Search results

This study aims to improve the survivability and maneuverability of the fighter,and study the stealth performance of fighter in the jet noise of aeroengine, it is of great significance to study the jet noise characteristics of double S-bend nozzles.

The multiparameter coupling and super-ellipse design methods are used to design the cross section of double S-bend nozzle. Taking unsteady flow information as the equivalent sound source, the noise signal at the far-field monitoring points were calculated with Ffowcs Williams–Hawkings (FW–H) method, and then, the sound source characteristics of the double S-bend nozzle are analyzed.

The results show that the internal flow of the S-bend nozzle with rectangular section is smoothed and the aerodynamic performance is better than super-ellipse section, the shear layer length of rectangular section is longer, the thickness is smaller and the mixing ability is stronger. The sound pressure level of the two S-bend nozzles decreases with the increase of the monitoring angle, and the sound pressure on the horizontal plane is greater than the vertical plane. In the direction of 40°–120°, the jet noise of rectangular nozzle is smaller, and the multiparameter coupled rectangular cross section structure is more applicable.

It is beneficial to reduce the jet noise of the engine tail nozzle and improve the stealth performance of the aircraft.

There is very little research on the jet noise characteristics of the double S-bend nozzle. The multiparameter coupling and the super-ellipse method are used to design the nozzle flow section to study the aerodynamic performance and jet noise characteristics of the double S-bend nozzle and to improve the acoustic stealth characteristics of the aircraft.

The purpose of this paper is to provide a way to analyze satellite images using various clustering algorithms and refined bitplane methods with other supporting techniques to prove the superiority of RIFCM.

A comparative study has been carried out using RIFCM with other related algorithms from their suitability in analysis of satellite images with other supporting techniques which segments the images for further process for the benefit of societal problems. Four images were selected dealing with hills, freshwater, freshwatervally and drought satellite images.

The superiority of the proposed algorithm, RIFCM with refined bitplane towards other clustering techniques with other supporting methods clustering, has been found and as such the comparison, has been made by applying four metrics (Otsu (Max-Min), PSNR and RMSE (40%-60%-Min-Max), histogram analysis (Max-Max), DB index and D index (Max-Min)) and proved that the RIFCM algorithm with refined bitplane yielded robust results with efficient performance, reduction in the metrics and time complexity of depth computation of satellite images for further process of an image.

For better clustering of satellite images like lands, hills, freshwater, freshwatervalley, drought, etc. of satellite images is an achievement.

The existing system extends the novel framework to provide a more explicit way to analyze an image by removing distortions with refined bitplane slicing using the proposed algorithm of rough intuitionistic fuzzy c-means to show the superiority of RIFCM.

The purpose of this paper is to reduce the acoustic noise of helicopter ducted tail rotor.

To predict the noise accurately, a thin-body boundary element method (BEM)/Ffowcs Williams–Hawkings method is developed in this paper. It is a hybrid method combining the BEM with computational aeroacoustics and can be used efficiently to predict the propagation of sound wave in the duct.

Compared with the experimental results, the proposed method of acoustic noise is rather desirable.

Then several geometry parameters are modified to investigate the noise reduction of ducted tail rotor by using the numerical prediction method.

The aerodynamic and acoustic performance of different modification tasks is discussed. These results demonstrate the validity of design parameters modification of ducted tail rotor in acoustic noise reduction.

This paper aims to guide the implementation of noise reduction measures in hoistway and reduce the aerodynamic noise generated by elevator operation, this paper aims to propose an aerodynamic noise analysis method that can solve the flow field in hoistway.

A turbulence-acoustic model solving the flow field in a hoistway and a numerical wind hoistway model of the ultra-high-speed elevator were established by using large eddy simulation (LES) and Curle acoustic theory.

The characteristics of pulsating flow field and aerodynamic noise around ultra-high-speed elevator are analyzed. The asymmetric characteristics of the flow field could be observed using the turbulent kinetic energy and the instantaneous vortexes in the wind hoistway model. Vortex shedding, air flow separation and recombination around the car were the key factors for aerodynamic noise generation. The sound pressure level was approximately linear to the logarithm of car speed. The increase of car deflection angle in a certain range would reduce the peak frequency of wake noise and increase the sound pressure level (SPL) value.

This paper provides important guidance for researches studying the aerodynamic noise in the hoistway and the technical personnel that look for the reduction measures, which greatly improves the shortcomings in the numerical simulation of the aerodynamic noise of the hoistway.

This paper aims to assess the aeroacoustic and aerodynamic performance of a morphing airfoil with a flexible trailing edge (FTE). The objective is to make a comparison of the aerodynamic noise characteristics between the conventional airfoil with a flap and morphing airfoil and analyse the noise reduction mechanisms of the morphing airfoil.

The computational fluid dynamic method was used to calculate the aerodynamic coefficients of morphing airfoil and the Ffowcs-Williams and Hawking’s acoustic analogy methods were performed to predict the far-field noise of different airfoils.

Results show that compared with the conventional airfoil, the morphing airfoil can generate higher lift and lower noise, but a greater drag. Additionally, the noise caused by the one-unit lift of the morphing airfoil is significantly lower than that of the conventional airfoil. For the morphing airfoil, the shedding vortex in the trailing edge was the main noise resource. As the angle of attack (AoA) increases, the overall sound pressure level of the morphing airfoil increases significantly. With the increase of the trailing edge deflection angle, the amplitude and the period of sound pressure of the morning airfoil fluctuation increase.

Presented results could be very useful during designing the morphing airfoil with FTE, which has significant advantages in aerodynamic efficiency and aeroacoustic performance.

This paper presents the aerodynamic and aeroacoustic characteristics of the morphing airfoil. The effect of trailing edge deflection angle and AoA on morphing airfoil was investigated. In the future, using a morphing airfoil instead of a traditional flap can reduce the aircraft`s fuel consumption and noise pollution.

Food waste (FW) is widely recognized as a serious threat to global food security, the economy, and the environment. FW is a major contributor to the three global crises of climate change, biodiversity loss, and pollution and waste because it complicates waste management systems and worsens the magnitudes of food insecurity. If it were a nation, food loss and waste would be the third-largest source of greenhouse gas (GHG) emissions as revealed by the Food Waste Index Report of 2021 by the United Nations Environment Program (UNEP). The growing countries in the South Asian region are not an exception to this major problem. Under this backdrop, the present study is aimed at investigating the long-term relationships as well as short-term causal interplays between FW and GHG emissions for the South Asian countries from 1990 to 2018. Employing time-series cointegration and Granger causality techniques, the results show that there is long-run relationship between these two variables in Afghanistan, Bangladesh, and Sri Lanka, and the results of the Granger causality test demonstrate that GHG is significantly influenced by FWs in Bangladesh, India, and the Maldives. So the governments in these countries should plan for minimizing the magnitudes of FWs so far as the goal of reaching sustainable development is concerned.

This study aims to examine the effects of various physical and chemical pre-treatments on antioxidant properties of tree bean (Parkia roxburghii G. Don) in combination with storage conditions.

The whole pods and seeds of tree bean were treated with gamma rays (γ-rays), sodium hypochlorite (NaOCl), chlorine dioxide (ClO₂) and hydrogen peroxide (H₂O₂) and stored at room temperature (RT, 25°C) for 30 days. The physical and chemical pre-treated seeds and pods were compared with the same stored at RT and refrigerated storage at 4°C and −20°C. During storage, physical (moisture content) and antioxidants like total phenolics, ascorbate content, reduced glutathione, total flavonoids, along with free radical scavenging activities (FRSA) were measured.

Chemical pre-treatments with NaOCl, ClO₂ and H₂O₂ significantly accelerated (p = 0.05) the total phenolics (1.9 mg/g FW in seeds and 2.4 mg/g FW in pods), flavonoids content (0.3 mg/g FW each in seeds and pods) and ABTS activities (73.3 per cent in seeds and 92.3 per cent in pods) at 30 days of storage. A significant decrease (p = 0.05) in ascorbate content (6.1 mg/g FW in seeds and 3.5 mg/g FW in pods), reduced glutathione (5.1 mg/g FW in seeds and 3.7 mg/g FW in pods), FRAP (0.3 mg equi Fe/g FW in seeds and 0.4 mg equi Fe/g FW in pods) and reducing power (1.8 mg/g FW in seeds and 3.7 mg/g FW in pods) was observed under all the treatments at 30 days of storage. However, DPPH increased under γ-irradiation and decreased under chemical pre-treatments, storage at RT and refrigerated storage. The overall result showed that pre-treatment of H₂O₂ at 10-20 mM maintains antioxidants and radical scavenging activities in tree bean during storage.

The application of H₂O₂ at 10-20 mM prior to storage of tree bean maintains the physical, antioxidant properties and FRSA in tree bean seeds and pods as compared to natural ambient conditions. Hence, this technique will help in improving the keeping quality of this legume and avoid spoilage after harvest for an extended period.

This study aims to investigate the performance of fundamental weighted portfolios (using sales, cash flows, dividends, book values and a composite of all these variables), an equal weighted portfolio and a smoothed cap-weighted (CW) portfolio in Middle East and North Africa (MENA) markets. The performance of these portfolios is compared with that of a CW portfolio for the period 2005 to 2015.

The portfolios are formed using different concentration levels, different construction schemes and different sub-regions. The performance is assessed using a large set of risk-adjusted performance measures, including more robust measures in the context of multi-factor models, such as the Fama and French (1993) three-factor model, the Fama and French (2015) five-factor model and a seven-factor model.

The results show that the fundamental portfolios, with the exception of the sales portfolio, underperform the CW portfolio using either the traditional or more robust risk-adjusted performance measures. The underperformance of the fundamental portfolios is found to be robust using different concentration levels, different construction schemes and different sub-regions. The results also show that the equal weighted portfolio outperforms the CW portfolio using traditional risk-adjusted measures. However, after controlling for additional risk factors, this outperformance disappears.

The failure of fundamental indexation in the emerging markets could help the researchers and the academics to search for the best weighting method that could be used as an alternative to the CW indexation method.

The results of the study add evidence to the debatable propositions on the performance of fundamental portfolios in emerging markets. Furthermore, the findings may help domestic and international investors, practitioners and decision-makers to deepen their knowledge in terms of the best portfolio construction scheme in the MENA region.

Early involvement of the construction team is increasingly utilized in demanding projects to incorporate versatile expertise in their planning. For public owners this is a challenge since they are obliged to use competitive, transparent team selection based on the ‘most economically advantageous’ criterion which ensures that both price and quality viewpoints are taken into account. In the case of early involvement, the price component naturally does not include the total price, but may consist only of the fee-percentages of competing service providers. This study examines such a selection situation in project alliancing in the European context and seeks to find a way to integrate the fee component in a multi-criteria selection system and determine reasonable fees for different levels of capabilities. The study builds on the performance difference between different capabilities, derived from a survey of practitioners, and determines an indifference curve arithmetically for the planning of a selection method. The influence of the owner‘s risk attitude and risk premiums are also considered exploratively based on the pricing methods of the theory of finance.

Although the challenge of food waste (FW) in the foodservice sector is significant, restaurant managers do not always engage in its reduction. The psychological reasons for this disengagement remain insufficiently understood. This study aims to explore the antecedents of behavioural intention of restaurateurs (not) to reduce FW. The influence of three factors is tested, namely, market orientation; environmental apathy alongside selected neutralization techniques, namely, appeal to higher loyalties; denial of injury and denial of responsibility.

The study uses the method of a large-scale managerial survey (n = 292) administered in the commercial foodservice sector of Spain. The data are analysed via structural equation modelling with partial least squares.

The study finds that market orientation affects managerial intention to reduce FW but not their attitude, while environmental apathy influences managerial attitudes but not their behavioural intention. The study confirms the negative effect of such neutralizers as the appeal to higher loyalties and the denial of injury on suppressing managerial intention to reduce FW. Contrary to initial anticipations, another established neutralizer, the denial of responsibility, exerts no significant effect.

The study elaborates on the interventions necessitated to neutralize the effect of the neutralizers on managerial (un)willingness to reduce FW in the commercial foodservice sector.

This is the first known attempt to understand the drivers of managerial engagement in FW reduction in the commercial foodservice sector through the prism of environmental apathy, market orientation and neutralization theory.