Mechanical Coupling Effects Research Articles

Two-Degree-Of-Freedom Dynamic Model-Based Terminal Sliding Mode Control with Observer for Dual-Driving Feed Stage

The position synchronous control of multi-axis gantry-type feed stage is crucial in precision machine tools. Industrial position control which aims to widen the bandwidth and improve disturbance rejection of single axis is not enough to achieve precise synchronization in a dual-driving feed stage. The characteristics diversity, transmission-mechanism deformation, and mechanical coupling effect between dual axes will degrade the control accuracy. Hence, the novel two-degree-of-freedom (2-DOF) dynamic model-based terminal sliding mode control (TSMC) with disturbance and state observer is proposed in this paper for the synchronous control of a 2-DOF dual-driving feed stage. The 2-DOF dynamic model, based on Lagrange equation, is established along with the parameters identification method. The predictive natural frequencies and vibration modes frequencies by the proposed dynamic model are compared by a modal experiment. Then, the 2-DOF dynamic model-based TSMC is provided to satisfy the tracking and synchronization control. In order to reduce the chattering and to increase the robustness against the mechanical coupling, the disturbance and state observer is designed. Moreover, Lyapunov stability criterion is used to analyze the stability of the proposed control scheme. Finally, an industrial application of 2-DOF dual-driving feed stage is utilized to validate the effectiveness of the proposed control scheme. The proposed 2-DOF dynamic model-based TSMC with observer has been effectively demonstrated to improve synchronous performance and tracking accuracy.

Thermal and mechanical coupling effects on permeability of weakly cemented sandstone

The weakly cemented sandstone is the host rock in the Cretaceous and Jurassic strata with low intensity, high water-bearing capacity and sensitivity to disturbance. In order to investigate the influence of temperature and confining pressure on the permeability of weakly cemented sandstone, scanning electron microscope were used to characterize microstructure of the particles, a series of triaxial creep tests were performed on coarse sandstone, medium sandstone and fine sandstone separately, and the effect of particle size on the permeability of sandstone was also analyzed. The results indicate that the increase of confining pressure led to the plastic deformation between the rock particles, that permeability was irreversible as the confining pressure changed, and that the permeability reduction rate of coarse sandstone was lower than that of fine sandstone. The sensitivity of weakly cemented sandstone to temperature and confining pressure increased as the sizes of the particles decreased, and the effect on permeability was more obvious.

Thermal-Mechanical-Electrochemical Coupling Simulation for Electric Vehicle Batteries

The major trend toward vehicle electrification intensifies the need for increased battery energy densities. During the development of new electric vehicle battery technologies, it has become clear that thermal, mechanical, and electrochemical coupling effects play an important role in battery performance, degradation, and response to abusive conditions. The macro-homogeneous Dualfoil model, which solves ion transport and charge transfer dynamics, predicts the electrical response of a single small battery cell. However, when considering large cells or assembled battery modules and packs, inhomogeneity of electric potential and temperature throughout the cell volume becomes severe enough to impact battery performance. Cell expansion and contraction during charge/discharge cycles further increase such inhomogeneity, and the resulting potential and temperature imbalances cause non-uniform current distribution in the cell. Heavily cycled cell regions generate additional heat and stress, causing severe degradation in the performance and life of the battery. Given the strong coupling between thermal, mechanical, and electrochemical phenomena, it is imperative to integrate multiple physical models in the simulation of complete battery packs. In this work, a modified Dualfoil electrochemical model is coupled to a thermo-mechanical finite element solver to represent such multiphysics coupling effects. Outputs from the 3D thermo-mechanical solver, such as temperature and stress, are supplied as inputs to the Dualfoil model, which in return computes the electrochemical response and provides the local heat generation rate and Li intercalation induced volume change to the thermo-mechanical solver. Using this coupled multiphysics simulation framework, the impact of external mechanical loading under different charge/discharge profiles was investigated. The transient, non-linear behavior of internal variables, such as SOC, overpotential, and current density, during and after cycles, was obtained in the entire 3D battery pack domain. This information provides good insights for design and optimization of battery packs with high performance and long life time.

Effect of hydro mechanical coupling on natural fracture network formation in sedimentary basins

Effect of hydro mechanical coupling on natural fracture network formation in sedimentary basins

The influences of adiabatic shear evolution on tool failure in high-speed machining of railway steel

Adiabatic shear evolution in serrated chip will lead to inevitable impacts on the tool failure with the cutting speed increasing. The high-speed machining experiment of railway steel was carried out by applying the cemented carbide insert. The chip morphology transformation with white layer during adiabatic shear evolution was observed, and its influence on the tool failure mechanism on rake face was further investigated microscopically. The experimental results were concluded that the isolated segment chip formation due to adiabatic shear fracture weakened the wear effects on the rake face under higher cutting speed. The periodical cycle from adiabatic shear banding to fracture which resulted in a thermal–mechanical coupling effect mainly influenced the rake face failure mechanisms.

Vibration Characteristics Analysis of Cylindrical Shell‐Plate Coupled Structure Using an Improved Fourier Series Method

A simple yet accurate solution procedure based on the improved Fourier series method (IFSM) is applied to the vibration characteristics analysis of a cylindrical shell‐circular plate (S‐P) coupled structure subjected to various boundary conditions. By applying four types of coupling springs with arbitrary stiffness at the junction of the coupled structure, the mechanical coupling effects are completely considered. Each of the plate and shell displacement functions is expressed as the superposition of a two‐dimensional Fourier series and several supplementary functions. The unknown series‐expansion coefficients are treated as the generalized coordinates and determined using the familiar Rayleigh‐Ritz procedure. Using the IFSM, a unified solution for the S‐P coupled structure with symmetrical and asymmetrical boundary conditions can be derived directly without the need to change either the equations of motion or the expressions of the displacements. This solution can be verified by comparing the current results with those calculated by the finite‐element method (FEM). The effects of several significant factors, including the restraint stiffness, the coupling stiffness, and the situation of coupling, are presented. The forced vibration behaviors of the S‐P coupled structure are also illustrated.

A coupled THMC modeling application of cemented coal gangue-fly ash backfill

Cemented coal gangue-fly ash backfill (CGFB) is prepared by mixing coal gangue, fly ash, cement and water. The CGFB mixtures are filled into mined-out areas of coal mines for ground control and waste disposal. Once placed underground, the performance of CGFB is subjected to the thermal (T), hydraulic (H), mechanical (M) and chemical (C) processes and THMC coupling effects. Understanding the coupled THMC influence on CGFB is crucial for predicting the behavior of CGFB. This paper develops a THMC coupling model to describe and analyze the coupled THMC processes that occur in CGFB. The developed model considers the courses of thermal conduction and convection, fluid flow, suction development, chemical shrinkage, thermal expansion, and binder hydration. The simulation and prediction results of the developed model are compared with the experimentally tested data from 3 case studies. Good agreement is found between the modeling results and experimental data, validating the capability of the developed model to well characterize the properties of CGFB under coupled THMC loadings. The modeling results can also contribute to a better design of stable, durable and environment-friendly CGFB structures.

Twin-waves propagation phenomena in magnetically-coupled structures

The use of magnetic dipoles embedding in an elastic support introduces long-range interaction forces. This is a completely new paradigm in structural mechanics, classically based on local short-range particle interaction. The features of long-range forces produce very new mechanical coupling effects. This paper examines the case in which two identical rod-like structures, each with a dipole distribution embedded, vibrate side by side. Waves generated in one of the rods propagate also in the second and vice versa creating a new effect we name twin-waves. The present investigation unveils the existence of an infinite set of numerable waves even in one-dimensional infinite structures, a new and unusual behaviour in classical waveguides. The physics behind this phenomenon is further investigated also by numerical simulations.

Analysis of Harvesting Energy from Mistuned Multiple Harvesters with and without Coupling

Energy harvesting has received a lot of attention in the recent past. At present a single device does not harvested energy enough to power up an electronic sensors. In order to increase the power output multiple identical harvesters are used. When multiple harvesters are used, they bring in non-uniformity in their physical parameters due to variability during manufacturing or even during deployment. Therefore, ‘n’ numbers of harvesters do not necessary produce ‘n’ times the harvested power of a single device. The variability in parameters is less enough to be coined as mistuning. In this paper, an analysis of multiple energy harvesters is studied. The harvesters are assumed to show mistuning. The study is further extended to understand the effect of mechanical coupling between the harvesters. For simplification, pendulums are considered as the harvesters, with magnetic tip masses for the electromagnetic energy harvesting. Mistuning is achieved by varying the length of the pendulums. A generalized mathematical model for n coupled harvesters with mistuning is developed. Simulations are performed with the number of harvesters varying from 2 to 6 with ±1% non-repetitive mistuning in the lengths of the harvesters, and a comparison of the power harvested between mechanically coupled and uncoupled harvesters is presented.

A fully coupled thermal-hydrological-mechanical-chemical model for CO2 geological sequestration

The importance of thermal-hydrological-mechanical-chemical (THMC) interactions is well recognized in the procedure of CO2 geo-sequestration. Geo-mechanics and geo-chemistry may have significant effects on the aqueous phase composition, porosity and permeability of the formation, which in turn affect flow and transport processes. Using a mean stress formulation, geomechanical effects are considered such as stresses, displacements, and rock deformation in CO2 sequestration. Chemical equilibrium and kinetics are taken into account in the mass balance equation, which is able to quantitatively simulate fluid flow, solute transport and geo–chemical reaction in the operation of CO2 geo-sequestration. Since rock strength decreases with increasing amounts of reactive minerals, substantial dissolution/precipitation of rock composition may lead to significant changes in the mechanical behavior, a generic computational scheme has been developed to take the mechanical and chemical coupling effects into account. Based on these theories, a novel mathematical model of the THMC processes is developed in this paper. A fully coupled computational framework is proposed and used to simulate reactive transport of water, CO2 gas and species in subsurface formation with geomechanics. The novel frameworks are designed to keep a generalized computational structure for different THMC processes. The coupled THMC simulators focus on: (1) fluid and heat flow, solute transport in a three-phase mixture, (2) stress and displacement related to mean stress, (3) non-isothermal effects on fluid properties and reaction processes, and (4) the equilibrium and kinetics of water-rock and gas-rock chemical interactions. A practical reactive transport examples with cold supercritical CO2 injection into saline aquifer has been proposed to analyze the THMC processes quantitatively. It is indicated that the geochemical reactions do not have significant impact on pore pressure, mean stress and temperature. The thermal energy transport with low temperature significantly affects the mean stress and geochemical reactions in the saline aquifer. Low temperature accelerates equilibrium dissolution of gas and mineral, but slows down kinetic dissolution/precipitation of minerals, such as anorthite and kaolinite.

Trans-scale modeling framework for failure analysis of cryogenic composite tanks

The mechanical performances of cryogenic composite tanks need strict evaluation due to its extreme temperature condition of service. In this paper, a trans-scale modeling strategy is developed for the failure analysis of cryogenic composite structures, which is based on theories from micromechanics to continuum mechanics. Micromechanical model of representative volume element is developed to obtain the thermo-mechanical coupling properties of materials in the composite structure. Continuum mechanics model is sub-sequentially developed to predict the fields of physical properties in the composite structures. The predictions of performances of composite structures at cryogenic and different temperatures are of good agreement with conventional theoretical solutions. Numerical examples of cryogenic composite tanks indicate that the large temperature change can directly cause the fracture of matrix that can result in the overall failure of composite tanks. In addition, the thermal–mechanical coupling effect can reduce the prediction of critical thermal loads in the failure analysis of cryogenic composite tanks, which is more favorable for engineering designs due to the strict requirements of safety.

Equivalent nonlinear beam model for the 3-D analysis of shear-type buildings: Application to aeroelastic instability

Tower buildings can be very sensitive to dynamic actions and their dynamic analysis is usually carried out numerically through sophisticated finite element models. In this paper, an equivalent nonlinear one-dimensional shear–shear–torsional beam model immersed in a three-dimensional space is introduced to reproduce, in an approximate way, the dynamic behavior of tower buildings. It represents an extension of a linear beam model recently introduced by the authors, accounting for nonlinearities generated by the stretching of the columns. The constitutive law of the beam is identified from a discrete model of a 3D-frame, via a homogenization process, which accounts for the rotation of the floors around the tower axis. The macroscopic shear strain in the equivalent beam is produced by the bending of columns, accompanied by negligible rotation of the floors. A coupled nonlinear shear–torsional mechanical model is thus obtained. The coupling between shear and torsion is related to a non-symmetric layout of the columns, while mechanical nonlinearities are proportional to the slenderness of the columns. The model can be used for the analysis of the response of tower buildings to any kind of dynamic and static excitation. A first application is here presented to investigate the effect of mechanical and aerodynamic coupling on the critical galloping conditions and on the postcritical behavior of tower buildings, based on a quasi-steady model of aerodynamic forces.

Nonlinear vibration for PMSM used in HEV considering mechanical and magnetic coupling effects

Rotors of permanent magnet synchronous motors (PMSM) used in hybrid electric vehicles are an electromechanical-coupled dynamic system. Magnetic field-induced mechanical vibration has an important effect on the performance of these high-speed and high-power-density PMSMs. In this paper, the model of an unbalanced magnetic pull (UMP) resulting from a non-uniform magnetic field is investigated theoretically and numerically. Equations of motion of an unbalanced Jeffcott rotor are established. Approximate solution to the equation of nonlinear vibration under UMP is obtained using the averaging method, and stability of the steady response is discussed using eigenvalue analysis. Nonlinear phenomenon, which is an effect of the electromagnetic stiffness coefficient, mass imbalance parameter and effective damping on overall responses, was studied in detail. It is demonstrated that response curves manifest soft characteristics, with a jump phenomenon and unstable areas pointed out. The response obtained using analytic method was compared with the numerically results. Conclusions from this work can be adopted to identify instability locus in rotors with mechanical and magnetic coupling effects taken into consideration. In addition, outcomes from this work provide theoretical and practical ideas to control the systems and optimize their operation.

Water transport in planetary ice shells by two-phase flow – a parametric study

We present a two-phase model for the generation of meltwater and its propagation through the outer shells of icy satellites such as Europa, Enceladus or Titan. We exploit the analogy with the process of partial melt generation in the Earth’s interior by adopting the formalism of two-phase flow developed in the mantle-dynamics community, and by means of scaling analysis we derive a reduced system appropriate for our planetary application. The resultant system couples Darcy’s law with the deformation of the viscous ice matrix. We numerically investigate the system in a simplified one-dimensional geometry, corresponding to a laterally uniform ice layer, and analyze the role of various physical parameters. We focus on the leading-order effects, namely (i) the key importance of ice permeability, (ii) the role of complex ice rheology depending on temperature, deformation mechanisms and water content, (iii) the possible contribution of surface tension and (iv) the effects of mechanical coupling between the phases. Our analysis suggests that the global water transport through temperate ice is mainly controlled by ice permeability and can be well approximated by a model in which the complex ice rheology is parameterized in terms of a constant viscosity. While the mechanical coupling between the phases dramatically affects the flow at the local scale, the surface tension appears to be insignificant.

A shear–shear torsional beam model for nonlinear aeroelastic analysis of tower buildings

In this paper, an equivalent one-dimensional beam model immersed in a three-dimensional space is proposed to study the aeroelastic behavior of tower buildings: linear and nonlinear dynamics are analyzed through a simple but realistic physical modeling of the structure and of the load. The beam is internally constrained, so that it is capable to experience shear strains and torsion only. The elasto-geometric and inertial characteristics of the beam are identified from a discrete model of three-dimensional frame, via a homogenization process. The model accounts for the torsional effect induced by the rotation of the floors around the tower axis; the macroscopic shear strain is produced by bending of the columns, accompanied by negligible rotation of the floors. Nonlinear aerodynamic forces are evaluated through the quasi-steady theory. The first aim is to investigate the effect of mechanical and aerodynamic coupling on the critical galloping conditions. Furthermore, the role of aerodynamic nonlinearities on the galloping post-critical behavior is analyzed through a perturbation solution which permits to obtain a reduced one-dimensional dynamical system, capable of capturing the essential dynamics of the problem.

Prediction of hydrodynamic performance of an FLNG system in side-by-side offloading operation

Floating liquefied natural gas (FLNG) is a type of liquefied natural gas (LNG) production system that shows prospects in exploitation of stranded offshore gas fields. The dynamic performance of an FLNG system in side-by-side configuration with a LNG carrier under the combined actions of wave, current and wind can be quite complex. This paper presents a comprehensive study on the hydrodynamics of an FLNG system with a focus on the nonlinear coupling effects of vessels and connection systems based on the concept FLNG prototype recently designed for South China Sea. In this study, the hydrodynamic characteristics of the two floating vessels connected through hawsers and fenders are investigated using a state-of-the-art time-domain simulation code SIMO, considering their mechanical and hydrodynamic coupling effects. The simulation model consisting of FLNG and LNG carrier is developed and calibrated by a series of model tests including a tuned damping and viscous levels. The hydrodynamic performances of the two floating vessels under an extreme sea state during side-by-side offloading operation are obtained, and their relative motions and the force responses of the connection hawsers and fenders are analyzed. Sensitivity studies are conducted to clarify contributions from the pretension and the stiffness of the connection hawsers. The effects on the hydrodynamic performance of the vessels and on the loads of the connection system are also investigated.

Role of Intertube Interactions in Double- and Triple-Walled Carbon Nanotubes

Resonant Raman spectroscopy studies are performed to access information about the intertube interactions and wall-to-wall distances in double- and triple-walled carbon nanotubes. Here, we explain how the surroundings of the nanotubes in a multiwalled system influence their radial breathing modes. Of particular interest, the innermost tubes in double- and triple-walled carbon nanotube systems are shown to be significantly shielded from environmental interactions, except for those coming from the intertube interaction with their own respective host tubes. From a comparison of the Raman results for bundled as well as individual fullerene-peapod-derived double- and triple-walled carbon nanotubes, we observe that metallic innermost tubes, when compared to their semiconducting counterparts, clearly show weaker intertube interactions. Additionally, we discuss a correlation between the wall-to-wall distances and the frequency upshifts of the radial breathing modes observed for the innermost tubes in individual double- and triple-walled carbon nanotubes. All results allow us to contemplate fundamental properties related to DWNTs and TWNTs, as for example diameter- and chirality-dependent intertube interactions. We also discuss differences in fullerene-peapod-derived and chemical vapor deposition grown double- and triple-walled systems with the focus on mechanical coupling and interference effects.

Electronic and Mechanical Coupling in Elastically Bent ZnO Micro/Nanowires

ABSTRACTElastic engineering strain has been regarded as a low-cost and continuously variable manner for altering the physical and chemical properties of materials, and it becomes even more important at low-dimensionality because at micro/nanoscale, materials/structures can usually bear exceptionally high elastic strains before failure. The elastic strain effects are therefore greatly magnified in micro/nanoscale structures and should be of great potential in the design of novel functional devices. The purpose of this overview is to present a summary of our recently progress in the energy band engineering of elastically bent ZnO micro/nanowires. First, we present the electronic and mechanical coupling effect in bent ZnO nanowires. Second, we summary the bending strain gradient effect on the near-band-edge (NBE) emission photon energy of bent ZnO micro/nanowires. Third, we show that the strain can induce exciton fine-structure splitting and shift in ZnO microwires. Our recent progresses illustrate that the electronic band structure of ZnO micro/nanowires can be dramatically tuned by elastic strain engineering, and point to potential future applications based on the elastic strain engineering of ZnO micro/nanowires.

Three-Degree-of-Freedom Dynamic Model Based IT2RFNN Control for Gantry Position Stage

A three-degree-of-freedom (3-DOF) dynamic model based interval type-2 recurrent fuzzy neural network (IT2RFNN) control system is proposed in this study for a gantry position stage. To consider the effect of inter-axis mechanical coupling, a Lagrangian equation based 3-DOF dynamic model for gantry position stage is derived first. Then, to minimize the synchronous error and tracking error of the gantry position stage, the 3-DOF dynamic model based IT2RFNN control system is proposed. In this approach, the adaptive learning algorithms of the IT2RFNN on-line are derived from the Lyapunov stability theorem. Finally, some experimental results of optical inspection application are illustrated to show the validity of the proposed control approach.

On the significance of aeration in the assessment of erosion of unlined spillways

For economic reasons, many large spillways discharge into unlined rock channels or into the river bed directly. The acceptability of such designs is based on engineering assessment that the unlined channel is sited in rock judged to be sufficiently resistant to erosion at least for high frequency floods. It is accepted that under larger low frequency floods there may be some erosion and damage to these unlined channels, but the damage must be limited and must not endanger the structural integrity of the dam.However, in recent years in Australia there have been some unlined spillways which have experienced significantly greater erosion than was initially anticipated and have required substantial remedial works costing tens of millions of dollars.Many of the methods currently used to assess rock erosion on steep slopes are developed based on limited experimental data and involve significant level of uncertainly [Annandale, 1995, 2006]. There has also been recent development of process models that incorporate fluid-rock matrix mechanical coupling effects [e.g. for plunge pools, Bollaert, 2004]. It is well established that aeration significantly changes the drag characteristics of supercritical flow on steep concretelined spillways [Wood, 1991; Chanson, 2004].The purpose of this present contribution is to evaluate the potential significance of aeration in determining drag levels, and therefore influencing rock detachment processes on unlined spillways. This has been undertaken using conceptual characterisations of aeration have been developed across hydraulic engineering.Specifically, we summarise present understanding of the inception, behaviour and implications of aerated flow down steep, rock-lined slopes and the consequences for scour protection design. We also critically review numerical techniques presently being developed and applied to this problem.The most significant aspect of this contribution is a successful reconciliation of recent conceptual microphysical characterisations of aerated flow with conventional engineering approaches based on dimensional analysis of large-scale test data. Further work will be directed at reconciling recently-developed mechanical coupling approaches for unlined spillways with analyses for aerated flow over placed rock in steep channels.