Unloading Process Research Articles

Unloading responses of pre-flawed rock specimens under different unloading rates

Abstract Based on the stress redistribution analysis of rock mass during the deep underground excavation, the unloading process of pre-flawed rock material was simulated by distinct element method (DEM). The effects of unloading rate and flaw inclination angle on unloading strengths and cracking properties of pre-flawed rock specimens are numerically revealed. The results indicate that the unloading failure strength of pre-flawed specimen exhibits a power-function increase trend with the increase of unloading period. Moreover, combined with the stress state analysis on the flaws, it is found that the unloading failure strength increases with the increase of flaw inclination angle. The cracking distribution of pre-flawed specimens under the unloading condition closely depends on the flaw inclination angle, and three typical types of flaw coalescence are observed. Furthermore, at a faster unloading rate, the pre-flawed specimen experiences a sharper and quicker unloading failure process, resulting in more splitting cracks in the specimens.

Research on Rheological Properties of Rockfill Material under Stress Unloading

A number of super high earth-rock dams will be built in China in the near future. Deformation control is the key issue in the safety construction and operation of these major water conservancy projects.In this paper, the effect of stress loading process on the subsequent rheological development is studied, and a new accumulation rule of rockfill rheology is proposed, that is, the current rheological variable of rockfill unit at a certain time is equal to the hardening rheological variable that can cause additional hardening of rockfill at that time.Then, the influence of stress unloading process on the subsequent rheological development law is further studied. It is found that after stress unloading, there are positive rheological zone, no rheological zone and reverse rheological zone in the rheological behavior of rockfill material. The rheological accumulation rule proposed in this paper is also applicable to the case of stress unloading.

Numerical analysis of hard rock tunnel excavated by double shield TBM based on CWFS model

In order to study the mechanical response of a hard rock tunnel excavated by double shield tunnel boring machine (DS-TBM), a numerical method was introduced to simulate the TBM excavating process. The failure modes of surrounding rock mass described based on the cohesion weakening and frictional strengthening (CWFS) Mohr-Coulomb strain-softening criterion. The characteristics of stress field and plastic zone on the cross and longitudinal section of the tunnel were analyzed in detail, and the results were compared with those in the intrinsic condition (when TBM model is not activated). The simulation results indicate that the stress paths at the vault are relatively simple, and the stress concentration caused by excavation unloading is obviously reduced by lining and backfill grouting, while the sidewall is less disturbed by the excavation of TBM. The invert experiences three unloading processes, due to excavation, the contact between the rear shield and the bottom of surrounding rock, as well as backfill grouting at gap between the lining and the rock mass. The vault has a larger plastic zone than the invert, attributing to the geometrical difference between the cutter-head and the front shield, as well as the conicity of the front and rear shields. The area of plastic zones gradually increases along the tunnel route, but it becomes stable after the rear shield.

Models of simulation in the making of decisions in the mining operation

In open pit mining, the loading, unloading and hauling system can represent a high percentage of the operating cost. The objective of this document is to provide an overview of the different approaches in the application of simulation models as an alternative applied to open pit mining operations that can help in decision making to optimize resources. It talks about the different types of simulation models that can be applied in mining operations such as stochastic, deterministic and discrete events. The underlying idea of this text is to highlight that with the increase in competitiveness, mining companies are in need of using simulation techniques to reduce costs, time and risks when making decisions, since simulation allows the creation of scenarios that approximate reality. In the end, the document concludes that simulation models are a tool to help in decision-making, for the optimization of resources, increased improvement and efficiency of the processes of loading, transport and unloading in open pit mines.

Proposing an Algorithm to Solve the Forward and Reverse Logistics Distribution Problem with One Door Container

Forward and reverse logistics are two types of distribution methods that shall be synergized in practices. Two problems in synergizing the two distributions type are (1) how to route vehicles and (2) how to pack the goods inside the vehicle. A truck with only one door for loading and unloading process could create numerous problems of item packing activities. An item picked up from a customer could occasionally block other goods which need to be delivered; hence, the courier shall unload other items before the loading process. This condition will increase the probability of item damage, longer on-loading/off-loading (lo/lo) time, and higher lo/lo cost because of the rapid item movement. Therefore, this article aims to propose an algorithm to solve the problem by creating an algorithm hybrid of routing and packing to find the solution for routing and packing problem, sequentially, with a metaheuristic approach. The proposed method calculates the cost from routing procedure and sum of item movement in every loading and unloading process. Based on the trial on 25 cases, this algorithm generates 59.64% of the containers have zero goods repacking. Several potential future research avenues are also proposed in this article.

Diseminasi Perangkat Keselamatan Pelayaran Moda Waterway Sungai Tallo Makassar bagi Masyarakat Pulau Lakkang

Mode of transport waterway river tallo Makasar has been operated since long transports passengers, luggage and a motor vehicle, and the only access mode for the island lakkang people through tallo to kera-kera, the eastern and the southern of Makassar city. In the operation of waterway mode, the owner ignored the shipping safety of waterway. It was proven that there is not any other safety devices above the waterway mode. Shipping safety device is an absolutely thing must be required for sea transportation, rivers and lakes. Hence it is necessary to disseminate the importance of shipping safety device for the owner of the river tallo makassar to increase the quality of service of shipping safety for passengers mode independently in accordance with national and international regulations. The safety of the device is based on land transport minister regulation no. PM 25 years 2015, transportion safety standards on the river lakes and crossing. Disseminate gives users of security and safety and public service quality shipping safety for passengers in the river tallo makassar when sailing and the process of loading and unloading of passengers and a motor vehicle.

Improving Efficiency of Mineral Terminal Performance using Lean Railroading

The purpose of this study is to investigate and identify the waste from the unloading station of mineral cars using the lean thinking approach. In this paper, one of the largest steel producers is investigated as a case study. The time information was collected from the database system of the factory and railway company from April to July 2017. The wastes were identified by using the value stream map, and to reduce the waste, ten solutions have been proposed based on the changes in: (a) operation management; (b) purchase of new equipment; and (c) infrastructure development. Implementation of solutions using the Planimate simulator software shows that the best strategy consists of a combination of three operational management solutions without having to purchase new equipment and without any infrastructure development, which can improve station performance by up to 52% with regards to the total time for the unloading process. In addition, the valuable time of the whole process has been increased from 9 to 19%. This improvement will result in an increase of 21% in the annual turnover of cars to the station destination. As a result, each car annually carries on average 450 tons more freight, in which case the railway’s revenues from carrying iron ore would be increased by 24% for this destination.

Permeability evolution under true triaxial stress conditions of Longmaxi shale in the Sichuan Basin, Southwest China

Shale permeability is considered the critical parameter for commercial gas production. In this work, we investigated the permeability evolution under true triaxial stress conditions of Longmaxi shale. The results showed that shale permeability decreased significantly with increasing intermediate principal stress σ2 and increased gradually with decreasing σ2. And permeability was larger when σ2 was perpendicular to the bedding than that when σ2 was parallel to the bedding. A theoretical model was derived to describe the permeability of shale with respect to effective stress and the results agreed well with the experiment. The matching results showed that the fracture was compressed more easily when σ2 was perpendicular to the bedding and the shale sample was generally compressed in the loading process while swelled during the unloading process. Strong hysteresis was observed for both permeability and strain results. It also warrants testing other gas shales to specifically determine this effect.

Experimental Study on Mechanics and Permeability Properties of Water-Bearing Raw Coal Samples Under In-Situ Stress

In this paper, we investigated the mechanical and permeability characteristics of water-bearing raw coal samples under in-situ stress, and came to some conclusions, as follows: the peak strength and peak axial strain of samples gradually decrease with the increase of water content. Under the same stress condition, the higher the water content is, the lower the axial strain and radial strain will be. The peak strength and peak strain of the sample both decrease with the water content as a quadratic function. During the post-peak loading and unloading process, with the increase of the number of cycles of loading and unloading, the radial strain decrement and increment of the raw coal sample gradually decrease after loading and unloading confining pressure. The permeability of samples gradually decreases with the loading confining pressure, and the permeability of the sample gradually increases with the unloading confining pressure. The permeability of coal samples increases volatility with the increase of axial strain, and the fitted sample permeability and effective stress are subject to the ExpDec1 function distribution.

Phase change materials embedded in porous matrices for hybrid thermal energy storages: Experimental results and modeling

It is well-known that the use of the latent heat absorption phenomenon associated with the melting process of a suitable Phase Change Material (PCM) can be considered an effective way to improve energy storage capabilities in many applications. This work experimentally investigates the effects of six open-cell aluminum foams and of a 3-D periodic aluminum structure during the phase change process of a paraffin wax with melting temperatures of 40 °C in a hybrid water thermal storage unit. The storage is set at two different temperatures (50 °C and 60 °C) during the melting process, and at around 23 °C during the solidification one. Moreover, in order to simulate the possible advantages of hybrid water thermal energy storages, a Trnsys Type developed to simulate the loading (melting) and unloading (solidification) processes of paraffin waxes for latent thermal energy storages is presented and validated against the data collected during experimental tests.

On the Influence of Loading Order in Nanostructural Fatigue Crack Propagation in BCC Iron—A Molecular Dynamics Study

Most investigations dealing with fatigue crack propagation on the nanoscale, limit their studies on a loading scenario of constant stress or strain amplitudes. Since such a load scenario is rather rare, this paper aims to examine the influence of the load sequence on the crack growth using bcc iron. For this purpose, a specimen containing a central crack was loaded repeatedly by varying the load amplitude. All computations were carried out using molecular dynamics methods (MD), and the material behaviour was represented by utilising an embedded atom method (EAM) potential. Significant deviation in the crack growth behaviour was observed when loading the specimens with variable amplitudes rather than with constant amplitudes. Cracks did not only extend during the loading phase but also in the initial phase of the unloading process where cracks expanded from voids that had been formed in the last phase of loading. These voids coalesced with the main crack as the specimen was subjected to further loading.

Study of high-pressure air curtain and combined dedusting of gas water spray in multilevel ore pass based on CFD-DEM

In order to solve the problem of dust pollution caused by ore unloading in ore pass, this paper, taking Li Lou Mining as a case study, conducted the wind speed variation law in the fluid domain and the impact of the collision between the ore in the unloading process on the fluid to determine the key dust control point based on the CFD-DEM coupling software. By Fluent software, the air curtain dust-proof efficiency under the action of unloading airflow is analyzed, and the relationship between the dust-control wind speed and the impinging airflow is known. And an experimental model of gas water spray is established to analyze the effect of spray dust removal. By analyzing the impact airflow and dust migration caused by ore unloading and the effect of air curtain dust control through numerical simulation, it can be seen that when the ore discharging quantity Mo = 4000 kg, the dust production is mainly concentrated in the fourth middle section. By high-pressure air shield assisting dust removal, dust diffusion can be better controlled when the ratio of impact wind speed of ore pass wellhead (denoted as λ) to high-pressure air curtain wind speed (denoted as ζ) is at least 1:8. When the dust removal effect is optimal, the ratio δ of the water supply amount ql and the gas supply amount Qg is determined by the gas water spray dust control experimental platform.

Large superelastic recovery and elastocaloric effect in as-deposited additive manufactured Ni50.8Ti49.2 alloy

A Ni50.8Ti49.2 alloy is fabricated by the Laser Solid Forming (LSF) technique by using prealloyed powder in this work. Characterization of the microstructure, phase transformation, and shape recovery of the as-deposited alloy are explored. Columnar grains with ⟨110⟩ preferred orientation are well aligned with the building direction, and the martensitic transformation (MT) behavior shows spatial distribution characteristics. With the increase in the deposited height, MT varies from the two-stage B2 →R→ B19′ transformation to the one-stage B2 → B19′ transformation. Shape recovery properties are studied by compression tests. The as-deposited material without any further heat treatment shows a remarkably large superelastic recovery strain of 9.2% at room temperature, which is the largest value in the additive manufactured NiTi alloy. A negative adiabatic temperature change of –18.6 K induced by the elastocaloric effect during the unloading process is obtained. The shape memory effect (SME) of the as-deposited LSF Ni50.8Ti49.2 alloy is not only dependent on the detwinning of martensite but also associated with the partial superelasticity of the parent phase in the present work, demonstrating a unique two-stage yielding behavior. A residual strain up to 6% is recovered while heating, indicating an excellent SME.

NUMERICAL STUDY OF THE GEOMETRIC INFLUENCE OF A FIN IN A CYLINDRICAL HEAT EXCHANGER FOR MELTING OF PCM

The thermal heat storage it’s an effective way to suit the energy availability with the demand schedule. It can be stored in the means of sensible or latent heat, the latter applying a material denominated Phase Change Material (PCM), which is provided as organic compounds, hydrated salts, paraffins, among others. The latent heat storage systems offer several advantages, like the practically isothermal process of loading and unloading and the high energy density. However, the low thermal conductivity makes the cycle prolonged on these systems, restricting its applicability. Applying computational fluid dynamics, the behavior of the PCM melting process was studied in cylindrical cavities with horizontal and vertical fins, aiming the optimization of the fin geometry. In this way the fin area was kept constant, varying its aspect ratio. The numerical model was validated with results from the literature and it’s composed of the continuity, momentum and energy equations increased by the phase change model. Qualitative and quantitative results are presented, referring to mesh independence, contours of velocity, net fraction and temperature at different moments of the process. The results of the study indicate that the position of the fin in the heat exchanger influences the melting process, although the vertical fins have a faster total melting process, horizontal fins can reach larger partial liquid fractions in less time in the heat exchanger. Such as the position of the fin, the increase of its length propitiates the reduction of the melting time, evidencing the optimal aspect ratio.

Investigation on mechanical behaviour of dacite under loading and unloading conditions

Dacite is the dam site material of Rumei Hydropower Station, Tibet, China. To study the deformation and failure mechanisms of dacite under loading and unloading conditions, a series of triaxial compression tests and unloading confining pressure tests were carried out. Experimental results indicate that the deformation and strength behaviour of dacite are different between loading and unloading conditions. The lateral strain is more sensitive to the decreasing of the confining pressure under unloading process. In a uniaxial compression test, the sample is axial splitting. Shear failure takes place under the confining pressure. However, the samples failed with combined shear and tensile fractures in unloading confining pressure tests. From the viewpoint of energy conversion, the failure of dacite in triaxial compression process is determined by the released elastic strain energy, while the dissipated strain energy plays a major role in unloading confining pressure process.

Through-Process Finite Element Modeling for Warm Flanging Process of Large-Diameter Aluminum Alloy Shell of Gas Insulated (Metal-Enclosed) Switchgear.

The large diameter metal shell component (LDMSC) is an important part of gas insulated (metal-enclosed) switchgear (GIS). The LDMSC with multi branches is filled with gas under certain pressure. The plastic forming process is an efficient approach to manufacturing the high reliability LDMSC. The warm flanging process has been widely used to form LDMSC using aluminum alloy. The forming process is characterized by local heating, and the distribution of temperature is strongly inhomogeneous. Although the wall thickness of the shell is 10 mm to 20 mm, the ratio of outer diameter to thickness is more than 40. These present some difficulties in the flanging process and result in some forming defects. Detailed forming characteristics are hard to obtain by analytical and experimental methods. Thus, the through-process finite element (FE) modeling considering heating, forming, unloading, and cooling is one of the key problems to research the manufacturing process of LDMSC. In this study, the through-process FE modeling of the warm flanging process of LDMSC using aluminum alloy was carried out based on the FORGE. The thermo-mechanical coupled finite element method was adopted in the modeling, and the deformation of the workpiece and the die stress were considered together in the modeling. A full three-dimensional (3D) geometry was modeled due to inhomogeneous distribution in all directions for the temperature field. The simulation data of local flame heating could be transferred seamlessly to the simulations of the deforming process, the unloading process, and the cooling process in the through-process FE model. The model was validated by comparison with geometric shapes and forming defects obtained from the experiment. The developed FE model could describe the inhomogeneous temperature field along circumferential, radial, and axial directions for the formed branch as well as the deformation characteristic and the unloading behavior during the warm flanging process. By using the FE model, the forming defects during the flanging process and their controlling characteristics were explored, the evolution of the temperature field through the whole process was studied, and deformation and springback characteristics were analyzed. The results of this study provide a basis for investigating deformation mechanisms, optimizing processes, and determining parameters in the warm flanging process of a large-diameter aluminum alloy shell component.

Payload pendulation and position control systems for an offshore container crane with adaptive‐gain sliding mode control

AbstractWhen container ports are not available for heavy ships, the offshore ship‐to‐ship transfer operation is an alternative method to an inland container terminal. This process is performed between a large container ship and a smaller ship, which is equipped with a container crane, called the mobile harbor or the ship‐mounted crane. The sea‐state condition is a crucial factor in open‐sea operations. The presence of waves, wind, and current disturbances excite the pendulum oscillations of the crane's hanging container. In this study, the problem of payload pendulation and container position for an offshore container crane using an adaptive‐gain sliding mode control (SMC) scheme is investigated. The primary control task during the loading and unloading process is to keep the container in the desired region under the harsh oceanic environment. The proposed control architecture incorporates an adaptive‐gain SMC with a compensation part and a prediction mechanism. Therein, a sliding surface is design to combine the desired sway motion of the payload with the desired trolley trajectory. Furthermore, a varying control gain is proposed in the sliding control, obtained by an adaption law that transitions the system into sliding mode. By constructing an appropriate Lyapunov function, we show that the proposed control law ensures the asymptotic stability of the ship‐mounted crane. Numerical simulations are presented to show the effectiveness and robustness of the proposed control system.

Kinematics of Subduction Processes during the Earthquake Cycle in Central Chile

ABSTRACTSubduction processes at convergent margins produce complex temporal and spatial crustal displacements during different periods of the earthquake cycle. Satellite geodesy observations provide important clues to constrain kinematic models at subduction zones. Here, we analyze geodetic observations in central Chile, where two large earthquakes occurred: 2010 Mw 8.8 Maule and 2015 Mw 8.3 Illapel. We propose a model that considers the motion along both interfaces of the brittle subducting slab as the sources responsible for the movement of the crust in the different periods of the earthquake cycle. Using standard inversion techniques, we provide a consistent framework of the kinematic displacement during each period of the earthquake cycle. We show that during the interseismic period prior to the Maule and Illapel earthquakes, two patches of slip rate on the lower interface are determined. These patches are located just below the future hypocenters. Because the interseismic period corresponds to the loading process and the coseismic to the unloading process, it is interesting to note that the area where loading is stronger corresponds to the area where unloading is also strong. Furthermore, we show that the Maule earthquake causes a significant displacement on the lower interface, just below the epicenter of the future Illapel earthquake to the north, a few years later. We speculate that the interaction between motions along both interfaces is the key to understanding the evolution of stress and the occurrence of earthquakes at subduction zones. This framework improves the understanding of the observed loading and unloading processes and potential triggering between subduction earthquakes.

Characteristics of Unloading Creep of Tuffaceous Sandstone in East Tianshan Tunnel under Freeze-Thaw Cycles

The physicomechanical properties of tunnel surrounding rock are influenced by many factors such as the external environment and freeze-thaw cycles, especially in engineering in high cold regions. To understand the characteristics of freeze-thaw cycles on the creep properties of rocks in high cold regions, a freeze-thaw test, SEM test, triaxial compression test, and triaxial unloading creep test were carried out for tuffaceous sandstone in the G575 East Tianshan Tunnel in Hami, Xinjiang. The results show the following: (1) the freeze-thaw cycle reduces the degree of cementation of mineral particles in a microcosm, manifested on a macro scale by the scaling mode and crack propagation mode; (2) the effect of freeze-thaw cycles reduces the compressive strength and shear strength of rock samples (i.e., ductility enhancement); (3) for tuffaceous sandstone, the unloading process and freeze-thaw cycle each lead to improved creep deformation in rock samples, and radial deformation is more sensitive to rock deformation and failure; and (4) the creep rate of surrounding rock can be reduced by confining pressure. The peak creep rate increased with freeze-thaw time, as did the overall creep rate. Attention should be paid to deformation within a short period, and necessary supporting and protection measures should be taken to reduce creep.

Case Study on Boil-Off Gas (BOG) Minimization for LNG Bunkering Vessel Using Energy Storage System (ESS)

Liquefied natural gas (LNG) is recognized as a preferable alternative fuel for ship owners, since it can substantially reduce harmful emissions to comply with stricter environmental regulations. The increasing number of LNG-fueled vessels has driven up the number of LNG bunkering vessels (LNGBVs) as well. A key issue of LNGBVs is boil-off gas (BOG) generation, especially the huge amount of BOG that is generated during loading and unloading (bunkering) processes. This study proposes a hybrid system that combines conventional onboard LNG-fueled generators with an energy storage system (ESS) to solve the BOG issue of LNGBVs. This hybrid system is targeted at an LNGBV with the cargo capacity of 5000 m3. The amount of BOG generation is calculated based on assumed operation modes, and the economic study and the environmental analysis are performed based on the results. By comparing the conventional system to the proposed ones, some benefits can be verified: about 46.2% BOG reduction, 66.0% fuel saving, a 7.6-year payback period, and 4.8 tons of greenhouse gas (GHG) reduction for one voyage in the best case, with some assumptions. This proposed hybrid system using the ESS could be an attractive green solution to LNGBV owners.