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Co-design-based event-triggered proportional integral controller utilizing fixed period and combined triggering mechanism algorithms for cyber-physical system
No full textCyber-physical systems (CPSs) are integrated systems where the physical process incorporates cyber components which include computation and communication/networking. The integration is usually in the form of a feedback loop, in which the cyber component constantly monitors and controls the physical process. Conventionally, a controller is designed only to achieve a physical goal, bringing the physical output to the desired setpoint with specific performance criteria. On the contrary, CPS needs to take into account both cyber and physical performances by enhancing the integration between both elements. As a result, a co-design approach is required to support the CPS feedback controller design that has the capability to reduce the cyber energy while maintaining the physical performance as the integration enhancement criteria. Due to this benefit, the CPS has started to be implemented for control of process plants. This thesis presents two improved event-based Proportional-Integral (PI) controllers, namely Fixed Period Algorithm (FPA) and Combined Triggering Mechanism Algorithm (CTMA), as CPS feedback controllers for industrial process control. The FPA and CTMA are procedurally designed according to the new co-design framework, where the FPA is designed to reduce the control computation algorithm while the CTMA mitigates the sticking and limit cycles issues. The framework consists of controller design, trade-off design, and design's evaluation processes. A conventional PI is initially designed, then the integration’s enhancement is introduced by using the event-based strategy in trade-off design, hence producing the FPA and CTMA. The development of FPA and CTMA are based on previous event-based PI controllers, namely Durand and Marchand Saturation Algorithm (DMSA) and Durand and Marchand Hybrid Algorithm (DMHA). The CTMA is an extension of FPA that combines absolute and relative errors as a triggering mechanism. By using an improved algorithm, FPA and CTMA reduce the control computation algorithm by 25% (2.4 pJ) and more than 64% (12.8 pJ) as compared to DMSA and DMHA, respectively. The performances of FPA and CTMA in reducing control updates are also compared to DMSA and DMHA for the case with and without network delays on the lag-dominant, balance, and delay-dominant processes. Network delays are represented by constant and time-varying delays, where the maximum delay values are determined using a simple stability criteria and Monte Carlo simulation in the design’s evaluation process. It is found that CTMA reduces control updates by 50% for the lag-dominant process and 10% for the balanced process based on simulation results without the presence of delay. With the presence of delays, the superiority of the CTMA is confirmed especially for the lag-dominant process, where CTMA improves approximately 50% of the computational load reductions and 70% of the physical performance compared to DMHA. Another intriguing discovery is that the FPA can achieve comparable performance to the DMHA despite using a simpler computation algorithm. Taken together, the clear benefits of FPA and CTMA are the trade-off designs that reduce the computational energy by reducing the control updates while maintaining the physical performance. It is envisaged that FPA and CTMA can be utilised for efficient CPS feedback control in industrial process control
Fractal and probabilistic analysis on fatigue crack growth rate of metallic materials
Full text linkLoad-bearing and complex geometry structures such as aircraft wing spars, thick-walled chemical processing vessels, offshore platforms and jacket structures are designed based on damage-tolerant design philosophy. The design employs fracture mechanics and test data to ensure that structural cracks nucleating during the operation will not propagate before they are detected by periodic inspections. The fracture mechanics equation describing the crack tip stress field (fr-field) is expressed in terms of the far-field stress and relies on the crack geometry factor. Closed-form equations for the far-field stress and the crack geometry factors have been established for standard fracture test coupons and relatively simple structures. The unavailability of the crack geometry factor for complex structures and loading renders the use of the fracture mechanics equation impractical. Inaccurate assessment of the fatigue crack and crack growth rates could jeopardize the safety and integrity of the structures. An alternative approach employing fractal analysis to quantify the fatigue crack growth rates of single-phase metallic material is proposed and examined. The fractal approach avoids the need for the crack geometry factor when calculating the crack tip driving force. The fractal analysis is carried out on digital images of the crack with a precision of 1.19 pixel/^m2 employing the box-counting algorithm to determine the fractal dimension (dF) along the edge of the crack length. The analysis is confined to the power law crack growth rate stage (Paris crack growth regime). Compact tension, C(T) specimens fabricated from AISI 410 martensitic stainless steel provide the reference fatigue crack growth response. Results show that the crack initially exhibits a Euclidean nature (dF-1.0). The fractal dimension increases steadily with increasing crack length in Paris region with 1.05<dF <1.24. The corresponding extent of disparity in the crack tip driving force range is between 18<Afr<40 MPaVm. The fractal dimension (dF) correlates linearly with the normalized crack tip driving force range (Afr/frIC) within the Paris region. The coefficient of fractality (CF) is identified as a characteristic material parameter. This enables the multifractal crack growth rate semiempirical model to be established in terms of Paris coefficient and exponent, fractal characteristics, and fatigue fracture properties of the material. A significant statistical dispersion is noted which is typical of a fatigue response. Given this, a probabilistic model based on Walker’s crack growth rate equation considering the variability in the crack tip driving force range, AK and stress ratio, R is developed. The model's validity is examined using selected sets of fatigue crack growth curves of AI-7075-T6, Al- 2024-351 and Ti-6Al-4V alloys. A good fit of the experimental data is noted. The model variance shows a convergent trend with an increasing number of test coupons, thus providing the statistical means of establishing sample sufficiency. The probabilistic model is annexed to the fractal analysis to yield an integrated probabilistic-fractal fracture model. The application of the integrated model to the general structures that lack the crack geometry factor for fatigue crack growth analysis is demonstrated on a bell crack structure. The results are contrasted with AK estimate established through the contour integral (CI) approach using Abaqus software and a close resemblance is noted. Thus, the model could be employed for the prediction of the fatigue crack growth response of engineering structures where the crack geometry factor is not readily available
A dual-battery storage in microgrid system using pinch analysis method
No full textThe energy storage system plays a crucial role in maintaining the power balance between generation and consumption in the microgrid system. Most of the microgrid normally operated with a single built in battery which is not suitable to constantly charge and discharge the energy in short intervals. By having a dual battery storage, one for charging while the other one for discharging, it can be a better solution to prolong the battery lifespan and maintain the efficiency of the battery system. This study proposed that the battery storage is split into two portions for charge and discharge by putting a rule in pinch where the battery need to first be fully charged before discharging. The methodology has been constructed using electric system cascade analysis (ESCA) to determine the efficiency and lifespan of the battery. The results showed that the microgrid system are able to obtain the optimum capacity of solar pv and the method used will be able to optimized the system by identifying the schedule of charging and discharging the batteries. The microgrid system with integration of renewable source and dual-battery energy storage system is economically feasible to meet the load demand especially during peak hours
Development of integrated renewable energy system for sustainable energy supply in offshore platform
Full text linkMalaysia introduced renewable energy as the 5th fuel strategy in the energy-mix under the National Energy Policy in 2001. Malaysia has huge potential renewable energy resources in the form of solar, pico hydro and wind due to its geological characteristic and proximity to equator. Mai Farm in Kalumpang, Selangor is planning to implement a small scale integrated Solar PV, pico hydro, and wind for electricity to power up its facilities. The site has an average solar irradiation at 5.85 kWh/m2/day with the highest solar irradiation at 6.08 kWh/m2/day for month of October which is potential for implementation of solar PV system. The highest wind speed recorded is 5.58 m/sec on month of June. The average wind speed is 4.86 m/sec. The site has a consistent and continuous velocity of water flow coming from the nearest hill via gravity fed 3” PVC pipeline system. This research objective is to investigate the potential energy can be generated and to design an integrated renewable energy system consisting of floating solar PV, pico hydro and wind. The methodology of the research started by gathering data for geographical and meteorological information such as location, elevation, solar irradiation, wind speed and flow data for pico hydro. The load list for Mai Farm also investigated for demand and consumption. All the collected data is used as input to perform simulation and optimization of renewable energy system configurations by HOMER software. Different off-grid configurations of the integrated system proposed are investigated for its levelized cost of electricity (LCOE). The simulation shall be able to assess levelized cost of electricity (LCOE), CO2 avoidance and excess electricity resulting of the integrated renewable energy system
Identification of the unique spheroid by rotated and scaled first order polarization tensor
Full text linkIn the applications of electric and electromagnetic, polarization tensor is usually used to describe the perturbation in electrical field induced by the presence of conducting objects. Due to the fact that polarization tensor carries information about geometry and conductivity of those presented conducting objects, it is possible to substantially use the polarization tensor to describe the objects including reconstructing their images. Some recent applications of polarization tensor include electrical imaging for medical or industrial purposes, characterization of objects by weakly electrosensing fish and also metal detection. Specifically, this research is concerned with the first order polarization tensor when the conducting object is a conducting spheroid. Given the first order polarization tensor of any object, a spheroid can be numerically determined so that the spheroid has the same first order polarization tensor. Here, the main purpose of this research is to investigate the rotated or the scaled first order polarization tensor that is related to a unique spheroid. In order to achieve the objectives of this research, the depolarization factors of both prolate and oblate spheroids are first investigated. It is proven that the eccentricity of both spheroids are unique based on their depolarization factors. After that, the effect of scaling on the first order polarization tensor to the volume, depolarization factors, eccentricity and also semi axes of the spheroid are revealed. Some numerical calculations to identify the volume and semi axes of the spheroid based on a few scaled first order polarization tensors are presented in this research. Furthermore, the effect of rotation on the first order polarization tensor to the conductivity, volume, depolarization factors as well as semi axes of the spheroid are also identified. By the implementation of rotation, a new and improvised flowchart is provided in finding the semi axes of a spheroid based on the different forms of the first order polarization tensor. Last but not least, this research described the uniqueness of the spheroid at a fixed conductivity based on either rotated or scaled first order polarization tensor. As a conclusion, this research would be beneficial in gaining the information about the object specifically for spheroid based on the given first order polarization tensor
Damage-based fretting wear model for life prediction of steel wire ropes
Full text linkSteel wire ropes are designed with different configurations and arrangements to suit various applications. In most manufacturing industries, fatigue test is often conducted to assess the reliability of new wire ropes. The fatigue test is time-consuming and requires a large collection of stress-life data to suit various wire rope designs and stress ratios. Furthermore, during the reliability test, the sample wire rope is subjected to tension-tension fatigue loading and this would induce fatigue damage by fluctuating stresses in the wire material. The current fatigue life prediction method does not take into account the combined bulk fatigue due to tensile stress fluctuations and fretting wear due to relative sliding and contact stress between the stranded wires, which is the dominant damage mechanism in a wire rope. Therefore, the objective of this study is to develop a validated methodology for fatigue life prediction of newly-designed steel wire ropes that incorporates both bulk fatigue and fretting wear conditions. The interaction between wires is explicitly addressed through the friction and fretting wear damage coefficient. Drawn, bare (non-galvanized), as-received high carbon steel wires and steel rods (undrawn) are used as the reference materials. A series of metallurgical and mechanical testing including microstructure analysis, tensile, interrupted fatigue, hardness and sliding wear tests are conducted on the reference materials to obtain the required properties of the wire materials as the model parameters. The model is then integrated into the user material subroutine (UMAT) of the Abaqus finite element analysis (FEA) software to predict the fretting wear and fatigue life of the drawn steel wires. The load cycle block method with each block representing 10,000 cycles is employed for computational efficiency. The associated coefficient of fretting wear damage, cf was determined through calibration with reported experimental data and it was found that when cf = 0.10, the simulated wear depth showed a good agreement with the measured data. The criteria for material removal due to wear and fatigue fracture were established. The material is removed due to wear once the element reaches the terminal value of Dc = 0.90. A new fatigue fracture criterion is proposed based on the total dissipated energy, Ed when the wear depth is 1/3 of the initial wire diameter. Once the energy reaches the critical value of Edc = 32-34 J, fatigue fracture is expected to occur. The number of cycles associated with Edc is taken as the fatigue life of the wire. The calibrated fretting wear damage model was then examined for the reliability of 1x7 steel wire rope samples and the simulated fatigue life showed a good agreement with the measured data by Kiswire. This indicates that the fretting wear damage model is able to quantify the fatigue response of the newly-designed steel wire ropes with various configurations prior to the production of samples for the reliability test. In addition, the design, size, arrangement, and configurations of the wire rope could be improved at an earlier stage based on the reliability requirements. This will increase production productivity and significantly reduce the cost involved in the production and disposal of the steel wire rope that did not achieve the reliability criteria
Review of risk management in Rent to Own (RTO) scheme in Malaysia
Full text linkThis paper focuses on the review of risk management in Rent to Own (RTO) scheme in Malaysia. The objectives are to review the risk management factors in RTO scheme and the strategies to overcome the risk. This study employs a desktop study by collecting the research papers and data in the online databases. RTO Scheme is a concept that employs the rental market like Private Rented Sector (PRS) in the properties that allows ownership after the tenancy period has been expired. The RTO scheme is a type of financial schemes that allows property leasing for between twelve (12) months to five (5) years and ownership upon the maturity of the leasing period. This is an initiative by the Economic Planning Unit (EPU) and the Ministry of Housing and Local Government (MHLG) to implementing the National Housing Policy 2018-2025. The RTO scheme is for home buyers to have financial planning to rent before they buy. The calculation of the mortgage loan for RTO Scheme is based on the rental income and the rental deposit. Additionally, preliminary case study has been conducted to the RTO schemes through onsite and interview with the Developer. The results are to review the risk factors in the RTO Scheme and the marketing strategies. The outcomes of the research are to give input to the house buyers to be confident to buy houses under the RTO Scheme
Big data application in automated valuation model for valuation process
No full textThis research paper will firstly introduce the function of a property valuation in Malaysia and relating valuations needs to the institutional investors and bank. The valuation standards and bases together with the valuer skill sets were discussed in this paper. Thereafter, this paper will be describing the advance of technology like introduction of data and big data in Valuation, blockchain, artificial intelligence and automated valuation system (AVS), automated valuation models (AVM) and other type of potential advance technology. Furthermore, this paper will describe of the changing client expectations such as sustainability and value, long term value, valuation uncertainty and delivery time. Provided that the Automated Valuation Model have given the added value like the valuation uses in future roles, the valuation processin the future, the valuation standards, valuation approaches and basis of value and the skills of the Licensed Valuer. This research will be covering the Literature Review of different papers, reports, insights, journals and articles. Thereby, introduction of the Automated Valuation Models to the users in the Valuation Sector in the Business industry. The conclusion of the paper will summarize the evolution of the Automated Valuation Models (AVS) from the Traditional Valuation Models
Data driven time to collision model for unmanned aerial vehicle control system under various payload and speed conditions
No full textTime-to-collision (TTC) can be defined as the time required for vehicles to collide with another vehicle or static obstacle if they continue at their present speed and on the same path. Hence, the mathematical model of TTC is useful to assist the collision avoidance system (CAS) in any type of autonomous vehicle. This thesis, presents the data-driven TTC model for unmanned aerial vehicles (UAV) control systems under various payloads and speeds condition. The research consists of three phases. The first phase involved the design and development of a data logging system in the multirotor UAV platform. The data acquisition process for model development requires a UAV system, which consists of the quadrotor vehicle structure, onboard flight mission controller and a ground control system. The open sources platform UAV system development and Proportional–Integral–Derivative (PID) controller used for position, altitude and attitude control have been implemented. Experiments are conducted to collect the required flight data in an uncontrolled environment using a developed platform that has been recognized for its performance. In the second phase involved modelling TTC. Controller time stamps, radio control signal magnitude, global positioning system platform and speed parameters are recorded from different payloads, ranging from 0g to 200g. A data filtering algorithm was applied to eliminate data that does not meet the specified minimum horizontal speed. Particles Swarm Optimization (PSO) algorithm was used for optimizing the model and validating with the real data from the experiment. The collected onboard real experimental data for five different payloads have been analysed to develop a mathematical model of TTC through the PSO approach. Based on the experimental data, the fitness function relationship is considered to solve optimization between speed (m/s), payload (g) and their time-to-collision (s). The TTC model predicts the time required for the collision with a static obstacle based on its current flight parameters, such as speed and payload. Finally, the third phase involved the evaluation of the UAV control system with the TTC model throughout the simulation. The TTC model has been implemented in the UAV’s PID controller. Parameters such as initial speed, activation obstacle distances and final distance are introduced in the discussion of this thesis. Based on the workspace simulation environment that has been designed, the TTC model is applied to show the proposed speed based on the UAV's current speed. The activation obstacle distance obtained is a minimum of 5 metres with an initial speed of 2.0 m/s and the proposed speed will be given by the model, continuously. The distance between the obstacle and the reaching point is influenced by the payload. The distance without load is 2.589 metres, and the distance with a 200g load is 1.989 metres, both of which are safer than the specified final distance of 1 metre before a collision. In conclusion, the proposed TTC model has successfully determined the optimal proposed speed based on their current flight parameters under various payload and speed hence, it can be used as a risk assessment metric in UAV’s CAS
Interlaminar fatigue damage model of carbon fiber-reinforced polymer composite laminates
No full textLoad-bearing structures made of carbon fiber-reinforced polymer (CFRP) composite laminates, such as the skin of aircraft wings, helicopter rotors, and wind turbine blades, are likely to experience time-varying loads. The fluctuating stresses could result in fatigue damage and failure of the laminates in the form of matrix cracking, fiber breakage and buckling, fiber/matrix debonding, and interface delamination. The latter is a significant damage mechanism in view of the relatively weak interlaminar bonding. In this respect, the current research has developed the interlaminar damage-based fatigue life model of fibre-reinforced polymer (FRP) composite laminates. The model incorporates the observed continuous cyclic degradation of interlaminar properties. The bi-linear traction-relative displacement softening rule for the cohesive zone model (CZM) is extended to accommodate the normalized interlaminar strength and stiffness degradation under the fatigue load cycles. The normalized fatigue life model accounts for the effect of mean stress on the observed interlaminar fatigue lives. Fatigue crack nucleation (separation) is governed by the interface's critical strain energy release rates. Hybrid finite element-experimental approach is employed to establish material parameters for the quasi static CZM. The experimental fatigue data for Mode I and Mode II of CFRP composite laminates from literature is employed to extract the residual properties. The normalized properties versus normalized fatigue life curves are then quantified based on the “wear-out” failure model. The curves are characterized by the curve fitting parameters α, β, λ, γ, μ, and ϕ for the interlaminar tensile strength, stiffness, and fracture energy. In view of the relatively large number of load cycles to capture the initiation and propagation of the interlaminar crack, the load cycle block approach is devised to improve computational efficiency. The model is coded in the UMAT Subroutine of Abaqus FE software. It is examined for interlaminar fatigue of CFRP composite laminate under Mode I , Mode II and mixed-mode loading conditions with a stress ratio, κ = 0.11, 0.15, and 0.1, respectively. The damage begins at approximately 8200 cycles and interface crack extends after accumulating 14100 applied fatigue cycles for Mode I load case. The damage begins at approximately 220000 cycles and interface crack extends after accumulating 350700 applied fatigue cycles for Mode II load case. The stress is highly concentrated at the crack front region. The FE-predicted fatigue lives are comparable with measured data and within the experimental scatter, hence validating the model. The crack tip opening and sliding displacements evolve with an initially slow rate of 2.6x10-9 and 1.85x10-10 mm/cycle respectively up to the onset of fatigue crack nucleation event at approximately 188800 cycles and then peaks at 1.5x10-7 and 7.1x10-8 mm/cycle respectively as the interface crack begins to accelerate after accumulating 284700 applied fatigue cycles for mixed mode flexure fatigue loading. The developed model will benefit various industries, including aerospace, automotive, and maritime, involved in the structural design for performance, reliability prediction, life extension and failure investigation of CFRP composite laminate structures