Papers by Keyword: Instability

Abstract: Consequent upon the inestimably magnificent rise in the necessity to considerably minimize the worrisome menace of global dependency on fossil fuels (such as coal, oil and gas), combat the pollution caused by green house gas emission emanating from same and lead a crusade against energy insecurity; the renewable energy sources (RES) became a panacea to the incessant imbalance between the ever- increasing demand and meagre supply of energy throughout the entire universe. Nevertheless, the output of RES is characterized with some unpleasant traits which include intermittency coupled with variability and unpredictability since it is largely constrained by annual weather pattern thereby inflicting a very severe injury on transient and steady state stability, reliability and profitability index. Thus, the certainty that this attributes do not only possess a gigantic capability to render synchronization futile but also initiate regular system collapse in the grid network cannot be over-emphasized, especially if the necessary precautionary measures are not taken into consideration. Therefore, this research work provides a compact review on the impacts of integration of large scale renewable energy sources into grid-connected power system. The methodology would involve an elucidative investigation of the associated benefits and obstacles after which possible mitigations to the challenges are accorded an extensive analysis while useful inferences are drawn meticulously leading to qualitative conclusions and useful recommendations from the results and findings so obtained.

Abstract: Total knee arthroplasty is a successful procedure for treating chronic degenerative knee pathologies, many patients are dissatisfied with the results of the standard design. Improper tibia rotation of the implant is suspected to contribute to post-operative pain, polyethylene wears, aseptic loosening, and instability. Many factors can influence the alteration of knee kinematics after surgery including differences in implant design. Using magnetic resonance imaging, tibia rotation in a normal knee has -15.0º and -2.5º in weight-bearing males neutral tibia rotation, and tibia rotation in postoperative patients has 2.1º and 9.5º using computer tomography. In this study, a knee joint implant was developed to facilitate a high range of motion. Tibia rotation was observed with the axes of knee motion joint implants varied from 0°, 2°, 3° to 5° and knee bend measurements at 30°, 60°, 90°, 120°, and 150° of knee flexion using the knee kinematic motion simulator and the results will be compared with the results from magnetic resonance imaging and computer tomography. Using statistical analysis resulted for 0° and 2° kinematics alignment, the p-value of the development product is 0.072 and 0.054 (p > 0.05), for 3° and 5° kinematics alignment, the p-value of the development product is 0.039 and 0.031 (p ˂ 0.05). Thus, the kinematics development product at 0° and 2° kinematics alignment are similar to a normal human knee joint. Evaluation of knee kinematics implant using a knee motion simulator is expected to become a standard procedure before performing total knee arthroplasty surgery. This similarity in kinematics knee implant with a normal knee is to be expected to reduce postoperative pain, polyethylene wears, aseptic loosening, and instability during deep knee flexion and minimize the risk of implant failure.

Abstract: The development of road and highway networks sometimes involves passing through compressible soils of poor quality. Given their mechanical properties as foundation soils, these soils are characterized by low short-term shear strength, expressed by undrained cohesion, which increases during soil consolidation, and are also characterized by significant compressibility, resulting in large-scale settlements when a load is applied to them. Nowadays, there are reinforcement methods that make it possible to execute these structures while limiting the risks of instability. This study consists of the numerical analysis of a light-weight embankment of a highway section built on soft soils. Two reinforcement methods are investigated to support the embankment layers and reduce settlement. Interest is given to the behavior of the soils in place before and after the installation of the adopted reinforcement. The analysis is carried out in such a way as to show the importance of the complete consolidation of the soils in place in the long term, which makes it possible to take into account the dissipation of the pore pressures.

Abstract: The elastic constants of tungsten-rhenium alloy single crystals were calculated by simulation atomic method using embedded method atom of interatomic potential. The found results show that elastic constants are proportional to the rhenium concentration up to 25 at% Re at room temperature. By following, we observed the elastic constant C₄₄ dependency of temperature and decreased of elastic constant C’=1/2(C₁₁-C₁₂) when the Re atom addition increases. We have found that a growing instability of the bcc crystal structure. Our parameter calculation model is in good agreement with experimental data.

Abstract: Acute dislocation of the patella is a very common injury of the knee. In more than 90% of the cases the medial patellofemoral ligament (MPFL) is injured. Reconstruction of the MPFL has become a popular soft tissue procedure, which reduces hospitalization and the rehabilitation period. Bioabsorbable materials, in form of screws and anchors are ideal for soft fixation to bones in orthopedics. We would like to present our experience and short-term results after MPFL reconstruction with semitendinous autograft and bioabsorbable fixation devices. 10 patients were involved in this study with PF joint instability, who underwent to MPFL reconstruction. In order to evaluate the functional outcome of the procedure we applied the Tegner Lysholm scoring system before and after 3 Months of surgery. MPFL reconstruction significantly improved the functionality of the PF joint. Gender distribution of the studied group was: 7 female with an average age of 25 5,03 SD and 3 male patients with an average age of 29 1 SD. The key for the success in MPFL reconstruction is the positioning of the femoral tunnel, followed by an isometric tensioning of the graft. Bioabsorbable materials reduce inflammatory, and foreign body response facilitating biointegration of the autograft.

Abstract: Any power system network is subjected to disturbances at any time and place. It is considered as one of the most stochastic system ever seen by the human beings. To enhance the power system reliability, System Protection Scheme (SPS) is an effective tool for utilizing the power grid during rare contingencies. This method is often employed as secondary protection schemes. SPS is also termed as Special Protection Scheme. SPS is referred with different names by different users such as IEEE as System Integrity Protection Scheme (SIPS), Bonneville Power Administration (BPA) as Remedial Action Scheme (RAS) and WECC and others as SPS. In India, only in late 90s, the concept of SPS was introduced to solve the above problem. In Indian power grid different SPS has been designed and implemented successfully. This paper presents a complete knowledge, need , general structure, characteristics and a brief description of the major SPS employed in various Indian Power grids. Post - commissioning performance of these SPS has also been analyzed briefly. Finally, highlights of major issues involved with the employment of SPS in the Indian scenario.

Abstract: The behavior of specimens dynamically loaded during the split Hopkinson (Kolsky) bar tests in a regime close to simple shear conditions was studied. The lateral surface of the specimens was investigated in-situ using a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time allowed one to trace the evolution of plastic strain localization. The process of target perforation involving plug formation and ejection was examined using a high-speed infra-red camera and a VISAR velocity measurement system. The microstructure of tested specimens was analyzed using an optical interferometer-profiler and a scanning electron microscope. The development of plastic shear instability regions has been simulated numerically.

Abstract: Elevated temperature workability of Boron added modified 9Cr-1Mo steel is studied in temperature range 1223-1473K and strain rates of 0.001-10s^-1 using Dynamic Materials Model. Towards this end hot isothermal compression tests are carried out and the experimental results are used to obtain processing map. Extensive microstructural investigation is carried out to validate different domains of processing map. On the basis of the microstructurally validated processing map, parameters for the thermomechanical processing of P91B are recommended.

Abstract: This research focuses on the prediction of the forming limit of certain Advanced High Strength Steel grades under stretch-bending conditions. For these types of steels it is experimentally observed and shown that when there is a bending component added to the main membrane deformation the formability predicted by the regular FLCs underestimate the material behavior. Due to the added effects of thickness stress due to contact and small radius bending as well as bending stresses, a through-thickness stress gradient forms which gives additional stability to the material beyond the forming limits determined by tests that generate mostly uniform membrane deformation. It is observed experimentally and by the detailed simulations that the cross-sectional stability is not lost instantaneously but gradually. A surface dent forms first on the outer surface and progresses in a stable manner towards the contact side since on the contact side the material has still potential to harden. This process delays the localization of the strains and stabilizes the formation of the local neck. For the prediction of this phenomenon theoretically and using shell elements, a modified incremental form of the maximum tension stability criterion is proposed to be applied at integration points through thickness. It is shown that with this criterion the phenomenon of gradual loss of stability can be captured during stretch-bending with shell elements.

Abstract: Pressure transducers and high-speed photography technology were applied on the experimental device which formed the axisymmetrical dissemination of glycerine. The instability development at gas/liquid interface and the primary breakup were recorded by high speed photographs. It can be concluded that the wavelength of initial disturbance waves will decrease with the incensement of shock wave intensity. At the same time, the degree of mixing of spike and airflow will also be increased. The acceleration of liquid front remains unchanged in the earlier stage and rise rapidly in the later stage.