Literature survey

About: Literature survey is a research topic. Over the lifetime, 15372 publications have been published within this topic receiving 459196 citations.

Facial Landmark Detection: a Literature Survey

Abstract: The locations of the fiducial facial landmark points around facial components and facial contour capture the rigid and non-rigid facial deformations due to head movements and facial expressions. They are hence important for various facial analysis tasks. Many facial landmark detection algorithms have been developed to automatically detect those key points over the years, and in this paper, we perform an extensive review of them. We classify the facial landmark detection algorithms into three major categories: holistic methods, Constrained Local Model (CLM) methods, and the regression-based methods. They differ in the ways to utilize the facial appearance and shape information. The holistic methods explicitly build models to represent the global facial appearance and shape information. The CLMs explicitly leverage the global shape model but build the local appearance models. The regression-based methods implicitly capture facial shape and appearance information. For algorithms within each category, we discuss their underlying theories as well as their differences. We also compare their performances on both controlled and in the wild benchmark datasets, under varying facial expressions, head poses, and occlusion. Based on the evaluations, we point out their respective strengths and weaknesses. There is also a separate section to review the latest deep learning-based algorithms. The survey also includes a listing of the benchmark databases and existing software. Finally, we identify future research directions, including combining methods in different categories to leverage their respective strengths to solve landmark detection "in-the-wild".

Evaluation of Self-Starting Vertical Axis Wind Turbines for Stand-Alone Applications

Abstract: There is an urgent need for economical, clean, sustainable energy supplies, not only in densely populated areas where electricity grids are appropriate, but also in rural areas where stand-alone power supply systems are often more suitable. Although electrical power supply is very versatile and convenient, it introduces unnecessary complexity for some off-grid applications where direct mechanical shaft power can conveniently be provided by a wind turbine. Wind energy is one of the more promising renewable energy sources. Most wind turbines are of the horizontal axis type, but vertical axis wind turbines or VAWTs have some advantages for direct mechanical drive applications. They need no tail or yaw mechanism to orient them into the wind and power is easily transmitted via a vertical shaft to a load at ground level. Blades may be of uniform section and untwisted, making them relatively easy to fabricate or extrude, unlike the blades of horizontal axis wind turbines (HAWTs) which should be twisted and tapered for optimum performance. Savonius rotor VAWTs are simple and may have a place where the power requirement is only a few Watts, but they are inefficient and uneconomical for applications with larger power requirements. VAWTs based on the Darrieus rotor principle are potentially more efficient and more economical, but those with fixed pitch blades have hitherto been regarded as unsuitable for stand-alone use due to their lack of starting torque and low speed torque. This starting torque problem can be overcome by using variable pitch blades, but most existing variable pitch VAWTs, variously known as giromills or cycloturbines, need wind direction sensors, microprocessors and servomotors to control the blade pitch, making them impracticable for stand-alone, non-electrical applications. A simpler but less well known concept is passive or self-acting variable pitch in which the blades are free to pitch under the combined action of aerodynamic and inertial forces in such a way that a favourable blade angle of attack is maintained without the complexity of conventional variable pitch systems. Several fonns of self-acting variable pitch VAWTs or SAPVAWTs have been described in the literature, several patents exist for variants on the concept, and at least two companies world-wide have attempted to commercialise their designs. However the aerodynamic behaviour of these devices has been little understood and most designs appear to have been based on nothing more than a qualitative appreciation of the potential advantages of the concept. This thesis assesses the potential of both fixed and passive variable pitch vertical axis wind turbines to provide economical stand-alone power for direct mechanical drive applications. It is shown that the starting torque and low speed torque problems of VAWTs can be overcome either by passive variable pitch or by a combination of suitable blade aerofoil sections, either rigid or flexible, and transmissions which unload the rotor at low speeds so that high starting torque is not necessary. The work done for this thesis is made up of a sequence of stages, each following logically from the previous one: 1. Several tasks have been identified which could be performed effectively by a self-starting vertical axis wind turbine using direct mechanical drive. These include, a. pumping water, b. purifying and/or desalinating water by reverse osmosis, c. heating and cooling using vapour compression heat pumps, d. mixing and aerating water bodies and e. heating water by fluid turbulence. Thus it is apparent that such a system has the potential to make a useful contribution to society. 2. A literature survey of existing VAWT designs has been carried out to assess whether any are suitable for these applications. 3. As no suitable existing design was identified, an improved form of SAPVAWT has been developed and patented. 4. To optimise the performance of the improved SAPVAWT, a mathematical model has been developed in collaboration with Mr Leo Lazauskas of the University of Adelaide (see Kirke and Lazauskas, 1991, Lazauskas and Kirke, 1992). As far as the author of the present thesis is aware, this is the only existing mathematical model able to predict the performance of this particular type of SAPVAWT, and one of only two worldwide which model SAPVAWTs. 5. In order to use the mathematical model to predict the performance of a given SAPVAWT, it is necessary to have lift, drag and moment data for the aerofoil profile to be used, over a wide range of incidence and Reynolds numbers. A literature search has revealed large gaps in the existing data. 6. Wind tunnel testing has been carried out to assess the effect of camber on the performance of one set of NACA sections at low Reynolds number, and performance figures for other sections have been estimated by interpolation from existing data. 7. Using the assembled aerofoil data, both experimental and estimated, the mathematical model has been used to predict the performance of both fixed and variable pitch VAWTs. It has been found to predict correctly the performance of known fixed pitch VAWTs and has then been used to predict the performance of fixed pitch VAWTs with cambered blades using newly developed profiles that exhibit superior characteristics at low Reynolds numbers. Results indicate that fixed pitch VAWTs using these blade sections should self-start reliably. 8. To validate the mathematical model predictions for self-acting variable pitch, a two metre diameter physical model has been built and tested in a wind tunnel, and acceptable agreement has been obtained between predicted and measured performance. 9. To demonstrate the performance of a SAP VA WT under field conditions, a six metre diameter turbine has been designed, fabricated, erected and tested. 10. Because a prime mover such as a wind turbine is of no use unless it drives a toad, particular attention has been paid to the behaviour of complete systems, including the wind turbine, the transmission and the load. It is concluded that VAWTs with the improved self-starting and low speed torque characteristics described in this thesis have considerable potential in stand-alone, direct mechanical drive applications.

Fluid-structure interaction in liquid- filled pipe systems : a review

Abstract: A review of literature on transient phenomena in liquid-filled pipe systems is presented . Waterhammer , cavitation , structural dynamics and fluid-structure interaction (FSI) are the subjects dealt with . The emphasis is on the history of FSI research in the time-domain . Waterhammer is the most probable cause for the transient vibration of liquid-filled pipe systems . When correctly modelling the liquid and pipe vibrations , FSI must be taken into account . The development of adequate mathematical models and their validation by physical experiments is surveyed . ÷ 1996 Academic Press Limited W HEN STARTING HIS RESEARCH ON FLUID-STRUCTURE interaction (FSI) in liquid-filled pipe systems in 1986 , the author found the literature survey by Wiggert (1986) very helpful . This paper is an extension of Wiggert’s survey . Its aim is twofold : (i) to be a starting-point for researchers new in the field and (ii) to be a state-of-the-art record of relevant contributions to the subject . The emphasis of the present review is on transient phenomena and , consequently , time-domain analyses . FSI is presented as an extension of conventional waterhammer theory , as in Skalak’s (1956) classical article . FSI , and some practical sources of excitation , are shown schematically in Figure 1 . Pipe systems experience severe dynamic forces during a waterhammer event . When these forces make the system move , significant FSI may occur , so that liquid and pipe systems cannot be treated separately in a theoretical analysis : interaction mechanisms have to be taken into account . In the majority of the analyses reviewed , the pipes are slender , thin-walled , straight , prismatic and of circular cross-section . The liquid and the pipe-wall material are assumed linearly elastic and cavitation is assumed not to occur . The theories developed are valid for long (compared to the pipe diameter) wavelength , acoustical (convective velocities neglected) phenomena . Important dimensionless parameters in FSI analyses are (i) the Poisson ratio , (ii) the ratio of pipe radius to pipe-wall thickness , (iii) the ratio of liquid mass density to pipe-wall mass density , and (iv) the ratio of liquid bulk modulus to pipe-wall Young’s modulus . When the hydraulic and structural mass and elasticity , and hence the propagation speeds of pressure and stress waves , are of the same order of magnitude , FSI is likely to be of importance , provided that the transient excitation is suf ficiently rapid . FSI is usually of no importance in gas-filled pipes because the mass density and elasticity (bulk) modulus of gases are negligible compared to those of solid pipes . A classification of one-dimensional FSI models according to their basic equations , written as a hyperbolic set of first-order partial dif ferential equations , is often made . The two-equation (one-mode) model refers to classical waterhammer theory , where the liquid pressure and velocity are the only two unknowns . The four-equation (two-mode)