Unloading Process Research Articles

RECOMENDACIONES BASADAS EN EL EFECTO DESCARGA SOBRE LOS PARÁMETROS DE DETERIORO DE LAS ROCAS CIRCUNDANTES DURANTE LA EXCAVACIÓN DE TÚNELES PROFUNDOS

How to ensure the construction safety is one of the key problems for the deep tunnel excavation. Since a tunnel excavation is an unloading process in essence, a novel method to accurately evaluate the damage evolution of the surrounding rock was conducted to study the deformation and failure mechanism of the tunnel by considering the unloading effect. A typical tunnel in Shimen Mine in China was regarded as the background, the three-dimension computational model was built by using FLAC3D technique. Then the different unloading zones of the surrounding rock were determined according to the unloading principle of tunnel excavation. The results show that the mechanical parameters for the different unloading zones, such as cohesion, internal friction angle, elastic modulus, and Poisson’s ratio, display the nonlinear degradation characteristics. And it can be found that the increasing range of the mechanical response index, such as displacement, stress and force, increase about 0.73-2.10 times comparing the conventional analysis with the unloading calculation. The unloading effect has a great influence on the stress field, the displacement field, and the forces of the supporting during the tunnel excavation. So it is more practical to consider the unloading effect during the deep tunnel excavation. The conclusions obtained in the study are of important theoretical value to direct the similar engineering practice. Keywords: Deep tunnel, Surrounding rock, Unloading effect, Deformation mechanism, Mechanical parameter

Analysis of Model Loading and Unloading Time of Ships at Boom Baru Port, Palembang, Indonesia

Logistic transport passing through road transport in Palembang city has been very high. To support green Transport, it is recommended to convert some of land logistic transports to river transport. However, the river transport has not been ready in terms of dredging and maintaining water level of Musi River. Furthermore, Boombaru Port, which has been shallow, and has high tidal level difference, can cause the process of loading and unloading become longer. High dwelling time is one of many problems that happen in port’s container terminal in Indonesia. This is commonly caused by longer loading and unloading time than those ports with high navigability and good handling equipment. Loading and unloading time depends on some factors, i.e ship size, limitation of equipment and stacking yard, a shallow port basin, tidal period and tidal magnitude. This paper aims to model the loading and unloading Time at Container Terminal of Boombaru Port, and analyze the effect of some factors on loading and unloading time. The model derived is Y = 0.501 X1 – 0.021 X2 – 2.63 X3 – 29.745, which X1 is Length Over All (m), X2 is Low Tide Elevation (cm) and X3 is duration of tidal period (hour).

Combination of nearest neighbor and heuristics algorithms for sequential two dimensional loading capacitated vehicle routing problem

Vehicle Routing Problem (VRP) is a method for determining the optimal route of vehicles in order to serve customers starting from depot. Combination of the two most important problems in distribution logistics, which is called the two dimensional loading vehicle routing problem, is considered in this paper. This problem combines the loading of the freight into the vehicles and the successive routing of the vehicles along the route. Moreover, an additional feature of last-in-first-out loading sequencesis also considered. In the sequential two dimensional loading capacitated vehicle routing problem (sequential 2L-CVRP), the loading must be compatible with the trip sequence: when the vehicle arrives at a customer i, there must be no obstacle (items for other customers) between the item of i and the loading door (rear part) of the vehicle. In other words, it is not necessary to move non-i’s items whenever the unloading process of the items of i. According with aforementioned conditions, a program to solve sequential 2L-CVRP is required. A nearest neighbor algorithm for solving the routing problem is presented, in which the loading component of the problem is solved through a collection of 5 packing heuristics.

Residual stresses in shape memory alloy fiber reinforced aluminium matrix composite

Process-induced residual stress in shape memory alloy (SMA) fiber reinforced aluminum (Al) matrix composite was simulated by ANSYS APDL. The manufacturing process of the composite named as NiTi/Al is start with loading and unloading process of nickel titanium (NiTi) wire as SMA to generate a residual plastic strain. Then, this plastic deformed NiTi wire would be embedded into Al to become a composite. Lastly, the composite is heated form 289 K to 363 K and then cooled back to 300 K. Residual stress is generated in composite because of shape memory effect of NiTi and mismatch of thermal coefficient between NiTi wire and Al matrix of composite. ANSYS APDL has been used to simulate the distribution of residual stress and strain in this process. A sensitivity test has been done to determine the optimum number of nodes and elements used. Hence, the number of nodes and elements used are 15680 and 13680, respectively. Furthermore, the distribution of residual stress and strain of nickel fiber reinforced aluminium matrix composite (Ni/Al) and titanium fiber reinforced aluminium matrix composite (Ti/Al) under same simulation process also has been simulated by ANSYS APDL as comparison to NiTi/Al. The simulation results show that compressive residual stress is generated on Al matrix of Ni/Al, Ti/Al and NiTi/Al during heating and cooling process. Besides that, they also have similar trend of residual stress distribution but difference in term of value. For Ni/Al and Ti/Al, they are 0.4% difference on their maximum compressive residual stress at 363K. At same circumstance, NiTi/Al has higher residual stress value which is about 425% higher than Ni/Al and Ti/Al composite. This implies that shape memory effect of NiTi fiber reinforced in composite able to generated higher compressive residual stress in Al matrix, hence able to enhance tensile property of the composite.

MODELING AND SIMULATION OF QUAY CRANE CONTROL SYSTEM FOR PID CONTROLLER OPTIMAL PARAMETERS DETERMINATION / KRANTINĖS KRANO VALDYMO SISTEMOS KOMPIUTERINIS MODELIAVIMAS OPTIMALIOMS PID VALDIKLIO VERTĖMS NUSTATYTI

The main control object of Quay crane, which is operating in seaport intermodal terminal cargo loading and unloading process, is the crane trolley. One of the main frequent problem, which occurs, is the swinging of the container. This swinging is caused not only by external forces but also by the movement of the trolley. The research results of recent years produced various types of control algorithms by the other researchers. The control algorithms are solving separate control problems of Quay crane in laboratory environment. However, there is still complex control algorithm design and the controller’s parameter estimation problems to be solved. This paper presents mathematical model of the Quay crane trolley mechanism with the suspended cargo. The mathematical model is implemented in Matlab Simulink environment and using Dormand-Prince solving method. The presented model of laboratory quay crane mathematical model is dedicated to parameter estimation of PID controller of closed loop system with the usage of S –form speed input profile. The article includes the dynamic model of the presented system, the description of closed loop system and modeling results. These results will be used as an initial information for the PID parameters estimation in real quay crane control system. The simu-lation of the model was performed using estimated values of controller. The sway influence of the cargo, the usage of the trolley speed input S-shaper and the PID controller was used to control the trolley speed. Jūriniame įvairiarūšiame terminale atliekant konteinerių krovos procesus, vienas iš krantinės kranų valdymo objektų yra vežimėlis. Viena iš problemų, su kuria susiduriama dažniausiai, yra konteinerio svyravimai, kuriuos, be išorinių veiksnių, taip pat sukelia ir vežimėlio judėji-mas. Remdamiesi paskutinių kelerių metų tyrimais, mokslininkai sukūrė įvairių valdymo algoritmų, kurie laboratorinėmis sąlygomis spren-džia atskiras krantinės kranų valdymo problemas. Tačiau kompleksinių ir efektyvių valdymo algoritmų ir jų valdymo sistemos parametrų nustatymo metodai vis dar kuriami ir tobulinami. Šiame darbe sudarytas krantinės krano vežimėlio su kabančiu kroviniu mechanizmo sis-temos matematinis modelis. Šis modelis realizuotas Matlab Simulink aplinkoje ir sprendžiamas taikant Dormand-Prince metodą. Sukurtas laboratorinio krantinės krano valdymo sistemos kompiuterinis modelis skirtas uždarosios valdymo sistemos PID valdiklio parametrams nustatyti, kai užduoties signalui taikomas S formos greičio kitimo profilis. Darbe pateiktas sistemos dinaminis modelis, aprašyta uždaroji valdymo sistema, pateikti kompiuterinio modeliavimo rezultatai, kuriuos planuojama panaudoti kaip pradinę informaciją realaus krano PID valdiklio parametrams derinti. Atlikta simuliacija naudojant nustatytas vertes ir įvertinti krovinio svyravimai taikant S formos greičio kitimo profilį kartu su PID valdikliu vežimėlio greičiui valdyti.

Effects of scour-hole dimensions and soil stress history on the behavior of laterally loaded piles in soft clay under scour conditions

Bridge pile foundations in the midst of water current are often subjected to scour, which induces the loss of soil support around the piles and thus results in a significant decrease of foundation capacities or even the failure of bridges. In the current practice, when the scour-affected behavior of the pile foundations is analyzed, either the whole scour-hole geometry or the possible changes in the stress history of the remaining soils is often ignored. In reality, however, scouring creates scour holes with certain dimensions around the pile foundations and the remaining soils that are not scoured away undergo an unloading process at the same time, which will increase the over-consolidation ratios of the remaining soils and accordingly changes of their mechanical properties. This paper examines the behavior of laterally loaded piles in soft clay under scour conditions by using the p-y method. The conventional p-y curves have been modified appropriately to reasonably reflect the effects of three-dimensional scour-hole geometry as well as the stress history of the soils, with the aid of integration of Mindlin’s fundamental solutions. A field test is used to serve as a reference case and to investigate the effects of stress history, scour depth, scour width, and scour-hole slope angle on the responses of laterally loaded piles in soft clay. The results indicate that neglecting the stress history effect can be unconservative for scour-affected pile foundations in soft clay, whereas neglect of the scour-hole dimensions and geometry would lead to over-conservative predictions/design of the laterally loaded piles under scour condition.

Cyclic constitutive model for strain-hardening cementitious composites

A uniaxial cyclic constitutive model for strain-hardening cementitious composites (SHCCs) is proposed based on the response of the material at the stress–strain level under different loading regimes. The ascending branch of the compressive envelope curve was developed using the form of a parabolic curve, while the descending branch adopted the bilinear form. The full tensile stress–strain curve was approximately simulated by a trilinear form comprising ascending, strain-hardening and descending branches. Using the method of setting a reference point, the characteristics of the unloading and reloading process were determined, with consideration of the partial unloading–reloading scheme. Furthermore, the transition between tension and compression was taken into account in the model development. The proposed cyclic constitutive model was coded into the OpenSees platform and applied to simulate the responses of specimens at material and member levels. The simulation results indicate that the proposed model is reasonably accurate in simulating the mechanical properties of SHCC material and the cyclic behaviour of SHCC flexural elements.

A new theoretical model of the quasistatic single-fiber pullout problem: The energy-based criterion with unloading process

A theoretical analysis for the single-fiber pullout with unload process is presented based on the energy-based debonding criterion and the modified analysis of stress transfer between fiber and matrix(Qing [1]). The relationship between the applied stress and the interfacial relative displacement is expressed as a function of the radial residual thermal stress, fiber pullout rate and volume content as well as the length of reverse frictional sliding. The influence of fiber pullout rate on interfacial frictional coefficient is also taken into consideration. The calculation results show that the applied stress result in further debonding increases with the increase of the radial residual thermal stress and the fiber volume content and the decrease of the fiber pull-out rate. There is a drop for the applied stress when the interface debonding close to the model length and the drops of short models are larger than those of long models. Under different conditions, the model length almost has no influence on the debonding and reverse sliding in unloading processes at the initial debonding region.

Fracture and deformation mechanism of Ti(C,N)/TiAlSiN multilayer coating: FE modeling and experiments

Ti(C,N)/TiAlSiN multilayer coating was deposited on GTD450 using the Cathodic Arc PVD method to protect compressor blades from erosion damage. The fracture and deformation mechanisms of coating were investigated. To better observe fracture and deformation events and thus the need to apply high loads, Vickers microhardness test was performed and imprint diagonals were measured. Then, using SEM analysis, indent surfaces were investigated to observe crack initiation and deformation patterns at different loadings. It was found that crack initiated at the coating top surface (top surface of TiAlSiN layer) at a loading range of 250–500mN. Cross-section SEM images of indent surfaces at lower loads revealed shear sliding and radial cracking below the indenter in the coating-substrate interface (bottom surface of Ti(C,N) layer). To better understand coating fracture and deformation, a 3D FE model was used to determine stress distribution in the coating. FEM results showed that maximum Von Mises stresses occur beneath the indenter and its edges, causing shear sliding to take place. Also, maximum principal stresses at lower loads take place beneath the indenter at the coating-substrate interface. As load increases, the maximum principal stress zone changes and is transferred to the coating top surface. Maximum principal stress was produced during the unloading process at the coating top surface or median plane and may cause lateral cracking. Experimental and FEM results were in good agreement.

Sucrose Transporter ZmSut1 Expression and Localization Uncover New Insights into Sucrose Phloem Loading.

Sucrose transporters (SUTs) translocate sucrose (Suc) across cellular membranes, and in eudicots, multiple SUTs are known to function in Suc phloem loading in leaves. In maize (Zea mays), the Sucrose Transporter1 (ZmSut1) gene has been implicated in Suc phloem loading based upon RNA expression in leaves, electrophysiological experiments, and phenotypic analysis of zmsut1 mutant plants. However, no previous studies have examined the cellular expression of ZmSut1 RNA or the subcellular localization of the ZmSUT1 protein to assess the gene's hypothesized function in Suc phloem loading or to evaluate its potential roles, such as phloem unloading, in nonphotosynthetic tissues. To this end, we performed RNA in situ hybridization experiments, promoter-reporter gene analyses, and ZmSUT1 localization studies to elucidate the cellular expression pattern of the ZmSut1 transcript and protein. These data showed that ZmSut1 was expressed in multiple cell types throughout the plant and indicated that it functions in phloem companion cells to load Suc and also in other cell types to retrieve Suc from the apoplasm to prevent its accumulation and loss to the transpiration stream. Additionally, by comparing a phloem-mobile tracer with ZmSut1 expression, we determined that developing maize leaves dynamically switch from symplasmic to apoplasmic phloem unloading, reconciling previously conflicting reports, and suggest that ZmSut1 does not have an apparent function in either unloading process. A model for the dual roles for ZmSut1 function (phloem loading and apoplasmic recycling), Sut1 evolution, and its possible use to enhance Suc export from leaves in engineering C3 grasses for C4 photosynthesis is discussed.

Nonlinear dynamic properties of silty clay from Warsaw area

Abstract In this work, the small-strain and nonlinear dynamic properties of silty clay samples were studied by means of the low- and high-amplitude resonant column (RC) tests at various mean effective stresses (p’). The tested specimens were collected from the centre of Warsaw, district Śródmieście. Initially, the low-amplitude tests (below 0.001%) were conducted. Subsequently, the nonlinear testing was performed, at shearing strains greater than 0.001%. These tests were carried out in order to receive the dynamic properties of silty clay specimens in the nonlinear shear strain range. The small-strain material damping ratios (Dmin) of silty clay samples were also measured during the low-amplitude resonant column testing. The results show that increasing shear strain (γ) above the elastic threshold (γte) causes a decrease of the shear modulus (G) and normalized shear modulus (G/Gmax) of analyzed soil samples. Simultaneously, it is observed a increase of its damping ratio (D) and normalized damping (D/Dmin) with increasing shear strain (γ). Predictive equations for estimating normalized shear modulus and material damping of silty clay soils were presented here as well. The equations are based on a modified hyperbolic model and a statistical analysis of the RC tests results. The influence of unloading process on dynamic properties of the tested material was also discussed in the paper.

Plastic deformation analysis and forming quality prediction of tube NC bending

Plane strain assumption and exponent hardening law are used to investigate the plastic deformation in tube bending. Some theoretical formulae including stress, curvature radius of neutral layer, angle of neutral layer deviation, bending moment, wall thickness variation and cross-section distortion, are developed to explain the phenomena in tube bending and their magnitudes are also determined. During unloading process, the springback angle is deduced using the virtual work principle, and springback radius is also given according to the length of the neutral layer which remains unchanged before and after springback. The theoretical formulae are validated by the experimental results or the validated simulation results in literature, which can be used to quickly predict the forming quality of tube numerical control (NC) bending.

Matched-filter detection of the missing pre-mainshock events and aftershocks in the 2015 Gorkha, Nepal earthquake sequence

The 25 April 2015 Mw 7.8 Gorkha, Nepal earthquake occurred at the bottom edge of the locked portion of the Main Himalayan Thrust, where the Indian plate underthrusts the Himalayan wedge. The earthquake was followed by a number of large aftershocks, but not preceded by any foreshocks within ~3weeks according to the NEIC or ISC catalog. However, due to the limited station coverage of the local seismic network, a large portion of events may not be reported in routine catalogs. Here, we employ the matched filter technique to recover the undocumented earthquakes for the period beginning 80days before through 30days after the 2015 Gorkha earthquake. We detect twice as many aftershocks as those listed in the ISC catalog. We observe an along-strike aftershock expansion after the mainshock and before the largest Mw 7.3 aftershock that occurred on 12 May 2015. Repeating earthquakes are found to the ESE of the mainshock rupture area, suggesting that the expansion may be partially driven by afterslip. In addition, we observe a significant increase in seismicity rate ~3–4days prior to the mainshock, initiating ~6h after a M 5.2 earthquake, located ~240km to the NW of the mainshock. The increase of seismic activities occurs in a wide region around the Gorkha principal slip zone, indicating the effect of delayed dynamic triggering may contribute to the large-scale unloading process prior to the 2015 Gorkha mainshock.

Numerical and experimental simulation of damaged rock with randomly oriented cracks by shock disturbance

The aim of this study is to investigate the effect of shock-disturbed cracks on the dynamic fragmentation of granite. Considering the complex behavior of rock materials, the Walsh’s model was revisited and extended by including the stress effect required to close an initially open crack and examining the unloading process in detail. This analysis leads to closed-form expressions for loading and unloading portions of the effective Young’s modulus, as functions of the crack density, characteristic aspect ratio, and crack friction coefficient. Subsequently, the effective Young’s modulus and cutting force are simulated and the influence of cracks is studied. The analysis results with different crack density and disturbed frequency are compared in terms of effective Young’s modulus and cutting force. Finally, the tool and damaged rock model with randomly oriented cracks by shock disturbed at a different frequency was demonstrated by the test. The good agreement between the simulation results and experimental data demonstrates the validity of the simulation method.

Framework for the validation of simulation-based productivity analysis: focused on curtain wall construction process

As construction projects have become more complicated in design and construction, it is necessary to establish the construction operational plans in advance. However, there were some limitations in analyzing construction produc­tivity due to the difficulty of collecting accurate data. To address this challenge, this study aimed to develop the frame­work for the validation of simulation-based productivity analysis, which consisted of three measures: (i) validation of the measured productivity data as target variable; (ii) validation of the measured duration data as input variable; and (iii) validation of the simulation model compared to the actual construction process. To verify the feasibility of the proposed framework, this study focused on the curtain wall construction project of “S” office building as a case study. The T-test was applied to investigate the statistical difference between the measure and simulated productivity. It was determined that the significance level α in the T-test for the unloading process was 0.136 with 95% confidence interval; the lifting process, 0.106; and the installing process, 0.311. As a result, there was no significant difference between the measured and simulated productivity. The proposed framework could enable executives and managers in charge of project plan­ning and scheduling to accurately predict the simulation-based productivity.

Investigation of thermomechanical couplings, strain localization and shape memory properties in a shape memory polymer subjected to loading at various strain rates

This paper presents experimental and modeling results of the effects of thermomechanical couplings occurring in a polyurethane shape memory polymer (SMP) subjected to tension at various strain rates within large strains. The SMP mechanical curves, recorded using a testing machine, and the related temperature changes, measured in a contactless manner using an IR camera, were used to investigate the polymer deformation process at various loading stages. The effects of thermomechanical couplings allowed the determination of the material yield point in the initial loading stage, the investigation of nucleation and development of the strain localization at larger strains and the estimation of the effects of thermoelastic behavior during the unloading process. The obtained stress–strain and thermal characteristics, the results of the dynamic mechanical analysis and estimated values of the shape fixity and shape recovery parameters confirmed that the shape memory polymer (Tg = 45 °C) is characterized by good mechanical and shape memory properties, as well as high sensitivity to the strain rate. The mechanical response of the SMP subjected to tension was simulated using the finite element method and applying the large strain, two-phase model. Strain localization observed in the experiment was well reproduced in simulations and the temperature spots were correlated with the accumulated viscoplastic deformation of the SMP glassy phase.

Mechanical characterisation of Si–C–N thin films prepared by electron cyclotron resonance plasma chemical vapour deposition at low microwave power and low temperature

Si–C–N thin films with smooth surfaces were synthesised by electron cyclotron resonance plasma chemical vapour deposition at low microwave powers without heating silicon substrates. Mechanical properties of obtained films were examined by nanoindentation based on Oliver and Pharr method. High elastic recovery was observed. Hardness and reduced modulus show no clear relation with the elastic/plastic work calculated from load–displacement curves. The energy dissipation kept almost constant with respect to the variation of stiffness during loading and unloading process. This opens the possibility of potential industrial applications due to the insensitivity of the deposited films to external stress.

A novel approach to fabricating a nanotwinned surface on a ternary nickel alloy

Deformation nanotwinning is performed using molecular dynamics (MD) on a single crystal in a ternary nickel (Ni) alloy. Generalized embedded-atom method (EAM) potential functions are obtained for the ternary Ni alloy. The critical twinning stress is 4.48GPa, calculated by the MD simulations. Detwinning, restoring and regenerating of nanotwins take place during the unloading process, contributing to the remaining of the ductility. According to the MD simulations, a novel approach is proposed to fabricating a nanotwinned surface using nanoindentation at room temperature. This is different from previous reports, in which high temperature, high pressure or chemical regents are employed.

Multistage throttling characteristics of reverse direction impact of pilot operated check valve

The aim of this study was to improve the reverse impact characteristics of large-flow pilot operated check valves, meanwhile reduce oscillation, cavitation and unloading time. Three different main poppets were selected, and the impact pressure and flow were set as 30 MPa and 1000 L/min, respectively. The cavitation phenomenon was explored based on the analysis of gas-liquid two-phase flow by Fluent software, and then experimental verification was performed. Meanwhile, the dynamic characteristics of pilot operated check valves were analyzed by the impact test system. The simulation results showed that the fluid pressure clearly decreased while flowing through the poppet area. The sudden decrease of flow area at the orifice port of the poppet resulted in an increase in flow-velocity, because the cavitation area appears on the side of the main poppet. A stepped throttling structure could effectively reduce the cavitation area, preventing the generation of cavitation. The experimental results showed that the pressure oscillation of a stepped main poppet significantly reduced during the process of unloading, at 28.41 MPa; with a flow gradient of 4.86×105 L/min2; unloading time significantly reduced, for 711 ms; indicating it opened more rapidly and dynamic characteristics was superior. It can be concluded that the stepped throttling structure could effectively reduce the pressure oscillation of a pilot operated check valve during the process of unloading, improve response speed, enhance the impact properties, and reduce cavitation. This verified the correctness of the simulation and the rationality of the cavitation index.

Vibration of a prestressed tube in the presence of plastic zone

The paper is devoted to a problem of radial steady state vibrations for a tube taking into account the inhomogeneous residual stress (RS) field. According to the theory of ideal plasticity the RS field is caused by elastoplastic deformation due to the internal pressure and the further unloading process. Various RS distributions inside both elastic and plastic zones are described. A finding of displacement function is reduced to the numerical solving of the first-order differential equations. Within the framework of the acoustical method, the inverse problem for RS field identification is stated. On the basis of the free radial vibration problem for tube, we derived the formula for a dependency of eigenfrequency on RS distribution by using the linearization method. By using this formula for two different values of eigenfrequencies, we state the system of two equations to identify the plasticity zone radius and RS level. Examples of numerical solution of this system for different values of parameters (RS level and tube thickness) are demonstrated. The estimation accuracy of eigenfrequencies measurement for successful implementation of the proposed approach is given.