Analytical gradient-based optimization of offshore wind turbine substructures under fatigue and extreme loads

Design optimization of offshore wind turbine support structures is an expensive task due to the highly-constrained, non-convex and non-linear nature of the design problem. A good depth of detail in the problem formulation can give useful insights in the practical design process, but may also compromise the efficiency. This paper presents an analytical gradient-based method to solve the problem in an effective and efficient way. The design sensitivities of the objective and constraint functions are evaluated analytically, while the optimization procedure is performed in the time domain, subjected to sizing, eigenfrequency, extreme load and fatigue load constraints. A case study on the OC4 and UpWind jacket substructures show that the method was reliable and consistent in delivering superior efficiency and accuracy in the optimization study, as compared with the conventional finite difference approach. The global optimum was probably achieved in the design optimization process, where the large number of design constraints implemented can possibly be the blessing in disguise, as they seem to enable the optimizer to find the global optimum. Both the buckling and fatigue load constraints had significant influence over the design of tubular members and joints, while each component is oriented to maximize the utilization against the prescribed limit state functions.© 2016 Published by Elsevier Ltd. Open Access

Influence of substrate heating on hole geometry and spatter area in femtosecond laser drilling of silicon

The objective of this research is to evaluate the effects of the hole geometry and the spatter area around the drilled hole by femtosecond laser deep drilling on silicon with various temperatures. Deep through holes were produced on single crystal silicon wafer femtosecond laser at elevated temperatures ranging from 300K to 873K in a step of 100K. The laser drilling efficiency is increased by 56% when the temperature is elevated from 300K to 873K. The spatter area is found to continuously decrease with increasing substrate temperature. The reason for such changes is discussed based on the enhanced laser energy absorption at the elevated temperature.open0

Application of infrared thermography in computer aided diagnosis

The invention of thermography, in the 1950s, posed a formidable problem to the research community: What is the relationship between disease and heat radiation captured with Infrared (IR) cameras? The research community responded with a continuous effort to find this crucial relationship. This effort was aided by advances in processing techniques, improved sensitivity and spatial resolution of thermal sensors. However, despite this progress fundamental issues with this imaging modality still remain. The main problem is that the link between disease and heat radiation is complex and in many cases even non-linear. Furthermore, the change in heat radiation as well as the change in radiation pattern, which indicate disease, is minute. On a technical level, this poses high requirements on image capturing and processing. On a more abstract level, these problems lead to inter-observer variability and on an even more abstract level they lead to a lack of trust in this imaging modality. In this review, we adopt the position that these problems can only be solved through a strict application of scientific principles and objective performance assessment. Computing machinery is inherently objective; this helps us to apply scientific principles in a transparent way and to assess the performance results. As a consequence, we aim to promote thermography based Computer-Aided Diagnosis (CAD) systems. Another benefit of CAD systems comes from the fact that the diagnostic accuracy is linked to the capability of the computing machinery and, in general, computers become ever more potent. We predict that a pervasive application of computers and networking technology in medicine will help us to overcome the shortcomings of any single imaging modality and this will pave the way for integrated health care systems which maximize the quality of patient care

Quantification of the effect of electrical and thermal parameters on radiofrequency ablation for concentric tumour model of different sizes

10.1016/j.jtherbio.2015.03.002Journal of Thermal Biology5123-3

Flight maneuverability characteristics of the F-16 CFD and correlation with its intake total pressure recovery and distortion

An investigation of the intake pressure recovery and distortion effects observed by varying maneuverability conditions of the F-16 was conducted. Simulations were conducted by using the Partial Differential Equation (PDE) calculator COMSOL. Results were validated with the classical s-duct, showing reasonable qualitative agreement. The maneuverability of the F-16 was defined using three factors: Mach number, angle of attack and angle of sideslip. The values of pressure recovery and distortion were measured at the Aerodynamic Interface Plane (AIP). Two sets of simulations were conducted: one to compare the sea level and 10 km altitude flight condition and another to correlate the required air intake and engine performance with pressure recovery and distortion at the AIP. Results of the flight level comparisons showed a slightly higher pressure recovery at 10 km of 0.985 compared to sea level condition value of 0.983. Distortion coefficient values for both conditions were however similar at 0.120. The difference in recovery values is attributed to the less viscous characteristic of air at higher altitude. This resulted in lower secondary flow formations in the intake. With increasing altitude, temperature plots showed a linear decreasing profile throughout the intake. The study provides a platform to a future model which couples the results obtained from the intake as inlet conditions to turbine flow simulations. This would provide a more holistic understanding of the propulsion system in the F-16

Effect of the angle of attack on the YF-16 inlet

A k-ε numerical analysis of a fuselage-shielded inlet similar to that of the YF-16 was conducted. The simulations were conducted at Mach 0.6 at -10° to 40° angles of attack. Results were validated with experimental values obtained in the 90° bending pipe and circular S-duct. Pre-entry separation effects were simulated by a flat plate and offset by the diverter height. Results showed that the pressure recoveries resembled that of the YF-16 inlet, where negligible losses were up to 30° angle of attack (AOA). The increase in the angle of attack also resulted in the diminishing strength of the twin swirls

Applying Taguchi’s off-line quality control method and ANOVA on the maneuverability of the F-5E intake

Air quality leading up to the compressor face of a fighter aircraft determines the engine performance considerably. A deficiency in the quality could lead to flutter or stall in the engines. In this study, two statistical methods; the Taguchi Method (TM) and the Analysis of Variance (ANOVA) are used to evaluate airflow quality through the intake via fighter aircraft maneuvers. The three factors associated directly with aircraft maneuverability are the Mach number (M), Angles of Incident (α) and Sideslip (β). Desirable air quality can be described as having high pressure recoveries as well as low distortion at the Aerodynamic Interface Plane (AIP). The intake studied is the port side F-5E duct. Results show that an increase in the Mach number affects the streamwise diffusion of the fluid more than the changing the angles of attack and sideslip, resulting in lower pressure recovery. The secondary flow formation in the streamwise direction is unable to dissipate and increases in strength with increasing Mach number. The curvature in the z-axis is more pronounced than that existing in the x-axis, leading to the formation of more adverse pressure gradients forming and hence greater secondary flow strength. This results in a more distorted flow leading to the AIP. This observation is in tandem with the values of the DC (60) readings obtained. The F-5E’s Taguchi’s Method results show that Mach number had the greatest effect on pressure recovery, and AOA affected distortion most considerably. Results from ANOVA show that Factors A, B and C and Interactions AC and BC affect the distortion of airflow. However, Factor B or the angle of attack affects this distortion most significantly

Separable and non-separable discrete wavelet transform based texture features and image classification of breast thermograms

Highly sensitive infrared cameras can produce high-resolution diagnostic images of the temperature and vascular changes of breasts. Wavelet transform based features are suitable in extracting the texture difference information of these images due to their scale-space decomposition. The objective of this study is to investigate the potential of extracted features in differentiating between breast lesions by comparing the two corresponding pectoral regions of two breast thermograms. The pectoral regions of breastsare important because near 50% of all breast cancer is located in this region. In this study, the pectoral region of the left breast is selected. Then the corresponding pectoral region of the right breast is identified. Texture features based on the first and the second sets of statistics are extracted from wavelet decomposed images of the pectoral regions of two breast thermograms. Principal component analysis is used to reduce dimension and an Adaboost classifier to evaluate classification performance. A number of different wavelet features are compared and it is shown that complex non-separable 2D discrete wavelet transform features perform better than their real separable counterparts