Rectangular Test Research Articles

Experimental and numerical prediction of LBO performance in a centrally staged combustor

A new type of centrally staged combustor was proposed for an aeroengine combustor with a fuel–air ratio of 0.037. The combustor dome comprised a three-stage swirler, which included a pilot stage and main stage. The pilot stage was composed of Stage 1 and Stage 2 swirlers, and all swirlers were radial. The effects of different inlet Reynolds numbers and swirler structural parameters, including the installation angle of the first radial swirler, installation angle of the second radial swirler, installation angle of the main stage, and co– and counter-rotation of Stage 1 and Stage 2 swirlers on the lean blow-out (LBO) performance of the centrally staged combustor were examined at an atmospheric pressure and inlet temperature of 473 K. Experiments with single-dome rectangular test pieces and numerical methods were used. The results showed that the fuel–air ratio decreases with an increase in the inlet Reynolds number, indicating that the increase in inlet Reynolds number plays an important role with respect to the LBO. When the rotation directions of Stage 1 and Stage 2 swirlers were opposite, the fuel–air ratio of the LBO was smaller than that of Stage 1 and Stage 2 swirlers in the same rotation direction, indicating that the rotation directions of Stage 1 and Stage 2 swirlers significantly affect the LBO performance. Stage 1 and Stage 2 swirlers exhibited the best LBO performance when they rotated in opposite directions, and the rotation direction of the main stage slightly affected the LBO performance. The best combination of rotation directions is that the rotation directions of Stage 1 and Stage 2 swirlers should be opposite and rotation direction of Stage 2 swirler should be the same as that of the main stage. With the increase in the installation angle of Stage 1 and Stage 2 swirlers, the LBO fuel–air ratio decreased by nearly 4% and 9%, respectively, and the LBO performance improved. The prediction of the LBO limit of 0.00553, using the fuel steady-state successive approximation method, was less than 0.0066, which was measured in the test, indicating that the method should be improved. The flow field characteristics of the LBO process, which could not be obtained in the test process, were obtained via numerical simulation.

Expansive Soil Swelling Test of Small Scale Laboratory Model on Sambungmacan Soil, Central Jawa

Soil is one of the most important elements in any civil engineering work, almost all construction activities are related to soil. One of the most common soil problems is expansive soil. This type of soil has a high potential to expand when compared to other types of soil. This research aims to find out how expansive the tested soil is and how it reacts when wetting. The test in this research is experimental, where the expansive soil test is modeled in a rectangular test box with a soil volume of 0.08 m3. The swelling and expansion pressures were measured using proving rings and dials, each totaling five units. The expansive soil used came from Sambungmacan Subdistrict, Sragen Regency, Central Java. The results of the property index test of Sambungmacan soil have a plasticity index percent value of 49.33% and a liquid limit (LL) of 90.16%. The test results showed that the maximum swelling reached 28.3% of the initial soil height of 200 mm and the maximum soil swelling pressure reached 103.23 kPa with a moisture content of 22.62%. The maximum pressure that occurs in each proving ring is at an average moisture content of 31.81%. The results of this study also show the effect of every 1% moisture content will produce a percent soil swelling of 0.40% to 1.08% and the average percentage of swelling pressure that occurs is in the range of 4.65 kPa to 10.26 kPa at every 1% swelling.

Determination of mode-II critical energy release rate using mixed-mode phase-field model

To overcome the harsh experimental conditions of obtaining the mode-II critical energy release rate GIIC, an easy and flexible method for determining GIIC is proposed based upon the mixed-mode fracture experiments and corresponding simulations using the mixed-mode phase-field model. In details, a mixed-mode fracture experiment is first conducted to determine the initial crack deflection angle. Subsequently, a range of phase-field numerical simulations are conducted through adjusting the value of GIC/GIIC to reproduce the experimental results so as to determine the value of GIIC with a known GIC. Three mixed-mode fracture tests (single edge cracked circular test, central crack rectangular tension test and compact tension shear test) of PMMA indicate that the determined GIIC is a stable material parameter independent of test and loading conditions. Meanwhile, the determined prediction of GIIC is compared with those in other references with a deviation of about 3.5%, which demonstrates that the proposed method can quantitatively and qualitatively obtain GIIC. Furthermore, the determined parameter GIIC is used to develop the mixed-mode phase-field model through using the mode-mixity factor (GIC/GIIC) to regular the relative proportions of volumetric and distortional crack driving energy, which results in better numerical results than the classical phase-field model (with relative deviation < 1.0%). Without the harsh conditions of the pure mode-II fracture experiment, the proposed method is of significant practice in the determination of GIIC.

Effect of stress level on creep-fatigue interaction of woven angle ply GFRP laminates

In this study, effect of stress level on creep-fatigue interaction of woven angle ply glass fiber reinforced polymer (GFRP) has been studied. The rectangular test specimens were manufactured using bidirectional woven ply (45˚/-45˚) E-glass fiber of eight layers with 300 GSM and layer thickness to be 0.25 mm used as fibre reinforcement and LY556 epoxy Araldite based on Bisphenol A and HY951 hardener mixed as matrix material in the ratio of 10:1. Rectangular specimens were made from the prepared laminates and tested under tensile cyclic loading of constant amplitude at stress ratio 0.1 for three stress levels 80%, 70% and 60% of ultimate tensile strength (UTS) as per ASTM standard D3479. The results showed that cyclic creep strain depends on the stress level and rapid increase in strain happens after 75% of lifecycle at all stress level.

Failure Analysis of Beam Composite Elements Subjected to Three-Point Bending Using Advanced Numerical Damage Models

Abstract This paper deals with the experimental and numerical analysis of three-point bending phenomenon on beam composite profiles. Flat rectangular test specimens made of carbon–epoxy composite, characterised by symmetric [0/90/0/90]s laminate ply lay-up, were used in this study. Experimental testing was carried out with a COMETECH universal testing machine, using special three-point bending heads. In addition, macroscopic evaluation was performed experimentally using a KEYENCE Digital Microscope with a mobile head recording real-time images. Parallel to the experimental studies, numerical simulations were performed using the finite element method in ABAQUS software. The application of the above-mentioned interdisciplinary research techniques allowed for a thorough analysis of the phenomenon of failure of the composite material subjected to bending. The obtained research results provided a better understanding of the failure mechanism of the composite material.

Numerical and experimental investigation on the melting heat transfer of nanographene-enhanced phase change material composites for thermal energy storage applications

Phase change materials (PCMs) low thermal conductivity limit the performance of latent heat thermal energy storage systems. To enhance the thermal conductivity of the heat storage medium, highly conductive additives could be added to the base PCM. Hence, the present work aims to perform numerical and experimental investigations on the melting heat transfer of the PCM (OM 65) loaded with highly conductive graphene nanoparticles (GNPs) at weight fractions of 1%, 2%, and 3%. Based on the aforementioned weight fractions of graphene nanoparticles in the PCM, the nanographene-enhanced PCM (NPCM) composites are named NPCM 1, NPCM 2, and NPCM 3 respectively. The temperature-dependant thermal conductivity and dynamic viscosity were measured. A transient heat transfer during the melting of the PCM and NPCMs in a two-dimensional rectangular domain heated from the bottom-up configuration was considered for the numerical study. The base temperature was maintained at a constant temperature (Th = 70 °C), and the remaining walls are adiabatic. The transient variation of liquid fraction and temperature were presented. The PCM and NPCMs are experimentally studied using the proposed three-dimensional rectangular test section with twenty-four thermocouples and a temperature logger. Compared to the base PCM, the reduction in melting time from the numerical and experimental study was 37.5% and 36.5% for NPCM 3. It was evident that adding GNPs to PCM enhances its thermal conductivity. However, the higher concentration of GNPs could drastically increase the NPCMs viscosity, as well as cause agglomeration and sedimentation of GNPs during melting. Therefore, adding a maximum of 3wt% GNPs into the PCM was recommended.

Flow Behavior and Microstructure of Hot-Worked Fe-30.9Mn-4.9Al-4.5Cr-0.4C and Fe-21.3Mn-7.6Al-4.3Cr-1C Low-Density Stainless Steels

Two as-cast low-density steels grades (austenite-based duplex Fe-30.9Mn-4.9Al-4.5Cr-0.4C and austenitic Fe-21.3Mn-7.6Al-4.3Cr-1C) with an initial dendritic microstructure were subjected to hot working conditions to understand the influence of deformation parameters on flow behavior and microstructural evolution. The alloys were produced using electric arc melting, and their phase constituents were determined using optical microscopy and X-ray diffraction analysis. This was then corroborated with the phase predicted from Thermo-Calc simulation. The as-cast alloys were machined to 10 × 10 × 7 mm specimen configurations for rectangular axial testing on the Gleeble 3500 thermomechanical simulator. The samples were deformed to a total strain of 0.5 at different deformation temperatures (800, 900, and 1000 °C) and strain rates (0.1 and 5 s−1). Thereafter, a hardness test was conducted on the deformed samples, and post-deformed microstructures were analyzed using optical and scanning electron microscopes. The results showed that the alloys’ dendritic structures were effectively transformed at temperatures below 1000 °C regardless of the strain rate. At all deformation conditions, the peak flow stress of Fe-21.3Mn-7.6Al-4.3Cr-1C alloy was at least 50% higher than that of Fe-30.9Mn-4.9Al-4.5Cr-0.4C alloy owing to the higher carbon content in the austenitic low-density stainless steel. The hardness of all the deformed samples was superior to that of the as-cast samples, which indicates microstructural reconstitution and grain refinement in the alloys. Dynamic recrystallization, dynamic globularization, and dynamic recovery influenced the softening process and the microstructural changes observed in the alloys under different deformation conditions.

Conceptual design of narrow rectangular channel test section for research reactor application

Conceptual design was carried out on test section for studying heat transfer characteristics of narrow rectangular channel for research reactor application. Thermal hydraulic design requirements were specified through literature study on mid- to high-powered research reactors currently under operation or design. Engineering design was then carried out in streamlined fashion with help of in-house design code and computational fluid dynamics analysis. Considering various constraints and uncertainties in terms of engineering hot channel factors, sensitivity studies were performed and realistic test section design was obtained. For final design, stochastic operable heater power map is generated by merging individual operable ranges from each constraint, with random sampling of hot channel factors.

Classification of Corrosion Flaws on Front and/or Back Surfaces of Non-Magnetic Metal Plates Using a Rectangular Wave Eddy Current Testing System

If a rectangular wave excitation current is used for eddy current testing (ECT) instead of a sinusoidal wave, multifrequency testing can be performed directly because rectangular waves contain a fundamental wave as well as harmonic waves. Furthermore, considering the skin effect, it is possible to determine whether the specimen has a corrosion flaw on the front surface, back surface, or flaws on both surfaces. In this study, we first evaluate a method to classify these flaws on non-magnetic metal plates using rectangular wave ECT (RECT) systems with a linear amplifier. Here, we present an indicator in which each harmonic amplitude is divided by its fundamental amplitude. The results indicate that the amount of attenuation of the indicator in relation to the frequency depends on the type of flaw; therefore, we can classify the type of flaw using the indicator. Subsequently, we developed a RECT system with an inverter and conducted the same experiment. The results indicate that the tendency is the same as that when using the RECT system with a linear amplifier, which contributes to high efficiency, low cost, and weight reduction.

Examination of Convective Behavior of Pressure-Driven Flow in a Single-Sided Heated Rectangular Test Section based on micro-PIV Measurement

Examination of Convective Behavior of Pressure-Driven Flow in a Single-Sided Heated Rectangular Test Section based on micro-PIV Measurement

Improving tidal turbine array performance through the optimisation of layout and yaw angles

Tidal stream currents change in magnitude and direction during flood and ebb tides. Setting the most appropriate yaw angles for a tidal turbine is not only important to account for the performance of a single turbine, but can also be significant for the interactions between the turbines within an array. In this paper, a partial differentiation equation (PDE) constrained optimisation approach is established based on the Thetis coastal ocean modelling framework. The PDE constraint takes the form here of the two-dimensional, depth-averaged shallow water equations which are used to simulate tidal elevations and currents in the presence of tidal stream turbine arrays. The Sequential Least Squares Programming (SLSQP) algorithm is applied with a gradient obtained via the adjoint method in order to perform array design optimisation. An idealised rectangular channel test case is studied to demonstrate this optimisation framework. Located in the centre of the computational domain, arrays comprised of 12 turbines are tested in aligned and staggered layouts. The setups are initially optimised based on their yaw angles alone. In turn, turbine coordinates and yaw angles are also optimized simultaneously. Results indicate that for an aligned turbine array case under steady state conditions, the energy output can be increased by approximately 80\% when considering yaw angle optimisation alone. For the staggered turbine array, the increase is approximately 30\%. The yaw optimised staggered array is able to outperform the yaw optimised aligned array by approximately 8\%. If both layout and the yaw angles of the turbines are considered within the optimisation then the increase is more significant compared with optimising yaw angle alone.

Conjugate Heat Transfer Simulations of a Nozzle Flow over a Film-Cooled Plate

This paper presents Ansys Fluent results for a rectangular exhaust nozzle test case from the Fifth AIAA Propulsion Aerodynamics Workshop. The main objective of the workshop was to assess the aerothermal interaction of a heated air exhaust with a film-cooled plate downstream of a convergent nozzle exit, which is representative of engine exhaust flow applications with film cooling. Two sets of hierarchical computational meshes are employed. The first set of meshes consists of workshop-provided Pointwise® meshes. The second set of meshes is generated using Ansys Fluent meshing. Steady conjugate heat transfer simulations with radiation are performed to account for heat conduction through solid materials as well as the electromagnetic heat produced by the solid surfaces of the plate, plenum, and nozzle. Reynolds-averaged Navier–Stokes simulations using the shear-stress turbulence model are conducted for a workshop-defined nozzle condition, set point 42, using three blowing ratios. Computational fluid dynamics results are validated against experimental velocity and temperature measurements recorded above the film-cooled plate.

DEVELOPMENT OF HIGH ENERGY AND FUEL ECONOMY CERAMIC INSULATED BIOMASS MULTI COOKING SYSTEM

The analysis of Inyi clay and its utilization in the production of an improved cook-stove is significant to the existence of mankind and his community. This study was carried out to analyse the mixture of clay, cassava peel and grog and its utilization in the production of an improved cook-stove. The clay deposits were collected from Inyi Local Government, Enugu State. Different ratios of the mixture was used in the following percentage proportions by weight of clay to cassava peel to grog: A (40:40:20), B (40:30:30), C (40:20:40), D (40:10:50) at firing temperatures 900oC and 1000oC. The physical analysis (apparent porosity, linear shrinkage, dry-fired shrinkage, total shrinkage, bulk density, water absorption and percentage making moisture) was carried out using rectangular shape test piece to ascertain the feasibility in the lightweight stove production, the strength and the durability of products. The chemical analysis (xrd and xrf) was carried out using x-ray diffractometer and x-ray fluorescence in order to determine their crystallographic parameters and elemental composition respectively. The morphological analysis (SEM) was carried out using the scanning electrode microscope to obtain the resolutions and magnifications. The addition of cassava peel and grog was found to have great effect on the insulating properties (shrinkage, bulk density, apparent porosity and water absorption) of the clay. Chemical analysis revealed SiO2 (45.26%) and Al2O3 (35.19%) as major constituent. The result of this study showed that cassava peel was suitable in enhancing the insulating properties of Inyi clay and can be utilized to induce insulation in clay minerals when desired.

High power test of the power coupler for 325 MHz superconducting cavities with standing waves

The fabricated power coupler is a coaxial capacitive-type coupler based on a conventional 3 1/8-inch Electronic Industries Alliance 50-Ω coaxial transmission line with a titanium nitride (TiN)-coated ceramic disk window. A high-power test in a standing wave was performed with the 20 kW and 325 MHz solid-state power amplifier (SSPA). The standing wave test is similar to the RF conditioning condition of the cavity before beam operation. It is also possible to adjust the position of the maximum power applied to the power coupler. Two power couplers were connected to a rectangular test cavity with a high vacuum and various measuring equipment, such as an arc detector, a power meter, a temperature sensor, and an electron pick-up probe. The interlock system under vacuum and arc instrumentation prevented the RF window from breaking the power coupler window during the high-power test. The interlock system was operated when the temperature, arc discharge, and electron emission were measured and exceeded the threshold. We conducted high-power tests at 3 kW in a standing wave to verify the performance of the fabricated power coupler. In this paper, we present the results of the high-power test with standing waves using movable shorts.

Effect of turbulence modelling and non-condensable gas on cloud cavity dynamics

Turbulence modelling plays an important role in the prediction of unsteady and highly dynamic characteristics of cavitating flows. The models with turbulent viscosity modification as Density-Corrected Method (DCM) and Filter-Based Model (FBM), can deal with the dynamics of cavitating flows. Taking it into account, the application of these models to the cavitating flows of water with dissolved air (i.e. third phase) to predict the unsteady phenomena are worth to be analysed and compared. Due to poor self-oscillation characteristics of RNG k-epsilon model in modelling of the cavitating flow, in the present study, the DCM and FBM are implemented to perform the simulation of cavitating flow with consideration of dissolved air. Also, the numerical results are compared with the experimental data. The experiments are conducted in a rectangular test section equipped with Clark Y hydrofoil providing cavity visualisation, instantaneous pressure and vibration fluctuations. The simulations are carried out for different cavitation numbers with and without dissolved air. The Fast Fourier Transform and Continues Wavelet Transform are implemented to extract and compare the shedding frequency of experiments and numerical predictions. In addition, the influence of modification models on the cloud cavitation shedding evolution, dominant shedding frequency, vorticity, pressure, velocity profile, lift/drag coefficient is evaluated.

Feasibility of the photon spectrum generalisation model for rapid Monte Carlo dose calculation with a deep learning-based framework

PurposeWe propose a deep learning-based strategy for the training of the radiotherapy dose calculation using limited data based on two known energy spectra within the general range of radiotherapy linear accelerators. MethodsWe constructed a dose map using complete photon and electron Monte Carlo (MC) simulations with random rectangular field sizes, iso-centres, and gantry angles for pelvic computed tomography images with Mohan 4 and 24 MV spectrum photon beams. Two trained models, the virtual dose map-MC (VDM-MC) and improved VDM-MC (IVDM-MC) were tested under Mohan 4, 6, 10, 15, and 24 MV energy conditions in rectangular and intensity-modulated radiation therapy (IMRT) fields. A 3D gamma evaluation assessed the model's performance. ResultsFor VD-MC, the 3%/3 mm and 2%/2 mm criteria gamma pass rates were 92.58 ± 0.87% and 85.31 ± 1.56%, respectively, using the rectangular field test, whereas they were 97.03 ± 0.63% and 90.97 ± 1.46%, respectively, using the IMRT field test. For IVD-MC, the 3%/3 mm and 2%/2 mm criteria gamma pass rates were 97.86 ± 0.35% and 92.98 ± 0.77%, respectively, using the rectangular field test, and 98.57 ± 0.14% and 95.11 ± 0.33%, respectively, using the IMRT field test. ConclusionFeasibility of a single model to achieve accurate and rapid MC dose calculations for photons with different energy spectra was preliminarily verified. This data augmentation strategy effectively generalised the scope of the model.

Prolonging rubber fatigue life using hysteresis of strain-induced crystallization of natural rubber

Recently, soft robots have attracted considerable attention; however, they often undergo large deformations. Thus, their lifespans are critical issues. Therefore, this study proposes a novel method for extending the lives of rubber materials. We extend the fatigue life of rubber materials by focusing on the hysteresis of the strain-induced crystallization characteristics of rubber. Strain-induced crystallization is a phenomenon wherein rubber molecules exhibit crystal structures by elongation. These crystal structures are generated by elongation and disappear with relaxation. However, hysteresis occurs in both the generation and disappearance processes. Therefore, if the rubber is not completely relaxed, the disappearance of the crystal layers is slowed by hysteresis, and the formation of cracks is hindered. Herein, we select two types of rubbers: those exhibiting strain-induced crystallization characteristics (natural rubber (NR)) and those that do not (styrene-butadiene rubber (SBR)). First, wide-angle X-ray diffraction is used to confirm the formation of crystal layers under stretching for both types of rubbers. Fatigue life test is conducted using rectangular test pieces made of NR and SBR by repeated tensile tests. Subsequently, a fatigue life test is conducted for a straight-fiber-type pneumatic artificial muscle prepared by NR and SBR. The results reveal that the fatigue life is approximately 100 times longer than normal, thereby confirming the effects of prolonging the fatigue life using the hysteresis of strain-induced crystallization.

Wrinkling limit curves with consideration of anisotropic behaviour for the deep drawing of aluminium sheet alloys

In this work, a combined experimental and finite-element (FE)-based approach was introduced for determining the wrinkling limit curves (WLCs) of sheet metals during forming processes. Aluminium sheets of grade AA5052-O and AA5052-H32 with different formabilities and anisotropic behaviours were investigated. Modified Yoshida buckling tests were carried out for aluminium sheets in both the rolling (RD) and transverse direction (TD). In parallel, FE simulations of the buckling tests were conducted, in which the Hill’48 (both r- and stress-based) yield criteria and Swift strain hardening law were incorporated. Local principal strain histories of observed wrinkle areas on both surfaces of samples were gathered from the simulations and the state of wrinkling initiation was then identified at the inclination of these strain paths. The calculated strain values were verified with developed compressive stresses as well as corresponding strains measured by a digital image correlation technique. The influences of material anisotropies and used yield functions on the determined WLCs were discussed. Subsequently, the determined WLCs were applied for evaluating non-flange wrinkling formation during a rectangular cup drawing test. The forming tests were experimentally and numerically performed for the examined aluminium sheets in both RD and TD. It was found that strain distributions of critical side wall areas at predicted wrinkling onset and severe wrinkle states were well correlated with the WLCs. Thus, WLCs based on the r-based criterion could more accurately describe the non-flange wrinkling incidents of the cup-drawn samples than those of the stress-based model.

Sandwich structure with negative Poisson’s ratio of periodic rectangular tube: Mechanical properties and energy absorption

Due to its unique deformation form, Negative Poisson’s ratio sandwich structure has excellent energy absorption, but the low load capacity limits its engineering applications. In this paper, we design a new negative Poisson’s ratio rectangular tube periodic sandwich structure. There are many beams in this structure which appear plastic hinges when compressed. After further compression, the rectangular tube wall buckles and the core shrinks inward, which realizes that the structure exhibits high-performance energy absorption ability and excellent mechanical properties. Three-dimensional finite element model of sandwich structure with negative Poisson’s ratio of periodic rectangular tube quasi-static compression test and low-velocity impact were investigated by the use of ABAQUS/Explicit software. The accuracy of the simulation method was verified by the comparison of test and simulation results. Based on the validated numerical models were further investigated to comprehensively understand the influence of rectangular tube unit cell wall thickness ( t) and cell height ( h) on the load capacity and energy absorption capacity of the specimen. The energy absorption capacity and mechanical properties of the proposed negative Poisson’s ratio sandwich structure could be enhanced by optimizing the design of rectangular tube unit cell wall thickness ( t) and rectangular tube unit cell height ( h). The present findings offer insights into the application of negative Poisson’s ratio sandwich structure impact energy-absorbing structures in aerospace, automotive and other fields.

Sensory basis of food detection in tadpoles of Polypedates maculatus (Anura: Rhacophoridae): an experimental approach

The mechanism of food detection in tadpoles of Polypedates maculatus was experimentally tested. We used a rectangular glass test tank with stimulus zones in opposite ends to provide visual and/or chemical food. For visual cues, boiled spinach was placed inside a glass container, and for chemical cues boiled spinach was placed in a mesh cage. Each tadpole of P. maculatus (either at an early or medium developmental stage) was held at the center of the test tank for acclimation. The tadpole was released, and we recorded whether it approached or did not approach the caged food. Tadpoles of all stages failed to detect food using visual cues. Tadpoles of all stages detected food using chemical cues. In tests using chemical cues, they spent the majority of their time (69.3% by early stage tadpoles and 87.3% by medium-stage tadpoles) near the container with food than in the end with no containers or with only visual food cues. Tadpoles in medium stages spent more time near food (18.1% of total time) than tadpoles in early stages. These findings indicate that tadpoles of P. maculatus detect food by chemical sensory mechanisms rather than visual ones. Tadpoles in medium stages spent more time near food than tadpoles in early stages indicating that time spent foraging increases as tadpoles grow.