Communities in UTM Open Science
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Seismic performance of fixed offshore structures under far field earthquake
(Universiti Teknologi Malaysia, 2016) Wan Ahmad, Saffuan
Malaysia is located at a very low seismic activity area but the active earthquake fault line is through the centre of Sumatran, Indonesia which lies just approximately 350km from Peninsular Malaysia. The earthquake that occurs in Indonesia was due to the strike-slip fault that has affected the building structure in Malaysia. It happens because of the amplification process generated from the source of the event. The aim of this study was to evaluate performance and vulnerability of offshore structures using real peak ground acceleration. Between 2004 and 2012, a few interpolate earthquake events with magnitudes of Mw = 3.5 were recorded. These data were provided by Malaysia Meteorological Department Malaysia (MMD) and 10 of the events were shallow strikeslip events. The earthquake Off West Coast of Sumatra that happened on 26th December 2004 has been selected as the biggest earthquake event in the Malaysia region during that time. By using regression analysis, attenuation function that has been developed and the value of maximum ground acceleration that hit offshore platform was identified. Using the real peak ground acceleration, vulnerability and performance of 5 models of typical offshore platforms were evaluated. The typical fixed offshore platform was analysed by using SAP 2000 finite element software. Time history analysis and pushover analysis were done on the models in which the results were compared to the resistance value itself and the performance indicator produced by FEMA-365. The offshore structure was analysed by several steps in pushover in terms of x-direction and y-direction and some parts of the structure were classified as Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) level of performance. Moreover, the results retrieved from the real scale analysis were compared to the experimental work that employed the harmonic shaking table machine. In conclusion, the findings contribute to the seismic performance of offshore platforms in Malaysia. It proves that the offshore platforms in the country is very well sustained with a high-end performance.
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Hybrid peak to average power ratio reduction in orthogonal frequency division multiplexing system
(Universiti Teknologi Malaysia, 2017) Jaber, Ali Yasir
Multi-carrier systems based on Orthogonal Frequency Division Multiplexing (OFDM) is a widely-used modulation in wireless communication systems because it enables high throughput data transfer and is robust against frequency selective fading caused by the multipath wireless channel. Nevertheless, OFDM suffers from disadvantages such as high Peak-to-Average Power Ratio (PAPR) and high sensitivity to Carrier Frequency Offset (CFO) which leads to a loss of subcarrier orthogonality and severe system degradation. Thus, a suitable reduction technique should be used in OFDM system to mitigate these drawbacks. Mitigation of the impacts of PAPR and Inter-Carrier Interference (ICI) due to CFO at the OFDM transmitter is the main target of this work. In this work, PAPR and ICI reduction methods are proposed at the OFDM transmitter. Clipping Peaks Amplifying Bottoms (CPAB) method is developed to reduce PAPR, where the negative peaks of the clipped OFDM signal are amplified. However, to reduce further PAPR level, a combination of Partial Transmit Sequence (PTS) with Cascade CPAB (PTS-CCPAB) is proposed. To improve BER performance, a Carrier Frequency Offset (CFO) compensation method is added to the hybrid PTS-CCPAB. The proposed work was conducted in MATLAB simulator using the parameters of Wireless Access Vehicular Environment (WAVE) IEEE 802.11p standard. The hybrid PTS-CCPAB/CFO introduced a PAPR Reduction Gain (RG) of 39% compared to the conventional system. Also, system performance at BER =10-4 improved by 12% and 5% over Additive White Gaussian Channel (AWGN) and Rayleigh channels respectively compared to the conventional system. Overall results show that the proposed work is a suitable solution to mitigate the loss of subcarrier orthogonality and system degradation by improving both PAPR and BER performances. The proposed work can be used in most multicarrier wireless communication system.
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Enhancing efficiency and robustness against collision attack using mersenne number transform for hash function
(Universiti Teknologi Malaysia, 2022) Omar Maetouq, Ali Aboulqasim
The most popular hash algorithms functions are Message Digest 5 (MD5), Secure Hash Function1 (SHA-1) and Secure Hash Function 2 (SHA-2). These algorithms utilise the Merkle-Damgard structure. The structure's weaknesses have been discovered, especially against a collision attacks. In this attack, a colluder tries to find two different input messages that produce the same hash result with an effort of less than 2n/2 (where n = length of hash value). That required at most 239 MD5 operations to find a collision, much lower than the intended 264. For SHA-1 with n=160, the collision can be found with effort less than 269, much lower than the intended 280. The fact that collisions are now easily generated, means that these algorithms can no longer be reliably used. Therefore, this study proposed a hash function that is more efficient and robust against collision attacks using the New Mersenne Number Transform (NMNT) and a secret key to achieve the required robustness and maintain efficiency. NMNT is utilised due to its characteristics that are analogous to cryptographic requirements, such as sensitivity, diffusion, and parameterisation, while the secret key is used to increase the scheme’s security. The proposed hash scheme in this study is called Hash Mersenne Transform (HMT). It takes an arbitrary length as input to generate a hash value with variable lengths (128, 256 and 512-bits). HMT consisted of four main stages, namely: Pre-Processing, applying new Mersenne number transform, generating a secret key, and Hash value. Security and performance analyses are conducted to validate the robustness and efficiency of the proposed scheme HMT. To investigate the collision resistance capability of the HMT, collision tests are performed which focus on the possibility of collision between every two hash pairs. From the results, it found that the number of hits of HMT does not exceed 1 for 128-bits hash values, 2 for 256-bits hash values and 3 for 512- bit hash values. This indicates that the HMT has good collision resistance which provides high robustness against collision attacks. In terms of efficiency analysis, the proposed scheme HMT is considered more efficient than existing schemes due to its reduction in execution time. In particular, for long messages with a length equal to 10 MB, the time cost of the HMT is two times less than for SHA-2. In addition, statistical analyses are also employed, which involved the hash value distribution, confusion and diffusion, and sensitivity of hash value to message, secret key and image. Statistics related to mean changed bit number, mean changed probability and their standard deviations are considered the diffusion and confusion quality of the proposed scheme HMT. The results show that the standard deviations are very small for the proposed scheme HMT, the mean changed probability is very close to 50%, and the mean changed bit number is likewise close to half of the hash value lengths. This suggests that the proposed scheme HMT has a stable diffusion and confusion capability. Text messages and images are used to measure the sensitivity of the HMT. The results demonstrates that even a small alteration in the input message or image, such as 1-bit, can cause a significant change in the final hash value. These findings prove that HMT has high hash sensitivity. Comparing the security and performance analysis to other hash functions, it can be concluded that the proposed scheme HMT is suitable for data integrity, message authentication, and blockchain applications.
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A malicious URL detection framework using priority coefficient and feature evaluation
(Universiti Teknologi Malaysia, 2023) Rafsanjani, Ahmad Sahban
Malicious Uniform Resource Locators (URLs) are one of the major threats in cybersecurity. Cyber attackers spread malicious URLs to carry out attacks such as phishing and malware, which lead unsuspecting visitors into scams, resulting in monetary loss, information theft, and other threats to website users. At present, malicious URLs are detected using blacklist and heuristic methods, but these methods lack the ability to detect new and obfuscated URLs. Machine learning and deep learning methods have been seen as popular methods for improving the previous method to detect malicious URLs. However, these methods are entirely datadependent, and a large, updated dataset is necessary for the training to create an effective detection method. Besides, accuracy and detection mostly depend on the quality of training data. This research developed a framework to detect malicious URL based on predefined static feature classification by allocating priority coefficients and feature evaluation methods. The feature classification employed 39 classes of blacklist, lexical, host- based, and content-based features. A dataset containing 2000 real-world URLs was gathered from two popular phishing and malware websites, URLhaus and PhishTank. In the experiment, the proposed framework was evaluated with three supervised machine learning methods: Support Vector Machine (SVM), Random Forest (RF), and Bayesian Network (BN). The result showed that the proposed framework outperformed these methods. In addition, the proposed framework was benchmarked with three comprehensive malicious URL detection methods, which were Precise Phishing Detection with Recurrent Convolutional Neural Networks, Li, and URLNet in terms of accuracy and precision. The results showed that the proposed framework achieved a detection accuracy of 98.95% and a precision value of 98.60%. In sum, the developed malicious URL framework significantly improves the detection in terms of accuracy.
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Masonry infilled reinforced concrete frames retrofitted with vertical post-tensioned bars
(Universiti Teknologi Malaysia, 2016) Soltanzadeh, Gholamreza
Reinforced concrete (RC) frames filled with clay brick walls are among structures that have been damaged in many past earthquakes. The main aim of this study is to propose a new retrofit method, which can increase lateral strength, stiffness, energy dissipation capacity and ductility of infilled RC frames. To achieve this aim, at first seismic behaviour of several bare and infill RC frames were studied through experimental and numerical studies. Then the proposed retrofit method which was based on external post-tensioning of infilled frames by vertical bars was developed. Finally, the effectiveness of the proposed retrofit method was evaluated through experimental test. In the test, a total eight RC frames with two different aspect ratios of 0.5 and 1.0 were constructed with the scale of 1:3. Experimental test was performed using a quasi-static cyclic loading. For all experimental test, the values of initial lateral stiffness, effective stiffness and ultimate lateral strength were determined. The ductility and energy dissipation capacity were calculated using hysteresis curve obtained from cyclic loading. Results indicated that the presence of brick walls reduced the ductility of bare frames. Ductility of bare and infill frames are dependent on the aspect ratios. Bare frames with the higher aspect ratio has 70% higher ductility compared to that of lower aspect ratio. Failure mode of frames was also dependent on the aspect ratio. The presence of brick walls increased three and half times the energy dissipation capacity of the frame with higher aspect ratio. The proposed posttensioning method increased ultimate lateral strength and ductility of infilled frames two and five times, respectively. Increase in the ultimate lateral strength of infilled frames was dependent on their aspect ratio. Increase in the ultimate lateral strength of the frame with lowest aspect ratio was three times more than that of highest aspect ratio. Similarly, the ductility of retrofitted frame with the higher aspect ratio was 45% more than that of lower aspect ratio. The post-tensioning method increased the energy dissipation capacity of retrofitted frames. The retrofitted frame with higher aspect ratio dissipated 10% more energy compared to the frame with lower aspect ratio. The proposed retrofit method using post tensioning improved ductility, energy dissipation capacity and ultimate lateral strength of infill frames with opening. However compared to fully infill frames without opening, the rate of improvements was slightly lower. In general, results of experimental and numerical studies in this research showed that post-tensioning can improve stiffness, ductility, ultimate lateral strength and energy dissipations capacity behaviour of infilled RC frame.