External Load Research Articles

Analysis of cooling loads and air circulation in the passenger compartment of the CR400AF fast train trailer car

The air conditioning system is a system that regulates air circulation and air temperature on the train. The temperature standard for fast train passengers is in accordance with Permen No. 7th year 2022 is 22°C - 26°C. To achieve this temperature, a cooling system is needed that is suitable for the cooling load. This research was conducted on the CR400AF fast train trailer car with the aim of knowing the factors that influence cooling loads, calculating and analyzing cooling loads which are used as a reference in determining air conditioning technical specifications, as well as analyzing air circulation that affects air humidity. The data analysis method used is the quantitative data analysis method. This method is carried out by collecting primary and secondary data to be used as a basis for calculations in answering the problem formulation. Data analysis was carried out by calculating the OTTV (Overall Thermal Transfer Value) according to SNI 03-6389-2000, calculating the cooling load using the CLTD (Cooling Load Temperature Difference) method according to SNI 03-6572-2001, and carrying out an air circulation test referring to Permen No. . 7 of 2022. From the results of the analysis and calculations, the OTTV value is 15.6 Watt/m2. Room eligibility standards according to SNI 03-6389-2000 standards are OTTV values not greater than 45 Watt/m2. The internal cooling load is 15,010 W, the external load and ventilation is 22,688.92 W, the total cooling load is added 10% safety factor of 41.47 kW, the cooling capacity of the AC unit based on technical specifications is 45kW. The average value of air flow velocity during the air circulation test is 0.3 m/s. according to Ministerial Regulation No. 7 of 2022 maximum air circulation speed of 0.5 m/s. From several analysis and calculation results, it can be concluded that the passenger space of the CR400AF fast train trailer car is standard and feasible to operate

EFFECT OF SEGMENT DISLOCATION ON THE MECHANICAL PROPERTIES OF LINED TUNNELS IN A COMPLEX ENVIRONMENT

In complex environments, tunnels with a lined structure are more affected by the dislocation of a segment. This study uses finite element simulations to further investigate the relationship between environmental changes and segments in lined tunnels. Tunnels with and without a lining are simulated under varying strata resistance, buried depth, and water level conditions. The horizontal and vertical displacements and stress changes in the two tunnels are compared when segment dislocation occurs. The results show that the lateral displacement of the tunnel is relatively stable and less influenced by external loads. However, the longitudinal displacement change is the opposite, and it increases significantly when the displacement exceeds 10 mm. When the lined tunnel is subjected to a large external load and misalignment occurs, the performance of the tube sheet joint bolts deteriorates, resulting in a stress decrease. Furthermore, the lined tunnel exhibits an increased ability to resist deformation and does not exactly follow the law of small displacements from small misalignments. When a large misalignment occurs, the lined tunnel may be damaged by elliptical deformation along the 45° direction, and its internal forces would be much larger than those of the unlined tunnel.

A Deformation Analysis Method for Sluice Structure Based on Panel Data

Deformation, as the most intuitive index, can reflect the operation status of hydraulic structures comprehensively, and reasonable analysis of deformation behavior has important guiding significance for structural long-term service. Currently, the health evaluation of dam deformation behavior has attracted widespread attention and extensive research from scholars due to its great importance. However, given that the sluice is a low-head hydraulic structure, the consequences of its failure are easily overlooked without sufficient attention. While the influencing factors of the sluice’s deformation are almost identical to those of a concrete dam, nonuniform deformation is the key issue in the sluice’s case because of the uneven property of the external load and soil foundation, and referencing the traditional deformation statistical model of a concrete dam cannot directly represent the nonuniform deformation behavior of a sluice. In this paper, we assume that the deformation at various positions of the sluice consist of both overall and individual effects, where overall effect values describe the deformation response trend of the sluice structure under external loads, and individual effect values represent the degree to which the deformation of a single point deviates from the overall deformation. Then, the random coefficient model of panel data is introduced into the analysis of sluice deformation to handle the unobservable overall and individual effects. Furthermore, the maximum entropy principle is applied, both to approximate the probability distribution function of individual effect extreme values and to determine the early warning indicators, completing the assessment and analysis of the nonuniform deformation state. Finally, taking a project as an example, we show that the method proposed can effectively identify the overall deformation trend of the sluice and the deviation degree of each measuring point from the overall deformation, which provides a novel approach for sluice deformation behavior research.

Centrifuge modelling of end-bearing slender energy pile performance under temperature cycles

Slender energy pile shows a buckling deformation behavior under the coupling effect of temperature cycles and external loads, significantly affecting the long-term serviceability and even leading to the buckling failure. To investigate the thermo-mechanical performance of end-bearing slender energy piles under the long-term effect of temperature cycles, a centrifuge modelling experiment was conducted in this work, in which the temperature distribution, displacement, axial force and bending moment of the energy pile during the long-term temperature cycle were measured. The results unveiled that the axial force of the end-bearing slender pile increases as temperature rises, potentially leading to a displacement neutral point in the lower part of the pile. Meanwhile, there was an embedding effect in the lower part of the slender pile, with a preliminary calculated embedment depth of 36.2 meters. Temperature fluctuations can soften the soil at the pile end over time, diminishing the embedding effect on slender piles, and causing a reverse bending point to emerge at a depth of 45.5 meters. The appearance of bending moments in the pile signaled the horizontal displacement encountered in the pile service life, warning the bearing capacity loss problem from changes in pile deflection.

Neuromuscular Control during the Bench Press Exercise Performed with Free Weights and Pneumatic Loading

The main objective of the research was to determine neuromuscular control for different external loads, from 75% to 100% 1 RM (One Rep Max), during the flat bench press (BP) exercise performed with free weights and pneumatic loading. Despite extensive research on the internal structure of the BP exercise, few studies have examined the differences between muscular activity during the flat bench press movement between Free Weights and Pneumatic Loading. For this purpose, 10 male, trained subjects performed the BP exercise under two conditions with three different external loads (70%, 85%, and 100% 1RM), alternately with free weights and pneumatic loading. Pneumatic loading was performed on the Keiser Power Rack, where the pneumatic load was transferred as the resistance of the cables attached to the ground. EMG activity was recorded during the lifts for the following muscles: PM (Pectoralis Major), AD (Anterior Deltoid), Tblat, and TBlong (Triceps Brachii). The EMG signals were sampled at a rate of 1000 Hz. Signals were band-pass filtered with a cutoff frequency of 8 Hz and 450 Hz, after which the root-mean-square (RMS) was calculated. After completion of all the tests in a single day, 2–3 s evaluations of Maximal Voluntary Isometric Contraction (MVIC) of the prime movers in the bench press movement (AD, PM, and TBlong) were performed according to SENIAM procedures. The results of the present study indicate that pneumatic loading provides a significantly different muscle activation pattern compared to a standard bar during a heavy-loaded BP exercise. The pneumatic load was superior in activating the AD and TB muscles compared to the standard bar during the BP exercise.

Advances in Understanding the Evolution Mechanism of Micropore Defects in Metal Materials under External Loads

Micropores are one of the critical factors affecting materials’ performance and service life. As the need for a deeper understanding of micropore evolution and damage mechanisms grows, assessing the mechanical properties of materials containing micropores and predicting the lifespan of related metal structural components becomes increasingly complex. This paper focuses on the evolution process, regularities, and research methods of micropores in metal materials. Based on recent research and practical applications, the key stages of micropore evolution are discussed, encompassing nucleation, growth, coalescence, collapse, interaction, and the influence of other microstructures. Firstly, the advantages and limitations of commonly used characterization methods such as scanning electron microscopy, transmission electron microscopy, and X-ray computed tomography are introduced in the study of micropore evolution. Subsequently, critical theoretical models for micropore evolution, such as the Gurson model and its extensions, are summarized. By using a multiscale approach combining the crystal plasticity finite element method, dislocation dynamics, and molecular dynamics, the factors influencing the micropore evolution, such as external stress conditions, internal microstructures, and micropore characteristics, are specifically elaborated, and the basic physical mechanisms of micropore evolution are analyzed. Finally, a comprehensive review and summary of current research trends and key findings are provided, and a forward-looking perspective on future research directions is presented.

Probabilistic damage identification for bridges using multiple damage-sensitive features and FE model update

A specific damage-sensitive feature (DSF) is usually sensitive to damage in a certain area, and the specific location of damage in a specific area can be detected by selecting appropriate DSFs. However, damaged components are seldom known before inspections. This makes it difficult to find an appropriate DSF, and damage identification is sometimes challenging. This paper aims to propose a natural frequency and displacement ratio-based probabilistic damage identification method for bridges using the finite element (FE) model update to solve this issue. The displacement ratio measured at two positions on the bridge is proposed as a new DSF. It is a useful DSF because it is independent of external loads. By integrating displacement ratios and natural frequencies, that is, multiple DSFs, as a decision-level data fusion approach, this paper identifies damaged components without choosing an appropriate DSF beforehand. In addition, probability density functions (PDFs) of structural parameters are estimated from PDFs of derived DSFs through the FE model update to consider errors and uncertainties in measurements. An in-house model bridge experiment is carried out to investigate the feasibility. The results demonstrated that the two kinds of damages in a bearing and girder reproduced in the experiment were successfully identified without false positives even when these damages simultaneously occurred.

Experimental Study on Compression Failure of Type II Ballastless Track Slab Based on Optical Fiber Sensing

Ballastless track structures are widely employed in high-speed rail networks because of their superior safety and durability. Among the various types of ballastless track, the Type II slab is currently one of the most extensively used and mature technologies in practice. Over the course of its service life, the damage within the ballastless track structure gradually accumulates in response to increased external loads. Therefore, it is crucial to continuously monitor the health condition of the track structure. In this study, a quasi-distributed fiber optic sensing system is adopted to monitor the deformation capacity and force performance of a Type II ballastless track slab under vertical load. The investigation aims to analyze the damage mechanism of the track structure under vertical pressure by assessing the deformation differences among its different components. The findings reveal that the incorporation of vertical reinforcement can enhance the pressure bearing capacity of the cement asphalt mortar layer to a certain extent, subsequently affecting the stress dilation. The stress performance of the ballastless track slab can be effectively monitored using the quasi-distributed fiber optic sensing technology under pressure. The outcomes of this research offer valuable insights for controlling displacement and analyzing damage in ballastless railway systems subjected to compression.

Numerical Simulation on the Leakage-Induced Collapse of Segmental Tunnels

Sudden leakage during tunnel construction poses a great threat to the safety of the tunnel. There are relatively few studies on the mechanism of structural collapse induced by tunnel leakage, so it is difficult to propose effective control measures. To solve this problem, a coupled fluid–solid strata analysis model and a nonlinear FEM tunnel model were established based on model test results to analyze the mechanism of tunnel collapse. The following conclusions were drawn: (1) A DEM-based coupled fluid–solid model combined with a nonlinear FEM tunnel model can effectively simulate the physical process of tunnel collapse. (2) The mechanism of tunnel leakage-induced strata response is the continuous destabilization and reappearance of the soil arching effect, which restricts the erosion of the soil and results in macroscopic soil caves, and finally leads to the impact load of the destabilized soil. (3) The process of the tunnel structure collapse is as follows: firstly, a large deformation of the tunnel structure is caused by the redistribution of external loads generated by the earth arching effect; then, due to the multiple impact loads from the destabilization of the soil, plastic hinges are generated at the tunnel joints, and the tunnel collapses.

An Adaptive Robust Control Method for Chaotic State of Permanent Magnet Synchronous Motor

In this paper, a chaotic control method based on adaptive robust controller is proposed to solve the chaos phenomenon of the permanent magnet synchronous motor system by mathematically analyzing the dynamic model of the permanent magnet synchronous motor system to eliminate or suppress chaos in the permanent magnet synchronous motors. This method also takes into account the parameter uncertainties (structural uncertainties) of the system and the external load torque interference (unstructured uncertainty).The former is compensated by adaptive control, and the latter by robust term. Feedforward elimination technology can integrate them together, and effectively reduce the influence of chaos on system performance and realize the high precision position tracking of the permanent magnet synchronous motor system. The Lyapunov method is used to prove the stability of the controller. The simulation results show that the method is better in robustness and control precision.

Microstructure-based modeling of primary cilia mechanics.

A primary cilium, made of nine microtubule doublets enclosed in a cilium membrane, is a mechanosensing organelle that bends under an external mechanical load and sends an intracellular signal through transmembrane proteins activated by cilium bending. The nine microtubule doublets are the main load-bearing structural component, while the transmembrane proteins on the cilium membrane are the main sensing component. No distinction was made between these two components in all existing models, where the stress calculated from the structural component (nine microtubule doublets) was used to explain the sensing location, which may be totally misleading. For the first time, we developed a microstructure-based primary cilium model by considering these two components separately. First, we refined the analytical solution of bending an orthotropic cylindrical shell for individual microtubule, and obtained excellent agreement between finite element simulations and the theoretical predictions of a microtubule bending as a validation of the structural component in the model. Second, by integrating the cilium membrane with nine microtubule doublets and simulating the tip-anchored optical tweezer experiment on our computational model, we found that the microtubule doublets may twist significantly as the whole cilium bends. Third, besides being cilium-length-dependent, we found the mechanical properties of the cilium are also highly deformation-dependent. More important, we found that the cilium membrane near the base is not under pure in-plane tension or compression as previously thought, but has significant local bending stress. This challenges the traditional model of cilium mechanosensing, indicating that transmembrane proteins may be activated more by membrane curvature than membrane stretching. Finally, we incorporated imaging data of primary cilia into our microstructure-based cilium model, and found that comparing to the ideal model with uniform microtubule length, the imaging-informed model shows the nine microtubule doublets interact more evenly with the cilium membrane, and their contact locations can cause even higher bending curvature in the cilium membrane than near the base.

Seahorse-Tail-Inspired Soft Pneumatic Actuator: Development and Experimental Characterization

The study of bio-inspired structures and their reproduction has always fascinated humans. The advent of soft robotics, thanks to soft materials, has enabled considerable progress in this field. Over the years, polyps, worms, cockroaches, jellyfish, and multiple anthropomorphic structures such as hands or limbs have been reproduced. These structures have often been used for gripping and handling delicate objects or those with complex unknown a priori shapes. Several studies have also been conducted on grippers inspired by the seahorse tail. In this paper, a novel biomimetic soft pneumatic actuator inspired by the tail of the seahorse Hippocampus reidi is presented. The actuator has been developed to make a leg to sustain a multi-legged robot. The prototyping of the actuator was possible by combining a 3D-printed reinforcement in thermoplastic polyurethane, mimicking the skeletal apparatus, within a silicone rubber structure, replicating the functions of the external epithelial tissue. The latter has an internal channel for pneumatic actuation that acts as the inner muscle. The study on the anatomy and kinematic behaviour of the seahorse tail suggested the mechanical design of the actuator. Through a test campaign, the actuator prototype was characterized by isotonic tests with an external null load, isometric tests, and activation/deactivation times. Specifically, the full actuator distension of 154.5 mm occurs at 1.8 bar, exerting a maximum force of 11.9 N, with an activation and deactivation time of 74.9 and 94.5 ms, respectively.

Study on the bond-slip behavior between steel bar and rammed earth

The steel bars significantly enhance the mechanical properties of rammed earth, as they together withstand external loads. In order to investigate the bond performance between steel bars and rammed earth, the pull-out tests were conducted on 60 specimens. This study investigated the distribution of bond stress along the anchorage length of steel bars by embedding strain gauges inside the bars. The effects of four types of anchorage length, three types of cover thickness, three types of steel bar diameter and three types of compressive strength of rammed earth on the bond-slip behavior were investigated. Through experimental research and theoretical analysis, the distribution law of the bond stress along the anchorage length was obtained. The transfer mechanism of the bond stress and the failure mode of the specimens were analyzed. An improved bond-slip constitutive model was proposed to reflect the influence of the position function of bond stress distribution. Furthermore, a theoretical formula for the bond strength was proposed based on the analytical approach of elastic solid mechanics and the failure modes of the specimens, and its accuracy was validated by experimental results.

On a lack of stability of parametrized BV solutions to rate‐independent systems with nonconvex energies and discontinuous loads

AbstractWe consider a rate‐independent system with nonconvex energy under discontinuous external loading. The underlying space is finite‐dimensional and the loads are functions in . We investigate the stability of various solution concepts w.r.t. a sequence of loads converging weakly* in with a particular emphasis on the so‐called normalized, ‐parametrized balanced viscosity solutions. By means of three counterexamples, it is shown that common solution concepts are not stable w.r.t. weak* and even intermediate (or strict) convergence of loads in the sense that a limit of a sequence of solutions associated with these loads need not be a solution corresponding to the load in the limit. We moreover introduce a new solution concept, which is stable in this sense, but our examples show that this concept necessarily allows “solutions” that are physically meaningless.

Flexible piezoresistive pressure sensor based on a graphene-carbon nanotube-polydimethylsiloxane composite

Flexible sensors are used widely in wearable devices, specifically flexible piezoresistive sensors, which are common and easy to manipulate. However, fabricating such sensors is expensive and complex, so proposed here is a simple fabrication approach involving a sensor containing microstructures replicated from a sandpaper template onto which polydimethylsiloxane containing a mixture of graphene and carbon nanotubes is spin coated. The surface morphologies of three versions of the sensor made using different grades of sandpaper are observed, and the corresponding pressure sensitivities and linearity and hysteresis characteristics are assessed and analyzed. The results show that the sensor made using 80-mesh sandpaper has the best sensing performance. Its sensitivity is 0.341 kPa−1 in the loading range of 0–1.6 kPa, it responds to small external loading of 100 Pa with a resistance change of 10%, its loading and unloading response times are 0.126 and 0.2 s, respectively, and its hysteresis characteristic is ∼7%, indicating that the sensor has high sensitivity, fast response, and good stability. Thus, the presented piezoresistive sensor is promising for practical applications in flexible wearable electronics.

Anisotropic Liesegang pattern for the nonlinear elastic biomineral-hydrogel complex.

The Liesegang pattern is a beautiful natural anisotropic patterning phenomenon observed in rocks and sandstones. This study reveals that the Liesegang pattern can induce nonlinear elasticity. Here, a Liesegang-patterned complex with biomineral-hydrogel repetitive layers is prepared. This Liesegang-patterned complex is obtained only when the biomineralization is performed under the supersaturated conditions. The Liesegang-patterned complex features a nonlinear elastic response, whereas a complex with a single biomineral shell shows a linear behavior, thus demonstrating that the Liesegang pattern is essential in achieving nonlinear elasticity. The stiff biomineral layers have buffered the concentrated energy on behalf of soft hydrogels, thereby exposing the hydrogel components to reduced stress and, in turn, enabling them to perform the elasticity continuously. Moreover, the nonlinear elastic Liesegang-patterned complex exhibits excellent stress relaxation to the external loading, which is the biomechanical characteristic of cartilage. This stress relaxation allows the bundle of fiber-type Liesegang-patterned complex to endure greater deformation.

Acute Response to Training after Returning from the Off-Season in Elite Rugby League Athletes.

The purposes of this study were to quantify the physiological response to the initial two-week preseason period in elite male rugby league (RL) athletes, and to determine if a repeated bout effect (RBE) occurs. Eighteen RL players were monitored for the initial two-week preseason period. Blood samples were collected on days (D)1, D2, D4, D5, D8, D9, D11 and D12 to measure creatine kinase (CK). Neuromuscular power was assessed on D1, D5, D8 and D12. During field-based sessions, the external training load was quantified using global positioning system technology, whilst the internal load was quantified using the training impulse and the session rating of perceived exertion. Resistance-based gym session volume was quantified by total repetitions x weight lifted. Perceived measures of fatigue and muscle soreness were assessed on all training days. Two-way (day x week) repeated measures analysis of variance and Bonferroni's corrected post-hoc tests identified significant changes. There were no significant changes in CK activity (649.2 ± 255.0 vs. 673.8 ± 299.1 µL; p = 0.63) or internal training load measures from week 1 to week 2. External training load measures including total distance (4138.1 ± 198.4 vs. 4525.0 ± 169.2 m; p < 0.001) and repeated high-intensity efforts (12.6 ± 1.8 vs. 17.5 ± 1.8 au; p < 0.001) significantly increased in week 2 compared to week 1. Internal training loads and CK activity did not change in response to an increase in external training loads during the initial preseason. The current results provide support for a 'real world' perspective of the RBE phenomenon that may be more applicable for team sport practitioners.

The Effect of Different Motocross Circuit Typologies on Internal Load and External Load Responses in Riders

Background: Several physical and physiological changes occur during a motocross race, mainly due to the type of circuits, and therefore the impact of different types of circuits on training load responses continues to need to be fully clarified. Objective: The main aim of the present study was to compare the internal load and external load responses of motocross riders from different classes and on circuits of different types. Method: A quasi experimental design research was used in the study.The sample consisted of 10 motocross riders (28.10 ± 7.53 years; 74.60 ± 9.70 kg; 176.50 ± 7.18 cm; 23.88 ± 2.18 BMI), male., distributed by the Mx Elite and Mx Hobby categories. The pilots were evaluated before and after the race in relation to indicators of external load (accelerations and decelerations, maximum speed and average speed and impacts) and internal load (Heart rate, blood lactate and rating of perceived exertion) on two circuits of different types. Results: There was a trend towards higher internal load responses in the Mx Hobby class compared to the Mx Elite class (p ≤ 0.05), regardless of the circuit. Regarding external load responses, the Mx Hobby class has a tendency towards higher maximum and average speeds, while the Mx Elite class presents the same tendency for accelerations and decelerations. Conclusions: Different circuit types appear to influence pilots’ internal load and external load responses.

Fatigue Life and Crack Initiation of K and N Type Jacket Structure Using 3D Fatigue FE Analysis

Jacket structures are widely used as foundation structures for offshore wind energy. The jacket structure as a truss shape structure is not deformed easily and has the advantage of keeping the structure stable under wind load. The offshore jacket structures are subjected to unstable repetitive loads such as wind, and wave loads in the deep sea. These harsh environments lead to the deterioration of material performance and fatigue failure with cracks in the structure. It is crucial to locate fatigue cracks since they might compromise a structure's overall stability.In this study, fatigue life and crack initiation for different braced jacket structures were investigated. First, 3D non-steady heat conduction analysis and thermal elastic-plastic analysis were performed to reproduce the initial state of the weld joint in the jacket structure. The heat history obtained from the 3D non-steady heat conduction analysis was enforced as an input in thermal elastic-plastic analysis to calculate welding deformation and residual stress. Next, the fatigue FE analysis of the jacket welding structure was carried out using the residual stress and welding deformation as initial values along with the external cyclic loadings. The 3D fatigue FE analysis employed cyclic hysteresis constitutive equations and fatigue damage theory to calculate the fatigue life and crack initiation. The 3D fatigue FE results were compared with the S-N curve by European code 3 and the hot spot stress (HSS) method. The results show that the 3D fatigue FE method effectively calculates the fatigue life and finds crack initiation.

Experimental Research on the Anti-Reflection Crack Performance of Basalt Fiber Modified Rubber Asphalt Stress-Absorbing Layer.

Reflection cracks are one of the most common problems in semi-rigid base pavement. Setting a stress absorption layer can effectively delay the occurrence of reflection cracks, but further improvement is still needed in its interlayer bonding performance and anti-reflection crack performance. Considering the excellent crack resistance of basalt fibers and the good elastic recovery ability of rubber asphalt, it is considered worthwhile to incorporate them into traditional stress absorption layers to improve performance. To simulate the actual pavement layer effect, composite specimens consisting of a cement-stabilized macadam base + basalt fiber rubber asphalt stress-absorbing layer + AC-20 asphalt mixture surface layer were prepared to evaluate their performance through interlayer direct shear tests, interlayer tensile tests, three-point bending tests, and overlay tests (OTs). To determine the optimal fiber blending combination, four fiber lengths (3 cm, 6 cm, 9 cm, 12 cm) and four fiber proportions (120 g/m2, 140 g/m2, 160 g/m2, 180 g/m2) were selected respectively. The specific effects of basalt fibers with different lengths and dosages were analyzed. The results show that compared with the absence of fibers, the improvement of interlayer bonding performance of rubber asphalt with basalt fibers is not significant, and it has certain limitations; however, the improvement of anti-reflective crack performance is significant, with an increase of up to 305.5%. This indicates that the network structure formed by basalt fibers and rubber asphalt stress absorption layer can effectively absorb and disperse external loads, causing an excellent crack resistance effect. Meanwhile, the results indicate that the main factor affecting its interlayer bonding strength and anti-reflective crack performance is the fiber content. Based on the comprehensive analysis of the performance and economy of the stress absorption layer of basalt fiber rubber asphalt, the optimal fiber parameter combination recommended is as fiber length 9 cm and fiber content 160 g/m2. These results can provide a reference for the design and performance evaluation of basalt fiber rubber asphalt stress absorption layer, and have certain application value.