Background: Since three decade ago, the application of the concept of finite element analysis (EEA) have received a keen interest among dental investigators. In practice the FEA provides detailed stress information regarding to a non-homogenious body such as craniofocal skeletal growth, tooth post ceramo-metal crowns and etc. The aim of this study was the determination of the influence of stress distribution at the cement interface of metal ceramic restoration-dentin. Materials and Methods: An idealized metal-ceramic crown model was developed. The model was divided into very small segments. Various loading conditions was applied to the model. A super sap software was used for analyzing the stress distribution. Results & Conclusion: The results of this study suggest that the higher shear stress was developed in the cervical region by two dimensional methods.

Purpose: Application of heavy forces to maxillary dentition during treatment with headgear, induces high concentration of stresses in periodontal tissue. Quantification of this stress is of great concern in orthodontics. This study was designed to investigate the quantity and quality of stress response in the PDL of maxillary first molar which was subjected to high pull headgear traction using Finite Element method.Methods and Material: In an experimental study, a three-dimensional finite element model of maxillary dentition, consisting of 17096 elements and 23013 nodes, was developed based on a young human skull. The forces were applied to the maxillary first molar in the stabilized Arch by means of a rectangular full size arch wire in (022) slot bracket. Mechanical properties of this model were based on previous studies. A 350 gram force was used for high pull headgear to affect the dentition (+30 degree) and stress distribution was investigated in buccal, palatal, mesial and distal side and in cervical, middle, apical sections of the PDL. The quantity of stresses were expressed as principal stresses (1,2,3), while the negative and positive signs indicated compressive and tensile stresses.Results: The buccal surface of PDL of mesiobuccal root and the buccal, palatal and distal surface in cervical region of PDL of distobuccal root and the distal surface of the PDL of palatal root had received a great deal of stresses, in addition, the over all stress distribution in roots of molar had intrusive nature.Conclusion: The extension of high stress concentration areas observed after using high pull headgear is limited to some root surfaces specially the distobuccal root.

The proposed method by Shiono and Knight (SKM) is able to predict the lateral depth-averaged velocity and shear stress distribution in open channels. The SKM is needed to be calibrated. The calibration parameters are friction factor f, lateral eddy viscosity l, and secondary flow G. In practical problems, the assumption of l=0.07 from among these is considered as a standard value for the eddey viscosity. Thus, the accuracy of the depthavergad and the shear stress distributions using SKM will be subject to the determination of ¦ and G. In the present paper, we present the secondary flow cell pattern (G) and friction factor distribution (¦) in a straight prismatic triangular channel with a uniform roughness. The trial and error approach is used to define the best pattern of friction factor to produce the most appropriate results. The results of predicted depth-averaged velocity as well as shear stress distributions obtained from SKM as compared to measured values indicate that SKM can accurately predict the velocity and shear stress distributions if the two coefficients of ¦ and G are chosen based on accurate patterns.

Hydraulic characteristics of wide channels differ from narrow channels due to the higher ratios of width to depth, b/h. In this research, using a physical model of a rigid boundary channel having 60m length, 1. 5m width and a bed slope of 0. 001 with b/h ratio of 12 to 56, hydraulic characteristics of wide channels including: stagedischarge relationship, velocity and shear stress distributions were experimentally considered. The results indicate that the maximum velocity in the wide channel was occurred nearby the water surface. Investigation of the vertical velocity distribution reveals that the flow velocity follows the well-known logarithm distribution law. The also results show that the shear stress was maximized in the centerline of channel section, and the dimensionless shear stress was increased by increasing the ratio of b/h. In ratios of b/h less than 30, the dimensionless bed shear stress value is less than 0. 9 and in case of b/h greater than 30, it is greater than 0. 9. A comparison of the results for wide channels and channels with an optimal width of b/h=2, reveals that the relationship between b/h and shear stress in narrow channels is linear, while in wide channels a power relationship is governing. Moreover, in wide channel sections, the percentage of shear force on the walls (%SFW), due to the low depth of flow which is less than 10 and negligible, so that to contribute the walls to the shear stress can be ignored for design purposes.

This study makes use of the Tsallis entropy to predict the shear stress distribution in rectangular channels. Given a definition of the Tsallis entropy, it is maximized using the probability density function, which then is used to attain a novel shear stress equation. This is then employed for calculating the shear stress distribution in rectangular channels in different aspect ratios and finally, for viability, these calculations are compared with some relevant experimental results. This derived shear stress equation is capable of describing the variation of shear stress in both the wall and the bed of channels. The comparison shows that this equation appears to be efficient for predicting the shear stress distribution in rectangular open channels. The shear force percentage and mean values of the bed and wall shear stress calculated by the proposed equation have good agreement with the experiments.

Reliable prediction of boundary shear force distributions in open channel flow is crucial in many critical engineering problems such as channel design, calculation of energy losses and sedimentation. During floods, part of the discharge of a river is carried by the simple main channel and the rest is carried by the floodplains located to its sides. For such compound channels, the flow structure becomes complicated due to the transfer of momentum between the deep main channel and the adjoining floodplains that magnificently affects the shear stress distribution in floodplain and main channel sub sections. In the present study experiments were conducted in a compound rectangular section with different discharges and 3 different aspect ratios. The results showed that in each aspect ratio, shear stress increases by increasing the water level. It is also shown that by increasing the aspect ratio, shear stress is decreased significantly.

Compound channels are consisting of two hydraulic sections namely main channel and floodplain. In meandering rivers, with the passage of time and lateral movement of the meanders, the external bending progression and the sinusoidal or curvature is increased. The curvature of meandering sections can be defined by a dimensionless parameter as the sinusoidal number which is the ratio of meandering length of main channel to the floodplain length. In this research work, the hydraulic characteristics of flow including the velocity magnitude, boundary shear stress, turbulence intensity and turbulence energy of the main channel along the meandering compound channel have been investigated numerically, regarding changes in the sinusoidal ratio for six types of channels with different sinusoidal ratios. In order to investigate the effect of sinusoidal ratio in meandering compound channels on the hydraulic characteristics of the flow, the FLOW3D software is applied. Numerical simulation results show that by increasing the channel sinusoidal number from 1 to 1. 641, the velocity and bed shear stress decrease and the turbulence intensity and energy increases. So that the maximum value of the above parameters occurs in the inner arc.