Papers by Keyword: Numerical Model

Abstract: This study aimed at development and application of a numerical model; WHPANM (Water Hammer Phenomenon Analysis Numerical Model), to investigate the water hammer phenomenon in the penstock of the Keyal Khawar hydropower plant in Khyber Pakhtunkhwa, Pakistan. The model, written in Visual Basic, utilized the numerical method of characteristics to solve the momentum and continuity water hammer equations. Results indicated that using a 2.2 m diameter pipe resulted in a maximum and minimum pressure head of 1462 m and 1420 m. Increasing the diameter to 3.0 m decreased the maximum pressure head to 1448 m, while the minimum pressure head increased to 1422 m. Conversely, decreasing the diameter to 1.0 m led to a maximum and minimum pressure head of 1522 m and 1363 m, respectively. Regarding pipe length, a standard length of 900 m maintained maximum and minimum pressure heads at 1462 m and 1420 m, respectively. Extending length to 1400 m increased maximum pressure head to 1485 m. Conversely, shortening length to 300 m resulted in a decreased maximum pressure head of 1436 m, with minimum pressure head remaining constant at 1420 m. To prevent water hammer damage in high head hydropower plants, study recommends utilizing a 2.2 m diameter penstock pipe and coordinating valve closure times accordingly. The study suggests a systematic design approach, optimal penstock diameter, and less rigid pipe materials to mitigate water hammer effects. The WHPANM model demonstrated strong concordance with the original data generated by the commercial software employed by the consultant for the Kyal Khwar hydropower plant.

Abstract: Friction Stir Process (FSP) is considered one of the most convenient, effective, and environmental friendly manufacturing processes. In these processes, a tool involves a pin that blends the material around it and a shoulder that creates frictional heat. On the other hand, the pin mixes the soft material to refine the grain structure. This paper aims to investigate a thermal model using Altair to numerically simulate the temperature distribution profiles of 7075 Aluminum Alloy material using FSP. Using a novel technique called Smoothed-Particle Hydrodynamics (SPH), we extracted the temperature distribution in the Stir Zone (SZ) for 900 RPM, 1200 RPM, and 1500 RPM Tool Rotational Speed (TRS) with constant Tool Traverse Speed (TTS). The temperature results obtained are incremental with increasing TRS. As a result, the temperature achieved from 900 RPM to 1500 RPM has increased by 21.20%. In addition, the obtained temperature is almost 50% of the melting point. The material flow on both Advancing Side (AS) and Retreating Side (RS) shows the thorough material mixing. The SPH technique helps to investigate the proper material flow modeling by dividing the AS and RS nodes and it was observed that they have thoroughly been mixed near the FSP tool pin.

Abstract: Coefficient of friction (cof) is an important variable when dealing with con-tact between mechanical parts. It depends on various tribological variables and the value can be determined only by experiments. Cof correlates with the wear of material and this is a severe problem in biomedical engineering. This research numerically studied the effects of cof between talar and bear-ing in the total ankle replacement (TAR) implants. The aim is to evaluate the contact situations affected by cof. The TAR models consist of cobalt chrome (CoCr) alloy and ultra high molecular weight polyethylene (UHMWPE) bio-materials. Five cof values of the dry, lubricated and frictionless TAR me-chanical contacts under ankle gait load were examined. The models use a fixed 1 mm element size for UHMWPE bearing component and four element sizes for the talar component, range from 1 mm to 0.4 mm. Results show that, 1) higher cof induces higher contact pressure, 2) contact stress is not af-fected by cof, 3) proper talar element size is 0.4 mm and 4) frictionless model can be used for the TAR contact mechanic computation. Frictionless model calculates equal contact stress and lower contact pressures with an error of 2.68 % compared to the smooth model.

Abstract: This paper focuses on the theoretical and experimental verification of a behaviour composite reinforced concrete bed for installation in high-precision machine tools. The design solution consists of coupling the steel shell and HPC concrete filling, which ensures the high rigidity of the bed. Studies in this article were aimed at describing, in detail, the behaviour of the bed, from production to setting into its final position. An integral part of the solution was implementing the measurement of the response of the real bed segment using the installed monitoring system as well as the numerical simulations performed on the assembled FEM model. Thanks to the modular design of the bed, it was possible to verify the behaviour of the simulated load during the operation of the machine tool on a smaller sample. The aim is to verify the functionality of the coupling and, based on the comparison of measured and theoretical data, to define the critical points of the composite and, thus, provide a basis for design optimisation in order to maximise the monitored parameters.

Abstract: The Solid Ankle Cushioned Heel (SACH) foot is a commonly prescribed prosthetic foot for the rehabilitation of lower limb amputees. From the viewpoint of its biomechanical performance, the foot is known to cause drop-off effect and asymmetry in amputee gait. Therefore, the objective of this work is to improvise the effective foot length ratio (EFLR) and the progression of the centre of pressure (CoP) of the SACH foot by providing a novel design approach that utilizes finite element analysis. Boundary conditions employed for evaluating the roll-over characteristics of prosthetic feet were numerically incorporated in this work. The non-linear mechanical behavior of the foot was included with the incorporation of large deformation, a hyperelastic material model and the Augmented Lagrangian contact formulation. Outcomes from the simulations were experimentally verified using an inverted pendulum-like apparatus, thereby substantiating the numerical approach. The design process of the SACH foot involved the modification of the elastic modulus of its components for enhancing the parameters of interest. Results obtained presented a 5.07% increase in the EFLR and a 9.29% increase in the anteroposterior progression of the CoP, which may improve amputee stability. The design solution presented may support the large user base of the SACH foot towards achieving enhanced gait characteristics during ambulation. Moreover, this work successfully demonstrates a novel design procedure for a prosthetic foot through an effective numerical implementation.

Abstract: This paper proposes a novel approach of ultra-high frequency induction cladding with metal wire, in which AISI type 316L stainless steel wire (SS316L) is coated on gray cast iron to improve the specific surface properties of gray cast iron. The corresponding numerical model coupled with electromagnetic field and temperature field has been developed to obtain the representative distribution of induction heat. The established numerical model has been validated experimentally, and the temperature distribution captured in experiment shows good agreement with the calculated results. Given the high heating efficiency and selective heating characteristics of ultra-high frequency induction cladding technology, this method can be applied to the micro-crack repair on the surface of the thermal-sensitive materials.

Abstract: The results of single-lap shear tests, performed on specimens with Fiber Reinforced Cementitious Matrix (FRCM) or Steel Reinforced Grout (SRG) composite strips bonded to masonry unit, are presented in this paper. This study indicates a different type of failure modes occur in PBO FRCM and SRG – masonry joints, respectively. The PBO-FRCM exhibited the typically telescopic failure mode while the SRG shows a slippage of the fibers and fracture of the external matrix layer at the fiber-matrix interface for both the composite systems investigated. Moreover, a 3D numerical model by the commercial code ABAQUS was realized, it is calibrated on the results present in this study. The macro model approach was used with two different bond-slip relationships present in literature. The validity of the numerical model is verified by the comparison with the experimental results in terms of the applied load-global slip and the crack patterns.

Abstract: The paper presents the comparison of the results between the numerical model developed for the simulation of the fluid-structure interaction problem and the experimental tests. The model is based on the so called “partition scheme” in which the equations governing the fluid’s pressures and the equations governing the displacement of the structure are solved separately, with two distinct solvers. The SPH (Smoothed Particle Hydrodynamics) method is used for the fluid and the standard FEM (Finite Element Method), based on shell elements, is used for the structure. Then, the two solvers are coupled to obtain the coupled behaviour of the fluid structure system. The elasto plastic material model for the structure includes some important nonlinear effects like yielding in compression and tension. Previously experimentally tested (on a shaking table) rectangular tanks with rigid and deformable walls were used for the verification of the developed numerical model. A good agreement between the numerical and the experimental results clearly shows that the developed model is suitable and gives accurate results for such problems. The numerical model results are validated with the experimental results and can be a useful tool for analyzing the behaviour of liquid tanks of larger dimensions.

Abstract: The article proposes applying energy from law deformation mechanics of the rigid body to deformation method for calculating the strength of reinforced concrete constructions with the use of diagrams illustrating the deformation of concrete and reinforcement. In terms of the energy theory of strength, concrete and rebar accumulate potential energy in the section of the construction component under stress; based on the contours of the diagram used in calculation it is possible to distinguish a stress diagram for concrete of the compressed zone. The value of the strains is equivalent to the force used for the deformation of the concrete specimen under stress (prism-or cylinder-shaped); the force is equal to the area used in the calculation of the normable diagram. The resolving balance equations are deduced with the use of the flat section hypothesis. The conditions of the stress balance in the section of the construction component are tested with the method of the successive approximation. The variable parameter of approximation is the construction component bending. General deformations (deflections) of the construction components are significantly higher than their limit stress values permitted for safe operation.

Abstract: This contribution discusses numerical models of three different fracture tests – three-point bending (3PB), modified compact tension (modCT) and wedge-splitting test (WST). The aim is to compare loading diagrams (loading force vs. crack mouth opening displacement) obtained from these numerical models, created with real material properties. These properties were acquired from experimental data measurement. To assemble the numerical models, ATENA Science FEM software was used. In this software, damaging of the structure/specimen occurred by cracks can be modelled, their initiation and progressive propagation can be seen throughout the loading process.