Parametric instability of static shafts-disk system using finite element method

Parametric instability condition is an important consideration in design process as it can cause failure in machine elements. In this study, parametric instability behaviour was studied for a simple shaft and disk system that was subjected to axial load under pinned-pinned boundary condition. The shaft was modelled based on the Nelson's beam model, which considered translational and rotary inertias, transverse shear deformation and torsional effect. The Floquet's method was used to estimate the solution for Mathieu equation. Finite element codes were developed using MATLAB to establish the instability chart. The effect of additional disk mass on the stability chart was investigated for pinned-pinned boundary conditions. Numerical results and illustrative examples are given. It is found that the additional disk mass decreases the instability region during static condition. The location of the disk as well has significant effect on the instability region of the shaft

Impact damage resistance and post impact tolerance of optimum banana-pseudo stem fiber reinforced epoxy sandwich structures

Banana fiber has a high potential for use in fiber composite structures due to its promise as a polymer reinforcement. However, it has poor bonding characteristics with the matrixes due to hydrophobic-hydrophilic incompatibility, inconsistency in blending weight ratio, and fiber length instability. In this study, the optimal conditions for a banana/epoxy composite as determined previously were used to fabricate a sandwich structure where carbon/Kevlar twill plies acted as the skins. The structure was evaluated based on two experimental tests: low-velocity impact and compression after impact (CAI) tests. Here, the synthetic fiber including Kevlar, carbon, and glass sandwich structures were also tested for comparison purposes. In general, the results showed a low peak load and larger damage area in the optimal banana/epoxy structures. The impact damage area, as characterized by the dye penetration, increased with increasing impact energy. The optimal banana composite and synthetic fiber systems were proven to offer a similar residual strength and normalized strength when higher impact energies were applied. Delamination and fracture behavior were dominant in the optimal banana structures subjected to CAI testing. Finally, optimization of the compounding parameters of the optimal banana fibers improved the impact and CAI properties of the structure, making them comparable to those of synthetic sandwich composites

Inefficient Processing Time as Hidden Time Loss in Assembly Operations

Hidden Time Loss (HTL) occurs along the production processes that have a significant effect to productivity. Overall Equipment Efficiency (OEE) is the most popular performance measurement tool used in the production line. However, OEE doesn’t really fit in measuring operation performance of manual assembly process and semi-auto assembly process. In this case, there would be the amount of HTL have occurred along the assembly processes that become critical when to involve high product variety in the same production line. Thus, the purpose of this paper is to introduce Inefficient Processing Time (IPT) as one of the component of Time Loss Measures (TLM) in the manual assembly process and semi-auto assembly process. The structure of IPT is developed through a thorough literature study on manufacturing operations and its performance measures. The IPT structure is validated by using case study at five automotive manufacturing companies. The results show that the IPT can contribute to HTL in the manual assembly process and semi-auto assembly process

Scalability challenges in healthcare blockchain system - a systematic review

Blockchain technology is a private, secure, trustworthy, and transparent information exchange performed in a decentralised manner. In this case, the coordination and validation efforts are simplified as the records are designed to update regularly and there is no difference in the two databases. This review focuses on how the blockchain addresses scalability challenges and provides solutions in the healthcare field through the implementation of blockchain technology. Accordingly, 16 solutions fell under two main areas, namely storage optimization and redesign of blockchain. However, limitations persist, including block size, high volume of data, transactions, number of nodes, and protocol challenges. This review consists of six stages, namely identification of research question, procedures of research, screening of relevant articles, keywording based on the abstract, data extraction, and mapping process. Through Atlas.ti software, the selected keywords were used to analyse through the relevant articles. As a result, 48 codes and 403 quotations were compiled. Manual coding was performed to categorise the quotations. The codes were then mapped onto the network as a mapping process. Notably, 16 solutions fell under two main areas, namely storage optimization and redesign of blockchain. Basically, there are 3 solutions compiled for storage optimization and 13 solutions for the redesign of the blockchain, namely blockchain modelling, read mechanism, write mechanism, and bi-directional network

The elastic properties of unidirectional bamboo fibre reinforced epoxy composites

Natural fibres such as kenaf, jute, bamboo, flax and wood have been the subject of intensive researches in the area of fibre reinforced composite due to their environmental advantages of being renewable, biodegradable and sustainable. Bamboo fibre can be a good choice of natural fibre reinforcement for structural applications due to its excellent strength to weight ratio that is comparable to that of mild steel. In this study, mechanical properties of both continuous and short bamboo fibre reinforced composites are predicted using micromechanical approaches. The finite element method was used where three-dimensional micromechanical representative volume element with square and hexagonal packing geometry was implemented. The results were then compared with the findings from analytical approach that includes the rule of mixture and the Halpin-Tsai model. It was found that for all properties, the FEM and analytical methods give comparable trends of property on volume fraction plots. Furthermore, the longitudinal modulus given by all models are in excellent agreement as it increases linearly with the increase in bamboo fibre volume fraction

Enhancing the stabilization of aircraft pitch motion control via intelligent and classical method

The pitching movement of an aircraft is very important to ensure passengers are intrinsically safe and the aircraft achieve its maximum stability. The equations governing the motion of an aircraft are a complex set of six nonlinear coupled differential equations. Under certain assumptions, it can be decoupled and linearized into longitudinal and lateral equations. Pitch control is a longitudinal problem and thus, only the longitudinal dynamics equations are involved in this system. It is a third order nonlinear system, which is linearized about the operating point. The system is also inherently unstable due to the presence of a free integrator. Because of this, a feedback controller is added in order to solve this problem and enhance the system performance. This study uses two approaches in designing controller: a conventional controller and an intelligent controller. The pitch control scheme consists of proportional, integral and derivatives (PID) for conventional controller and fuzzy logic control (FLC) for intelligent controller. Throughout the paper, the performance of the presented controllers are investigated and compared based on the common criteria of step response. Simulation results have been obtained and analysed by using Matlab and Simulink software. The study shows that FLC controller has higher ability to control and stabilize the aircraft's pitch angle as compared to PID controller

The effect of changing disk parameters on whirling frequency of high speed rotor system

The requirement for efficiency improvement of machines has caused machine rotor to be designed to rotate at high speeds. It is known that whirling natural frequency of a shaft changes with the change of shaft speed and the design needs to avoid points of resonance where the whirling frequency equals the shaft speed. At high speeds, a shaft may have to carry a huge torque along and this torsional effect has been neglected in past shaft analyses. Whirling behaviour of high speed rotating shaft is investigated in this study with consideration of the torsional effect of the shaft. The shaft system under study consists of a shaft, discs and two bearings, and the focus is on the effect of the disc parameters. A finite element formulation is developed based on Nelson's 5 degrees of freedom (DOF) per node element that includes the torsional degree of freedom. Bolotin's method is applied to the derived Mathieu-Hill type of equation to get quadratic eigenvalues problem that gives the forward and backward frequencies of the shaft. Campbell's diagrams are drawn in studying the effect of discs on the whirling behaviour of the shaft. It is found that the addition of disks on the shaft decreases the whirling frequency of the shaft and the frequency is lower for mass located at the centre of the shaft compared to the one located near to the end. The effect of torsional motion is found to be significant where the difference between critical speed of 4DOF and 5DOF models can be as high as 15%

Load-deformation analysis on a slope at Gunung Pulai water treatment plant, Sultan Ibrahim reservoir

The Sultan Ibrahim Reservoir located at Gunung Pulai catchment area was previously managed by the Singapore's Public Utilities Board before the Board handed over the reservoir to Johor State Government under current management of the Syarikat Air Johor. At the present time, the Syarikat Air Johor is operating a Gunung Pulai Water Treatment Plant consisted of two main plants, i.e. Water Sedimentation Plant and Water Filtration Plant for treating raw water from the reservoir before supplying to the consumers. However, the integrity of water treatment plant's structure should be checked due to several cracks were observed, and moreover the structure was built over more than 90 years. The formation of the cracks in the Gunung Pulai Water Treatment Plant may be induced by movement of the sloping area to the south-east of Water Sedimentation Plant. The calculated Factor of Safety (FOS) via sensitivity analysis for cross sections of original slope indicates any decrease in friction angle and/or cohesion strength or increase in horizontal seismic load will further cause instability on slope. Also, the results of Load-Deformation analysis on cross sections of original slope show significant vertical displacement and horizontal displacement on the bottom and both sides of sedimentation tanks, respectively. The results indicate applied structural and water loads significantly affect deformation at both vertical and horizontal directions which could have contributed to FOS < 1 in slope stability analysis

Revisiting QRS detection methodologies for portable, wearable, battery-operated, and wireless ECG systems

Cardiovascular diseases are the number one cause of death worldwide. Currently, portable battery-operated systems such as mobile phones with wireless ECG sensors have the potential to be used in continuous cardiac function assessment that can be easily integrated into daily life. These portable point-of-care diagnostic systems can therefore help unveil and treat cardiovascular diseases. The basis for ECG analysis is a robust detection of the prominent QRS complex, as well as other ECG signal characteristics. However, it is not clear from the literature which ECG analysis algorithms are suited for an implementation on a mobile device. We investigate current QRS detection algorithms based on three assessment criteria: 1) robustness to noise, 2) parameter choice, and 3) numerical efficiency, in order to target a universal fast-robust detector. Furthermore, existing QRS detection algorithms may provide an acceptable solution only on small segments of ECG signals, within a certain amplitude range, or amid particular types of arrhythmia and/or noise. These issues are discussed in the context of a comparison with the most conventional algorithms, followed by future recommendations for developing reliable QRS detection schemes suitable for implementation on battery-operated mobile devices.Mohamed Elgendi, Björn Eskofier, Socrates Dokos, Derek Abbot

Free vibration analysis and design optimization of SMA/Graphite/Epoxy composite shells in thermal environments

Composite shells, which are being widely used in engineering applications, are often under thermal loads. Thermal loads usually bring thermal stresses in the structure which can significantly affect its static and dynamic behaviors. One of the possible solutions for this matter is embedding Shape Memory Alloy (SMA) wires into the structure. In the present study, thermal buckling and free vibration of laminated composite cylindrical shells reinforced by SMA wires are analyzed. Brinson model is implemented to predict the thermo-mechanical behavior of SMA wires. The natural frequencies and buckling temperatures of the structure are obtained by employing Generalized Differential Quadrature (GDQ) method. GDQ is a powerful numerical approach which can solve partial differential equations. A comparative study is carried out to show the accuracy and efficiency of the applied numerical method for both free vibration and buckling analysis of composite shells in thermal environment. A parametric study is also provided to indicate the effects of like SMA volume fraction, dependency of material properties on temperature, lay-up orientation, and pre-strain of SMA wires on the natural frequency and buckling of Shape Memory Alloy Hybrid Composite (SMAHC) cylindrical shells. Results represent the fact that SMAs can play a significant role in thermal vibration of composite shells. The second goal of present work is optimization of SMAHC cylindrical shells in order to maximize the fundamental frequency parameter at a certain temperature. To this end, an eight-layer composite shell with four SMA-reinforced layers is considered for optimization. The primary optimization variables are the values of SMA angles in the four layers. Since the optimization process is complicated and time consuming, Genetic Algorithm (GA) is performed to obtain the orientations of SMA layers to maximize the first natural frequency of structure. The optimization results show that using an optimum stacking sequence for SMAHC shells can increase the fundamental frequency of the structure by a considerable amount