Surface wrinkling of mucosa induced by volumetric growth: Theory, simulation and experiment

Mechanics of living tissues focusing on the relationships between growth, morphology and function is not only of theoretical interest but can also be useful for diagnosis of certain diseases. In this paper, we model the surface wrinkling morphology of mucosa, the moist tissue that commonly lines organs and cavities throughout the body, induced by either physiological or pathological volumetric growth. A theoretical framework of finite deformation is adopted to analyze the deformation of a cylindrical cavity covered by mucosal and submucosal layers. It is shown that compressive residual stresses induced by the confined growth of mucosa can destabilize the tissue into various surface wrinkling patterns. A linear stability analysis of the critical condition and characteristic buckling patterns indicates that the wrinkling mode is sensitive to the thicknesses of the mucosal and submucosal layers, as well as the properties of the tissues. The thinner the mucosal layer and the lower its elastic modulus, the shorter the buckling wavelength. A series of finite element simulations are performed to validate the theoretical predictions and to study local wrinkling or non-uniform patterns associated with inhomogeneous growth. Our postbuckling analysis shows that the surface pattern may evolve towards a period-doubling morphology due to continuous growth of mucosa or submucosa beyond the critical state. Finally, the theoretical predictions and numerical simulations are compared to experimental observations.     

Surface waves induced by external periodic pressure in a fluid with an uneven bottom

The behavior of waves generated by periodic pressure on the free surface is considered within the linear shallow-water theory. The fluid depth is a piecewise-constant function, which implies the presence of a finite-size bottom trench or elevation. For an arbitrary shape of bottom unevenness, the solution of the problem reduces to a system of integral boundary equations. Manifestation of wave-guiding properties of bottom unevenness is illustrated by an example of an extended rectangular elevation.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 70–77, January–February, 2005.     

Surface responses induced by point load or uniform traction moving steadily on an anisotropic half-plane

Surface responses induced by point load or uniform traction moving steadily with subsonic speed on an anisotropic half-plane boundary are investigated. It is found that the effects of the material constant on surface displacements are through matrices L^?1(v) and S(v)L^?1(v), while those on surface stress components are through matrices Ω(v) and Γ(v). Explicit expressions for the elements of these four matrices are expressed in terms of elastic stiffness for general anisotropic materials. The special cases of monoclinic materials with symmetry plane at x₁ = 0, x₂ = 0 and x₃ = 0, and the case for orthotropic materials are all deduced. Results for isotropic material may be recovered from present results. For monoclinic materials with a plane of symmetry at x₃ = 0, two of the elements of matrix Ω(v) are found to be independent of subsonic speed.     

Condition monitoring of bones using piezo-transducers

This paper explores the feasibility of employing piezoelectric ceramic (PZT) patches as bio-medical sensors for monitoring condition of bones, through experimental studies on human and rabbit bones. Conductance signatures of PZT patches bonded to bones are acquired using the electro-mechanical impedance (EMI) technique, while the bones are subjected to varying conditions such as and density changes, occurrence of cracks and fracturing. The changes in the signature correlate fairly well with the changes in the condition of the bones. Finally, the effect of healing process is experimentally simulated on rabbit bones, which showed that the conductance signature of the bones shifted back towards the original state after rejoining. The overall results of the study demonstrate good prospects of using PZT patches as bio-medical sensors.     

The compressive properties of long bones

In this study, compressive tests of the bones along the axial direction have been carried out on some wet specimens of the right femur and humerus, from which there have been obtained the elastic modulus of femur E=9.98×10⁹N/mM² and.’that of humerus E=11.37×10⁹N/m² Also comparisons and discussions have been made with reference to the available data reported abroad and at home.As indicated in this paper, bone tissues obviously possess viscoelastic properties. Their hysteresis loops are shown in Fig. 3 far and (b) and some mechanical phenomena observed during the test are illustrated elsewhere.     

Surface wave profile measurement by image analysis

A way of measuring the geometrical characteristics of progressive steep water surface waves is to use a visualization technique connected with image analysis processing. In the laboratory, visualization of wave profiles can be realized with quite simple procedures: a previous paper (Bonmarin and Ramamonjiarisoa 1985) has described a technique allowing such a visualization in a large water tank 40 m long, 3.2 m wide and about 1 m deep. This paper reported also on a manual process for analysing the wave pictures obtained. In the present paper, we describe an automated image analysis method which is complementary to the manual process mentioned above. It uses a video technique and allows analysis of a large number of pictures leading to statistical measurements.List of symbols L total wave length - H total wave height - crest elevation above still water level - trough depression below still water level - wave steepness = H/L - crest steepness = /L - F ₁ forward horizontal length from zero-upcross point (A) to wave crest - F ₂ backward horizontal length from wave crest to zero-downcross point (B) - crest front steepness = /F ₁ - crest rear steepness = /F ₂ - vertical asymmetry factor = F ₂/F ₁ (describing the wave's asymmetry with respect to a vertical axis through the wave crest) - horizontal asymmetry factor = /H (describing the wave's asymmetry with respect to a horizontal axis: SWL) - L ₃ vertical asymmetry factor = L ₂/L ₁ (describing the asymmetry between the crest and the trough) - E _p potential energy of the wave - e ₊ ratio between the potential energy located in the crest and the total potential energy of the wave     

Surface waves created by low-frequency magnetic fields

This paper analyses the effects of a low frequency A.C. magnetic field on the free surface of a liquid metal. The action of the vertical and uniform magnetic field is twofold. First it creates forced standing surface waves which generally exhibit symmetry related to that of the container; second it triggers non-symmetric free surface instabilities superimposed on the forced regime. A previous paper considered the case of a circular cylindrical tank where axisymmetric forced standing waves caused an electric current perturbation which then excited non-axisymmetric waves at a critical A.C. field intensity. Nonlinear interaction between the symmetric and non-symmetric modes was not taken into account. The present work treats the problem from a more general standpoint. Equilibrium perturbations are developed systematically to order $\text{N}{}^2$ (where $\text{N}$ is the magnetic interaction parameter) and at this level of approximation we also need to consider nonlinear mode interactions and electromagnetic damping. The theory applies to tanks of arbitrary shape and the $\text{O}\text{(}\text{N}\text{)}$ irrotational motion may be described by the torsion function for the particular pool cross-section. For circular and annular tanks we then derive a system of coupled Mathieu–Hill equations for the time-development of non-symmetric surface modes. Two main types of parametric resonance are predicted, namely the single or combination mode, and the particular type observed may depend on the geometry of the tank. Results of the stability analysis are confirmed by experimental work carried out in mercury pools.     

液体的爆炸抛撒特征

针对液体爆炸抛撒过程设计了实验装置,利用高速摄像仪进行记录。通过研究不同中心装药量和 填充液体的抛撒过程,发现在壳体破裂后,液体沿裂缝处向外飞散。药量较小时,液体分散成树枝状形态,然 后破碎成液滴;药量较大时,则形成液体环状区。对于不同粘度的液体,环状区分别由小液滴及已雾化、汽化 的液体,或大液滴、液体丝及液膜等组成,抛撒过程中其宽度越来越大,大液滴、液体丝及液膜等也逐渐破碎成 细小的液滴。     

Surface topography by multisource moiré patterns

Moiré patterns produced by interference of a series of periodically arranged linear light sources with a line-specimen grating of similar pitch are located at a plane parallel to the sources and the specimen grating and at some distance away from these planes. A transparent or reflecting specimen located at a distance from the specimen grating distorts the image of the multisource projected on the specimen grating due to its surface irregularities and forms a moiré pattern. This pattern yields the partial-slope contours of the topography of the specimen along a direction normal to the lines of the grating. Two such contour patterns taken at mutually perpendicular directions are sufficient to yield the complete topographic picture of the surface. The method was used for determining gradients of thickness variations in two-dimensional specimens due to lateral contraction. The technique is highly accurate in determining the values of thickness in such cases, since the integration of the slope of thickness variation along any traverse of the specimen is a steady and accurate process.     

Surface waviness removed by orthogonal machine cutting

A thermoelastoplastic analysis is made to study the surface waviness of orthogonal machine cutting. As a workpiece experiences heavy cutting, chips are formed incrementally in a steady fashion leaving a sinusoidal wavy surface as evidence of the varying thickness of the uncut chips. The finite difference method is applied to determine the temperature distribution in the chip and tool while a large deformation thermoelastoplastic finite element analysis is made to simulate the wave removing process whereby the wavy surface is modelled by saw-tooth shaped meshes. Determined are the chip geometry, residual stresses in the machined surface, temperature distributions in the chip and tool forces. The cutting forces are also calculated and they agree well with the test results.     

Determination of mechanical properties of the bones of the skull

This paper presents the initial results of a research project concerning the mechanism of head injury. In order to begin to define the mechanism, it is necessary to determine mechanical properties of the various skull bones, organize them into constitutive equations, and develop a structural model of the skull. The material presented is concerned primarily with the development of experimental procedures and the results which have been obtained. The specimen-testing program has been split into four parts: (1) The procural of 3/4-in. and 11/2-in.-diam plugs from human skulls at autopsy and the precise determination of specimen location and orientation; (2) the fabrication and strain gaging of small test specimens for basic tension, compression, tension-compression, and shear tests; (3) the conducting of tests; and (4) the correlation of experimental findings with microscopic structure by standard and nonstandard techniques of histology.     

高压泄爆导致的二次爆炸

基于计算结果和相关实验结果,通过理论分析,对高压泄爆导致的二次爆炸机理进行了系统的阐述。泄爆后,泄出的高压可燃气体在泄爆口附近形成可燃云团,由于欠膨胀,云团内存在稀疏波低压区和Mach干高压区。火焰射流泄出后,在一定条件下,可使Mach干高压区内的可燃云团爆炸式燃烧,压力迅速上升,以致产生二次爆炸。     

Crack growth induced by thermal-mechanical loading

Advanced aerospace structures are often subjected to combined thermal and mechanical loads. The fracture-mechanics behavior of these structures may be altered by the thermal state existing around the crack. Hence, design of critical structural elements requires the knowledge of stress-intensity factors under both thermal and mechanical loads. This paper describes the development of an experimental technique to verity the thermal-stress-intensity factor generated by a temperature gradient around the crack. Thin plate specimens of a model material (AISI-SAE 1095 steel) were used for the heart transfer and thermal-mechanical fracture tests. Rapid thermal loading was achieved using high-intensity focussed infrared spot heaters. These heaters were also used to generate controlled temperature rates for heat-transfer vertification tests. The experimental results indicate that thermal loads can generate stress-intensity factors large enough to induce crack growth. The proposed thermal-stress-intensity factors appear to have the same effect as the conventional mechanical-stress-intensity factors with respect to fracture.     

Fluid mixing induced by vibrating walls

Recent progress in micro-fluid dynamics has identified an increased demand for efficient mixing of highly viscous fluids in small channels and cavities. One way to do this is through the steady streaming generated by the vibration of solid boundaries. In this paper we investigate the mixing properties of such streaming flows in an infinite channel. A Newtonian fluid is confined within flexible walls with transverse motion in the form of standing waves of small amplitude. The velocity field is determined using a perturbation approach with the slope of the wall as a small parameter [Phys. Fluids 16 (2004) 1822]. Streaming occurs at second order with the formation of cellular flow patterns in the channel. The Lagrangian velocities were found to mimic the Eulerian except for flows at large channel half-widths and low frequencies. Most effective mixing is observed for flows at channel half-widths of similar, or lower, order than the vibratory wavelength and for sufficiently high frequencies.     

Internal waves induced by potential vortices

A linearized equation of the internal waves developing in an ideal stratified gas under the action of potential vortices concentrated in a vertical cylinder is obtained. The Cauchy problem for the internal wave equation with right side depending on the vortex intensity is solved by the integral transform method. In the case of a vortex filament the exact solution is found. Approximate formulas are obtained on the basis of the steady-phase method when the vorticity is exponentially stratified along the vertical. Expressions for the phase velocity and amplitude of the radial wave traveling away from the cylindrical vortex are found. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 118–123, January–February, 1998. The work was carried out with the support of the Russian Foundation for Fundamental Research (project No. 96-01-04599).     

Oscillations of a Cylinder Induced by Free Surface Flow

The results of experiments in which a cylinder freely located on a fixed shaft performs small harmonic oscillations driven by a subcritical free stream in an open channel are given. Examples of the strong feedback effect of the cylinder oscillations on the hydrodynamic wake and surface gravity waves are obtained.     

Surface characters of internal waves generated by Rankine ovoid

A linear theory on the internal waves generated in the stratified fluid with a pycnocline is presented in this paper. The internal wave fields such as the velocity fields in the stratified fluid and velocity gradient fields at the free surface are also investigated by means of the theoretical and numerical method. From the numerical results, it is shown that the internal wave generated by horizontally moving Rankine ovoid is a sort of trapped wave which propagates in a wave guide, and its waveform is a kind of Mach front-type internal wave in the pycnocline. Influence of the internal wave on the flow fields at the free surface is represented by the velocity gradient fields resulted from the internal waves generated by motion of the Rankine ovoid. At the same time, it is also shown that under the hypothesis of inviscid fluid, the synchronism between the surface velocity gradient fields at the free surface and the internal wave fields in the fluid is retained. This theory opens a possibility to study further the modulated spectrum of the Bragg waves at the free surface.The project supported by the National Natural Science Foundation of China (40576010). The English text was polished by Keren Wang.     

电镀法测表面应力

电镀法是在被测物表面镀铜或镀镍,在交变应力作用下,利用镀层内的组织变化来测定表面弹性应力应变的方法。本文简述电镀法原理,讨论其在实物交变应力及高温应力测量中的应用。