Experimental Tests Research Articles

Dynamic characteristics of refrigerant evaporation temperature in air-water heat source heat pump

In order to improve the problem of reduced heat capacity and unstable heating ability of air source heat pump (ASHP) in the heating mode during the cold season, a heat pump evaporator using air and surface water as a heat source is designed in this paper. A heat transfer unit's calculation model of an air–water heat source evaporator is established. Experimental tests and simulation studies are conducted on the refrigerant evaporation temperature and heat pump heating performance. On this basis, a refrigerant evaporation temperature prediction model is constructed using a multiple linear regression (MLR) model. The trend of refrigerant evaporation temperature under air–water heat source is analyzed by taking the winter meteorological parameters in Xiangtan City as an example. The results show that the air–water heat source heat pump (A-WSHP) has a higher refrigerant evaporation temperature and a smaller temperature fluctuation range than the ASHP. The average values of refrigerant evaporation temperatures under the experimental conditions were 5.3 °C and 4.6 °C, respectively. The temperature fluctuation ranges were 3.8 °C-6.7 °C and 2.8 °C-7.0 °C, respectively. The A-WSHP has higher heating capacity and heating stability. Air temperature, air velocity, water spray temperature and water spray flow rate are all important parameters that affect the refrigerant evaporation temperature of a heat pump. Evaporation temperature changes are positively correlated with these factors. In the refrigerant evaporation temperature prediction model, the air temperature change has the most significant effect on the evaporation temperature, followed by spray water temperature, air velocity, and spray flow rate, whose influence weights are 82.5 %, 38.8 %, 29.4 %, and 25.3 %, respectively. Selecting different temperatures of spray water and adjusting the evaporator's inlet spray flow rate can improve the refrigerant evaporation temperature and heat pump heating stability.

Finite element modeling and analysis of the self-piercing riveting forming process with the ball-shaped die

Self-Piercing Riveting (SPR) technique faces challenges as it expands to low ductile materials. In this paper, the ball-shaped die is suggested to prevent the formation of cracks in sheets during the SPR process. The SPR model with the ball-shaped die was developed using the finite element method, and simulations of the joint forming process and tensile test were conducted. The influence of die depth and diameter on SPR forming process and quality was analysed. The simulation results showed that as the die diameter increases, the undercut decreases, and the remaining thickness of bottom increases. The undercut and the remaining thickness of bottom decreases with the increase of the depth of the die. When employing a ball-shaped die with a 1mm depth and 10mm diameter, the SPR joint with tight interlock and excellent mechanical properties can be obtained. The results of the simulation and experimental tests are consistent.

Analysis of mechanical response and failure characteristics of tunnels crossing active faults considering axial force and geometrical nonlinearity

Tunnels subjected to active fault dislocation may experience significant damage. This paper establishes a novel methodology and solution procedure for analyzing the mechanical response and failure characteristics of tunnels subjected to active fault dislocation based on an elastic foundation beam model. The proposed methodology includes axial, transverse, and vertical soil-tunnel interaction terms, in addition to geometrical nonlinearity and axial force terms in the governing equation. This approach has a significantly extended application range, effectively addressing the problems encountered in tunnels crossing active faults with diverse crossing angles, dip angles, and fault types. The proposed methodology is verified by comparison to a 3D FEM model with various fault types, experimental tests, and on-site case, and the results are in excellent quantitative and qualitative agreement with the numerical, experimental, and on-site results. When fault displacement is below 0.5m, disregarding geometric nonlinearity results in calculation errors of approximately 10% to 17% for peak axial force (Nmax), 18% to 22% for peak shear force (Vmax), and 20% to 30% for peak bending moment (Mmax). Finally, the responses caused by different factors, i.e., fault type, fault displacement, tunnel stiffness, and tunnel diameter, are investigated in detail to better understand tunnels crossing active faults. The results show that amongst the various fault types, the Vmax and the Mmax experienced by tunnels subjected to oblique slip-fault dislocation surpass those of other fault types, accompanied by the most extensive failure range. The augmentation of fault displacement, tunnel stiffness, and tunnel diameter precipitates a corresponding escalation in the Nmax, Vmax, Mmax, and failure range. Under oblique-slip fault dislocation, the tunnel undergoes an initial phase of shear failure, followed by tension-bending failure, delineated by distinct fault displacement thresholds of 0.1m and 0.2m, respectively. The proposed methodology provides the advantage of reliable stability analysis and design of tunnels crossing active faults.

Analysis of magnetic saturation effects in the squirrel cage induction generators

This work concerns an investigation on the analysis of the magnetic saturation effects in the three-phase squirrel cage induction generator which is considered as a main device in wind energy conversion systems. The magnetic saturation is considered as an important factor causing destructive effects on power qualities such as harmonics and distortion. Several approaches have been presented in the literature for the modeling of the electric machines considering magnetic saturation. The widely used and precise approach is the finite elements method which is particularly characterized by its high computational time. The novelty in this paper is that a state model has been developed for the healthy conditions of the three-phase squirrel cage induction generators considering the experimental variation of the magnetizing inductance in terms of the magnetizing current. Simulation and experimental tests are provided to extract some important signatures on stator voltages and currents. It will be deduced that the spectrum analysis of stator currents contains useful information on magnetic saturation. Experimental and theoretical results illustrate the consistency of this approach for the modeling and analysis of the squirrel cage induction generators considering the magnetic saturation.

Effect of combined additions of Sc, Zr and Ti on hot-cracking resistance and precipitation behaviour in Al-Mg alloy by L-PBF

The request for high-performance aluminum components prompts research into innovative alloys compatible with laser-based additive manufacturing processes, leveraging grain refiners in their composition to mitigate hot-cracking and enhance strength. While the addition of Sc and Zr in Al-Mg alloys has been widely investigated, the high cost and supply risks associated with Sc necessitate reducing its amount and replacing, at least partially, with other inoculants. In this preliminary study, the amount of Sc replaceable with different concentrations of Zr or Ti is evaluated investigating the laser powder bed fusion processability of three powder feedstocks: a pre-alloyed Al-Mg-Zr-Sc powder, a blend of the previous alloy with addition of Zr particles, and a further blend of an alloy depleted of Zr with added Ti particles. The experimental analyses on the laser-processed alloys showed that the standard and the Zr-enriched alloys featured a bimodal microstructure free from cracks with fine equiaxed grains at the edge of the molten pools and coarser grains at their centers. In the alloy variant depleted in Zr with addition of Ti particles a columnar structure was observed and hot-cracks appeared. Thermodynamic simulations of phase formation allowed defining the precipitation kinetics during solidification and direct aging, showing increased precipitation in alloys with higher Zr content, while the presence of Ti resulted in sluggish precipitation. Experimental aging tests demonstrated significant increases in microhardness, with peak values of the modified alloys achieved after 12 h at 375°C.

Impact-Echo for Crack Detection in Concrete with Artificial Intelligence based on Supervised Deep Learning

Aging concrete infrastructure such as bridges and tunnels need to be appropriately maintained in their service life because these structures must be employed with ensured safety level. Inspection and maintenance with reasonable measures are typically operated for the reinforced concrete before severe damage and failure are developed. Especially, the crack propagation in concrete can significantly affect the structural integrity, durability and overall performance of structural elements. Effective maintenance strategies are required for material and structural assessment with detection and repair of cracks to prevent further deterioration. Identification of cracks in concrete is effectively operated to extend the service life of structures for mitigating the potential safety hazards and minimize the repair costs. In order to detect the cracks in the concrete structure member, non-destructive testing (NDT) system can be often introduced to satisfy the technical issues in terms of damage evaluation and estimation of repair condition. Currently, various NDT methods have been utilized for quantitative analysis of internal damage/defects using elastic wave method such as impact-echo method, focusing on reflection of P-wave in concrete as wave propagation behavior. In experimental laboratory tests, concrete specimens are usually prepared with interior damages (cracks) which are simulated as embedded plastic plate or styrofoam. In this study, starch- type polysaccharide sheet is used to form the simulated cracks in concrete specimen. This study aims at applying impact-echo method with AI (Artificial Intelligence) to identify the internal crack information based on the waveform characteristics obtained from the elastic wave propagation behavior. The waveform results are converted to frequency spectrum by FFT analysis. Consequently, it is found in this study that AI, which is employed by supervised deep learning models, successfully evaluates the data and displays the probability of crack existence in concrete. Since FFT is a powerful algorithm that quickly converts a signal from the time domain to the frequency domain, it gives efficient analysis to the impact echo method for crack detection with the application of AI system.

Anion trapping-coupling strategy driven asymmetric nonflammable gel electrolyte for high performance sodium batteries

Gel polymer electrolytes, promising electrolyte candidates for advanced sodium metal batteries (SMBs), suffer from the great challenges of combustion risk and inferior interfacial stability caused by poor mechanical properties and low Na+ selectivity. Herein, we proposed a rational anion trapping-coupling strategy to build a mechanically robust asymmetric nonflammable composite gel electrolyte (AS-NFCGE) by introducing in-situ coupled boron nitride nanosheets (BNNs) on glass fiber matrix embedded with synchronous polymerized flame-retardant polymer. Theoretical calculations, finite-element simulations, and experimental tests prove that the high coupling BNNs with anion trapping effect constructed asymmetric structure can significantly accelerate selective Na+ migration kinetics, enhance mechanical properties of AS-NFCGE and endow a similar single-ion conducting behavior to homogenize ion-distribution at the anode side, thus improving interfacial stability and suppressing dendrite growth to achieve ultra-stable SMBs. Specifically, the AS-NFGE delivers high ionic conductivity and Na+ transference number (0.73) together with excellent flam-retardant. Consequently, the dendrite-free Na/Na symmetric cell exhibits considerable cycling life for over 3000 h at 0.1 mA cm−2 with low overvoltage. Applications of the AS-NFCGE in SMBs further demonstrate the excellent electrochemical performances, and no thermal runaway and no electrolyte leakage occur for pouch cells using AS-NFCGE. This strategy provides new insight into the development of safe and high-energy SMBs and the beyond.

Health monitoring system using ECG and PPG techniques

The demand for portable health monitoring systems has grown rapidly in recent years due to the increasing prevalence of chronic diseases and the need for continuous health monitoring. This article introduces the development and implementation of a portable health monitoring system using photo plethysmography (PPG) and electrocardiogram (ECG) technologies. The system integrates the Node MCU ESP8266 microcontroller, AD8232 ECG sensor, and MAX30100 sensor to measure vital signs such as heart rate and blood oxygen saturation level. The proposed system provides a cost-effective and efficient solution for real-time health monitoring, enabling early detection of abnormalities and timely intervention. The feasibility and performance of the system were proven through experimental tests.

Deep ensemble learning for chickenpox detection from clinical images

Chickenpox caused by the varicella-zoster virus is an extremely contagious viral infection common in children and quickly develops into a severe problem. Over 90% of unvaccinated people have been infected. Still, infection occurs at different ages in different parts of the world- Over 70 % of people become infected by the age of 10 years in the United States, the United Kingdom, and Japan, and by the age of 20 in India, West Indies, and South East Asia. Automatic classification of the specific disease is a challenging task to present clinicians to distinguish between different kinds of skin conditions and recommend suitable treatment. Convolutional Neural Networks have recently achieved great success in many machines learning purposes and have presented a state-of-the-art performance in various computer-assisted diagnosis applications. This study proposes a deep neural network-based method that follows an ensemble approach by combining VGG-16, VGG-19, and ResNet-50 architectures to distinguish chickenpox from other skin conditions. Experimental test results have achieved accurate classification with an assuring test accuracy up to 93%.

Combining wake redirection and derating strategies in a load-constrained wind farm power maximization

Abstract. Power derating and wake redirection are two wind farm control techniques proposed in the last decade as means for increasing the overall wind farm power output. While derating operations are associated with a limited gain in terms of farm energy harvesting and with a decrease in turbine loading levels, farm controls based on wake redirection proved, both in silico and experimental tests, to entail significant increases in the overall wind farm power output. However, according to wake redirection strategies, the upstream wind turbines may typically operate at large yaw misalignment angles, and the possible increase in loads that the machines may experience in such conditions represents a source of concern when it comes to testing this control on existing farms that are not specifically designed for prolonged misaligned operations. In this work, it is first demonstrated that a suitable derating level can compensate for the increase in the rotor loads associated with large misalignment angles. Secondarily, two load-constrained wind farm controls based on a combination of wake redirection and derating are proposed with the aim of maximizing the overall farm output while maintaining unaltered design load envelope of the wind turbines operating within the controlled wind farm.

Impact of Electrochemical Impedance Spectroscopy Dataset Curation on Solid Oxide Cell Degradation Assessment

Abstract Electrochemical impedance spectroscopy (EIS) has become a standard measurement technique for detecting degradation in single cells and stacks of solid oxide cells (SOCs). Depending on the experimental setup and test equipment, instabilities and unexpected results can be observed in EIS measurements. For example, in the low-frequency range, instabilities can be induced by feed gas flow fluctuations. Another phenomenon are parasitic, inductive impedances that degrade the high-frequency range. To compensate for such influences in large EIS data sets, we propose a specially developed EIS data curation pipeline. Based on the results of its application, we demonstrate the impact on the quantitative and qualitative attribution of electrochemical processes from EIS using equivalent circuit modeling and distribution of relaxation times. Furthermore, the substantial differences in the temporal evolution of the latter during long-term experiments are highlighted for EIS measurements obtained at the SOC stack and single cell level. In addition, the significant misestimation of aging rates, especially with respect to the fuel electrode and the high-frequency series resistance, is shown when comparing EIS measurements, few of which exhibit a parasitic inductive impedance.

Design of a Compliant Sternum Prosthesis for Improving Respiratory Dynamics

This study presents a novel approach to sternum prosthesis design, aiming to address the limitations of the current solutions by employing compliant mechanisms. The research focuses on developing a prosthetic design capable of generating lifting movements on ribs during breathing. First, a videogrammetry experimental test and virtual simulations were conducted to ascertain the vertical forces applied to each sternum joint. Subsequently, a compliant mechanism design was initiated, involving optimization and finite element analysis (FEM). A comprehensive kinematic performance analysis was performed to evaluate the prosthetic design. The results indicate that the obtained displacements of each rib closely align with those reported in the existing literature, demonstrating the effectiveness of the proposed solution. In conclusion, the developed sternum prosthesis exhibits the capability to recover approximately 56% of the ribs’ natural movements, highlighting its potential as an innovative and promising solution in the field of chest prosthetics.

Assistance force-line of exosuit affects ankle multidimensional motion: a theoretical and experimental study

BackgroundThe talocrural joint and the subtalar joint are the two major joints of the ankle-joint complex. The position and direction of the exosuit force line relative to these two joint axes can influence ankle motion. We aimed to understand the effects of different force-lines on ankle multidimensional motion.MethodsIn this article, three assistance force line schemes for ankle exosuits were proposed: perpendicular to the talocrural joint axis (PT), intersecting with the subtalar joint axis (IS), and parallel to the triceps surae (PTS). A theoretical model was proposed to calculate the exosuit’s assistance moment. Seven participants completed four experimental tests of ankle plantarflexion, including three passive motions assisted by the PT, PTS and IS schemes, and one active motion without exosuit assistance (Active).ResultsThe simulation results demonstrated that all three exosuits were able to produce significant moments of ankle plantarflexion. Among these, the PT scheme exhibited the highest moments in all dimensions, followed by the PTS and IS schemes. The experimental findings confirmed the effectiveness of all three exosuit schemes in assisting ankle plantarflexion. Additionally, as the assistive force lines approached the subtalar joint, there was a decrease in ankle motion assisted by the exosuits in non-plantarflexion directions, along with a reduction in the average distance of ankle angle curves relative to active ankle motion. Furthermore, the linear correlation coefficients between inversion and plantarflexion, adduction and plantarflexion, and adduction and inversion gradually converged toward active ankle plantarflexion motion.ConclusionsOur research indicates that the position of the exosuit force line to the subtalar joint has a significant impact on ankle inversion and adduction. Among all three schemes, the IS, which has the closest distance to the subtalar joint axes, has the greatest kinematic similarity to active ankle plantarflexion and might be a better choice for ankle assistance and rehabilitation.

Elucidating the Impact of Polyol Functional Moieties on Exothermic Poly(urethane-urea) Polymerization: A Thermo-Kinetic Simulation Approach

The pursuit of sustainable polyurethane (PU) product development necessitates a profound understanding of precursor materials. Particularly, polyol plays a crucial role, since PU properties are heavily influenced by the type of polyol employed during production. While traditional PUs are solely derived from hydroxyl functionalized polyols, the emergence of amine-hydroxyl hybrid polyols has garnered significant attention due to their potential for enhancing PU product properties. These hybrid polyols are characterized by the presence of both amine and hydroxyl functional groups. However, characterizing these polyols remains a daunting challenge due to the lack of established experimental testing standards for properties, such as fractional hydroxyl and amine moieties and thermo-kinetic parameters for amine reactions with isocyanates. Additionally, characterization methods demand extensive time and resources and pose risks to health and the environment. To bridge these gaps, this study employed computational simulation via MATLAB to determine the moieties’ fractions and thermo-kinetic parameters for hybrid polyols. The computational method integrated energy balance and reaction kinetics analysis for various polyols to elucidate the influence of functional moieties on the thermo-kinetic behavior of PU formations. Validation of the simulated results was conducted by comparing their experimental and simulated prepolymer and foam temperature profiles, highlighting the direct influence of fractional moieties on PU formations. The comparisons revealed an average relative error of less than 5%, indicating the accuracy and credibility of the simulation. Thus, this study represents a pivotal opportunity for advancing knowledge and driving sustainable developments in bio-based polyol characterization for PU production streamlining and formulation optimization.

Structure prediction of protein-ligand complexes from sequence information with Umol

Protein-ligand docking is an established tool in drug discovery and development to narrow down potential therapeutics for experimental testing. However, a high-quality protein structure is required and often the protein is treated as fully or partially rigid. Here we develop an AI system that can predict the fully flexible all-atom structure of protein-ligand complexes directly from sequence information. We find that classical docking methods are still superior, but depend upon having crystal structures of the target protein. In addition to predicting flexible all-atom structures, predicted confidence metrics (plDDT) can be used to select accurate predictions as well as to distinguish between strong and weak binders. The advances presented here suggest that the goal of AI-based drug discovery is one step closer, but there is still a way to go to grasp the complexity of protein-ligand interactions fully. Umol is available at: https://github.com/patrickbryant1/Umol.

Optimizing Individual HIV Testing and Counseling for Emerging Adult Sexual Minority Men (Aged 18 to 24) in Relationships: A Pilot Randomized Controlled Trial of Adjunct Communication Components.

The majority of new HIV infections in the US occur among sexual minority men (SMM) with older adolescent and emerging adult SMM at the highest risk. Those in relationships face unique HIV prevention challenges. Existing sexual HIV transmission risk interventions for male couples often encounter implementation challenges and engaging younger SMM early in relationships may be particularly difficult. This pilot randomized controlled trial evaluated the acceptibility and feasibility of We Test HIV testing - a behavioral health intervention tailored for younger SMM in realtionships - and generated preliminary estimates of effect size. The intervention comprises two adjunct moduls - video-based communication skills training as well as communication goal setting and planning - delivered in conjunction with routine HIV testing and counseling in individual or dyadic formats. A sample of 69 SMM aged 17 to 24 were recruited online. Following baseline assessment, youth were randomized to receive either the experimental, We Test, intervention or routine HIV testing (the control condition). Follow-up assessments were completed 3 and 6 months post-baseline. Results suggested the study was feasible and the individually delivered format was acceptible. We Test HIV testing was associated with significant improvements in communication skills. In addition, youth who remained in a relationship experienced an increase in communal coping to reduce HIV infection risk and relationship power. While groups did not differ with respect to condomless anal sex with casual partners, these psycho-social constructs (communication, communal coping with HIV prevention, and relationship power) may serve as mediators of intervention effects on sexual risk reduction in a larger study.

Multi‐Functional Design of TPMS‐Structures for Temporary Paediatric Fixation Devices

Fracture fixation and limb deformity correction in paediatric orthopaedics often use temporary metallic fixation devices. These devices’ higher stiffness compared to cortical bone leads to stress shielding, causing significant bone density reduction, periprosthetic loosening, and bone growth interference. 3D‐printed triply periodic minimal surface (TPMS) structures present a promising engineering solution to match bone stiffness while ensuring reliable implant strength. This study employs finite element modelling and experimental testing to identify optimal multi‐functional TPMS‐based lattices that meet the required design constraints of (1) stiffness in the range of cortical bone, (2) strength in the range of cortical bone, (3) minimum osteointegration to facilitate the implant removal after healing, and (4) manufacturability with limited defect sensitivity. Six different types of Ti‐6Al‐4V material TPMS structures manufactured via Laser Powder Bed Fusion were evaluated for their ability to target the lower and upper bounds of paediatric cortical bone stiffness. Lattices based on the Primitive unit cell design were superior, demonstrating the highest strength/stiffness ratio, best manufacturability, and potentially reduced osteointegration due to larger pore size, smaller surface area, and lowest negative Gaussian curvature compared to other investigated TPMS types.This article is protected by copyright. All rights reserved.

Hands-Free Haptic Navigation Devices for Actual Walking.

In this survey, we give an overview of hands-free haptic devices specifically designed for navigation guidance while walking. We present and discuss the devices by body part, namely devices for the arm, foot and leg, back, belly and shoulders, waist and finally the head. Although the majority of the experimental tests were successful in terms of reaching the target while being guided by the device, the experimental requirements were wide-ranging. The distances to be covered ranged from just a few meters to more than a kilometer, and while some of the devices worked autonomously, others required the experimenter to act as Wizard of Oz. To compare the usefulness and potential of these devices, we created a table in which we rated several relevant aspects such as autonomy, conspicuity and compactness. Major conclusions are that outdoor devices have the highest technology readiness level, because these allow autonomous navigation through GPS, and that the most compact devices still require the action of an experimenter. Unfortunately, none of the hands-free devices are at a level of readiness where they could be useful to people with visual impairments. The most important factor that should be improved is localization accuracy, which should be high and available at all times.

Enhancing sustainability in construction: experimental testing and finite element investigation of falsework ringlock joints

Enhancing sustainability in construction: experimental testing and finite element investigation of falsework ringlock joints

A practical leader–follower hybrid control scheme for wheeled mobile robots

This paper addresses the problem of tracking control of wheeled mobile robots in leader–follower formation. By applying the backstepping technique, a hybrid control scheme consisting of continuous control and intermittent control is proposed, and leader–follower formation tracking is achieved in the presence of model uncertainty and external disturbance. A relationship between the intermittent control width and control gain and the convergence of the position errors is obtained for the tracking accuracy estimation. As a special case, the concerned intermittent control can be converted to impulsive control with a sufficiently small control width, and tracking of the trajectory can be realized by directly driving the state variables of the follower at well-designed discrete instants. The main novelty of the proposed hybrid control scheme is to drive the tracking errors into a preset region via intermittent control (or impulsive control) signals and then achieve the tracking goal in the practical sense via continuous control signals. An example with the corresponding numerical simulations and experimental tests is given to illustrate the effectiveness of the proposed method.