Dynamic Characteristics Of Model Research Articles

Dynamic characteristic modeling of left ventricular assist devices based on hysteresis effects

ObjectiveThe purpose of this study is to develop a new model for the dynamic characteristics of left ventricular assist devices (LVADs) interacting with the cardiovascular system under constant-speed modes. MethodsA new hysteresis model is established on the basis of the hysteresis effect and turbomachinery principles. The simulation results from the hysteresis model were compared with the inertia model. The in-vitro experiment results of a centrifugal pump (from literature) and the unsteady computational fluid dynamics (CFD) simulation results of an axial pump were used as the benchmarks. ResultsCompared with the inertia model, at the partial support mode, the relative estimation error of the time to the maximum and minimum pump flow (Q) in the hysteresis model decreased at least 16.3% cardiac cycle (Tc) in the centrifugal pump and at least 1.9% Tc in the axial pump, indicating its ability to simulate more realistic Q fluctuations. Moreover, the hysteresis model could predict an accurate time distribution of different Q. ConclusionThe hysteresis model provides a general calculation method for simulating the dynamic characteristics of constant-speed LVADs under interaction with the cardiovascular system. It is more accurate than the inertia model. SignificanceThe hysteresis model is helpful for the rapid estimation of unsteady dynamic characteristics in absence of a physical pump prototype at the preliminary design stage.

Geometric design and dynamic characteristics of a novel abnormal cycloidal gear reducer

A precision reducer with a high ratio and a small size is essential for precise control of the position of a robotic arm. The rotate vector (RV) is a reducer widely applied in robotic joints. However, its complex structure, over-positioning and difficult assembly restrict its application industrial robots. Herein, a novel abnormal cycloidal gear (ACG) reducer is proposed. In comparison to the RV reducer, the proposed reducer has the characteristics of compact structure, less over-positioning and high ratio. The compound tooth profile of “epicycloid-involute hypocycloid” is used as the driving teeth for improving the performance of the reducer. The operating principle, mechanism design and reduction ratio of the proposed reducer is investigated, and the design method of the ACG tooth profile is also introduced. A dynamic characteristic model is established to verify the correctness of the design method of the reducer. A prototype of the ACG reducer is fabricated by using the computer numerical control (CNC) machining technology. Results show that the ACG reducer is capable to cover a wide range of reduction ratios with a simple mechanism. The numerical and theoretical results are in agreement, which depict the structural feasibility and correctness of the design method of the reducer. The adaptation of the ACG tooth profile as the driving teeth helps in improving the performance of the reducer.

Co-Simulation Modeling and Multi-Objective Optimization of Dynamic Characteristics of Flow Balancing Valve

The poor dynamic characteristics of the flow balance valve used in a ship’s HVAC system are the main reasons for the hydraulic imbalance and high energy consumption of the system. A new adjustable dynamic flow balance valve structure is designed, which is composed of a self-operated pressure regulator and an electric V-shaped ball valve in series. When the V-shaped ball valve is fully opened at the 20 t/h flow level, the dynamic characteristics of the flow balance valve cannot meet the requirements. A new co-simulation method that combines MATLAB/Simulink and the UDF dynamic grid is proposed to study the dynamic characteristics of a flow balance valve with a 20 t/h flow rate under different pressure drop step signal interference. When the calculation of each micro-element time converges, the valve core motion parameters, the pressure boundary conditions, the valve core axial medium force, and the valve outlet flow are interactively transmitted in the two simulation environments. The discrepancy between the co-simulation and test results is less than 5%, which verifies the accuracy of the co-simulation model. Aiming at the most severe dynamic characteristic working condition where the pressure drop is stepped from 30 to 300 kPa, the influence of different structural parameters on the dynamic characteristics of the balance valve is analyzed. A new surrogate model combining RSM and RBF with the co-simulation method improves the optimization efficiency and fitting accuracy. To improve the convergence of the traditional NSGA-II algorithm, key structural parameters are optimized by combining the NSGA-II algorithm and SDR. The test results show that the dynamic characteristics of the optimized valve are improved, the discrepancy between the stabilized flow rate and 20 t/h does not exceed 4.5%, and the flow is relatively constant. Therefore, the proposed co-simulation and optimization method can be applied to the dynamic characteristic prediction of self-operated valves, such as dynamic flow balance valves, to provide guidance for developing high-precision self-operated valves.

Imaging Simulation Method for Novel Rotating Synthetic Aperture System Based on Conditional Convolutional Neural Network

The novel rotating synthetic aperture (RSA) is a new optical imaging system that uses the method of rotating the rectangular primary mirror for dynamic imaging. It has the advantage of being lightweight, with no need for splicing and real-time surface shape maintenance on orbit. The novel imaging method leads to complex image quality degradation characteristics. Therefore, it is vital to use the image quality improvement method to restore and improve the image quality to meet the application requirements. For the RSA system, a new system that has not been applied in orbit, it is difficult to construct suitable large datasets. Therefore, it is necessary to study and establish the dynamic imaging characteristic model of the RSA system, and on this basis provide data support for the corresponding image super resolution and restoration method through simulation. In this paper, we first analyze the imaging characteristics and mathematically model the rectangular rotary pupil of the RSA system. On this basis, combined with the analysis of the physical interpretation of the blur kernel, we find that the optimal blur kernel is not the point spread function (PSF) of the imaging system. Therefore, the simulation method of convolving the input image directly with the PSF is flawed. Furthermore, the weights of a convolutional neural network (CNN) are the same for each input. This means that the normal convolutional layer is not only difficult to accurately estimate the time-varying blur kernel, but also difficult to adapt to the change in the length–width ratio of the primary mirror. To that end, we propose a blur kernel estimation conditional convolutional neural network (CCNN) that is equivalent to multiple normal CNNs. We extend the CNN to a conditional model by taking an encoding as an additional input and using conditionally parameterized convolutions instead of normal convolutions. The CCNN can simulate the imaging characteristics of the rectangular pupil with different length–width ratios and different rotation angles in a controllable manner. The results of semi-physical experiments show that the proposed simulation method achieves a satisfactory performance, which can provide data and theoretical support for the image restoration and super-resolution method of the RSA system.

Modeling of dynamic and spectral viscoelastic characteristics of composite materials

When designing products made of composite materials intended for use in difficult conditions of inhomogeneous deformations and temperatures, it is important to take into account viscoelastic, including spectral and dynamic, properties of the binder and fillers. The article considers dynamic characteristics (complex modulus, complex malleability, their real and imaginary parts, loss angle tangent) and spectral characteristics of relaxation and creep and their dependence on each other. The abovementioned characteristics were found for all known types of creep kernel and relaxation kernel. To find the spectral characteristics, one of the numerical methods of reversing the Laplace transformation was used - the method of quadrature formulas. Algorithms and computer programs have been compiled to implement this method.

Research on Dynamic Characteristic Analysis and Energy Consumption Modeling of Five-axis CNC Machine Tool Based on Bond Graph

Research on Dynamic Characteristic Analysis and Energy Consumption Modeling of Five-axis CNC Machine Tool Based on Bond Graph

Automatic detection method of abnormal vibration of engineering electric drive construction machinery

<abstract> <p>Aiming at the problem that the extraction effect of abnormal vibration characteristics of current engineering electric drive construction machinery is poor, an automatic detection method of abnormal vibration of engineering electric drive construction machinery is proposed. Firstly, the abnormal data of mechanical abnormal vibration are collected and identified, and based on the identification results, the dynamic characteristic model of engineering electric drive construction machinery is constructed. The empirical mode decomposition and Hilbert spectrum are used to decompose the abnormal vibration of machinery, calculate the response amplitude and time lag value generated by the operation of the engineering electric drive construction machinery to simplify the diagnosis steps of the abnormal vibration of the engineering electric drive construction machinery and realize the positioning and detection of the transverse and torsional vibration characteristics. Finally, through experiments, it was confirmed that the automatic detection method of the abnormal vibration of the engineering electric drive construction machinery has high accuracy, which can better ensure the healthy operation of mechanical equipment. This endeavor aims to establish scientific methodologies and standards for fault detection techniques in construction machinery, ultimately forging a versatile solution better suited for detecting and resolving issues across various categories of construction equipment.</p> </abstract>

Study on empirical model and CFD about pressure rising in Cab during door closure

Aiming at the problem that there is a strong eardrum pressure in the passenger car during the closing process, two analysis and prediction methods, fast formula prediction and CFD simulation based on accurate models, are proposed. The regression model of ear pressure comfort was established by DOE method and multiple linear regression; The simulation software star-CCM+ is applied to simulate and analyze the dynamic characteristics of the flow field in the cockpit during the closing process by using the overlapping grid technology, and the pressure change curve near the ear is obtained. Finally, the CFD numerical simulation model is established by comparing and analyzing the regression prediction analysis results and the real vehicle test data. The results show that the effects of closing speed, effective opening area of pressure relief valve and air tightness of the whole vehicle on the pressure of passengers’ eardrums decrease in turn, and the prediction error of multiple linear regression equation is 17 %; The analysis error of the internal flow field dynamic characteristic model based on refined modeling is 8 %. This study provides a theoretical basis for solving the problem of rapid prediction of eardrum pressure and optimization of engineering structure.

Modeling and analysis of high-frequency dynamic characteristics of double isolation rubber mounts

Rubber mounts are the vital component to reduce the vibration translated from the powertrain to the vehicle body. The dynamic stiffness of the conventional rubber mount increase with the increase of the excitation frequency, and form a peak under high-frequency excitation in the battery electric vehicle (BEV). So the double isolation rubber mount has gradually been used in the BEV powertrain to improve the vibration isolation performance in the high-frequency range. Compared with conventional rubber mounts, the double isolation rubber mount has smaller dynamic stiffness in the high-frequency range. However, the traditional simulation model of the dynamic characteristics cannot consider the influence of the metal bracket of the double isolation rubber mount on the dynamic characteristics. Therefore, it is necessary to carry out the modeling and analysis of the dynamic characteristics simulation model of the double isolation rubber mount. In this paper, a general dynamic model of double isolation rubber mounts is proposed to describe the high-frequency dynamic characteristics. In this general dynamic model, the complex stiffness element representing the viscoelasticity of rubber is expressed using the fractional derivative model and the Maxwell model, respectively, and two high-frequency dynamic models are established. Two model parameter identification methods are proposed for high-frequency dynamic models of double isolation rubber mounts, and the identification results are compared and analyzed. Then, two high-frequency dynamic models are used to simulate the high-frequency dynamic characteristics of double isolation rubber mounts. The simulation results show that both high-frequency dynamic models can calculate the high-frequency dynamic characteristics of double isolation rubber mounts. Among them, the dynamic model based on fractional derivative elements has relatively high accuracy, and the dynamic model based on Maxwell elements has relatively high stability. The high-frequency dynamic characteristic modeling method of double isolation rubber mounts presented in this paper is helpful to the vibration and noise analysis of electric vehicle powertrain systems under high-frequency excitation.

Maneuvering target state estimation based on separate modeling of target trajectory shape and dynamic characteristics

The state estimation of a maneuvering target, of which the trajectory shape is independent on dynamic characteristics, is studied. The conventional motion models in Cartesian coordinates imply that the trajectory of a target is completely determined by its dynamic characteristics. However, this is not true in the applications of road-target, sea-route-target or flight route-target tracking, where target trajectory shape is uncoupled with target velocity properties. In this paper, a new estimation algorithm based on separate modeling of target trajectory shape and dynamic characteristics is proposed. The trajectory of a target over a sliding window is described by a linear function of the arc length. To determine the unknown target trajectory, an augmented system is derived by denoting the unknown coefficients of the function as states in mileage coordinates. At every estimation cycle except the first one, the interaction (mixing) stage of the proposed algorithm starts from the latest estimated base state and a recalculated parameter vector, which is determined by the least squares (LS). Numerical experiments are conducted to assess the performance of the proposed algorithm. Simulation results show that the proposed algorithm can achieve better performance than the conventional coupled model-based algorithms in the presence of target maneuvers.

A combined analytical model for orifice-type and pipe-type air springs with auxiliary chambers in dynamic characteristic prediction

The frequency-domain properties of air springs with an auxiliary chamber are highly dependent on the type of air flow passages. The dynamic characteristics of air springs with different flow passages are so variated that they are modeled separately. This paper aims to develop a combined dynamic characteristic model for both orifice-type and pipe-type air springs, which newly considers the viscoelasticity of bellows and the frequency- and amplitude-dependency of air damping. Firstly, experiments are conducted to study the dynamic characteristics of air springs. Then a combined analytical model is developed based on thermodynamic theory. The generation mechanism and criteria for resonance peaks in dynamic stiffness are illustrated. Further, model parameters are identified using the ellipse features of Nyquist diagrams. The predicted stiffness and loss angle of ASAC are compared with measured results for validations. Finally, the calculated results of the proposed model are compared with that of three other common models in the reported literature. The results show that the proposed models are more accurate and are generated for both orifice-type and pipe-type air springs.

Dynamic characteristic modeling and simulation of an aerospike-shaped pintle nozzle for variable thrust of a solid rocket motor

To utilize propulsion energy effectively, it is necessary to develop technology that can enable variable thrust by altering the area of the nozzle throat in a solid rocket motor in real time. In this study, an aerospike-shaped pintle nozzle, an altitude compensation nozzle technology, was designed to improve the performance compared to that of the existing pintle nozzles. Pressure fluctuations caused by the movement of the pintle led to the hysteresis of the combustion chamber pressure, which sharply increased the pintle load. Depending on the design conditions of the actuator, a load that was approximately 2.5 times larger than that in the normal state could be applied to the actuator. Additionally, cold flow tests were conducted under static conditions to verify the reliability of the design code for the actuator load prediction results. Moreover, firing tests were performed to verify the reliability of the internal ballistic simulation code. Finally, factors related to the thermal expansion of the pintle and the deformation of the nozzle throat, which caused changes in the nozzle throat area during combustion, were identified and mathematically modeled. Additional firing tests were conducted to validate the updated numerical model. Before the model was updated, a pressure difference occurred at most three times or more between the performance prediction model and the firing test results, but the performance prediction error was reduced when the modified numerical analysis was used. If the present results are applied to a guided missile system, the high-altitude operation performance will improve and precision thrust control will become possible, enabling flexible guided missile system operation.

Dynamic damage characteristics of rock under multiple loads during high-voltage pulse fragmentation

To analyze the damage characteristics of rocks during high-voltage pulse fragmentation (HVPF), two kinds of loads, shockwave and cavity, are determined by optical observation, and the pressure–time characteristics of these two and their mechanism of damage to rocks in mesoscopic view are analyzed. A model of dynamic damage characteristics of brittle rock under multiple loads is established, which includes numerical calculation and discrete element simulation. In the discrete element simulation, the rock is simplified as a circular region without reflection boundary with a certain size of the circular hole inside, and the grains in the region are discretized as rigid spheres with a definite bonding relationship. The shockwave is considered the time-varying pressure loaded to the grains of the circular hole, and the cavity is considered the quasi-static pressure loaded to the grains on both sides of the fracture. The results of the model show that shear cracks and tensile cracks are produced during the shockwave action, but tensile cracks are predominant. The shockwave acts as a preload for the expansion of cracks, and the damage radius is small. Most of the cracks in HVPF are caused by the cavity. A comparison of the numerical calculation results with the discrete element simulation results shows that the model can describe the distribution characteristics of cracks under multiple loads, which lays a foundation for further analysis of the internal mechanism of HVPF.

Research on Wet Clutch Switching Quality in the Shifting Stage of an Agricultural Tractor Transmission System

In order to improve the working quality of wet clutch switching in an agricultural tractor, in this paper, we took a power shift system composed of multiple wet clutches as the research object for full-factorial performance measurement, multi-factor analysis of the degree of influence, establishment of a single evaluation index model, formation of a comprehensive evaluation index, and formulation of adjustable factor control strategies. We studied the simulation test platform of an agricultural tractor power transmission system based on the SimulationX software and obtained 225 sets of sample data under a full-use condition. Partial least squares and range analysis were applied to comprehensively analyze the influence of multiple factors on the working quality of wet clutches. In this paper, we proposed a modeling method for a single evaluation index of the wet clutch (combined with polynomial regression and tentative method, the goal is determined in the form of a model with the maximum coefficient of determination) and two control strategy optimization methods for the wet clutch adjustable factors, i.e., Method 1 (integrated optimization) and Method 2 (step-by-step optimization), both methods were based on an improved genetic algorithm. The results showed that oil pressure, flow rate, and load had significant effects on the dynamic load characteristics (the degrees were 0.38, −0.44, and −0.63, respectively, with a negative sign representing an inverse correlation); rate of flow and load had significant effects on speed drop characteristics (the degrees were −0.56 and 0.73, respectively). A multivariate first-order linear model accurately described the dynamic load characteristics (R2 = 0.9371). The accuracy of the dynamic load characteristic model was improved by 5.5037% after adding the second-order term and interaction term of oil pressure. The polynomial model containing the first-order oil pressure, first-order flow rate, second-order flow rate, and interaction terms could explain the speed drop characteristics, with an R2 of 0.9927. If agricultural tractors operate under medium and large loads, the oil pressure and flow rate in their definitional domains should be small and large values, respectively; if operating under small loads, both oil pressure and flow rate should be high. When the wet clutch dynamic load and speed drop characteristics were improved, the sliding friction energy loss also decreased synchronously (the reduction could reach 70.19%).

Modeling and analysis of dynamic characteristics of rubber isolators for electric vehicles under high-frequency excitation

The rubber isolator is a key component connecting the vehicle body and the powertrain, which plays a significant role in reducing the vibration transmission from the engine to the vehicle body. With the development of electric vehicles, the excitation frequency generated by the powertrain can exceed 2 kHz. The conventional dynamic models are usually used to simulate the low-frequency dynamic characteristics of rubber isolators, in the range of 0–200 Hz, which is the main excitation frequency range of the traditional internal combustion engine vehicle. However, they cannot simulate the high-frequency dynamic characteristics accurately since the inertial force caused by the mass of rubber isolators increases greatly under high frequencies. And the high-frequency dynamic characteristics of rubber isolators is of great significance for isolator fatigue life prediction, powertrain system vibration isolation design and noise control caused by the high-frequency resonance of the isolator. In this paper, a general model with mass elements is proposed to describe the effect of the inertial force on high-frequency dynamic stiffness. Based on the proposed model and considering the different expressions of the viscoelastic properties of rubber isolators, three improved dynamic models of rubber isolators are established, and used to analyze the high-frequency dynamic characteristics of rubber isolators. It has been demonstrated that the inertial force plays a non-negligible role in the dynamic characteristics of rubber isolators under high-frequency excitation. The proposed model can be used to analyze the effect of the inertial force on the dynamic characteristics at high frequencies accurately. The high-frequency dynamic characteristic modeling method of rubber isolators presented in this paper is helpful to the vibration and noise analysis of electric vehicle powertrain systems under high-frequency excitation.

Experimental research on damage identification of topping dangerous rock structural surface based on dynamic characteristic parameters

Rock block tilting is one of the most common types of dangerous rock block failures with no clear indicator of displacement prior to failure. Existing stability evaluation methods remain limited in their ability to constrain the non-penetrating section area, which is closely related to rock stability, and stability evaluations are therefore associated with large uncertainties. The dynamic characteristic parameters of toppling dangerous rock are closely related to structural plane strength. Under vibration loading, rainfall, and/or excavation unloading conditions, the structural plane becomes damaged and the dynamic characteristic parameters change. In this study, we present a dynamic characteristic model of rock tilting and identify the quantitative and qualitative relationship between dynamic characteristic parameters and the bonded area of the structural plane. The model accuracy is verified by experiments. The experimental results show that the damping ratio decreases linearly with structural plane damage, whereas the maximum vibration speed and particle trajectory increases nonlinearly and the natural vibration frequency decreases nonlinearly. The dynamic characteristic model and experimental results can be used to evaluate the degree of structural surface damage of toppling dangerous rock.

Разработка имитационной модели двухмассовой технологической вибрационной установки с электромагнитным возбуждением

The research performed is actual because it is necessary to improve methods of calculations of rapid dynamic processes in electrical units. The object of research is the construction of a two-mass technological vibration unit with electromagnetic excitation. The subject of research is the method of calculation based on the created simulation model of the vibration unit dynamic cha-racteristics in transient and stationary modes with respect to a form and frequency of the source voltage. The mathematical model is based on non-linear differential equations of the electrical and mechanical balance. The main objective of research is the development of a simulation model of a two-mass technological vibration unit with electromagnetic excitation using modern methods of computer simulation. The example of the numerical implementation of the mathematical model by structural modeling methods in the Matlab Simulink is considered and the computer model of the electromagnetic vibration unit is created. The examples of the calculation of dynamical cha-racteristics of electromagnetic vibration unit for the analysis of electromechanical processes in transient and stationary modes are presented. Some of calculated values of integral indicators describing conversion processes of electric energy consumed from a power supply are given. The proposed simulation model of a technological vibration unit can be used to calculate rapid dyna-mic processes in different modes to provide a rational choice of vibration unit parameters when it is designed. The model is also useful for the analysis and synthesis of automatic systems to control the supplied voltage amplitude, frequency and form. The results of the research can be of particular interest to specialists in the area of machine strength dynamics and vibration protection.

A nonlinear dynamic characteristic modeling method of shift manipulator for robot driver with multiple clearance joints

A nonlinear dynamic characteristic modeling method of shift manipulator for robot driver with multiple clearance joints

Sliding Mode Bifurcation Control Based on Acceleration Feedback Correction Adaptive Compensation for Maglev Train Suspension System With Time-Varying Disturbance

In order to ensure the suspension stability of maglev train, the active control problems of static suspension and dynamic suspension are studied. First, the mathematical model of dynamic suspension characteristics of medium- and low-speed maglev train is established. Second, the PID controller is studied. The results show that the controller is very sensitive to time-varying disturbances such as nonuniformity and load, which leads to the decrease in system robustness. In order to suppress the disturbance effectively, a suspension control method based on the sliding mode reaching law is proposed. Based on the bifurcation phenomenon, the bifurcation point is solved to determine the main control parameters. On the basis of this, an acceleration feedback correction and adaptive control module based on the radial basis function (RBF) network is constructed to effectively suppress the vibration of the electromagnet. The controller consists of a sliding mode bifurcation control law, an acceleration feedback correction module, and an adaptive compensation loop. The simulation and experimental results show that the proposed control algorithm can significantly reduce the variation range of suspension gap with a smoother control current in the presence of complex disturbances and significantly suppress the coupled vibration.

Circuit Models of Power MOSFETs Leading the Way of GaN HEMT Modelling—A Review

Gallium nitride high-electron-mobility transistor (GaN HEMT) is a key enabling technology for obtaining high-efficient and compact power electronic systems. At the design stage of a power converter, the proper modelling of the GaN HEMT is essential to benefit from their good features and to account for the limits of the current technology. Circuit models of power MOSFETs have been deeply investigated by academia and industry for a long time. These models are able to emulate the datasheet information, and they are usually provided by device manufacturers as netlists that can be simulated in any kind of SPICE-like software. This paper firstly highlights the similarities and differences between MOSFETs and GaN HEMTs at the datasheet level. According to this analysis, the features of MOSFET circuit models that can be adopted for GaN HEMT modelling are discussed. This task has been accomplished by overviewing the literature on MOSFETs circuit models as well as analysing manufacturers netlists, thus highlighting the models MOSFETs valid or adaptable to GaN HEMTs. The study has revealed show that some models can be adapted for the GaN HEMT devices to emulate static characteristics at room temperature while the MOSFET models of dynamic characteristics can be used for GaN HEMT devices. This study enables the devices modellers to speed up the GaN HEMT modelling thanks to the use of some well-established MOSFET models. In this perspective, some suggestions to develop accurate GaN HEMT models are also provided.