Unloading Mode Research Articles

Damage evolution and acoustic emission characteristics of sandstone under different true triaxial cyclic loading and unloading modes

In the process of deep coal mining, the cyclic mining disturbance behavior produces significant cyclic loading and unloading effects, to ensure safe production in the mining area, it is necessary to study the damage characteristics and acoustic emission characteristics of the rock body under different cyclic loading and unloading effects. This study developed a TAWZ-5000/3000 rock true triaxial (disturbance) test system and used it to carry out true triaxial cyclic loading and unloading tests in different modes, with acoustic emission (AE) monitoring of the deformation and damage processes. The test results proved that a large number of cycles weakens the rock’s ability to control deformation, and this weakening ability is also related to the types of cyclic loading and unloading modes. The hysteresis loop characteristics and mechanical parameters show obvious path dependence. Based on the damage equivalence method, it is found that the absolute damage parameter increases with the increase of the number of cycles in the same mode, and the accumulation rate of the cumulative damage parameter is faster; the cumulative damage parameter in the equal amplitude cyclic loading and unloading (EAC) mode is always higher than that in the other two modes. The normalized AE ring count rate in the rock samples under cyclic loading and unloading has a significant relationship with the damage percentage, and the crack extension scale function (b-value) shows the “steady increase – strong fluctuation − significant decline” trend. By analyzing the AE characteristic parameters, namely rise time/amplitude (RA) and ringing count/duration (AF), it is found that the sandstones in EAC, graded cyclic loading and unloading (GC), and stepped cyclic loading and unloading (SC) modes are mainly damaged by tension-shear and shear, respectively. By analyzing the values of the acoustic emission parameters RA-AF, it is found that the sandstone is mainly damaged by tensile shear, tensile tension, and shear under EAC, GC, and SC modes, respectively, corresponding to the rock samples’ damage patterns. The study results have important guiding significance for preventing and controlling disasters in deep mines.

Comprehensive assessment of the effectiveness of the hydrogen production and transportation system

Based on the energy development strategy of Russia until 2035, the article substantiates the prospect for the development of nuclear energy, according to which nuclear plants are planned to be forced to unload in the range of up to 50% of the rated power while participating in the regulation of daily unevenness of the electrical load. In addition, nuclear power plants will be involved in primary frequency regulation, which is also associated with the unloading mode of operation of nuclear power plants. All these circumstances force us to look for ways to provide nuclear power plants with base load. Along with pumped storage power plants, the article considers an alternative option in the form of using a hydrogen complex based on the electrolysis production of hydrogen, which satisfies the concept of its carbon-free production. The article presents the global dynamics of the introduction of electrolyzers, and in addition to the increase in the share of electrolysis hydrogen produced at nuclear power plants. The hydrogen complex in this case is a means of providing the nuclear power plant with a base load, which involves the consumption of unclaimed electricity at cost. This allows hydrogen to be produced at a competitive price compared to individual producers on the market. The resulting hydrogen is in great demand as a useful product in a number of industries. The article provides examples of hydrogen consumption in various areas of consumption depending on purity, taking into account the requirements of GOST. A number of consumer industries use hydrogen of a special degree of purity, i.e., more than 99.999% vol. In this regard, additional hydrogen purification on palladium membranes was taken into account. A comprehensive assessment of the efficiency of the hydrogen production system was carried out, taking into account its additional purification and delivery to the consumer in various ways, mastered and in demand in world practice. A comparison has been made of the methods of delivering hydrogen to the consumer in comparison with the production of hydrogen by electrolysis at the point of consumption. A comparison was made using the criterion of net present value for the option of third-party consumers who do not have their own hydrogen production.

Circulating factors, in both donor and ex-vivo heart perfusion, correlate with heart recovery in a pig model of DCD

BackgroundHeart transplantation with donation after circulatory death and ex-situ heart perfusion offers excellent outcomes and increased transplantation rates. However, improved graft evaluation techniques are required to ensure effective utilization of grafts. Therefore, we investigated circulating factors, both in-situ and ex-situ, as potential biomarkers for cardiac graft quality. MethodsCirculatory death was simulated in anesthetized male pigs with warm ischemic durations of 0, 10, 20, or 30 min. Hearts were explanted and underwent ex-situ perfusion for 3h in an unloaded mode, followed by left ventricular loading for 1h, to evaluate cardiac recovery (outcomes). Multiple donor blood and ex-situ perfusate samples were used for biomarker evaluation with either standard biochemical techniques or nuclear magnetic resonance spectroscopy. ResultsCirculating adrenaline, both in the donor and at 10 min ex-situ heart perfusion, negatively correlated with cardiac recovery (p <0.05 for all). We identified several new potential biomarkers for cardiac graft quality that can be measured rapidly and simultaneously with nuclear magnetic resonance spectroscopy. At multiple timepoints during unloaded ex-situ heart perfusion, perfusate levels of acetone, betaine, creatine, creatinine, fumarate, hypoxanthine, lactate, pyruvate and succinate (p <0.05 for all) significantly correlated with outcomes; the optimal timepoint being 60 min. ConclusionsIn heart donation after circulatory death, circulating adrenaline levels are valuable for cardiac graft evaluation. Nuclear magnetic resonance spectroscopy is of particular interest, as it measures multiple metabolites in a short timeframe. Improved biomarkers may allow more precision and therefore better support clinical decisions about transplantation suitability.

Research on Train Loading and Unloading Mode and Scheduling Optimization in Automated Container Terminals

In some automated container terminals, railway lines have been implemented into the port, saving container transfer time. However, the equipment scheduling level of the railway yard needs to be improved for managers. In the equipment scheduling of loading and unloading containers for railway trains, the operation modes “full unloading and full loading” and “synchronous loading and unloading” are often adopted. Due to the long length of the railway yard and the line of one train, there are two ways to arrange loading and unloading tasks for automated rail-mounted gantry cranes (ARMGs): one is to pre-assign tasks for ARMGs, and the other is to not pre-assign tasks for ARMGs. To investigate the efficacy of these different operation modes and methods of assigning tasks, this study formulated three mixed-integer linear programming (MILP) models with the goal of minimizing the ARMG task completion time. An adaptive large neighborhood search algorithm was used to tackle the scheduling problem. The scheduling effects of different operation modes and methods for assignment tasks were compared in terms of their calculation time and the completion time of ARMG tasks. Notably, the findings reveal that, with an increase in the number of tasks, the “pre-assign” task arrangement had a limited effect on the completion time of the ARMG tasks, made the calculation time shorter, and reduced the complexity of the problem. From the perspective of the completion time of ARMG tasks, the time under the “synchronous loading and unloading” operation mode was less than that of the “full unloading and full loading” operation mode. Therefore, it is recommended that the managers of the railway yard in an automated container terminal adopt the “synchronous loading and unloading” operation mode but determine the task assignment method according to decision time requirements. In addition, when the number of tasks is large, to decrease the time to complete ARMG tasks, the manager can adopt the “non-pre-assign” task distribution method.

Impact of Hemoglobin Level in Ex Vivo Heart Perfusion on Donation After Circulatory Death Hearts: A Juvenile Porcine Experimental Model.

Ex vivo heart perfusion (EVHP) of donation after circulatory death (DCD) hearts has become an effective strategy in adults; however, the small circulating volume in pediatrics poses the challenge of a low-hemoglobin (Hb) perfusate. We aimed to determine the impact of perfusate Hb levels during EVHP on DCD hearts using a juvenile porcine model. Sixteen DCD piglet hearts (11-14 kg) were reperfused for 4 h in unloaded mode followed by working mode. Metabolism, cardiac function, and cell damage were compared between the low-Hb (Hb, 5.0-5.9 g/dL; n = 8) and control (Hb, 7.5-8.4 g/dL; n = 8) groups. Between-group differences were evaluated using 2-sample t -tests or Fisher's Exact tests. During unloaded mode, the low-Hb group showed lower myocardial oxygen consumption ( P < 0.001), a higher arterial lactate level ( P = 0.001), and worse systolic ventricular function ( P < 0.001). During working mode, the low-Hb group had a lower cardiac output (mean, 71% versus 106% of normal cardiac output, P = 0.010) and a higher arterial lactate level ( P = 0.031). Adjusted cardiac troponin-I ( P = 0.112) did not differ between the groups. Morphological myocyte injury in the left ventricle was more severe in the low-Hb group ( P = 0.028). Low-Hb perfusate with inadequate oxygen delivery induced anaerobic metabolism, resulting in suboptimal DCD heart recovery and declined cardiac function. Arranging an optimal perfusate is crucial to organ protection, and further endeavors to refine the priming volume of EVHP or the transfusion strategy are required.

A new constitutive model of shape memory alloy and its seismic mitigation capacity compared with existing models

The existing constitutive models of shape memory alloy (SMA) cannot accurately describe the mechanical behavior in martensitic strengthening segment since their loading and unloading paths in strengthening segment completely overlap. This study proposes a multi-segment linear mathematical model for SMA, which realizes the separation of loading path and unloading path in strengthening segment. A four-story steel frame structure and corresponding braced structures with various SMA constitutive models are designed, and seismic control effects of SMA braces with these models are analyzed and compared through time history analysis. The results show that the sub-cycle unloading mode of SMA constitutive model affects the seismic mitigation capacity of SMA brace in a certain extent. The position of the inflection point of unloading path has very little influence on the structural control ability of SMA braces. The SMA brace using the SMA constitutive model with a single linear sub-cyclic unloading path has the minimal seismic response and the highest seismic reduction ratio. For most evaluation indexes, the seismic mitigation ability calculated by the proposed path separation constitutive model is in the middle of the results calculated by the existing models. SMA models without considering the mechanical behavior of strengthening segment may lead to an erroneous estimation of the energy consumption of SMA brace and the structural damage. The difference of simulation results among various SMA constitutive models is almost independent with ground motion.

A coordinated switch in sucrose and callose metabolism enables enhanced symplastic unloading in potato tubers.

One of the early changes upon tuber induction is the switch from apoplastic to symplastic unloading. Whether and how this change in unloading mode contributes to sink strength has remained unclear. In addition, developing tubers also change from energy to storage-based sucrose metabolism. Here, we investigated the coordination between changes in unloading mode and sucrose metabolism and their relative role in tuber sink strength by looking into callose and sucrose metabolism gene expression combined with a model of apoplastic and symplastic unloading. Gene expression analysis suggests that callose deposition in tubers is decreased by lower callose synthase expression. Furthermore, changes in callose and sucrose metabolism are strongly correlated, indicating a well-coordinated developmental switch. Modelling indicates that symplastic unloading is not the most efficient unloading mode per se. Instead, it is the concurrent metabolic switch that provides the physiological conditions necessary to potentiate symplastic transport and thereby enhance tuber sink strength .

Research on the Multi-Equipment Cooperative Scheduling Method of Sea-Rail Automated Container Terminals under the Loading and Unloading Mode

A sea-rail automated container terminal (SRACT) plays a crucial role in the global logistics network, combining the benefits of sea and railway transportation. However, addressing the challenges of multi-equipment cooperative scheduling in terminal and railway operation areas is essential to ensure efficient container transportation. For the first time, this study addresses the cooperative scheduling challenges among railway gantry cranes, yard cranes, and automated guided vehicles (AGVs) under the loading and unloading mode in SRACTs, ensuring efficient container transportation. This requires the development of a practical scheduling model and algorithm. In this study, a mixed integer programming model was established for the first time to study the multi-equipment cooperative scheduling problem of a SRACT under the loading and unloading mode. A self-adaptive chaotic genetic algorithm was designed to solve the model, and the practicability and effectiveness of the model and algorithm were verified by simulation experiments. Furthermore, this study also proposes an AGV number adjustment strategy to accommodate changes in vessel arrival delays and train container types. Simulation experiments demonstrated that this strategy significantly reduces loading and unloading time, decreases equipment energy consumption, and improves the utilization rate of AGVs. This research provides valuable guidance for ongoing SRACT projects and advances and methodological approaches in multi-equipment co-operative scheduling for such terminals.

Twenty-Four Hour Normothermic Ex Vivo Heart Perfusion With Hemofiltration In an Adult Porcine Model

Historically, cardiac transplantation relied on cold static storage at 5 °C for ex vivo myocardial preservation. Currently, machine perfusion is the standard of care at many transplant centers. These storage methods are limited to 12 hours. We sought to evaluate the efficacy of hemofiltration and filtrate replacement in adult porcine hearts using normothermic heart perfusion (NEVHP) for 24 hours. We performed 24-hour NEVHP on 5 consecutive hearts. After anesthetic induction, sternotomy, cardioplegia administration, explantation, and back-table instrumentation, NEVHP was initiated in beating, unloaded mode. After 1 hour, plasma exchange was performed, and hemofiltration was initiated. Heart function parameters and arterial blood gasses were obtained hourly. All hearts (n=5) were viable at the 24-hour mark. The average left ventricular systolic pressure at the beginning of the prep was 36.6 ± 7.9 mm Hg compared with 27 ± 5.5 mm Hg at the end. Coronary resistance at the beginning of prep was 0.79 ± 0.10 mm Hg/L/min and 0.93 ± 0.28 mm Hg/L/min at the end. Glucose levels averaged 223 ± 13.9 mg/dL, and the lactate average at the termination of prep was 2.6 ± 0.3 mmol/L. We successfully perfused adult porcine hearts at normothermic temperatures for 24 hours with results comparable to our pediatric porcine heart model. The next step in our research is NEVHP evaluation in a working mode using left atrial perfusion.

Investigation of the influence of model control parameters on fracture characteristics of GPU parallel FDEM

Surrounding rock mass fracture characteristics play a significant role in the understanding of the CO2 geological storage and utilization (CGSU) engineering practices in abandoned mines. The combined finite discrete element method (FDEM) shows advantages in simulating fracture and fragmentation of rock-like materials, however, many computational parameters and a lack of basis for accurate values affect the simulation results. For systematic explorations of the influence of the effect of model parameters with different time steps, this study conducted different loading rate specimen tests and unloading rate tests both in laboratory-scale tests and field-scale based on the CUDA-based GPU parallel FDEM program. In laboratory-scale uniaxial compressive strength (UCS) tests, a smaller loading rate ensures a quasi-static loading process and should be below 0.1 ms−1 for simulation. Then, continuous optimization and improvement of the GPU parallel FDEM in tunnel excavation were proposed, and the model parameters reflect the continuous improvement of the simulation results. In the process, the tunnel excavation simulation method with the reduction rate of the opening zone’s Young's modulus in the excavation was performed to investigate the unloading mode and rate by continuing to optimize the GPU parallel FDEM program and model parameters. Besides, the main factor in fracture mode and failure mechanism of the surrounding rock mass also was calibrated. The results indicate that the system kinetic energy of the model is maintained at a small level with the reasonable unloading mode and critical threshold set at a small value, the damping parameters, dissipation mechanism, and excavation fractures are clearer and reasonable, and the computational cost is significantly reduced with GPU parallel FDEM.

Simultaneous unloading of shear and normal stresses induces activation of naturally rough-walled sandstone fractures

The unloading mode of shear and normal stresses and the number of shear cycles have important influences on the unloading-induced slip of rock fractures. Clarifying the slip mechanism of rock fractures disturbed by deep excavation is critically important for the exploitation of underground energy and the mitigation of seismicity. In this research, the simultaneous unloading tests of normal stress and shear stress on the rough-walled sandstone fractures are carried out cyclically. Experimental results indicate that the ratio of unloading rate of shear stress to that of normal stress (i.e., vs/vn) mainly controls the slip modes of the fracture. When vs/vn is less than 0.66, the sandstone fracture will be activated to slip, which involves a quasi-static slip stage and a dynamic slip stage. And, a lower value of vs/vn tend to produce a larger duration of the quasi-static slip stage and a lower peak slip velocity at the initiation point, vice versa. The quasi-static slip stage is essentially dominated by the asperity damage process and the cycle number mainly affects the initial stress state of the fracture. Our observations suggest that adjusting the unloading rate ratio during the excavation process may reduce the possibility of fracture slip-induced dynamic hazards.

ANALYSIS OF TEST RESULTS OF THE ENBANKMENT REINFORCEMENT WITH REINFORCED SOIL-CEMENT PILES

Purpose. The purpose of the work is to analyze the results of the test of the embankment reinforcement with reinforced soil-cement piles. Methodology. An analysis of the ground reinforcement situation was carried out with the definition of modern trends in the use of geosynthetic materials and soil-cement piles. An algorithm for strengthening the embankment with reinforced soil-cement piles using a special square bit has been developed and implemented in practice. The load-bearing capacity of reinforced soil-cement piles was determined by reasoned selection of the structure, soil base, material, depth of pile laying in accordance with engineering and geological conditions, the structural scheme of the building and the method of their arrangement. Findings. 6 piles with a length of 21 m to 23 m were tested. During the manufacture of piles Nos. 1, 4 and 6, the length of which was 22...23 m, during drilling it was found that massive monolithic granite lies at their base (the granite was sunk by 0.5 m), the presence of cracks in which was not fixed. Piles Nos. 2, 3, 5 had cracked granites as their base, they were also deepened by 0.5 m. For these reinforced soil-cement piles, the values of the vertical displacements of the pile during its loading and unloading in stages were obtained. The calculated pressing load on the tested pile ranges from 268.3 t·s to 275.0 t·s. Originality. It consists in obtaining dependences of settlements of reinforced soil-cement piles, created on the basis of jet mixing technology, during their testing in loading and unloading modes. Practical value. It was determined that by changing the stiffness of the embankment, since soil-cement reinforced elements can be manufactured with a deformation modulus of 300...600 MPa, the problem of its strengthening is solved. Practically, it is possible to reduce the difference in the stiffness of the artificial structure and the structure of the track superstructure, which will allow eliminating ballast recesses.

Simulation optimization for parcel hub scheduling problem in closed-loop sortation system with shortcuts

With the growth of e-commerce, the quantity of delivery orders and parcels is steadily increasing. Reliable and fast parcel delivery services are of utmost importance to customers. To achieve this target, the central parcel consolidation terminals (CPCT) known as parcel sorting hubs are dedicated to improving the operational efficiency especially in the optimal scheduling of inbound trucks. This study aims to determine the optimal schedule and assignment of inbound trucks to the inbound docks, known as the parcel hub scheduling problem with shortcuts (PHSPwS), for minimizing the expected makespan and expected waiting time of inbound trucks in the closed-loop automated sorting conveyor (ASC) system with shortcuts of the parcel sorting hubs. We first construct a mathematical formulation to present the PHSPwS problem based on the traffic control model. However, due to the congestion behavior on the conveyors and stochastic and dynamic nature of the ASC system, the expected objective functions are not analytically available from the mathematical model. Then, a simulation optimization (SO) approach combined with an adaptive genetic-based discrete particle swarm optimization (AGDPSO) algorithm is proposed to tackle the PHSPwS problem in a stochastic and dynamic ASC environment. The closed-loop ASC simulation model is first established to describe the detail operation of the closed-loop ASC sortation system with shortcut. Based on performance evaluation of this simulation model, a novelty algorithm AGDPSO, which hybridized genetic algorithm and particle swarm optimization algorithm with self-tuning parameters is developed to search and find the optimal inbound truck schedule in the large-scale solution space. In particular, the time-varying acceleration coefficients embedded in the AGDPSO are adopted to amplify the effectiveness of the global and local best solutions to obtain a better balance between exploration and exploitation of the searching space. The experimental results reveal that AGDPSO outperforms other algorithms and provides a better and more stable solution. Moreover, the impact of the strategic and operational factors of the closed-loop ASC system for the expected makespan and truck queueing time are also investigated, while the automatic truck unloading mode is confirmed to significantly improve the system efficiency.

A Strategy of Multi-edge Collaborated Task Offloading Based on Edge Servers Placement in Metropolitan Area Networks

At present, multi-access edge computing is applied to “cloud-edge-terminal” collaborative computing, in which the task of computing offloading is used to unload the computing tasks of “terminal” to “edge”, i. e. edge servers, but the placement of edge servers is often not considered, resulting in low efficiency of computing offloading. Therefore, this paper proposes a multi-edge collaborative task unloading strategy for the effective placement of edge servers in 5G metropolitan area networks (MAN). First, the strategy weights the average user delay, the average edge server load and the average edge server resource utilization, and improves the firefly algorithm (FA) to optimize the number and effective location of edge servers. Secondly, a multi-edge collaborative task unloading architecture is presented. The computing tasks in this architecture can be executed locally, on a local server, on a remote server or in the “cloud”. The delay and energy consumption of the four unloading modes are modeled respectively. Thirdly, a new variable, i. e. the maximum cooperation cost that the “terminal” can bear, is introduced to attract more remote edge servers to cooperate to complete the calculation of the “terminal” task. Furthermore, the immune particle swarm optimization (IPSO) algorithm was designed to solve the problems of the traditional PSO algorithm. The simulation results show that the improved firefly algorithm can find the optimal coordinates of the edge server, and then carry out the task unloading of the multi-edge server. Compared with the local offload strategy, immune algorithm (IA) and PSO, the total cost of the proposed IPSO algorithm is reduced by 66.7%, 54% and 45.5%, respectively. Therefore, the algorithm in this paper can improve the execution efficiency of computing tasks and effectively reduce the total cost of the whole system.

Experimental assessment of the temperature state of tractor diesel pistons

INTRODUCTION: The paper presents the operating conditions of tractor diesel engines that cause the appearance of thermal fatigue cracks on the edges of the piston combustion chamber. The presence of sharp edges of the combustion chamber in the pistons, which are stress concentrators, leads to an increase in the probability of their destruction and thereby limits the engine life of the diesel engine. The main reasons for the formation of cracks in the zone of the edge of the combustion chamber are indicated.&#x0D; AIMS: The aim of this study is the assessment of the temperature state of pistons of the D-240 and the D-245 tractor diesel engines, produced by Minsk Motor Plant (MMP).&#x0D; METHODS: Temperature gauging was carried out according to the method in order to identify the nature of changing of piston heads temperatures under stationary and nonstationary operation modes of diesel engines. Transfering of thermal electromotive force from thermocouples to measuring devices was carried out by means of an intermittent current collector. Imitaion of nonstationary operation modes was carried out by means of changing the cyclic feed of a high pressure fuel pump, using a reversible electric motor.&#x0D; RESULTS: The data of the temperature state of pistons under various stationary and nonstationary operation modes of engines is provided. It is noted that the temperature state of the D-245 diesel pistons has a higher level of heat stress compared to the D-240 diesel pistons. The maximum amplitude of low-frequency temperature fluctuations at the edge of the combustion chamber and their radial differences along the piston bottom are determined, depending on the parameters of thermal loading cycles. It is noted that the most dangerous modes of diesel operation, in terms of the destruction of the edge of the combustion chamber, are sharply changing modes (eg.: theloading unloading mode).&#x0D; CONCLUSIONS: It is proposed to increase the fuel injection advance angle in the thermal loading cycle in order to conduct accelerated comparative tests of piston variants for thermal resistance. The developed thermal loading cycle, in which the total duration of the load increase is 180 s and the total duration of the load decrease is 90 s, can be recommended for accelerated motor tests of pistons for thermal cycling resistance. The obtained temperature measurement data is recommended to clarify boundary conditions of the first kind when calculating the piston using the FEM method.

Multi-equipment coordinated scheduling strategy of U-shaped automated container terminal considering energy consumption

In order to meet the green development trend of today's ports and accelerate the formation of green and low-carbon transportation modes. In this paper, the coordinated scheduling efficiency of quay crane, automatic double cantilever, intelligent guided transport vehicle and external truck in the multi-point loading and unloading mode of U-shaped automated container terminal is optimized to reduce the overall operation energy consumption of the terminal. A decision tree learning based on heuristic Monte Carlo tree search algorithm with the objectives of minimizing road conflicts and minimizing the total task energy consumption is proposed to solve the mixed integer planning model. The proposed regional coordinated scheduling strategy and flexible neighborhood search strategy effectively reduces operational conflicts and improves the optimal container scheduling sequence in the yard. The proposed predictive-based pruning strategy and other pruning strategy effectively improves the operational efficiency. This paper conducted experiments comparing the algorithms on a large scale and a small scale scheduling problems, and the total energy consumption value gap rate was reduced by 0.03%-14.15%. The results show that the proposed algorithm and model can not only effectively handle the conflicts between transportation equipment, but also further improve the transportation efficiency and reduce energy consumption.

Experimental Study on Shear Behavior of Interface between Different Soil Materials and Concrete under Variable Normal Stress

At present, the interface shear test is mainly used to evaluate the anti-sliding performance of the new foundation base. However, the traditional interface shear test has certain limitations in simulating the load change during the construction process and cannot accurately simulate the interface shear characteristics between the structure and the soil under the continuous change of the normal stress. Based on the self-developed large-scale interface shear equipment, this paper carried out the interface shear test and mechanism research of cement soil concrete, sand concrete, clay concrete and other materials in different curing cycles under the loading and unloading modes of variable normal stress repeated steps and continuous loading modes of variable normal stress steps. In addition, this paper deduced the formula of the minimum interface friction coefficient based on Mohr–Coulomb criterion. The experimental results show that the curing effect of cement soil can significantly improve the shear mechanical properties of the interface, and the friction coefficient of the cement soil concrete interface will also increase step by step with the increase of the curing time of the cement soil. The sliding shear surface can be remolded under the preloading of normal pressure, so that the interface shear characteristics of each shear material under repeated loading and unloading can be approximately equal to the interface shear characteristics of multiple equivalent materials under separate loading. In the case of a continuous change of normal stress, the rapid increase of normal stress will lead to accelerated entry into the limit shear state, resulting in plastic failure of the shear plane as a whole. In the engineering with a continuous change of stress, the interface shear friction coefficient of the material with high cohesion fluctuates greatly. The minimum interface friction coefficient formula and test proposed in this paper can be used to evaluate the interface friction coefficient range, and the sand concrete interface shear performance under the continuous normal stress loading mode showed good consistency. The self-developed large-scale interface shearing equipment and its test data provide theoretical basis and solutions for the improvement of traditional interface shearing equipment.

Mechanical properties of C60 at finite temperature from first-principles calculations

C60 has been the focus of many studies since its discovery, but the mechanical properties of this unique molecule remain poorly known. To remedy that, we performed density functional theory molecular dynamics calculations of the compression of C60 at finite temperature, within a large strain range. The possible recovery of the molecule after unloading was also investigated with first principles accuracy, for two different modes. We found that the behavior of C60 follows three regimes depending on the compression strain. Up to 0.48 ± 0.02, the deformation is elastic with a small but distinct influence of the compression orientation. A relation between the electronic gap and the orientation is also revealed. The second regime starts for larger strains up to 0.75 ± 0.02, after a 30–32 nN force plateau. It is characterized by stochastic carbon bond breakings. Although bonds rupture is generally the fingerprint of plastic deformation in materials, we found that the C60 structure can be dynamically recovered in a significant fraction of cases, following a fast unloading. This mode also yields defected structures with low energies compared to a slow unloading mode. Finally, the third regime corresponds to irreversible deformation of the molecule, for strains larger than 0.75 ± 0.02.

Integrated scheduling optimization of U-shaped automated container terminal under loading and unloading mode

This paper proposes an integrated scheduling optimization model based on mixed integer programming to analytically characterize the U-shaped automated container terminal layout and handling technology. We focus on dual trolley quay cranes, conflict-free automated guided vehicles (AGVs) and dual cantilever rail cranes under loading and unloading mode, which have rarely been simultaneously studied in the literature, as most prior research has addressed traditional container terminals. We eliminate the waiting time during the interaction between AGV and dual cantilever rail crane to realize spatiotemporal synchronization and minimize the completion time of all tasks. We employ a reinforcement learning based hyper-heuristic genetic algorithm to solve the model, specifically, better solution results for reward and punishment mechanism incorporating reinforcement learning, higher versatility independent of specific problems, stronger scalability of low-level algorithms. We investigate which algorithm is better by comparing the proposed algorithm with bi-level genetic algorithm, adaptive genetic algorithm, hybrid genetic algorithm and cuckoo search algorithm. We conduct small-sized and large-sized experiments to validate the performance of the proposed model and algorithm. The results show that the proposed model and algorithm can not only avoid the conflicts among AGVs but also significantly improve handling efficiency.

Effect of transport vehicles on the grain harvester idle time during harvesting

Abstract. The article studied the effect of transport vehicles on the grain harvester idle time during wheat, barley and rapeseed harvesting in 6 agricultural farms. In each of the farms one grain harvester and the established harvesting organization were studied without changing the unloading mode and the specific activities performed by the harvester operators and transportation vehicles. By multifactor regression analysis the effect of time for moving the transport vehicle on the grain harvester idle time was established. In addition, the value of the determination coefficient R2=0.54 reveals that 54% of the harvester idle time for unloading the grain hopper (Т1) change is due to the change of significant times and 46% to the effect of unmanageable factors. It has been established that the change in the time from opening the unloading auger to its activation depends on the position of transport vehicles on the field (t1) and the time for their movement to the harvester auger (t2). The results obtained can be used to minimize costs in the technological process of crop harvesting.