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The purpose of this paper is to propose an identification method of acquiring aircraft mode characteristics based on fast Fourier transform and half-power bandwidth method, aiming at the common oscillation met in flight test.

The feasibility of this method is demonstrated through derivation; the robustness analysis is conducted through three examples, and finally the method was applied on a set of sideslip angle record from flight test.

The derivation and numerical analysis both show that the presented method can have high accuracy and good robustness under coupled mode and noise condition.

The method proposed is of robustness, and it is concise and easy to apply on flight data record.

This paper demonstrates the feasibility of half power bandwidth to be applied on oscillation mode characteristics identification from flight data record, which is different from other method applied.

The purpose of this study is to set up a dynamic model of material extrusion (ME) additive manufacturing plates for the prediction of their dynamic behavior (i.e. dynamic inherent characteristic, resonant response and damping) and also carry out its experimental validation and sensitivity analysis.

Based on the classical laminated plate theory, a dynamic model is established using the orthogonal polynomials method, taking into account the effect of lamination and orthogonal anisotropy. The dynamic inherent characteristics of the ME plate are worked out by Ritz method. The frequency-domain dynamic equations are then derived to solve the plates’ resonant responses, with which the damping ratio is figured out according to the half-power bandwidth method. Subsequently, a series of experimental tests are performed on the ME samples to obtain the measured data.

It is shown that the predictions and measurements in terms of dynamic behavior are in good agreement, validating the accuracy of the developed model. In addition, sensitivity analysis shows that increasing the elastic modulus or Poisson’s ratio will increase the corresponding natural frequency of the ME plate but decrease the resonant response. When the density is increased, both the natural frequency and resonant response will be decreased.

Future research can be focused on using the proposed model to investigate the effect of processing parameters on the ME parts’ dynamic behavior.

This study shows theoretical basis and technical insight into improving the forming quality and reliability of the ME parts.

A novel reliable dynamic model is set up to provide theoretical basis and principle to reveal the physical phenomena and mechanism of ME parts.

The purpose of this paper is to present weighted residual method (WRM) for evaluating damping ratio of unreinforced glued‐laminated (glulam) wood beams and also reinforced glulam beams with E‐glass reinforced epoxy polymer (GRP) plates.

In this method, created error from the regression curve to the peak points of experimental displacement values is minimized. Several weight functions such as Galerkin weight function, Petrov‐Galerkin weight functions, and least square weight function are used for minimizing this error and results from these methods are compared to the existing methods as; logarithmic decrement analysis (LDA), Hilbert transform analysis (HTA), moving block analysis (MBA), and half power bandwidth (HPB).

Because WRM tries to minimize the error function provided from differences between theoretical and experimental fitted curves, comparison among these methods indicate that proposed procedure is useful for any range of damping ratios and it gives better values in comparison with the other methods. Due to the initial conditions and weight function used in Galerkin weighted residual method, damping ratio values obtained from this method have different values from the other weighted residual methods. Among the existing methods, HPB method could not predict damping ratio of the glulam beams accurately.

This paper is a high quality research paper that presents weighted residual method (WRM) for evaluating damping ratio of unreinforced glued‐laminated (glulam) wood beams and also reinforced glulam beams with E‐glass reinforced epoxy polymer (GRP) plates. In this paper, LDA, HTA, MBA, and HPB methods are used and an analytical investigation of damping ratios of glulam beams unreinforced and reinforced with GRP plates is proposed by using weighted residual method (WRM). Although there is a simplifier assumption in some of existing methods, proposed method shows the damping ratio can be calculated without any requirement to simplifier assumption.

Condition assessment on reinforced concrete (RC) structures is one of the critical issues as a result of structure degradation due to aging in many developed countries. The purpose of this paper is to examine the sensitivity and reliability of the conventional dynamic response approaches, which are currently applied in the RC structures. The key indicators include: natural frequency and damping ratio. To deal with the non-linear characteristics of RC, the concept of random decrement is applied to analyze time domain data and a non-linear damping curve could be constructed to reflect the condition of RC structure.

A full-scale RC structure was tested under ambient vibration and the impact from a rubber hammer. Time history data were collected to analyze dynamics parameters such as natural frequency and damping ratio.

The research demonstrated that the measured natural frequency is not a good indicator for integrity assessment. Similarly, it was revealed that the traditional theory of viscous damping performed poorly for the RC with non-linear characteristics. To address this problem, a non-linear curve is constructed using random decrement and it can be used to retrieve the condition of the RC structure in a scientific manner.

The time domain analysis using random decrement can be used to construct a non-linear damping curve. The results from this study revealed that the damage of structure can be reflected from the changes in the damping curves. The non-linear damping curve is a powerful tool for assessing the health condition of RC structures in terms of sensitivity and reliability.

Unlike conventional aircraft, birds can glide without a vertical tail. The purpose of this paper is to analyse the influence of dihedral angle spanwise distribution on lateral-directional dynamic stability by the simulation, calculation in the development of the bird-inspired aircraft and the flight testing.

The gliding magnificent frigatebird (Fregata magnificens) was selected as the study object. The geometric and mass model of the study object were developed. Stability derivatives and moments of inertia were obtained. The lateral-directional stability was assessed under different spanwise distributions of dihedral angle. A bird-inspired aircraft was developed, and a flight test was carried out to verify the analysed results.

The results show that spanwise distribution changing of dihedral angle has influence on the lateral-directional mode stability. All of the analysed configurations have convergent Dutch roll mode and rolling mode. The key role of dihedral angle changing is to achieve a convergent spiral mode. Flight test results show that the bird-inspired aircraft has a well-convergent Dutch roll mode.

The theory that birds can achieve its lateral-directional stability by changing its dihedral angle spanwise distribution may explain the stability mechanism of gliding birds.

This paper helps to improve the understanding of bird gliding stability mechanism and provides bio-inspired solutions in aircraft designing.

The purpose of this paper is to evaluate the applicative potentiality of functional/self-responsive materials in aeronautics. In particular, the study aims to experimentally validate the enhancement of structural performances of carbon fibers samples in the presence of nanofillers, as multi-walled carbon nanontubes or microcapsules for the self-healing functionality.

The paper opted for a mechanical study. Experimental static and dynamic tests on “blank” and modified formulations were performed in order to estimate both strength and damping parameters. A cantilever beam test set-up has been proposed. As a parallel activity, a numerical FE approach has been introduced to assess the correct modeling of the system.

The paper provides practical and empirical insights about how self-responsive materials react to mechanical solicitations. It suggests that reinforcing a sample positively affects the samples properties since they, de facto, improve the global structural performance. This work highlights that the addition of carbon nanotubes strongly improves the mechanical properties with a simultaneous slight enhancement in the damping performance. Damping properties are, instead, strongly enhanced by the addition of self-healing components. A balanced combination of both fillers could be adopted to increase electrical conductivity and to improve global performance in damping and auto-repairing properties.

The paper includes implications for the use of lightweight composite materials in aeronautics.

This paper fulfills an identified need to study new lightweight self-responsive smart materials for aeronautical structural application.

The prediction of critical velocity at instability threshold for shell and tube heat exchangers is important to avoid failure of tubes as a result of flow-induced vibrations due to water cross flow. The flow-induced vibration in finned tube heat exchangers is affected by various parameters such as fin height, fin pitch, fin material, tube array, pitch ratio, fin type, fluid velocity etc. In this paper, an experimental investigation of fluid elastic instability in shell and tube heat exchangers is carried out by subjecting normal square finned tube arrays of pitch ratio 1.79 to water cross flow.

The five tube arrays, namely plain array, two finned tube arrays with 3 fpi and 9 fpi fin density, and two finned tube arrays with 3 mm and 6 mm fin height are tested in the experimental test setup with water flow loop and vibration measurement system. The research objective is to evaluate the effect of fin density and fin height on the instability threshold. The critical velocity at instability threshold is determined to characterize the fluid elastic instability behavior of different tube arrays. The vortex shedding behavior of the tube arrays is also studied by determining Strouhal number corresponding to the small peaks before fluid elastic instability.

The fluid elastic instability behavior of the tube arrays was found to be the function of fin tube parameters. The experimental results indicate that an increase in fin density and fin height results in delaying the instability threshold for finned tube arrays. It is also observed that critical velocity at instability is increased for finned tube arrays compared to plain tube arrays of the same pitch ratio. The design modifications in the outer box have resulted in further reduction in the natural frequency. This enabled to reach clear instability for all the five-tube arrays.

The research data add the value to the present body of knowledge by knowing the effect of fin height and fin density on the fluid elastic instability threshold of normal square finned tube arrays subjected to water cross flow.

The purpose of this study is to investigate the efficiency of applied vibration in improving the forming quality (mechanical property and dynamics characteristics) of fused filament fabrication (FFF) parts.

A vibrating FFF three-dimensional printer was set up, with which the samples fabricated in different directions were manufactured separately without and with vibration applied. A series of experimental tests, including tensile tests, dynamics tests and scanning electron microscopy (SEM) tests, were performed on these samples to experimentally quantify the effect of applied vibration on their forming quality.

It has been found that the applied vibration can significantly increase the tensile strength and plasticity of the samples built in Z-direction, and obviously decrease the orthogonal anisotropy. It can also significantly change the sample’s natural frequency, decrease the resonant response and increase the modal damping ratio, thus improve the anti-vibration capability of FFF samples. In addition, the SEM analysis confirmed that applying vibration into FFF process could improve the forming quality of the fabricated part.

Future research may be focused on investigating the efficiency of applied vibration in improving the forming quality of parts fabricated by the other additive manufacturing techniques.

This study helps to improve the reliability of FFF parts and extend the application range of FFF technology.

A novel method to improve the forming quality of FFF parts is provided and the available information about the performance of dynamics characteristics.

In many cases, the external pipelines of aero-engine are subjected to random excitation. The purpose of this paper is to reduce the vibration response of the pipeline system effectively by adjusting the hoop layout.

In this paper, a spatial pipeline supported by multi-hoops is taken as the object, the methods of solution of the vibration response of the pipeline system by using pseudo excitation and hoop layouts optimization with amplitude reduction of vibration response as the goal are presented. First, the finite element model of the spatial pipeline system is presented. Then, an optimization model spatial pipeline is established. Finally, a case study is carried out to prove the rationality of the random vibration response analysis of the pipeline system. Furthermore, the proposed optimization model and genetic algorithm are applied to optimize the hoop layout.

The results show that the maximum response variance after optimization is reduced by 32.8%, which proves the rationality of the developed hoop layout optimization method.

The pseudo excitation method is used to solve the vibration response of aero-engine pipeline system, and the optimization of the hoop layout for aero-engine spatial pipelines under random excitation to reduce random vibration response is studied systematically.

This paper aims to analyze the effect of fin geometry on mechanisms of flow induced vibration. Finned tube arrays are used in a heat exchanger to increase its efficiency. Therefore, it is necessary to investigate the effect of geometric parameters of the fin fluid elastic instability and vortex shedding. In this paper, the effect of fin height, fin density and tube pitch ratio for parallel triangular tube array on fluid elastic instability and vortex shedding is analyzed.

Experimental analysis was carried out on a parallel triangular finned tube array with a pitch ratio of 1.79 subjected to water crossflow. The experimentation aims to study fluid elastic instability and vortex-induced vibration mechanism responsible for flow induced vibration for finned tube array. A fully flexible finned tube array of the copper tube was used with its base diameter of 19.05 mm and thickness of 2 mm. Over the tube surface, crimped fins of height 6 mm and the same material are welded spirally with fin density 8.47 mm and 2.82 mm. Experimental analysis was carried out on a test setup developed for the same. The results obtained for the finned tube array were compared with those for the plain tube array with the same base tube diameter.

For parallel triangular tube array of copper material, test results show that critical velocity increases with an increase in fin pitch density for low pitch tube array. Before the occurrence of instability, the rate of growth in tube vibrations is high for plain tubes compared to that with fin tubes. The results based on Owen’s hypothesis show vortex shedding before the occurrence of fluid elastic instability. The effect of fin geometry on vortex-induced forces is analyzed. For the tube array pattern understudy, the values of Conner’s constant K for coarse fin-tube and fine fin tube array are obtained, respectively, 6.14 and 7.25.

This paper fulfills the need for research on the effect of fin geometry on fluid elastic instability and Vortex shedding on a tube array subjected to water cross flow when the pitch ratio is less than two, i.e. with a low pitch ratio.