Aims The use of intrauterine devices (IUDs) has been one of the most effective, the safest and cost-effective methods for preventing pregnancy, for a long time. However, some complications have been reported for IUDs. The complications may be reduced by using a specific technique for placement of IUD. The objective of this study was to introduce the Rotating withdrawal technique for the first time, which was investigated to reduce the complications of IUD insertion. Materials & Methods This historical cohort study was conducted on 1199 females who referred to Sarem Medical Center for IUD insertion from 1984 to 1995. After primary examinations, IUD was inserted by Rotating withdrawal technique. The subjects were followed up for 2 years. Findings Displacement was observed just in 20 cases (1. 67%). All of them were seen in the first month after placement. For these cases, IUD insertion was done again. After the second replacement, displacement was observed in 4 cases (0. 035%) after one month. Therefore, it was recommended to them to use another preventive method. There was no pregnancy or displacement in the other cases during 2 years. Conclusion The Rotating withdrawal technique can minimize the pregnancy rate when IUD is used. In addition to the type and quality of IUD, insertion method of IUD can increase its effectiveness.

As Rotating-sleeve Flow Distribution system (RFDS) running, the cavitation of the hydraulic pump may lead to the decreased volume efficiency, increment of vibration and noise, then affecting the operation of system. To deeply analyze the cavitation characteristics of RFDS, the Singhal cavitation model of RFDS was established, meanwhile corresponding experiments were carried out. Cavitation characteristics of RFDS were investigated under various revolving speed, inlet pressure and CAM groove profile. The results demonstrate that the variation trend of experimental volumetric efficiency is the same as that of simulation results. The maximum error is 2% and 3. 2% at different Rotating speeds and different inlet pressures respectively. Maximum gas volume fraction and cavitation time ratio increase monotonically as the Rotating speed increases, and volumetric efficiency increases first and then decreases with the increase of Rotating speed. Volumetric efficiency reaches up to 92. 13% under the Rotating speed of 500r/min. The increased inlet pressure can slow down the cavitation of RFDS and improve volumetric efficiency. Linear profile exhibits the best cavitation characteristic under both different Rotating speed and inlet pressure.

The main objective of this study is to perform the passive balancing of a Rotating mechanical system having multi-discs. Reducing the bearing vibrations is considered an optimization problem, and the Genetic Algorithm (GA) approach is used for solving it under the appropriate constraints. Therefore, bearing amplitudes are formulated as an objective function, and the eccentricity directions of 2nd, 3rd, ..., nth discs are defined as design variables relative to the first one. The conditions making the forces at the bearings minimum are taken as the nonlinear constraints in the optimization process. On the other hand, a Rotating mechanical system having three unbalanced discs is evaluated as a numerical example to show the effectiveness of the proposed approach. Commercial software, ADAMS, is also used for simulating the system and testing the accuracy of the obtained values for the design variables. Theoretical and simulation results show that the proposed approach gives a certain decrease in bearing amplitudes and forces.

Production and application of polymeric pipes are nowadays increased together with the progress in polymer science and technology. The conventional production of plastic pipes, i.e. using extrusion with plain die, is not technically evaluated due to the axial orientation of long polymeric chains and the existence of spiders which cause weld line (s), so the produced pipes have no significant hoop strength. To diminish the effect of weld line and to produce strong pipes in the hoop direction, the Rotating die system can be used. In this work, the variation of mechanical properties of unreinforced and reinforced pipes was investigated as a function of die core rotation speed. The results show the hoop strength of HDPE, PP and glass reinforced samples (20% by weight) is increased 20%, 25% and 34%, respectively at 20 rpm rotation speed of inner member. Also, the results of hydrostatic tests indicate that the pipes produced with the Rotating die system exhibit higher load-bearing capacity and good lifetime. In this case, 13% of extrudate increment at 30 rpm of inner member was observed. Also, isotropic properties for pipes produced with HDPE and pp were obtained at 10 rpm and 4 rpm of Rotating inner member, respectively. X-Ray shows that the crystallinity increased by 20% at 20 rpm rotation speed of mandrel. In this system not only the die swell does not occur, but also deswelling phenomenon is observed.

The quality of the pipes produced by extrusion, and the quality of extrudate depends heavily on the detailed design of the die. The production of the pipes using extruder equipped with plain die is not sufficiently correct, because of axial orientation of polymeric chains and the existence of weld line (s) due to spiders. The pipes produced in this manner have no significant strength in the hoop direction. One of the methods to produce weldless pipes with reasonable hoop strength is by Rotating die system. In this system, the inner or outer members or both rotate. The simple shape of Rotating die is assumed as an annulus with Rotating capability for each inner or outer members. The fluid flows through the nip of annulus under the pressure gradient across the pipe, i.e. DP/L, also is influenced (affected) with shear (drag) flow. In this work, to describe the non Newtonian behaviour of fluid, a power Law model was used. Non-Newtonian fluid flow and fiber orientation in the pile-like die were investigated using the finite element method. The results were compared with experimental data for short fiber orientation. This comparison clearly shows the validity of the resultant velocity vector as a controlling factor for fiber orientation.