Test Configuration Research Articles

Experimental Investigation on Off-Design Performances of Double-Swept Waverider

Wind-tunnel tests of the double-swept waverider were performed in the off-design states, aiming to analyze its potential advantage in wide-speed performances. The test configurations were generated using the planform-customized waverider design, developed from the osculating-cone method. Then models of double-swept waveriders with the bend and cusp head were fabricated, and compared with a model of a single-swept waverider also built using the same method. A variety of experiments in their on-design and off-design states were performed in the hypersonic wind tunnel FD-07 of our institute, and computational fluid dynamics were employed to simulate flowfields as a supplement. According to the wind-tunnel tests and flow simulations, the aerodynamic forces and longitudinal stability were obtained and analyzed. The aerodynamic performance of the double-swept waverider did not fall significantly when deviating from the design states. The general trend was that, as Mach number increased, the lift-to-drag ratios dropped slightly. The double-swept waverider featured large longitudinal stability margin in hypersonic states, and the change in Mach number had little effect on longitudinal stability. Compared with the single configuration, the double-swept waverider suffered a decrease in lift-to-drag ratio, but showed a significant improvement in longitudinal stability.

Testing of highly configurable cyber–physical systems — Results from a two-phase multiple case study

Cyber–physical systems are commonly highly configurable. Testing such systems is particularly challenging because they comprise numerous heterogeneous components that can be configured and combined in different ways. Despite a plethora of work investigating software testing in general and software product line testing in particular, variability in tests and how it is applied in industry with cyber–physical systems is not well understood. In this paper, we report on a multiple case study with four companies maintaining highly configurable cyber–physical systems focusing on their testing practices, with a particular focus on variability. Based on the results of the multiple case study, we conducted an interactive survey with experienced engineers from eight companies, including the initial four. We reflect on the lessons learned from the multiple case study. We conclude that experience-based selection of configurations for testing is currently predominant. We learned that variability modeling techniques and tools are not utilized and the dependencies between configuration options are only partially modeled at best using custom artifacts such as spreadsheets or configuration files. Another finding is that companies have the need and desire to cover more configuration combinations by automated tests. Our findings raise many questions interesting to the scientific community and motivating future research.

Extraction and selective promotion of zero-group velocity and cutoff frequency resonances in bi-dimensional waveguides using the electromechanical impedance method

This study showcases the electromechanical impedance (EMI) technique for extracting and promoting zero-group velocity (ZGV) and cutoff frequency resonances in a waveguide structure. We identify the mechanisms of multiple resonances in the EMI spectra via a wave propagation perspective. Both simulation and experiments reveal the fact that sharp resonances in the conductance spectra are associated with either ZGV or cutoff frequency points. Consequently, we design four test configurations to enhance local resonances by aligning induced motions with considered mode shapes. Reasonable agreement between simulation and experiment results is observed. We evaluate the performance of considered configurations in terms of mode enhancement, and configurations that can selectively promote certain mode families are summarized. This study also shines the light on the EMI technique for quantitative non-destructive evaluation (NDE) by potentially supporting the inverse characterization of mechanical properties of host structures.

On the Design of a Network Digital Twin for the Radio Access Network in 5G and Beyond.

A Network Digital Twin (NDT) is a high-fidelity digital mirror of a real network. Given the increasing complexity of 5G and beyond networks, the use of an NDT becomes useful as a platform for testing configurations and algorithms prior to their application in the real network, as well as for predicting the performance of such algorithms under different conditions. While an NDT can be defined for the different subsystems of the network, this paper proposes an NDT architecture focusing on the Radio Access Network (RAN), describing the components to represent and model the operation of the different RAN elements, and to perform emulations. Different application use cases are identified, and among them, the paper puts the focus on the training of Reinforcement Learning (RL) solutions for the RAN. For this use case, the paper introduces a framework aligned with O-RAN specifications and discusses the functionalities needed to integrate the NDT. This use case is illustrated with the description of a RAN NDT implementation used for training an RL-based capacity-sharing solution for network slicing. Presented results demonstrate that the implemented RAN NDT is a suitable platform to successfully train the RL solution, achieving service-level agreement satisfaction values above 85%.

Evaluation of equivalent crack propagation length and fracture energy of two commonly used rock fracture toughness test configurations based on Bažant’s size effect law

Purpose of this research is to apply the Bažant’s size effect law to investigate the effects of material properties, specimen size, normalized crack length and loading span on the equivalent crack propagation (ECP) length and fracture energy test results of cracked straight through Brazilian disc (CSTBD) specimens and notch semi-circular bend (NSCB) specimens, and to clarify the relationship between ECP length and fracture process zone (FPZ) length. The results indicate that the ECP length is positively correlated with the specimen radius, cf (the ECP length of the infinite-size specimen) and the loading span, and the influence of the normalized crack length on the ECP length has the dependence of specimen configuration. Both the apparent fracture energy and the equivalent fracture energy have size effect, and the fracture energy tested by the specimen with smaller cf are more reliable. Based on the analysis of the influence of normalized crack length and loading span on fracture energy test results, CSTBD specimen with normalized crack length of 0.4 is recommended for rock fracture toughness test. In addition, the FPZ length determined by digital image correlation technique is more accurate than that determined by stress intensity factor method and finite element model method, and the ratio of ECP length to FPZ length decreases with the increase of specimen size.

Comparison of player perceptions to mechanical measurements of third generation synthetic turf football surfaces

Mechanical testing of synthetic turf football surfaces is considered essential to ensure player performance and safety. However, it remains unknown how well the mechanical outputs reflect player perceptions of these surfaces. The first objective of this study was to investigate the agreement between the outputs from the Rotational Traction Tester and the Advanced Artificial Athlete with player perceptions across a range of controlled third generation turf football surfaces. The second objective was to identify the modifications to the Rotational Traction Tester and the Advanced Artificial Athlete configurations and output variables that give the strongest agreement with player perceptions. An indoor test area containing ten third generation turf surfaces with controlled hardness and traction properties was constructed. Each surface was tested using the Advanced Artificial Athlete and Rotational Traction Tester in their current configuration and in several modified configurations aimed at better replicating the player–surface interaction. Using a trained panel paired comparisons technique, 18 University footballers (11 males and 7 females) identified differences in the surfaces based on four sensory attributes Movement Speed, Slip, Leg Shock and Give. Results indicated strong agreement (correlation coefficients between 0.7 and 1.0) across several Rotational Traction Tester and Advanced Artificial Athlete testing configurations and output variables with player perceptions. It is recommended that the current Rotational Traction Tester is improved through added instrumentation to allow surface stiffness to be evaluated (the rate of generation of traction resistance). It is further recommended that the Advanced Artificial Athlete adopts a new algorithm to improve the accuracy of the surface’s Vertical Deformation and Energy Restitution, and the number of drops is reduced from three to one.

Flexural Strength of Partially Concrete-Filled Steel Tubes Subjected to Lateral Loads by Experimental Testing and Finite Element Modelling

In this paper, the flexural strength and buckling of the partially concrete-filled steel tubes (PCFST) under laterally repeated loads was investigated through three-point bending test configuration. Three-dimensional Finite Element (FE) models of the bending tests of the PCFST were developed, in which the concrete filling was modelled using elastic-plastic-fracture model capturing crack development and the tube steel was modelled using elastic-plasticity model. The bond between concrete and tube was considered as frictional touching contact. The validation showed the FE results including the ultimate flexural load and buckling failure mode of the steel tube were in excellent agreement with the experimental ones. A parametric study was then conducted using the verified FE models to investigate the effects of the tube diameter-to-thickness ratio, the concrete filling length ratio, the compressive strength of concrete, and the tube steel’s yield and tensile strengths on the PCFST’s ultimate flexural strength. Based on this study, buckling modes, the optimal concrete filling lengths, and the confined compressive strengths of concrete were determined considering the effects of all these parameters. The confined compressive stresses and strains in concrete predicted by the FE models were evaluated against those determined by theoretical models. The results revealed that the effects of concrete compressive strength to the PCFST’s flexural capacity was insignificant while increasing the tube diameter-to-thickness ratio or the tube steel’s yield and tensile strengths could significantly increase the PCFST’s flexural capacity and the confined compressive strength of concrete; and there was an optimal length of concrete filling at about 66% of the tube length. It demonstrated that the Finite Element analysis can therefore be used as a powerful method to the analysis and design the PCFST columns under lateral loads.

Effect of test configurations and loading protocols on performance of timber-concrete connectors

To examine the effect of test configurations and loading protocols on the performance of timber-concrete composite (TCC) shear connectors, a total of twenty-seven TCC shear connections with glued – in threaded steel rod (GIR) were designed to experience push-out tests. The experimental variables include rod diameter, test configurations (single - and double - shear), and loading protocols including the loading protocol (EN26891) and the displacement rate (0.5 mm/min, 2 mm/min, and 4 mm/min). The results indicate that both the test configurations and the displacement rates showed different influences on the performance of the shear connections. Most of the tested TCC shear connections with GIR mainly failed by the double – hinge yield mode of GIR. Double – shear specimens with 16 mm – diameter GIR exhibited a 49 % higher maximum load compared to the single – shear specimens. The slip modulus of the specimens tested at a displacement rate of 4 mm/min was about 40 % lower than that of the specimens tested at the displacement rates of 0.5 mm/min and 2 mm/min, respectively. Among the single-shear specimens, the 16 mm– diameter GIR showed the lowest ductility, by 65 % and 59 %, as compared to the 10 mm – and 12 mm – diameter specimens. Finally, theoretical analytical formulas were proposed to predict the load carrying capacity and the slip modulus of the TCC shear connections with GIR. The experimental slip modulus was also compared with the results obtained by existing calculation models.

Magnetorheological behavior of thermoplastic elastomeric honeycomb structures fabricated by additive manufacturing

3D printing of magnetorheological elastomers (MREs) can potentially create versatile and complex mechanical structures with reversible stiffening properties. Several additive manufacturing (AM) methods, like direct printing and stereolithography (SLA), have been used to achieve magnetic thermoset and elastomer composite structures. For the first time, we demonstrate the use of MREs based on thermoplastic elastomers (TPE) in AM and we investigate their magnetorheological (MR) effect when used in lightweight honeycomb designs. Due to the low shore hardness of TPE, a screw extruder-based printing head is employed to print disk-shaped samples with honeycomb patterns at infill percentages varying from 15% to 50%. In order to compare the MR effect of disks with varying honeycomb infills through a compression method, we investigated the effect of different testing configurations. We observe that different permanent magnet configurations, as it has been used in literature so far, create an additional effect on the measured MR effect of the MRE samples. To eradicate this effect, a test setup with an unpaired permanent magnet configuration is proposed. MRE structures with an infill density of 20% showed, at 1% deformation range, the highest MR effect, almost four times as high as 100% infilled samples. MRE structures with an infill density between 30% and 50% showed a lower MR effect than at 20%, but were still higher than at 100%. We observe in simulations that the magnetic flux density of 100% infilled samples was higher at the edges of the samples and lower at the center. For samples with honeycomb infill, the magnetic flux density was higher at the outer rim of the samples and edges of the walls within the sample, which causes a higher MR effect. Our work demonstrates that the MR effect can be tuned by designing a MRE structure with a honeycomb infill. The honeycomb infill results in lightweight MREs with improved MR effect useful for various downstream applications that require reversible strong stiffening while remaining comparatively lightweight.

Safety factors comparison of landfill lining components using single & double interface shear strength results

The design of a competent basal lining system is crucial in ensuring a long-lasting and functional engineered municipal solid waste (MSW) landfill. However, due to the inclusion of numerous geosynthetics and geomaterials forming a multi-layered lining system, there rises an uncertainty on determining the critical or weakest interface. This is exacerbated by the different properties offered by these lining materials and their inter-crossing functions in landfills. According to ASTM D5321-20 standard, the interface shear strengths used in design of bases and side-slopes of lining systems are determined through a single interface testing configuration. However, minimal research has been done to evaluate the consequences of multi-interface testing configurations on the minimum factors of safety (FoSmin). The present study was thus conducted to further investigate this phenomena while establishing the appropriateness of double interface testing configuration using large direct shear equipment. It was found that, the difference in the FoSmin was insignificant for critical interfaces observed under single and double interface testing configurations.

Assessment of static performance of welded mesh along mesh overlap used at Kiirunavaara mine

Localized failure of mesh, i.e., the mesh was cut or torn by rock blocks as a result of a seismic event, was observed at LKAB’s Kiirunavaara mine. This is especially common along mesh overlap where mesh sheets are joined together. However, the performance of welded mesh along mesh overlap is not well understood. A series of tests was conducted at the laboratory at Luleå University of Technology, Sweden. The tested mesh sheets are made of 5.5 mm diameter wires welded along orthogonal directions spaced on a grid of 75 mm by 75 mm. The mesh sheet(s) was placed on a steel rig and fixed with bolts with spacing of 1.0 m by 1.0 m. A 300 mm loading plate made of concrete was placed underneath the mesh and pull/push load was applied on the mesh through the plate. For comparison purpose, the loading plate was placed at the mesh center following a dice five pattern as well as in the middle between two bolts (overlap position). The force-displacement curves of different test configurations were measured and failure modes of the mesh were observed. Laboratory test results show that the load-carrying and deformation capacity of the mesh is highly dependent on the load spreading and loading position relative to the holding points. When the mesh overlap was loaded, it shows: i) the highest stiffness; ii) the highest rupture load; iii) lower residual load-carrying capacity; and iv) the lowest deformation capacity. Two failure modes were observed in the conducted tests. Heat affected zone failure is the most common one and the second is the tensile failure along wires. Based on the laboratory results, an optimized mesh layout and bolting pattern was suggested for the Swedish underground mines.

Active vibration control for milling operations including frequency response function uncertainties

Active vibration controllers are designed to mitigate chatter vibrations and increase the productivity of machines. Such controllers, however, often do not perform well in real applications if uncertainties are present in the system. In this study, a controller design is presented for a test configuration, where the actuation is utilized by an electromagnetic actuator. The robust stability charts, which take into account the bounded uncertainties in the measured frequency response functions (FRFs), are calculated in frequency domain using the zero-order approximation method. The predictions for the experimental configuration are validated in cutting tests.

Measuring Array Mutual Impedances Using Embedded Element Patterns

The radiation pattern of an antenna element embedded in a multiport antenna such as a phased array depends on the loads connected to the array element ports. If the embedded element patterns (EEPs) are measured using at least two known loading conditions, the patterns can be used to determine the array mutual impedance matrix. In previous work, this result has been derived with the simplifying assumption that the impedance of the source connected to the driven element changes along with the load impedances connected to the nondriven elements. In a practical test configuration, the source impedance cannot be readily changed. We analyze the case of EEPs measured with a fixed source impedance and changing impedances on the nondriven elements. The transformation from one set of EEPs to another with fixed source impedance is more complex than in the case of a source impedance that changes with the load impedances. The transformation depends on the coupling between elements and is only weakly sensitive to the element self-impedances. With measured EEPs for an array of identical elements, the impedance matrix can be found up to a scale factor. We demonstrate the method experimentally by measuring the patterns of an antenna array terminated with one loading condition and repeating the pattern measurements with a different loading condition. The mutual impedance matrix extracted from the pattern measurements compared to network analyzer mutual impedance measurements is accurate to within 1– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2~\Omega $ </tex-math></inline-formula> for most of the mutual impedances.

Initiation of Electrical Discharge at the Triple Junction of the Lightning Protection of an Aircraft Radome

This article highlights challenges in aircraft design focusing on lightning protection of an aircraft radome. A Multiphysics analysis is performed in conjunction with various laboratory high voltage test configurations, and the effects of high temperature and pressure are discussed.

Managing Health Treatment by Optimizing Complex Lab-Developed Test Configurations: A Health Informatics Perspective

Managing Health Treatment by Optimizing Complex Lab-Developed Test Configurations: A Health Informatics Perspective

Weakly special test configurations of log canonical Fano varieties

Let $X$ be a strictly log canonical Fano variety, we show that every lc place of complements is dreamy, and there exists a correspondence between weakly special test configurations of $(X,-K_X)$ and lc places of complements.

A modified split-Hopkinson pressure bar setup enabling stereo digital image correlation measurements for flexural testing

A novel experimental setup for dynamic material characterisation that combines a ring-on-ring test configuration for equibiaxial flexural testing with a modification of the well-known split-Hopkinson pressure bar (SHPB) is presented. The design is generic, but in the present paper intended for and validated by experiments on flat circular glass samples at high strain rates. The novel modification allows an unobstructed view of a significant part of the sample’s tensile surface that is made possible by replacing the conventional transmission bar with a tube through which the incident bar passes. This modification enables the application of high-speed cameras for assessing the fracture together with stereo digital image correlation (stereo-DIC) for non-contact out-of-plane displacement measurements and, at the same time, reduces the total length of the setup compared to the original design. An FE-model of the bar/tube system was generated to characterise the setup better. From that, information on strain gauge locations was extracted. Two similar experiments on glass show that the required dynamic force equilibrium could be established and that the application of high-speed cameras work as intended. Lastly, promising results were achieved from the pilot stereo-DIC measurements, indicating pure bending deflections of the sample in line with theory.

How to Create Trusted Tribological Characterization Data of Soft Polymers as Input for FEM Simulations?

Soft polymers such as the investigated polyurethane, characterized by low Young's moduli and prone to high shear deflection, are frequently applied in pneumatic cylinders. Their performance and lifetime without external lubrication are highly determined by the friction between seal and shaft and the wear rate. FEM simulation has established itself as a tool in seal design processes but requires input values for friction and wear depending on material, load, and velocity. This paper presents a tribological test configuration for long stroke, reciprocating movement, allowing the generation of data which meet the requirements of input parameters for FEM simulations without the geometrical influences of specific seal profiles. A numerical parameter study, performed with an FEM model, revealed the most eligible sample geometry as a flat, disc-shaped sample of the polymer glued on a stiff sample holder. At the same time, the study illustrates that the sensitivity of the contact pressure distribution to Poisson's ratio and CoF can be minimized by the developed and verified setup. It ensures robust, reliable, and repeatable experimental results with uniform contact pressures and constant contact areas to be used in databases and FEM simulations of seals, enabling upscaling from generically shaped samples to complex seal profiles.

Simple Millimeter Wave Identification System Based on 60 GHz Van Atta Arrays.

The paper presents a proof-of-concept of a millimeter-wave identification system based on Van Atta array tags in the 60 GHz band. For interrogation of the tags, a vector network analyzer and a measurement transceiver were employed in alternative test configurations. The design, fabrication and measurements of co- and cross-polarized Van Atta arrays are presented in the paper. They can be treated as simple chipless RFID tags with frequency-response-based identification. Tags with various resonance frequencies are designed by scaling an optimized base model. The designed 57-67 GHz co-polarized and cross-polarized tags have small dimensions of approximately 23 mm × 21 mm and 40 mm × 25 mm, and they exhibit radar cross-section (RCS) levels of -16 dBsm and -21 dBsm, respectively. Owing to the retrodirective properties of Van Atta arrays, the RCS can be maintained at a high level within a broad range of angles of incidence. The system was validated in an anechoic chamber where the spectral responses of all the manufactured tags can be clearly distinguished from the environment, enabling their identification. Tests in a reflective environment were also performed, and they have shown that only the cross-polarized tags could be detected and identified in the presence of reflections from the tags' surroundings.

Optimal destabilization of K–unstable Fano varieties via stability thresholds

We show that for a K-unstable Fano variety, any divisorial valuation computing its stability threshold induces a non-trivial special test configuration preserving the stability threshold. When such a divisorial valuation exists, we show that the Fano variety degenerates to a uniquely determined twisted K-polystable Fano variety. We also show that the stability threshold can be approximated by divisorial valuations induced by special test configurations. As an application of the above results and the analytic work of Datar, Sz\'ekelyhidi, and Ross, we deduce that greatest Ricci lower bounds of Fano manifolds of fixed dimension form a finite set of rational numbers. As a key step in the proofs, we adapt the process of Li and Xu producing special test configurations to twisted K-stability in the sense of Dervan.