Papers by Norhafizan Ahmad
Virtual reality (VR) is a promising technology which has the ability to immerse a user in a virtu... more Virtual reality (VR) is a promising technology which has the ability to immerse a user in a virtual world through the use of 3D real time computer graphics. The user works "together" with the virtual objects to complete the desired task. Therefore. a physical environment is needed to make the users feel. see and interact with virtual objects in the most natural and ergonomic position so that the unnecessary awkward posture and others physical discomfort that could be detrimental to the users of the virtual system can be avoided. The objective of this research is to design an Ergonomic virtual reality station that will reduce the unnecessary awkward posture and others physical discomfort when using VR system. Anthropometries data was collected from Malaysian population. Statistical analysis was conducted to analyze the uniformity of anthropometries data and required number of sample. Result of the research shows that the appropriate design to the anthropometries data of use...
Brain Computer Interfaces (BCI) provide a vast possibility in enabling the brain to communicate d... more Brain Computer Interfaces (BCI) provide a vast possibility in enabling the brain to communicate directly with the computer, hence providing an alternative in controlling the machines without much effort. In fields of rehabilitations robotics, the applications of an exoskeletons in assisting a spinal cord injured (SCI) patients were growing. Steady state visually evoked potentials (SSVEP) based BCIs that utilizes the human visual reactions to the constant flickered stimulus quickly showed its potentials among the BCIs used in rehabilitations devices because of its advantages such as a higher immunity to noises and artefacts and also its robustness compared to other BCIs. Rehabilitation exoskeletons demands an approach that are more user friendly and the aspects of control scheme and mechanical parts that are more focused on assisting the patients in rehabilitations and providing a SCI patients an alternatives to explore their surroundings in a more intuitive ways. This paper highligh...
IOP Conference Series: Materials Science and Engineering
The Acehnese traditional boat, known as Jalo Kayoh, is a mean of transportation used by Acehnese ... more The Acehnese traditional boat, known as Jalo Kayoh, is a mean of transportation used by Acehnese fishermen. The main constituent of the boat is wood. However, due to the decline of high-quality wood supply and as a preventative measure of illegal logging, fiberglass and jute fiber are used instead of wood. This study compares the strength of the two materials using finite element method. The Jalo Kayoh model plan stands at 4m in length, 0.6 m in width, and 0.4 m in height. A 2500 N static load is applied to the surface, using a C3D10 quadratic tetrahedron 0.02 mesh. The result of the simulation to the fiberglass is a maximum displacement of 7.123 x 10-5m, while the jute fiber has a maximum displacement of 2.255 x 10-4 m. The maximum stress stands at 1.612 x 106 Pa for the fiberglass and 1.523 x 106 Pa for the jute fiber. The maximum strain occurs at 1.654 x 10-5 for the fiberglass and 4.581 x 10-5 for the jute fiber. To conclude, fiber glass has more stress 1.05 % and less strain 2.76 % than jute fiber and both the materials can sustain the load given.
Journal of Mechanical Science and Technology
This study focuses on introducing a criteria for conducting harmonic excitation signal eliminatio... more This study focuses on introducing a criteria for conducting harmonic excitation signal elimination as well as investigating its effectiveness towards achieving complete isolation of harmonic disturbance in performing EMA under operational condition. By modulating the ratio between harmonic excitation and impact knocking frequencies, it was revealed that the harmonic signal was efficiently attenuated with sufficient number of averaging blocks. The results highlighted close agreement between simulation and experimental approaches with maximum deviation of 2 %, under specific design criteria. It was determined that a non-periodic triggering frequency significantly affect the elimination performance in terms of trend and amplitude reduction. This work underlines the importance of controlling the triggering frequency to yield the desired design criteria for achieving rapid and highly efficient elimination of harmonic excitation signal. The results have proven that the proposed technique can be further adapted to isolate the harmonic in conventional EMA conducted under operational condition.
PLOS ONE
Prolong walking is a notable risk factor for work-related lower-limb disorders (WRLLD) in industr... more Prolong walking is a notable risk factor for work-related lower-limb disorders (WRLLD) in industries such as agriculture, construction, service profession, healthcare and retail works. It is one of the common causes of lower limb fatigue or muscular exhaustion leading to poor balance and fall. Exoskeleton technology is seen as a modern strategy to assist worker's in these professions to minimize or eliminate the risk of WRLLDs. Exoskeleton has potentials to benefit workers in prolong walking (amongst others) by augmenting their strength, increasing their endurance, and minimizing high muscular activation, resulting in overall work efficiency and productivity. Controlling exoskeleton to achieve this purpose for ablebodied personnel without impeding their natural movement is, however, challenging. In this study, we propose a control strategy that integrates a Dual Unscented Kalman Filter (DUKF) for trajectory generation/prediction of the spatio-temporal features of human walking (i.e. joint position, and velocity, and acceleration) and an impedance cum supervisory controller to enable the exoskeleton to follow this trajectory to synchronize with the human walking. Experiment is conducted with four subjects carrying a load and walking at their normal speed-a typical scenario in industries. EMG signals taken at two muscles: Right Vastus Intermedius (on the thigh) and Right Gastrocnemius (on the calf) indicated reduction in muscular activation during the experiment. The results also show the ability of the control system to predict spatio-temporal features of the pilots' walking and to enable the exoskeleton to move in concert with the pilot.
Movement, Health & Exercise, 2015
Sepak takraw is a traditional sport in Asia in which the players use various parts of their bodie... more Sepak takraw is a traditional sport in Asia in which the players use various parts of their bodies to hit the ball, with the exception of their hands. Unlike other sports such as soccer, boxing, and rugby, it is observed that none of the studies in the literature have examined the injuries resulting from the impact of the sepak takraw ball on the players' heads during a game. This study was initiated following the incidents of the 24 th SEA Games in Korat, Thailand, in year 2007, whereby a number of players from the Malaysian Sepak Takraw Association (PSM) had to withdraw themselves from the championship. These players suffered from headaches which were believed to be caused by the impact of the sepak takraw ball, considering the fact that heading is one of the basic movements used to hit the ball. Moreover, it is expected that the sepak takraw ball travels at high velocities during the game. Hence, the objective of this study is to investigate the impact of the sepak takraw ball and its corresponding level of head injury among sepak takraw players in Malaysia by means of numerical simulations and experiments. In order to achieve this objective, a model of the scalp, skull, cerebrospinal fluid and brain is first developed and simulations are then carried out using finite element analysis (FEA) software. The results show that the maximum speed of the sepak takraw ball before heading is 13.581 m/s while the maximum impact force on the head obtained from the simulations is 688.11 N. The maximum displacement and maximum linear acceleration of the brain's centre of gravity is found to be 0.0080 m and 1674.5 m/s 2 , respectively, while the head impact power (HIP) is determined to be 11.366 kW. According to Newman et al. (2000), the probability of concussion is 39% and based on the results obtained in this study, it can be concluded that the players may suffer from mild traumatic brain injuries (MTBI) due to the high impact of the sepak takraw ball during heading. Hence, it is recommended that the players wear protective headbands to reduce the impact during heading and prevent the occurrence of MTBI in the long term.
This paper presents an investigation of pressure drop which occurred in an OWC system as the effe... more This paper presents an investigation of pressure drop which occurred in an OWC system as the effect of spherical hub-nose position in an annular duct. Study has been carried out by means of computational fluid dynamics (CFD) under steady flow conditions for several hub-nose positions. As a result, the CFD analysis has been able to reveal the characteristic of pressure drop which was relatively reasonable. It was found that the hub-nose position influenced pressure drop occurred in the OWC system. In this study, the ...
The takraw ball is a very unique interwoven ball used in the action game of sepak takraw. To date... more The takraw ball is a very unique interwoven ball used in the action game of sepak takraw. To date there has been no studies on the dynamic behavior and mechanical properties of the takraw ball. The purpose of this study is to predict the dynamic behavior and mechanical properties of the takraw ball in particular of normal impact on flat surfaces at low speeds. Two methods are employed to measure the dynamics behavior and mechanical properties of the takraw ball. The impact force, contact time, coefficient of restitution, deformation of the ball, inbound and rebound velocity were measured by using two dimensional motion analysis of high-speed video data and force plate data. Then, a finite element (FE) model of the homogeneous takraw ball is constructed, based on the experimental results. This FE model is used to predict modulus elasticity and Poisson ratio of the takraw ball. The FE analysis solution of the ball model was found to be reasonable close with the experimental results. H...
Desalination and Water Treatment, Mar 23, 2015
ABSTRACT Energy is one of the most important factors in the socioeconomic development of a countr... more ABSTRACT Energy is one of the most important factors in the socioeconomic development of a country. In a developing country like Malaysia, the development of islands is mostly related to the availability of electric power. As an island surrounded by sea, power generated by wave energy source will become one of the most promising solutions for the electrification of island areas. But, the unpredictable nature of the wave energy source is the main drawback. This paper presents a novel stand-alone wave energy supply system modeling with maximum power tracking and an energy storage-based power management algorithm in MATLAB/Simulink environment. The main contributions of this research work are eliminating the intermittent power generation nature of wave energy and efficiently extract the maximum wave power. In the proposed stand-alone system, a DC-DC bidirectional buck-boost converter controller is used to maintain the constant dc-link voltage. It also accumulates the surplus wave power in the battery bank and supplies this power to the load during the wave power shortage. A three-phase complex vector control scheme voltage source inverter is used to control the load-side voltage in terms of the frequency and voltage amplitude. Based on the simulation results obtained from MATLAB/Simulink, it has been found that the overall system is capable of working under variable weather and load conditions, and it can also able to extract the maximum wave power.
The sport industry has become ever more adept at exploiting leading-edge technologies to create m... more The sport industry has become ever more adept at exploiting leading-edge technologies to create more efficient equipment. One parameter that requires the utilisation of such technological advancement is the coefficient of restitution (COR). COR is important in sports engineering research especially in the development of new material of the sport’s ball, sport injury anaelysis as well as game performance. This study proposed a standard test method to determine the COR using high-speed video in a two-dimensional setting for capturing the behaviour at different point of contact (i.e. along line of impact). Hitherto, there is no proper method in determining the takraw ball’s COR upon considering different point of impacts that may affectby the ball’s trajectory and spin.
Body anthropometry and size are two significant ergonomic factors that defines the performance of... more Body anthropometry and size are two significant ergonomic factors that defines the performance of an athlete in any sports. The intricate nature of the human foot plays an important role for the performance of a soccer player amongst other factors. The human foot has been studied extensively around the globe with respect to forensic study, shoe design and also for shoe sizing system. A good understanding of foot anthropometry and shape is also helpful in designing a footwear that enhances the athletes’ performance. To the best of the authors’ knowledge, this is the first study ever conducted in evaluating Malaysian youth soccer players’ foot anthropometry. The ultimate objective of this study is to establish a fact that there is a need for a new sizing system for Malaysians that is not only based on one’s foot length, but also other significant anthropometric parameters, however this paper will only report preliminary findings on the Malaysian youth soccer players’ foot anthropometr...
PLOS ONE, 2015
Energy is one of the most important factors in the socioeconomic development of a country. In a d... more Energy is one of the most important factors in the socioeconomic development of a country. In a developing country like Malaysia, the development of islands is mostly related to the availability of electric power. Power generated by renewable energy sources has recently become one of the most promising solutions for the electrification of islands and remote rural areas. But high dependency on weather conditions and the unpredictable nature of these renewable energy sources are the main drawbacks. To overcome this weakness, different green energy sources and power electronic converters need to be integrated with each other. This study presents a battery storage hybrid standalone photovoltaic-wind energy power supply system. In the proposed standalone hybrid system, a DC-DC buck-boost bidirectional converter controller is used to accumulates the surplus hybrid power in the battery bank and supplies this power to the load during the hybrid power shortage by maintaining the constant dc-link voltage. A three-phase voltage source inverter complex vector control scheme is used to control the load side voltage in terms of the voltage amplitude and frequency. Based on the simulation results obtained from MATLAB/Simulink, it has been found that the overall hybrid framework is capable of working under variable weather and load conditions.
Advances in Mechanical Engineering
This paper describes a robotic bone drilling and screwing system for applications in orthopedic s... more This paper describes a robotic bone drilling and screwing system for applications in orthopedic surgery. The goal is to realize two robot manipulators performing cooperative bone drilling. The proposed cooperative bone drilling system can be divided into hardware and software development. The hardware development section consists of two robot manipulator arms, which perform drilling and gripping of the bone, and operates using two joysticks. The software section assists the surgeon in visual and navigation control of those robot manipulators. Controller used in this system can be included in the hardware and software sections. Disturbance observer based position control was used in the robot manipulator maneuver and reposition controller (cooperative control) was used in cooperative drilling operation to maintain the alignment of the drill bit during drilling. A mathematical model for the control system was designed and a real environment mimicking simulation for bone drilling was d...
Desalination and Water Treatment, 2015
ABSTRACT Energy is one of the most important factors in the socioeconomic development of a countr... more ABSTRACT Energy is one of the most important factors in the socioeconomic development of a country. In a developing country like Malaysia, the development of islands is mostly related to the availability of electric power. As an island surrounded by sea, power generated by wave energy source will become one of the most promising solutions for the electrification of island areas. But, the unpredictable nature of the wave energy source is the main drawback. This paper presents a novel stand-alone wave energy supply system modeling with maximum power tracking and an energy storage-based power management algorithm in MATLAB/Simulink environment. The main contributions of this research work are eliminating the intermittent power generation nature of wave energy and efficiently extract the maximum wave power. In the proposed stand-alone system, a DC-DC bidirectional buck-boost converter controller is used to maintain the constant dc-link voltage. It also accumulates the surplus wave power in the battery bank and supplies this power to the load during the wave power shortage. A three-phase complex vector control scheme voltage source inverter is used to control the load-side voltage in terms of the frequency and voltage amplitude. Based on the simulation results obtained from MATLAB/Simulink, it has been found that the overall system is capable of working under variable weather and load conditions, and it can also able to extract the maximum wave power.
Advances in Mechanical Engineering, 2014
ABSTRACT There have been a significant number of researches on computational fluid dynamic (CFD) ... more ABSTRACT There have been a significant number of researches on computational fluid dynamic (CFD) analysis of balls used in sports such as golf balls, tennis balls, and soccer balls. Sepak takraw is a high speed court game predominantly played in Southeast Asia using mainly the legs and head. The sepak takraw ball is unique because it is not enclosed and made of woven plastic. Hence a study of its aerodynamics would give insight into its behaviour under different conditions of play. In this study the dynamics of the fluid around a static sepak takraw ball was investigated at different wind speeds for three different orientations using CFD. It was found that although the drag did not differ very much, increasing the wind velocity causes an increase in drag. The lift coefficient varies as the velocity increases and does not show a regular pattern. The drag and lift coefficients are influenced by the orientation of the sepak takraw ball.
Desalination and Water Treatment, 2015
ABSTRACT Our earth is a water planet; nearly two thirds of the earth’s surface is covered by ocea... more ABSTRACT Our earth is a water planet; nearly two thirds of the earth’s surface is covered by ocean water. But the shortage of fresh water is a major problem in many areas, especially in rural villages near to the sea or islands. Now, renewable energy-based desalination system is rising around the world due to the adverse environmental effect and high-energy requirements of the conventional fuel-based desalination system. This paper describes the prospect of an off-grid stand-alone wave-powered reverse osmosis desalination system for those areas. A simulation model for the prediction of the wave power delivered for a given value of the wave height and period is adopted. Based on the availability of the wave data, the amount of the water produced at different sites of Malaysia can be calculated in this paper. In addition, this paper deals with an economical analysis of wave energy production for reverse osmosis desalination system.
2014 IEEE 8th International Power Engineering and Optimization Conference (PEOCO2014), 2014
In developing country like Malaysia, the demand for electricity is expected to rise with increasi... more In developing country like Malaysia, the demand for electricity is expected to rise with increasing urbanization and rapid industrialization. Currently energy production is mainly dependent on fossil fuel but in the near future fossil fuels will not be sustainable because of the depletion of existing reserves and their impact on the environment. Wave energy is an environmentally friendly and fastest growing renewable energy source for a sustainable electrical power generation of the future. Unlike others renewable energy resources, wave energy can produce electric power all over the year. As Malaysia has a total coastline of 4,675 kilometers so there is a great potential for utilization of wave energy in Malaysia especially along the coast and the islands. This paper presents a feasibility study of wave energy at different locations in Malaysia including the estimation of the total power available from the seas surroundings Malaysia. Furthermore, the analysis of investment, operation and maintenance cost for a wave farm is also presented.
2013 IEEE Conference on Systems, Process & Control (ICSPC), 2013
ABSTRACT The motion of human body is complex but perfect and integrated effort of brain, nerves a... more ABSTRACT The motion of human body is complex but perfect and integrated effort of brain, nerves and muscles. Exoskeleton is a promising idea for human rehabilitation of the lower limb that is weak enough to move. EMG signal contains the information of human movement and can be considered as one of the most powerful input to exoskeleton controller. In this research, the activity of the lower limb muscles that are responsible for human sit to stand and stand to sit movement has been studied. In this regard, the activities of three muscles viz. rectus femoris, vastus lateralis and biceps femoris have been observed and recorded to perceive their activation pattern. The experimental results show that the maximum voltage of vastus lateralis at activation moment is greater or equal to +0.1 mV or lesser or equal to -0.1 mVduring sit to stand and stand to sit movement whereas same throughput was found for biceps femoris during sit to stand and for rectus femoris during stand to sit movement only.
Uploads
Papers by Norhafizan Ahmad