Unloading Process Research Articles

Buckling analysis of thin-walled metal liner of cylindrical composite overwrapped pressure vessels with depressions after autofrettage processing

Abstract The cylindrical filament wound composite overwrapped pressure vessels (COPV) with metal liner has been widely used in spaceflight due to their high strength and low weight. After the autofrettage process, the plastic deformation of the metal liner is constrained by composite winding layers, which introduce depressions to the metal liner that causes local buckling. To predict the local buckling of the inner liner with depressions of the pressure vessel after the autofrettage process, a local buckling analysis method for the metal liner of COPV was developed in this article. The finite element method is used to calculate the overall stress distribution in the pressure vessel before and after the autofrettage process, and the influence of local depressions on the buckling is evaluated. The axial buckling of the pressure vessel under external pressure is analyzed. The control equation of the metal liner with depressions is developed, considering the changes in the pressure and the bending moment of the liner depressions and its vicinity during the loading and unloading process. Taking the cylindrical COPV (38 L) with aluminum alloy liner as an example, the effects of liner thickness, liner radius, the thickness-to-diameter ratio, autofrettage pressure, and the length of straight section on the autofrettage process are discussed. The results show that the thickness of the inner liner has the most significant influence on the buckling of the liner, followed by the length of the straight section and the radius of the inner liner, while the autofrettage pressure has the least influence.

Switch from symplasmic to aspoplasmic phloem unloading in Xanthoceras sorbifolia fruit and sucrose influx XsSWEET10 as a key candidate for Sugar transport

The process of phloem unloading and post-unloading transport of photoassimilate is critical to crop output. Xanthoceras sorbifolia is a woody oil species with great biomass energy prospects in China; however, underproduction of seeds seriously restricts its development. Here, our cytological studies by ultrastructural observation revealed that the sieve element-companion cell complex in carpellary bundle was symplasmically interconnected with surrounding parenchyma cells at the early and late fruit developmental stages, whereas it was symplasmically isolated at middle stage. Consistently, real-time imaging showed that fluorescent tracer 6(5)carboxyfluorescein was confined to phloem strands at middle stage but released into surrounding parenchymal cells at early and late stages. Enzymatic assay showed that sucrose synthase act as the key enzyme catalyzing the progress of Suc degradation post-unloading pathway whether in pericarp or in seed, while vacuolar acid invertase and neutral invertase play compensation roles in sucrose decomposition. Sugar transporter XsSWEET10 had a high expression profile in fruit, especially at middle stage. XsSWEET10 is a plasma membrane-localized protein and heterologous expression in SUC2-deficient yeast strain SUSY7/ura3 confirmed its ability to uptake sucrose. These findings approved the transition from symplasmic to apoplasmic phloem unloading in Xanthoceras sorbifolia fruit and XsSWEET10 as a key candidate in sugar transport.

An Experimental Study Into the Effects of Cumulative Energy Damage on the Mechanical Properties of Coal

The accumulated damage of the surrounding rocks induced by the existing coal mining activities (such as excavation and extraction) is the initial mechanical background of the rock and coal for the further mining operations. An energy-based Cumulative Initial Damage (CID) variable was proposed to account for such existing damage. With the MTS815 electro-hydraulic servo-controlled system, coal samples with different CID value were prepared by cyclic pre-loading and unloading process, and a novel experimental framework was presented to investigate the effect of CID on the further mechanical properties of the CID coal samples. The deformation characteristics, peak strength, peak strain, dilatancy characteristics, brittle-ductile transformation behavior, and microscopic structure of the CID coal samples were investigated in detail. The triaxial compression tests showed that with the increased of CID value, the compaction part of the coal samples was shorter and the strain softening stage became longer. When the CID value was increased from 0 to 0.521, the deviation stress and peak strain of the coal decreased by 31.4 and 37.7%, respectively and the main characteristic of the fracture morphology changed from cleavage steps to dimpling.

Consecutive Heat Treatment of Pre-lathed Pebble Fuel Elements for HTGR

In current manufacture process of pebble fuel elements for HTGR, the green pebbles were first carbonized, then lathed and purified at high temperature. The whole heat treatment process included two cycles of heating and cooling and corresponding two loading and unloading processes, which took approximately 90 hours in total. In order to reduce the time and energy consumed and improve the efficiency during the heat treatment process, a consecutive heat treatment process of pebble fuel elements for HTGR was established. In the newly established consecutive heat treatment process, the pebble fuel elements were carbonized and high temperature purified continuously in a specific furnace. The consecutive heat treatment process took less than 60 hours, which included only one cycle of heating and cooling and corresponding one loading and unloading process. Moreover, in order to recycle the matrix graphite powder after lathing, the green pebbles were machined to a certain size before suffering the heat treatment. However, in order to make the size of pebble fuel elements after the consecutive heat treatment meet the technical requirements, it is necessary to figure out their dimension changes during the heat treatment. As the pebbles were prepared by cold quasi-isostatic molding method, their dimension changes parallel and perpendicular to the molding direction were different. In order to better control the dimension changes of pebbles in the heat treatment process, the effects of physical properties such as apparent density, and particle size distribution of matrix graphite powder on the prepared pebbles were comparatively studied. Finally, the consecutive heat treatment of pre-lathed pebble fuel elements for HTGR was established. The comprehensive properties of pebbles prepared with the newly established consecutive heat treatment process satisfied all the technical requirements.

Unloading-creep test and long-term strength study of different initial conditions of limestone

The high-slope limestone on the right bank of the Wudongde Hydropower Station dam site was considered as a research object to conduct a triaxial unloading-creep test, and then to analyze in detail the limestone’s creep characteristics under different test conditions so as to investigate the limestone’s unloading-creep mechanical properties under different unloading rates and initial stress levels. The results show that the faster the unloading rate, the greater the limestone’s axial and lateral creep rate when under the same stress state. Furthermore, the lateral creep rate is greater than the axial creep rate, indicating an apparent lateral expansion. When the unloading rate is constant, the stress difference has a significant impact on the limestone. The specific manifestation is that the greater the deviator stress, the more pronounced the limestone creep phenomenon, and the rock sample is prone to damage. The steady-state rate intersection method is employed to determine the limestone’s long-term strength, and the λ parameter is introduced to reduce the influence of the axial and lateral strain increments on the long-term strength determination during the unloading process.

Analysis of residual stress and strain in the cylindrical part of the composite pressure vessel with load-sharing metallic liner

As a result of experimental studies of the composite pressure vessel with load-shearing metallic liner during the unloading and cyclic-loading processes, the deformation of structure is nonlinear [1,2]. A method for purpose of describing and analyzing residual stress and strain in the cylindrical part of a composite pressure vessel type 3 after autofrettage is developed, which is based on the linear-elastic model of the fibrous composites and the relations of the theory of plasticity with translational hardening for isotropic material [3]. The theoretical results obtained from constitutive equations are written in matrix form and fit the experimental data well. In comparison, the results based on finite element method and classical Prandtl-Reuss flow rule are proposed. The results show that it is necessary to consider the plastic deformation in metallic liner of composite pressure vessel type 3 when analyzing the stress-strain state.

Study on the mechanical properties of thin-layered marbleized dolomite by in situ tests in the Wudongde hydropower station, China

Transverse isotropy is one of the most distinctive features of layered rock, and many previous researchers have studied the layered rock structure using mechanical laboratory tests; however, very little work has been done based on large-scale mechanical in situ tests. In this paper, we studied typical thin-layered strata that are composed of dolomite marble embedded with phyllite in the Wudongde hydropower station of China. To determine the deformation and failure behavior of the thin-layered rock mass during excavation, a set of large-scale cubic in situ samples were prepared. First of all, polyaxial deformation tests with confining stress were carried out on each sample, then an unloading process perpendicular to the layers was undertaken to investigate strength parameters. Based on the experimental results, the anisotropy of the thin-layered rock has been discussed. Because of the weakness of the layered discontinuities, it is more deformable when loading perpendicular to the layers. It shows that the layered discontinuities would open to induce failure when lateral pressure is released that is perpendicular to the layers during the unloading strength tests. The strength parameters from in situ tests are fitted by the conventional Mohr–Coulomb criterion, and the cohesion is about 10.33 MPa, whereas the internal friction angle is about 27.9°, which is slightly less than the strength deduced from the triaxial test in the laboratory.

Experimental study on the mechanical of deep-buried soft rock under triaxial loading and unloading

This study investigated the changes in the mechanical properties of the soft surrounding rocks in the deep-buried cavern during the excavation unloading process. The argillaceous sandstone in the main diversion tunnel of the Panlong pumped storage power station in Chongqing is the case study. Triaxial loading and unloading tests were carried out to discuss rock samples’ strength, deformation, and failure characteristics under different stress paths. The results showed that the soft rock’s peak strength, strain, deformation modulus, and cohesion in the triaxial loading test are greater than those of the unloading test. During the loading process, the soft rock’s elastic modulus and deformation modulus increase with the confining pressure. However, a more significant increase was observed in the deformation modulus. Under loading conditions, the soft rock suffers from double-shearing shear failure with a failure angle of about 65°. Under unloading conditions, single-shearing shear failure is dominant and accompanied by tensile failure. There are many tension cracks on the surface of the rock sample under low confining pressure, and lateral expansion occurs under high confining pressure.

Deformation and Stability Analysis of Surrounding Rock Mass in Deep Underground Cavern Based on Microseismic monitoring and Numerical Modelling

In the excavation and unloading process of large-scale underground engineering, surrounding rock mass damages such as splitting, rock burst and collapse will often occur, affecting the progress and safety of the project. Correctly identifying and delineating the potential instability and failure area of surrounding rock mass and forecasting in advance can effectively reduce the hidden dangers of engineering safety. In this paper, a comprehensive analysis method combining microseismic (MS) monitoring and numerical simulation is proposed to analyse the effect of structure planes on the stability of surrounding rock mass of underground cavern and predict the deformation. First, numerical simulation is applied to analyse and predict the deformation and stress evolution characteristics of surrounding rock mass. Second, based on the MS monitoring data of the underground powerhouse and field investigation, the temporal and spatial distribution characteristics of MS activity were analysed, and the failure region was revealed and delineated. Finally, the effectiveness of the proposed method is verified by the comparison of MS monitoring results and numerical simulation. The results show that MS events are obviously concentrated in the surrounding rock mass damage area. The failure of spalling and rock-burst in underground powerhouse area is the typical brittle failure under high in-situ stress and low strength-to-stress ratio. In essence, the collapse at the top arch of auxiliary powerhouse is caused by the combined action of high in-situ stress and unfavourable structural plane. The results of MS monitoring and numerical simulation have a good corresponding relationship, and the conclusions provide technical guidance for subsequent construction schemes and support measures.

SIMULATION MODELING AND RESEARCH WORKS OF THE HYDRAULIC DRIVE OF THE STEM SEPARATOR FEED FROM TRENCH STORAGE

The issue of accelerated creation of efficient and energy-saving hydraulic drive of stem forage separator from trench storages by simulation modeling of technical systems. It is noted that the use of simulation allows to avoid significant investments required for the manufacture of a prototype of an agricultural machine, provided a detailed study physical model of the hydraulic drive of the stem feed separator. And also allows you to check the adequacy of the results obtained in process of mathematical modeling, and determine the necessary improvement of the proposed hydraulic drive. A fundamentally new constructive-technological scheme is presented stem feed separator from trench storage that allows to carry out process of unloading of a stalk forage from trench storages according to zootechnical requirements. The stand for simulation modeling of transients in the hydraulic drive of the stem forage separator from trench storages is offered. The design of the experimental stand also allows to investigate the hydraulic drive of the stem feed separator in the dynamic mode, when changing the technological load on the working bodies and changing the parameters of the adaptive fluid flow separator and the system in general. As a result of research and analysis of transients in the hydraulic drive, a fairly close coincidence of the results of mathematical and simulation modeling of the hydraulic drive of the stem feed separator, which allows us to recommend obtaining the calculated dependencies for use in the development hydraulic drives of stem feed separators.

PROMISING PULSE AND VIBRATION SHOCK DEVICE FOR UNLOADING OF TRAILERVEHICLES

Due to the growth of bulk cargo transportation by road, it is necessary to increase the level of mechanization and automation of loading and unloading operations. In recent years, various powerful high-performance unloading machines of original designs (car tippers, vibrating platforms, elevators, etc.) have been created to mechanize unloading processes. This makes it possible to speed up unloading, reduce costs and reduce excessive downtime of dump trucks under unloading. However, the use of such machines is cost-effective at unloading points with a turnover of more than 30 dump trucks per day. Therefore, the problem of creating simple and cheap equipment that ensures efficient unloading of dump trucks with bulk cargo, as well as cleaning of rolling stock from cargo residues, as regardless of the type and composition of cargo, some of them are delayed on the floor, in stamped ribs. pockets of all-metal body walls. The largest amount of cargo remains on the hatch covers, the angle of which is on average 300, while the angle of the actual slope of the cargo reaches 450 and more. Due to this ratio of angles, even dry material cannot fall out completely through the hatch opening, let alone moistened or viscous bulk cargoes. The amount of bulk cargo residues depends on many factors (type of cargo, its humidity, size of pieces, air temperature, distance of transportation, method of unloading) and can be from 2 to 30% of the total weight of the cargo [1]. The use of useful vibrations allows to solve this problem the most expediently. Therefore, the development of a vibratory shock device for unloading vehicles is a promising and urgent task.

Study on the Damage Process and Numerical Simulation of Tunnel Excavation in Water-Rich Soft Rock

The weakening effect is one of the most important causes triggering large deformation and failure of soft-rock engineering; however, few studies paid attention to damage evolution and constitutive relationship of rock in tensile damage in the excavation unloading and water-weakening process, not to mention the coupling process of unloading and water-weakening. In this paper, the mechanism and engineering characteristics of unloading softening and water-softening of water-rich soft rock are analyzed and summarized. Then with the aid of the strain equivalent principle, the damage of surrounding rock caused by unloading softening and water-softening is coupled, and the compression shear damage and the tensile damage of surrounding rock under the unloading process are analyzed. A damage constitutive model of rock subjected to excavation unloading and water-weakening is proposed considering the influence of water immersion time, and the proposed model is applied in a newly established finite element simulation method, which is suitable for excavation in the water-rich soft rock. Based on the mechanical-hydraulic-damage coupled method, the progressive failure process of surrounding rock under the dual softening effects can be reflected by the deteriorated parameters of damage elements. Finally, the field monitoring data of a typical section in the Xujiadi tunnel is used to verify the applicability and accuracy of the proposed dual softening model and simulation method.

Numerical study of deformation behavior of rolled AZ31B plate under cyclic loading in different material orientations based on the EVPSC-TDT model

The EVPSC-TDT model is employed to mimic the stabilized stress-strain hysteresis loops of the rolled AZ31B plate under cyclic loading in different material orientations. The predicted stabilized stress-strain hysteresis loops for different material orientations are generally in good agreement with the corresponding experimental data. The key features associated with twinning and detwinning are interpreted in terms of activities of deformation modes. To appropriately mimic the cyclic plastic response of the rolled AZ31B plate, cyclic loading experiments should also be accounted for in determining the Voce-type hardening law parameters in the current model. The equation proposed in the literature is used in the current model to describe the evolution of residual twinning during cyclic loading, and a threshold equation with a new parameter is proposed to constrain fresh twinning and retwining. The effects of parameters in the two equations on cyclic plastic response are investigated. To approximately describe the apparent easier reverse motion of twin boundaries, the initial CRSS of detwinning is set to be half of that of twinning, and for simplicity the other voce-type hardening law parameters are kept the same for both twinning and detwinning. The effect of initial CRSS of detwinning on plastic response during reverse loading is also investigated. The inelastic behavior is predicted to occur at the very end of the unloading process for the 90° (ND) material orientation, which is ascribed to detwinning. It is assumed that the magnitude of internal tensile stress upon unloading together with that of the activation stress for detwinning determine when or whether detwinning will occur during unloading. The discrepancies between numerical simulations and experiments of the pseudo-elasticity behavior might be because the current mean field model based on self-consistent schemes might not properly describe some microstructure related properties of the AZ31B plate and so underestimates the internal tensile stresses of twinned grains before unloading, which deserves further investigation.

The meso-fracturing mechanism of marble under unloading confining pressure paths and constant axial stress

Failure tests on marble during unloading confining-pressure under constant axial stress and simulations with the particle flow code were performed. The influence mechanism of the unloading rate of the confining pressure, initial unloading stress, and confining pressure on the failure characteristics of, and crack propagation in, marble was studied. By using the trial-and-error method, the conversion relationship between the unloading rates of confining pressures in laboratory tests and numerical simulations was ascertained. Micro-cracks formed in the unloading process of confining pressure are dominated by tension cracks, accompanied by shear cracks. The propagation of shear cracks lags that of tension cracks. As the confining pressure is increased, more cracks occur upon failure of the samples. The proportion of shear cracks increases while that of tension cracks decreases. The failure mode of samples undergoes a transition from shear-dominated failure to conjugated shear failure.

Automated Container Terminal Production Operation and Optimization via an AdaBoost-Based Digital Twin Framework

Digital twin (DT), machine learning, and industrial Internet of things (IIoT) provide great potential for the transformation of the container terminal from automation to intelligence. The production control in the loading and unloading process of automated container terminals (ACTs) involves complex situations, which puts forward high requirements for efficiency and safety. To realize the real-time optimization and security of the ACT, a framework integrating DT with the AdaBoost algorithm is proposed in this study. The framework is mainly composed of physical space, a data service platform, and virtual space, in which the twin space and service system constitute virtual space. In the proposed framework, a multidimensional and multiscale DT model in twin space is first built through a 3D MAX and U3D technology. Second, we introduce a random forest and XGBoost to compare with AdaBoost to select the best algorithm to train and optimize the DT mechanism model. Third, the experimental results show that the AdaBoost algorithm is better than others by comparing the performance indexes of model accuracy, root mean square error, interpretable variance, and fitting error. In addition, we implement empirical experiments by different scales to further evaluate the proposed framework. The experimental results show that the mode of the DT-based terminal operation has higher loading and unloading efficiency than that of the conventional terminal operation, increasing by 23.34% and 31.46% in small-scale and large-scale problems, respectively. Moreover, the visualization service provided by the DT system can monitor the status of automation equipment in real time to ensure the safety of operation.

Investigation of the process of gravitational unloading of energy willow cuttings in conditions of static and dynamic arch formations

Investigation of the process of gravitational unloading of energy willow cuttings in conditions of static and dynamic arch formations

Tingkat Kesesuaian Kinerja dan Harapan Pelanggan pada Terminal Peti Kemas Tanjung Priok

Tanjung Priok Container Terminal is a terminal that serves the loading and unloading process of containers with high service performance standards. Termnal Container customers expect the performance of the services provided by the company to meet their satisfaction or expectations. This study aims to determine the level of conformity between service performance and customer satisfaction or expectations at the container terminal. This study analyzed the data of 67 Container Terminal customers obtained by providing a questionnaire to the customers. The results of the suitability level analysis show that the service performance provided by the container terminal management is satisfied or very satisfied because it has a conformity percentage of 91.93%, besides that the index value of the gap or gap between performance and customer satisfaction / expectations is at -0.28. Where at this value, Container Terminals generally have met customer expectations, but in terms of reliability and assurance, it is still necessary to improve so that it is expected to increase the number and loyalty of Container Terminal customers.

Tunnel failure mechanism during loading and unloading processes through physical model testing and DEM simulation

Geo-materials may present varying mechanical properties under different stress paths, especially for tunnel excavation, which is typically characterized by the decreased radial stress and increased axial stress during the complex loading and unloading process. This study carried out a comparative analysis between the loading and unloading model testing, which was then combined with PFC2D simulation, aiming to reveal the fracture propagation pattern, microscopic stress and force chain distribution of the rock mass surrounding the tunnel. Comparisons of extents and development of tensile strain between loading and unloading testing results were made. The overall stability, the integrity of rock mass, and the failure pattern transition under loading and unloading processes were systematically examined. In addition, for the two unloading cases with different vertical stresses imposed, the failure patterns were both identified as the collapse of the V − shaped extruded sidewall, due to the coupling of the shear failure and the vertical tensile failure in the sidewall wedge.

Numerical investigation on the effects of circuit parameters on the plastic deformation of fastener holes in thin aluminum alloy via electromagnetic expansion process

The size of the plastic deformation zone caused by fastener hole strengthening is a critical indicator of the strengthening performance. In this study, 2A12-T4 aluminum alloy specimens with a hole diameter of 6 mm and thickness of 1.5 mm were strengthened by Lorentz force through the electromagnetic strengthening method. The numerical results show that the Lorentz force can introduce tensile stress in both hoop and radial directions in the specimen during the strengthening process and produce a high compressive hoop residual stress around holes without serious axial deformation compared with the conventional cold hole expansion process. The simulation results are experimentally validated by the grid method in verifying the residual strain, and the fatigue life can be improved by several times after strengthening. Furthermore, under the same discharge energy, there is an optimal capacitance of around 40 μF in this work to achieve the maximum size of the plastic deformation zone. In addition, a larger crowbar resistance can cause a stronger radial inward Lorentz force during the unloading process and result in lower residual stress; therefore, the crowbar resistance should be as small as possible.

Optimization of truck allocation in open pit mines using differential evolution algorithm

The allocation of trucks in open pit mines is a field with great potential for optimizing resources and applying advanced computer modeling techniques, mainly because many companies still choose to use manual allocation, which is premised on the decisions made by the operator, being subject to common failures and not reaching the maximum potential that the equipment can provide. Therefore, this work focuses on optimizing the allocation of trucks in order to increase production, reducing queue time and keeping ore grades within proper limits. The proposed algorithm was based on the differential evolution technique, where two types of mutation operators were used: rand/1/bin and best/1/bin, thus verifying the most suitable to solve the problem. The trucks were allocated in the ore loading and unloading process, aiming to improve the production capacity in a virtual mine. The results brought a convergence to the maximum global production, in addition to which, the allocation of unnecessary transport equipment to the planned routes was avoided. The two mutation operators compared had certain advantages and disadvantages, each better adapting to certain types of situations. The proposed technique can still be extended to other areas, for example, in the transport of grain on the road network or in the implementation of an allocation in freight cars that transport grain.