bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of turning parameters on surface integrity of nickel alloy 625
Authors: Loureiro Daniel , Diniz Anselmo E , Farina Alexandre B , Delijaicov Sérgio
Published: December 2017

Nickel-based alloys are used in industrial sectors where high mechanical strength and corrosion resistance are required at high temperatures. However, these alloys have low machinability as a consequence of inherent properties. Some of these properties such as high cold work hardening rate and low heat conductivity may cause damages to the machined surface. Among the nickel-based alloys, one that has good properties for oil exploration is alloy 625. As the components made of this alloy are frequently used in very rough environments, this study sought to evaluate the influence of tool geometry, cutting conditions (feed and cutting speed) and tool condition (fresh or worn) on the surface integrity of turned alloy 625 parts in order to discover turning practices for this alloy that result in minimal damage to the workpiece surface. A secondary aim was to evaluate how these input variables affected the life of the coated carbide tools used in the turning experiments with this alloy. The main conclusions are that (a) the surfaces produced with a fresh tool with positive geometry had compressive residual stresses, while those produced with negative tool geometry had tensile residual stresses and (b) when a worn tool was used all the surfaces produced had compressive residual stresses.
Location optimization of interchangeable parts in sheet metal assembly
Authors: Huan Honglun
Published: December 2017

Stiffened panel is a kind of structure that is widely used in aviation manufacturing. Some sheet metal parts in the structure have three characteristics: place-interchangeable, large quantity and stochastic variation caused by spring back or distortion in manufacturing process, which prominently impacts the assembly variation. In order to minimize the influence and improve the assembly quality of stiffened panel, a model based on flexible beam is established and a simplified and approximate assembly variation prediction method is obtained. Furthermore, for the interchangeable sheet metal parts, the assembly location optimization method based on the algorithm of perfect match of weighted complete bipartite graph is proposed. At last, case study on a fuselage panel assembly is implemented. The finite element analysis results show the reliability of the simplified variation prediction method and the necessity of assembly location optimization.
Study of the control process and fabrication of microstructures using a tip-based force control system
Authors: Zhang Jingran , Yan Yongda , Hu Zhenjiang , Zhao Xuesen
Published: December 2017

The atomic force microscopy tip-based nanomechanical machining method has already been employed to machine different kinds of nanostructures with the control of the normal force of the tip. The previous studies verified the feasibility of the nanomachining approach with the force control. However, there are still some shortcomings of small normal force, small machining scale, high cost and low machining efficiency. Therefore, in this study, a tip-based micromachining system with normal force closed-loop control is established based on the principle of atomic force microscopy. The control parameters are optimized based on an analysis of the control process to enable the production of a constant normal force during machining when using a tip tool. The maximum machining velocity that can be attained using this system while maintaining a constant normal force is obtained based on an analysis of the normal force variations during machining. By controlling nanoscale accuracy and high-precision stage, more complex microstructures, including microsquares, millimeter-scale microchannels and three-dimensional step microchannels, are successfully fabricated using the proposed force control method. Experimental results show that the tip-based normal force control method is a simple, low-cost and versatile micromachining method with the potential ability to machine more complex structures and is likely to find wider applications in the micromachining field.
Experimental investigation and modelling of drilling on multi-wall carbon nanotube–embedded epoxy/glass fabric polymeric nanocomposites
Authors: Singh Kalyan Kumar , Kumar Dhiraj
Published: December 2017

The primary objective of this research is to investigate the effect of multi-wall carbon nanotubes on drilling of multi-wall carbon nanotube–embedded epoxy/glass fabric polymeric nanocomposites. The experiments were conducted on composites with varying the weight percentage of multi-wall carbon nanotubes content to analyse drilling-induced delamination and surface roughness, which affect the quality and property of the drilled holes. The drilling parameters considered are spindle speed, feed rate and drill diameter. The microstructure of the holes was characterized using field emission scanning electron microscopy methods. For correlating the effect of the weight percentage of carbon nanotubes with the referred drilling parameters, a mathematical model was used, based on response surface methodology. For development of the mathematical model, four factors, namely, spindle speed, feed rate, diameter of drill and weight percentage of carbon nanotubes, were taken into account. The result established that delamination and surface roughness are reduced as multi-wall carbon nanotubes’ content increases. Maximum improvement in delamination factor was observed in the case of 1.0 wt% multi-wall carbon nanotube–embedded epoxy/glass fabric polymeric nanocomposite, which is 25% and 31.09% at the entrance and exit sides of the hole, respectively. With an increase in the feed rate and the drill diameter, delamination factor increases; however, with an increase in spindle speed, delamination factor decreases. Lower value of surface roughness (1.113 µm) was observed in 1.5 wt% of multi-wall carbon nanotube–embedded epoxy/glass fabric polymeric nanocomposite. However, surface roughness increases with an increase in feed rate and drill diameter.
Electrochemical micromachining of large-area micro-dimple arrays with high machining accuracy
Authors: Hou Zhibao , Qu Ningsong , Chen Xiaolei
Published: December 2017

Surface textures, especially micro-dimple arrays, can significantly improve the friction performance of engineering parts. Through-mask electrochemical micromachining is an effective method for generating micro-dimple arrays. In this article, a new method is introduced to fabricate a large-area polydimethylsiloxane mask containing micro through-holes. Using this technique, a stainless steel mould with micro-pillar arrays is generated by wire electrical discharge machining. A combination of pressure and weight of electrolyte is then proposed to keep the polydimethylsiloxane mask closely attached to the workpiece, which helps to achieve high machining accuracy. The effects of applied voltage, effective machining time and pulse duty cycle on the micro-dimples are investigated. The profiles of the micro-dimples are not sensitive to applied voltage, but pulse duty cycle is a significant factor influencing the depth of the micro-dimples. Micro-dimples of width 95 µm, depth 19 µm and a machining area of diameter 40 mm are successfully generated using a polydimethylsiloxane mask, and the standard deviations of the micro-dimple width and depth are only 0.84 and 0.23 µm, respectively. The present experiments verify that it is feasible to obtain large-area micro-dimple arrays with high machining accuracy using this technique.
Study on grinding surface deformation and subsurface damage mechanism of reaction-bonded SiC ceramics
Authors: Li Chen , Zhang Feihu , Ma Zhaokai
Published: December 2017

In order to explore the grinding surface deformation and subsurface damage mechanism for reaction-bonded SiC ceramics, the grinding experiment for reaction-bonded SiC ceramics was carried out under the condition of different grinding depths using two different kinds of grain sizes of grinding wheel. The ground surface morphology of specimen was observed using the field emission scanning electron microscope (5000 ×), and the value of surface roughness Rz was measured by the confocal microscope, which found that there were the brittle removal region and the plastic removal region on the ground surface of reaction-bonded SiC ceramics and it could improve the ground surface quality and proportion of ductile region using the fine grinding wheel and reducing the grinding depth. The specimen was polished by the ion cross section polisher and the ground subsurface was analyzed by the field emission scanning electron microscope, which found that there were transgranular fracture, intergranular fracture, crack bifurcation, ladder-shaped crack and other phenomenon in the grinding process. And it could control the subsurface damage depth using the fine grinding wheel and reducing the grinding depth. The relationship between surface roughness and subsurface damage was analyzed based on the indentation theory, which found that the simulation results were close to the experiment results when the value of m is in the range of 1/8–1/4. When m is 0.2143 calculated by genetic algorithm, the simulation results are the best.
Design and development of a software tool to assist ISO 50001 implementation in the manufacturing sector
Authors: Bruton Ken , O’Donovan Peter , McGregor Andrew , O’Sullivan Dominic DTJ
Published: December 2017

Certified energy management systems suffer from a perception that they require exhaustive quantities of time and resources to operate, and that this time could be more beneficially spent saving energy through improvement projects. It is commonplace for processes such as energy performance indicator development, energy review and action planning to be implemented in manual and hence resource-intensive processes. No effective web-based tools currently exist to aid end users in processes. As part of an embedded study working with three large manufacturing companies, it was found that 5–75 days were spent implementing these three key aspects of a structured energy management system. Web-based solutions offer the potential to streamline the operation of these resource heavy components of energy management systems. This article focuses on the early stage development and beta testing of a web-based action planning and energy project visualisation tool which has been developed and tested on one of the embedded study participants. The results from this testing demonstrate a wiliness of the participant companies to engage with web-based tools to minimise their ISO 50001 resource requirements once they are designed in such a way as to facilitate ease of use.
An intelligent approach towards optimal assembly sequence generation
Authors: Bahubalendruni MVA Raju , Biswal Bibhuti Bhusan
Published: December 2017

In this paper, a novel and efficient method is developed and proposed to obtain all valid assembly sequences and optimized assembly sequence for a given assembled product. The working principle of methodology is clearly illustrated with different example products. Four basic predicates namely “liaison predicate, geometrical feasibility, mechanical feasibility, and stability” are considered to validate each sequence. The proposed method is effective and proven efficient in the resulting all set of feasible assembly sequences described. Tool/gripper changes, assembly orientation changes, and part trajectory distances are considered to state the optimality of a valid assembly sequence. Achieving optimized assembly sequence through the proposed method for user-defined objective function is briefly illustrated. The computational performance of the method in achieving all valid assembly sequences is illustrated for various dissimilar products.
Investigation of the effect of sheet thickness on residual stresses in resistance spot welding of aluminum sheets
Authors: Sedighi M , Afshari D , Nazari F
Published: December 2017

The main purpose of this study is to investigate the effect of sheet thickness on nugget size and residual stresses in resistance spot welding. A two-dimensional coupled electro-thermo-mechanical finite element model is employed to predict the residual stresses in aluminum alloy 6061-T6. The simulation results are compared with the results obtained from the experimental nugget size and the residual stresses are measured by the X-ray diffraction method. The results indicate that the highest tensile residual stress occurs at the center of the nugget and diminish along the nugget radius. The residual stresses increase on increasing the electrical current and reducing the welding time. By increasing the sheet thickness, the affordable range of welding current and welding cycle increase. It also leads to the enlargement of the nugget, which consequently results in the increase of the residual stresses.
A reliability optimization allocation method for the hydraulic system of CNC honing machine considering the operating condition information
Authors: Zhou Guanghui , Chang Fengtian , Tian Changle , Lu Qi
Published: December 2017

In recent years, reliability optimization allocation has drawn a broad spectrum of attentions, especially for complex systems consisting of a large number of subsystems and components. Hydraulic system, deemed as a complex system, plays a great role in reliability increment of the CNC honing machine. In order to realize the CNC honing machine tool’s balanced operating performance, the crucial hydraulic system is designed to obtain the optimal and well-balanced allocation solution under the constrains of cost and reliability. Meanwhile, the quantified operating factor that influences the allocation solution is rarely considered adequately when operating samples are insufficient. So, if hydraulic systems are used in a new required longer operating mission duration or a new severer operating environment, the dissatisfied reliability could not be better reallocated to adapt to this environment with appropriate methods. Aimed at overcoming the abovementioned shortcomings and optimizing the dissatisfied reliability for existing hydraulic systems, this paper proposes a reliability optimization allocation method considering operating the condition information. From the standpoint of the complex system, this method firstly builds a three-level reliability optimization allocation model based on the analytic target cascading for the specific hydraulic system of CNC honing machine 2MK2263 × 200. It transforms the complex reliability allocation problem to a set of smaller and coordinated optimization sub-problems. Secondly, through studying the operating reliability problems of small samples in the new operating scene, the reliability prediction results based on the operating condition information are applied to build the initial reliability targets, which are regarded as the initial constrains for the optimization. With the help of analytic target cascading model and initial target reliability, the optimal reliability for the complex hydraulic system would be obtained. It is also shown to provide an innovative route for the reliability redesign of the related complex systems for this new required operating scene.
An improved adaptive stochastic resonance method for improving the efficiency of bearing faults diagnosis
Authors: Huang Dawen , Yang Jianhua , Zhang Jingling , Liu Houguang
Published: December 2017

The general scale transformation (GST) method is used in the bistable system to deal with the weak high-frequency signal submerged into the strong noisy background. Then, an adaptive stochastic resonance (ASR) method with the GST is put forward and realized by the quantum particle swarm optimization (QPSO) algorithm. Through the bearing fault simulation signal, the ASR method with the GST is compared with the normalized scale transformation (NST) stochastic resonance (SR). The results show that the efficiency of the GST method is higher than the NST in recognizing bearing fault feature information. In order to simulate the actual engineering environment, both the adaptive GST and the NST methods are implemented to deal with the same experimental signal, respectively. The signal-to-noise ratio (SNR) of the output is obviously improved by the GST method. Specifically, the efficiency is improved greatly to extract the weak high-frequency bearing fault feature information. Moreover, under different noise intensities, although the SNR is decreased versus the increase of the noise intensity, the ASR method with the GST is still better than the traditional NST SR. The proposed GST method and the related results might have referenced value in the problem of weak high-frequency feature extraction in engineering fields.
Optimization of tube drawing process through FE analysis, intelligent computation, and experimental verification
Authors: Jafari Mirshaban , Hosseinzadeh Morteza , Elyasi Majid
Published: December 2017

In present study, an attempt based on a hybrid approach was made to find optimal tube drawing parameters combination (i.e., die semi-angle, friction coefficient, tube entrance velocity, deformation length, and primary tube diameter) achieving minimum forming force, minimum dimensional error along with maximum thickness in longitudinal and circumferential directions. In order to form a design matrix, Taguchi L27 design was used and required data were derived from finite element model of the process. Adaptive neuro-fuzzy inference system (ANFIS) was then used to correlate process inputs to and responses aforementioned response outputs. Prediction accuracy of created ANFIS models was further checked by FE simulation and experimental testing data. Finally, the models were integrated to form objective function that was optimized by teaching–learning-based optimization (TLBO) algorithm. To check the adequacy of optimization, a finite element run and an experiment were carried out by obtained optimal parameter setting and the results were compared. The findings indicated that that the proposed methodology, that is, FEA-ANFIS-TLBO has superiority in identifying the optimal results.
Aiding and opposing of mixed convection Casson nanofluid flow with chemical reactions through a porous Riga plate
Authors: Abbas Tehseen , Bhatti Muhammad Mubashir , Ayub Muhammad
Published: December 2017

In the present study, simultaneous effects of the chemical reaction and electromagnetohydrodynamic on the Casson nanofluid over porous Riga plate has been investigated. The governing flow problem consists of linear momentum, thermal energy, and nanoparticle concentration equation, which is modeled with the help of Oberbeck–Boussinesq approximation. Shooting method is employed to obtain the solution of the resulting nonlinear coupled ordinary differential equation. The behavior of the velocity profile, temperature profile, and nanoparticle concentration profile are discussed against modified Hartman number, porosity parameter, chemical reaction parameter, Prandtl number, Brownian motion parameter, thermophoresis parameter, Schmidt number, nanoparticle flux parameter, and Richardson number, respectively. The governing flow is also discussed for aiding and opposing flow by considering the negative and positive values of the modified Hartman number. The Nusselt number and Sherwood number are also computed numerically. Moreover, it is also found that the porosity parameter also enhances the velocity profile. A numerical comparison is also presented with previously published results to ensure the validity of the current methodology and results.
The dynamic interaction effects of railway tunnels: Crossrail and the Grand Central Recording Studios
Authors: Brookes Daniel , Hamad Waleed I , Talbot James P , Hunt Hugh EM , Hussein Mohammed FM
Published: December 2017

In cities around the world, underground railways offer an environmentally friendly solution to society’s increasing demand for mass transport. However, they are often constructed close to sensitive buildings, where the resulting ground-borne noise and vibration can cause disturbance to both the occupants and the equipment. Such a scenario occurred in central London, where the new twin tunnels of Crossrail were bored beneath the Grand Central Recording Studios, causing an immediate concern. As a result, vibration in the studios’ building was monitored throughout the Crossrail construction period. Since Crossrail is yet to operate, the resulting data provide a unique opportunity to investigate the effect of new tunnels, acting as passive buried structures, on the existing vibration environment. This paper presents the results of such an investigation, together with complementary results from a theoretical four-tunnel boundary-element model. The data analysis, presented in the first half of the paper, indicates that the construction of the second Crossrail tunnel has led to an overall reduction in the noise and vibration levels beneath the studios, due to the operation of the nearby Central line trains of London Underground. This is predominantly due to a reduction of approximately 6 dB in the 63 Hz band-limited levels but accompanied by a slight increase, of approximately 2 dB, in the 125 Hz band. Further analysis indicates that any seasonal variations in vibration levels over the measurement period are negligible, adding weight to the conclusion that the observed changes are a causal effect of the tunnel. The second half of the paper presents results from the model, which aims to simulate the dynamic interaction between the Central line tunnels and those of Crossrail. With nominal parameter values, the results demonstrate qualitative similarities with the measurement findings, thereby adding to the growing body of evidence that dynamic interaction between neighbouring tunnels can be significant.
On the ballast–sleeper interaction in the longitudinal and lateral directions
Authors: De Iorio Antonio , Grasso Marzio , Penta Francesco , Pucillo Giovanni Pio , Rossi Stefano , Testa Mario
Published: December 2017

In service, railway tracks must withstand the transverse and longitudinal forces that are caused by running vehicles and thermal loads. The mechanical design that adopts any of the track models available in the technical literature requires that the strength of the track is fully characterised. In this paper, the results of an experimental research activity on the sleeper–ballast resistance along the lateral and the longitudinal directions are reported and discussed. In particular, the work is aimed at identifying the strength contributions offered by the base, the ballast between the sleepers, and the ballast shoulder to the global resistance of the track in the horizontal plane. These quantities were experimentally determined by means of an ad hoc system designed by the authors. Field tests were carried out on a series of track sections that were built to simulate scenarios in which the ballast was removed from the crib and/or the shoulder. The results of this study indicate that the strength percent contributions from the crib, the sleeper base, and the shoulder are, respectively, equal to about 50%, 25%, and 25% in the lateral direction, and 60%, 30%, and 10% in the longitudinal direction. Moreover, the comparison of the acquired data with literature results reveals that a detailed knowledge about the testing conditions and the activated ballast failure mechanisms is needed in order to correctly use the test data for the design purpose.
Potential for external reinforcement of insulated rail joints
Authors: Gallou M , Temple B , Hardwick C , Frost M , El-Hamalawi A
Published: December 2017

This paper aims to investigate the alternative ways of reducing the deterioration and failure of insulated rail joints of railway tracks. Joints deteriorate faster than rails due to the presence of structural discontinuity. This weakness results in extra displacement due to the applied load and dynamic force that results as a consequence. Overtime, this situation worsens as the impacts and applied stresses damage and soften the ballast and the supporting subgrade under the joint. This study initially presents a static finite element model designed to simulate the mechanics of insulated rail joints, and then a comparison is made between the plain rail and a suspended insulated rail joint under various support stiffnesses. The product design options of the reinforced insulated rail joints are then chosen as input variables of the model. The results of the model are compared with the field and laboratory data acquired via the Video Gauge, which is a new high-resolution optical measurement technique. The results show that the use of strap rails or more robust I-beam sections in the vicinity of the insulated rail joint to stiffen the support structure can significantly reduce the displacement and the subsequent dip angle seen in an insulated rail joint. This potentially presents a means of improving the behaviour of the insulated rail joints. Their impact becomes more significant for soft support conditions. Although these results are indicative of new conditions for insulated rail joints, the field measurements indicate that the magnitude of deflection of insulated rail joints is a result of the structural discontinuity of the rails, the dynamic P2 force, the wheel condition, the degraded ballast and it significantly increases with time under repeated load. Thus, it is recommended that a careful field implementation and testing will indicate the effect of an external enhancement on the timely degradation of insulated rail joints.
A design method for rail profiles based on the geometric characteristics of wheel–rail contact
Authors: Mao Xin , Shen Gang
Published: December 2017

Designing a proper rail profile carries more significance than designing a wheel profile because of the amount of work and cost involved in the maintenance of rails. A better rail profile will not only help to ensure achieving the desired dynamic performance of rail vehicles but it also extends the service life of rails. This paper presents a unique design method for the design of rail profiles based on the given geometric contact characteristics. The proposed method utilizes a given wheel profile and two typical functions respectively to set the main design targets. The first function is the rolling radii difference and the second one is the contact angle difference. Wheel–rail contact distribution is chosen as the secondary target to prevent stress concentration and the associated fatigue failure. With certain assumptions, the solution process becomes a reverse designed one, which can be solved by using proper discrete numerical methods. Two examples of rail profile designs have been discussed in detail for rigid and independent wheelsets.
A global optimization control for turbo-fan engine acceleration schedule design
Authors: Zheng Qiangang , Zhang Haibo
Published: December 2017

A new optimization control method, which is based on the optimization employing Bezier curves of control variables, is proposed to improve engine thrust response performance. The minimum of the time consumption for control variables changing from start to end point is selected as objective function. Unlike conventional methods, the optimization variables are altered to the Bezier curves of the control variables in this scheme. This new acceleration optimization control only establishes one optimization problem for the overall acceleration process instead of establishing a series of sub optimization problems, which is usually adopted by conventional optimization controls. Hence, the proposed method is easier to overcome the disadvantage of the conventional ones, which just search for the optimal engine performance in local time period. Finally, for comparisons, the simulations for the proposed method and the conventional one have been both conducted. The simulations demonstrate that, although the conventional optimization control shows better performance in initial half part of acceleration process, however, the overall acceleration performance turns to be worse whereas for the new one, the acceleration time from idle to 95% of the maximum power is surprising decreased by 1.4 s compared to the conventional optimization control.
Application of a diagnostic technique for evaluating the quality of the air–fuel mixture and the ignition quality of a spark-ignition reciprocating aircraft piston engine
Authors: Antonopoulos AK , Papagiannakis RG , Hountalas DT
Published: December 2017

The performance characteristics of an aircraft piston engine are affected mainly by the air–fuel mixture quality (i.e. condition of the fuel injection system) and by the spark timing and spark duration (i.e. condition of ignition system). Thus, the present work focuses on investigating the effect of both fuel injection and spark ignition systems on performance characteristics of two aircraft piston engines which are of the same type but have overhauled by two different workshops. The investigation is conducted by applying an existing diagnostic technique, which is based on the simultaneous recording and processing of two electric signals: one corresponding to cylinder pressure and the second corresponding to the ignition system. The basic characteristics of the proposed methodology are simplicity and field applicability on engines of this type. A detailed experimental investigation has been conducted on the aforementioned two aircraft piston engines on a dedicated test bench. From the results, it is revealed that the proposed diagnostic methodology provides reliable information for the effect of both the ignition and fuel injection systems on engine performance characteristics. The results derived from the specific work enable the comparative evaluation of the engines and their ignition and fuel injection systems. Finally, based on this first investigation, the proposed methodology seems to be promising, because it can be easily applied on any type of spark-ignited engine and especially on aircraft piston engine, where due to its geometry and multicylinder nature, the application of lab techniques on the field is, if not impossible, extremely difficult.
Study on navigation and manual steering strategies in the fly-around phase of teleoperation rendezvous and docking
Authors: Li Tao , Huang Ruixue , Li Haiyang , Zhang Yakun
Published: December 2017

Teleoperation rendezvous and docking can be used as a supporting technology for unmanned spacecraft. An attempt to apply this technology to an unmanned spacecraft’s fly-around maneuver in a space station-based rendezvous and docking task is described in this paper; relative navigation (state determination) strategies and manual steering strategies are proposed sequentially. Parameters to delineate the relative motion states between spacecraft were specifically defined, and an estimation strategy for the parameter set was designed based on the configured relative measurement sensors. Then, manual steering strategies, characterized by decoupling control of the line-of-sight (LOS) orientation between the unmanned spacecraft and the relative orbit motion, were developed to ensure that the unmanned spacecraft, piloted by operators on the space station, flies with almost invariant radial velocity and angular velocity in the LOS axis. A human-in-the-loop simulation result demonstrated the feasibility and effectiveness of the strategies proposed.
Multiple flight vehicles cooperative guidance law based on extended state observer and finite time consensus theory
Authors: Zhao Enjiao , Chao Tao , Wang Songyan , Yang Ming
Published: December 2017

An extended state observer based cooperative guidance method is proposed for multiple flight vehicles intercepting a coming maneuver target. The guidance geometry for multiple flight vehicles-target is established, and a cooperative guidance law used multi-agent cooperative control theory is designed for multiple flight vehicles. To deal with the uncertainty of the maneuver target, the target acceleration is considered as a disturbance, which is observed using an extended state observer, and compensated in the guidance law. Simulation results show that the designed extended state observer can estimate the target acceleration accurately, and the proposed cooperative guidance can satisfy the demands for controlling the intercept time, and hence the cooperative interception can be achieved.
Aerodynamic optimisation of a winglet-cavity tip in a high-pressure axial turbine cascade
Authors: Zhou Zhihua , Chen Shaowen , Wang Songtao
Published: December 2017

Tip clearance flow between rotating blades and the stationary casing in high-pressure turbines is very complex and is one of the most important factors influencing turbine performance. The rotor with a winglet-cavity tip is often used as an effective method to improve the loss resulting from the tip clearance flow. In this study, an aerodynamic geometric optimisation of a winglet-cavity tip was carried out in a linear unshrouded high-pressure axial turbine cascade. For the purpose of shaping the efficient winglet geometry of the rotor tip, a novel parameterisation method has been introduced in the optimisation procedure based on the computational fluid dynamics simulation and analysis. The reliability of a commercial computational fluid dynamics code with different turbulence models was first validated by contrasting with the experimental results, and the numerical total pressure loss and flow angle using the Baseline k-omega Model (BSL κ-ω model) shows a better agreement with the test data. Geometric parameterisation of blade tips along the pressure side and suction side was adopted to optimise the tip clearance flow, and an optimal winglet-cavity tip was proven to achieve lower tip leakage mass flow rate and total pressure loss than the flat tip and cavity tip. Compared to the numerical results of flat tip and cavity tip, the optimised winglet-cavity design, with the winglet along the pressure side and suction side, had lower tip leakage mass flow rate and total pressure loss. It offered a 35.7% reduction in the change ratio [Formula: see text]. In addition, the optimised winglet along pressure side and suction side, respectively, by using the parameterisation method was studied for investigating the individual effect of the pressure-side winglet and suction-side winglet on the tip clearance flow. It was found that the suction-side extension of the optimal winglet resulted in a greater reduction of aerodynamic loss and leakage mass flow than the pressure-side extension of the optimal winglet. Moreover, with the analysis based on the tip flow pattern, the numerical results show that the pressure-side winglet reduced the contraction coefficient, and the suction-side winglet reduced the aerodynamic loss effectively by decreasing the driving pressure difference near the blade tips, the leakage flow velocity, and the interaction between the leakage flow and the main flow. Overall, a better aerodynamic performance can be obtained by adopting the pressure-side and suction-side winglet-cavity simultaneously.
Type-2 fuzzy adaptive sliding mode control of hypersonic flight
Authors: Jiao Xin , Fidan Baris , Jiang Ju , Kamel Mohamed
Published: December 2017

This paper proposes a type-2 fuzzy adaptive sliding mode control scheme for tracking control of hypersonic aircraft with uncertainties. This method uses full-state feedback to linearize the nonlinear model of hypersonic aircraft. Combining the interval type-2 fuzzy approach and adaptive sliding mode control keeps the system stable in the existence of uncertain parameters. For rapid stabilization of the system, the adaptive laws are designed using a direct constructive Lyapunov analysis together with a well-established type-2 fuzzy logic control. Simulation test results indicate that the proposed control scheme provides enhancement of robustness to parametric uncertainty and improvement in tracking performance of the hypersonic aircraft.
Active flow control of bi-stable asymmetric vortices on a slender body by alternating synthetic jets
Authors: Wang Qite , Cheng Keming , Gu Yunsong , Zuo Wei
Published: December 2017

A synthetic jet actuator with double nozzles is developed to control the leeward vortices behind the slender body at a high angle of attack. Periodic alternating disturbance at the nose tip of the slender body is continuously provided by the alternating synthetic jets. A series of experiments is conducted in a low speed and low turbulence wind tunnel. The results show that the alternating synthetic jets at the nose tip can achieve a suitable control effect in which the lateral force is eliminated. For a very high angle of attack, the leeward vortices behind the slender body are in the inherently bi-stable state; in this state, the symmetric distribution formation by the leeward vortices is nearly impossible. However, the alternating disturbance of the nose tip can break the bi-stable state and transform it into other two states, which are the unsteady switched state of the leeward vortices and the quasi-steady symmetric state. Varying the control frequency significantly affects the state of the leeward vortex. In the range of the lower control frequency, the leeward vortices switch back and forth and follow the cycle of the alternating disturbance at the nose tip. In the range of the higher control frequency, the leeward vortices are in a stable symmetric distribution state. As the alternating disturbance frequency increases from lower to higher, the switched amplitude of the leeward vortices decreases and the unsteady switched state of the leeward vortices gradually changes to the quasi-steady symmetric state. This amplitude reduction occurs because the position of the leeward vortices is very sensitive to the alternating disturbance of the nose tip and is related to the inertia effect of the fluid.
Multi-sensor target tracking in the presence of clutter using game theory
Authors: Ghazal M , Doustmohammadi A
Published: December 2017

The problem of multi-sensor target tracking in the presence of clutter has not been studied from a game theory point of view. This paper presents a game theory approach for such a problem. Fundamental sub-problems are state estimation and data association in multi-sensor target tracking systems. In this paper, the state estimation problem is formulated as zero-sum game and a minimax filter is developed to estimate the target characteristics, including its position, velocity, and acceleration. To extend the filter in the presence of clutter, a data association framework is proposed. In data association framework, set of new hypotheses in each step is produced from set of validated measurements and the ith global hypothesis is obtained from the previous step. Next, posteriori estimate of ith global hypothesis is updated based on the filter for each new hypothesis. To manage exponential growth of new hypotheses, a new k-best algorithm is implemented. Simulation results illustrate the improved performance of the proposed filter compared to multiple hypothesis tracking and nearest-neighbor fuzzy filters.
Finite time fault-tolerant attitude control for rigid-flexible coupling satellites based on Legendre neural network
Authors: Xiao Yan , Ye Dong , Sun Zhaowei
Published: December 2017

This paper investigates the finite time fault-tolerant attitude control for rigid-flexible coupling satellites in large angle rapid maneuver when some of the actuators are in the fault condition. Based on the first-order approximate method, a more accurate dynamic model for rigid-flexible coupling satellites is set up. Then, Legendre polynomial-based neural network is introduced to estimate the lump perturbation including the estimation error of the fault control torque, high-order flexible coupling terms, external disturbances, and model uncertainties. With the estimation value as the compensation effort, a finite time fault-tolerant attitude controller is designed based on the nonsingular fast terminal sliding mode. And in order to guarantee that the output of the Legendre polynomial-based neural network stays inside the bound of the lump perturbation, a switch mechanism is introduced to generate a switching between the proposed fault-tolerant attitude controller and a robust controller. The proposed fault-tolerant attitude controller is shown to have the finite time stability, with fast convergence rate, high accuracy, disturbance rejection, chattering attenuation, flexible vibration damping through theoretical analysis and simulations, meanwhile the better representation capability of the Legendre polynomial-based neural network, whose basic functions are implemented using only the desired attitude, makes the controller design simple and efficient.
Aircraft spin characteristics with high-alpha yawing moment asymmetry
Authors: Malik Bilal , Akhtar Suhail , Masud Jehanzeb
Published: December 2017

This paper analyzes the open-loop spin dynamics of a fighter configuration that exhibits yawing moment asymmetry at high angles of attack. High-fidelity aerodynamic model, in a look-up-tables form, is developed using the experimental data from static, coning, and oscillatory coning rotary balance wind tunnel tests. As a first step, all attainable equilibrium spin modes along with their sensitivity to control settings are predicted. Investigation of the dynamic characteristics of the predicted spin modes is performed using six degrees-of-freedom time history simulations, which showed that both, right and left flat spins are oscillatory and divergent. Influence of high-alpha yawing moment asymmetry on the spin recovery piloting strategies with control inputs is also studied with six degrees-of-freedom time history simulations. Our studies reveal that the proposed spin recovery strategies effectively reduce the recovery time for the left flat spins. However, aircraft’s inherent tendency to yaw rightwards due to high-alpha yawing moment asymmetry renders proposed spin recovery strategies ineffective in accelerating the recovery of the right flat spins.
Design and optimization of three-dimensional supersonic asymmetric truncated nozzle
Authors: Zhu Meijun , Fu Lei , Zhang Shuai , Zheng Yao
Published: December 2017

Three-dimensional supersonic nozzle is an important component of air-breathing hypersonic vehicles to produce thrust and lift force. Since the length of nozzle with ideal design is too long to meet the trim requirements of integrated air-breathing hypersonic vehicles, it is necessary to design a truncated nozzle to provide excellent aerodynamic performance. In the present study, an axisymmetric minimum length nozzle was firstly designed using method of characteristics. Then, streamlines trace technique with an offset circular entrance was adopted to extract the three-dimensional asymmetric nozzle. Nonlinear compression method was applied to compress the nozzle to a suitable length. Afterward, a surrogate-based optimization of three design variables, namely pressure ratio of nozzle’s exhaust to ambient, reserved initial expansion ratio, and average compression ratio was performed with the objectives of thrust and lift force, and a Pareto optimal front was therefore obtained. Numerical simulations were also made at six selected Pareto front cases to offer an insight into the flow fields. An infection point was observed in the Pareto front due to the maximum constrained length. The pressure ratio was found to be the most influential parameter, and the middle parts of Pareto front revealed better uniformity of exit flow.
Experimental investigations on high altitude airship propellers with blade planform variations
Authors: Liu Zhenchen , Liu Peiqing , Hu Tianxiang , Qu Qiulin
Published: December 2017

Wind tunnel tests of five propellers with different blade tip widths are carried at pitch angles between 20.5° and 40°. The aerodynamic performance are provided, which can be treated as a supplement of the high altitude airship propeller database. The influences of the blade planform and advance ratio on both power coefficient and propulsive efficiency are analyzed. It is found that at advance ratio below 0.8, the propeller with narrow tip has higher efficiency but limited power coefficient. While at advance ratio above 0.8, the propeller with wider tip has the advantages of higher power coefficient and acceptable efficiency. The variation of the propulsive efficiency with planform and advance ratio is dominated by the radial distributions of the airflow angle and interference angle.
How can those engaging in chemsex best be supported? An online survey to gain intelligence in Greater Manchester
Authors: Tomkins Andrew , Vivancos Roberto , Ward Chris , Kliner Merav
Published: December 2017

Reports of sexualised drug taking (chemsex) have increased significantly in recent years. There is currently limited intelligence on chemsex outside of London. An anonymous survey was promoted via several sources including voluntary services and a sexual health clinic in order to establish the risks associated with chemsex, and how support services can best be tailored to meet the needs of those in Greater Manchester, UK. Quantitative and qualitative data were collected on demographics, drug use, sexual practices and barriers and facilitators to accessing support. Fifty-two men who have sex with men completed the online survey. Thirty-nine (75%) were HIV-positive and 11 (21%) were hepatitis C virus (HCV) positive, all of whom were HIV/HCV co-infected. The most commonly used drugs were mephedrone (81%) and gamma hydroxybutyrate/gamma butyrolactone (79%). Nineteen (37%) reported ever injecting drugs. High-risk sexual practices were reported by respondents. Barriers to accessing support included a fear of being recognised. Findings demonstrate those engaging in chemsex are participating in a number of high-risk sexual practices, taking substances with significant risks and administering these substances in potentially high-risk ways. Results demonstrate the need for promotion of existing services, with key areas to target where chemsex sessions are most commonly arranged. Results may be useful in other metropolitan cities, both for commissioning and tailoring of chemsex support services.
Thermodynamic investigation of dual-separator Kalina cycle system: Comparative study
Authors: Bahrampoury Rasool , Behbahaninia Ali
Published: December 2017

In this study, an arrangement of Kalina cycle is proposed in which it is intended to implement weak solution of Kalina cycle system 11 (KCS 11) for more power production. In this cycle, which is a version of KCS11 (KCS111), the weak solution of the traditional separator is heated in hot section of the evaporator. The stream that now includes vapor is separated in high-temperature separator that brings about an extra potential to produce work. In order to set pinch temperature in each of the heat exchangers included in the cycles an iterative method is used. The two cycles are compared for the same conditions as the base case, which is followed by a comprehensive sensitivity analysis. The consequences of streams’ curves in the heat exchangers are considered to present analytical justification for the improvements. Comparing the cycles at the base condition, it is observed that the presented cycle improves the exergy efficiency by nearly 18% while more than 17% improvement at the optimum ammonia mass fraction is achievable. Results show that, the proposed cycle produces larger mass flow rate of vapor passing through the turbines and is more efficient than KCS 11 for varying ammonia mass fractions. Results indicate that the trend of thermal efficiency versus ammonia mass fraction is descending for the both cycles.