This letter shows that accuracy can be improved by considering line models with uniformly distributed parameters. Analytical evaluations of the PV curve and of the voltage collapse point of a two-bus system are obtained by applying the Ossanna's theorem. Then the impact of different line models on large-scale systems is evaluated through a continuation power flow analysis of a real-world model of the Sicilian transmission system including the Sicily-Malta 120 km cable connection.

Review of Modeling Techniques for Analysis and Assessment of RC Beam-Column Joints Subjected to Seismic Loads.

Beam-column connections are the most critical components of reinforced concrete (RC) structures. They serve as a load transfer path and take a significant portion of the overall shear. Joints in RC structures constructed with no seismic provisions have an insufficient capacity and ductility under lateral loading and can cause the progressive failure of the entire structure. The joint may fail in the shear prior to the connecting beam and column elements. Therefore, several modeling techniques have been devised in the past to capture the non-linear response of such joints. Modeling techniques used to capture the non-linear response of reinforced-concrete-beam-column joints range from simplified lumped plasticity models to detailed fiber-based finite element (FE) models. The macro-modeling technique for joint modeling is highly efficient in terms of the computational effort, analysis time, and computer memory requirements, and is one of the most widely used modeling techniques. The non-linear shear response of the joint panel and interface bond-slip mechanism are concentrated in zero-length linear and rotational springs while the connecting elements are modeled through elastic elements. The shear response of joint panels has also been captured through rigid panel boundary elements with rotational springs. The computational efficiency of these models is significantly high compared to continuum models, as each joint act as a separate supe-element. This paper aims to provide an up-to-date review of macro-modeling techniques for the analysis and assessment of RC-beam-column connections subjected to lateral loads. A thorough understanding of existing models is necessary for developing new mechanically adequate and computationally efficient joint models for the analysis and assessment of deficient RC connections. This paper will provide a basis for further research on the topic and will assist in the modification and optimization of existing models. As each model is critically evaluated, and their respective capabilities and limitations are explored, it should help researchers to improve and build on modeling techniques both in terms of accuracy and computational efficiency.

Automatically generated detailed and lumped reaction mechanisms for low- and high-temperature oxidation of alkanes

In this work, we present a methodology on automatic generation of predictive lumped sub-mechanisms for normal and branched alkanes. This methodology aims at obtaining lumped reaction mechanisms that preserve the chemical behavior of each reaction class in the detailed model. To achieve this goal, detailed sub-mechanisms for combustion of alkanes are generated by employing an updated version of the MAMOX++ software developed in this work; recent progress in the low-temperature reaction classes and rate rules are incorporated into the updated software. Instead of computing the selectivities of several primary products with MAMOX++ and fitting the selectivities between the detailed and lumped models, this work proposes a new methodology to generate the lumped sub-mechanisms for fuel molecules. The stoichiometric parameters and the reaction rates for each reaction class in the lumped sub-mechanism are fitted to match those in the detailed model. Based on the present methodology, both the detailed and lumped sub-mechanisms for normal C5C10 alkanes and branched C5C8 alkanes, that is for 15 different fuels, are automatically generated and merged into a base chemistry model (i.e. AramcoMech 2.0), respectively. The detailed and lumped models are validated against the experimental data in the literature. The automatically generated detailed models for alkanes are able to capture the experimental targets across a wide range of conditions, demonstrating the robustness of the reaction classes and rate rules adopted. The lumped models for normal alkanes have similar performance to their respective detailed models, and are able to predict the oxidation behavior of normal alkanes. However, prediction deviations between the detailed and lumped models for branched alkanes are shown to be slightly greater.

LQR Active Control of Fractional-Order Pantograph-Catenary System Based on Feedback Linearization

Fractional-order calculus has exclusive advantages in modeling the viscoelastic components with obvious fractional-order characteristics such as air springs and metal rubbers in the pantograph structure. In this paper, the air spring is tested, and fractional-order calculus is applied to the modeling of pantograph-catenary system of the high-speed train. The parameter identification method of fractional-order derivative is analytically derived. The traditional lumped mass model is improved and a coupling two-degree-of-freedom model of the fractional-order pantograph-catenary system is established. The fractional-order derivative term in the pantograph-catenary model is approximately calculated by the Oustaloup filter algorithm. Taking the time-varying nature into consideration, the catenary is treated as an extended variable to obtain an augmented model. On this basis, the system is linearized based on differential geometry theory, and an LQR controller is designed to control the pantograph-catenary system. The feedback linearized LQR control and PID control are used to control the same type of traditional pantograph, and the results are compared. Meanwhile, the control effects of feedback linearized LQR control under different pantograph parameters and at different train speeds are analyzed. The results show that the feedback linearized LQR control can present a much better control performance than PID control, and the pantograph-catenary contact force and pantograph head vibration amplitude are both reduced obviously. Even at different train speeds or under different pantograph parameters, it can also effectively reduce these control indexes and provide more robust control performance. These results help to put forward new control ideas and theoretical basis for the vibration control of the pantograph-catenary or similar dynamical system.

A thermally activated VO2-based attenuator with SRR structure

To meet the requirement of blocking unwanted or interfering signals in modern communication systems, wideband phased-array antenna systems, and 5G mobile communications, we proposed a radio frequency (RF) attenuator based on a split ring resonator (SRR) that used a phase change material (PCM) vanadium dioxide (VO2). The SRR was transformed into a thermally activated attenuator by depositing a 120 nm VO2 thin film between the two gold rings of an SRR. We achieved an obvious attenuation (about 18 dB) at 3.55 GHz when the temperature increased from room temperature to 100 °C due to the dielectric constant drop and wide resistance variation of VO2 thin film during the phase change process. At the same time, we observed a hysteresis property on the S parameters due to the resistance hysteresis of VO2 during the heating and cooling process both in the theoretical and experimental results. Finally, considering the resistance of the VO2 thin film between two gold rings, we proposed a modified lumped RLC circuit model for the VO2-based RF attenuator.

Modeling thermal runaway of lithium-ion batteries with a venting process

Thermal runaway poses a critical challenge for the safety of electric vehicles powered by lithium-ion batteries. A series of drastic exothermic reactions take place with gas generation during thermal runaway, making it challenging to accurately model the process. In this work, we present a reliable lumped thermal runaway model by incorporating heat transfer and gas generation reactions based on an experimentally kinetic analysis. The proportions of reactants in 18,650 lithium-ion batteries are determined by disassembling the batteries and weighing the components, while the reaction frequencies and activation energies of gas generation reactions are identified through the thermal gravity analysis tests on the anode and cathode components using Kissinger’s method. The reaction kinetic equations are then combined with energy and mass conservation equations to form the thermal runaway model, which is validated against accelerating rate calorimeter tests. Simulation results show that it is the pressure rather than temperature that triggers the ejection. Therefore, gas generation that can depict the internal gas change should be included in the model to accurately predict the time of the battery venting. Moreover, it is revealed that when the safety pressure increases from 1600 to 2400 kPa, although the venting moment delays from 4294 to 4465 s, the thermal runaway takes place 54 s earlier. Hence, an appropriate safety pressure design range is suggested to be 1800–2200 kPa. This work develops a robust thermal runaway model and offers new insights into the mechanisms of thermal runaway, which provides valuable guidance for the thermal safety design of lithium-ion batteries.

Coupled acoustic resonance for wave control and sensing

Coupled resonance enables many intriguing physical phenomena, leading to wave control and sensing. This review discusses fundamental understanding of coupled resonance by providing detailed comparison between lumped parameter-based models including coupled mode theory (CMT) and harmonic oscillator model (HOM). While reviewing recent progress in research concerning coupled resonance, emerging research areas related to coupled resonance are discussed.

The Effect of Training Data Series Length on the Performance of the Tank Model for Transforming Rainfall into Runoff Data Series

The Tank model by Sugawara is included in the lumped model category. As with other types of lumped models, the effectiveness of the application of the Tank model is largely determined by the parameter optimization method applied and the quantity of training data involved in the calibration process. This article proposes the Tank-DE model to transform rain data series into discharge in a watershed. The Tank-DE model is built from a combination of a simulation equation system based on the Tank model and a multi-parameter optimization equation system based on the Differential evolution (DE) Algorithm. This article also examines the sensitivity analysis of the model to study the effect of the length of the training data series involved in the calibration process on the predictive discharge quality generated by the Tank-DE model. Thus, the minimum length of the training data series can be recommended, related to the application of the model. The results of the analysis show that the Tank-DE model can present the relationship between rainfall data series and daily period discharge very well. The results of the sensitivity analysis show that there is an indication that the longer the training data series, the more quantitatively positive impact on the performance of the model. The calibration process involving a training data set for 1 year produces a very good value of the coefficient of determination (r2 = 0.94), but the indicator decreases drastically at the validation stage. The calibration process involving a relatively long training data series produces a more consistent value of the coefficient of determination. This indicates that the Tank-DE model can be an alternative solution to solve the problem of scarcity of discharge data series which is a classic problem in water resource development activities.

Systematic Lumped Modeling of all-Vanadium Redox Flow Batteries

Recently, the lumped models for all-vanadium redox flow batteries (VRFBs) have gained a lot of interest among battery designers for system-level studies because of their simplified mathematical approach with the minimum computational procedure. In this paper, we, therefore, aim to systematically derive a reduced lumped mathematical model for VRFB. In essence, we carry out an analysis to arrive reduced lumped model by orderly reducing the distributed three-dimensional (3D) model to one dimensional (1D) model by providing justified conditions/assumptions. Subsequently, from the analytical solution of 1D, we obtain the expression for lumped model. A further analysis and reduction of this analytical lumped model are carried out to obtain a reduced lumped model. We then verify both this analytical and reduced lumped model by comparing the charge-discharge predictions of the lumped model with the distributed model of higher dimensions at different values of current density. A good agreement between the model predictions is obtained, which indicates that the derived lumped model can capture the behavior of a higher dimensional model with high accuracy and without compromising internal physics.