Viscous Coefficient Research Articles

Simulation model for the determination of energy losses during vibrations of the working equipment of a earth-moving machine in the transport mode

A simulation model for a earth-moving machine is developed using a motor grader as an example. The model comprises a chassis base frame, a front balancing bridge, rear balancing carts and working equipment – a traction frame with a moldboard. These elements are included in the form of separate moving elements. The simulation model allows the vibrations of the machine units to be explored while it moves along the microrelief of a reference surface, as well as the energy loss due to friction in the suspension elements of the working equipment to be determined. Using this simulation model, the amount of energy accumulated with the help of improved suspension devices for the working equipment of the motor grader can be assessed. This allows for the combination of the vibration damping of the working equipment in the transport mode and the oscillation energy accumulation. The effect of the stiffness and viscous friction coefficients of the hydraulic cylinders for raising and lowering the moldboard with a device for dynamic vibration damping and the accumulation of their energy on the total amount of energy spent on dissipation in the hydraulic components of the working equipment suspension elements is established. The resulting graphical functional dependence allows the optimization of the parameters of the hydraulic, mechanical and electrical parts of the system of the vibration damping and energy storing device to be implemented.

Advanced Numerical Methodology to Analyze High-Temperature Wire-Net Compact Heat Exchangers For a Micro-Combined Heat and Power System Application

The objective of this paper is to predict compact heat exchanger (CHE) performance for a miniaturized combined heat and power system by a detailed modeling of the complex microchannels and assessing the collector performance using a new reduced order modeling (ROM). The ROM was introduced to decrease the computational size and predict the collector performance with a reasonable accuracy. The CHE is assembled as a stack of counter-flow passages with optimized thickness and an isotropic wire-net (to provide required stiffness and enhance the mixing) which separates the thin partition foils. Computational fluid dynamics (CFD) methodology comprises of conjugate heat transfer (CHT) analysis for a microchannel section and ROM to analyze the entire CHE performance based on the collector performance. The porous medium model, based on the Darcy-Forchheimer law, is modified (constant integration method) to account for the temperature evolution and localized turbulence effects. The resulting microchannel characteristics from a series of three-dimensional CFD-CHT analysis are used to calculate the inertial and viscous coefficients using the constant integration method. These characteristics have been implemented and verified numerically as well as experimentally. The best-revised methodology allows obtaining pressure drop with less than three percent error with respect to the CHT model.

Asymptotic stability of the viscous shock wave for the one-dimensional compressible Navier–Stokes equations with density dependent viscous coefficient on the half space

In this paper, taking the boundary effect into consideration, we investigate the asymptotic stability of a viscous shock wave for one-dimensional isentropic compressible Navier–Stokes equations with density dependent viscous coefficient. Under the assumption that the viscous coefficient is given as a power function of the density, we prove that, for any positive power index of the viscous coefficient, if the amplitude of the corresponding outgoing viscous shock wave is suitably small and the initial data are close to the outgoing viscous shock wave which is far from the boundary, then a global solution exists uniquely in time and tends towards the properly shifted viscous shock wave as the time goes to infinity. The proof is given by an elementary energy method.

Modelling rocking response via equivalent viscous damping

SummaryThe assessment of the out‐of‐plane response of masonry structures has been largely investigated in literature assuming that walls respond as rigid or semi‐rigid bodies, and relevant equations of motion of single‐degree‐of‐freedom and multi‐degree of freedom systems have been proposed. Therein, energy dissipation has been usually modelled resorting to the classical hypotheses of impulsive dynamics, delivering a velocity‐reduction coefficient of restitution applied at impact. In fewer works, a velocity‐proportional damping force has been introduced, by means of a viscous coefficient being constant or variable. A review of such models is presented, a criterion for equivalence of dissipated energy is proposed, equations predicting equivalent viscous damping ratios are derived and compared with experimental responses. Finally, predictive equations are examined in terms of incremental dynamic analyses for large sets of natural ground motions.

A Feasibility Study of a Novel Piezo MEMS Tweezer for Soft Materials Characterization

The opportunity to know the status of a soft tissue (ST) in situ can be very useful for microsurgery or early diagnosis. Since normal and diseased tissues have different mechanical characteristics, many systems have been developed to carry out such measurements locally. Among them, MEMS tweezers are very relevant for their efficiency and relative simplicity compared to the other systems. In this paper a novel piezoelectric MEMS tweezer for soft materials analysis and characterization is presented. A theoretical approach has developed in order to carry out the values of the stiffness, the equivalent Young’s modulus, and the viscous damping coefficients of the analyzed samples. The method has been validated by using both Finite Element Analysis and data from the literature.

Boundary slip phenomena in multicomponent gas mixtures

The slip phenomena in multicomponent gas mixtures are studied. The moment equations, derived from the linearized Boltzmann equation by using the 13-moment approximation of the Grad’s method, are used to obtain the full (containing the contribution from the Knudsen layer) and asymptotic (valid far from the plane physical boundary of the domain) expressions for the nonequilibrium macroscopic parameters of the mixture species. The latter relations are employed to deduce the expressions for the mixture slip velocity and the viscous, thermal, and diffusion slip coefficients by using the modified Maxwell method and the diffuse-specular model of molecule scattering on the wall. The derived relations for the slip coefficients are given in the convenient form expressed in terms of basic transport coefficients, such as partial viscosity and thermal conductivity coefficients, diffusion and thermal diffusion coefficients, and coefficients of molecule momentum accommodation at the wall. The expressions found are used to calculate the slip coefficients for binary (He-Ar) and ternary (He-Ar-Xe) gas mixtures. The numerical results are in good agreement with the data calculated by using other methods.

Adaptive integral backstepping controller for linear induction motors

Linear induction motors offer the possibility to perform a direct linear motion without the nead of mechanical rotary to linear motion transformers. The main problem when controlling this kind of motors is the existence of indesirable behaviours such as end effect and parameter variations, which makes obtaining a precise plant model very complicated. This paper proposes an adaptive backstepping control technique with integral action based on lyapunov stability approach, which can guarantee the convergence of position tracking error to zero despite of parameter uncertainties and external load disturbance. Parameter adaptation laws are designed to estimate mover mass, viscous friction coefficient and load disturbance, which are assumed to be unknown constant parameters; as a result the compensation of their negative effect on control design system. The performance of the proposed control design was tested through simulation. The numerical validation results have shown good performance compared to the conventional backstepping controller and proved the robustness of the proposed controller against parameter variations and load disturbance.

Blow-up of smooth solutions to compressible quantum Navier-Stokes equations

This paper investigates the blow-up phenomena of smooth solutions to the Cauchy problem of multi-dimensional compressible quantum Navier-Stokes equations. Different from the blow-up results of the smooth solutions to the classical Navier-Stokes equations, for any adiabatic exponent bigger than one, we prove the smooth solutions to the compressible quantum Navier-Stokes equations will blow up in finite time under some reasonable restrictions of initial data, when the viscous coefficient is small relative to the Planck constant.

Creep Characteristics and Model of Key Unit Rock in Slope Potential Slip Surface

The creep characteristics of the key unit rock in a slope potential slip surface play an important role in the evolution of slope slip. In this research, a systematic restrictive shear creep experimental study was conducted to investigate the restrictive shear creep characteristics of the key unit rock in a slope potential slip surface. A new plastic nonlinear model (PFY model) was developed to characterize the progressive-failure creep characteristics reflected in the process of the restrictive shear creep of rock. A variable-parameter restrictive shear creep model was established to reflect the progressive-failure characteristics and describe the whole process of restrictive shear creep of the rock and the two failure mechanisms of the rock, which can provide the reference base for the prediction of the time of shear creep failure of the rock. The constitutive equations characterizing the shear creep characteristics of the rock were established, and the methods to solve model parameters were determined. In addition, according to the obtained experimental data, the model parameters were solved, and the theoretical curves of the model were fitted with the experimental curves. The new model was validated, and the sensitivity of the model parameters to creep-failure time were analyzed. The results show that the overburden pressure and the maximum creep strain of the key unit rock in a slope play a leading role in the progressive failure and instability of the rock, and the shear creep rate with time fits the power function well. The theoretical curves of the new model match well with the experimental curves, and the differences in the creep-failure time between the model calculation values and the experimental values are small, which indicates the new model is appropriate in describing the creep characteristics of the rock. For the shear creep-failure time, the viscous coefficient η_2 is the most sensitive, the accelerating point strain γ_a comes next, and the progressive-failure coefficient β is the least sensitive.

Fast Dynamics of Guided Magnetic Flux Quanta

The dynamics of Abrikosov vortices in superconductors is usually limited to vortex velocities $v\simeq1$ km/s above which samples abruptly transit into the normal state. In the Larkin-Ovchinnikov framework, near the critical temperature this is because of a flux-flow instability triggered by the reduction of the viscous drag coefficient due to the quasiparticles leaving the vortex cores. While the existing instability theories rely upon a uniform spatial distribution of vortex velocities, the measured (mean) value of $v$ is always smaller than the maximal possible one, since the distribution of $v$ never reaches the $\delta$-functional shape. Here, by guiding magnetic flux quanta at a tilt angle of $15^\circ$ with respect to a Co nanostripe array, we speed up vortices to supersonic velocities. These exceed $v$ in the reference as-grown Nb films by almost an order of magnitude and are only a factor of two smaller than the maximal vortex velocities observed in superconductors so far. We argue that such high $v$ values appear in consequence of a collective dynamic ordering when all vortices move in the channels with the same pinning strength and exhibit a very narrow distribution of $v$. Our findings render the well-known vortex guiding effect to open prospects for investigations of ultrafast vortex dynamics.

Seismic behavior of semi-rigid steel joints—Major axis T-stub and minor axis end-plate

Due to its cost-effective nature and satisfactory seismic performance, semi-rigid steel frame is often considered as an alternative to conventional fully rigid steel frames. To date, the seismic behavior of semi-rigid connection has typically been documented in two dimensions. To fill this gap, an experimental investigation was made to study the behavior of the internal semi-rigid joints through spatial quasi-static tests with loads applied to the ends of the columns from both the major and minor axes. In our newly proposed semi-rigid joint, the minor beam is attached to the column web by an end-plate connection and the major one attached to the column flange by a T-stub connection, where the loading effect from the minor direction on the major direction of semi-rigid joints was considered. Results show the major beams failed with T-stub fractures and the minor beams failed with substantial bending deformations at the end-plates, which are easy failures to repair. In addition, the initial rotational stiffness and angular ductility coefficient of the minor beam decreased with increases in the thickness of the end-plate. Compared with the semi-rigid steel joints with T-stub connections in both axes, the major beams of our proposed joints exhibited obviously increased bending resistances, equivalent viscous damping coefficients and equivalent energy dissipations.

Characterization of Viscoelastic Behavior of Poly(dimethylsiloxane) by Nanoindentation

In this study, we characterize the viscoelastic behavior of polymers using nanoindentation. We applied the indentation representative stress approach and elastic solution to the Maxwell model and determined that there was a linear relationship between the inverses of the initial unloading stiffness and indentation unloading rate. From nanoindentation tests with various unloading rates on poly(dimethylsiloxane), the linear relationship between the indentation unloading rate and the initial unloading stiffness was confirmed. We have suggested two parameters such as, elastic coefficient and viscous coefficient, represent the viscosity and elasticity of the polymer material based on their relation. In order to check the dependency of the elastic and viscous coefficients on mechanical properties, we performed nanoindentation on poly(dimethylsiloxane) with different crosslinking densities by mixing different proportions of curing agent. The viscosity and elasticity depend on the crosslinking density of polymer, and it was confirmed that the elastic coefficient and viscous coefficient obtained from nanoindentation varied with the same trend depending on crosslinking density. Key words: nanoindentation, viscoelasticity, PDMS, crosslinked polymer, Maxwell model

Striated Regularity of 2-D Inhomogeneous Incompressible Navier–Stokes System with Variable Viscosity

In this paper, we investigate the global existence and uniqueness of strong solutions to 2D incompressible inhomogeneous Navier-Stokes equations with viscous coefficient depending on the density and with initial density being discontinuous across some smooth interface. Compared with the previous results for the inhomogeneous Navier-Stokes equations with constant viscosity, the main difficulty here lies in the fact that the $L^1$ in time Lipschitz estimate of the velocity field can not be obtained by energy method (see \cite{DM17,LZ1, LZ2} for instance). Motivated by the key idea of Chemin to solve 2-D vortex patch of ideal fluid (\cite{Chemin91, Chemin93}), namely, striated regularity can help to get the $L^\infty$ boundedness of the double Riesz transform, we derive the {\it a priori} $L^1$ in time Lipschitz estimate of the velocity field under the assumption that the viscous coefficient is close enough to a positive constant in the bounded function space. As an application, we shall prove the propagation of $H^3$ regularity of the interface between fluids with different densities.

A mechanical model for spherical fragments penetrating gelatine

The behaviour and effects of a spherical fragment penetrating a simulant and those of biological tissue are similar. To accurately describe the interaction between spherical fragments and muscle tissue, this study first discusses the wounding mechanism and establishes a mechanical model considering the effects of strain rate based on the properties of gelatine, which is a widely used representative simulant in physical surrogates for muscle tissue. Subsequently, experiments wherein gelatine was penetrated by spherical fragments with diameters of 3, 4, and 4.8 mm were conducted. The inertial and viscous resistance coefficients were identified using the least squares method and the experimental results obtained for the 4-mm spherical fragment. Numerical calculations show that the mechanical model agrees well with the experimental values. Further, the mechanical model's ability to adequately describe the motion of spherical fragments penetrating gelatine with good generality is proved. The proposed model can therefore provide a scientific basis for small arms ammunition design and protection evaluation.

ИДЕНТИФИКАЦИЯ ПАРАМЕТРОВ МЕХАНИЧЕСКОЙ СИСТЕМЫ ВИБРАЦИОННОГО ЭЛЕКТРОМАГНИТНОГО АКТИВАТОРА ПО ГРАНИЧНЫМ ОКОЛОРЕЗОНАНСНЫМ ЧАСТОТАМ

Актуальность исследования обусловлена тем, что вибрационные электромагнитные активаторы являются эффективными устройствами для перемешивания суспензий, эмульсий, приготовления буровых растворов, разжижения высоковязких нефтепродуктов. Якорь специальной конструкции представляет собой гидравлический вентиль. При вибрации якоря на частотах, близких к резонансной частоте, в обрабатываемой жидкой среде создаются глубоко затопленные струи, которые при относительно невысоком энергопотреблении вибрационного электромагнитного активатора обеспечивают высокую эффективность перемешивания жидкой среды и снижение вязкости нефтепродуктов на достаточно продолжительном интервале времени. Резонансная частота механической системы зависит от жесткости пружины, массы якоря-активатора, присоединенной массы колеблющейся с якорем жидкой среды и от коэффициента вязкого трения, определяющего отведение энергии из колеблющейся механической системы. При изменении реологических свойств обрабатываемой жидкой среды изменяются как параметры механической колебательной системы, так и вид амплитудно-частотных характеристик вибрационного электромагнитного активатора. Способ организации мониторинга изменения реологических свойств обрабатываемой вибрационным электромагнитным активатором жидкой среды на основе прямых измерений, например с помощью вискозиметров, пригоден только для лабораторных условий и не годится для промышленного внедрения. По мнению авторов, более перспективным является подход, основанный на решении обратной математической задачи, когда, анализируя вид амплитудно-частотных характеристик вибрационного электромагнитного активатора, в частности граничные околорезонансные частоты, можно получить достоверные оценки параметров механической колебательной системы вибрационного электромагнитного активатора. Эти оценки удобно применять для организации как косвенного мониторинга изменения реологических свойств обрабатываемой жидкости в процессе работы вибрационного электромагнитного активатора, так и для усовершенствования структуры системы автоматического управления вибрационным электромагнитным активатором. Цель исследования заключается в разработке метода идентификации параметров механической системы вибрационного электромагнитного активатора на основе анализа граничных околорезонансных частот и определении границ применимости метода в сильно нагруженных колебательных механических системах. Методы: обыкновенные дифференциальные уравнения, преобразование Лапласа, передаточные функции, амплитудно-частотные характеристики, алгебраические уравнения. Результаты. Получены аналитические выражения, связывающие граничные околорезонансные частоты с параметрами механической колебательной системы, на основе которых составляются системы алгебраических уравнений. Показаны границы применимости метода в сильно нагруженных колебательных механических системах.

Study on Equivalent Viscous Damping Coefficient of Sucker Rod Based on the Principle of Equal Friction Loss

Equivalent viscous damping coefficient is an important parameter of wave equation for sucker rod string. In this paper, based on the principle of equal friction loss, when the viscous energy consumption and the local damping energy consumption are taken into account, effects of equivalent viscous damping coefficients are obtained. Through deducing energy consumption equation of oil and energy consumption equation of the coupling, theoretical formula for equivalent damping coefficient of sucker rods is received. Results show that the smaller the K is (K is the ratio of sectional area of tubing to sucker rod), the larger the proportion of damping coefficient caused by viscous energy consumption in the equivalent damping coefficient of sucker rod system is. When K< 0.095, the proportion of damping coefficient caused by viscous energy consumption is more than 90%. Reducing the sudden change of cross-section area at sucker rod coupling has remarkable effect on reducing damping force of the sucker rod system. The research provides a theoretical basis for the application and design of sucker rod and tubing.

Laboratory investigation of nonlinear flow characteristics through natural rock fractures

This paper aims to assess the influence of in situ stresses and geometry of the fracture surface on the behaviour of fluid flow through rock fractures. In this regard, fluid flow tests were performed on four mated, natural limestone fractures, under changing confining pressure ranging between 1.0 and 14 MPa. Based on the experimental observations, three types of relationship between pressure gradient and flow rate can be determined (linear, nonlinear induced by inertial effect and nonlinear induced by fracture dilation). Regression analyses of experimental data show that the nonlinearity induced by the inertial effect can be well quantified by the Forchheimer equation. The results of the experiments demonstrated that the confining pressure can change flow patterns from linear to nonlinear at higher flow rates, although by increasing the confining pressures the viscous and inertial coefficients in the Forchheimer equation show an increase of 10–40 and 2–10 times the initial magnitude, respectively. However, the rate of increase of the nonlinear coefficient b used in the Forchheimer equation steadily diminishes with the increase of confining pressure. The critical Reynolds number was successfully determined by taking a non-Darcy effect factor of 0.1, and the calculated critical Reynolds numbers show a decrease with further increase of the confining pressure and fracture roughness.

Global strong solutions to 3-D Navier-Stokes system with strong dissipation in one direction

We consider three dimensional incompressible Navier-Stokes equation $(NS)$ with different viscous coefficient in the vertical and horizontal variables. In particular, when one of these viscous coefficients is large enough compared to the initial data, we prove the global well-posedness of this system. In fact, we obtain the existence of a global strong solution to $(NS)$ when the initial data verify an anisotropic smallness condition which takes into account the different roles of the horizontal and vertical viscosity.

One particle distribution function and shear viscosity in magnetic field: A relaxation time approach

We calculate the $\delta f$ correction to the one particle distribution function in presence of magnetic field and non-zero shear viscosity within the relaxation time approximation. The $\delta f$ correction is found to be electric charge dependent. Subsequently, we also calculate one longitudinal and four transverse shear viscous coefficients as a function of dimensionless Hall parameter $\chi_{H}$ in presence of the magnetic field. We find that a proper linear combination of the shear viscous coefficients calculated in this work scales with the result obtained from Grad's moment method in \cite{Denicol:2018rbw}. Calculation of invariant yield of $\pi^{-}$ in a simple Bjorken expansion with cylindrical symmetry shows no noticeable change in spectra due to the $\delta f$ correction for realistic values of the magnetic field and relaxation time. However, when transverse expansion is taken into account using a blast wave type flow field we found noticeable change in spectra and elliptic flow coefficients due to the $\delta f$ correction. The $\delta f$ is also found to be very sensitive on the magnitude of magnetic field. Hence we think it is important to take into account the $\delta f$ correction in more realistic numerical magnetohydrodynamics simulations.

Thermal characterizations and investigation of the drawing region in Ge-As-S glasses for IR optical fibers

Several glass compositions of the Ge-As-S ternary system were prepared and their thermal and physical properties were investigated as Tg, Td, theoretical drawing temperature Ts, viscous flow activation energy, density, visible and IR absorption coefficients. The measured values, which are in excellent agreement with the literature, were used to explore the drawing capability of the glass samples. In this work, we report wide range of Ge-As-S optical fiber compositions using the classical preform-to-fiber drawing technique. We show the possibility to obtain optical fibers with sulfur concentration ranging from 35 to 75%, and germanium concentration as high as 35%. In addition, based on the drawing tests we present a fiber drawing domain in the Ge-As-S ternary diagram. The attenuation losses measured at 1310 nm wavelength were between 8.4 and 12.3 dB/m.