Unloading Process Research Articles

Dynamic Unloading Instability Mechanism of Underground Cavern Based on Seepage-Damage Coupling

The seepage-damage coupling effect will aggravate the instability of the surrounding rock during the unloading process of underground cavern excavation. Considering this coupling effect and excavation disturbance, the theoretical solution of the stress state of surrounding rock is derived by using the elastic-brittle damage model. The dynamic criterion of the instability and water inrush is presented. Based on the theoretical derivation, the calculation program for the seepage-damage analysis of the surrounding rock under dynamic unloading is programmed, and the seepage flow and the radius of the damage zone of the surrounding rock are calculated. By analysing the variation of radius of the damaged zone with pore water pressure and excavation radius under different calculation conditions, the influence of dynamic unloading disturbance on the damaged zone of the surrounding rock is discussed. The radius of the damaged zone increases with the pore water pressure and excavation radius. Considering the effect of dynamic unloading, the calculation result of the damaged zone radius and seepage discharge of underground cavern are much larger than the theoretical calculation and coupling calculation of seepage-damage without dynamic unloading. Research methods and results can provide guidance and reference for similar engineering research.

Analysing the cause of idle time in loading and unloading operation at Indonesian international port container terminal: Port of Tanjung Priok case study

Prior study shows that major Indonesian ports still need some improvements to achieve a better logistics performance. This study aims to analyze which variables can influence the present of idle time during loading and unloading process at Container Terminal Operation 2 Tanjung Priok Port Jakarta. The Tanjung Priok Port is chosen since the port is designed as the hub port in the national sea transport system of the country where it handles more than 50% Indonesia’s trans-shipment cargo traffic. This study uses service blueprint, multiple regression analysis, and one-way anova method. The findings show that at the existing Tanjung Priok Port Container Terminal has 17 (seventeen) failure spots, which are categorized into 6 (six) variables namely head truck, computer system, weather, stevedoring worker, equipment failure, and operator activities, that cause the idle time at the port service. Nevertheless, based on the multiple regression analysis, only 5 (five) variables have a significant influence on the cause of idle time excluding weather variable. Finally, with one-way anova test it is found that operator activities at the gate-in process is the most significant influence to the idle-time at the port service.

Investigation on Numerical Simulation of supercritical CO2 Power Equipment

The supercritical CO2 (S-CO2) Brayton cycle has recently been gaining a lot of attention for application to solar energy. This paper introduces the MATLAB simulation experiment of supercritical carbon dioxide power generation system, and analyses relevant important operation parameters for supercritical CO2 effect of power system performance. The mathematical model of supercritical CO2 power equipment system is established on modular non-linear method using Matlab and its software package Simulink. Using this dynamic simulation model, the loading and unloading process characteristics of supercritical CO2 power device were analyzed. The results show that: the rotor speed, turbine exhaust, motor power and mechanical power loss is slowly strengthened with the increase of heating output, then increased to the maximum at the same time immediately. Thereafter, the rotor speed, turbine exhaust, motor power and mechanical loss power is slowly decreased and remain stability. The dynamic matching characteristics of compressor, turbine and other equipment in the system are good, and the operation is stable.

O papel do transbordo de carga na relação entre roteirização e adição de valor

The aim of this article was to verify the impact of cargo transshipment on the relationship between routing and value addition of companies specialized in the road transport of long steels for civil construction. Cargo transshipment is a process of loading and unloading, fractional of products, that consumes time, causes disruption to the industrial activities, commercial and mainly, generates costs inadequately. Considering this context, a research of an exploratory nature of the quantitative type was carried out, in which a sample of 74 transport companies, linked to the steel and independent mills, were used. The collected data, treated by modeling in structural equations using the Partial Least Squares – Path Modeling (PLS-PM), revealed that the transshipment, partially, mediates the relationship between routing and value addition. From this result, it was evidenced that transport managers still need to evolve in the processes of cargo transshipments, through managerial training and elaboration of solutions, involving loading and unloading of products, which are vital for the addition of logistic value to the construction industry.

Dynamic fracturing process of fissured rock under abrupt unloading condition: A numerical study

Unloading can cause many geotechnical disasters, e.g., the rock burst. The underlying mechanism of rock failure is the propagation and coalescence of cracks. To get insight into rock unloading failure, the discretized virtual internal bond (DVIB) model in conjunction with element partition method (EPM) is used to simulate the dynamic fracturing process under unloading conditions. At first, the samples with the single flaw are simulated under unloading conditions. It is found that the fracturing pattern exhibits the tensile-shear transition with the initial stress level increasing. When the flaw inclination is closer to 45 degree or the flaw is longer, shear cracks are more likely to occur. Then, the unloading failure process of rock with multiple flaws are simulated. It is found that the inclination of the parallel flaws has remarkable influence on the unloading failure of rock. When the inclination angle is about 45 degree, the rock is easier to fail. For the rock with multiple randomized flaws, the amount of flaws has slight influence on acoustic emission counts. However, the configuration of randomized flaws can significantly affect the fracture process and failure patterns. These findings can improve understanding of rock burst and provide valuable references for the prediction of unloading failure of rock.

Теоретическое обоснование параметров процессов загрузки, хранения и выгрузки комбикормов

Теоретическое обоснование параметров процессов загрузки, хранения и выгрузки комбикормов

A fractal model of contact between rough surfaces for a complete loading–unloading process

The mechanical properties of contact between rough surfaces play an important role in the reliability of the electromechanical system. In order to improve the design accuracy of precision instruments, an elastic-plastic contact model for three-dimensional rough surfaces based on the fractal theory is developed for a complete loading–unloading process based on the Majumdar and Bhushan model. The truncation size distribution functions of asperities for different values of asperity level in the loading process are given. Relationships between true contact area and total contact load in the complete loading–unloading process are obtained according to the truncation size distribution functions of asperities. The results show the range of asperity levels has significant effects on contact mechanical behaviors of fractal rough surfaces. When the first six levels of asperities do not exceed the critical elastic level, the fractal rough surfaces exhibit elastic behavior in a complete contact process, and the load–area relationships in the loading and unloading processes are coincident approximately. When the critical elastic level is less than the minimum level of asperity, the inelastic deformation begins to appear in fractal rough surfaces and the true contact area during the unloading process is always greater than the true area during the loading process for a given total contact load. In comparison with the K-K-E model, the present model is proved to be reasonable.

Study on Transient Unloading Response Characteristics of Brittle Coal Samples Under Different Stress Paths

During the unloading process of engineering excavation, the high energy storage in brittle coal is induced to release, which leads to the failure of surrounding rock. The response characteristics of brittle coal samples under instantaneous unloading are analyzed by numerical simulation of different unloading stress paths in this paper. The results show that under the condition of limited lateral displacement, there is a certain linear relationship between the lateral stress and the vertical stress in a certain range before unloading. With the increase of the level of vertical stress loading, the maximum displacement increases obviously after the instant unloading and the failure is more serious. The critical impact stress value of the brittle coal sample is 17 MPa. Under the condition of equal lateral pressure on both sides, the maximum displacement and the vertical stress increase in the form of quadratic polynomial after instant unloading. The relationship between vertical stress and lateral stress on the critical failure envelope is a fourth-order quartic polynomial. With the increase of lateral stress, the impact liability of brittle coal samples is changed from being controlled by vertical stress to being controlled by lateral stress. Under the condition of unequal lateral pressure on both sides, the burst liability of brittle coal samples after instantaneous unloading is most affected by the vertical stress, followed by the minimum stress, and least affected by the intermediate stress.

Electric Current Approach Studying Both Auroral Substorms and Solar Flares Together

Auroral substorms and solar flares are basically various manifestations of electromagnetic energy dissipation, so that it is useful to consider both phenomena in terms of a chain of processes, consisting of power supply (dynamo), transmission (currents/circuits) and dissipation (auroral substorms, solar flares), the electric current approach. In this short review, we briefly describe both phenomena together on the basis of the chain process. It is shown that the introduction of a dynamo process in this consideration provides a step-by-step way of studying both phenomena. It is shown: (a) Both the solar wind-magnetosphere dynamo and a photospheric dynamo proposed by Lee et al. (1995) have enough power to accumulate enough energy for the explosive features of both phenomena, respectively. (b) For substorms, the power is accumulated in the inner magnetosphere and inflates it, and for flares the power is likely to be accumulated in a loop current along and above two-ribbon flares. (c) For substorms, the energy release (unloading) process deflates the inner magnetosphere, resulting in an earthward electric field, and for flares the disruption of the loop current suggested by Alfven (1950) may be responsible for the energy release. (d) The processes in (c) are responsible for the explosive features of both phenomena.

Real Cyclic Load-Bearing Test of a Ceramic-Reinforced Slab

Ceramic-reinforced slabs were widely used in Spain during the second half of the 20th century, especially for industrial buildings. This solution was popular due to the lack of materials at that time, as it requires almost no concrete and low ratios of reinforcement. In this study, we present and discuss the results of a real load-bearing test of a real ceramic-reinforced slab, which was loaded and reloaded cyclically for a duration of one week in order to describe any damage under a high-demand loading series. Due to the design of these slabs, the structural response is based more on shear than on bending due to the low levels of concrete and the geometry and location of re-bars. The low ratio of concrete makes these slabs ideal for short-span structures, mainly combined with steel or RC frames. The slab which was analyzed in this study covers a span of 4.88 m between two steel I-beams (IPN400), and corresponds to a building from the mid-1960s in the city of Igualada (Barcelona, Spain). A load-bearing test was carried out up to 7.50 kN/m2 by using two-story sacks full of sand. The supporting steel beams were propped up in order to avoid any interference in the results of the test; without the shoring of the steel structure, deflections would come from the combination of the ceramic slab together with the steel profiles. A process of loading and unloading was repeated for a duration of six days in order to describe the cyclic response of the slab under high levels of loading. Finally, vibration analysis of the slab was also done; the higher the load applied, the higher the fundamental frequency of the cross section, which is more comfortable in terms of serviceability.

The Loading–Unloading Model of Contact Between Fractal Rough Surfaces

A loading–unloading elastic–plastic model of contact between three dimensional fractal rough surfaces has been presented in this paper. During loading process, the mechanical properties of a single asperity follow Hertzian theory. During unloading process, the load-area relationships of a single asperity are obtained by EK model. The truncation size distribution functions for different levels of asperities are deduced. And total true contact area and total contact load are obtained during a loading–unloading process. The results show as the rough surface is in elastic deformation, the load-area relationships during loading and unloading process are identical. As the rough surface is in inelastic deformation, the total true contact area during unloading process is greater than that during loading process. An experiment is designed to verify the validity of the present model.

Ultrafast pump-probe ellipsometry and microscopy reveal the surface dynamics of femtosecond laser ablation of aluminium and stainless steel

An ultra-short laser pulse irradiated surface passes through a sequence of physical processes that occur over a wide temporal range, from femtoseconds to microseconds. In this paper for the first time, the complete laser ablation process for industrially relevant metals, aluminium (Al) and stainless steel (AISI 304) is tracked from the initial pulse impact to the final state. Time-resolved surface analytical techniques provide a complementary description of the surface dynamics. The pump-probe ellipsometry reveals changes of the complex refractive index for the first tens of picoseconds and time-resolved microscopy of the irradiated surface gives access to changes of the relative reflectivity from the initial femtosecond pulse impact to the final state at 10 μs. The changes in optical indices are affected by an ultrafast decrease in the density of the surface within the pressure unloading process in the first picoseconds and reveal spallation as the dominant mechanism for laser ablation in Al and stainless steel. The study also implies that the ablation volume is kept at an optimum when the ablation is initiated with ultrafast pulses within the pressure unloading process and is able to evolve over eight orders of magnitude without external perturbations.

The visualization study of dust pollution generated during unloading of the multi-level in high ore pass based on CPFD software and similar experiments

In addition to dust pollution of the environment, during the unloading process of the multi-level high ore pass, it also causes problems such as ore pass wall wearing and noise pollution. The dust pollution is harmful to the health of employees, which captures people’s attention. To grasp the diffusion law of the unloading dust in the ore pass and reduce the amount of dust discharged, the computational particle fluid dynamics (CPFD) software and similarity experiments were used to study the dust generation and diffusion principle under different unloading conditions. According to the results of the numerical simulations and similarity experiments: when the unloading flow rate is 1.0 kg/s, the dust production and wind speed at the ore pass mouth is the largest, and the maximum wind speed is 2.64 times the dust diffusion speed. The amount of dust generated during the falling of the ore accounts for 78% of the total dust production, and the secondary dust production after the ore falls into the mine bunker accounts for 22%. In the first level unloading, the third and fourth level are the main dust-producing points; the overall wind speed at the main dust-producing point first increases and then decreases, with the increase of the unloading flow. The wind speed and dust generated by unloading are inversely proportional to the change of ore particle size and proportional to the change of unloading height. It is possible to control the dust pollution of the ore pass, to a certain extent, by controlling the unloading flow, reducing the unloading height and increasing the ore particle size.

Work Safety Risk Assessment at Container Load Unloading Jobs at PT. Pelabuhan Indonesia II (Persero) Palembang Branch 2017

Loading and unloading of container goods is carried out using cranes and truck containers as a means of transportation besides facilitating activities, which can also lead to the risk of workplace accidents. In 2014 there was a work accident in Kuningan Jakarta, workers were crushed by a container during the loading and unloading process. Container loading and unloading is a routine activity carried out at PT. Pelabuhan Indonesia II (Persero) Palembang Branch. This activity involves tools that can cause accidents such as being hit by a container and hit by a truck head, therefore a risk assessment is carried out on container loading and unloading work. The purpose of this study was to analyze occupational safety risk assessments on container loading and unloading work. This study uses a qualitative research design, using Job Safety Analysis (JSA) for the risk identification process, the US / NZ 4360: 1999 semi-quantitative risk assessment table for risk analysis and semi-quantitative risk level Cross (1988) for risk evaluation. The results of the study indicate that container loading and unloading work consists of the preparation stage, the operation phase of the QCC and the stage of moving containers. The risks identified based on the stage of work are overtaken by containers, falling from heights, collisions between head trucks, falling lifts, hit by a lock lock, getting hit by a truck head, falling into the river, collisions between QCCs and electric shock. The hazards included in the acceptable risk category include being crushed by repair equipment, hands pinched, tripping, slipping lubricants and head banging. The suggestion of this research is that all activities in the field should be carried out in accordance with the applicable regulations and supervision should be carried out more specifically in the use of PPE and conduct periodic health checks on workers. © 2020, Indian Journal of Forensic Medicine and Toxicology. All rights reserved.

The study of the lifting mechanism of the crane arm to a barge

During cargo loading and unloading, the vessels’ lifting gear, even if anchored or moored, is affected by the pitch and roll movements, in addition to the usual stresses, a similar shore crane is subjected to. This paper aims at presenting an analysis of the lifting operations of a boom crane pertaining to a self-propelled barge. The analysis starts with the meshing with triangle elements, the stresses and the embedding using the finite elements method. The crane and the pertaining boom were modeled using CAD design, NX 10.0 from Siemens. The lifting equipment of the ships boom crane may be subject to dangerous defects occurring during the loading and unloading process. Subsequently, the research emphasizes the stresses occurred in the piston rod and in the eye of the lifting equipment, using the finite element method (FEM). After the stress analysis, several fatigue matters are studied: fatigue safety factor, fatigue life, strength safety factor and crack. The damaging or breaking of the eye or of the piston rod from the lifting equipment of the ships boom crane is leading to the blocking of the cylinder with the result of unfavorable events, such as deformation of the boom crane, damaging the loads and even the danger of sinking the barge. The results of this analysis provide ship-owner and maintenance engineers a useful tool to take appropriate decision during inspection of the lifting gear of the ship, prior commencement of the loading and unloading operations.
 

Influences of test method and loading history on permeability of tight reservoir rocks

Steady-state and unsteady-state (downstream pressure build-up) gas permeability tests were conducted on low permeability siltstone at a series of upstream pressures during the loading and unloading processes. The characteristics of downstream pressure build-up curves are analysed in detail, and the permeability is calculated based on the data in the stabilization stage. Analysing approaches with and without consideration of the sample pore volume are used to obtain the unsteady-state permeability for both the real pressure and the pseudo pressure. Findings suggest that the permeability based on the pseudo pressure is generally lower than that based on the real pressure, with their ratio ranging from 0.75 to 0.98. The sample pore volume corrected permeability is 1.42–1.51 times of that without the consideration of sample pore volume. The apparent steady-state gas permeability is higher than the sample pore volume corrected permeability due to slip flow, while its intrinsic permeability is lower as the pore pressure is smaller in the steady-state test. The permeabilities decrease with the confining pressure in the loading path especially at lower confinements, while only part of the reductions is recovered during the unloading process. Increase of pore pressure enhances permeability under low confinement conditions. Water permeability is lower than gas permeability in steady-state test due to the water-rock interaction and the residual gas inside the sample.

Agent-based modelling and simulation for ship unloading processes: determining the number of trucks and container cranes

Loading and unloading activities generate nearly fifty per cent of the total cost in port. The loading and unloading process of the container at the port is considered as a complex process since it involves several interrelated components, such as ships, cranes, and trucks. The uncertainty of these component activities might impact the loading and unloading time and cost. Agent-based modelling and simulation (ABMS) approach is a method for analyzing and modelling a complex system. This study aims to simulate the unloading process to determine a strategy to reduces unloading process time in the largest port in Indonesian using ABMS approach. The results show that the agent-based simulation approach is feasible to be applied in port activities. This approach can assist decision-makers in predicting the number of facilities that must be used to minimize processing time.

Mechanical properties and energy features of high-water material under cyclic loading and unloading

The mechanical properties and energy features of high-water material under cyclic loading and unloading were studied. Results show that: cyclic loading and unloading has a weakening effect on the peak strength and has a strengthening effect on the residual strength of high-water material. During cyclic loading and unloading process, the stress-strain hysteresis effect is obvious. In the cyclic loading and unloading test with gradual increase of stress level, elastic modulus increases first and then decreases, total work, elastic energy, dissipation energy and energy dissipation rate of specimens increase as cycle number increases. In the cyclic loading and unloading test with constant stress level, elastic modulus decreases gradually, total work, elastic energy and dissipated energy of specimens remain stable overall as cycle number increases. Comparing with cyclic loading and unloading test with constant stress level, mass loss rate and energy dissipation rate of the same water to cement ratios specimen are greater in the cyclic loading and unloading test with gradual increase of stress level, it is easier to promote the accumulation and development of internal damage of high-water material. [Received: October 27, 2017; Accepted: July 31, 2018]

Experimental Study on Deformation and Acoustic Emission Characteristics of Arch Roadway under Different Unloading Rates

The essence of roadway excavation is a process of unloading at the periphery, and the influence of unloading paths on surrounding rock damage is directly related to the selection of support design and construction technology. The real stress state of surrounding rock is often affected by different excavation conditions in the actual construction process. Therefore, a testing system of excavation and unloading model was developed to simulate the unloading process of the arch roadway under different excavation conditions. Small hollow cylindrical specimens used in this experiment were made of cement mortar. The load at the inner cavity of specimens was removed under the constant action of external pressure and axial force to simulate the real excavation unloading process. The deformation, the failure modes, and the acoustic emission evolution characteristics at the inner of specimens were obtained under unloading conditions using the strain and acoustic emission monitoring systems. The experimental results indicate that deformation laws of surrounding rock were similar under different unloading rates and initial geostresses, but failure modes and acoustic emission characteristics were quite different. Compared with that of slow unloading, the damage of surrounding rock under rapid unloading mainly accumulated after unloading, and it is easier to induce rockburst after unloading. As initial geostress increased, the occurring time of the main fracture may be delayed relatively, and the phenomenon that the distribution range of peak frequency expanded and the amplitude rose gradually can be regarded as the precursor information of the main fracture occurring. This study can be used to provide experimental support for the failure and supporting design of surrounding rock in deep underground engineering.

Two-stage activated nano-truck enhanced specific aggregation and deep delivery for synergistic tumor ablation

Although nanomedicines have shown high performance in tumor theranostics, their anticancer activity is still limited by the drug delivery capacity, especially lack of targeting capability, poor tumor accumulation, and insufficient tumor deep-penetration. To address this challenge, a high biocompatibility nano-truck (BMP NT) with a two-stage delivery mechanism is designed and developed to achieve the precision therapeutic efficacy of cancer. In view of the enhanced permeability retention (EPR) effect, the surface cleavable layer of BMP NTs can be selectively removed by the overexpressed MMP-2 in a tumor-microenvironment to expose the hydrophobic segments for an induced "braking effect" strategy, resulting in a significant increase in tumor accumulation. Once internalized into cancer cells with the overproduced glutathione (GSH) and H2O2, the BMP NTs undergo the second-stage "unloading process" to release Mn2+ ions and ultrasmall Bi2S3@BSA nanoparticles, and the obtained Mn2+ ions can act as a Fenton-like catalyst for continuously catalyzing the endogenous H2O2 into highly toxic hydroxyl radicals (˙OH) for CDT. The GSH depletion will in turn improve the Mn2+-H2O2 reaction, further enhancing CDT efficiency. Meanwhile, the ultrasmall Bi2S3@BSA endows BMP NTs with excellent photothermal conversion ability to generate local hyperthermia and accelerate the intratumoral Fenton process, thus leading to an effective tumor therapeutic outcome in the synergistic function of CDT/photothermal therapy (PTT). Moreover, the BMP NTs can be used for in situ self-generation magnetic resonance imaging (MRI) and photoacoustic (PA) imaging to guide precision cancer therapy.