Surface modification of lean duplex stainless steels by low temperature plasma nitriding

Duplex stainless steels (DSS) have been considered as one of new materials for equipment used in the offshore gas and oil industry since these steels possess favourable mechanical and high corrosion-resistance properties. However, the surface hardness and wear resistance of DSS are relatively poor and it had shown that their wear in sea water is a major concern. Improving the wear resistance without losing corrosion resistance was an arduous challenge throughout the surface engineering industry. Recently, a new low-temperature plasma surface alloying technique has been developed to achieve combined improvements in hardness, wear resistance and fatigue properties for austenitic stainless steels without impairing their corrosion behaviour due to the formation of S-phase (Prof. Hanshan Dong, 2010). A great quantity reports have been published about S-phase in austenite stainless steels during the past two decades. A few researches have been reported on formation of S-phase in duplex stainless steels. However, no conclusions have been made and some disputes are still active. Hence, the aim of this project is to study the response of three duplex stainless steels on forming S-phase surface layer by low-temperature plasma nitriding

Performance Analysis and Optimization of Compressed Air Energy Storage Integrated with Latent Thermal Energy Storage

Recovering compression waste heat using latent thermal energy storage (LTES) is a promising method to enhance the round-trip efficiency of compressed air energy storage (CAES) systems. In this study, a systematic thermodynamic model coupled with a concentric diffusion heat transfer model of the cylindrical packed-bed LTES is established for a CAES system, and the numerical simulation model is validated by experimental data in the reference. Based on the numerical model, the charging–discharging performance of LTES and CAES systems is evaluated under different layouts of phase change materials (PCMs) in LTES, and the optimal layout of PCM is specified as a three-stage layout, since the exergy efficiency of LTES and round-trip efficiency are improved by 8.2% and 6.9% compared with a one-stage layout. Then, the proportion of three PCMs is optimized using response surface methods. The optimization results indicate that the exergy efficiency of LTES and round-trip efficiency of the CAES system are expected to be 80.9% and 73.3% under the PCM proportion of 0.48:0.3:0.22 for three stages, which are 7.0% and 13.1% higher than the original three-stage PCMs with equal proportions

Combating the Tribo-Corrosion of LDX2404 Lean Duplex Stainless Steel by Low Temperature Plasma Nitriding

A lean duplex stainless steel, LDX2404, was DC plasma nitrided under a range of treatment conditions. The microstructure characterisation evaluation of the treated samples revealed that a dense, super-hard surface layer can be produced by low-temperature (<450 °C) plasma treatments. The original austenite phase became S-phase and the ferrite phase was supersaturated with nitrogen and ε-Fe3N nitride precipitated from it. When plasma nitriding was carried out at above 450 °C, chromium nitrides precipitated in the surface nitrided layer. Compared to the untreated samples, the surface hardness of the lean duplex stainless steel (DSS) is increased up to four times. The dry wear resistance increased when increasing the treatment temperature. In contrast, the low-temperature treated samples showed the best performance in the electrochemical corrosion and corrosion-wear tests; the performance of the high temperature (>450 °C) plasma nitrided samples was found to be significantly worse than that of the untreated material

Evaluation of ideal double-tank hybrid pneumatic engine system under different compression cycle scenarios

A double-tank hybrid pneumatic engine system, with one low pressure tank and one high pressure tank has been proposed to improve the energy conversion efficiency and auxiliary braking power output of regenerative braking of vehicles. The performance of three ideal compression cycle scenarios for the double-tank system has been investigated and the results are compared with that of ideal one-tank scenario in order to identify the optimal compression cycle under different primary performance requirements. Results indicate the maximum brake mean effective pressure can be improved to not over 0.2 MPa less than the HP tank pressure and the highest improvement of total air mass recovered can reach over 40% utilising the double-tank scenarios. Scenario 3 performs the best at the braking power output ability, while scenario 4 shows the greatest high pressure compressed air recovery potential. Considering about the LP tank air sources, scenario 2 is the only one that can operate independently without other air complements, which also performs the best at the energy conversion efficiency among the three double-tank scenarios

Three-dimensional reversible watermarking with tamper detection and localization capability for volumetric DICOM images

Teleradiology brings the convenience of global medical record access along with the concerns over the security of medical images transmitted over the open network. With the prevailing adoption of 3-D imaging modalities, it is vital to develop a security mechanism to provide large volumes of medical images with privacy and reliability. This Final Year Project aims to develop a 3-D fully reversible dual layer digital watermarking scheme with tamper localization capability for volumetric DICOM images. Firstly, a new and improved method of implementing tamper localization, which involves utilizing the 3-D property of volumetric data and developing an improved adaptive data insertion algorithm, was developed to achieve much faster processing time at both transmitter and detector sides without compromising tamper localization accuracy. The performance of the scheme based on the proposed method was evaluated by using sample volumetric DICOM images. Results show that the scheme achieved on average about 65% and 72% reduction in watermarking and de-watermarking processing time, respectively, and was able to ensure confidentiality, authenticity and integrity. For cases where the images had been tampered, the scheme can detect and localize the tampered areas in the images accurately. A second method was developed to achieve the full recovery of tamper-free regions in tampered image slices, which allows re-watermarking of tampered image slices. Performance evaluations show that the scheme implemented by the second method achieves the complete restoration capability and retains the desirable features and functionalities achieved by the first method. The new property allows tampered images to be re-watermarked and circulated among radiologists for medical practice as long as the tamper is located inside the regions of non interest, which substantially avoids unnecessary retransmission that is time consuming and costly.Bachelor of Engineerin

UAS Collision Warning and Passive Sensor Fusion Algorithms for Multiple Acoustic Transient Emitter Localization

This dissertation considers two important topics in the area of estimation, target tracking and sensor fusion. The first topic is closest point of approach (CPA) prediction for unmanned aircraft systems (UAS) collision warning and the second topic is passive sensor fusion for multiple acoustic transient emitter localization. To operate within a controlled airspace, UAS must have the capability to sense and avoid collisions with non-cooperative aircraft. This dissertation presents an inexpensive system design and develops an algorithm for estimating the CPA between the ownship and the intruder and a collision warning scheme using only bistatic range and range rate measurements from a multistatic radar. Since it is vital for soldiers to be able to accurately localize sources of hostile fire in the battlefield for situational awareness and threat assessment, this dissertation develops both centralized and distributed passive sensor fusion algorithms to accurately estimate the number of acoustic transient emitters and their locations using bearing and time of arrival measurements

An improved tamper detection and localization scheme for volumetric DICOM images

The development of teleradiology brings the convenience of global medical record access along with the concerns over the security of medical images transmitted over the open network. With the prevailing adoption of three-dimensional (3-D) imaging modalities, it is vital to develop a security mechanism to provide large volumes of medical images with privacy and reliability. This paper presents the development of a new and improved method of implementing tamper detection and localization based on a fully reversible digital watermarking scheme for the protection of volumetric DICOM images. This tamper detection and localization method utilizes the 3-D property of volumetric data to achieve much faster processing time at both sender and receiver sides without compromising tamper localization accuracy. The performance of the proposed scheme was evaluated by using sample volumetric DICOM images. Results show that the scheme achieved on average about 65 % and 72 % reduction in watermarking and dewatermarking processing time, respectively. For cases where the images had been tampered, it is possible to detect and localize the tampered areas with improved localization resolution in the images using the scheme

Modeling and control strategy for hydrogen production systems coupled with PV and battery storage

Environmental conditions can significantly affect the performance of photovoltaic (PV) hydrogen production systems, resulting in fluctuations in PV output and suboptimal hydrogen production. In order to solve these problems, a voltage stabilization control based approach has been implemented for a photovoltaic integrated hydrogen production system, which is based on an existing hydrogen production model coupled to PV storage. The aim of this approach is to enhance system stability, improve the quality of photovoltaic power generation, and optimize hydrogen production. The strategy includes maximum power point tracking (MPPT) control for the PV system, as well as coordinated control of the electrochemical energy storage system to ensure stable bus voltage and efficient use of solar resources. The effectiveness of this control strategy was demonstrated by simulation

Performance Analysis and Optimization of Compressed Air Energy Storage Integrated with Latent Thermal Energy Storage

Recovering compression waste heat using latent thermal energy storage (LTES) is a promising method to enhance the round-trip efficiency of compressed air energy storage (CAES) systems. In this study, a systematic thermodynamic model coupled with a concentric diffusion heat transfer model of the cylindrical packed-bed LTES is established for a CAES system, and the numerical simulation model is validated by experimental data in the reference. Based on the numerical model, the charging–discharging performance of LTES and CAES systems is evaluated under different layouts of phase change materials (PCMs) in LTES, and the optimal layout of PCM is specified as a three-stage layout, since the exergy efficiency of LTES and round-trip efficiency are improved by 8.2% and 6.9% compared with a one-stage layout. Then, the proportion of three PCMs is optimized using response surface methods. The optimization results indicate that the exergy efficiency of LTES and round-trip efficiency of the CAES system are expected to be 80.9% and 73.3% under the PCM proportion of 0.48:0.3:0.22 for three stages, which are 7.0% and 13.1% higher than the original three-stage PCMs with equal proportions