Dynamic Coefficient Research Articles

Model-Informed Generative Adversarial Network (MI-GAN) for Learning Optimal Power Flow

The optimal power flow (OPF) problem, as a critical component of power system operations, becomes increasingly difficult to solve due to the variability, intermittency, and unpredictability of renewable energy brought to the power system. Although traditional optimization techniques, such as stochastic and robust optimization approaches, could be leveraged to address the OPF problem, in the face of renewable energy uncertainty, i.e., the dynamic coefficients in the optimization model, their effectiveness in dealing with large-scale problems remains limited. As a result, deep learning techniques, such as neural networks, have recently been developed to improve computational efficiency in solving OPF problems with the utilization of data. However, the feasibility and optimality of the solution may not be guaranteed, and the system dynamics cannot be properly addressed as well. In this paper, we propose an optimization model-informed generative adversarial network (MI-GAN) framework to solve OPF under uncertainty. The main contributions are summarized into three aspects: (1) to ensure feasibility and improve optimality of generated solutions, three important layers are proposed: feasibility filter layer, comparison layer, and gradient-guided layer; (2) in the GAN-based framework, an efficient model-informed selector incorporating these three new layers is established; and (3) a new recursive iteration algorithm is also proposed to improve solution optimality and handle the system dynamics. The numerical results on IEEE test systems show that the proposed method is very effective and promising.

Resistance of Heterogeneous Metal Compositions to Fracture under Dynamic and Cyclic Loads

This paper presents the results of experimental data analysis, which indicate an increased resistance of heterogeneous multilayer clad composites to dynamic loading destruction compared with homogeneous materials. The reason for this is the crack retardation caused by lamination at the boundary of the layers. The destruction of heterogeneous compact composite samples by cyclic off-center stretching also occurs with crack retardation, with the fractogram clearly demonstrating the transverse tightening of the sample section. We argue that crack nucleation plays a decisive role in the process of dynamic destruction of heterogeneous composites obtained by both multilayer cladding and explosion welding. This study presents generalized calculated data confirming the influence of the sign and magnitude of residual stresses (the appearance of a stress discontinuity) on the conditions of fatigue surface crack nucleation and propagation. Unlike homogeneous materials obtained by casting, forging (rolling), or cladding, which are characterized by a linear dependence of the crack propagation velocity on the dynamic stress intensity coefficient, for multilayer composites consisting of strong and viscous layers, a sharp crack deceleration is observed. This is due to the transition of the crack boundary between the strong and viscous layers. This paper presents studies of the corresponding properties of adjacent layers on the integral characteristics of the deposited composite.

Effects of Block Copolymer Terminal Groups on Toughening Epoxy-Based Composites: Microstructures and Toughening Mechanisms.

Despite the considerable research attention paid to block copolymer (BCP)-toughened epoxy resins, the effects of their terminal groups on their phase structure are not thoroughly understood. This study fills this gap by closely examining the effects of amino and carboxyl groups on the fracture toughness of epoxy resins at different temperatures. Through the combination of scanning electron microscopy and digital image correlation (DIC), it was found that the amino-terminated BCP was capable of forming a stress-distributing network in pure epoxy resin, resulting in better toughening effects at room temperature. In a 60 wt.% silica-filled epoxy composite system, the addition of a carboxyl-terminated BCP showed little toughening effect due to the weaker filler/matrix interface caused by the random dispersion of the microphase of BCPs and distributed silica. The fracture toughness of the epoxy system at high temperatures was not affected by the terminal groups, regardless of the addition of silica. Their dynamic mechanical properties and thermal expansion coefficients are also reported in this article.

Research on the bidirectional sliding phenomena of a toppling rod under frictional situations

In this work, we investigated the phenomenon of spontaneous bidirectional sliding on a toppling rod under a frictional situation. We explained the reasons for sliding is the friction force from the table is not sufficient to support the horizontal acceleration of the mass center when toppling, so the rod itself has to obtain a horizontal acceleration and apply the inertia force to play the role of supporting the acceleration of the mass center. This phenomenon and converted the question into a mathematical model. We pick the contacting point between the rod and the horizontal surface as the reference point for our computing of physical quantity, therefore the torque caused by friction and normal force can be ignored. With this model, we finished the theoretical analysis of the effects of varying static friction and dynamic friction coefficients on the phenomenon, with computer simulations verified.

Fluid Film Bearings and CFD Modeling: A Review

This paper is a review of the literature about CFD modeling and analysis of journal, thrust, and aerostatic bearings; the advantages and disadvantages of each are specified, and the bearing problems that have been analyzed are discussed to improve their designs and performance. A CFD transient analysis of journal bearings was conducted using the dynamic mesh method together with movement algorithms while keeping a structured mesh of a good quality in the ANSYS Fluent software to determine the equilibrium position of the journal and calculate the dynamic coefficients. Finally, areas of opportunity for analyzing and designing fluid film bearings to improve their performance are proposed.

Inverse estimation of mode I fracture energies for structural adhesives from impact wedge peel tests

This work presents a practical approach to estimate mode I fracture energy of structural adhesives at high strain rates from impact wedge peel (IWP) tests. For this purpose, an inverse estimation approach is used which requires relevant input quantities for the associated IWP simulations, e.g., primarily the dynamic friction coefficient between the wedge and the fractured adhesive and the adhesive strength. We describe two new impact-pendulum-based test devices to measure these unknown parameters. These parameters serve as input for the IWP simulation from which the remaining unknown fracture energy of the structural adhesive is estimated by an efficient regression scheme. An uncertainty quantification approach is used to approximate the statistical deviation of the generated material parameters based on the deviation of the measured input parameters. Experimental IWP test results are matched to IWP simulation results for three different substrates. The entire workflow is tested and validated for two different structural adhesives.

Dynamic Characteristics Study of Elastic Ring Squeeze Film Damper with Rigid–Elastic–Oil Coupled Model

Due to the coupling of the damper journal with the elastic ring and oil film, the elastic ring squeeze film damper (ERSFD) shows better dynamic performance in comparison with the traditional squeeze film damper (SFD). Therefore, a novel rigid–elastic–oil coupled mathematical model was established. The elastic ring deformation, as the key point, is solved according to the planar bending theory. Then, based on the pressure governing equation of the oil film, using the central finite difference method, the oil film pressure was addressed. Meanwhile, the Simpson method was implemented to calculate the dynamic characteristic coefficients (equivalent stiffness and damping Ce) of ERSFD (DCCEs). Also, we analyzed the influence of journal eccentricity, oil film radius clearance, flexibility coefficient and damping hole diameter on the DCCEs, and the results were compared and verified with the existing literature. The sensitivity of each parameter to the DCCEs was analyzed by using the linear regression method. According to the results, the flexibility coefficient has the greatest effect on the DCCEs, followed by the oil film radius clearance. The eccentricity of the journal and damping hole diameter have the least impact. This work will provide a theoretical basis for reflecting on the bearing dynamic characteristics more truly and accurately.

Type series of resonant vibration equipment for concrete mixtures compaction and its main parameters calculation method

Introduction. Increasing the energy efficiency of vibration technology poses a number of challenges for its developers. A promising direction for reducing energy costs for driving vibration machines is the use of the resonance phenomenon. Due to the dynamic properties of the oscillatory system, it is possible to significantly reduce the power consumption of resonant vibration equipment, and in some cases, improve the quality of the products. The purpose of this article is to develop a standard range of resonant vibration equipment for compacting concrete mixtures and a methodology for calculating its main parameters.The object of research is the oscillatory system of a vibrating machine, consisting of two masses connected by the elastic and dissipative elements. In addition, the first mass is connected to a fixed base through elastic and dissipative elements.Materials and methods. The basic principles of theoretical mechanics, mathematical modelling and statistical processing of results were used in the research.Results. According to the research results, it was established that with an increase in the mass ratio of the oscillatory system, the dynamic coefficient decreases, and the width of the resonant zone increases. The regression equations are given. It has been established that with increasing rigidity of the working body, the dynamic coefficient decreases, and the horizontal section on the frequency response, the width of which does not change significantly, shifts to the region of higher frequencies. With an increase in the damping coefficient, the dynamic coefficient decreases, and the width of the resonant zone and the frequency range practically do not change. A wide range of nomenclature and masses of precast reinforced concrete justifies the development of a standard-size range of resonant vibration equipment. A standard range of light (up to 2 tons), medium (2-6 tons) and heavy (6-10 tons) types has been developed. Based on the analysis and generalization of research results, a method for calculating resonant vibration equipment for compacting concrete mixtures has been developed, which makes possible to increase its energy efficiency.

Fatigue Reliability Assessment of RC Beams in Heavy-Haul Railways Based on Point Estimate Method.

Heavy-haul railways have a high passing frequency of trains with a large axle weight, causing rapid accumulation of fatigue damage in reinforced concrete (RC) bridge structures, which significantly affects the safety of the bridges. To study the fatigue reliability of RC beams in heavy-haul railways, the fatigue performance function for RC beams in heavy-haul railways was established, and the fatigue reliability assessment method for bridge structures in heavy-haul railways based on the point estimate method (PEM) was developed. An 8 meter-span plate beam in an existing heavy-haul railway illustrates the method. The train axle weight and dynamic coefficient were considered random variables, and the first four moments of equivalent stress ranges were obtained. The traffic quantity of the heavy-haul railways was investigated, and the fatigue reliability was evaluated using the proposed method. In addition, the effects of annual freight volume and train axle weight on fatigue reliability were discussed. Results indicate that PEM can effectively and accurately evaluate the fatigue reliability of RC beams in heavy-haul railways. In the first 20 years of operation, the fatigue failure probability was less than the limit value specified in the standard. The increase in annual traffic volume and train axle weight will cause a significant increase in fatigue failure probability. The research results of this paper are expected to provide an important basis for the design and maintenance of reinforced concrete bridges for heavy-haul railways in the future.

Condition assessment of a concrete filled steel tube arch bridge using in-situ vibration measurements and an Improved Artificial Fish Swarm Algorithm

This study aims to assess the condition of a Concrete-Filled Steel Tube (CFST) arch bridge using in-situ vibration measurements, Finite Element Model Updating (FEMU) and an Improved Artificial Fish Swarm Algorithm (IAFSA). Dynamic coefficients, derailment coefficients and wheel unloading rates are extracted from the responses of running safety assessment. An updated finite element model using a kriging model and IAFSA is employed to evaluate the strength and rigidity of the structures. The results indicate that the natural frequencies and damping ratios of the CFST arch bridge meet the requirements of design code. The maximum bridge dynamic coefficient is found to be 1.085, indicating that the bridge dynamic performance is good. The wheel unloading rates of vehicle and locomotive exceed the specification limit, indicating that the track condition has to be improved before the bridge is operated. By updating an initial FE model, the errors between the predicted and the measured parameters are reduced to less than 5%.

Use of repeated indenter sliding coupled with finite element computations to investigate the tribological response of nano-twinned 316L stainless steel

The wear response of dynamically deformed 316 L austenitic stainless steels with varying percentages of compressive strain has been investigated. A relatively high strain rate of 80 s−1 has been used while compressing 316 L at engineering strains of 20 % and 80 %. Nano-indentation coupled with inverse algorithm approaches were used to extract the yield strength and strain hardening exponent of all the specimens. The strain hardening exponent decreased with deformation percentage while the strength enhanced, and these properties have been used in the finite element model (FEM) to find out the stresses and strains during repeated sliding to make scratches. A depth-sensing instrumented nano-indenter with a conical tip was used to make multiple scratches on all the specimens, and the damage in the form of scratch groove depth and width was characterized using a combination of profilometry and scanning electron microscopy. The results showed that the 80 %deformed sample exhibited the least wear damage evident in the form of thinnest scratch profiles, shallowest scratch depths and hence the least specific wear rate. However, after multiple cycles of sliding, undeformed and 20 % deformed samples showed similar wear rates. The friction coefficient decreased with an increase in the percentage deformation, but the dynamic friction coefficient for all the specimens saturated after about 30 passes of sliding. Cross-sectional scanning electron microscopic (SEM) imaging of the scratches revealed refinement and alignment of the microstructure along the shape of the bottom of the groove after repeated sliding. We discovered through the utilization of transmission electron microscopy imaging and selected area diffraction pattern that the region affected by scratching exhibited partial transformation of the initial austenitic phase into martensitic phase.

Effect of irregular silicon carbide and tackifying phenolic resin on friction coefficients of rubber compounds

AbstractRubber compounds with high friction coefficients are widely used in safety shoes, functional shoes, etc. However, in the presence of a liquid lubrication layer, friction coefficients between rubber compounds and the opposing surface are generally very low. In this work, friction coefficients of rubber compounds are improved by a two‐pronged method. First, micron silicon carbides (SiC) with irregular shape and knife‐edge are selected as fillers to improve the plowing friction in dry state, and to improve the adhesive friction in wet state via piercing the liquid lubrication layer. Second, tackifying phenolic resin is added to increase the damping performance of rubber compounds, so as to improve the hysteresis friction in both dry and wet states. The results show that the comprehensive static and dynamic friction properties of rubber compounds are the best in both dry and wet states (0.5 wt% sodium dodecyl sulfate solution or 90 wt% glycerol solution), when SiC size is 7–14 μm and SiC content is 75–90 phr. Phenolic resin can increase the loss factor (tanδ) and loss modulus (E") of rubber compounds, and improve the static and dynamic friction coefficients in wet state (90 wt% glycerol solution). At the same time, it can improve the hardness of rubber compounds and reduce the relative content of SiC, thus reducing the static and dynamic friction coefficients of rubber compounds in dry and wet states (0.5 wt% sodium lauryl sulfate aqueous solution). In general, the optimal content of phenolic resin is 10–15 phr.Highlights Rubber friction coefficients improved via both adhesion and hysteresis friction. Irregular silicon carbides pierce liquid layer to improve adhesive friction of rubber. Phenolic resin increases hysteresis friction of rubber via damping property.

The role of rolling resistance in the rheology of wizarding quidditch ball suspensions

To elucidate the effect of particle shape on the rheology of a dense, viscous suspension of frictional, non-Brownian particles, experimental measurements are presented for suspensions of polystyrene particles with different shapes in the same solvent. The first suspension is made of spheres whereas the particles which compose the second suspension are globular but with flattened faces. We present results from steady shear and shear-reversal rheological experiments for the two suspensions over a wide range of stresses in the viscous regime. Notably, we show that the rheology of the two suspensions is characterised by a shear-thinning behaviour, which is stronger in the case of the suspension of globular particles. Since the shear-reversal experiments indicate an absence of adhesive particle interactions, we attribute the shear thinning to a sliding friction coefficient which varies with stress as has been observed previously for systems similar to the first suspension. We observe that the viscosity of the two suspensions is similar at high shear stress where small sliding friction facilitates particle relative motion due to sliding. At lower shear stress, however, the sliding friction is expected to increase and the particle relative motion would be associated with rolling. The globular particles attain a higher viscosity at low shear stress than the spherical particles. We attribute this difference to a shape-induced resistance to particle rolling that is enhanced by the flattened faces. Image analysis is employed to identify features of the particle geometry that contribute to the resistance to rolling. It is shown that the apparent rolling friction coefficients inferred from the rheology are intermediate between the apparent dynamic and static rolling friction coefficients predicted on the basis of the image analysis. All three rolling resistance estimates are larger for the globular particles with flat faces than for the spherical particles and we argue that this difference yields the stronger shear thinning of the globular particle suspension.

The effect of carrier locking position on the dynamic characteristics of gapless miniature linear guideway

The analysis of the load position of the miniature linear guideway is very important for the dynamic friction characteristics of the linear motion equipment. In this paper, a miniature guideway dynamic friction coefficient tester will be designed. And the effect of load position, movement speed, and load on the friction force of linear guideway will be investigated according to the gapless. The experimental results show that the friction force will be dependent on the load position, load, and movement speed. Among them, the lowest frictional load position can be obtained at any speed of movement and load condition, which occurs at the central load position. The main reason for this is that the effect of the moment is minimum. On the same load position and movement speed, then load is proportional to friction. In the case of fixed load and load position, the effect of velocity on friction is positively correlated in the longitudinal offset position. The frictional force is aggravated by the unevenly distributed pressure on the inner ball due to the moment generated by the slider. At the same time, by observing the loading and the inclination angle of the carrier in the experiment with the laser displacement meter, it can be found that the inclination angle also tends to increase when the load increases.

SIMULATION OF THE AUTOMATIC CONTROL SYSTEM OF A HORIZONTAL-AXIAL WIND POWER PLANT

We considered the results of modelling the operating modes of an electric power generation system of a horizontal-axial wind turbine. The system consist of an aerodynamic blades of a wind wheel connected by an elastic shaft to a generator through a multiplier. Engineering part of the automatic control system (ACS) is the mechanism of rotation of the blades relative to the angle of wind flow. A method for optimizing the main parameters: geometric, dynamic and ACS coefficients is proposed. The method allows a comprehensive assessment of the operation of wind turbines. The value of the average annual electricity generation was used as an optimization criterion. As a result, a deep optimization of the adjustment depth coefficient was carried out. Secondly, we investigated the system in dynamics. A stochastic wind model was used as a disturbing effect. We constructed the system by mathematic simulation methods. As a reference control algorithm, a direct linear dependence of the angular velocity of the turbine rotation on the wind speed with restrictions on the minimum and maximum values was used. Also we described the mathematical model of system and the initial results of the theoretical calculations of algorithms for controlling. The versatility of the calculation system makes it possible to use any aerodynamic profiles of the blades in its composition. The characteristics of aerodynamic moments for the calculation of force moments are obtained by converting Lilienthal curves as initial data for the considered aerodynamic profiles.

Study on the Dynamic Stability and Spectral Characteristics of a Toppling Dangerous Rock Mass under Seismic Excitation

To evaluate the dynamic stability of dangerous rock masses under seismic excitation more reasonably, a mass viscoelasticity model was adopted to simulate the two main controlling surfaces of a toppling dangerous rock mass. Based on the principles of structural dynamics, a dynamic response analysis model and motion equations were established for toppling dangerous rock masses. The Newmark-β method was utilized to establish a calculation method for the dynamic stability coefficient of a toppling dangerous rock mass. This method was applied to the WY2 dangerous rock mass developed in a steep cliff zone in Luoyi Village, and the dynamic stability coefficient time history was calculated. Subsequently, the acceleration response signals of the dangerous rock mass in different directions were analyzed using wavelet packet transform. The results show that the sum of the energy proportions of the first to third frequency bands in the n1 and s2 directions exceeded 95%. This suggests that the n1 and s2 directions of the WY2 dangerous rock mass suffered the initial damage under bidirectional seismic actions. Finally, the marginal spectra variations of the acceleration response signals in different directions were analyzed based on the HHT. The results show that the seismic energy in the n1 and s2 directions of the dangerous rock mass was found to be the most significant under seismic loading, indicating that the rock mass experienced the most severe damage along these two directions. This reveals that the failure mode of the dangerous rock mass is inclined toppling, consistent with the results of wavelet packet analysis.

Influence of Wear on the Cross-Coupled Dynamic Coefficients and Threshold Speed of Conical Hybrid Fluid Film Bearing

Influence of Wear on the Cross-Coupled Dynamic Coefficients and Threshold Speed of Conical Hybrid Fluid Film Bearing

How Does the Time-Varying Network Structure Evolve between the EU Carbon Futures Prices and Industrial and Energy-Related Indices? A Study Based on a Time-Varying T-Copula

Industrial and energy-related industries are major sources of carbon dioxide emissions, and their interdependence, as reflected in the financial field, has attracted the attention of scholars. For the purpose of exploring the evolutionary characteristics of the short-term dynamic correlation coefficient between the EU carbon futures price and the industrial and energy-related indices, this paper selected the settlement price of EU carbon emission quota futures, the MSCI energy I index on three dimensions, and the Dow Jones industrial index and West Texas crude oil futures price, as sample data. Using the time-varying t-copula model to measure the dynamic correlation coefficient between variables, the time-sliding window idea and coarse-grained method were combined to establish the correlation fluctuation mode, and a complex network theory and analysis methods were used to study the evolutionary traits of the time-varying network structure between the EU carbon price and the industrial and energy-related index. The results show that the transmission objects of the key correlation fluctuation modes in the network are stable and maintain their own state with a high probability. Second, the clustering effect exists in the transmission process. Some nodes with high mediating abilities are also the key correlation wave modes in the dynamic correlation evolution network. This study provides ideas for the study of the correlations between multiple variables and is also a useful reference for international investors.

High-resolution sampling aliasing frequency distribution

Rotating blades are core but fragile working parts in turbomachinery, and damage to the rotating blades severely endangers operational safety; thus, it is critical to monitor the blade condition to find the incipient failure. Blade tip timing (BTT) is a potential measurement for rotating blades owing to its non-contact nature, high efficiency, and long service life. Identifying vibration parameters for condition monitoring is a core issue. Most existing BTT methods rely on multi-probe layouts to overcome undersampling to extract parameters. However, restricted by weight, safety, installation, and maintenance costs, it is desired to extract vibration parameters on the premise of the minimal layout. Motivated by this demand, we propose a single probe-based parameter identification method, where sampling aliasing frequency (SAFE) distribution plays a significant role. To improve the accuracy of parameter identification, a synchrosqueezing adaptive window length short-time Fourier transform (SS-AWSTFT) is proposed to construct a high-resolution SAFE distribution. Moreover, a new fitting model considering rotational effect is developed to extract engine order (EO), static frequency, and dynamic frequency coefficient from the SFAE distribution. Owing to considering the rotational effect, the new fitting model performs better in parameter estimation. Finally, the effectiveness and robustness of the proposed method were demonstrated by simulations and experiments.

Acceleration response of part-screw pile composite foundation under long-term train load excitation

This paper investigates the vibration response of a new part-screw pile composite foundation under moving train loads via a model test method. Based on the acceleration signals of the pile and the surrounding soil, a non-linear fitting method is used to establish the relationship between the dynamic attenuation coefficient and the depth of the foundation. Next, the effect of spatial location and train speed on the pile-soil dynamic interaction is investigated by introducing the pile-soil spectral amplitude ratio δ p − s . In addition, the dynamic susceptibility of the part-screw pile to damage under dynamic train loads is revealed with a wavelet packet energy distribution index E DIS . Afterwards, the cumulative deformation evolution characteristics of screw pile composite foundations under long-term train loading were revealed using the frequency domain integration method. The results of this work reveal that the faster the train runs, the larger the pile-soil spectrum amplitude ratio and the more prominent the ‘dynamic concentration effect’ of the part-screw pile. The change in cross-section of the part-screw pile results in a sudden change in the vibration energy transmitted from the top of the pile, which makes the variable section of the part-screw pile more likely to cause dynamic damage or even deformation. The cumulative deformation evolution process of soil between part-screw piles under long-term cyclic train loading can be divided into three stages: slow change period, fluctuation rising period and stable deformation period. The research results have important reference significance for the optimization design of high-speed railway part-screw pile composite foundation and the planning of railway running speed.