Tangential Displacement Research Articles

Iterative PIV interrogation for complex wall-bounded flows

The strategy of the iterative PIV algorithm is discussed with the aim of investigating transitional wall-bounded flows. It is proposed to start the algorithm with a coarse prediction of the large-scale tangential velocity gradient to eliminate its negative effect. A window correlation with image deformation technique is then iteratively conducted to capture the fluctuating flow structures. Synthetic particles are created based on the DNS result of a typical hypersonic transitional boundary layers to evaluate the performance of the algorithm. Effects of several parameters, including the mean tangential displacement gradient, particle diameter, particle density and background noise on the level on the evaluation, are systematically investigated. Four methods to initially predict the near-wall flow are compared, including the directly-used window correlation with image deformation (WC) (Scarano 2002 Meas. Sci. Technol. 13 R1–19), the WC method with static particles added in the solid region (Zhu et al 2013 Meas. Sci. Technol. 24 125302), the image gradiometry method (Nguyen et al 2009 Proc. 6th Int. Symp. on Turbulence and Shear Flow Phenomena (Seoul, Korea, 2009)) and the newly-proposed joint-translation-shear correlation method method. The results show that, compared with the other three approaches, the performance of the new method is greatly enhanced for evaluating the dynamical flow properties, even if the displacement gradient is very high. Finally, experimental data on artificially disturbed boundary layers from a low-speed and a high-Mach-number wind tunnel are used to evaluate the new method, which is able to evaluate the mean and instantaneous velocity fields in both cases.

Simple and high-performance stick-slip piezoelectric actuator based on an asymmetrical flexure hinge driving mechanism

This article presented a new type of stick-slip piezoelectric actuator based on an asymmetrical flexure hinge driving mechanism. The key of the driving mechanism was a four-bar mechanism with different minimum thicknesses of right-circle flexure hinges. Combined with a symmetrical indenter, the asymmetrical flexure hinge driving mechanism generated controllable tangential displacement by changing the locking force. Therefore, the simple structured stick-slip piezoelectric actuator achieved considerable improvements especially in output speed and efficiency. In order to obtain improved actuator properties, the minimum thicknesses of asymmetrical flexure hinge driving mechanism, the tangential and normal displacements of the indenter were analyzed and investigated by finite element method. A prototype was fabricated and experiment investigation of the actuator characteristics was presented. Testing results indicated that the actuator achieved the maximum velocity of 15.04 mm/s and its maximum load reached 440 g under a voltage of 100 Vp-p and a frequency of 490 Hz. The maximum efficiency of the actuator was 3.66% with a load of 280 g under a locking force of 5 N and the actuated velocity of 10.17 mm/s.

Numerical study on dynamic mechanism of brain volume and shear deformation under blast loading

Blast-induced traumatic brain injury (b-TBI) is a kind of significant injury to soldiers in the current military conflicts. However, the mechanism of b-TBI has not been well understood, and even there are some contradictory conclusions. It is crucial to reveal the dynamic mechanism of brain volume and shear deformations under blast loading for better understanding of b-TBI. In this paper, the numerical simulation method is adopted to carry out comprehensive and in-depth researches on this issue for the first time. Based on the coupled Eulerian–Lagrangian method, the fluid–structure coupling model of the blast wave and human head is developed to simulate two situations, namely the head subjected to the frontal and lateral impacts. The simulation results are analyzed to obtain the underlying dynamic mechanisms of brain deformation. The brain volume deformation is dominated by the local bending vibration of the skull, and the corresponding frequency for the forehead skull under the frontal impact and the lateral skull faced to the lateral impact is as high as 8 kHz and 5 kHz, respectively. This leads to the high-frequency fluctuation of brain pressure and the large pressure gradient along the skull, totally different from the dynamic response of brain under head collisions. While the brain shear deformation mainly depends on the relative tangential displacement between the skull and brain and the anatomical structure of inner skull, being not related to the brain pressure and its gradient. By further comparing the medical statistics, it is inferred that diffuse axonal injury and brain contusion, the two most common types of b-TBI, are mainly attributed to brain shear deformations. And the von Mises stress can be adopted as the indicator for these two brain injuries. This study can provide theoretical guidance for the diagnosis of b-TBI and the development of protective equipment.

Novel numerical method for parameterising fretting contacts

Fretting regime transition is traditionally achieved by qualitative assessment of the fretting loops (tangential force, Q vs tangential displacement δ) and material response. Other studies used parameters in which thresholds are theoretically determined to exceed friction at the contact for regime transition identification. This study successfully developed a flexible loop analysis method based on simple vector principles that is able to quantify and characterise its constituent parts. In terms of fretting contact analysis the loop analysis method provided a complementary method of regime transition identification to those based on theoretically overcoming friction at the contact, with strong agreement between the two. This novel method provides an efficient way to correlate regime transition with other data sets, with additional insights into the mechanical response of the contact compared to other regime transition criteria. Possible applications of this method include enabling smart asset monitoring and in the development of engineering components that are subject to fretting. This is an extremely flexible technique that has applicability for other types of loop analysis.

Shear coupling effect of monotonic and cyclic behavior of the interface between steel and gravel

Three-dimensional behavior of the interface between a structure and gravelly soil is of great concern in the design and construction of large-scale projects. A series of three-dimensional tests were conducted to investigate the effect of shear coupling on the monotonic and cyclic behavior of such an interface. In these tests, monotonic shear was applied to the interface first and then the monotonic and cyclic shears were applied in the orthogonal direction while the original shear was maintained. Based on the test observations, the shear strength of the interface was found to be independent of the shear coupling and proportional to the normal stress. Significant tangential displacement is induced by the orthogonal shear application and the deflection direction of the tangential displacement is proportional to the square of the ratio between the orthogonal shear stress and shear strength. The interface exhibits significant dilatancy due to a three-dimensional shear application, which is divided into reversible and irreversible components. Shear coupling remarkably affects the magnitude and transition shear stress of the reversible dilatancy component. There persists a significant aeolotropy of the interface evenly under the shear coupling condition. Particle crushing near the structure was observed to be enhanced due to the shear coupling.

Prediction of interface stiffness of single-walled carbon nanotube-reinforced polymer composites by shear-lag model

Interfacial stress transfer of single-walled carbon nanotube-reinforced polymer composites subjected to uniaxial tension was investigated by a newly developed shear-lag model integrated with a spring layer model. A linear relationship between the tangential relative displacement and the interfacial shear stress was assumed for the interface which is determined by van der Waals forces. The interface stiffness parameter was determined through comparing the stress distribution of the shear-lag model with multiscale simulation results. The effect of the interface stiffness and the nanotube’s aspect ratios on the distribution of stress in CNT-reinforced composites was studied.

Large displacement analysis of ellipsoidal pressure vessel heads using the fundamental of differential geometry

This paper presents an investigation of the large displacement analysis of ellipsoidal pressure vessel heads, based on the membrane shell theory. The strain components of deformed shell configurations could be obtained by using the fundamental knowledge of differential geometry. Energy functional of the ellipsoidal shell was derived from the principle of virtual work, which is expressed in the appropriate forms. Based on the nonlinear finite element procedures, the nodal displacements of the shell configuration were numerically obtained. Analytical method for the small displacement was derived in order to validate the numerical results obtained from the FEM. Interesting features from parametric study of normal and tangential displacements for arbitrary shapes of ellipsoidal shells are presented and discussed. It is revealed that the point of zero normal displacement for arbitrary shapes of ellipsoidal shells is always the same point which is independent of the applied internal pressure and thickness of shell. Furthermore, there exists the maximum point of tangential displacement and it is always at the same points of the radial distance when the internal pressure and thickness of shells are varied.

Dynamical stability and vibrational properties of Pt clusters

While cohesive and structural properties of Pt clusters have been widely investigated, there is scarce knowledge on their vibrational properties. In this work we investigate, by ab initio methods, the vibrational properties of Ptn (n = 13, 19, 55, 79) clusters. We pay particular attention to the structural stability of the typical octahedral (Oh) and icosahedral (Ih) symmetric Pt13 clusters. Their vibrational density of states (νDOS) reveal that these geometries are magnetically unstable, while these isomers are metastable in their non-magnetic states. By performing finite-temperature molecular dynamic runs, we find that Oh and Ih clusters evolve towards layered lower energy structures. A new lowest energy isomer is thus predicted. For these Pt13 layered clusters, and for Oh bulk type Ptn (n = 19, 55, 79) clusters, the νDOS and heat capacity are calculated and compared to their bulk counterparts. For the Pt13 layered clusters we inspect and interpret, in terms of bond-order analysis, the vibrational modes for the enhanced low- and high-frequency ends of the cluster's νDOS. We identify mostly shear, tangential type displacements for their lowest frequency modes, and mostly longitudinal, intralayer antiphase displacements for the highest frequency modes of the νDOS.

Dynamic load and stress analysis of a large horizontal axis wind turbine using full scale fluid-structure interaction simulation

A dynamic load and stress analysis of a wind turbine is carried out using transient fluid-structure interaction simulations. On the structural side, the three 50 m long commercial glass-fiber epoxy blades are modelled using shell elements, accurately including the properties of the composite materials. On the fluid side, a hexahedral mesh is obtained for every blade and for the hub of the machine. These meshes are then overlaid to a structured background mesh through an overset technique. The displacements prescribed by the structural solver are imposed on top of the rigid rotation of the turbine. The atmospheric boundary layer (ABL) is included using the k-epsilon turbulence model. The computational fluid dynamics (CFD) and computational solid mechanics (CSM) solvers are strongly coupled using an in-house code. The transient evolution of loads, stresses and displacements on each blade is monitored throughout the simulated time. The ABL induces oscillating axial displacements in the outboard region of the blade. Furthermore, the influence of gravity on the structure is accounted for and investigated, showing that it largely affects the tangential displacement of the blade. The oscillating deformations lead to sensible differences in the torque provided by each blade during its rotation.

The influence analysis of curvature on transverse vibration of multi-curved shafting based on numerical and experimental results

Shafting would be a curved status for the heavy propeller. This article addresses a numerical and experimental vibration analysis of curved shafting. In the numerical theory, the shafting is simplified as a multi-curved beam system with a tail point mass. The system model is derived based on the so-called spectro-geometric method (SGM) in which the transverse and tangential displacement over each sub-structure is invariably expressed as a modified Fourier series expansion. All the unknown Fourier coefficients are treated as a set of independent generalized coordinates and solved directly from the Rayleigh-Ritz procedure. The experimental was carried out on a laboratory-size shafting model which is curved factitiously. The numerical results show that the relationship between the frequency and the beam curvature is complex. It strongly depends on the boundary conditions. The experimental results indicate that the frequency of the shafting would decrease with the increase of the curvature compared with straight shafting.

Finite Element Modeling Method of Centrifugally Rotary Processing

In the present work, the process of interaction of an abrasive particle with the surface of a component is modeled in the framework of dynamic problems of the theory of thermoelasticity, considering plastic deformation, friction and wear of the surface in the contact region. Two boundary contact problems are considered. The first problem deals with the contact interaction of an element of an abrasive particle in the form of a truncated cone and the surface of a part. The circle of smaller diameter of the cone contacts the surface of the part taking into account the friction and plastic deformation of this surface. Kinematic or force boundary conditions are applied to the circle of greater diameter. In the case of kinematic conditions, the normal and tangential displacements of the circle and its rotation are specified. In the case of force conditions, the force and moment are given. In the second task, the hard stamp slides at a constant speed along the flat boundary of the workpiece, the value of the die insertion is set. In the contact area, the sliding friction force is expressed through normal pressure and heating due to the friction and wear. The stress and temperature fields near the contact region are investigated.

The effect of adhesion and roughness on friction hysteresis loops

Friction hysteresis results from an oscillating friction force at a contact interface. At nano-scale, this phenomenon is affected by the roughness of the contact interface and adhesion. In nanotribology, therefore, it is highly desirable to understand and predict this behavior to estimate the energy loss and possible wear. This paper presents a boundary element model (BEM) for the adhesive friction hysteresis contact at the interface of two bodies of arbitrary geometry. In the model, adhesion is represented by means of a Dugdale approximation of the total work of adhesion at local areas with a very small gap between the two surfaces. The amplitude of the oscillating tangential displacement is very small compared to the contact area which means that the interface does not experience gross-sliding between the two surfaces (the contact remains in the pre-sliding state). Hence, the frictional contact is divided into sticking and slipping regions, defined based on the local values for shear stress and normal pressure, and the rate of relative displacement. The model is first verified by comparing the numerical and analytical (Mindlin theory) solutions for the contact of a smooth ball and a flat of identical materials under a fixed normal force and an oscillating friction force. Then, the problem is solved at the smooth interface between a rigid ball and an elastic flat for various values of the work of adhesion. It is shown that as the work of adhesion increases, both static friction force and pre-sliding displacement increase due to the increase in the contact repulsive force. In addition, the rough interface between a glass ball against a silicon wafer and a DLC (Diamond-Like Carbon) coating is considered. Since adhesion depends on the interface roughness, the corresponding contact repulsive force is different for these interfaces. For the smoother interface, a larger contact repulsive force and consequently, a larger static friction force and pre-sliding displacement are obtained.

Seismic Performance of Curved Bridges with Longitudinal Slope

A curved bridge test model with a scale ratio of 1:10 was constructed to investigate the influence of site conditions on curved bridges with longitudinal slopes based on a similar theory. The natural ground motions of five different groups, namely, Sites A–E, were selected from the Pacific Earthquake Engineering Center (PEER) seismic database, and the shaking table model test was conducted under horizontal unidirectional and bidirectional excitations. Results showed that the structural response of the curved bridge is sensitive to the ground motion of different site conditions. Spatial characteristics are observed in the main girder structural response of the curved bridge. When the curved bridge is parallel to the direction of the principal ground motion, the rotation effect of the main girder is greater than that perpendicular to the direction of the principal ground motion. The rotation effect of the main girder leads to evident beam end and bearing displacements at the low pier. The seismic excitation direction and pier height notably affect the displacement response of the pier, and the tangential displacement response of the fixed pier is sensitive to seismic excitation.

A Soft Pneumatic Haptic Actuator Mechanically Programmed for Providing Mechanotactile Feedback

Tactile sense provides us with the necessary information and feedback to determined tasks. Within this context, haptic devices represent a growing and highly interesting field to be included in biomedical devices, teleoperation applications, and video games. These devices are usually developed with rigid materials, motors, and mechanisms to provide tactile feedback to individuals that corresponds to a defined task, producing pressure, tangential force or vibrations as stimuli on the skin. Here, we present a prototype of a soft pneumatic haptic device based on an inflatable hyperelastic membrane, that can provide two stimuli over skin such as pression and traction with only one input of energy. The device was fabricated using different types of silicone materials and membrane shapes. This exhibits experimentally a maximum vertical deformation of 13 mm and a tangential displacement of 10 mm at 7 kPa. These two mechanically programmed movements open the possibility of using this technology in mechano-tactile feedback for wearable devices, with low-cost hardware, soft interaction between devices and skin, and lightweight.

Large deformation mixed finite elements for smart structures

Recently, “Tangential Displacement Normal Normal Stress” elements were introduced for small-deformation piezoelectric structures. Benefits of these elements are that they are free from shear locking in thin structures and volume locking for nearly incompressible materials. We extend these elements to the large deformation case for electro-active polymers in the framework of an updated Lagrangian method. We observe that convergence does not deteriorate as the material becomes nearly incompressible with growing Lamé parameter λ, and that the discretization of slender structures by flat volume elements is feasible. The elements are freely available in the open source software package Netgen/NGSolve.

Analytic stress solutions for a lined circular tunnel under frictional slip contact conditions

The contact condition on the interface between the lining and the surrounding rock is assumed to be frictional slip contact. The state of the minimum relative sliding on the interface is considered as the true working state of the lining. The mechanical process of the support delay is taken into consideration, and the stress analytic solutions for a lined circular tunnel subjected to in situ stress and internal water pressure are derived based on the complex variable method and optimization theory. The analytic solutions are verified by finite element method. Under different friction coefficients and lateral pressure coefficients, the distributions of the tangential stresses along the inner and outer boundaries of the lining, the contact stresses and the tangential displacement discontinuity value along the interface are given. There exists a threshold of the friction coefficient that distinguishes the cases of the perfect bonding contact and the frictional slip contact, which is related to the lateral pressure coefficient and the material parameters.

Alternate tangential impact treatments for the soft-sphere collision model

The linear-slider-dashpot (LSD) soft sphere model is used extensively to model particle collisions in dense particle systems. The contact mechanics in the normal and tangential directions are modeled by a spring, damper, and dashpot system. The current work evaluates different existing tangential direction implementations of the LSD model. The existing models require storing the cumulative tangential displacement for each collision pair. The article evaluates existing tangential models and develops alternative methods which do not require storing the tangential deformation. The models are tested for two canonical single particle experiments of oblique impacts and sphere traveling on a surface. It is shown that some of the existing implementations fail to validate with at least one of the test cases. In one proposed model, Model-C, the tangential displacement is approximated as the product of the characteristic time of collision with the instantaneous particle tangential contact velocity. In a second proposed model, Model-D, the instantaneous non-dimensional impact angle is used to characterize the impact according to Maw et al.’s analysis. Both models give reasonably good predictions in the two test cases with the quality of predictions as good or better than some existing implementations which require the storage of the tangential deformation.

Components for Simulation of piezoelectrically actuated Systems with SyMSpace

The concept of automating the computation steps in a design process along different simulation tools leads to a more efficient use of knowledge and computational resources. In this paper the software tool SyMSpace, which realizes this automatization, and the available components concerning the simulation of piezoelectrically actuated systems is presented. The finite element model of a circular piezoelectric patch on a rectangular aluminium substrate using novel mixed finite elements is used as an example to show how to create a well-documented and easy-to-use component. Tangential displacements and normal normal stresses (TDNNS) are used as mechanical degrees of freedom and the finite elements are readily available in open source software package Netgen/NGSolve.In order to simplify the installation and usage of specialized (open source) software tools and help to reproduce results in scientific publications, the concept of (docker) containers is integrated in SyMSpace.

УПРУГОЕ МОМЕНТНОЕ ПОЛУПРОСТРАНСТВО ПОД ДЕЙСТВИЕМ ОСЕСИММЕТРИЧНЫХ НЕСТАЦИОНАРНЫХ ПОВЕРХНОСТНЫХ КИНЕМАТИЧЕСКИХ ВОЗМУЩЕНИЙ

The article deals with elastic homogeneous isotropic half-space filled with the Cosserat medium. A cylindrical coordinate system is used. A closed system of equations includes equations for the non-trivial components of the displacement and rotation potentials, as well as relations relating the displacements to the potentials and components of the stress and moment stress tensors with displacements and the angle of rotation. On the boundary plane, normal displacements are specified, and the angle of rotation and tangential displacements are absent. Initial conditions are zero. All components of the stress-strain state are assumed to be limited. A system of dimensionless quantities is used. The solution is represented as a convolution with respect to time and a generalized convolution with respect to the radius of surface perturbations with influence functions. To construct them, Hankel transforms are applied along the radius and Laplace in time, as well as expansion in power series in a small parameter in the linear approximation. Found image of all surface influence functions. For example, the following function is considered corresponding to the normal voltage. Its original is on the border of a half-space using the connection of axisymmetric and plane problems, namely, taking into account the proportionality of the Hankel and Fourier images respectively. It uses the previously constructed solution of the planar problem. As a result, the desired function is represented as integrals, which are understood in the sense of regularized values. Analytic expressions for these integrals and the influence function itself are found. Examples of calculations of the influence functions of a granular composite of aluminum shot in an epoxy matrix are given. Two variants of action on the half-space of surface normal displacements are also considered: the disturbance concentrated at the origin and distributed in a circle. Analysis of the results shows that the effect of the moment properties of the medium depends significantly on the value of the parameter characterizing the relationship of elastic displacements and rotational motions. For the material in question in quantitative terms it is not great. However, consideration of moment stress leads to qualitative changes. Namely, there is an additional wave front.

SUBSTANTIATION OF THE METHOD FOR ASSESSING ADHESION OF FIBROUS MATERIALS TO BINDER WHEN PRODUCING YARN BY ADHESIVE METHOD

When yarn is formed by adhesive methods, the strength of the yarn is ensured by gluing the sliver with some binder, i.e. due to adhesion. The analysis of the existing methods of instrumental assessment of adhesion of materials to binders of various compositions is carried out. Based on the well-known classification of methods, a method for assessing adhesion is justified, which consists in determining the breaking load during the tangential displacement of fibres in the bundle, as the most suitable for fibrous materials. A single indicator was established – breaking load, related to the average length of the fibres that glide upon destruction of the sample in the form of a bunch of the studied fibres, which allows an objective comparison of the various composition of adhesives. A preliminary estimate of the length of the sliding fibres in the beam was carried out.