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FAILURE of panels under static compression, or for that matter under any loads, involves a vast array of problems ranging from properties of material to initial instability and post‐buckling phenomena as occurring in various types of panels. It is not intended here to do justice to all these aspects of the subject but to select a single—but at the same time very important—topic, develop its analysis as fully as possible, and present the results in a readily applicable form. The structure investigated is the single skin stiffened panel under compression and the mode of failure considered, denoted by flexural cum torsional failure, involves predominantly flexure and torsion of the stringer with a wavelength of greater order of magnitude than stringer height and pitch. By torsional deformation of the stringer we understand a rotation of its undistorted cross‐section about a longitudinal axis R in the plane of the plate, the position of which will be selected later on (see FIG. 1b). The panel may, of course, also fail in a local mode of stringer and plate with a short wave‐length of the order of magnitude of stringer height and pitch, but the analysis of this case is not included here (see, however, Argyris and Dunne). Note that a local mode of deformation of a stringer formed by straight walls is commonly defined as a distortion of the cross‐section in which the longitudinal edges where two adjacent walls meet remain straight (see FIG. 1c).

With the advancement of technology, size, cost, and losses of the switched mode power supply (SMPS) have been decreasing. However, due to the high frequency switching, design of magnetic drives and isolation circuits are becoming a crucial factor in SMPS. This paper presents design criteria, procedure and implementation of AC-DC half bridge (HB) converter with lower cost, smaller size and lower voltage stress on the power switch.

The HB converter is designed in a symmetrical mode with a series coupling capacitor. Isolated power supplies are used for the converter and control circuit. Further, a transformer based isolated gate driver is used to drive both MOSFETs. The control IC works in voltage control mode to regulate voltage by controlling the duty cycle of the MOSFETs.

Control characteristics and performance of the HB converter is simulated using the MATLAB software and prototype of 170 W HB converter is built to validate the analytical results under variable load current and source voltage. The power quality and variation of load voltage at 2 A, 5 A, 7 A are reported.

This paper presents the design of a low-cost HB converter in a symmetrical mode which saves the additional cost of symmetric correction circuit normally required in asymmetrical mode design. This paper also focuses on the selection of primary and secondary side switch, series coupling capacitor, commuting diode, isolated drive and charge equalizer resistor.

MUCH reference is made in the aeronautical field to the flutter problem and the subject is receiving the attention of many persons engaged in research, testing, and design. Many aeronautical engineers are well acquainted with some aspect of the problem, and although only a few are concerned with its several phases it is safe to say that all aeronautical men regard it with some degree of interest. It is fitting, therefore, that although it has been adequately treated by many authors from other points of view, a statement be here made summarizing the flutter problem as one of the aeroplane designer. In order that the exact nature of this problem be appreciated it is first necessary that a few of the fundamentals be reviewed.

This paper aims to propose a new MLI topology with reduced number of switches for photovoltaic applications. Multilevel inverters (MLIs) have been found to be prospective for renewable energy applications like photovoltaic cell, as they produce output voltage from numerous separate DC sources or capacitor banks with reduced total harmonic distortion (THD) because of a staircase like waveform. However, they endure from serious setbacks including larger number of capacitors, isolated DC sources, associated gate drivers and increased control difficulty for higher number of voltage levels.

This paper proposes a new three-phase multilevel DC-link inverter topology overpowering the previously mentioned problems. The proposed topology is designed for five and seven levels in Matlab/Simulink with gating pulse using multicarrier pulse width modulation. The hardware results are shown for a five-level MLI to witness the viability of the proposed MLI for medium voltage applications.

The comparison of the proposed topology with other conventional and other topologies in terms of switch count, DC sources and power loss has been made in this paper. The reduction of switches in proposed topology results in reduced power loss. The simulation and hardware show that the output voltage yields a very close sinusoidal voltage and lesser THD.

The proposed topology can be extended for any level of output voltage which is helpful for sustainable source application.

The purpose of this paper is to find an influence of the reduced stiffness of actuators, located on the most outer parts of ailerons, flaperons, rudders, elevators and elevons on the excitation of flutter. This phenomenon is especially important for unmanned aerial vehicles because they continuously use all these control surfaces for trimming and stabilisation and on the other hand, the numerous statistics show that failure of elements of flight control systems are still the most probable reasons of aircraft critical failure.

Flutter calculations were performed by use of the classical modal approach. The normal vibrations of the free aircraft were measured in the ground vibration test (GVT). Test results were used either for verification of the FEM model of the structure – in this case for flutter calculation the MSC.Nastran software was used, or directly for flutter calculation. Based on the flutter analysis, the control surfaces critical for flutter were determined.

These so‐called critical control surfaces –, i.e. surfaces responsible for flutter excitation at first – are localized on outer parts of wing and empennage. It was found that the critical surfaces should have been mass balanced or should be irreversible. In the second case, i.e. when the control surfaces are irreversible, the actuators and drivers should have been of a high reliability, because disconnection of these elements could involve flutter.

This approach within the computational analysis is limited to linear case, otherwise NASTRAN software cannot be used for flutter analysis. GVTs could be performed successfully independently if the structure has linear or non‐linear properties.

It was found that before any flight the stiffness in the flight control system of all control surfaces must carefully be checked and kept above the critical stiffness value. Safety level strongly depends on the reliability of actuators used on such unmanned aerial vehicles. The simulation of disconnection (as a result of damage) of selected control surfaces is possible even if the GVT were provided on undamaged vehicle. To do it, the rotational mode of so‐called “free control surface” should be prepared (as an artificial resonant mode) for all deflected control surfaces; next all the resonant modes should be orthogonalized, relative to this artificial control surfaces mode.

This paper was based on two big European and national projects, and all presented results are original and were never published before. Some selected graphs were shown during the EASN Workshop, Paris, September 2010 at the presentation entitled: “Aeroelastic analysis of remotely controlled research vehicles with numerous control surfaces”.

A series of examples illustrates the application and results of the method previously given for improving the conditioning of the primary redundancies. The transformation matrix giving locally orthogonal redundancies for the parent station is used also to generate the primary self‐equilibrating stress systems for sections with different (but related) geometry and varying ring stiffness. A double‐cell cross‐section is also treated and a brief investigation shows that the general methods developed for establishing primary redundancies in the fuselage can be usefully and economically applied to certain kinds of wing structure. Preparatory to a detailed discussion of cut‐outs and modifications in the fuselage structure, the necessary general theory is collected and summarized.

The methods developed in sections (5)–(7) are now applied to the determination of the torsional cum flexural failing stresses in two panels. The following points should be noted:

If a thin oblique plate (i.e. in the shape of a parallelogram) is subjected to a uniform shear stress parallel and perpendicular to two of the sides, the critical value of the stress depends on the direction in which it is applied. The higher critical value is obtained when the shear is tending to decrease the obliquity of the plate. The ratio between the two critical shear stresses lies between 1 and 8 for a simply supported 45 deg. oblique plate and between 1 and 2·69 for a clamped 45 deg. oblique plate. This paper discusses the phenomenon for 45 deg. oblique plates and shows that even for plates of practical proportions the ratio between the two critical shear stresses may be of the order of 4 if the edges are simply supported.

A sustainable freight transportation system involves freight processes that are economically efficient, socially inclusive and environment friendly. For enhancing sustainability in the freight operations, mode selection is a crucial strategic decision. Therefore, the purpose of this paper is selecting the best mode, or a combination of modes based on various criteria to carry shipments from origin to destination.

This study has used an integrated grey relational analysis based intuitionistic fuzzy multi-criteria decision-making process (GRA–IFP) and fuzzy multi-objective linear programming model. Three scenarios have been developed for analyzing sensitivity of decision variables with the variations in parameters under relevant conditions. A real case of Indian third-party logistics service provider has been used to demonstrate the effectiveness of the model.

The most relevant criterion emerged out in this study for multi-mode selection problem is costs. It can be concluded from the study that multi-modal freight transportation has the potential to improve the sustainability of freight transportation by reducing the costs, damages, emissions, traffic congestion and by increasing the speed of delivering the shipment. The sensitivity analysis further shows that road is the economical mode, whereas sea and rail together are the greenest as well as socially responsible modes of transportation.

This study provides an integrated tool, which can be used by freight transporters to decide upon the sustainable modes of transportation for their various shipments.

The conditioning of the redundancy equations is discussed and a method is given for drastically reducing any serious coupling between primary redundancies originating at the same ring station. Making use of the latent root programme of the computer, a revised transformation matrix, for the definition of the primary redundancies, is developed for the specific cross‐sectional shape and geometry when this is markedly non‐circular. The method is illustrated by application to a number of sample cases. Coupling between redundancies at different ring stations is also discussed, but is not considered to be serious except with unusual patterns of frame flexibility.