Control efficiency optimization and Sobol’s sensitivity indices of MTMDs design parameters for buffeting and flutter vibrations in a cable stayed bridge

This paper studies optimization of three design parameters (mass ratio, frequency ratio and damping ratio) of multiple tuned mass dampers MTMDs that are applied in a cable stayed bridge excited by a strong wind using minimax optimization technique. ABAQUS finite element program is utilized to run numerical simulations with the support of MATLAB codes and Fast Fourier Transform FFT technique. The optimum values of these three parameters are validated with two benchmarks from the literature, first with Wang and coauthors and then with Lin and coauthors. The validation procedure detected a good agreement between the results. Box-Behnken experimental method is dedicated to formulate the surrogate models to represent the control efficiency of the vertical and torsional vibrations. Sobol’s sensitivity indices are calculated for the design parameters in addition to their interaction orders. The optimization results revealed better performance of the MTMDs in controlling the vertical and the torsional vibrations for higher mode shapes. Furthermore, the calculated rational effects of each design parameter facilitate to increase the control efficiency of the MTMDs in conjunction with the support of the surrogate models.     

Analysis of tapered preforms in cold upsetting

Upset forging is usually carried out with a sequence of stages and the tapered preforms are commonly used. The preforms should be free from flash formation and buckling injuries. In this paper, the results that depend on elastic–plastic finite element analysis of taper upset forging are given. The buckling analysis was realized by using the Modified Riks method. For a given upset ratio which is the ratio of unsupported length to diameter of the initial billet, reduction in the height of the billet and the diameter ratio are the important design parameters in taper upsetting. For several values of the design parameters, the analysis has been carried out and the results have been compared with the results of the well-known Meyer's experiment and Gökler's suggestions. In the analysis, the perfectly square end (ideal billet case) and the end with face inclination angle were considered as two different end conditions of the billet. The results for the ideal billet case are in good-agreement with Meyer's results. The end-face inclination angle, which is a significant imperfection on the billet, reduces the limits of allowable upset ratio. It has been observed that although the tapered header dies designed at the limits suggested by Meyer produce flashless preforms, in some of the cases, injuries due to buckling are not eliminated. However, Gökler's suggested limits provide elimination of both flash formation and injuries due to buckling.     

An Investigation into the Forming of Fiber Metal Laminates with Different Thickness Metal Skins Using Hydromechanical Deep Drawing

Applied Composite Materials - Lightweight composite materials are being extensively used in the aerospace and marine industry, considering environmental concerns. Fiber metal laminates are one such...     

Fuzzy multiobjective system reliability optimization by genetic algorithms and clustering analysis

System reliability optimization is a key element for a competitive and safe industrial plant. This paper addresses the multiobjective system reliability optimization in the presence of fuzzy data. A framework solution approach is proposed and based on four steps: defuzzify the data into crisp values by the ranking function procedure, the defuzzified problems are solved by the non-sorting genetic algorithms II and III (NSGA-II and NSGA-III), the Pareto fronts are compared by the spacing method for selecting the best one, and then the best Pareto front is reduced by the clustering analysis for helping the decision maker. A case study presented in the literature as a mono-objective redundancy allocation problem with fuzzy data is investigated in the present paper as multiobjective redundancy allocation and reliability-redundancy allocation problems show the applicability of the approach.     

Reliable and fully distributed trust model for mobile ad hoc networks

A mobile ad hoc network (MANET) is a wireless communication network which does not rely on a pre-existing infrastructure or any centralized management. Securing the exchanges in MANETs is compulsory to guarantee a widespread development of services for this kind of networks. The deployment of any security policy requires the definition of a trust model that defines who trusts who and how. Our work aims to provide a fully distributed trust model for mobile ad hoc networks. In this paper, we propose a fully distributed public key certificate management system based on trust graphs and threshold cryptography. It permits users to issue public key certificates, and to perform authentication via certificates' chains without any centralized management or trusted authorities. Moreover, thanks to the use of threshold cryptography; our system resists against false public keys certification. We perform an overall evaluation of our proposed approach through simulations. The results indicate out performance of our approach while providing effective security.     

Characteristics of multiple-component defects and architectural hotspots: a large system case study

The architecture of a large software system is widely considered important for such reasons as: providing a common goal to the stakeholders in realising the envisaged system; helping to organise the various development teams; and capturing foundational design decisions early in the development. Studies have shown that defects originating in system architectures can consume twice as much correction effort as that for other defects. Clearly, then, scientific studies on architectural defects are important for their improved treatment and prevention. Previous research has focused on the extent of architectural defects in software systems. For this paper, we were motivated to ask the following two complementary questions in a case study: (i) How do multiple-component defects (MCDs)—which are of architectural importance—differ from other types of defects in terms of (a) complexity and (b) persistence across development phases and releases? and (ii) How do highly MCD-concentrated components (the so called, architectural hotspots) differ from other types of components in terms of their (a) interrelationships and (b) persistence across development phases and releases? Results indicate that MCDs are complex to fix and are persistent across phases and releases. In comparison to a non-MCD, a MCD requires over 20 times more changes to fix it and is 6 to 8 times more likely to cross a phase or a release. These findings have implications for defect detection and correction. Results also show that 20% of the subject system’s components contain over 80% of the MCDs and that these components are 2–3 times more likely to persist across multiple system releases than other components in the system. Such MCD-concentrated components constitute architectural “hotspots” which management can focus upon for preventive maintenance and architectural quality improvement. The findings described are from an empirical study of a large legacy software system of size over 20 million lines of code and age over 17 years.     

Chemically reacting mixed convective Casson fluid flow in the presence of MHD and porous medium through group theoretical analysis

This paper explores the consequences of chemically reacting magnetohydrodynamic mixed convective fluid substances driven by the porous medium, slippery, incompressible, and laminar vertical channel flow. Casson fluid model in a vertical channel is strengthened with mixed convection flow. The effects of the heat source-sink parameter, the suction-injection parameter, slips on the slide wall, and thermal radiation are also considered. A Lie group method is taken into consideration and nonlinear partial differential equations are converted into nonlinear ordinary differential equations (ODEs). The NDSolve command solves these ODEs and shows the action of the related parameters in the velocity, temperature, and concentration figures. The Casson fluid parameter increases the velocity profile but reduces the concentration profile. The parameter of suction-injection enhances the velocity, temperature, and concentration profiles. The variations in skin-friction coefficient in the heat and mass transfer rate are addressed in the diagrams. Moreover, streamlines are plotted for suction-injection parameter.     

Neuroprotective potential of some terebinth coffee brands and the unprocessed fruits of Pistacia terebinthus L. and their fatty and essential oil analyses

In the current study, neuroprotective effects of the ethyl acetate and methanol extracts of four terebinth coffee brands and the fruits of Pistacia terebinthus L. were investigated through enzyme inhibition tests against acetylcholinesterase, butyrylcholinesterase, and tyrosinase as well as antioxidant test systems. Antioxidant activity was measured using radical scavenging activity tests and metal-related tests including metal-chelation capacity, ferric-reducing antioxidant power (FRAP), and phosphomolybdenum reducing power (PRAP). The fatty oils of the coffee brands and the fruits and the fruit essential oil were examined by GC–MS. Total phenol and flavonoid contents were calculated spectrophotometrically. The extracts had moderate inhibition against butyrylcholinesterase (9.78–45.74% at 200 μg mL⁻¹) and potent scavenging activity against DPPH. They exerted strong activity in FRAP and metal-chelation tests and modest activity in PRAP test. Oleic acid was identified as the major fatty acid in the fatty oils, while α-pinene (26.31%) was dominant in the essential oil.     

Computational intelligence techniques for HVAC systems: A review

Buildings are responsible for 40% of global energy use and contribute towards 30% of the total CO2 emissions. The drive to reduce energy use and associated greenhouse gas emissions from buildings has acted as a catalyst in the development of advanced computational methods for energy efficient design, management and control of buildings and systems. Heating, ventilation and air-conditioning (HVAC) systems are the major source of energy consumption in buildings and ideal candidates for substantial reductions in energy demand. Significant advances have been made in the past decades on the application of computational intelligence (CI) techniques for HVAC design, control, management, optimization, and fault detection and diagnosis. This article presents a comprehensive and critical review on the theory and applications of CI techniques for prediction, optimization, control and diagnosis of HVAC systems. The analysis of trends reveals that the minimisation of energy consumption was the key optimization objective in the reviewed research, closely followed by the optimization of thermal comfort, indoor air quality and occupant preferences. Hardcoded Matlab program was the most widely used simulation tool, followed by TRNSYS, EnergyPlus, DOE-2, HVACSim+ and ESP-r. Metaheuristic algorithms were the preferred CI method for solving HVAC related problems and in particular genetic algorithms were applied in most of the studies. Despite the low number of studies focussing on multi-agent systems (MAS), as compared to the other CI techniques, interest in the technique is increasing due to their ability of dividing and conquering an HVAC optimization problem with enhanced overall performance. The paper also identifies prospective future advancements and research directions.