Increase In External Load Research Articles

Characterizing PFASs in aquatic ecosystems with 3D hydrodynamic and water quality models

Understanding how per- and polyfluoroalkyl substances (PFASs) enter aquatic ecosystems is challenging due to the complex interplay of physical, chemical, and biological processes, as well as the influence of hydraulic and hydrological factors and pollution sources at the catchment scale. The spatiotemporal dynamics of PFASs across various media remain largely unknown. Here we show the fate and transport mechanisms of PFASs by integrating monitoring data from an estuarine reservoir in Singapore into a detailed 3D model. This model incorporates hydrological, hydrodynamic, and water quality processes to quantify the distributions of total PFASs, including the major components perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS), across water, particulate matter, and sediments within the reservoir. Our results, validated against four years of field measurements with most relative average deviations below 40%, demonstrate that this integrated approach effectively characterizes the occurrence, sources, sinks, and trends of PFASs. The majority of PFASs are found in the dissolved phase (>95%), followed by fractions sorbed to organic particles like detritus (1.0–3.5%) and phytoplankton (1–2%). We also assess the potential risks in both the water column and sediments of the reservoir. The risk quotients for PFOS and PFOA are <0.32 and < 0.00016, respectively, indicating an acceptable risk level for PFASs in this water body. The reservoir also exhibits substantial buffering capacity, even with a tenfold increase in external loading, particularly in managing the risks associated with PFOA compared to PFOS. This study not only enhances our understanding of the mechanisms influencing the fate and transport of surfactant contaminants but also establishes a framework for future research to explore how dominant environmental factors and processes can mitigate emerging contaminants in aquatic ecosystems.

Entrance process and interface distribution of nanoparticles in point contact

Nanoparticles have proven to be effective in reducing friction and wear in tribological systems. Previous research mainly focused on the behavior of nanoparticles within the contact region, often overlooking the dynamics of particle's ingress into the interface. This study introduces an innovative model to elucidate the entry process of particles in point contact, grounded in mechanical analysis. The model is employed to investigate the distribution and load-bearing capacity of nanoparticles within the interface, considering variables such as velocity, applied load, particle concentration, particle size, and friction coefficient. Relative ball-on-disk experiments were conducted to verify the model’s prediction, with particular attention to the elemental distribution of particles along the wear tracks. Both theoretical and experimental results indicate that the distribution of particles shifts from covering the whole contact interface to concentrating at the edge in the movement direction as the external load increases and the velocity decreases. Additionally, while the spatial distribution of particles remains constant, the particle concentration within the interface significantly increases with higher nanoparticle concentrations. The enhanced tribological performance of nanofluid is attributed to a greater number of particles entering the contact region.

Effect of Training Load Intensification on the Sleep Pattern of Young Soccer Players

ABSTRACT Purpose: The aim of this study was to examine how intensifying training loads over a week affects the sleep patterns of young soccer players on the nights immediately following the intensified training sessions. Methods: Quasi-experimental study. Fifteen young athletes participants of a team engaged in national level competition, underwent two weeks of training with varying load magnitudes—Week 1: low accumulated training load and Week 2: intensified training loads [40% increase in external training load(ETL)]. To characterize the intensification of the workload, the methods PlayerLoad and RPE-Session were employed to measure ETL and internal training load(ITL), respectively. Total sleep time(TST), total time in bed(TTB), sleep efficiency(SE), sleep latency(SL), and wake after sleep onset(WASO) were obtained using actigraphy and daily sleep log. The variables were compared among the days of week (e.g. Monday of week 1 with Monday of week 2, and so forth). Results: Acute training intensification in week 2 led to significant increases in ETL and ITL on Monday and on Wednesday(p < .05), and ETL(p < .05) on Friday on the second week. Improvements in sleep were observed (Tuesday—TST:+80 min, WASO:-29.3 min, SL:-8 min, SE:+9%; Thursday—TST:+86 min, SL:-4 min, SE:+4%; Saturday—TST:+40 min, SL:+1 min) compared to the same day of the previous week. Correlations between ETL and ITL(r = 0.637), ITL and TST(r = 0.572), ITL and SE(r = 0.548) were found. Conclusion: Intensification of training loads results in alterations in sleep variables, notably an elevated TST and SE in the days subsequent to the acute load increment.

Nonlinear Dynamic Analysis of FG Fluid Conveying Micropipes with Initial Imperfections

This paper investigates the nonlinear dynamics of FG-FCMPs with initial imperfections. Based on the MCST, the nonlinear equations of motion and the corresponding boundary conditions are established by applying Hamilton’s principle, the Euler–Bernoulli beam theory, and von-Kármán geometric nonlinearity. To describe the initial geometric imperfection of the FG-FCMP, the first-order vibrational mode is employed. Subsequently, in cases of primary parametric resonance, 1:2 subharmonic resonance for the first-order mode, as well as primary resonance for the second-order mode, Galerkin’s method, and the multiple scale method are utilized to analyze the amplitude–frequency responses of the imperfect FG-FCMP. The numerical simulations test the influence of flow velocity, micro-scale parameter, geometrical imperfections, and external loads on the nonlinear characteristics of a coupled system with two DOFs. It is found that, as the increase of flow velocity, micro-scale effect, and external load, the amplitude of the first two modes can be increased. The hardening characteristics are converted into the softening characteristics due to the imperfect effect. Furthermore, numerical results provide a more comprehensive understanding of the nonlinear dynamics of FCMPs for both periodic and chaotic motions.

Prediction of Wear Resistance of In-situ Zinc Matrix Composites Reinforced by Silicon Phase Based on Neural Network

Silicon phase reinforced zinc-aluminium alloy composites were prepared by in-situ method. The effect of silicon content and external load on the wear resistance of in-situ zinc--aluminium composites was studied by BP artificial neural network. The test results show that the silicon phase, as a hard material, plays the role of supporting load and improves the wear resistance of the alloy. With the increase of Si content, the wear resistance of in-situ zinc--aluminium composites increased first and then decreased. When the amount of silicon added exceeds 2.5-3%, the wear resistance will be reduced, which is related to the silicon phase aggregation and the easy separation of large silicon phases from the matrix. With the increase of external load, the relative wear continues to increase, which is related to the increase of friction. The neural network platform can successfully predict the general trend of wear resistance with the change of silicon content and load.

Algorithm for calculating the problem of unilateral frictional contact with an increscent external load parameter

The subject of the study is the contact interaction of deformable elements of linear complementarity problem (LCP). To solve the linear complementarity problem, the Lemke method with the introduction of an increasing parameter of external loading is used. The proposed approach solves the degenerated matrix in a finite number of steps, while the dimensionality of the problem is limited to the area of contact. To solve the problem, the initial table of the Lemke method is generated using the contact matrix of stiffness and the contact load vector. The unknowns in the problem are mutual displacements and interaction forces of contacting pairs of points of deformable solids. The proposed approach makes it possible to evaluate the change in working schemes as the parameter of external load increases. The features of the proposed formulation of the problem are shown, the criteria for stopping the stepwise process of solving such problems are considered. Model examples for the proposed algorithm are given. The algorithm has shown its efficiency in application, including for complex model problems. Recommendations on the use of the proposed approach are given.

Opinion: inappropriate applications of phosphorus loading models in lake management regulatory policy

Lehman J. 2023. Opinion: inappropriate applications of phosphorus loading models in lake management regulatory policy. Lake Reserv Manage. 39:273–277.Imposition of total maximum daily load (TMDL) regulations based on external loading has little or no effectiveness when nuisance conditions are caused almost entirely by internal loading. A case study example from southeastern Michigan illustrates how persistent application of flawed management theory fails to achieve water quality objectives. Observations reveal that nuisance blooms are nearly contemporaneous with polymictic episodic injections of anoxic, phosphorus-rich hypolimnetic water into surface waters. Even a 10-fold increase in external loading during the Great Northeast Blackout of 2003 failed to trigger a nuisance bloom.

Bond stress distribution and suggestions for anchoring length of deformed steel bars in different types of cementitious grout

Eight sets of pull–out specimens were tested by considering four types of cementitious grout (CGM-380, CGM-340, CGM-300, and CGM-270) and two anchoring lengths (3d and 10d) in this study. Discussions were had on the failure modes, bond load–slip curves, stress distribution of steel bars, and bond stress distribution. Results indicated that the relationship between the magnitude of peak bond load of 3d–group specimens composed of different types of cementitious grout was shown as CGM-270>CGM-300>CGM-340>CGM-380. Simultaneously, the stress of the steel bars in specimens gradually increased with the increase in external load, and the steel bars were in the elastic stage. For the 10–group specimens, the peak bond load of each specimen was basically the same, and the steel bars had yielded when the specimen was damaged. In addition, the stress distribution of the steel bars was similar to that of 3d–group specimens before the steel bars yielding. After the load reached the yield load, however, the yield position gradually shifted toward the free end with the load further increased, and the yield section length of the steel bars gradually increased. Besides, in contrast to the unimodal bond stress distribution curves of the 3d–group specimens, the bond stress distribution curves of the 10d–group specimens were all in the shape of a multimodal distribution. The peak bond stress of 10d–group specimens were located near the loading end before the steel bars yielding. However, as the load was raised continuously after the steel bars yielded, the bond stress in the yield section dramatically dropped, the yield penetration depth progressively grew, and the peak bond stress gradually shifted towards the free end. Additionally, design suggestions for the critical anchoring length of steel bars in cementitious grout and the anchoring length of steel bars after yielding were provided.

Study On Rehabilitation Treatment of Patients with Lumbar Disc Herniation by Acupuncture and Massage

In clinical practice, lumbar disc herniation is also called lumbar disc herniation due to the rupture of the annulus fibrosus. The degenerative changes of the nucleus pulposus, annulus fibrosus, cartilage plate and other positions with different degrees and symptoms make it difficult to bear excessive external force, which leads to the increase of external load. For patients with lumbar disc herniation, acupuncture has the functions of dredging meridians, promoting blood circulation, and harmonizing qi and blood, and can improve local blood circulation through acupuncture. Relieve muscle spasm and dilate blood vessels, which can play a therapeutic or auxiliary role in the treatment of lumbar disc herniation. Acupuncture therapy is generally divided into general acupuncture, electroacupuncture, acupuncture plus moxibustion, acupuncture plus massage therapy, etc., which have good clinical effects. Therefore, this paper adopts the random control method to study and discuss the curative effect analysis of acupuncture, massage and rehabilitation nursing intervention on patients with lumbar disc herniation. There are many reports on the clinical observation of acupuncture in the treatment of lumbar protrusion. At the same time, supplemented by massage, it can open the channels of patients, regulate their qi and blood, promote blood circulation and remove blood stasis, relieve the muscle tension of patients, and at the same time act on protrusions to promote their movement or retraction, and improve the state of patients' back.

Multi-scale simulation of the fracture behavior of non-stoichiometric gadolinia-doped ceria solid electrolytes under the coupled mechanical and electrochemical field

Solid oxide fuel cell (SOFC) works in a complex working environment, which is affected by many factors such as temperature, load and electrochemical reaction. When there are cracks in the material, the multi-field coupling effect will cause the electrolyte performance degradation, even failure and damage. In this paper, the coupling effects of mechanical and electrochemical field on mechanical behavior of gadolinia-doped ceria (GDC) electrolyte are investigated by using the Atom-to-Continuum (AtC) multi-scale method combining molecular dynamics (MD) and finite element method (FEM). Based on the electrochemomechanical coupling theory, we derive the defect diffusion equation of the finite element form. The non-stoichiometry of the cracked GDC electrolyte is calculated, and it is found that the stress concentration at the crack tip will induce non-stoichiometric effects, causing further concentration of oxygen vacancy defects at the crack tip. Subsequently, the effect of electrochemomechanical coupling effect on the fracture toughness of GDC electrolyte is studied by using the AtC multi-scale method. At 800°C under oxygen partial pressure logPO2=−22, this multi-field coupling effect reduces the fracture toughness of 10GDC and 20GDC by 16.13% and 23.33%, and this effect is more apparent with the increase of oxygen partial pressure gradient and external load.

Modeling fibrous soft tissue dissection with elastic-plastic deformation for simulation of brain tumor removal

Background and objective: Realistic modeling the dissection of brain tissue is of key importance for simulation of brain tumor removal in virtual neurosurgery systems. However, existing methods are unable to characterize inelastic behaviors of brain tissue, such as plastic deformation and dissection evolution, making it ineffective in simulating brain tumor removal procedures.Methods: In this paper, a model of fibrous soft tissue dissection for the simulation of brain tumor removal is proposed. A dissection variable of representative volume element is used to characterize the dissection state of the fibrous soft tissue. The evolution of dissection with elastic-plastic deformation under the effects of external loads is presented.Results: Simulation results show that the proposed model provides realistic, stable and intuitive results in the simulation of fracture in fibrous soft tissues. As the external load increases, the fibrous soft tissue begins to crack, with the cracks growing and multiplying until they eventually merge to form a fracture. The proposed model is incorporated into the simulation of brain tumor removal.Conclusions: The experimental results demonstrate the feasibility of modeling fibrous soft tissue dissection with elastic-plastic deformation. A relative high degree of realistic visual feedback is achieved.

Numerical investigation on the effect of intergranular contact bonding strength on the mechanical properties of granite using PFC3D‐GBM

AbstractIn rock materials, the intergranular structure is more affected by various external conditions than the transgranular structure, and then dominates the macroscopic mechanical properties of rocks. In this paper, an innovative three‐dimensional grain‐based model based on Particle Flow Code (PFC3D‐GBM) for reproducing granite crystalline structures was developed. Based on this model, the Brazilian splitting test was conducted to investigate the effects of intergranular contact (IC) bonding strength on the mechanical properties and micro‐cracking behavior of the granite. Additionally, in this paper, the force chains and the orientation distribution of the force chains are shown in the form of three‐dimensional rose diagrams. The results are compared to the numerical results obtained by an initial particle‐based model to demonstrate the superiority of the proposed PFC3D‐GBM. The results indicate that the stress–strain curve of the sample in the Brazilian splitting test can be classified into four distinct stages: initial compaction, linear elasticity, damage, and splitting failure. ICs fracture at a higher rate than transgranular contacts (TCs) under static loading, as evidenced by experimental results of laboratory tests; during the entire loading process, all force chains uniformly distribute in all directions of a sample. As the external load increases, the number of total force chains decreases and the number of cracks increases. The main orientation of the high‐strength force chains is consistent with the external loading direction and is vertical with respect to the main orientation of the cracks. Furthermore, the number of high‐strength force chains increases with the level of external load. The sample's failure mechanism in the Brazilian splitting test is always a tensile failure, and this characteristic is unaffected by the modeling method or the IC bonding strength. Both the tensile strength and peak strain increase as the IC bonding strength increases. In this process, the number of total cracks in PFC3D‐GBM decreases, the proportion of transgranular cracks (Tcs) increases, and the proportion of intergranular cracks (Ics) decreases. The micro‐cracking behavior described above based on the PFC3D‐GBM can be explained more rationally. As the bonding strength of the IC increases, the particles involved in sample deformation are subjected to a greater stress concentration prior to the sample experiencing macro‐fracture, leading to an increase in the number of high‐strength force chains, which is the fundamental reason for the increase of the sample's tensile strength.

INFLUENCE OF POSITION ERRORS ON THE STABILITY OF A LOADBEARING VERTICAL ROD OF GREAT FLEXIBILITY

Many building structures are considered as rod systems. Bearing elements of rod systems are under load and experience large stresses and deformations. When external loads increase, these stresses and strains also increase. There may come a point where some elements lack strength, stiffness or stability. Such cases may arise due to uneven settlement and roll of the structure in conjunction with errors in the manufacture and installation of structures, insufficient development of projects, etc. One of the main measures for the timely prevention of emergency situations is the properly organized monitoring of the stress-strain state of the elements. In this paper, we consider a model of stressed structure, which combines elements in the form of flexible deformable rods and elements acting on them, represented by force vectors. As an example, we consider a structure of two vertical rectilinear rods pointing along one plumb line and connected in a node. The lower rod is pinched in the base and is a load bearing element. The upper rod is an external load for the lower one and is represented by the equivalent force vector. In theory, the lines of action of forces lie on one vertical line, so there are no other forces and moments besides axial longitudinal forces; the forces are applied at one point with given coordinates. When constructing the rod system, each rod must be set to a given design position. There will be position errors of the elements during the installation phase of the structure. Position errors are generally represented by errors in the specified angles of inclination of the rods and errors in the position of the ends of the rods in the assembly. In a stressed structure, these errors are equivalent to the errors of the force vectors. A modified system of force vectors arises. In such a system, due to position errors, a horizontal force arises which has the main influence on the stability of the supporting flexible rod when the external load increases.

Fretting fatigue experiment and simulation of WC-12Co coating taking into account the wear effects

WC-12Co coating can be used to improve the wear resistance of mechanical connectors, but due to the fretting behavior between the contact interfaces during service, the problem of fretting fatigue cannot be ignored. Through the fretting fatigue experiment and simulation study of the WC-12Co coating, the fretting fatigue mechanism of the coating was investigated under the premise of considering the competitive or coupling relationship between fretting wear and fretting fatigue. Based on Smith-Watson-Topper (SWT) fatigue damage parameter and Miner-Palmgren (M-P) linear cumulative fatigue damage theory, a prediction model for fretting fatigue crack initiation life of WC-12Co coating was established, and the stress redistribution caused by fretting wear was analyzed by Archard wear theory. The analysis results show that the fretting fatigue cracks of the WC-12Co coating mainly initiate at the edge of the wear pits and gradually extend to the substrate; the increase of external load and friction coefficient will accelerate the fretting fatigue process of WC-12Co coating and reduce its fretting fatigue crack initiation life; the change of fretting fatigue crack initiation life and position of WC-12Co coatings caused by fretting wear depends on the change of contact state between contact interfaces.

Dynamic response of a Li2O-Al2O3-SiO2 transparent glass-ceramic under shock compression

Li2O-Al2O3-SiO2 transparent glass-ceramics (LAS-TGCs) are promising candidates for transparent armour materials due to their excellent physical and mechanical capabilities. In this work, the dynamic behaviour of a LAS-TGC were further investigated using the planar impact technique and photon Doppler velocimetry. The shock stress, shock wave velocity, failure wave velocity and spall strength were obtained. In addition, the recompression signal, as a signature of failure waves, was observed to evolve into an oscillation signal as the impact stress decreases, indicating that the failure wave is gradually formed at a threshold. It has been noted that the failure wave velocity decreases with the increase in external loading and then turns upwards. The damage parameter of the LAS-TGC was assessed to be 0.410(5) under a shock stress of ~5.5 GPa, which is smaller than that of K9 glass. It is suggested that the LAS-TGC has better shock resistance than K9 glass.

A New Two-Stage Degradation Model for the Preload of Linear Motion Ball Guide Considering Machining Errors

Abstract Preload, which is widely applied in linear motion ball guide (LMBG) to eliminate clearance and increase stiffness, gradually decreases owing to wear, resulting in the degradation of the load-bearing capability and dynamic response of LMBG. However, no solution can be found on the modeling of the preload degradation of LMBG considering raceway profile error, ball diameter error, etc. Therefore, this paper presented a new two-stage degradation model to predict the preload variation of LMBG with considering machining errors. The model was experimentally verified with the prediction accuracy much higher than the model considering no machining errors at either of the two wear stages, which demonstrates the effectiveness of considering machining errors. Additionally, the effects of waviness errors, external load, and feed speed on the preload degradation of LMBG were discussed. The simulation results indicate that the preload loss rate rises with the increase of waviness error, external load and feed speed. For obtaining a longer effective service life of LMBG, it is helpful to select appropriate external load and feed speed conditions and improve the processing technique as well as the machined surface quality.

Sublimation of composite ice and its influence on performance of ice shells

The long-span ice composite shell structure is a new type of ice and snow structure developed in recent years. The engineering practice of ice composite shell shows that sublimation is one of the important reasons for its damage and even collapse. In this paper, we firstly supplemented the existing H-K equation and obtained the revised ice sublimation equation through indoor evaporative plate experiment considering the influence of admixtures and wind speed. Afterwards, combining the simulations of solar radiation and CFD, the numerical simulation of sublimation distribution on the surface of were realized by programming in Grasshopper platform. During sublimation, the thickness of the ice composite shell decreases by 0.38 mm every 10 days and the sublimation rate on the sunny side was 1.7 times that on the shady side. Finally, the static performance and stability of the sublimated ice composite spherical shell were analyzed. After 70 days of sublimation, the thickness of the ice composite shell structure becomes thinner and uneven, which leads its sensitivity to external load increases.

Modeling the deformation process of a plate with a stress concentrator taking into account the postcritical stage of material deformation

Postcritical deformation of a material is a process which is characterized by a decrease of stress during growing deformations as a result of accumulation of structural damage. The design becomes unable to withstand the external load only when zones with weakened connections are developed enough. Evolution of postcritical deformation zones can occur with an increase of the external load applied to the construction. It means that taking into account the softening of the material allows determining the strength and deformation reserves of constructions more accurately. The mathematical formulation of the boundary value problem of supercritical deformation mechanics is given in the paper. The features of the experimental study of the postcritical stage of material deformation are listed. Strain curves of various steels with a long section of softening are obtained. Numerical solutions for the problems of deforming a thin plate with stress concentrators of different geometries under kinematic loading are obtained. Piecewise linear approximations and real strain curves of steel 20 and steel 40Cr4 obtained experimentally are considered. The evolution of zones of postcritical deformation in the material is considered. The correspondence between the value of the decline modulus and the nature of the evolution of the softening zones is determined. A stress plot is constructed that reflects how the complete material deformation diagram is realized near the concentrator. The calculated loading diagrams are constructed. It is noted that even after the appearance of softening zones, an increase in external load is possible. The strength and deformation resources of structures are determined, and the influence of the geometry of the stress concentrator on their values is considered. It is noted that the consideration of softening in modeling the behavior of structures with stress concentrators is appropriate.

Muscle-Specific Contributions to Lower Extremity Net Joint Moments While Squatting With Different External Loads.

Kipp, K, Kim, H, and Wolf, WI. Muscle-specific contributions to lower extremity net joint moments while squatting with different external loads. J Strength Cond Res 36(2): 324-331, 2022-The purpose of this study was to determine muscle-specific contributions to lower extremity net joint moments (NJMs) during squats with different external loads. Nine healthy subjects performed sets of the back squat exercise with 0, 25, 50, and 75% of body mass as an added external load. Motion capture and force plate data were used to calculate NJMs and to estimate individual muscle forces via static optimization. Individual muscle forces were multiplied by their respective moment arms to calculate the resulting muscle-specific joint moment. Statistical parametric mapping (α = 0.05) was used to determine load-dependent changes in the time series data of NJMs and muscle-specific joint moments. Hip, knee, and ankle NJMs all increased across each load condition. The joint extension moments created by the gluteus maximus and hamstring muscles at the hip, by the vastii muscles at the knee, and by the soleus at the ankle all increased across most load conditions. Concomitantly, the flexion moment created by the hamstring muscles at the knee also increased across most load conditions. However, the ratio between joint moments created by the vastii and hamstring muscles at the knee did not change across load. Similarly, the ratio between joint moments created by the gluteus maximus and hamstring muscles at the hip did not change across load. Collectively, the results highlight how individual muscles contribute to NJMs, identify which muscles contribute to load-dependent increases in NJMs, and suggest that joint moment production among synergistic and antagonistic muscles remains constant as external load increases.

Fully-coupled thermomechanical analysis for sliding contact between textured slipper and swashplate in axial piston pump

A fully coupled thermo-mechanical model is developed to investigate the transient sliding contact between textured slipper and swashplate considering the frictional heating. The model is capable of predicting the friction stress, contact temperature distribution and friction coefficient of the textured slipper pair. The effects of the sliding rate on the friction stress and contact temperature are studied. In addition, the effects of material stiffness and friction coefficient on contact temperature are further discussed. Based on the thermo-mechanical model, a parametric study is conducted to evaluate the friction coefficient and flash temperature. It is found that the greater the slip rates, the higher the contact temperature, and thus, the more the friction reduction. The shear bearing capacity of the interface material decreases with the increase of contact temperature, and finally results in the friction stress reduction. Due to the effect of friction force, contact temperature increases with the increase of friction coefficient. The change of material stiffness have little effect on temperature rise. The effective parameters combination of the textured slipper pair can be selected to achieve minimum coefficient. For selected texture parameters, the flash temperature between textured slipper and swashplate becomes higher due to the increase of slip rate and external load, but the friction coefficient decreases.