Dynamic Coefficient Research Articles

Influence of roughness and cross slope induced dynamic loads on flexible pavement responses

ABSTRACT Among all the factors influencing flexible pavement design, vehicular loads are of prime importance. Thus the present study evaluates the dynamic wheel loads on the pavement by considering the prime factors related to the vehicle and the pavement. Relationships are developed for three different trucks considering the combined effects of vehicle speed, gross vehicle weight, and pavement roughness on dynamic loads. The study further quantified the effect of pavement cross slope on vehicular loading in the outer wheel path. Furthermore, the critical responses for a flexible pavement section are determined using finite element analysis by considering the viscoelastic properties of asphalt layers and moving loads. The findings of this study reveal that, even for a smooth pavement with roughness ranging between 1 and 2 m/km, the dynamic load can be 7–13% higher than the static weight. The dynamic loads further increase rapidly as the pavement deteriorates. Compared to the conventional static analysis, incorporating dynamic loads into pavement analysis revealed an increase in the critical responses by 6–50%. Further, due to the interplay between vehicle speed, dynamic load coefficient, effective load, dynamic modulus, and loading frequency, a non-linear decrease in critical responses is observed with increased vehicle speed.

Effect of thermal oxidative ageing on the molecular structure and tribological properties of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE), which has an extremely low coefficient of friction and good thermal and chemical stability, is widely used as a self-lubricating material. In this study, the thermal oxidative-ageing mechanisms of PTFE were studied using infrared spectroscopy and molecular dynamics simulations, and the influence of the thermal oxidative-ageing time on its tribological properties was investigated under a high load (20 MPa). Results indicated that thermal oxidative-ageing resulted in oxidation fracture, generating CF2O products, followed by further oxidation to CFO2 as ageing time increased. The dynamic friction coefficient of PTFE fluctuated significantly under heavy load, and its wear rate fluctuated over a small range but showed a decreasing trend with increased ageing.

Dynamical behavior and transport coefficients of the pseudo hard-sphere fluid

In this work, we employ a recent approach to characterize the hard-sphere (HS) fluid by means of a continuous interaction potential, commonly referred to as pseudo hard-sphere potential, in order to determine HS transport coefficients as a function of the volume fraction for the three-dimensional mono disperse fluid. Using equilibrium molecular dynamics simulations, we determine time-dependent velocity, shear stress, and energy flux autocorrelation functions in order to use them within the Green–Kubo framework to compute the self-diffusion, shear viscosity, and thermal conductivity coefficients, respectively. Results are discussed as a function of the volume fraction and were compared to theoretical and simulations results previously reported by other authors. The main purpose of this work is twofold: first, testing the continuous approach of the HS fluid for the computation of dynamic properties and second, performing a systematic determination of aforementioned transport coefficients to analyze them as a function of fluid volume fraction. Furthermore, our results are used to provide a practical correction to the Chapman–Enskog equations for the HS self-diffusion, shear viscosity, and thermal conductivity predictions in a wide range of volume fractions.

Lateral Adaptive Control of Parafoil-Payload System

The motion of a parafoil is characterized by nonlinear dependence of aerodynamic loads on angle of attack. Nonlinear dynamics and non-rigidity of parafoil-payload system causes difficulty in estimating aerodynamic coefficients of the parafoil with respect to angular rates. The present paper addresses the problem of lateral control of a generic 9 degree of freedom parafoil-payload system under small perturbations. A Lyapunov based dynamic adaptive controller is proposed in order to control such a system with known static coefficients and unknown dynamic coefficients. It is demonstrated numerically that the proposed controller is capable of controlling the system without estimating dynamic coefficients (theoretically or experimentally).

Research on the Dynamic Characteristics of Perfluoroalkoxy Alkane Springs.

Semiconductor cleaning system ultra-clean flow control pumps are critical equipment in the semiconductor industry. Among them, the perfluoroalkoxy alkane (PFA) spring is a pivotal component to control the pump, and its dynamic performance is crucial to ensure the efficient operation of the system. However, the dynamic performance of the spring is often affected by the operating frequency. This paper studied the effect of different working frequencies on the dynamic property of the spring through compression-cycle experiments under uniaxial sinusoidal excitation. The force-displacement curves under different compression frequencies were fitted to obtain the dynamic stiffness of the PFA spring under different cyclic loading frequencies. The variation in the spring's hysteresis coefficient was evaluated using the hysteresis curves of different cyclic loading conditions. After 2 million compression experiments, the changes in dynamic stiffness, hysteresis coefficient, and spring height were investigated. The obtained results revealed that, as the frequency increases, the dynamic stiffness of the spring increases. The hysteresis coefficient of the PFA spring is the largest at 10 Hz and the smallest at 6 Hz. Upon conducting 2 million compression tests, it was discovered that the dynamic stiffness experiences the greatest attenuation rate of 4.19% at a frequency of 8 Hz, whereas the hysteresis coefficient undergoes the largest attenuation of 42.1% at a frequency of 6 Hz. The results will help to improve the design and application level of PFA springs.

Artificial neural network for tilting pad journal bearing characterization

Tilting pad journal bearings (TPJBs) are modeled with Reynold-based models or computational fluid dynamics (CFD) approach. In both cases, the estimation of the dynamic coefficients of the oil-film forces and the static characteristic, can be computationally expensive and time consuming. Artificial Intelligence (AI) is assuming a key role in engineering but is rarely applied in fluid film bearing analysis. A properly trained Deep Learning (DL) model can perform very fast predictions of TPJB behavior with accuracy comparable to more time-consuming models. In this case, the main drawback is the time required to build the training dataset. In this work, an Artificial Neural Network (ANN) is trained to predict the dynamic stiffness and damping coefficients along with the main static quantities of TPJBs, such as minimum oil-film thickness and inlet flowrate. At first, a design of experiment is performed to build an appropriate training dataset. Secondly, a Reynolds-based thermo-hydrodynamic (THD) model is used to populate the training dataset and an appropriate test dataset. Then, a feed-forward ANN is trained with Levenberg–Marquardt backpropagation and its architecture is optimized to increase accuracy. Finally, the accuracy of the ANN is tested using the test dataset and experimental data. The time and computational effort required by the ANN regression are much less than those required by the THD model. Therefore, the trained ANN is an effective and efficient tool for the characterization of TPJBs.

Study on the Dynamic Response of the Component Failure of Drum-Shaped Honeycomb-Type III Cable Dome with Quad-Strut Layout

The drum-shaped honeycomb-type cable dome departs from traditional concepts and incorporates the idea of multiple strut configurations. It is the most diverse type of cable dome structure. Both cables and struts serve as the main load-bearing components. Analyzing the effects of local component failure is crucial for designing large-scale cable domes able to resist continuous collapse. A numerical analysis model using the ANSYS finite element method with a 120 m span is established. Dynamic analysis methods are employed to study the response of structural internal forces and displacements during the failure of different component types. By defining the internal force dynamic coefficient and change coefficient, the structural continuity collapse resulting from component failure is determined based on computational results and observation of structural deformations. Furthermore, the importance of the various components within the overall structure is classified. The research findings indicate that the failure of individual components does not cause overall instability of the structure. The importance level of the ring cables and some upper chord ridge cables is higher than that of the inclined cables. Class a struts have a higher importance level than class b struts. Additionally, the importance level of outer ring components is higher than that of inner ring components.

CONSTRUCTION SAFETY INSPECTION PLATFORM OF HIGH-SPEED RAILWAY SUPER LARGE SWIVEL BRIDGE BASED ON NUMERICAL SIMULATION

In recent years, when building bridges across existing railways, in order to reduce the interference to the railway operation line during the construction process, parallel railways are often used to cast bridges and then rotate them. In this paper, combined with the engineering example of Zhaochuan Super Swivel Bridge on Beijing-Zhanghai High-speed Railway, the key and difficult points of the swivel bridge during construction are monitored, and compared with the computer simulation data, the static friction coefficient, dynamic friction coefficient and friction couple distance of the swivel system are obtained. Model each component of the bridge body, establish a safety monitoring and early warning method, system, storage medium, and early warning platform, and visually display the safety degree of components at different stages and locations by color discrimination.

Development of a new dynamic smagorinsky model by an artificial neural network for prediction of outdoor airflow and pollutant dispersion

Fast fluid dynamics (FFD) with the dynamic Smagorinsky model can provide accurate predictions of outdoor airflow and pollutant dispersion. However, it is a time-consuming process because the model coefficient is calculated through a formula consisting of subgrid stress difference Lij and strain rate tensor difference Nij, which are obtained by filtering the flow field twice. To reduce the computing time, this investigation proposed a new dynamic Smagorinsky model which calculated Lij and Nij by means of an artificial neural network (ANN). The method was implemented in an open-source program, OpenFOAM. A single-building case was selected as the training set for the ANN. Other cases of varying complexity were used as testing sets to verify the model's generalizability. The dynamic model coefficient has the same distribution characteristics and similar values in different outdoor cases. The ANN model can capture those distribution characteristics and predict the dynamic model coefficient accurately. This study compared the accuracy and computing efficiency of FFD with the new dynamic Smagorinsky model, the standard Smagorinsky model, and the original dynamic Smagorinsky model. Compared with the original dynamic Smagorinsky model, the new dynamic Smagorinsky model saved the computing time by more than 60% when calculating turbulent viscosity, thus reducing the overall computing time by more than 20%, while maintaining similar accuracy. The use of FFD with the new dynamic Smagorinsky model is recommended for outdoor airflow and pollutant dispersion studies.

Vibration characteristics of turbocharger rotor system considering internal thread texture parameters of semi-floating ring bearing

The internal thread texture causes changes in the dynamic characteristics of the oil film of the semi-floating ring bearing, which affects the amplitude of vibration and operating life of the turbocharger rotor system. Based on the fluid lubrication theory, the oil film governing equation of a semi-floating ring bearing with surface texture parameters is derived. The effects of the texture depth, position, and number of turns of the internal thread on the dynamic characteristics of the bearing oil film, such as the maximum pressure, load-carrying capacity and stiffness damping, are analyzed. Taking a type of turbocharger as an example, a hydrodynamic model is established to analyze the oil film lubrication in the semi-floating ring bearings, and the dynamic characteristic of the oil film is analyzed by computational fluid dynamics method. The results show that the maximum pressure, bearing capacity, and stiffness damping coefficient of oil film increase firstly and then decrease with the increase of texture depth and the number of thread turns in the range of journal rotation speed from 1000 to 20,0000 r/min. Compared with the non-texture bearings, the dynamic characteristics coefficients of the oil film such as bearing capacity and stiffness damping increase the most, when the depth of texture is 0.006 mm and the number of thread turns is 9. Secondly, the dynamic characteristic coefficient of oil film is improved when the texture is distributed in the middle than on both sides. The thread texture with appropriate parameters can suppress the rotor system vibration amplitude. The conclusion can provide a reference for the design of textual parameters of semi-floating ring bearings.

A novel specialized material removal rate model considering the synergistic effect of dynamic pressure and shear stress for the permanent-magnet small ball-end magnetorheological polishing

Permanent-magnet small ball-end magnetorheological polishing is often used to process small glass workpiece. During polishing, the pressure and shear stress are generated by magnetorheological fluid on the workpiece surface. When conducting fixed-point polishing experiment on fused silica plane workpiece, it was found that the polished pits were mainly distributed on one side of the polishing head's rotation axis. However, the available material removal model considering only a single force cannot explain the cause of polished pit offset phenomenon. It is speculated that the synergistic effect of the two forces on material removal may lead to the offset phenomenon. In order to accurately describe the material removal mechanism of this polishing method, a novel material removal rate model is established in this research. First, a group of actual polished pits are obtained through fixed-point polishing experiment. Then, a novel pressure-shear stress synergistic material removal rate model with unknown coefficients is established. Based on this model, the fixed-point polishing process is simulated by finite element method. The simulated polished pits under different model coefficients are obtained, and the influence rules of model coefficients on the polished pit contour is analyzed. Finally, by seeking the minimal fitting error between the simulated and actual contours, a group of optimal model coefficients are determined, namely, the shear stress coefficient is 1, the dynamic pressure coefficient is 1.2, and the weight coefficient of polishing velocity is 1.9. Through verification, the relative error between the simulated and actual contours can be as low as −9.12 % to 7.13 %. The novel model reveals that the material removal is caused by both shear stress and dynamic pressure. The dynamic pressure is distributed on one side of the polishing head axis and plays a leading role in material removal, which can well explain the cause of offset phenomenon. This research fills the blank of material removal mechanism of this polishing method, and the novel model provides a theoretical basis for process optimization research.

A Simplified Model for the On-Line Identification of Bearing Direct-Dynamic Parameters Based on Algebraic Identification (AI)

In this paper, a mathematical model is presented to identify the direct dynamic coefficients (kxx, kzz, cxx, czz) of a pressurized bearing in a rotor-bearing system. The presented mathematical model for online identification is the result of the application of the algebraic identification approach to a two-degree-of-freedom rotor-bearing model. The proposed identification model requires only the vibration response as the input data. The performance of the model was assessed by theoretically and experimentally testing the proposed identifier at different shaft frequencies and, for the experimental test, a pressurized bearing that has hydrodynamic and hydrostatic characteristics at a support pressure of 10 psi was considered. The working fluid is Chevron GST 32 oil. The results show negligible differences between the vibration response of the experimental rotor and those obtained numerically using the identified direct dynamic coefficients of the pressurized bearing. In addition, it is observed that the algebraic identifier determines the identified parameters in a time less than 0.2 s. The proposed identifier can be used in other types of bearings, which is a great advantage over other identifiers.

Mechanical and friction properties of agricultural plastic film during autumn harvest period of cotton in Xinjiang, China.

Agricultural plastic films have caused serious plastic pollution. There are many studies that consider mechanical recycling an appropriate system for the recovery of post-consumption agricultural mulch film. The recovery effect of plastic film depends on the mechanical properties, the level of dirtiness of the post-consumption film, and the recycling process itself. In this study, the mechanical properties of four types of polyethylene plastic films with a thickness of 8, 10, 12, and 10μm, weather-resistant, commonly used in Xinjiang cotton fields, were tested. As well as the friction coefficient between the film and soil, the cotton stalk, boll shell, and leaf with different moisture contents were measured. Then, the self-propelled straw chopping and residual film recycling combined machine collected the four types of mulch films. The results showed that the longitudinal mechanical properties of the plastic film were greater than the transversal ones, with the exception of the nominal tensile strain at break, and the tensile characteristics of the mulching film covered with soil were greater than those without soil. The dynamic or static friction coefficient between the film and the contact material had a linear relationship with the moisture content of the material. During the recycling operation, the better the mechanical properties of the plastic film, the higher the pick-up rate of the mulch film. The maximum longitudinal tensile force of 12-μm plastic film was 3.42 N, and the nominal tensile strain at break was 303.09%. The pick-up rate reached more than 93% when the 12-μm plastic film was recovered in autumn, which effectively reduced the residue of plastic film coverage in the current year. Moreover, the more soil that was present on the much film, the greater the soil content of the recycled film roll, and the stalk content also increased, but the change was small. The research provides a reference for the mechanical and the friction features of agricultural plastic film in Xinjiang, and provides a theoretical basis for the formulation of standards for film thickness and mechanical properties, as well as the design and optimization of a residual film collecting machine in the cotton field.

Calculation of Dynamic Coefficients of Air Foil Journal Bearings Using Time-Domain Identification

Dynamic coefficients of a bearing are basic elements of rotor dynamics analysis. At present, there are still some issues in the calculation of the dynamic coefficient of air foil bearing. In this paper, the dynamic coefficients of the air foil bearing are calculated by time-domain identification. This method does not need to linearize the system equations, so it is generally applicable to different models for air foil bearings. Using the established method, this paper verified the calculation results using the foil model with axial uniform deformation for the first time, and the influence of the foil model on the dynamic coefficients was studied. The calculation results of the foil models with axial uniform deformation and axial independent deformation have significant differences. Furthermore, the accuracy of the dynamic coefficient method for different disturbance amplitudes was compared. The results indicate that the dynamic coefficient method has good accuracy over a large disturbance range.

Dynamic Behavior of a Tilting-Pad Thrust Bearing Operating Under a Hybrid Lubrication Regime

Abstract The present contribution aims to evaluate the effects of the oil pressure injection on the dynamic behavior of a hybrid-lubricated tilting-pad thrust bearing. First, a thermohydrodynamic model is applied to determine the equilibrium position as dictated by pressure and temperature distributions resulting from both hydrodynamic and hybrid lubrication regimes. Subsequently, the perturbation and frequency reduction methods are applied to determine the stiffness and damping coefficients of the bearing for various operational conditions. The results show that the dynamic force coefficients are strongly dependent on the operational conditions of the bearing, such as static load and rotating speed, as well as the perturbation frequency, for both lubrication regimes. The quantification of the injection pressure influence on the force coefficients of hybrid-lubricated thrust bearings is the main original contribution of this work.

Remarks on the experimental behaviour of curved surface sliders of the new Polcevera Bridge in Genoa

This work presents the results of the procedure of certification and acceptance for the sliding behavior of non-standard devices curved surface sliders, used for the seismic isolation of the New Polcevera Bridge. Indeed, the deck is seismically isolated from the piers. The supporting scheme withstands the seismic actions, wind actions and thermal actions, very relevant in a 1067 m length bridge without middle expansion joints. The paper aim is to describe the approach followed during the construction supervision process for the functional certification and acceptance tests of the bearing devices coherently with Italian and European codes. The paper highlights the main issues encountered during the application of the different specifications. A description of the different functional tests required during the construction supervision process is presented as well as an overview of the different acceptance criteria of the tests results. The intent is to prepare a series of useful recommendations for the definition of the seismic acceptance tests for bearing devices for highway bridges in Italian and European contest. Finally, all the results regarding the static and dynamic frictional coefficients, have been used to derive regressions laws, by also comparing them with the outcomes of previous literature studies.

Influence of Morphological Characteristics of Coarse Aggregates on Skid Resistance of Asphalt Pavement.

This research aims to improve the durability of skid resistance of asphalt pavement from the perspective of coarse aggregates based on on-site investigation. Firstly, the skid resistance of six representative actual roads was tested during two years by employing the Dynamic Friction Tester and the attenuation characteristics of skid resistance of different types of asphalt pavements were analyzed. Secondly, core samples were drilled onsite and coarse aggregates were extracted from the surface layer of the core samples. The morphological parameters of coarse aggregates were collected by a "backlighting photography" system and three-dimensional profilometer, and the variation rules of angularity and micro-texture of coarse aggregates were investigated. Finally, the correlation between the morphological characteristics of coarse aggregates and the pavement skid resistance was established based on the grey correlation entropy. The research results show that with the increase in service time, the attenuation rate of skid resistance of asphalt pavement gradually slows down; the angularity of coarse aggregates gradually decreases, and the micro-texture on the wearing surface gradually wears away. The grey correlation entropy between all the micro-texture indexes of coarse aggregates and dynamic friction coefficient, as well as between the roundness and skid resistance is more than 0.7, whereas the correlation between other evaluation indicators and the dynamic friction coefficient is poor, indicating that compared with the angularity of coarse aggregates, the micro-texture affects the skid resistance of actual asphalt pavement more greatly. In engineering applications, the use of coarse gradation, coarse aggregates with high roughness or high anti-wear performance can slow down the attenuation of pavement skid resistance, so that the pavement can maintain superior long-term anti-skidding performance.

Improved Nelder-Mead algorithm for output voltage control of a synchronous generator

It is known that the standard Nelder-Mead algorithm (NMA) is subject to the problem of local minimum. This paper proposes an improved Nelder-Mead algorithm (INMA) based on dynamically varying the reflection, expansion, contraction and the shrinkage coefficients, following a cosine function. Dynamical coefficients intensify the search space exploration and also increase the ability of quickly finding the optimal solution. Firstly, the effectiveness and validity of this approach are confirmed by using some benchmark functions. Secondly, the approach is also verified by applying it for tuning a Proportional–Integral–Derivative (PID) controller used to regulate the voltage of a synchronous generator (SG) under different loading conditions. The PID controller parameters are obtained by a minimisation of the quadratic output error between the reference and the SG output voltage calculated from the adopted model. A comparison is established between INMA, standard NMA, genetic algorithm (GA) and particle swarm optimisation (PSO). The Obtained results show that the INMA has a better performance compared to other algorithms.

Numerical and experimental investigation on autoparametric resonance of multi-system structures

The analysis of dynamic stability in frame structures has always been a critical issue in engineering and mechanical design. Autoparametric resonance instability problems present a more complex dynamic instability mechanism than general parametric resonance, and determining the unstable regions of frame structures with multiple subsystems requires consideration of the coupled vibration of each subsystem. Unfortunately, existing approximate formulas are inadequate to analyze the stable boundary of autoparametric resonance in frame structures. To address this issue, this paper proposes a novel method called the dynamic axial force transfer coefficient (DTC) method to investigate the spatial dynamic instability characteristics of complex frame structures under parametric excitation due to autoparametric resonance. The proposed method, in conjunction with the harmonic balance method and the finite element method (FEM), established the global finite element equation of the frame and derived the stable boundary equation of autoparametric resonance for general frame structures. A complex spatial frame model is built to verify the effectiveness of the DTC method, and a comprehensive parametric analysis is conducted to investigate the dynamic instability mechanism of autoparametric resonance, including structural damping, static load coefficient, connection and boundary conditions of subsystems, and cross-sectional dimensions of subsystems. The results show that autoparametric resonance stability analysis of frame structures should consider the design parameters of each subsystem independently. In addition, strong coupling interaction between subsystems may induce autoparametric internal resonance of structure subjected to dynamic load. An autoparametric resonance test of a Γ-shaped frame is presented to further verify the proposed method. The test reveals the mechanism of the strong coupling effect, which may lead to a high risk of structural failure. More importantly, the DTC method can accurately determine the unstable boundary of multi-system frame structures, which is consistent with conventional methods (EGE) and experimental results, and predict the strong coupling effect of practical structures. The proposed method is simpler and more convenient than the existing methods for stability analysis of the autoparametric resonance of general frame structures, and can provide more effective guidance for structural design.

Comparative study of instrumental measurement and sensory evaluation methods for the repairing effect of mildly damaged hair bundles.

This study explores the applicability and scientific accuracy of instrument measurements in repairing hair products on slightly damaged hair bundles. Sixty hair bundles mildly damaged with hydrogen peroxide and ammonia standards were divided into two groups: the treatment and control groups (30 hair bundles each). The treatment group used commercial hair care essential oil, whereas the control group used tap water to treat the damage. The two groups were measured using an instrument before and after the product application. The objective indicators included the gloss of hair, along with hair cuticle dynamic friction coefficient, and against hair cuticle dynamic friction coefficient. At the same time, two evaluators conducted sensory evaluations on the gloss and frizz levels of the hair bundles. Therefore, data comparison and verification were carried out together with instrumental measurement data. We verified that the instrumental measurement methods could obtain data trends that are consistent with sensory assessment methods; hence, they have the advantages of accuracy, convenience, and quantifiability. Thus, the instrumental measurement methods we verifiedcan provide objective evidence for the efficacy of hair care products in repairing hair.