Endoscopic Imaging Using a Multimode Optical Fibre Calibrated with Multiple Internal References

The interferometric acquisition of the transmission matrix (TM) of a multimode optical fibre (MMF), which is at the heart of multimode fibre-based endoscopic imaging methods, requires using a reference beam. Attempts to use an internal reference, that is to provide the reference in a common pathway geometry through the MMF itself, lead to a speckled reference intensity and consequential occurrence of “blind spots”—locations where insufficient optical power in the reference wave inflicts strong measurement errors. Here we show that combining a relatively small number of TMs, which are measured using different internal references, facilitates a complete elimination of blind spots, and thereby a significant enhancement of the imaging quality.

Phase-shifting digital holography with an unknown reference beam

In digital holography, errors of the reference field degrade the quality of the reconstructed object field. In this paper, we propose an effective method in phase-shifting digital holography in which the reference field does not need to be known and perfect. The unknown complex amplitudes of both reference and object fields are derived simultaneously. The method employs only five digital holograms and a single execution of a phase retrieval algorithm. So, the required measurements and algorithm executions in this method are fewer than those in other methods; it suggests a simpler and faster method. The effectiveness of the suggested method is indicated by simulation, under noise-free and noisy conditions. Moreover, the capability of the method to extract full information about the phase singularities in both fields is demonstrated.

Flexural Strengthening of Reinforced Concrete Beams with Externally Bonded Hybrid FRP Laminate

This paper enumerates the effectiveness of externally bonded Hybrid Fiber Reinforced Polymers (HyFRP) laminates on reinforced concrete beams for flexural strengthening. A total of 5reinforced concrete beams of size 150 x 250 in cross section and length of 3000mm were considered in this study. All the beams were tested in four-point bending over a simple span of 2800 mm. Of the above five beams, one beam served as reference beam and the other four beams were HyFRP laminated. The variables considered in this study included thickness of HyFRP laminate and composite ratio. Adequate measurement was acquired on load and deflection characteristic of HyFRP strengthened as well as reference beam.

EFFICIENCY OF FLEXURAL STRENGTHENING OF REINFORCED CONCRETE BEAMS BY NEAR SURFACE MOUNTED CARBON FIBER REINFORCEMENT POLYMER RODS AND EXTERNALLY BONDED SHEETS

This study investigated the flexural behavior of reinforcement concrete beam strengthened with different techniques. The purpose of this research to study the various techniques of strengthening and knowing the effect of each technique on the beam behavior .Ten simply supported beams tested in this study. The total length of the beams and clear span were 1800mm and 1650mm, respectively. The cross section was (180×250) mm. Tested beams were divided into two categories’ the first category consist of one beams and considered as reference, while the second category consist of nine beams divided into Two groups according to the Strengthening techniques such as near surface mounted (NSM) and external bonded reinforcement (EBR).The experimental results showed improvement in ultimate load capacity for strengthened beams ranging from (6 to 89%) for NSM and (31 to 96%) for EBR and reduction in deflection for strengthened beams ranging from (6 to 43%) as compared with reference beam. When the number and length of CFRP bars are increased, the number of cracks increase while the width of the cracks and the spacing decrease, and the same observation is made when the width of the CFRP sheet is increased. The experimental load capacities of strengthened beams were compared with the design provisions given by ACI440.2R-17 guideline for NSM and EBR technique and EC2 guideline for EBR technique, the average ratio (1.2 and 0.97) respectively ,which showed that reasonable and a good agreement for all strengthened beams.

Experimental study on flexural strengthening of reinforced concrete beams with U-shaped steel under secondary load

This study proposes a new method to strengthen reinforced concrete (RC) beams with U-shaped steel, which can achieve rapid construction and great improvement in the flexural performance of RC beams. To investigate the influence of secondary load defined as newly applied loads after strengthening on the strengthening effect, a total of nine specimens were tested under four-point bending, including a reference beam, a strengthened beam under initial load, and seven strengthened beams under secondary load. The initial loading degree, the thickness of the bottom plate, and the height of the steel box were the main variables considered in this study. Testing results showed that compared with the reference beam, the flexural performance of strengthened beams was significantly enhanced, indicating the good joint performance of the U-shaped steel and the RC beams. Among the three main variables, the initial loading degree was found to have a minimal effect on the flexural performance while the thickness of the bottom plate and the height of the steel box had considerable influence, with the latter having a more pronounced effect. Testing results also showed that most of the strengthened beams experienced flexural failures, which were reflected by steel web peeling and buckling, and concrete crushing. Moreover, a formula was derived for calculating the flexural capacity of strengthened beams under secondary load. The results from the derived formula were found to be in good agreement with those from experiments.

Application of the contact and non-contact measuring techniques for on-ground resonance testing of the mini-UAV

Purpose The paper describes the application of two different vibration measurement methods for the identification of natural modes of the miniature unmanned aerial vehicle (UAV). The purpose of this study is to determine resonant frequencies and modes of mini-airplane within the specified range of frequency values. Design/methodology/approach Special measuring equipment was used including both contact and non-contact techniques. The measuring systems on equipment of the Institute of Aviation Technology in the Faculty of Mechatronics, Armament and Aerospace of Military University of Technology (Warsaw, PL) were used to conduct measurements. In traditional ground vibration testing (GVT) methods a large number of sensors should be attached to the aircraft. The weight of sensors and cables is negligible in relation to the mass of the large aircraft. However, for small and lightweight unmanned aerial vehicles, this could bring a significant mass component in relation to the total mass of the tested object. Findings The real mini-UAV construction was used to investigate its resonant modes in the range of frequencies between 0 and 50 Hz. After receiving the output values it is possible to perform some flutter calculations within the range of operational velocities. As there is no certainty that the computed modes are in accordance with those natural ones some parametric calculations are recommended. Modal frequencies depend on structural parameters which are quite difficult to identify. Adopting their values from the reasonable range it is possible to assign the range of possible frequencies. The frequencies of rudder or elevator modes are dependent on their mass moments of inertia and rigidity of controls. The critical speeds of tail flutter were calculated for various combinations of stiffness or mass values. Practical implications In this paper, some specific techniques of performing the GVT test were presented. Two different measuring methods were applied, i.e. the contact method and the non-contact method. Using the dedicated apparatus in relation to the mini-airplane, properly prepared in terms of mass distribution, rudders deflection stiffness and proper support, some resonant characteristics can be determined. The contact measuring system consists of a multi-channel analyzer, piezoelectric accelerometers, electrodynamic exciters, amplifiers, impedance heads and a computer with the Test.Lab Software. As the non-contact method, a laser scanning vibrometer was used. The principle of its operation is based on the separation of the emitted laser beam. The returning beam reflected from a vibrating object is captured by the camera and compared to the reference beam. Dedicated software analyzes collected data and on the basis of it creates animations of structural vibrational shapes and spectral plots within the investigated frequency range. Originality/value The object used for research is the mini-UAV Rybitwa – composite mini-plane with a classic aerodynamic layout manufactured in Institute of Aviation Technology Military University of Technology. In the work, both measurement methods and some sample results were presented. Results referenced to dynamic properties of the mini-UAV can be applied in the future for its finite element model tuning, what would be useful for the needs of some parametric analyzes in case of some UAV modifications because of its structural or equipment modifications.

Ductility of simply supported rubberized concrete beams

Dispose of waste rubberized tires become a dangerous problem around the world, represented a big serious risk to the sur-rounded environment. Many studies show that over 1000 million tires reach their expired date yearly and this figure is anticipated to be 5000 million tires by reaching 2030. A minor part of them is employed as recycled materials and the residual amount is stockpiled or buried. This paper aimed to successfully utilize the vast amounts of tire rubber waste existing currently in landfills. This paper represents a practical investigation of the ductility performance of the reinforced rubberized concrete beams. Thirteen reinforced concrete beams simply supported, with waste rubber tires mixtures vary from 0 to 8 percentage as aggregates replacements, were tested by mid-span load. Therefore, to examine the ductility performance of reinforced rubberized concrete beams, three sets of samples were made. In the first group, coarse aggregates in the concrete mix were replaced by different percentages of the waste rubber partials, while for the second group, crumb rubber was replaced for the fine aggregates, and for the third one, a mix of waste and crumbed rubber were replaced for both types of aggregates. Experimental results of rubberized specimens were also compared with that of the reference beam (without rubber replacement), the comparison results declare that concrete contains rubber particles is less ductile than conventional concrete.

Experimental investigations on concrete beams reinforced with equivalent service steel pipe

Different techniques were employed for the passage of different utilities through structural elements. The reduction of the overall building weight was the main concern that needs to be achieved, especially for a multistory building. It can be done with the eliminating of a suspended ceiling with a portion of the beam’s weight by taking the advantages of the hollow sections. In this study, an equivalent reinforcement to the traditional ribbed reinforcement was employed to fabricate a reinforced concrete (RC) beam with a hollow section along the length of the beam. A steel pipe was used based on the equivalent moment from section analysis. Two diameters were selected of steel pipes as an equivalent to the commercial reinforcement. A total of four RC beams were cast and tested, two of them with traditional reinforcement and the other with steel pipe reinforcement. The comparison showed a promising result in terms of ductility, cracking pattern, ultimate strength, and mode of failure compared to the reference beam. The peak loads for the specimens with steel pipe were 160.6 kN and 184 kN, while they were 192 kN and 203.5 kN for the beams with traditional reinforcement.

Digital analysis of a speckle pattern of chaotic mode composition and restoration of a regular intensity pattern after a multimode fiber

A process of mode matching in a chaotic speckle pattern without a reference beam responsible for the formation of a holographic grating was studied experimentally and theoretically. Our approach was based on measuring the amplitudes and phases of the Hermite-Gauss (HG) and Laguerre-Gauss (LG) modes in a speckle pattern formed by the radiation of a multimode gradient fiber. The speckle pattern was formed in a hologram of a spatial light modulator using a multimode gradient fiber model while taking into account the mode and polarization dispersion, as well as random phase jumps of each eigenmode. We managed to match 210 modes of the speckle pattern and restore not only the original pattern, but also each structured LG mode and the entire chain of HG eigenmodes.