Peeling of an elastic membrane tape adhered to a substrate by a uniform cohesive traction

An analytical model is provided for the peeling of a tape from a surface to which it adheres through cohesive tractions. The tape is considered to be a membrane without bending stiffness and is initially attached everywhere to a flat rigid surface. The tape is assumed to deform in plane strain, and finite deformations in the form of elastic strains are accounted for. The cohesive tractions are taken to be uniform when the tape is within a critical interaction distance from the substrate and then to fall immediately to zero once this critical interaction distance is exceeded. When the distance between the tape and the substrate is zero, repulsive and attractive tractions balance to zero; in this segment, sliding of the tape relative to the substrate is forbidden when we pull the tape up somewhere in the middle, though we permit such sliding when the tape is peeled from one end. In the cohesive zone and where the tape is detached, the interaction of the tape with the substrate is frictionless. Results are given for the force to peel a neo-Hookean tape at any angle up to vertical when one end of it is pulled away from the substrate, as well as for scenarios when the tape is lifted somewhere in the middle to form a V shape being pulled away from the substrate.     

Orientational effect of the extensional flow field on solutions of rigid rodlike macromolecules-disappearance of the isotropic to nematic phase transition

The effect of steady state uniaxial extensional flow on a solution of rigid rodlike macromolecules is theoretically studied. The mean field theory of Maier and Saupe is extended to cover situations in which the macromolocular solution is subjected to an extensional flow field. It is found that for a given solution a critical flow gradient exists beyond which the first order nematic-isotropic phase transition, which is typical of such solutions in the absence of flow, disappears. A similar result is obtained when the theory of Onsager is applied to the problem. Order parameter as a function of flow gradient is calculated and it is shown that the contribution of flow to the ordering of macromolecules is most significant when the stationary solution is isotropic but close to the transition point.     

Large strain elasto-plastic model of paper and corrugated board

An anisotropic elasto-plastic constitutive model of paper material is presented. It is formulated in a spatial setting in which anisotropic properties are accounted for by use of structural variables. A multiplicative split of the deformation gradient is employed to introduce plasticity. A similar approach is used to model the plastic deformation of the substructure. The yield surface adopted is based on the Tsai–Wu failure criterion, used previously to model failure of paper material. A non-associated plasticity theory is employed to calibrate the model to experimental data. It turns out that a multi-axial loading situation is needed to calibrate the model and here a biaxial tension test is audited. The model was implemented into a finite element environment and the creasing process of a corrugated board panel is investigated.     

Interaction of heated filaments with a blunt cylinder in supersonic flow

A computational study is performed to examine the influence of pulsed energy deposition on a cylinder in supersonic flow. A code is written to solve the compressible Navier–Stokes equations. The energy deposition is modeled as a high temperature, low density filament introduced at the inflow boundary, and the frequency of energy deposition pulses is varied. It is shown that the energy deposition reduces both the average drag and the average heat transfer to the front face of the cylinder. The effectiveness of drag reduction is shown to be inversely proportional to the energy deposition pulsation period. The efficiency of drag reduction is shown to be approximately 100. The average heat transfer to the face is reduced from the steady state, with a maximum reduction of 30%.     

Effect of surface charge state on the thermal conductivity of nanofluids

Thermal conductivity enhancement of nanofluids is very attractive to thermal and heat transfer engineering, however its mechanism is not clear yet. In this study, it is proposed that the surface charge state of nanoparticles is to explain the thermal conductivity enhancement of nanofluids. By comparing to the previous reported results, it is shown that the interparticle interaction due to the surface charge state is the most important factor to increase of thermal conductivity of nanofluids.     

An elementary consideration of some extrusion defects

Summary It is shown that the best upper bounds to the load in direct extrusion when the fault known as piping is anticipated are less than the best upper bounds obtainable by the use of similar deformation patterns, when piping is assumed not to be going to occur. A similar approach is made to the case in which a short slug is pierced by two equal size punches and which results in faults at the container wall; this instance is important because it is analogous to the new method by which gudgeon pins are formed.     

Adaptive Space-Time GLS FEM with Direct Projection for 2D Advection-Diffusion Problem

A space-time scheme is an unconditional stable time-integration scheme and its domain is discretized into space-time slabs, which are employed to weakly enforce the continuity of the solution across the time slabs. It is applied in this study to two-dimensional advection-diffusion problems, and space-mesh adaptation is introduced. Mesh adaptation is a powerful scheme to reduce discretized errors: however, it is found that an error due to the projection between adaptive meshes in successive time slabs is another source of error. To reduce projection errors, the direct projection scheme for space-time method will be used in this study. Galerkin/Least Squares scheme is applied to prevent numerical instability due to the skew-symmetric term in the weak form of the advection-diffusion equation.     

基于LuGre摩擦模型的接触约束法旋转柔性梁斜碰撞研究

基于接触约束法和LuGre摩擦模型对在重力场作用下作大范围旋转运动的柔性梁系统和斜坡发生含摩擦斜碰撞的动力学问题进行研究. 首先运用刚柔耦合的多体系统动力学理论对大范围运动的柔性梁进行离散化和动力学建模, 在碰撞时采用冲量动量法求出跳跃速度, 其次在法向上引入接触约束求解出碰撞力, 在切向上采用LuGre摩擦模型分两种方式求解摩擦力, 第一种是在滑动时摩擦力由摩擦系数和碰撞力计算得出, 黏滞状态下引入切向约束计算拉格朗日乘子反应实际摩擦力, 根据黏滞/滑动切换判断计算出碰撞过程摩擦力(与Coulomb摩擦模型计算摩擦力一致); 第二种根据LuGre摩擦模型摩擦系数和法向碰撞力计算其摩擦力, 从而在碰撞时无需黏滞/滑动切换, 采用相同的摩擦力计算公式. 通过与Coulomb摩擦模型对比发现, LuGre摩擦模型描述碰撞切向摩擦过程更精确, LuGre摩擦模型黏滞时建立约束方程和碰撞采用统一的摩擦力公式这两种建模方式描述的斜碰撞动力学特性没有区别, 进而说明采用法向接触约束和LuGre摩擦模型具有满足碰撞非嵌入情况、避免黏滞/滑动切换、描述摩擦力相对准确的优势.      

A study of sloshing absorber geometry for structural control with SPH

A liquid sloshing absorber consists of a container, partially filled with liquid. The absorber is attached to the structure to be controlled, and relies on the structure's motion to excite the liquid. Consequently, a sloshing wave is produced at the liquid free-surface within the absorber, possessing energy dissipative qualities. The primary objective of this work is to numerically demonstrate the effect of a sloshing absorber's shape on its control performance. Smoothed Particle Hydrodynamics (SPH) is used to model fluid–structure interaction of the structure/sloshing absorber system in two dimensions. The structure to be controlled is a lightly damped single degree-of-freedom structure. The structure is subjected to a transient excitation and then allowed to respond dynamically, coming to rest either due to its own damping alone or with the added control of the sloshing absorber. It is identified that the control performance of the conventionally used rectangular container geometry can be improved by having inward-angled walls. This new arrangement is robust, and of significant advantage in situations when the external disturbance is of uncertain magnitude.     

感应同步器测角系统误差分析及补偿

本文讨论了提高感应同步器精度的硬件方法和软件方法。硬件方法即根据误差来源，针对不同谐波成分误差，用电路调节的方法消除误差。软件方法就是采用计算机通过误差曲线拟合来减小误差。     

Non-linear response of a beam to periodic loading

The steady state response of a non-linear beam under periodic excitation is investigated. The non-linearity is attributed to the membrane tension effect which is induced in the beam when the deflection is not small in comparison to its thickness. The effects of multimode participation are investigated for simply supported and clamped boundary conditions. The finite element technique is used to formulate the non-linear differential equations of the straight beam and the method of averaging is used to obtain an approximate solution to the non-linear equations under harmonic loading. An analog computer was used to simulate the non-linear beam equation which was subjected to harmonic excitation. The agreement between theoretical and experimental values is reasonably good.     

On the simultaneous elongation and inflation of a tubular membrane of BKZ fluid

This work considers a viscoelastic fluid membrane which is initially tubular and bonded at each end to a rigid circular disc. The membrane is subjected to prescribed elongational and internal pressure histories causing it to undergo quasi-static axisymmetric deformation. This example is intended to simulate an experiment which has been recently proposed for the determination of constitutive properties for viscoelastic fluids as well as some polymer sheet forming process.The constitutive equation is presumed to be of integral type. The formulation of the problem leads to a basic system of equations which is intended for numerical solution. It has the structure of a two-point boundary value problem for a system ordinary differential equations at each time. The formulation has the advantage that the equations do not have to be rederived if the constitutive equation is changed. A change in the sub-program for computing stress from stretch history is all that is needed.A numerical method of solution is presented. In a numerical example, the material is taken to be polyisobutylene, modeled as a BKZ fluid.     

Linear constitutive model for mechano-sorptive creep in paper

The creep of paper is accelerated by moisture cycling. This effect is known as mechano-sorptive creep. It is assumed that this is an effect of transient stresses produced during moisture content changes in combination with non-linear creep behaviour of the fibres. The stresses produced by the moisture content changes are often much larger than the applied mechanical loads. If this is the case, the mechanical loads are only a perturbation to the internal stress state, and it will appear as if the mechano-sorptive creep is linear in stress. It is possible to take advantage of this feature. In the present report the pure moisture problem is first solved. The mechanical load is then treated as a perturbation of the solution to the moisture problem. Using this strategy, it is possible to linearize a non-linear network model for mechano-sorptive creep and to formulate a continuum model. As a result, the number of variables in the model is reduced. This is a significant improvement as it will be possible to use the linearized model to describe the material in a finite element program and solve problems with complicated geometries.     

Quasi-steady prediction of coupled bending–torsion flutter under rotating stall

A method is presented in this paper to predict cascade flutter under subsonic stalled flow condition in a quasi-steady manner. The ability to predict the occurrence of aeroelastic flutter is highly important from the compressor design point of view. In the present work, the well known Moore–Greitzer compression system model is used to evaluate the flow under rotating stall and the linearized aerodynamic theory of Whitehead is used to estimate the blade loading. The cascade stability is then predicted by solving the structural model, which is posed as a complex eigenvalue problem. The possibility of occurrence of flutter in both bending and torsional modes is considered and the latter is found to be the dominant one, under subsonic stalled flow, for a large range of frequency ratios examined. It is also shown that the design of compressor blades at frequency ratios close to unity may result in rapid initiation of torsional flutter in the presence of stalled flow. A frequency ratio of 0.9 is primarily emphasized for most part of the study as many interesting features are revealed and the results are physically interpreted. Roughly a pitchfork pattern of energy distribution appears to occur between bending mode and torsional mode which ensures that only one flutter mode is possible at any instant in time. A bifurcation from bending flutter to torsional flutter is shown to occur during which the frequency of the two vibrating modes appear to coalesce for a very short period of time.     

Feedback control of vortex shedding from two tandem cylinders

The effect of feedback control on vortex shedding from two tandem cylinders in cross-flow is investigated experimentally. The objective is to reduce the downstream cylinder response to vortex shedding and turbulence excitations. Feedback control is applied to a resonant case, where the frequency of vortex shedding coincides with the resonance frequency of the downstream cylinder, and to a nonresonant case, in which the shedding frequency is about 30% higher than the downstream cylinder resonance frequency. A “synthetic jet” issuing through a narrow slit on the upstream cylinder is employed to impart the control effect to the flow. The effect of open-loop control, using pure tones and white noise to activate the synthetic jet, is also examined. It is demonstrated that feedback control can significantly reduce the downstream cylinder response to both vortex shedding and turbulence excitations. For example, the cylinder response is reduced by up to 70% in the resonant case and 75% in the nonresonant case. Open-loop control also can reduce the cylinder response, but is less effective than feedback control. The frequency of vortex shedding is found to increase substantially when white noise is applied. This increase in the shedding frequency is higher than the largest frequency shift that could be produced by open-loop tone excitation.     

The use of an image derotator in hologram interferometry and speckle photography of rotating objects

An image derotator is described that consists of a folded Abbé inverting prism built into the center of a hollow-shafted torque motor. The alignment and operation of the unit is discussed, and resolution of the derotated image in excess of 15 cyc/mm is shown. Its application to vibration analysis of rotating objects is demonstrated via double-exposure holograms recorded with a Q-switched, double-pulse, ruby laser. The necessity for using such a derotator is to maintain image alignment between pulses, rather than for stopping image motion during the pulses. The technique is shown to apply to contoured objects, to resonant and nonresonant vibrations, and to speeds up to 9200 rpm. In addition, application of the system for recording large-vibration amplitudes via double-exposure, speckle photography is demonstrated. Finally, concomitant observation of vibration with stroboscopic illumination synchronized to the rotation is described, where the vibration is manifested as a streaking of defocused speckles.     

An Integral Method to Calculate Water Saturation in a Centrifuge Experiment to Determine Capillary Pressure

The centrifuge method is commonly used to determine the capillary pressure of a porous medium, and the original approximating method for data analysis developed by Hassler and Brunner is still being used. Its limitations are, however, not well understood. Application to analyze experiments where one of the assumptions was obviously violated had been given in the literature. While the result appeared to be quite reasonable, it was not clear how close was it to reality. One of the objectives of this paper is to review the assumptions that is required to develop this method, so that the experimental condition in which it is applicable can be established. The other objective is to derive a completely different solution technique to this problem. There is no need to assume that the ratio of the inlet radius to the exit radius of the core to the center of the centrifuge be close to 1. With the freedom from this limitation it is, therefore, possible to construct machines at lower cost and to improve on the data quality by allowing longer cores.     

Precise tracking control of piezoelectric actuators based on a hysteresis observer

In this paper, a precise tracking control method for piezoelectric actuators based on a hysteresis observer is considered. A nonlinear observer to estimate the hysteretic nonlinearity in the piezoelectric actuator is designed, and then the hysteretic nonlinearity is compensated for by a feedforward control. The proposed observer is easy to design and has better performance compared to the previous work presented in the literature. A feedback controller is also designed to track reference signals. A numerical simulation is presented to verify the method proposed.     

3D pore network modeling and simulation for dynamic displacement of gas and condensate in wellbore region

Condensate dropout in near a wellbore region in gas condensate reservoir is the main reason of low well deliverability. Many researchers have studied gas and condensate relative permeabilities (RPs) in this region to find the condition for better deliverability. It is known that RP is a function of capillary number in low interfacial tension (IFT) systems such as gas-condensate. The positive dependency of RPs to velocity which is referred to as "positive coupling effect" is related to the simultaneous flow of gas and condensate associated with intermittent opening and closure of channels in porous media. The negative dependency of RPs to velocity named "negative inertia" is due to non-Darcy high-velocity flow. In this study, a 3D pore network modeling is developed to investigate fluids distribution in a gas-condense system at a pore scale to find out the effects of IFT and velocity on RPs. A new method is developed that applies a flash calculation in all throats in the network to estimate the amount of accumulated condensate in throats' corners at different time steps. A modified form of Poiseuille's law for polygonal cross-sectional throats is used to find and update pressure field and fluids distribution in the network and to determine the quantity of pushed out condensate from closed throats to neighboring throats. The displacement mechanism is considered to be determined by the volume of displaced phases in throats without applying any correlation. Simulation results indicate that gas and condensate RPs are increased by an increase in velocity. However, RPs sensitivity to velocity is reduced by increasing IFT which is in agreement with previous studies.