Combined Dynamic Model Research Articles

A Combined Approach for the Analysis of Ocular Fluid Dynamics in the Presence of Saccadic Movements.

One of the main ocular diseases is age-related macular degeneration, actually treated with antibodies injections into the eye. This problem has been faced by computational approaches, taking into account either the influence of the tissues surrounding the vitreous, or the saccades. The aim of this work is to propose a combined fluid dynamic model of the vitreous chamber that analyses the impact of the saccades on the fluid dynamic mechanisms. The ocular vitreous humor was modeled considering liquefaction occurring in presence of age-related macular degeneration. We identified two kinds of boundary conditions, one related to the physiological environment outside the chamber, and one related to the saccades. The scleral hydraulic conductivity was evaluated by means of experimental permeability tests. An exponential decay was used to describe the trend of the scleral hydraulic conductivity with the acting pressure drop. The streamline analysis shows two main stagnant regions on the equatorial plane and peculiar fluid dynamics in absence of saccades. This study demonstrates the major role played by the saccades in determining the fluid dynamic mechanisms inside the vitreous chamber of the eye and represents a powerful tool to investigate vitreous dynamics and its relation to clinical issues.

Numerical and experimental study on noise reduction of concrete LRT bridges

Rolling noise and structure-borne noise radiating from the bridge are two major sources of noise in light rapid transit (LRT) bridges. To control the noise radiation from LRT bridges, an efficient numerical method for noise prediction is needed. In this study, a combined three-dimensional dynamic model and 2.5-dimensional acoustic model were used to investigate noise reduction in a rail and in a U-shaped girder bridge. The effects of three noise mitigation measures on noise control were then compared: installation of a noise barrier, use of a rail pad with a lower stiffness, and use of a floating ladder track. The corresponding noise reduction was investigated using the numerical method. A field test was conducted to validate the noise reduction effects. It was found that the noise barrier was more effective in reducing the rail noise, and the soft rail pad is more effective to control the bridge noise. The floating ladder track can significantly reduce bridge vibration, but the excessive vibration of the ladder track itself became another major noise source. The findings should guide the selection of appropriate mitigation measures for noise reduction in LRT bridges.

Torsional vibration moment analysis of a three-cylinder internal combustion engine

In this study, a combined dynamic and thermodynamic model of a three-cylinder diesel engine has been developed and moments causing torsional vibration of the engine body have been estimated. The model involves motion equations of pistons, connecting rods and crankshaft as well as thermodynamic relations. The heat generation required for the thermodynamic cycle was provided by an algebraic equation established via the Gaussian function. The heat equation was optimised so as to avoid diesel knocking and formation of harmful emissions. The minimisations of pitch and yaw moments were examined via adding counterweights onto the crankshaft. The yaw moment was found to be totally eliminable but the pitch moment was not. According to a coordinate system whose origin is at the mass centre of the engine and its z axis is co-directional with cylinder axes, the flexible mounting elements of the engine were found to be able to set at somewhere on x and y axes.

Investigation of rail noise and bridge noise using a combined 3D dynamic model and 2.5D acoustic model

Bridge noise and rail noise are two major sources of an elevated rail transit bridge in the low and medium frequency range (20–1000Hz). However, in most of the existing literature, the noise radiated from the bridge and rail was investigated separately or using a simplified source model. In this study, an accurate method is proposed to simulate both the rail noise and bridge noise simultaneously. First, the dynamic responses of the rail and multi-span bridge are obtained using a three-dimensional (3D) vehicle-track-bridge interaction analysis model. Then, the two-dimensional (2D) infinite element model is used to calculate 3D modal acoustic transfer vectors of the rail and bridge based on the wavenumber transformation, in order to overcome the singularity and non-uniqueness of the conventional boundary element method and reduce the computation cost. Third, a field test is conducted, and the accuracy of the proposed simulation procedure is verified. Finally, the contribution of the rail and bridge noise to the total noise level is investigated in the whole space near the bridge. Generally the bridge noise occupies a higher contribution in the space beneath the girder due to the shielding effect of the bridge shape on the rail noise, while the rail noise is dominant in the upper space above the bridge. It is found the presence of the vehicle bodies has considerable effect on the rail noise but little influence on the bridge noise. The slope of the roughness level spectrum has significant influence on the dominant field of bridge noise and rail noise. For the excitation of the assumed ISO roughness level used in this study, the difference between the rail noise and bridge noise is only about 3dB at field points 15–30m away from the track center, which indicates both the bridge and rail noise should be included in the noise prediction for an elevated rail transit bridge.

Design of the filling-rate controller for water medium retarders on the basis of coolant circulation

Water medium retarders are auxiliary braking devices which can reduce the vehicle speed by converting the mechanical energy of a driving vehicle to the total energy of the working fluid. These retarders can replace service brakes in non-emergency braking conditions. This study analysed the dynamic and thermodynamic characteristics of water medium retarders. An observer was designed to identify the optimal braking power of the water medium retarder under different braking conditions. The braking process involving the retarder can be divided into three stages. The controller was designed separately at each stage to control the braking torque of the water medium retarder according to braking requirements. A combined dynamic and thermodynamic vehicle model was also constructed with MATLAB/Simulink. The effects of the controller on the vehicle feedback control system were analysed. The results show that the controller equipped with the observer can effectively control the water medium retarder to satisfy the braking requirements of vehicles on the assumption that the coolant circulation is sufficiently radiated. Finally, an experiment was conducted to determine the performance of the controller and to validate the simulation results.

A Forecasting Model for Feed Grain Demand Based on Combined Dynamic Model.

In order to improve the long-term prediction accuracy of feed grain demand, a dynamic forecast model of long-term feed grain demand is realized with joint multivariate regression model, of which the correlation between the feed grain demand and its influence factors is analyzed firstly; then the change trend of various factors that affect the feed grain demand is predicted by using ARIMA model. The simulation results show that the accuracy of proposed combined dynamic forecasting model is obviously higher than that of the grey system model. Thus, it indicates that the proposed algorithm is effective.

Effect of entrance channel on dynamics of heavy ions collision

A combined dynamical model using concept of dinuclear systems (DNS) and one-dimensional (1D) Langevin equations was applied to investigate the effect of entrance channel on dynamics of heavy ions collision. The [Formula: see text]Si+[Formula: see text]Er, [Formula: see text]O+[Formula: see text]W and [Formula: see text]F+[Formula: see text]Ta reactions which formed the compound nucleus [Formula: see text]Pb have been considered to study this effect. We studied these reactions dynamically and calculated the ratio of evaporation residue cross-section to fusion cross-section [Formula: see text] as a tool for investigation of entrance channel effect. Results of combined model are compared with available experimental data and results of 1D Langevin equations. Obtained results based on combined model are in better agreement with experimental data in comparison with results of Langevin equations. We concluded for [Formula: see text]Si+[Formula: see text]Er and [Formula: see text]F+[Formula: see text]Ta reactions the results of combined model that support the quasi-fission process are different relative to Langevin dynamical approach, whereas for [Formula: see text]O+[Formula: see text]W system the two models give similar results.

Qualitative and quantitative combined nonlinear dynamics model and its application in analysis of price, supply–demand ratio and selling rate

The qualitative and quantitative combined nonlinear dynamics model proposed in this paper fill the gap in nonlinear dynamics model in terms of qualitative and quantitative combined methods, allowing the qualitative model and quantitative model to perfectly combine and overcome their weaknesses by learning from each other. These two types of models use their strengths to make up for the other’s deficiencies. The qualitative and quantitative combined models can surmount the weakness that the qualitative model cannot be applied and verified in a quantitative manner, and the high costs and long time of multiple construction as well as verification of the quantitative model. The combined model is more practical and efficient, which is of great significance for nonlinear dynamics. The qualitative and quantitative combined modeling and model analytical method raised in this paper is not only applied to nonlinear dynamics, but can be adopted and drawn on in the modeling and model analysis of other fields. Additionally, the analytical method of qualitative and quantitative combined nonlinear dynamics model proposed in this paper can satisfactorily resolve the problems with the price system’s existing nonlinear dynamics model analytical method. The three-dimensional dynamics model of price, supply–demand ratio and selling rate established in this paper make estimates about the best commodity prices using the model results, thereby providing a theoretical basis for the government’s macro-control of price. Meanwhile, this model also offer theoretical guidance to how to enhance people’s purchasing power and consumption levels through price regulation and hence to improve people’s living standards.

A combined simulation of high speed train permanent magnet traction system using dynamic reluctance mesh model and Simulink

This paper presents a combined dynamic parameter model (DPM) of a high speed train permanent magnet traction system using a dynamic reluctance mesh model and MATLAB Simulink. First, the dynamic reluctance model of the permanent magnet synchronous motor is introduced. Then the combined models of the traction system under id=0 and maximum torque per ampere control are built. Simulations using both constant parameter models and DPM models are carried out. The speed and torque characteristics are obtained. The results confirm that the DPM model provides higher accuracy without much sacrifice of time consumption or computation resource.

Simultaneous State and Parameter Estimation Based Actuator Fault Detection and Diagnosis for an Unmanned Helicopter

Abstract Simultaneous state and parameter estimation based actuator fault detection and diagnosis (FDD) for single-rotor unmanned helicopters (UHs) is investigated in this paper. A literature review of actuator FDD for UHs is given firstly. Based on actuator healthy coefficients (AHCs), which are introduced to represent actuator faults, a combined dynamic model is established with the augmented state containing both the flight state and AHCs. Then the actuator fault detection and diagnosis problem is transformed into a general nonlinear estimation one: given control inputs and the measured flight state contaminated by measurement noises, estimate both the flight state and AHCs recursively in each time-step, which is also known as the simultaneous state and parameter estimation problem. The estimated AHCs can further be used for fault tolerant control (FTC). Based on the existing widely used nonlinear estimation methods such as the unscented Kalman filter (UKF) and the extended set-membership filter (ESMF), three kinds of adaptive schemes (KF-UKF, MIT-UKF and MIT-ESMF) are proposed by our team to improve the actuator FDD performance. A comprehensive comparative study on these different estimation methods is given in detail to illustrate their advantages and disadvantages when applied to unmanned helicopter actuator FDD.

Integrated Design of Control Actuator Layer and Economic Model Predictive Control for Nonlinear Processes

In the present work, an economic model predictive control (EMPC) system is designed that accounts for the dynamics of the control actuators. A combined process-actuator dynamic model is developed to describe the process and control actuator dynamics and is used within the EMPC system. Integrating the design of the regulatory control layer, which controls the control actuators, and the supervisory control layer consisting of an EMPC system is an important consideration given the fact that EMPC may force an unsteady-state operating policy to optimize the process economics and the dynamics of the control actuator layer may affect the closed-loop process-actuator dynamics. Moreover, integral or average input constraints are often imposed within the EMPC solution. However, if the actuator layer is not accounted for in the EMPC system, the actuator output trajectory may not satisfy the integral input constraints. To address closed-loop stability of the combined process-actuator closed-loop system, stability constraints, designed via Lyapunov-based techniques, are imposed on the EMPC problem to guarantee closed-loop stability of the process system under the EMPC. An EMPC system accounting for the control actuator dynamics is applied to a benchmark chemical process example to study the impact of the actuator dynamics on closed-loop economic performance and reactant material constraint satisfaction.

Drought adaptation policy development and assessment in East Africa using hydrologic and system dynamics modeling

Drought is a natural disaster that affects millions of people across the globe. Lack of rainfall reduces crop yields and livestock productivity and, in turn, food availability and income. In developing countries, these effects are even more detrimental. As droughts become more frequent, adaptation is a fundamental concern for countries and their policymakers. To support a development of drought adaptation policies, a combined hydrologic and system dynamics model was developed for a region in East Africa, focused on the Horn of Africa (i.e., a region bordering Kenya, Somalia, and Ethiopia), an area that has endured multiple droughts in the last few decades. The model simulates the interdependencies between water availability, land degradation, food availability, and socioeconomic welfare. The impacts of new adaptation policies on the region were evaluated over a 10-year simulation period using historical weather data. It was found that a combination of increased hydraulic infrastructure and innovative agricultural practice policy can reduce domestic water deficits by 54–100 % while increasing the income per capita up to 285 % over the 10 years. Innovatively combining hydrologic and systems dynamic modeling produces a realistic simulation of water scarcity and the effects on natural systems. Implementation of policies within the model aids the selection process by evaluating multiple options, quantifying the effectiveness the policies have on individual stakeholder livelihood (i.e., pastoralist, agro-pastoralists, and farmers), and analyzing the overall outcome to ensure equitable costs and benefits among the stakeholders.

An investigation on motor-driven power steering-based crosswind disturbance compensation for the reduction of driver steering effort

This paper describes a lateral disturbance compensation algorithm for an application to a motor-driven power steering (MDPS)-based driver assistant system. The lateral disturbance including wind force and lateral load transfer by bank angle reduces the driver's steering refinement and at the same time increases the possibility of an accident. A lateral disturbance compensation algorithm is designed to determine the motor overlay torque of an MDPS system for reducing the manoeuvreing effort of a human driver under lateral disturbance. Motor overlay torque for the compensation of driver's steering torque induced by the lateral disturbance consists of human torque feedback and feedforward torque. Vehicle–driver system dynamics have been investigated using a combined dynamic model which consists of a vehicle dynamic model, driver steering dynamic model and lateral disturbance model. The human torque feedback input has been designed via the investigation of the vehicle–driver system dynamics. Feedforward input torque is calculated to compensate additional tyre self-aligning torque from an estimated lateral disturbance. The proposed compensation algorithm has been implemented on a developed driver model which represents the driver's manoeuvreing characteristics under the lateral disturbance. The developed driver model has been validated with test data via a driving simulator in a crosswind condition. Human-in-the-loop simulations with a full-scale driving simulator on a virtual test track have been conducted to investigate the real-time performance of the proposed lateral disturbance compensation algorithm. It has been shown from simulation studies and human-in-the-loop simulation results that the driver's manoeuvreing effort and a lateral deviation of the vehicle under the lateral disturbance can be significantly reduced via the lateral disturbance compensation algorithm.

Raw material procurement with fluctuating prices using speculative inventory under consideration of different contract types and transport modes

The paper develops a combined dynamic procurement and transport model for performance evaluation by explicitly considering fluctuating prices of raw material, alternative transport modes as well as contract types. In a dynamic environment the procurement managers face (i) the challenge to select the ‘right’ strategy (i.e. transport mode and contract type) and (ii) in each period the decision whether to procure or not, depending on the price; in case of procurement, the price-dependent quantity must be determined. For tackling the decision problems of procurement, contract price and transport mode, we propose an approach motivated by demand models depending on the reservation price which is derived from revenue management. Alternative strategies are characterised by the contract type (short-term, long-term and portfolio), by the possibility to hold speculative inventories or not, and by the modes of transport including intermodal and multi-mode transport. Based on the procurement, transport and inventory costs, the performance of selected strategies is illustrated for a real supply process in the chemical industry using dynamic process analysis. The findings show that the most efficient strategies lead to reduction of average total procurement costs between 8 and 18%. Subsequently, managerial guidelines are derived for the selection of the most appropriate strategy.

Interplay of population genetics and dynamics in the genetic control of mosquitoes

Some proposed genetics-based vector control methods aim to suppress or eliminate a mosquito population in a similar manner to the sterile insect technique. One approach under development in Anopheles mosquitoes uses homing endonuclease genes (HEGs)—selfish genetic elements (inherited at greater than Mendelian rate) that can spread rapidly through a population even if they reduce fitness. HEGs have potential to drive introduced traits through a population without large-scale sustained releases. The population genetics of HEG-based systems has been established using discrete-time mathematical models. However, several ecologically important aspects remain unexplored. We formulate a new continuous-time (overlapping generations) combined population dynamic and genetic model and apply it to a HEG that targets and knocks out a gene that is important for survival. We explore the effects of density dependence ranging from undercompensating to overcompensating larval competition, occurring before or after HEG fitness effects, and consider differences in competitive effect between genotypes (wild-type, heterozygotes and HEG homozygotes). We show that population outcomes—elimination, suppression or loss of the HEG—depend crucially on the interaction between these ecological aspects and genetics, and explain how the HEG fitness properties, the homing rate (drive) and the insect's life-history parameters influence those outcomes.

Ultrafast combined dynamics of Förster resonance energy transfer and transient quenching in cationic polyfluorene/fluorescein-labelled single-stranded DNA complex

The combined dynamic process of Förster resonance energy transfer and transient quenching is quantified in the time-resolved fluorescence of cationic polyfluorene/fluorescein-labelled single-stranded DNA complex. We found that the radiation boundary condition fails to predict transient quenching due to a single quenching rate at the encounter distance between a fluorophore and a quencher; however, the predictions of the micellar kinetics model were in good agreement with the measured time-resolved fluorescence as an alternative to the complicated distance-dependent quenching model. The combined dynamics model enables the separation of the rate of Förster resonance energy transfer from that of transient quenching, by which we obtained an accurate estimation of the donor–acceptor intermolecular distance (41±1.6Å) in comparison with the Förster distance (43Å).

CFD–DEM modeling of gas–solid flow and catalytic MTO reaction in a fluidized bed reactor

The methanol-to-olefins (MTO) process is currently being implemented successfully in fluidized bed reactors (FBRs) in China. Characterizing the gas–solid flow is crucial in operating MTO FBRs effectively. In this work, a combined discrete element method (DEM) and computational fluid dynamics (CFD) model is developed to describe the gas–solid flow behavior in an MTO FBR. In this model, the particles are modeled using DEM, and the gas is modeled using Navier–Stokes equations. The combined model incorporates the lumped kinetics in the gas phase to achieve the MTO process. Moreover, the combined model can characterize the heat transfer between particles as well as that between the gas and the particles. The distinct advantage of the combined model is that real-time particle activity can be calculated by tracking the motion history of the catalyst particle with respect to heat transfer. The simulation results effectively capture the major features of the MTO process in FBR. Moreover, the simulation results are in good agreement with the classical calculation and experimental data. The particle motion pattern and distributions of a number of key flow-field parameters in the reactor are analyzed based on the validated model. The effects of operating conditions on FBR performance are also investigated. The simulation results show that the particle motion exhibits a typical annulus–core structure, which promotes excellent transfer efficiency. The results also demonstrated that the feed temperature, inlet gas velocity, and feed ratio of water to methanol significantly affect reaction efficiency.

Hot workability in process modeling of a bearing steel by using combined constitutive equations and dynamic material model

The high temperature workability of a 1%C–1.5%Cr steel was investigated by means of torsion experiments carried out between 1125 and 1000°C. The main task of the study was the quantification of the effect of processing conditions (temperature and strain rate) on the flow stress, by means of constitutive models capable of providing the entire shape of the stress vs strain curves. An excellent description was indeed obtained by the Hensel and Spittel relationship, provided that the portions of each curve before and after the peak stress were described separately. The same model curves were then used to estimate the peak and steady state stress for each of the investigated conditions, again obtaining an excellent correlation with the experimental data. To further facilitate the identification of the optimum processing window for this material, dissipation efficiency maps were obtained using as input the stress vs strain rate values computed by a constitutive model, in this case based on the Garofalo sinh equation.

Dynamic Interaction between Manipulator and Omni-Directional Platform

Recent advancements in mechatronics has led to tremendous development of application of robots for industrial applications involving high health hazards, rough working conditions and difficult to reach locations. Robot assisted welding is one such high risk operation for human being. The industrial arc welding robots are either mounted on the floor, table or on overhead rails. In this scenario, the jobs to be welded are brought to shop floor. However, the on-sight joining of big pipes and structures with precision and speed, demands for mobility of welding robot. In this research work, a novel concept of mounting 5-dof welding robot on the omni-directional platform (Omni-WMR) is implemented to provides immense maneuvering mobility to the manipulator. This paper presents the combined dynamic model of omnidirectional mobile robot for welding operation to study the effect of dynamic interaction between manipulator and mobile platform. Dynamic interaction is carried out to find the variation in torque at manipulator link due to the motion of platform as well as its location on the platform. In addition, the variation in torque developed at platform wheels due to positioning the manipulator at two different locations on platform is accessed. For this, two case studies have been discussed to study the effect of dynamic interaction between manipulator and omni-directional platform.

Models and Algorithms for the Reconfiguration of Virtual Enterprise Information System Structure

In this article we will consider existing approaches to solving problems of complex object reconfiguration, as well as combined dynamic model and method of reconfiguring, which is viewed as a virtual enterprise information system. Reconfiguration is a process of the complex technical system structure alteration with a view to increase, keep or restore the level of complex technical system operability, or with a view to compensate for the loss of complex technical system efficiency caused by the degradation of its function. The dynamic interpretation of the processes of complex work planning in virtual enterprise integrated information systems allows describing in strict mathematical terms and comprehensive manner the mutual effect of business processes and information processing, storage, transmission (reception) processes in this system.