Interaction of an internal gravity current with a submerged circular cylinder

The problem of hydrodynamic loads due to the interaction of a gravity current propagating over a bottom channel with a submerged circular cylinder is studied experimentally. It was shown that in the examined range of parameters, the hydrodynamic loads are simulated after Froude. The hydrodynamic loads are maximal if the cylinder lies on the bottom, and they decrease rapidly with increase in the distance from the cylinder to the channel bottom. The effects of mixing and entrainment on the nature of the hydrodynamic loads are considered.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 2, pp. 81–90, March–April, 2005.     

Kinetic Approach to Prediction of the Life of Aluminum Alloys under Various Thermal–Temporal Loading Conditions

Results of investigation of the life of D16 T, AK41 T1, and 1201 T1 aluminum alloys are generalized on the basis of the kinetic concept of failure. The life is studied under creep at constant loads and loads increasing with different rates and at different temperatures. The temperature is varied within the range of 473–77 K, and the duration of tests ranges from fractions of a second to ten thousand hours. Information on the effect of internalstress relaxation on the life of alloys is obtained. A method for predicting the life with allowance for relaxation processes in solids is verified experimentally.     

Supersonic Three‐Dimensional Flow Around Two Bodies

A supersonic threedimensional flow around two bodies located one behind the other is experimentally studied. The flow structure between the bodies is analyzed. Zones of the maximum force loads on the surface of the rear body are determined.     

Model of Self‐Organization of an Ensemble of Cracks Radiating Sound

A model of selforganization of cracks arising in a rock specimen (granite) compressed by a press is proposed. The model is based on the assumption of acoustic wave interaction between the cracks. To construct the model of selforganization of cracks, solutions of the Fokker–Planck equation are used. The experimentally observed spontaneous increase in the activity of acoustic emission, spatial and temporal clusterization, and formation of a fractal structure in rock specimens under constant and slowly varying loads are explained.     

Spherical particle sedimentation along an inclined plane at high Reynolds numbers

At high Reynolds numbers (10²Re _p <10⁵), the gravity-driven motion of a solid spherical particle along an inclined surface in a Newtonian liquid at rest was studied experimentally. The parameters which determine the particle drag coefficient and its relation with the hydrodynamic force component normal to the wall were obtained.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 105–112, July–August, 1996.     

Experimental Study of the Dynamic Effect of an Internal Solitary Wave on a Submerged Circular Cylinder

The hydrodynamic loads due to the interaction of a small-amplitude internal solitary wave with a submerged circular cylinder in a two-layer system of miscible fluids were studied experimentally. The dependence of the internal-wave transmission coefficient on the position of the center of the cylinder relative to the pycnocline and on the ratio of the cylinder diameter to the fluid-layer thickness was obtained. The effects of the pycnocline thickness and the depth of the center of the cylinder on the value of the hydrodynamic loads were studied. Visualization of the flow structure was performed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 36–44, November–December, 2005.     

Stability of oval cylindrical shells

Elastic buckling under aial compression of finite, oval cylindrical shells with clamped boundaries was investigated experimentally. The determination of the buckling strength was made on a series of oval shells made of Mylar A. The test results indicated that the discrepancy between theoretical and experimental initial buckling loads for the ovals is similar to that of the circular cylindrical shells. However, in contrast to the circular case, a collapse load significantly exceeding the initial buckling load is observed in the case of ovals with moderate-to-large eccentricity.     

Effect of drop size distribution on the flow behavior of oil-in-water emulsions

The effect of drop size distribution on the viscosity was experimentally examined for oil-in-water emulsions at volume fractions of = 0.5, 0.63 and 0.8. At = 0.5, the hydrodynamic forces during drop collisions govern the viscosity behavior. The viscosity versus shear rate curve is scaled on the root-mean-cube diameter which is related to the number of drops per unit volume. At = 0.8, the resistance to flow arises from the deformation and rearrangement of thin liquid films between drops. The viscosity at a given shear rate is inversely proportional to the volume-surface mean diameter which is related to the total interfacial area per unit volume. However, since the drops come into contact and the liquid film separating adjacent drops is generated without drop deformation at = 0.63, the viscosity curve is not scaled on the mean diameter. The flow behavior near the critical volume fraction strongly depends not only on the mean drop size, but also on the width of the distribution.     

Stress-intensity factors for a semi-infinite plane crack with a wavy front

The stress-intensity factors for a semi-infinite plane crack with a wavy front are determined when the crack faces are subjected to normal and shearing tractions. The results are derived using asymptotic methods and are valid to O(²) where =A/1; A is the amplitude and is the wavelength of the wavy front. The normal and shearing tractions are in the form of line loads parallel to the crack front.The results are then used to evaluate, in a qualitative manner, the growth characteristics of a semi-infinite plance crack with a wavy front under combined mode loading. This provides a possible explanation of crack front segmentation observed experimentally.     

Experimental study of separation-zone pressure pulsation

We examine extremely nonuniform separated water flow in the initial segment of a penstock of rectangular section resulting from the separated flow past a two-dimensional gate. The meansquare deviations p', one-dimensional frequency spectra S(), spatial correlations r(x), and distribution functions F(p) of the pressure pulsation are determined experimentally at points of the solid stationary boundary above the roll zone for significantly different absolute pressures in the stream. Changes in the structure of the hydrodynamic action on the boundary resulting from phase transformations in the fluid—the appearance of air and air-vapor inclusions—are noted. The measurement data are compared with the results of theoretical calculations.The author wishes to thank V. M. Lyatkher for his interest in this study and helpful advice.     

A Novel Analysis of the Electrical Transport Mechanisms in Porous Media

Effects of water saturation and wettability on the dielectric constant are investigated experimentally using four-electrode impedance measurements, and theoretically using models that account for the electrical double layer polarization. Complex impedance measurements, performed on Berea sandstone and on Ottawa-sand packs in the frequency range 10Hz to 1MHz, appear to indicate that the dielectric constant varies linearly with water saturations above 50%. The rate of change of dielectric constant with saturation is found to be a function of frequency. As the frequency increases this rate of change decreases. The decrease in the slope of the dielectric constant-water saturation profile with frequency is not intuitively obvious, but has been proven theoretically in this work. The dielectric constant of water-wet samples is found higher than that of the oil-wet samples at all water saturations. The difference is more pronounced at high water saturations near unity. The wettability changes have been simulated using a generalized Maxwell–Wagner model by varying the amount of ionic surface charge of rocks. In general oil-wetting agents react with the formation matrix by connecting their positively charged tails to the negatively charged silica surfaces, lowering the surface charge density. Simulations show that the effect of wettability changes on the dielectric constant is very significant. These conclusions are consistent with the experimental results presented in this study.     

Elasto‐plastic Hardening and Shakedown of Masonry Arch Joints

The behavior of joints made of sand–lime mortar, such as used in a wide variety of structures from ancient times through the early twentieth century, can be clearly distinguished from the behavior of joints made with hydraulic cement mortar. Experiments on confined mortar specimens have confirmed that the weaker and more ductile sand–lime mortar can be accurately modeled as a Drucker–Prager material with a compression cap and exponential hardening on the cap portion of the yield surface. Joints of sand–lime mortar subject to axial thrust and moment are found experimentally to yield under very small loads, and to follow a linear hardening rule beyond the yield point. This behavior can be replicated analytically using a Drucker–Prager constitutive law with exponential hardening. The yield surface and hardening function for an entire mortar joint are representable by Maier's theory of piecewise linear yield function and interacting yield planes. As a consequence, an arch jointed with sand–lime mortar is found to shake down under moving loads above the yield limit and below the collapse load. The shakedown behavior of a sand–lime mortar jointed masonry arch is confirmed experimentally.Sommario. II comportamento dei giunti realizzati con malta di calce, del tipo di quelli utilizzati in unampia varietà di strutture dall antichità sino allinizio di questo secolo, può essere chiaramente distinto dal comportamento dei giunti realizzati con malta idraulica. Esperimenti condotti su provini confinati di malta hanno infatti evidenziato che il comportamento della malta di calce, meno resistente e più duttile, può essere accuratamente modellato con un materiale di Drucker–Prager, adottando un troncamento della resistenza a compressione ed un incrudimento esponenziale della superficie di snervamento nella porzione troncata. Si è rilevato sperimentalmente che i giunti di malta di calce, soggetti a sforzo assiale e momento flettente, raggiungono lo snervamento sotto carichi molto modesti, e quindi seguono una legge di incrudimento lineare oltre il punto di snervamento. Questo comportamento può essere riprodotto analiticamente utilizzando la legge costitutiva di Drucker–Prager con incrudimento esponenziale. La superficie di snervamento e la funzione di incrudimento per un giunto di malta sono rappresentabili mediante la teoria di Maier delle funzioni di snervamento lineari a tratti e dei piani di snervamento interagenti. Di conseguenza, un arco con giunti di malta di calce perviene alladattamento plastico (shakedown) sotto carichi mobili superiori al limite di snervamento ed inferiori al carico di collasso. Tale raggiungimento della condizione di adattamento plastico di archi di muratura con giunti di malta di calce è confermato sperimentalmente.     

The finite deflection equations of anisotropic laminated shallow shells

In this paper, basing on ref. [1] we improved and extended that which is concerned with a view of investigating the finite deflection equations of anisotropic laminated shallow shells subjected to static loads, dynamic loads and thermal loads. We have considered the most general bending-stretching couplings and the shear deformations in the thickness direction, and derived the equilibrium equations, boundary conditions and initial conditions. The differential equations expressed in terms of generalized displacements u₀, ₀ and are obtained. From them, we could solve the problems of stress analysis, deformation, stability and vibration. For some commonly encountered cases, we derived the simplified equations and methods.     

Prediction of the Compressible Stage Slamming Force on Rigid and Elastic Systems Impacting on the Water Surface

In this paper some models focusing on hydrodynamic and elasticforces arising during the impact of rigid and elastic systems on thewater surface are investigated. In particular, the supersoniccompressible stage of the impact is considered by modelling the slammingphenomenon through the Skalk–Feit acoustic approximation. The dynamicequations of the dropping system are coupled to those of the fluid and anonlinear fluid-solid interaction problem is stated. Generalrelationships between the body's shape, slamming force and body motionare determined. These equations are applied to the wedge water entrycases, and a closed-form expression for the maximum hydrodynamic forceis found. Moreover the theoretical correlation between the hydrodynamicforce and the body geometry allows us to control the inverse problem andthe shape associated to a constant slamming force is determined.Due to some simplifications allowed in the supersonic compressibleimpact, the results of the hydrodynamic analysis hold in closed form.This permits us to focus on the basic result of the paper addressed to asystematic correlation between hydrodynamic and elastic maximum forcesin terms of some characteristic dimensionless quantities involved influid-solid interaction.In particular, critical conditionscorresponding to those hydorelastic parameters combinations areinvestigated, leading to severe elastic response of the impactingsystem.     

The stability of a finitely inflated cylindrical elastic membrane under axial compression

The stability under overall axial compression of a finitely inflated cylindrical membrane composed of highly elastic material is investigated. The critical loads for inflated tubes with closed ends and with either simply-supported or fixed ends are determined in terms of the material properties of the membrane. For long tubes the results are compared with the Euler formulae for the buckling load for struts in compression. An equivalent Young's modulus is derived, and it is shown that the critical loads can be obtained from the Euler formulae by using the dimensions of the inflated state and the equivalent Young's modulus.     

Dynamic Behavior of Rigid–Plastic Sector Plates

The paper studies the dynamic behavior of perfect rigid-plastic plates in the form of a sector with hinged or clamped sides under short-term intensive loads. Two dynamic deformation mechanisms are demonstrated. The dynamic equation is derived for each of the mechanisms. The realization conditions for the mechanisms are analyzed. Analytical expressions are derived for the ultimate (high) loads and the maximum residual deflection. Numerical examples are given     

Attributes of a derived differential/difference energy equation within the platform of the Lévêque problem

The main idea of the Lévêque approximation was to provide a simple asymptotic solution for the development of the thermal boundary layer in a laminar tube flow with fully established velocity and uniform inlet temperature. Inspired in the flat plate passage idealization, Lévêque assumed that the hydrodynamic boundary layer was confined to a thin annular region near the wall so that the velocity varied linearly with the distance y = R - r measured from the wall in an equivalent parallel-plate passage. In contrast, this paper addresses the Lévêque problem adhering to the original energy conservation equation in cylindrical coordinates continually, but without making any geometric and/or hydrodynamic assumptions a priori. The semi-analytic solution procedure proposed here combines the Transversal Method Of Lines (TMOL) with the Fröbenius method, a particular case of the power series method.     

Motion of an ideal fluid of constant density in the presence of sinks

The problem under consideration is the unsteady motion of an ideal fluid with constant density in an unbounded volume when the velocity divergence is nonzero and is specified by the sink density a which depends on the coordinates r and the time t. It is well known that the introduction of such idealized hydrodynamic objects as a point vortex, a source, or a sink and the related studies of fluid flows are useful in solving a number of specific hydrodynamic problems [1, 2]. There have been many studies of point vortices, and some of the earliest are reviewed in [3], whereas the motion of free point sinks or sources has not been studied. The reason for this situation is that it is hard to find the appropriate hydrodynamic counterparts. The aim of the present paper is to study the basic laws governing the motion of a system of sinks and sources, both point and distributed, and then apply the results obtained to a simulation of thermal convection in a plane horizontal fluid layer consisting, for example, of periodic convective cells. Special attention is given to the asymptotic behavior of as t. Conservation laws for a system of N point sinks are derived and discussed. The qualitative behavior of the system for large t is investigated. Under the assumption of a frozen sink density in the velocity field of the fluid, an evolution equation for is obtained for an arbitrary initial distribution of the velocity divergence. In the case of a finite integrated intensity of the sink density in an unbounded volume, an exact solution of the evolution equation is given for a cylindrically symmetric initial distribution. The asymptotic behavior of this solution as t is studied in three qualitatively different cases. Finally, a steady-state solution of the evolution equation is obtained.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 21–27, July–August, 1976.The author thanks A. A. Zaitsev for his interest in the work, valuable advice, and discussion of the results.