Capillary effect on the sloshing of a fluid in a rectangular tank submitted to sinusoidal vertical dynamical excitation

Surface tension effects on fluid sloshing in a tank subjected to external excitation has been less studied. This work aims at understanding this phenomenon in order to derive practical solutions to problems faced in several engineering. A tank containing a fluid with a free surface is submitted to gravity and capillary forces and subject to external dynamic excitation. Introduction of vertical sinusoidal dynamical excitation leads to a problem of paramtric oscillations governed by the Mathieu equation. Analysis of the Mathieu equation shows the existence of stable and unstable regions in the stability diagram. Some results induced by harmonic excitations on the fluid sloshing are presented. When the external dynamical excitation amplitude ~ is small, periodic solutions appear in stable regions and when e increases, the fluid behavior is not perfectly periodic and the amplitudes are not regular. Nonlinear effects make the behavior of the fluid complicated and render it almost unpredictable. In stable regions, the solution remains bounded at any time. When changing the perturbation parameter 6, the phase difference increases and also with the increase of the surface tension.     

Comparison between rectangular and trapezoidal bonded composite repairs in aircraft structures: A numerical analysis

The optimization of the patch shape of bonded composite repair in aircraft structures is a good way to improve the repair performance. In this study, the three-dimensional finite element method is used to compare the repair performance of patches with rectangular and trapezoidal shapes in aircraft structures. The comparison is done by analysing the stress intensity factor (SIF) at the tip of repaired crack and the distribution of the adhesive stresses for the two patch shapes. The obtained results show that, when the crack length is ranged from 5 to 20 mm, the trapezoidal shape presents lower stress intensity factor at the crack tip, which is beneficial for the fatigue life and lower adhesives stresses, which is beneficial for the repair durability. These advantages disappear when the crack length reaches the value of 40 mm. It is also shown that the use of the trapezoidal shape reduce the mass of the patch, which can reduce the repair cost.     

Impact of interfacial stresses distribution of structures reinforced by composites FRP: new model of the laminate layers

This work allows us to determine the interfacial stresses concentrations which are the cause of the debonding phenomenon in the structures strengthened by composites fiber-reinforced plastic (FRP). This method permits to replace the classic techniques based on welding and bolting the elements of the structure that give stresses concentrations to the level of the assembly zone. The technique of reinforcement by patches in composites gives more resistance and rigidity, but it can give stresses concentrations to the edges of the reinforcement zone which can exceed the ultimate loads of the structure and cause failures. In this work, an original interfacial stress theory is developed between the structure and the composite (FRP) and has finalized, taking into account, the mechanical and thermal loads coupled with the shear lag effects. This original method carried out the terms neglected by the previous studies, such as shear lag effect of structure and composites, and thermal load coupled with the model of mechanical and fiber orientation effect. The geometrical and physical parameters taken into account play an important role in the stresses values concentration and thus the phenomenon of delamination     

A simplified approach to modeling the interaction between grounding grid and lightning stroke

In this work, a new approach for the modeling of the interaction between grounding grid and lightning stroke is described. We treat the case of direct and indirect effects of lightning strike. In the case of direct impact, we inject in point of grounding system a current with bi-exponential wave shape and we calculate the distribution of potentials and currents on the grid and the electromagnetic field it will emit. For the second case, we treat a problem of electromagnetic coupling, which is to calculate the induced currents that developed on the grounding grid when this later is illuminated by a lightning channel located in its vicinity. The presented model is validated by comparing the obtained results to the results arising from the full wave (antenna) model available in literature and to the results obtained by using NEC4 software. The principal advantage of the presented approach is the simplicity of the implementation providing a direct determination of the both current and potential distribution along the grounding grid and the related electromagnetic field in an arbitrary point in the air and/or soil, as well.     

Le glissement de terrain d’Ain El Hammam (Algerie): causes et evolution

Some natural slopes are or may become unstable. Instabilities are one of the most difficult problems of engineering geology. The difficulty arises because the estimate of the stability of a site depends on several factors that often interact simultaneously. To better analyze the landslide of Ain El Hammam, these factors were set into two broad categories (passive and active factors). The factors include the liabilities related to geological causes, to the geomorphology and to the hydrology of the site. The structure of the slope is conducive to landslides; the encountered formations are often altered and cracked. They are characterized by a dip and schistosity endorsements favoring the displacement of the layers and also by an alternation of shallow soils and other resistant layers as we go deeper. Tests results show that the geological formations encountered in this area have favorable characteristics to landslides. The mineralogical study shows that the shale rock has reached an advanced weathering and very low content of quartz makes little resistance. The morphological nature of this slope also affects considerably the instability, the steep slope of the site, the nature of the geological formations encountered and the high density of cracks make it vulnerable with regard to this phenomenon. The hydrology has an important role in the erosion and weathering of unstable slopes and on the initiation and activity of the movement. The active factors include climate measures, anthropogenic factors and the effect of seismicity in this region. An important link between the activity of movement and changes in climatic conditions has been observed for this instability. Two basic types of actions have been identified: the action of heavy rainfall and the action of snow cover. Human activity has also contributed to the emergence and evolution of this instability. We have noticed essentially the following effects: the effect of the significant overhead of the head of the unstable slope, the effect of the removal of drainage systems and the role of sewerage not connected flowing directly into the unstable slope. The seismicity of this region also plays an important role and its effects must be evaluated and taken care of in the study of this landslide. The landslide affects a formation of Shale (shale satin) frequently altered and cracked. The structure of this movement and deformation mechanisms induced are very complex. It is a multitude of overlapping and nested ruptures forming a global instability of the slope. Six sliding surfaces were determined on a longitudinal slope (profile EE); some are superficial and others are deep. The observed maximum depth of rupture is greater than 75?m. However, the presence of other sliding surfaces and more complex mechanisms which could not be determined at this stage of the study is not excluded. This shift is characterized by a very active movement extending over a large area and phases of calm and activation (accelerations of movement). The movement is changing both laterally and in depth. Four stages of evolution have been observed for this ground movement (period 1969–2005, the period of 2005–2008, the period from 2008 to April 2009 and the period from May 2009 to March 2011). However, its movement often gives rise to new shallow sliding surfaces (superficial to less deeper) in the basin. Predicting the future behavior of the slope is difficult, the mechanisms are generally poorly known and difficult to understand and model. Knowledge of factors leading to instability is essential in predicting disorders.     

Effect of humidity absorption by the adhesive on the performances of bonded composite repairs in aircraft structures

In this study, an experimental work was done to analyse the effect of the humidity absorption on the mechanical properties of the adhesive Adekit A140 epoxy. The measured properties were introduced in a finite element model in order to analyse the effects of the humidity absorption on the performances of bonded composites repair in aircraft structures by computing the J integral around the crack tip and the distribution of the adhesive shear stresses. The obtained results show that the adhesive losses its rigidity by the humidity absorption which reduce the repair efficiency but increases the repair durability.     

Numerical analysis of the notch effect and the behaviour of notch crack in adhesively bonded composite laminates

In this study the finite element method is used to analyse the notch effect and the behaviour of notch cracks in adhesively composite laminate under tension by computing respectively the stress concentration factor at the notch tip which characterize the notch strength and the stress intensity factor at the crack tip which characterize the resistance to the crack propagation. The effects of the adhesive properties and fiber orientation on the variation of both stress concentration and stress intensity factors are highlighted. The obtained results show that the notch strength is reduced in the layer of the laminate of which the fiber orientation is in the applied load direction; the resistance to the crack propagation is also reduced in this type of layer. The stress intensity factor at the tip of notch crack exhibits an asymptotic behaviour as the crack length increases.     

Numerical analysis of the beneficial effect of the double symmetric patch repair compared to single one in aircraft structures

This paper concerns a numerical study by the finite element method of the cracked structure repaired by single and double bonded composite patches. The stress intensity factor is used as fracture criteria. The obtained results showed the advantage of the double patch compared to single on the reduction of the stress intensity factor at the crack tip. The effects of the properties of the plate and the patch and the adhesive on the beneficial effect of the double patch are highlighted. The adhesive properties must be optimised in order to increase the advantage of the double patch and to avoid the adhesive failure. The patch properties have a significant effect on the beneficial effects of the double symmetric patch.