Engineering Journal (Faculty of Engineering, Chulalongkorn University, Bangkok)
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Novel Design and Implementation of a Knee Exoskeleton for Gait Rehabilitation with Impedance Control Strategy
Get PDFThis paper presents a novel cable-driven robotic joint for a gait exoskeleton robot. We discussed in detail a lightweight, low inertia, and highly back-drivable, 1-DOF tension amplification mechanism based on a pulley system and block-and-tackle technique. The exoskeleton is controlled using an impedance controller under the active-assistive and resistive approaches. Four experiments were conducted to evaluate the proposed exoskeleton’s safety and controller performance: mechanical transparency analysis, active-assistive trajectory tracking, resistance of trajectory tracking, and gait rehabilitation. The exoskeleton demonstrated high transparency with the root mean square (RMS) torque of 0.457 Nm under no-load condition, suggesting that the mechanism is highly back-drivable, has a low moment of inertia, and is mechanically safe to operate. The active-assistive trajectory tracking experiment indicated that the output torque was generated under assist-as-needed approach, as the average robotic-assistance torque was lowered by more than 73% when the user provided assistance force to complete the task on their own. Additionally, the resistance experiment revealed the feasibility of employing the exoskeleton to strengthen muscles with adjustable resistive torque from 0.94 Nm and 2.25 Nm. Finally, the result of gait rehabilitation experiment demonstrated that the robot was able to provide adequate torque to assist users in completing their gait cycle without causing any negative effects during or after the experiment
A Review of Packed Bed Reactor and Gradient-less Recycle Reactor for Determination of Intrinsic Reaction Kinetics
Get PDFIntrinsic reaction kinetics is an essential information in catalytic reaction engineering. This paper reviews the two laboratory reactors, i.e., the packed-bed reactor and gradient-less recycle reactor commonly employed for determining the intrinsic reaction kinetics of heterogeneous catalysts. Although both reactors have been well-known for kinetic studies for a long time, there are still efforts to address some essential issues and to further develop the reactors. For example, a new design of the gradient-less recycle reactor was developed to broaden the operating window for intrinsic kinetic studies at low pressure. Furthermore, the intrinsic kinetic modeling in the gradient-less recycle reactor and packed-bed reactor, including the effects of mass transfer and axial dispersion, was also investigated. This review article provides in detail the types of both reactors, the development of both packed-bed reactor and gradient-less recycle reactor, intrinsic kinetic modeling, and the methods for determining heat- and mass- transfer limitations. All of these point out the suitable methods for determining intrinsic kinetics and perspectives for future works
The Empirical Formula for the Stiffness of a Spur Gear Pair Based on Finite Element Solutions
Get PDFGear meshing stiffness is commonly determined by the analytical method or the finite element method (FEM). Both methods can be used to determine the meshing stiffness but the calculation for the analytical method is more complicated, while the FEM is impacted by the tooth contact setting and large computation time. Thus, both methods have limitations for practical use. Here, an empirical formula was proposed to calculate meshing stiffness of a spur gear pair with gear ratio 1:1 in moderate to large load conditions. The formula was divided into two parts as 1) an equation used to calculate the stiffness of the gear cylinder derived from the elasticity equations, and 2) an empirical formula to determine the meshing stiffness of the tooth pair based on FEM solutions. The second part of the formula was constructed by selecting the related parameters, finding the appropriate formula pattern, and determining the relation between these parameters and tooth stiffness at any meshing position. Meshing stiffness of the gear pair was determined by combining the stiffness of two parts connected in series. Accuracy of the empirical formula was verified by comparing the calculated meshing stiffness with previous research and indicated that the calculated meshing stiffness conformed well with other studies. Our proposed empirical formula can be applied to any spur gear pair with gear ratio 1:1 to accurately determine gear meshing stiffness
Efficiency of Heat Transfer Improvement Performed in Circular Tubes Utilizing Various Types of Ring-Shaped Turbulators
Get PDFThe enhancement of heat transfer performance by using different types of ring-shaped turbulators equipped in a circular tube was investigated through 3D numerical simulations (CFD) with the finite volume method. Three types of turbulators—orbicular-ring turbulator (ORT), pyramidal-ring turbulator (PRT) and proposed innovative cogwheel-ring turbulator (CRT)—were considered. Air at 300 K was passed through the tube with uniform wall heat flux conditions varying from Reynold’s numbers of 4,000 to 20,000. The standard k-ε turbulence model was used to simulate the flows via the ANSYS FLUENT commercial software. Geometric influences in the heat transfer were investigated in terms of compositing the diameter ratio (DR = 0.5, 0.6 and 0.7), the pitch ratio (PR = 4 and 8) and the number of teeth in the cogwheel-ring turbulator (N = 6, 8 and 10). In conclusion, the heat transfer rate in the tubes fitted with ORT and PRT were in the range of 87, which was 199% higher than that of the tube without a turbulator. The PRT offered a slightly higher heat transfer rate than the ORT. Decreasing the pitch and diameter ratio could increase the heat transfer rate. Moreover, it was demonstrated that the proposed innovative CRT outperformed both the ORT and PRT in terms of heat transfer performance. In the case of CRT, the highest number of teeth (N) offered the lowest friction factor and pressure drop
Digital-Twins towards Cyber-Physical Systems: A Brief Survey
Get PDFCyber-Physical Systems (CPS) are integrations of computation and physical processes. Physical processes are monitored and controlled by embedded computers and networks, which frequently have feedback loops where physical processes affect computations and vice versa. To ease the analysis of a system, the costly physical plants can be replaced by the high-fidelity virtual models that provide a framework for Digital-Twins (DT). This paper aims to briefly review the state-of-the-art and recent developments in DT and CPS. Three main components in CPS, including communication, control, and computation, are reviewed. Besides, the main tools and methodologies required for implementing practical DT are discussed by following the main applications of DT in the fourth industrial revolution through aspects of smart manufacturing, sixth wireless generation (6G), health, production, energy, and so on. Finally, the main limitations and ideas for future remarks are talked about followed by a short guideline for real-world application of DT towards CPS
Assessment of Flood Dynamics in Lower Mekong Delta Using Modeling Approach
Get PDFThe assessment of flood dynamics is essential in supporting the nation and all stakeholders for the better flood management and adaptation. Climate change and hydropower dam operation pose threat to water resources in the Lower Mekong Delta. Cambodia is vulnerable to the flood impact due to its low adaptive capacity. Historically, flood has big impact on Cambodian society, economics and environment. This research was conducted by using the 2D HEC-RAS Modeling Application to study the flood dynamics under the influence of climate change, hydropower operation and irrigation expansion. The analysis is based on the observed flow and water level of 5 years from 2015 to 2019 and digital elevation model (6 m x6 m). The indices indicated satisfactory performance for the simulation model with the value of NSE between 0.78 and 0.97 and R2 between 0.80 and 0.96. The impact of climate change, hydropower operation and irrigation expansion, on the Cambodian Mekong floodplain area in forms of the flood inundation characteristics using the above well-configured hydraulic model framework. The results show that the flood extent increases around 74% in dry season and decrease around 20% in rainy season. Comparing to the baseline, the results of the scenario study suggest that the study area is likely to experience larger floodplain area in dry season (October to April), and flood extent in rainy season is lesser (May to October). The simulated results will provide important hydraulic information to respond to the future change of flood extent. The increase of water level in the dry season will provide water availability in the water supply sector and agriculture
Effectiveness Evaluation for Bacteria and Fungi Disinfections of Developed Ozone Machine
Get PDFA low-cost ozone machine was developed to generate gaseous ozone for decontaminating the non-ventilated and unoccupied room within a 50-minute ozonation duration. This ozone machine, equipped with a centrifugal blower, could assist in thoroughly dispersing ozone gas throughout an enclosed area, as a result this ozone machine could raise the ozone concentration up to 2.4 ppm inside a 50 square-meter classroom after the ozonation period. Performances of this ozone machine were experimentally evaluated inside both non-ventilated and ventilated classrooms. First, an average total ozone dose of 58 ppm-min, which was close to an upper limit for the >90% viral disinfection, demonstrated the machine effectiveness in the viral inactivation. Second, a waiting period for ozone decomposition and removal using a ceiling ventilated fan could be predicted from an exponential decay rate of ozone concentration to be about 1.5 hour before the decontaminated room could be re-entered safely. Third, the disinfection of bacteria and fungi, which are tougher than most viruses, were validated by the cultural tests using standard plate count agars after the 50-minute ozone exposure. Results of the colony count and microorganism identification using the MALDI-TOF MS and the fungi slide culture technique revealed that 11 species of bacteria and 5 species of fungi could be inactivated by ozone gas after the specified ozonation period
Opportunities and Barriers to the Adoption of Blockchain-Based Games in an Online Gaming Company in Thailand
Get PDFThis research aims to explore potential opportunities and barriers related to the adoption of blockchain-based games in an online gaming company in Thailand. The identified opportunities are classified under the benefits framework proposed by Shang and Seddon [1], and the identified barriers are classified under the Technology-Organisation-Environment (TOE) framework. Based on the knowledge and experience of experts in the case company, all the opportunities and barriers are then assessed using the concept of Failure Mode and Effect Analysis (FMEA), which is further improved using the Analytic Hierarchy Process (AHP) by assigning a relative weight to each element of the FMEA before being used to find the priority number (PN). Next, the Pareto principle is applied to reveal the critical opportunities and barriers. As a result, a total of 21 critical opportunities are revealed and categorised into 5 dimensions: 4 operational opportunities; 3 managerial opportunities; 7 strategic opportunities; 4 infrastructure opportunities; and 3 organisational opportunities, and a total of 19 critical barriers are revealed and categorised into 3 dimensions: 7 technological barriers; 6 organisational barriers; and 6 environmental barriers. The TOWS matrix is then used to formulate possible strategies for the case company to exploit the opportunities and address the barriers to the adoption of blockchain-based games. As a result, a total of 7 SO, 12 ST, 5 WO, and 1 WT strategies are proposed. Based on the PNs and the interview with experts, a roadmap including short-, medium-, and long-term action plans is also developed to facilitate the adoption of blockchain-based games
Influence of Surface Stresses on the Deflection of Circular Nanoplate with Two-Parameter Elastic Substrate
Get PDFThis paper presents the influence of surface energy effects on the deflection of circular nanoplate with two-parameter elastic substrate. The governing equation for axisymmetric bending of the nanoplate, based on the Gurtin-Murdoch surface elasticity theory, resting on a Winkler-Pasternak elastic foundation is derived from a variational approach based on the concept of minimum total potential energy. The analytical general solution to the governing equation is then obtained in terms of the modified Bessel functions. Finally, closed-form solutions for deflections, bending moment and transverse shear in the nanoplate subjected to normally distributed loading are presented explicitly for the boundary conditions of simple, clamped, and free edges. A set of numerical solutions are selected to demonstrate the influence of surface material parameters and the substrate moduli on the deflection and bending moment profiles of a silicon nanoplate on Winkler-Pasternak foundation. It is found that the nanoplate clearly shows size-dependent behaviors, and becomes stiffer with the existence of surface stresses
Effects of Air-Entraining Agent, Defoaming Agent and Mixing Time on Characteristic of Entrained Bubbles in Air-Enhanced Self-Compacting Concrete Mixed at Concrete Plant
Get PDFThis paper presents a full-scale experimental study on the use of an air-entraining agent and defoaming agent combined with mixing time to entrain small-sized air bubbles in air-enhanced self-compacting concrete (Air-SCC). The fresh properties (flowability and V-funnel time) were determined. An air void analyzer (AVA) was used to measure the diameter size of bubbles entrained in the fresh stage. The dosages of both air-entraining agent (AE) and defoaming agent with different mixing times were investigated for their effects on the bubble size distribution. The results indicated that the portion of small bubbles with a diameter size less than 1,000 µm could be increased by increasing the AE dosage. Furthermore, prolonging the mixing time notably increased the volume of small bubbles, while producing no substantial change in the volume of large bubbles. Defoaming agent eliminated both small and large bubbles; however, small bubbles could be entrained concurrently with a reduction in large bubbles by increasing the dosage of defoaming agent or prolonging the mixing time after adding it. All investigated results confirmed that the effects of various parameters on characteristic of entrained air in concrete with full scale mixing are in agreement with the results of concrete investigated in laboratory by many researchers. These findings are beneficial for designing mixtures of Air-SCC containing high volumes of small bubbles that improve the self-compactability and freeze-thaw resistance of concrete