Transient Coupling Model Research Articles

Thermoelastic analysis of friction pairs in hydro-viscous drive combined thermal and mechanical loads under soft startup condition

Thermo-mechanical characteristics significantly impact the operating performance of the friction pairs in hydro-viscous drive. A three-dimensional transient thermo-mechanical coupling model was established for investigation of the distributions and coupling relationships of the temperature, stress, and displacement generated by the combination of the thermal and mechanical loads under soft startup condition. Then, the time-dependent contact pressure and velocity were extensively examined, as well as their effects on the thermo-mechanical coupling characteristics. Finally, the effects of the material and structural parameters were analyzed by the one-factor-at-a-time method. The observations confirmed plastic deformation of the steel disc will occur when the steel disc and friction disc are, respectively, restrained at the outer and inner diameters. However, there is a low likelihood of plastic deformation of the friction lining occurring. The thermal load and constraint locations were also found to crucially affect the stress and displacement distributions. Moreover, the circumferential stress was determined to be the most important stress component, and can thus be used as a basis for judging whether plastic deformation will occur. The results provide theoretical reference for predicting the thermal characteristics of the friction pairs, as well as a foundation for selecting the material and structural parameters.

Numerical simulation of a new early gas kick detection method using UKF estimation and GLRT

A gas kick may occur when drilling with narrow pressure margin, which can lead to significant non-productive time. This paper proposes an early gas kick detection method applicable to water-based mud (WBM), which integrates a transient pressure and temperature coupling model into an unscented Kalman filter (UKF) algorithm. Three pressure factors and a flow rate factor are estimated with the UKF algorithm using updated measurement data in a detection estimator, and a generalized likelihood ratio test (GLRT) is employed to automatically detect changes in the pressure factors and flow rate factor for prediction of the gas kick. Simulated results show that the estimated pressures and outlet flow rate trace synthetic measurements very well with continuous inversion of the pressure factors and flow rate factor. All of the estimated pressure factors and flow rate factor fluctuate to a little extent around a base value under normal drilling condition, while the pressure factor in annulus and flow rate factor both deviate from the base value when the gas kick occurs. Performances of the proposed method, pit gain monitoring method and delta flow monitoring method are contrasted. The kick detection times are gradually reduced for all the methods with the increase of gas kick rate. Moreover, the proposed method herein shows a much better performance than the pit gain and delta flow monitoring methods, especially at small gas kick rate.

An innovative diagnosis method for lost circulation with unscented Kalman filter

Lost circulation, as a widespread and costly drilling problem, not only wastes a lot of drilling fluid, but also produces a large amount of nonproductive time (NPT). Therefore, detecting the symptoms of lost circulation opportunely, pinpointing the loss depth and evaluating the loss rate precisely are extremely crucial.A diagnosis method for detecting the occurrence of lost circulation and identifying the loss depth as well as loss rate at an early stage is proposed, which combines a transient pressure and temperature coupling model with unscented Kalman filter (UKF) estimation. We first establish the transient pressure and temperature coupling model under the conditions of normal drilling operation and lost circulation. Then the detection and identification estimators for estimating pressure-loss factors, flow rate factor, loss depth and loss rate are constituted by embedding the detection and identification models, which are derived from the transient pressure and temperature coupling model, into UKF estimation. In the end, a simulated case study is presented to illustrate the performance of the diagnosis method.In the simulation, the estimated pressure and outlet flow rate trace the measurements well with the evolution of pressure-loss factors and flow rate factor. Moreover, the pressure-loss factor in annulus and flow rate factor, which fluctuate to a little extent in normal drilling condition, deviate from the base value once lost circulation occurs. The simulation indicates the superior performance of the diagnosis method with the introduction of pressure-loss factors and flow rate factor, and the average error of estimated loss depth is less than 5%. In addition, the parametric sensitivity analysis illustrates the universality of the diagnosis method, which has certain ability to improve drilling safety and efficiency with lower NPT.

Circuit model of transient cross‐coupling

Using a signal generator and an oscilloscope, measurements were made of the differential-mode current and the common-mode current in a twin-conductor cable installed on a test rig, over a range of frequencies which included half-wave resonances. Test data was used to assign component values to a Triple-T circuit model of the assembly. This model was then transformed into a transient coupling model. The signal generator was reset to generate square waves, and photographs were taken of the waveforms of the input voltage and the common-mode current. A close correlation was achieved between these waveforms and those of the transient coupling model. This demonstrates that the technique of circuit modelling and bench testing is reliable and accurate, in both the frequency domain and the time domain. The technique allows potential hazards due to transient interference to be analysed, tested, and quantified during the design process. Electromagnetic interference can be analysed without recourse to the mathematics of full-field modelling. It is also shown that, from the point of view of Electromagnetic Compatibility, the concepts of the single-point ground and the equipotential ground are both misleading and counter-productive.

Numerical simulation of the weathering performance of an exterior wall external insulation system under heating-cooling cycles

In the current construction industry, exterior wall external insulation systems are widely used but suffer some obvious weathering problems such as deformation, drop in thermal insulation, and fracture of the surface layers. To investigate the weathering performance of an exterior wall external insulation system from the perspective of wall temperature stability, ABAQUS finite element software was used to establish a three-dimensional transient thermal-structural coupling model of the effect of paint finishes, with added adhesive powder polystyrene particle insulation slurries, on exterior wall external insulation. Numerical simulation analysis was carried out to calculate the real-time temperature field, thermal stress, and displacement distribution of different functional layers under heating-cooling cycles. Results show that during the heating-cooling cycles, the temperature difference in the coating layer is the greatest, that in the interior layer is the smallest, and the daily change is within 2℃. The rate of temperature change in the insulation slurry layer in the thickness direction is higher than that in the other materials. The coating layer is subjected to tension-compression cycles with tension at low temperatures and compression at high temperatures. The inner surface of the primary wall is always under compression throughout these cycles and the stress variation in the primary wall is small. By comparison, the stress in the interfacial mortar layer is large and that in the insulation slurry layer is almost zero. The maximum displacement in the thickness direction occurs in the insulation slurry layer.

WITHDRAWN: A transient model for nozzle clogging – Part II: Validation and verification

Abstract Part I of this two-part work discusses a transient two-way coupling model for clogging of nozzle (fluid passage) due to deposition of suspended particles on the nozzle wall. The purpose of Part II is to validate and verify the model. To this end, the current model simulates a laboratory experiment, designed to study the clogging of a submerged entry nozzle (SEN) during steel continuous casting. It demonstrates that the model can reproduce the experiment satisfactorily: the numerically-calculated clogged section of the nozzle is qualitatively comparable with typically “as-clogged” sections in laboratory experiments; the calculated mass flow rate through the nozzle during clogging process as function of time is also in agreement with the experimentally-monitored result. The simulation-experiment agreement depends on parameters, e.g. mesh size, Lagrangian time scale, correction factor in interpolation of clog permeability, and porosity in the clog materials, which act as inputs for the numerical model. Uncertainties for choosing such parameters, model capabilities/limitations due to model assumptions have been studied and discussed in this paper. In this regard, further model refinements are suggested. The modeling results provide new knowledge about clogging behavior. (1) Clogging is a transient process, and it includes the initial coverage of the nozzle wall with deposited particles, the evolution of a bulged clog front, and then the development of branched structure. This transient growth of clog interacts with the flow. (2) Clogging is a stochastic and self-accelerating process.

Transient Coupling Model of Plasma and Laser Field in Water

Transient Coupling Model of Plasma and Laser Field in Water

Transient thermal-mechanical coupling behavior analysis of mechanical seals during start-up operation

A transient thermal-mechanical coupling model for a contacting mechanical seal during start-up has been developed. It takes into consideration the coupling relationship among thermal-mechanical deformation, film thickness, temperature and heat generation. The finite element method and multi-iteration technology are applied to solve the temperature distribution and thermal-mechanical deformation as well as their evolution behavior. Results show that the seal gap transforms from negative coning to positive coning and the contact area of the mechanical seal gradually decreases during start-up. The location of the maximum temperature and maximum contact pressure move from the outer diameter to inside diameter. The heat generation and the friction torque increase sharply at first and then decrease. Meanwhile, the contact force decreases and the fluid film force and leakage rate increase.

Effects of thermodynamics parameters on mass transfer of volatile pollutants at air-water interface

A transient three-dimensional coupling model based on the compressible volume of fluid (VOF) method was developed to simulate the transport of volatile pollutants at the air-water interface. VOF is a numerical technique for locating and tracking the free surface of water flow. The relationships between Henry's constant, thermodynamics parameters, and the enlarged topological index were proposed for nonstandard conditions. A series of experiments and numerical simulations were performed to study the transport of benzene and carbinol. The simulation results agreed with the experimental results. Temperature had no effect on mass transfer of pollutants with low transfer free energy and high Henry's constant. The temporal and spatial distribution of pollutants with high transfer free energy and low Henry's constant was affected by temperature. The total enthalpy and total transfer free energy increased significantly with temperature, with significant fluctuations at low temperatures. The total enthalpy and total transfer free energy increased steadily without fluctuation at high temperatures.

Magnetic Field Finite Element Analysis of Generator with Rotor Inter-Turn Short-Circuit Fault

Rotor inter-turn short-circuit is a common fault in generator and it is a research hotspot to identify the fault at its early stage. Considering the disadvantage of circuit analytical method, this paper establishes a 2D transient finite element electromagnetic-circuit coupling model, and calculates the magnetic field at normal and fault situations through the powerful post-processing function of ANSOFT, then magnetic flux density cloud pictures and air-gap magnetic flux density curves of different operating conditions are got. Using MATLAB to analyze and deal with the air-gap flux density cures, we can get the differences of faults in different levels and different positions, which provide a basis for further study of rotor inter-turn short-circuit fault.

Simulation and experimental study of a new structural rubber seal for the roller-cone bit under high temperature

Seal element is an important component of roller-cone bit. In order to improve the sealing performance and service life of roller-cone bit under high temperature, a new seal structure with multi-segment arcs is designed and the structural parameters of this sealing ring are optimized by response surface method and finite element method. Firstly, the hydrogenated nitrile-butadiene rubber is used to improve the seal performance under high temperature, and the uniaxial, planar, and biaxial tensile experiments are carried out to study the constitutive model of this rubber. Then, a three-dimension transient thermo-mechanical coupling model is established. The comparison of sealing performance between the new structural seal and the traditional O-ring seal is implemented under high temperature through the proposed FEM and laboratory experiments. The results show that the new structural seal has lower contact pressure and Mises stress than the standard O-ring seal, and the service life of the former is almost twice of the later one. Additionally, a composite drill bit using the new structural seal is applied to a deep drilling. After servicing a certain time, it shows that the wearing capacity is very small. The results show that the new structure seal ring can adapt to high temperature environment and the optimization method is feasible.

Effect of matrix chain length on the electrophoretic mobility of large linear and branched DNA in polymer solutions.

We study the effect of matrix chain molecular weight Mw and concentration c on the electrophoretic mobility micro of large linear and star-like, branched DNA in polymer solutions. Polyethylene oxide (PEO) with narrow molecular weight distributions form the main focus of this study. For PEO concentrations ranging from one half the overlap concentration, c*, to 3c*, the effective drag coefficient, zeta is identical with (mu0/mu) - 1, satisfies the following approximate scaling relationship, zeta approximately cMw(0.7). Here, mu0 is the electrophoretic mobility in free solution. While the concentration dependence is consistent with predictions from the transient entanglement coupling (TEC) model, the molecular weight dependence is significantly weaker. Although a similar dependence of mobility on Mw can be predicted when nonentangling collisions are the dominant source of drag, a model based on these collisions alone cannot reproduce the experimental observations. We also find that the architecture of large DNA does not affect either the concentration dependence or molecular weight dependence of the electrophoretic mobility.

Electrophoretic dynamics of large DNA stars in polymer solutions and gels

We have developed a procedure for synthesizing large stable branched DNA structures that enables visualization via fluorescence microscopy. Using this procedure we have synthesized large DNA stars and observed their electrophoretic behavior in polymer solutions and gels. In dilute polyacrylamide solutions, the DNA stars move as random coils and appear to experience only brief collisions with the polymer chains in solution. The effect of polymer solution concentration on the electrophoretic mobility of stars in the dilute regime is found to be in good accord with predictions of the transient entanglement coupling (TEC) model. In semidilute polymer solutions, the star arms extend in the field direction and drag the core through the matrix. The star arms form several U-shaped conformations as they collide and engage with polyacrylamide chains. The U-shaped conformations occasionally evolve into J-shaped conformations as the star arms slide off the matrix chains they engage during electrophoretic migration. In concentrated polymer solutions, the arms of the star extend and form V-shaped structures with the core as the apex. The arms then pull the core through the matrix. These V-shaped conformations are much longer-lived than U-shaped ones and, unlike the latter, do not transform to J-shaped conformations. In polyacrylamide and agarose gels, where matrix entanglements are fixed, DNA stars become trapped when entanglements with matrix molecules prevent the core from being pulled through the matrix by the extended arms. This trapping was observed at all gel concentrations and electric fields studied.

Numerical coupling models for analyzing dynamic behaviors of electromagnetic actuators

This paper presents two coupling models for analyzing dynamical behaviors of electromagnetic actuators. The first model is based on coupled finite element and parametrization methods. The second one is the transient coupling model, it makes use of an iterative technique for the coupled electric, magnetic and mechanical phenomena. A comparison of those models is given through the calculation of the dynamic behavior of a linear axisymmetrical actuator supplied by capacitor discharge voltage.