External Load Research Articles

Vibration energy harvesting system with cyclically time-varying potential barrier

Nonlinear kinetic energy harvesters are becoming more and more popular as well as advanced and efficient. This paper presents the study of the dynamics of such a system in a wide range of excitation parameters, assuming at the same time the possibility of a cyclical and smooth change of the potential function. We have designed a system that allows to obtain a wide spectrum of potential characteristics, from a single well to a three-well system, and we have analyzed its effectiveness. Next, we checked the influence of parameters characterizing the change of potential using bifurcation diagrams and their comparison with the effective voltage values. We also analyzed the behavior of the system in chaotic and periodic motion zones and presented selected sections of Poincare and Fourier amplitude-frequency spectra of chaotic solutions. The last element of the analysis was the impact of cyclic potential change on coexisting solutions. We have shown that the best effectiveness is achieved when the frequency of the external load is equal to the resonant frequency of the flexible cantilever beam and the change of potential is limited to extreme positions.

Updating Nonlinear Stochastic Dynamics of an Uncertain Nozzle Model Using Probabilistic Learning With Partial Observability and Incomplete Dataset

Abstract This article introduces a methodology for updating the nonlinear stochastic dynamics of a nozzle with uncertain computational model. The approach focuses on a high-dimensional nonlinear computational model constrained by a small target dataset. Challenges include the large number of degrees-of-freedom, geometric nonlinearities, material uncertainties, stochastic external loads, underobservability, and high computational costs. A detailed dynamic analysis of the nozzle is presented. An updated statistical surrogate model relating the observations of interest to the control parameters is constructed. Despite small training and target datasets and partial observability, the study successfully applies probabilistic learning on manifolds (PLoM) to address these challenges. PLoM captures geometric nonlinear effects and uncertainty propagation, improving conditional mean statistics compared to training data. The conditional confidence region demonstrates the ability of the methodology to accurately represent both observed and unobserved output variables, contributing to advancements in modeling complex systems.

Predicting fatigue crack growth rate of cement-based and asphalt paving materials based on indirect tensile cyclic loading tests

Fatigue crack growth rate (FCGR) is a critical indicator that reflects the rate at which material deterioration occurs under cyclic loads. However, there is currently a lack of a mechanistic quantitative analysis and prediction of the FCGR of paving materials under external indirect tensile (IDT) cyclic loads. To address this issue, this study aims to develop a mechanistic model for quantitative analysis and prediction of the FCGR in paving materials subjected to external IDT cyclic loads based on the J-integral based Paris’ law. Two types of paving materials, namely cement-treated aggregates and asphalt mixtures, were selected to demonstrate the results and model of the FCGR. The results indicate that the derived J-integral serves as the driving force for crack growth and is influenced by horizontal tensile stress, initial resilient modulus, damage density, specimen size, and surface energy of the paving materials. The fatigue life of cement-treated aggregates is primarily influenced by the crack initiation stage, while for asphalt mixtures, the crack growth stage plays a more significant role. The application of Paris’ law is found to be effective in predicting the FCGR at stable crack growth stage. The coefficients of Paris’ law exhibit minimal variation across different stress levels and loading frequencies, and can be utilized to evaluate the fatigue crack resistance of different paving materials.

Effectiveness of double cutout on lateral buckling analysis of fiber reinforced composites

AbstractLateral buckling, an essential mechanical phenomenon observed in composite beams subjected to specific external loads and boundary conditions, is influenced by various factors including cutout dimension, shape, position, and beam thickness in woven fabric laminated composite cantilever beams. The investigation focused on examining the lateral buckling behavior of beams containing two square or circular cutouts and comparing the experimental critical buckling loads of beams without any cutouts, which yielded results demonstrating a significant level of agreement. Through the experimental analysis, it was determined that square cutouts exhibit superior lateral buckling behavior when compared to circular cutouts.Highlights The effects of cutout shapes on lateral buckling analysis on fiber reinforced composites. The effects of cutout location on lateral buckling load on fiber reinforced composites. Comparison of the lateral buckling performances of fiber reinforced composites in relation to the type and position of cutouts.

Design and optimization of three segmented thermoelectric generator for nuclear reactor application

With the scientific exploration in deep space and deep sea, traditional fossil energy and solar energy cannot supply energy for deep space aircrafts and deep sea vehicles continuously, new energy power systems with the features of long endurance, high reliability and high energy density are imperative. Small nuclear reactor has become one of the best solutions for deep space energy demand in the future due to its strong environmental adaptability and long-life time. To improve the reliability of the static heat pipe reactor, the thermoelectric generators (TEGs) are utilized to convert fission heat into electrical energy. Focusing on the demands of improving the conversion efficiency, a new three segmented TEG is proposed based on the Bi2Te3, CoSb3 and Half-Heusler thermoelectric materials in this paper. Combined with the application requirements of heat pipe reactor, the geometric configuration such as different heights and the cross-sectional area of the three different materials in the PN legs is designed and optimized under different heat flux boundary conditions. The influences of contact electrical resistance and contact thermal resistance on the conversion efficiency have been investigated. When the contact electrical resistivity increases from 0.01 μΩ cm2 to 1000 μΩ cm2, the conversion efficiency loss increases from 2.6% to 80.1%. As the surface roughness rises from 0.1 μm to 100 μm, the conversion efficiency loss increases from 0.9% to 42.7%. Based on the heat flux boundary conditions provided by the heat pipes, the thermoelectric conversion performances of three segmented TEG under different external loads are investigated. Through the geometric optimization of the three segmented TEG with total height 20 mm, the thermoelectric conversion efficiency improves from 6.9% to 15.34%. For the simulation heat flux density conditions of 70 kW m−2, 75 kW m−2, 80 kW m−2, 85 kW m−2 and 90 kW m−2, the maximum output power of a thermoelectric generator can reach 8.56W, 9.71W, 10.85W, 12.00W, and 13.11W, respectively. The output characteristics of the three segmented TEGs meet the design demands of the static conversion system.

Transformation of Coherent Twin Boundary into Basal-Prismatic Boundary in HCP-Ti: A Molecular Dynamics Study.

The manufacturing process for wrought Ti alloys with the hexagonal close-packed (HCP) structure introduces a complicated microstructure with abundant intra- and inter-grain boundaries, which greatly influence performance. In the hexagonal close-packed (HCP) structure, two types of grain boundaries are commonly observed between grains with ~90° misorientation: the basal/prismatic boundary (BPB) and the coherent twin boundary (CTB). The mechanical response of the BPB and CTB under external loading was studied through molecular dynamic simulations of HCP-Ti. The results revealed that CTB undergoes transformation into BPB through the accumulation of twin boundary (TB) steps and subsequent emission of Shockley partial dislocations. When the total mismatch vector is close to the Burgers vector of a Shockley partial dislocation, BPB emits partial dislocations and further grows along the stacking faults. When a pair of CTBs are close to each other, severe boundary distortion occurs, facilitating the emission and absorption of partial dislocations, which further assists the CTB-BPB transformation. The present results thus help to explain the frequent observation of coexisting CTB and BPB in HCP alloys and further contribute to the understanding of their microstructure and property regulation.

High-temperature creep and corrosion behavior of 316LN stainless steel in oxygen-saturated sodium

The high-temperature performance and sodium corrosion of in-core components are the main problems of liquid sodium-cooled reactors, and low-carbon nitrogen-controlled 316 stainless steel (316LN) is the main research and development direction of the main materials for the core of sodium-cooled fast reactors. In this work, the creep behavior of 316LN in oxygen-saturated liquid sodium at high temperatures (650 ℃, 700 ℃ and 750 ℃) was tested and compared with the results of creep tests in air at the same conditions. It is found that the creep life in the sodium environment is reduced by 63.44%, 67.93% and 40.07%, respectively. The specimens in oxygen-saturated sodium exhibit reduction in ductility, selective dissolution as well as oxidative corrosion. The corrosion mechanism of 316LN under external loading in oxygen-saturated sodium is illustrated.

Design, modeling and experiments of bistable piezoelectric energy harvester with self-decreasing potential energy barrier effect

It is difficult for conventional bistable energy harvesters to undergo interwell motion in weak excitation environment. In this study, a bistable energy harvester with self-decreasing potential energy barrier effect is proposed, which innovatively turns a fixed end of S-shaped generator beam into the movable end with a spring oscillator, which effectively decreases the potential energy barrier and makes the harvester susceptible to interwell motion. Furthermore, a theoretical analysis of the nonlinear driving magnetic force and the system governing equations is carried out, then a numerical simulation of potential energy surface of harvester is performed to demonstrate the effect of the self-decreasing potential energy barrier in detail. The effect of spring pre-compression and stiffness of the moveable end on the system potential energy is analyzed by numerical simulation. Finally, the key parameters affecting the output performance, such as spring pre-compression, magnets distance, and external load resistance, are analyzed. The harvester has a maximum effective bandwidth of 6.62Hz (4.61–11.23Hz), a maximum peak-to-peak voltage of 10.2V, an RMS voltage of 1.3V, and a maximum output power of 2.91 μW. The proposed harvester achieves efficient broadband energy harvesting in low frequency environments.

Match-play running demands in a female soccer professional club: From academy to professional team

The objective of the study was to examine the match-running load of female soccer players competing at distinct age groups (U15, U18 and senior cohorts) belonging to the same professional club, over a competitive season. The external load variables of the official matches were monitored with Global Positioning System (GPS) technology: total distance (TD), at >18 km·h−1 (running), at >21 km·h−1 (high-speed running, HSR) and at >24 km·h−1 (sprint, SPR) distances, efforts at >85% of the maximal sprint speed (>85% MSS), acceleration load (aLoaD), accelerations (ACC2 and ACC3, >2 and >3 m·s−2) and decelerations (DEC2 and DEC3 <−2 and <−3 m·s−2). Overall, distances covered at running, HSR and sprinting were greater for senior players than their younger peers (U15 and U18; p < 0.05). Regarding HSR and sprints, no difference was found for sprints accumulated by central defender (CD) players in comparison to U18 and U15 ( p > 0.05). In addition, U18 and senior players engaged more often in ACC and DEC, >2 and >3 m·s−2, respectively, than U15 players ( p < 0.05). In conclusion, older female soccer players are exposed to higher match load than their younger peers. These findings could be useful for soccer coaches to design specific speed development programmes across the long-term athletic development pathway.

Membrane-Bound Ferric Hemoglobin in Nucleated Erythrocytes of the Black Scorpionfish Scorpaena porcus, Linnaeus 1758.

The content of membrane-bound methemoglobin (MtHb) in nucleated erythrocytes was studied in the black scorpionfish Scorpaena porcus (Linnaeus, 1758) in vitro. Spectral characteristics were determined for a whole hemolysate, a hemolysate obtained by stroma precipitation (a clarified hemolysate), and a resuspended stroma. The MtHb proportion in the erythrocyte stroma was found to exceed 80% (6.20 ± 0.59 µM). Clarified hemolysates were nearly free of MtHb (0.5 ± 0.2 µM). Membrane-bound ferric hemoglobin did not affect the erythrocyte resistance to osmotic shock. The osmotic fragility range was determined using a LaSca-TM laser microparticle analyzer (BioMedSystems, Russia) to be 102-136 mOsm/kg, much the same as in other bony fish species. A nitrite load (10 mg/L) significantly increased the MtHb content in the blood. However, the membrane-bound ferric hemoglobin content did not change significantly, amounting to 6.34 ± 1.09 µM (approximately 95%). The finding suggested a functional importance for MtHb present in the plasma membrane of nucleated erythrocytes. Membrane-bound MtHb was assumed to neutralize the external oxidative load and the toxic effect of hydrogen sulfide in bottom water layers, where the species lives.

Validation of the added mass effect in the narrow gaps of nuclear reactor pressure vessels

Nuclear reactor pressure vessels (RPVs) must be robust to external environmental excitations such as seismic loads. Precise numerical models that predict the dynamic responses to external loads are crucial for evaluating the safety of RPVs. Notably, in RPVs submerged in reactor coolant, it is necessary to examine the added mass effect of the fluid via fluid-structure interaction (FSI) analysis, employing either an analytical approach or a numerical analysis. The present study focuses on modeling and analyzing the added mass effect in the narrow gaps associated with the dense structural layout in the reactor. In this context, this paper validates analytical and numerical models that accurately describe the added mass effect for two cases: (i) simple concentric cylinders with a narrow gap filled with fluid and (ii) a complex small-scale RPV with narrow gaps also filled with fluid. Initially, the analytical model, employing Lagrange's equation of motion and velocity potential, and the numerical model, utilizing FE modeling in acoustic FSI through ANSYS, were validated through experimental modal testing for the added mass effect in the narrow gap between simple concentric cylinders. The analytical model for the concentric cylinders indicates that the added mass diverges to infinity as the gap approaches zero, which should be examined carefully. Through experiments for the concentric cylinders, the analytical and FEM-based added mass effects were validated with a natural frequency error of 3 %. Subsequently, based on the results for the concentric cylinders, a complex numerical model of the small-scale reactor with complex boundary conditions was developed and cross-validated through corresponding experimental modal testing of the small-scale RPV. The added mass model for the narrow gaps in the RPV was validated by substantial agreement of eight representative modes, as demonstrated by a 5 % natural frequency error.

Learning-based adaption of robotic friction models

In the Fourth Industrial Revolution, wherein artificial intelligence and the automation of machines occupy a central role, the deployment of robots is indispensable. However, the manufacturing process using robots, especially in collaboration with humans, is highly intricate. In particular, modeling the friction torque in robotic joints is a longstanding problem due to the lack of a good mathematical description. This motivates the usage of data-driven methods in recent works. However, model-based and data-driven models often exhibit limitations in their ability to generalize beyond the specific dynamics they were trained on, as we demonstrate in this paper. To address this challenge, we introduce a novel approach based on residual learning, which aims to adapt an existing friction model to new dynamics using as little data as possible. We validate our approach by training a base neural network on a symmetric friction data set to learn an accurate relation between the velocity and the friction torque. Subsequently, to adapt to more complex asymmetric settings, we train a second network on a small dataset, focusing on predicting the residual of the initial network’s output. By combining the output of both networks in a suitable manner, our proposed estimator outperforms the conventional model-based approach, an extended LuGre model, and the base neural network significantly. Furthermore, we evaluate our method on trajectories involving external loads and still observe a substantial improvement, approximately 60%–70%, over the conventional approach. Our method does not rely on data with external load during training, eliminating the need for external torque sensors. This demonstrates the generalization capability of our approach, even with a small amount of data – less than a minute – enabling adaptation to diverse scenarios based on prior knowledge about friction in different settings.

Peridynamic neural operators: A data-driven nonlocal constitutive model for complex material responses

Neural operators, which can act as implicit solution operators of hidden governing equations, have recently become popular tools for learning the responses of complex real-world physical systems. Nevertheless, most neural operator applications have thus far been data-driven and neglect the intrinsic preservation of fundamental physical laws in data. In this work, we introduce a novel integral neural operator architecture called the Peridynamic Neural Operator (PNO) that learns a nonlocal constitutive law from data. This neural operator provides a forward model in the form of state-based peridynamics, with objectivity and momentum balance laws automatically guaranteed. As applications, we demonstrate the expressivity and efficacy of our model in learning complex material behaviors from both synthetic and experimental data sets. We also compare the performances with baseline models that use predefined constitutive laws. We show that, owing to its ability to capture complex responses, our learned neural operator achieves improved accuracy and efficiency. Moreover, by preserving the essential physical laws within the neural network architecture, the PNO is robust in treating noisy data. The method shows generalizability to different domain configurations, external loadings, and discretizations.

DEVELOPMENT OF THE SUBJECTIVE TRAINING QUALITY SCALE FOR TEAM SPORTS SCALE

INTRODUCTION & AIMS In team sports, training is strategically designed to incorporate all training factors (i.e., physical, technical, tactical, mental) to improve an athlete’s performance during competition. The ultimate goal is for individual athletes to work together as a cohesive unit to complete training objectives and train at high quality. Although anecdotal, training quality is considered a key component in the training process. However, there is currently no team sport literature that has defined this construct. Nor a validated measurement instrument available to assess the quality of team sport training. Therefore, the present study developed the Subjective Training Quality for Team Sports (STQ-TS) scale. Furthermore, this study investigated the application of this scale within the context of a professional National Rugby League (NRL) team. METHODS Eleven rugby league players (24 ± 2 y; 62 ± 47 NRL games) were interviewed to explore how they define and assess training quality. Thematic analysis was used to analyse interview transcripts. The identified themes were used to develop a preliminary STQ-TS scale. The STQ-TS scale was completed by forty-two NRL players across two seasons. RESULTS Four themes were identified for the STQ-TS scale. These themes included physical, technical, mental, and teamwork (i.e., communication; connectedness). Players perceived pre-season training to be lower quality compared to in-season. In-season training quality showed a gradual improvement throughout both seasons, reaching its peak late in the season. CONCLUSION Professional rugby league players perceive training quality as their ability to complete physical, technical, mental, and teamwork objectives. The STQ-TS scale serves as a valuable tool for practitioners to assess training quality in team sports. The integration of the STQ-TS scale with external load, internal load, and athlete response measures can provide practitioners with a more nuanced and holistic understanding of the training process.

Hydrogen blistering and cracking of high-strength pipeline steel welds produced by electrochemical hydrogen charging

Pipeline steel system always faces a challenge of hydrogen embrittlement (HE) not only due to corrosion environments but also because of cathodic protection strategy. Especially in welded joint, heterogeneous microstructures lead to the difference in intrinsic HE resistance for different subzones. However, this aspect was often neglected when external loading was applied during evaluation of the HE. To eliminate the effect of external loading, the hydrogen damage behaviors of X100 pipeline steel weld were investigated only based on electrochemical hydrogen charging and the intrinsic HE resistance of each subzone was explored. The results showed that the HE resistance of the main regions in weld was decreased in order of weld metal, heat affected zone (HAZ) and base metal (BM), with different surface damage modes: the BM had predominantly hydrogen blistering; while others displayed mainly hydrogen cracking. The corresponding features for cross-sectional cracking were intergranular propagation along the pancaked grain boundaries in the BM and trangranular propagation in HAZ. For transgranular cracking propagation, the path first trended to initiate on the {100} cleavage plane, then grew on the {110} slip planes. The intergranular cracking was mainly attributed to the lamellar-structural prior grain boundaries that inherited numerous deformation dislocations during hot rolling of the base metal.

HOW DO PEOPLE WITH CHRONIC LOW BACK PAIN PERCEIVE SPECIFIC AND GENERAL EXERCISE?

INTRODUCTION & AIMS Exercise prescriptions for chronic low back pain (CLBP) often utilize reductionistic, trunk-focused exercise aimed at addressing proposed pain mechanisms. It is unknown if the use of these trunk focussed exercises imply beliefs to people with CLBP about the rationale for their use (e.g., aetiology), even without concurrent biomedical narratives. This study aimed to explore people’s perceptions of specific and general exercise without an accompanying narrative when experiencing CLBP. METHODS An anonymous online survey was distributed. Mixed methods were utilised for analysis. Six-point Likert scales categorised people’s beliefs about individual exercises. Open-ended questions were used to gather further beliefs which were then coded into themes. RESULTS 109 people with CLBP perceived specific exercise as more beneficial than general exercise. Eight themes and five sub-themes were defined. A high volume of positive beliefs were centred around strengthening the low back and abdominal musculature, emphasising the importance of correct technique. Negative beliefs were held against spinal flexion and external load. Both positive and negative beliefs were underpinned by spinal/pelvic stability being important as well as certain exercises being achievable or not. CONCLUSION This study demonstrated that people with CLBP consider specific exercises to be more beneficial than general exercises for CLBP. Specific exercises irrespective of an accompanying narrative can imply meaning about the intent of an exercise. Understanding this requires practitioners to be mindful when prescribing and communicating exercise.

Fatigue life prediction model for shot-peened laser powder bed fused 304L steel considering residual stress relaxation and defect distribution

Shot-peening (SP) is a post-treatment technology that enhances the surface smoothness, mechanical properties, and fatigue performance at the surface layer of metal materials produced through laser powder bed fusion (LPBF). Therefore, accurate life prediction is crucial to effectively design and evaluate the SP process and enhance fatigue life. This study employs a cost-effective and efficient analytical method to investigate relaxation in residual stress (RS). The method calculates the interaction between RS in SP and external loading and combines it with a life prediction model. In addition, a defect-based parameter area is employed to characterize the impact of the effective defect dimensions on the fatigue life of LPBF materials. The effects of compressive residual stress (CRS) introduced by SP and process-induced internal defects on the fatigue life of LPBF material are investigated via a modified Goodman‐Basquin model. The fatigue life of 304L stainless steel (SS) prepared by LPBF after SP is predicted, and good consistency between measurement and prediction is observed.

Confinement controls the creep rate in soft granular packings.

Flow in soft materials encompasses a wide range of viscous, plastic and elastic phenomena which provide challenges to modelling at the microscopic level. To create a controlled flow, we perform falling ball viscometry tests on packings of soft, frictionless hydrogel spheres. Systematic creep flow is found when a controlled driving stress is applied to a sinking sphere embedded in a packing. Here, we take the novel approach of applying an additional global confinement stress to the packing using an external load. This has enabled us to identify two distinct creep regimes. When confinement stress is small, the creep rate is independent of the load imposed. For larger confinement stresses, we find that the creep rate is set by the mechanical load acting on the packing. In the latter regime, the creep rate depends exponentially on the imposed stress. We can combine the two regimes via a rescaling onto a master curve, capturing the creep rate over five orders of magnitude. Our results indicate that bulk creep phenomena in these soft materials can be subtly controlled using an external mechanical force.

Fragility assessment for process pipelines in flood events through physically-based hazard response analysis

Natech events triggered by floods have occurred frequently, resulting in physical damage to process equipment and subsequent releases of hazardous substances, threatening the operational safety of the process industry. Therefore, it is necessary to conduct flood fragility assessments on typical process equipment, such as storage tanks and process pipelines. Compared to storage tank, there are relatively few flood risk analysis methods applicable to process pipelines, and there is a lack of dedicated fragility models to quantify the probability of pipeline damage in flood hazard scenarios. Thus, this paper develops a process pipeline fragility model to support the quantitative risk assessment (QRA) of flood-induced Natech events more comprehensively. This model simultaneously considers the structural physical damage caused by internal pressure and external load in the pipeline and establishes the limit state equation (LSE) corresponding to the failure mode. On this basis, parametric fragility functions are trained using Monte Carlo simulations and logistic regression. A pipeline case is used to test the proposed fragility functions, and the results show that the fitted parameterized fragility model can sensitively capture changes in the failure probability curve caused by hazard intensity and pipeline characteristics changes. The proposed pipeline fragility model is applied to a composite area of pipelines and storage tanks, accurately assessing the failure probability of different types of pipelines in flood scenarios.

Analysis of Vibration Characteristics of Horizontal Axis Wind Turbine Tower under Random Wind Action

As the main supporting structure of wind turbines, the service quality of towers directly affects the operational safety of wind turbines. Researching tower vibration characteristics, evaluating its service quality and early warning of damage is an important means to improve the operational safety of wind turbines. Firstly, the external load conditions of the wind turbine tower were determined through wind load calculation, and the load and dynamic theory of the variable pitch torque wind turbine tower were summarized. Secondly, based on the Euler-Lagrange energy equation, the Lagrange equation of the simplified dynamic model of the wind turbine tower is established, and the vibration characteristics of the tower under different wind speeds are analyzed. The research results can provide a theoretical basis for the research on the characteristics of the wind turbine tower.