Transient Dynamics Model Research Articles

Modeling of reinforced-concrete cutting with shield rippers using FEM-DEM-coupling method

With the increase in the number of underground structures, it is common to encounter reinforced concrete (RC) pile foundations of existing buildings or bridges during shield machine tunneling in densely constructed urban areas. The cutting of RC piles with the shield machines is a challenging task due to cutter damage and cutting efficiency issues. In this paper, the interaction between a ripper and an RC was studied based on the FEM-DEM coupling method. A three-dimensional transient dynamic model of two typical rippers (angular ripper and curved ripper) cutting RC piles was established, respectively. In the FEM-DEM coupling model, the mechanical behavior of concrete was described via DEM, and the impact of steel bars in concrete was considered via FEM. In addition, an experimental verification was conducted to validate the effectiveness of the numerical results. The damage characteristics of the steel bars and concrete, and the force patterns of the rippers were analyzed. The influence of the geometric parameters of the ripper, including blade width, blade angle, and blade anterior angle on the cutting performance was also investigated through a parametric study. Some recommendations are made for the geometric design of rippers used for cutting reinforced concrete. The results of this study could provide some references for cutting RC obstacles with a shield machine.

Search for Optimal Parameters in the Control Structure of a Surgical System for Soft Tissue Operations Based on In Vitro Experiments on Cardiovascular Tissue

The surgical robots currently used in cardiac surgery are equipped with a remote center of motion (RCM) mechanism that enables the required spherical workspace. The dynamics model of the surgical robot’s RCM mechanism presented in this work includes a direct current (DC) motor, an optimal proportional–integral–derivative (PID) controller, and a LuGre friction model that takes into account the Stribeck effect and surface deformation. A finite element method (FEM) analysis of transients was carried out using the energy hypothesis of von Mises with an optimal input signal from the mechatronic system with a PID controller obtained using the Runge–Kutta differentiation method in the Dormand–Prince ordinary differential equations variant (ODE45). Five criteria were adopted for the objective function: the safety factor related to the stress function in the time-varying strength problem, the first natural frequency related to stiffness and the resonance phenomenon, the buckling coefficient in the statics problem related to stability, the static factor of safety, and the displacement of the operating tip. The force inputs to the dynamics model were derived from in vitro force measurements on cardiovascular tissue using a force sensor. The normality of the statistical distribution of the experimental data was confirmed using the Kolmogorov–Smirnov statistical test. The problem of multi-criteria optimization was solved using the non-sorter genetic algorithm (NSGA-II), the finite element method, and the von Mises distortion energy hypothesis. Velocity input signals for the transient dynamics model were obtained from a second in vitro experiment on cardiovascular tissue using the minimally robotic invasive surgery (MIRS) technique. An experienced cardiac surgeon conducted the experiment in a modern method using the Robin Heart Vision surgical robot, and a system of four complementary metal–oxide–semiconductor (CMOS) optical sensors and ariel performance analysis system (APAS-XP 2002) software were used to obtain the endoscopic tool trajectory signal. The trajectory signal was accurate to ±2 [mm] in relation to the adopted standard, and it was smoothed using the Savitzky–Golay (SG) polynomial smoothing, whose parameters were optimally selected using the Durbin–Watson (DW) statistical test.

A model free method of predicting transient dynamics in anaerobic digestion.

Transient dynamics pose unique challenges when dealing with predictions and management of ecological systems yet little headway has been made on understanding when an ecological system might be in a transient state. As a start we consider a specific model, here focusing on a canonical model for anaerobic digestion. Through a series of simplifications, we analyse the potential of the model for transient dynamics, and the driving mechanisms. Using a stochastic analogue of this model, we create synthetic ecological data. Thus, combining our understanding of the deterministic transient dynamics with the use of empirical dynamical modelling, we propose several new metrics to indicate when the synthetic time series is leaving a transient state.

Modeling the Transient Dynamics of Arresting Hooks and Cables through the Parameter Inversion Method

Arresting gear systems play a vital role in carrier-based aircraft landing. In order to accurately understand the process of arresting hook and cable, this study introduces a parameter inversion method to model the arresting cable and applies it to the transient dynamics model of the arresting hook and cable. The feasibility of the arresting cable model and its application to the transient dynamics model of the arresting hook and cable are validated through arresting hook and cable impact tests. The study compares three different models of arresting cables for simulation results and concludes that assuming the arresting cable to be a beam with metal elastic parameters during the modeling process cannot ignore the influence of the cable’s torsional and bending stiffness on the modeling. The study also investigates the dynamic response of the arresting hook during the aircraft arrestment and hooking process and concludes that the stress peak of the hook arm is much lower throughout the entire arrestment process than at the moment of hooking the cable. The study further identifies factors that affect the stress on the arresting hook arm, such as the aircraft’s yaw angle, deck angle, cruising speed, and the initial position of the arresting hook and cable before engagement. The research results have significant implications for improving the design optimization of the structural strength of the functional components of the naval aircraft arresting system and provide theoretical guidance and technical reserves for subsequent related studies.

Continuous gas-phase synthesis of iron nanoparticles at ambient conditions with controllable size and polydispersity

HypothesisBy altering aerosol growth dynamics with unipolar charges, one can obtain aerosols with narrow particles size distributions, a highly desirable feature in applications of functional nanoparticles. ExperimentsUnlike liquid colloid systems, aerosol particles in the free molecular regime undergo coarsening due to Brownian coagulation and will eventually attain a self-preserving size distribution with a typical geometric standard deviation of 1.46 - 1.48. We developed a novel continuous one-step aerosol synthesis reactor that produces iron nanoparticles from ferrocene at ambient conditions, which confines the site of precursor breakdown and particle formation in the downstream vicinity of a positive corona discharge. FindingsWe demonstrated that the particle size could be controlled within 3 - 10 nm with a suppressed geometric standard deviation (1.15 - 1.35). The as-produced iron nanoparticles were successfully used as catalyst for the growth of single-walled carbon nanotubes with a narrow diameter range. With a transient aerosol dynamics model, we showed that a fraction (as small as 0.1%) of unipolar-charged particles could have a significant impact on the aerosol growth dynamics, which eventually results in a narrower particle size distribution with smaller size and higher number concentrations.

Assessment of the Required Maximum‐Power‐Point‐Tracking Speed for Vehicle‐Integrated Photovoltaics Based on Transient Irradiation Measurements and Dynamic Electrical Modeling

Fast changing irradiation on vehicle‐integrated photovoltaic (VIPV) modules may impose demanding requirements for maximum power point tracking (MPPT) to ensure high energy conversion efficiency. In this work, the results of simulations regarding the output and efficiency of an exemplary VIPV module under real‐life irradiation conditions as measured with high time resolution are resulted. Herein, resistive as well as voltage source load is used as two idealized models of the MPPT. The simulations show that, in most cases, tracking with a resistive load at 1 Hz preserves above 90%rel of the convertible energy determined by the cell performances under given irradiance levels. With a voltage source load, these values do not undercut 97%rel at 0.1 Hz. Herein, it is also found that partial shading across the exemplary series connected module can reduce the converted energy in the range of 5–10%rel in relation to complete negligence of this effect.

A multi-fidelity approach for reliability-based risk assessment of single-vehicle crashes

Road vehicles are highly susceptible to single-vehicle crashes (SVCs) under complex road geometry and inclement weather, which can significantly threaten traffic safety and mobility of the whole traffic system. Most existing studies involve various simplifications and approximations to assess the associated SVC risks promptly, and therefore the assessment accuracy is often compromised. A novel multi-fidelity approach is developed for the reliability-based risk assessment of SVCs to balance the simulation accuracy and efficiency. Specifically, a high-fidelity transient dynamic vehicle model is introduced for a robust estimation of the vehicle dynamics under various driving environments, assisted by a low-fidelity simplified physics-based vehicle model to improve the computational efficiency. Based on the simulations of the two models, a new multi-fidelity improved cross entropy-based importance sampling (MFICE) algorithm is proposed for integrating multi-fidelity information and facilitating accurate and efficient reliability analysis. Five demonstrative cases are studied to evaluate the performance of the proposed approach, including the comparison with existing representative approaches. The results show that the proposed innovative multi-fidelity approach can provide a reliability evaluation of SVCs both accurately and efficiently, with obviously superior performance over typical state-of-the-art counterparts. Therefore, the proposed approach bears great potential on developing proactive and near real-time intelligent traffic operation and management strategies against SVCs in both normal and hazardous conditions.

A multi-objective optimization design approach of large mining planetary gear reducer

A two-stage computational framework is proposed to optimize the radiated noise and weight of a large mining planetary gear reducer under the rated conditions, based on a combination of response surface methodology and multi-objective optimization. The well-established transient dynamic analysis model of a large mining planetary gear reducer, which is used to analyze the mechanical strength and acoustic characteristics of the gear reducer. A unified experimental design is developed to obtain the response surface of the gearbox radiated noise and the mass of the gearbox housing. After obtaining the multi-objective optimization function, the multi-objective optimization problem for a lightweight and low-noise gearbox is performed using non-dominated sorting from the Genetic Algorithm II (NSGA-II). The research results demonstrates the effectiveness of the proposed optimization method in reducing vibrating amplitude and weight of the gearbox. This is crucial for minimizing energy consumption and enhancing the overall performance of the system. Additionally, the optimized gearbox design not only saves energy but also contributes to the reduction of carbon emissions, making it environmentally friendly.

Applying artificial neural network to approximate and predict the transient dynamic behavior of CO2 combined cooling and power cycle

The CO2 combined cooling and power cycle (CCP) is a promising alternative for waste heat recovery due to its environmental friendliness and excellent performance. However, the transient dynamic behavior analysis and control of CCP systems are challenged by the instability of waste heat sources. In transient dynamic modeling, artificial neural networks, with their nonlinear mapping capabilities and relatively low computational requirements, prove advantageous over dynamic simulation models. In this study, six commonly used artificial neural network architectures are employed for approximating and predicting the transient dynamic behavior of CCP systems and subjected to preliminary applications. Results show that the multilayer feedforward neural network is the most suitable among the six networks for predicting and approximating the CCP system's transient dynamic behavior. Based on this model, a trajectory optimization control strategy is designed, leading to a 5.3 % improvement in CCP net power. This research underscores the effectiveness of artificial neural networks in the field of CCP dynamic modeling, offering valuable guidance for its application.

Analysis and optimization of tip-out transient dynamic characteristics of electric vehicle reducer under multi-bearing collaborative preloading

In this study, the transient dynamic response of an electric vehicle secondary reducer with a multi-bearing cooperative preload was studied. The time-varying mesh stiffness, mesh damping, backlash, axial dynamic stiffness, and axial preload of the system are considered. A novel transient dynamics model was established for the multi-bearing cooperative preloading of the electric vehicle secondary reducer suitable for transient conditions. The accuracy of the built model is verified using a bench test. Subsequently, the transient dynamic response of the reducer system under tip-out working conditions was determined. The optimal preload combination of the bearing was determined using an optimization algorithm. The simulation results show that, under the tip out working condition, increasing the bearing preload can effectively restrain the transient impact of the reducer system, and the optimal bearing preload combination obtained by multi-objective optimization using an optimization algorithm can significantly reduce the transient shock problem of the electric vehicle drivetrain. This study provides theoretical support for suppressing transient shocks in electric vehicle reducer.

Fatigue analysis of large anvil in the pile driving of offshore wind turbines

Pile foundations are commonly used as supports while installing offshore wind turbines (OWTs). An anvil is periodically stressed by impacts during construction. Owing to this cyclically varying stress, the anvil may eventually fail from fatigue. The influence of the verticality deviation on the impact pile driving is examined. A transient dynamic model is created using ABAQUS to examine the stress situation of the anvil. The dynamic analysis findings are used to predict the fatigue life of the anvil. The findings reveal that the anvil's maximum stress value is not considerably different when the verticality deviation is modest (0–2‰). However, the maximal stress exhibits a linear growth trend as the verticality deviation increases further. Even if the difference in the maximum stress while the verticality deviation is low is negligible, as the verticality deviation increases, the anvil's fatigue life rapidly shortens. The mean stress and fatigue life of an anvil are examined to determine the precise link between these two variables. The results reveal that although the fatigue life of the anvil in various locations is not entirely consistent with changes in the mean stress, in general, the life (logarithm) reduces linearly as the mean stress increases.

Research on Influence Law of Pressure Wave Based on Copper Ball Manometric Method

With the continuous improvement of artillery performance, internal ballistics and charge performance, abnormal phenomena of internal ballistic environment will appear during the firing process of artillery, mainly manifested as strong fluctuations in chamber pressure. If the pressure fluctuation exceeds a certain level, the pressure (overload) acting on the projectile will not be continuous and uniform, which will inevitably bring about the repeated loading process under dynamic conditions, resulting in the compatibility of the internal ballistic environment of the artillery launching guided munitions. According to the copper ball pressure measurement method commonly used in large-caliber artillery, this paper establishes the effect of the copper ball pressure gauge under different pressure curves in the bore, and verifies the established transient dynamic model. The force process of caliber-artillery projectiles under different transient pressure conditions in the bore (with and without pressure waves) is compared and analyzed, which provides a theoretical reference for the strength design of guided artillery projectiles and the coupling design of artillery projectiles, guns and powders.

Spatial and temporal averaging in the homogenisation of the elastodynamic response of periodic laminates

This paper suggests a methodology to obtain homogenised material properties from a transient dynamic numerical model. The standard Hill–Mandel Principle, based on spatial averages, is extended with time averaging. Thus, in addition to a sufficiently large Representative Volume Element (RVE) to carry out the averaging in space, a sufficiently large time window is required to carry out the time averaging. The space–time averaging procedure is validated for a periodic laminate bar subjected to a variety of boundary conditions, impedance contrasts and loading conditions. The homogenised results converge to the analytical solutions and confirm that having a higher impedance contrast between laminate components requires not only larger RVE sizes but also longer time averaging windows. The most efficient macroscopic approximation is obtained by a balanced increase in RVE size and time averaging window.

Influence of a transient bubble dynamics cavitation model for squeeze film dampers on the run‐up behaviour of a turbocharger rotor

AbstractThe force response of squeeze film dampers and hydrodynamic bearings is significantly influenced by the occurence of cavitation inside the lubricant films. The viscosity of the occuring mixture of oil and air bubbles is vastly different than that of pure lubricant and therefore changes the pressure build‐up and thereby the stiffness and damping properties of the lubrication films. To accurately predict the force response of a squeeze film damper, the cavitation and its effect on the pressure build‐up therefore has to be taken into account. Well known cavitation algorithms for lubrication problems, like the Elrod algorithm or the two‐phase‐model, neglect the transient nature of outgassing and assume instantaneous bubble formation and collapse. In the presented paper, a transient bubble dynamics model based on the Rayleigh‐Plesset‐Scriven equation is utilised instead and its effect on the rotordynamic behaviour of a turbocharger rotor is examined based on fully transient multi body dynamics simulations.

Analysis and Optimization of the Opening Dynamic Characteristics of Molten Salt Check Valves for Concentrating Solar Power

The poor opening dynamic characteristics of molten salt check valves, used in concentrating solar thermal systems, constitute the main cause of valve disc oscillation and low pressure difference difficulty in opening during molten salt delivery. A molten salt swing check valve is designed to meet the requirements of high-temperature and high-pressure sealing and anti-crystallization flow channels. A transient dynamics model of the valve motion components is established, dynamic mesh and UDF (user-defined function) techniques are used to simulate the non-constant flow of hot molten salt and the opening process of the check valve and to analyze the dynamic characteristics of the opening process. Topological optimization of the valve motion components is proposed for the first time in order to improve the opening performance of the check valve, and the topological optimization of the valve motion components is based on the solid isotropic material penalty (SIMP) model with the variable density method and thermal–fluid–mechanical coupling method. The design is also verified for the dangerous working condition of a molten salt hammer. The results show that the mass of the valve motion component is reduced by 57.76% after optimization while meeting the requirements of strength and stiffness. The optimized molten salt check valve achieves a larger angle and faster opening, the full opening angle is increased by 6°, the positive resting pressure difference of the valve is reduced by 5 kPa, the minimum opening pressure difference is reduced by 8.9 kPa, the optimized flow characteristics are smoother, and the valve disc oscillation problem is avoided. The study provides a method for researchers to use to optimize the design of a molten salt swing check valve and its dynamic characteristics for concentrating solar power, which is of great significance in efforts to improve the stability of the molten salt transport system.

Experimental research on the contact force of the bi-directional pig in oil and gas pipeline

The migration process of the pig in oil and gas pipeline is a complex dynamic problem. During the pigging operation, the variation of friction force caused by the nonlinear contact between the sealing disc and the pipe wall is the key factor affecting the dynamic characteristics of the pig motion. At present, the existed pigging models for predicting pigging behavior regard friction as an invariant constant. Experimental research indicates that the friction force of the pig varies with the contact force and the lubrication conditions. Therefore, the assumption that the friction force is constant cannot reflect the friction dynamic characteristics of the pig during pigging, and will also affect the accuracy of the pigging model. Exploring the variation of friction force of pig under different conditions is the basis of establishing the transient dynamic model of a pig. As a result, in this paper, a method of direct measurement of contact force between the pig and the pipeline is presented, the contact force, the friction force, as well as the friction coefficient of the pig are obtained from the experiment. Research results in this paper can help to establish a more accurate dynamic model of pig.

Influence of inlet pressure disturbance on transient performance of liquid oxygen lubricated mechanical seal and rub-impact phenomenon caused by excitation overload

The dynamic stability of the non-contacting mechanical seal (NMS) under variable working conditions is a vital factor for the reliable operation of rotating equipment. This paper presents a transient dynamic model to investigate the parametric response of liquid oxygen lubricated NMS under inlet pressure disturbance, which comprehensively considers asperity contact, micro-clearance lubrication and dynamic motion of a flexible mounted ring. Meanwhile, various forms of rub-impact phenomenon and dynamic instability caused by excitation overload are also analyzed. Lastly, an experimental research is proposed with diverse sensors to monitor the parameter data under pressure disturbance. In addition, the characteristics of acoustic emission signals when rub-impact of friction pair occurs are further investigated and processed, including various impact forms and location method.

Full-circle localization diagnosis of rolling bearing outer ring defects based on double-vibration signal fusion

Localization diagnosis (LD) of rolling bearing outer ring defects plays an important role in failure cause analysis and residual life prediction. This study aims to solve three main issues in the existing LD methods. Firstly, a full-circle functional relationship between outer ring defect and localization index is established based on the dynamics simulation analysis of bearing system. Secondly, the generation mechanism and solution method of the positioning datum are determined using a novel finite element transient dynamic model. Furthermore, variation law of the initial direction of the fault impact under different angular positions is investigated. Lastly, a general localization rule applicable to outer ring defects in the full-circle range is proposed. Therefore, a full-circle localization formula for outer ring defects based on the characteristic fusion of horizontal–vertical signals is proposed. Simulation results verify the effectiveness of the proposed localization formula. Additionally, a morphological filter for LD is investigated to resolve the diagnostic error caused by noise interference in the actual signal. Experimental results show that the presented method can considerably improve diagnostic accuracy.

Topology detection of a distribution network based on adaptive state observer

The traditional distribution network lacks real-time topology information, which makes the implementation of smart grid complicated. The smart grid needs to monitor and dispatch the grid to maintain the economic and safe operation of the system. In this paper, we propose a topology detection algorithm of the distribution network based on adaptive state observer. Based on the transient dynamic model of the distribution network, the line states of the distribution network are regarded as unknown parameters, a virtual adaptive state observation network is built, and the topology can be inferred by the changes of adaptive state parameters. Finally, the effectiveness of our algorithm is verified by the MATLAB simulation experiments.

Oil Friction Loss Evaluation of Oil-Immersed Cooling In-Wheel Motor Based on Improved Analytical Method and VOF Model

Oil-immersed cooling provides an effective cooling scheme for high-power hub motors with compact structure and serious heating problems. However, with this cooling method, some oil friction loss will be generated, making the output torque and efficiency of the motor lower, which limits its application in the motor. It is essential to get an exact calculation of the oil friction loss so that it can be reduced in the future research. Firstly, a new method was proposed to improve the accuracy of oil friction loss calculated by an existing analytical method (Kori’s method), while the influence laws of oil-soaked depth and rotation speed on it were explored. Secondly, a three-dimensional transient Computational Fluid Dynamic (CFD) model based on Volume of Fluid (VOF) was established, considering the actual complex structure and the disorderly mixing of oil and air inside the motor. Finally, the oil friction loss calculated with an improved analytical method and a VOF model was verified by a testing. It was indicated that the VOF model was more precise but more time-consuming. The proposed method has the second highest accuracy but takes less time.