scholarly journals Self-encapsulation, or the ‘dripping’ of an elastic rod

Author(s):  
F. Bosi ◽  
D. Misseroni ◽  
F. Dal Corso ◽  
D. Bigoni

A rod covering a fixed span is loaded at the middle with a transverse force, such that with increasing load a progressive deflection occurs. After a certain initial deflection, a phenomenon is observed where two points of the rod come in contact with each other. This is defined as the ‘dripping point’ and is when ‘self-encapsulation’ of the elastic rod occurs. Dripping seems at a first glance to be impossible and definitely cannot occur in the presence of ‘ordinary’ constraints (such as simple supports or clamps) at the ends of the span. However, the elastica governs oscillating pendulums, buckling rods and pendant drops, so that a possibility for self-encapsulation might be imagined. This phenomenon is indeed demonstrated (both theoretically and experimentally) to occur when at least one of the constraints at the ends of the rod is a sliding sleeve. This mechanical device generates a configurational force, causing the dripping of the rod, in a fully elastic set-up.

2011 ◽  
Vol 343-344 ◽  
pp. 661-667 ◽  
Author(s):  
Yun Xue ◽  
De Wei Weng ◽  
Gang Ming Gong

Mechanical model of nucleoside and its equilibrium equations are set up, and the mechanical properties on the equilibrium position are analyzed. In the case constraint force and electrostatic attraction between cylinder OH and elastic rod are balanced, the analytic expression of nutation angle of the section and its conditions of existence are given. It is show that the cylinder OH can maintain equilibrium at any range of the precession angle. In the other case when unbanced, there is phenomenon of separation of elastic rod from cylinder OH in the spiral wound 2 circles, and numerical solution of the precession angle at separation points are calculated. Analysis of equilibrium of cylinder H1 illustrates that the generatrix of cylinder H1 and OH are not parallel, and the angle between them is obtained


Author(s):  
I. N. Sneddon

SynopsisIf the temperature in an elastic rod is not uniform and if it varies with time, dynamic thermal stresses are set up in the rod. This paper is concerned with the calculation of the distribution of temperature and stress in an elastic rod when its ends are subjected to mechanical or thermal disturbances. Simple waves in an infinite rod are first discussed and then boundary value problems for semi-infinite rods and rods of finite length. The paper concludes with an account of an approximate method of solving the equations of thermoelasticity.


1996 ◽  
Vol 15 (2) ◽  
pp. 89-98 ◽  
Author(s):  
A.S. Bansal

Receptance methods have been used to set up general equations that govern the vibrational response of a finite array of N mono-coupled elements terminating at general boundaries. The equations have been modified to introduce ideal and the frequency dependent boundary conditions offered by semi-infinite periodic arrays attached at its ends. The general theory has been adapted to determine the natural frequencies of some finite 5-span beams on simple supports with their ends having various combinations of ideal and frequency dependent end conditions. Lowest group of natural frequencies of the finite beams having different disorders and different combinations of ideal, elastic and dissipative boundaries have been computed and discussed. The conditions under which the undamped combined systems can behave like spring-mass systems and spring-mass-damper systems have also been identified and explained.


2016 ◽  
Vol 21 (2) ◽  
Author(s):  
Ahmad Solgi ◽  
Ramin Naghdi ◽  
Mehrdad Nikooy

An extensive field trial was set up to examine the influence of traffic intensity (5, 10, and 15 skidding cycles) (i.e. pass back and forth on the skid trail) and skid trail slope (0-10, 10-20, and > 20)% on soil compaction, forest floor removal, and rut depth after logging. The results showed that dry bulk density and rut depth increased with the increase of traffic frequency and slope, but floor coverage decreased. Within each traffic treatment soil compaction raised with the increase of skid trail slope, so that significant differences in dry bulk density were observed between slopes lower than 20% and those greater than 20%. Bulk density has become quite close to the critical value after 15 cycles. We observed soil rutting on the treatments started with 10 cycles. Soil disturbance increased significantly on slopes with less than 20% inclination with a dry bulk density of 1.157 g cm-3 after 5 cycles compared to 0.923 g cm-3 on slopes lower than 10%. In addition the litter mass on the treatments with 10 cycles and slopes greater than 20% (386.586 kg ha-1) was significantly lower (p < 0.05) than treatments with 15 cycles and slopes lower than 10% (545.382 kg ha-1). Data suggest that disturbance increased earlier in the steep treatments than in less sloping conditions. The dramatic increase of soil disturbance on treatments with slopes greater than 20% may be associated with increasing load on the rear axle combined with slipping on steep slope trail.Efecto del arrastre en la compactación y remoción de suelo y en la formación de surcosSe realizó un extenso estudio de campo para examinar la influencia de la intensidad de tráfico (5, 10 y 15 ciclos de arrastre) (es decir, pasar de ida y vuelta en la pista de arrastre) y de la pendiente del terreno de arrastre (0-10, 10-20 y más de 20)% en la compactación del suelo, remoción suelo del bosque y la profundidad de la huella después de la tala. Los resultados mostraron que la densidad de masa seca y la profundidad de las raíces se incrementan conforme lo hacen la frecuencia del tráfico y la pendiente y que la cobertura de suelo disminuyó. Dentro de cada tratamiento de tráfico, la compactación del suelo aumentó con el incremento de la pendiente del terreno, se observaron diferencias significativas en la densidad aparente seca entre la pendiente menor a 20% y la mayor a 20%. La densidad aparente se acerca a su valor crítico después de 15 ciclos. Se observó la formación de surcos en el suelo en los tratamientos de 10 ciclos. La perturbación del suelo aumentó significativamente en las pendientes con más de 20% de inclinación, con una densidad seca aparente de 1,157 g cm-3 después de 5 ciclos en comparación con 0,923 g cm-3 en pendientes menores a 10%. Se observó que la masa de desechos vegetales (hojarasca) en el suelo en los tratamientos con 10 ciclos y laderas de más de 20% (386.586 kg ha-1) fue significativamente más baja (p <0,05) que en los tratamientos con 15 ciclos y laderas de menos de 10% (545,382 kg ha-1). Los datos sugieren que la perturbación se incrementa primero en los terrenos empinados que en aquellos con menor inclinación. El considerable aumento de la perturbación del suelo en los tratamientos con pendientes de más 20% puede estar asociado con el aumento de la carga en el eje trasero combinado con el deslizamiento sobre el terreno empinado.


1939 ◽  
Vol 16 (1) ◽  
pp. 18-33 ◽  
Author(s):  
L. E. S. EASTHAM

1. The six pairs of gills in Ephemera danica causing currents in the water are bilamellate and feather-like. 2. The gills move in metachronal rhythm from before backwards, and set up currents which are symmetrical with the body axis. Members of pairs of gills beat synchronously and in phase with each other. The difference of phase between two adjacent gills of the same side is about one-eighth of a complete oscillation. 3. For a single gill there is little or no difference in the angle presented by the gill to its own path of motion, in the two halves of an oscillation. This factor (angle of incidence) is not of great importance in directing water backwards. Forces of importance in moving water in the direction taken are (i) the resultant of axial and transverse force components for single gills, (ii) the pressure effected on the water over the animal's back by the two members of a pair of gills falling, (iii) the movement backwards of alternating pressure regions over the back, (iv) the undulations of the second screw-like gills which feed the main current from in front and from the sides. 4. The fringing filaments of adjacent gills overlap each other from before backwards (as seen from the middle line of the body), and thus each row of gills forms a "membrane" composed of separate gill units. The latter appear never to lose contact with each other during movement, and since no sideways flow is observed between the gills it is assumed that the overlapping filaments between the gills form a membrane impermeable to flow. 5. The adaptation of Ephemera to its sandy environment is shortly discussed.


Author(s):  
Dandan Yang ◽  
Jianfei Huang ◽  
Weijia Zhao

Recently the Kirchhoff rod and the methods of dynamical analogue have been widely used in modeling DNA. The features of a DNA such as its super slender and super large deformation raise new challenges in modeling and numerical simulations of a Kirchhoff rod. In this paper, Euler parameters are introduced to set up the quasi-Hamilton system of an elastic rod, then a symplectic algorithm is applied in its numerical simulations. Finally, a simplified surface model of the rod is given based on the hypothesis of rigid cross-section.


2009 ◽  
Vol 413-414 ◽  
pp. 677-682 ◽  
Author(s):  
Qing Kai Han ◽  
Hai Tao Luo ◽  
Bang Chun Wen

The nonlinear dynamical analyses of a dual-rotor system of an aero-engine are investigated with considering local rub-impacts based on rigid-flexible multi-body simulations. The dual-rotor system is set up from a practical aero-engine prototype, which includes an inner shaft (lower-pressure shaft) and an outer shaft (higher-pressure shaft). The two shafts are in internal-external arrangement and connected by six different rolling bearings. Firstly, a rigid-flexible multi-body model of the dual-rotor system with local rub-impacts is established with MSC.Adams. Then, for the rub-impacts happening between the higher-pressure disk and the fixed elastic rod, the rub-impact forces are described as a nonlinear one with piecewise stiffness and a constant friction. At last, the transverse vibrations of the dual-rotor system are simulated. From the obtained frequency spectra and shaft center orbits of given shaft nodes, many of them are composed of multi-frequencies and demonstrate nonlinear motion patterns.


Author(s):  
T. G. Naymik

Three techniques were incorporated for drying clay-rich specimens: air-drying, freeze-drying and critical point drying. In air-drying, the specimens were set out for several days to dry or were placed in an oven (80°F) for several hours. The freeze-dried specimens were frozen by immersion in liquid nitrogen or in isopentane at near liquid nitrogen temperature and then were immediately placed in the freeze-dry vacuum chamber. The critical point specimens were molded in agar immediately after sampling. When the agar had set up the dehydration series, water-alcohol-amyl acetate-CO2 was carried out. The objectives were to compare the fabric plasmas (clays and precipitates), fabricskeletons (quartz grains) and the relationship between them for each drying technique. The three drying methods are not only applicable to the study of treated soils, but can be incorporated into all SEM clay soil studies.


Author(s):  
T. Gulik-Krzywicki ◽  
M.J. Costello

Freeze-etching electron microscopy is currently one of the best methods for studying molecular organization of biological materials. Its application, however, is still limited by our imprecise knowledge about the perturbations of the original organization which may occur during quenching and fracturing of the samples and during the replication of fractured surfaces. Although it is well known that the preservation of the molecular organization of biological materials is critically dependent on the rate of freezing of the samples, little information is presently available concerning the nature and the extent of freezing-rate dependent perturbations of the original organizations. In order to obtain this information, we have developed a method based on the comparison of x-ray diffraction patterns of samples before and after freezing, prior to fracturing and replication.Our experimental set-up is shown in Fig. 1. The sample to be quenched is placed on its holder which is then mounted on a small metal holder (O) fixed on a glass capillary (p), whose position is controlled by a micromanipulator.


Author(s):  
O.L. Krivanek ◽  
J. TaftØ

It is well known that a standing electron wavefield can be set up in a crystal such that its intensity peaks at the atomic sites or between the sites or in the case of more complex crystal, at one or another type of a site. The effect is usually referred to as channelling but this term is not entirely appropriate; by analogy with the more established particle channelling, electrons would have to be described as channelling either through the channels or through the channel walls, depending on the diffraction conditions.


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