Control of the disturbed displacement of adjacent tunnel during excavation is a significant issue for design and construction. Based on the multi-objective optimization method, the multi-type monitoring data in the excavation of the excavation are integrated, the key soil parameters are inverted and identified, and the time effect of the tunnel displacement is quantified and corrected. A dynamic multi-objective optimization method with adaptive infill criterion (DMO-AIC) is proposed to improve the updating efficiency of dynamic surrogate models. The proposed method takes into account the computational redundancy of dynamic surrogate models in engineering optimization, and designs an adaptive point-adding discrimination strategy, which can autonomously identify invalid updates of surrogate models on the optimization path. The results show that the proposed DMO-AIC significantly reduces the invocations of the black-box model during optimization while ensuring the good search performance and the convergence speed of the algorithm. The improved computational efficiency of DMO-AIC is helpful for the application of dynamic surrogate models in engineering optimization. The results of the virtual numerical example show that DMO-AIC can predict and update multiple model responses during excavation, such as wall deflections and tunnel displacements. The engineering practice of Shanghai Bund 596 excavation indicates that the time effect is properly updated, and the staged vertical displacements of the adjacent tunnel are accurately predicted.
In the process of rock excavation, cyclic loading may occur before or after the peak value. In order to obtain the fracture damage evolution characteristics of rock under the pre-peak and the post-peak cyclic loading condition, the fracture tests of three-point bending granite beams were conducted by using the digital image correlation method and the acoustic emission technology. Based on the secant modulus, the acoustic emission energy and effective crack length, the rock fracture damage indexes DE, DAE, and DL were constructed respectively, and the rock fracture damage process was quantitatively analyzed. The results show that the damage index of the rock sample has an obvious rate effect. At the same number of cycles, as the loading rate increases, the damage index decreases. For the pre-peak cyclic loading condition, the fracture process of rock from elastic stage to elastic-plastic stage can be well reflected by DE. Under the condition of post-peak cyclic loading, DL can better represent the fracture damage process of rock from step up to continuous failure.
In order to evaluate the impact of shield tunnel construction on adjacent buildings, a method based on the fuzzy analytic hierarchy process (FAHP) and the interval number improvement technique for order preference by similarity to ideal solution (TOPSIS) is proposed. A risk assessment system based on soil properties, building factors, tunnel factors, shield tunneling parameters, and other factors is established after investigation. The FAHP is used to determine the weight of factors based on expert scoring. Based on the traditional TOPSIS method, 6 typical samples are selected according to the factor grading standard to determine the non-uniform risk rating criteria. For the first time, the interval improved TOPSIS method is applied to the risk assessment of shield tunneling beneath buildings. The engineering situation can be better represented by the interval number. Compared with traditional risk assessment methods, this method is more accurate, less affected by subjective factors, and more objective. The proposed method has been used to evaluate the risk of a certain masonry building, and the result is consistent with the actual situation, which proves its effectiveness of. Thus, the proposed method can provide reference for risk assessment of similar projects.
To study the stern vibration characteristics of the ship sailing in still water under the action of propeller induced pressure fluctuation, the propeller self-propulsion numerical simulation was conducted based on the Reynolds-averaged Navier-Stokes (RANS) method, in combination with the shear-stress transport (SST) k-ω model. Taking the obtained fluctuating pressure on the hull surface as the external excitation, the acoustic-structure coupling calculation was performed through the structural finite element model coupled with the flow field boundary element model, and a numerical prediction method for the stern vibration of the self-propulsion ship excited by the propeller surface force was established. By analyzing the fluctuating pressure characteristics in the time domain and frequency domain, it is found that the amplitude of the blade frequency component is much larger than that of other frequency components. For the right-handed propeller, the starboard side pressure amplitude above the propeller is higher than that on the port side. The analysis of the corresponding relationship between the propeller fluctuating pressure, the structural inherent characteristics, and the vibration response shows that the coupled mode natural frequency should be far away from the propeller excitation force frequency to reduce the vibration response. The exploration of the effect of modifying stern structure on the vibration response at the same excitation indicates that increasing the plate thickness or installing stiffeners can change the inherent characteristics of the structure, thus avoiding resonance and achieving the vibration reduction effect.
In order to investigate the evolution characteristics of gas-liquid two-phase flow passing through a 90° pipe bend, the volume of fluid (VOF) multiphase flow model and the Realizable k-ε turbulence model are used to conduct numerical simulations. The evolution of velocity, pressure distribution, gas void fraction, and flow pattern passing through a 90° pipe bend is studied in detail. The results show that different gas-liquid two-phase flow patterns will produce different degrees of secondary flow phenomenon after passing through the 90° pipe bend, and the tangential velocity presents a bimodal distribution, which eventually dissipates into a unimodal distribution in the horizontal pipe. The pressure on the outer wall of the pipe bend increases as the inlet velocity increases. The change of gas void fraction is related to the transformation of the flow pattern, the bubbly flow evolves into a slender slug flow in the horizontal pipe after passing through the 90° pipe bend, and the gas void fraction will decrease. The slug flow, the churn flow, and the annular flow evolve into the stratified-wave flow in the horizontal pipe after passing through the pipe bend, and the variation of the gas void fraction is relatively low. The research results can provide certain theoretical support for the design and development of gas-liquid two-phase flow conveying elbows and the prediction of induced stress.
Inclined structure is an important marine structure in the iced area. The change of the inclined angle will change the main failure mode of sea ice and affect the peak ice force acted on the structure. In order to simulate the random breaking characteristics of level ice, an irregular distributed dilated disk element model with bond-break function is constructed, and the dynamic process of interaction between the level ice and the inclined structure is simulated based on this model, which is verified by comparing the peak ice forces obtained by numerical simulation with the peak ice forces measured in the field. The influence law of the inclined angle on the ice force and the ice failure mode is analyzed. It shows that the variation of ice load with the changes of inclined angles simulated by the numerical method is basically consistent with the variation calculated by the two-dimensional theoretical model. With the increase of the incline angle, the proportion of bending failure decreases and the peak ice force and its occurrence probability increase. The inclined angle is an important factor in the change of sea ice failure modes and the peak ice force. This paper can be used as a reference for discrete element numerical simulation of sea ice and ice-resist design of inclined marine structures.
Based on the integrated jacket-support offshore wind turbine model of the National Renewable Energy Laboratory (NREL), the computational fluid dynamics (CFD) method is coupled with the wind turbine integrated analysis method to study the blade icing process and its influence on the overall dynamic performance of the wind turbine. First, the blade motion attitude calculated by the integrated analysis method is input into CFD. The discrete multiphase model and melting solidification model are used to simulate the icing growth of three-dimensional wind turbine blades. The k-ε turbulence model is used to calculate the aerodynamic performance before and after icing. Finally, the aerodynamic results after blade icing are returned to the integrated analysis method to analyze the influence of blade icing on the overall response of the wind turbine. The results show that the blade icing increases linearly along the blade span. The icing is mainly concentrated on the leading edge of the blade with the thickest ice accumulation at the tip. The lift coefficient decreases and the drag coefficient increases after icing. Blade icing will reduce the power of the whole machine, the torque, and the rotor speed. At the same time, it will lead to additional vibration response at the blade tip and tower top, and increase the wind speed required by the wind turbine to reach the rated power.
In order to investigate the influence of a dimensionless section position of a surface piercing propeller on the hydrodynamic characteristics of the surface piercing propeller cup section, the cup section of the surface piercing propeller at the dimensionless radius of 0.6, 0.7, and 0.8 is selected for modeling. By solving the RANS equation to simulate the cup section entry process, in combination with the volume of fluid method and the overlapping grid technique, a reliable numerical method is established. The hydrodynamic characteristics of the water entry process of the surface piercing propeller cup section at different section positions are studied. The effects of different section positions on the free surface form, ventilation cavity form, flow field, and the surface pressure distribution in the water entry process of the surface piercing propeller cup section are analyzed. The results show that with the position of the dimensionless radius section getting closer to the tip of the surface piercing propeller, the transition state between the fully ventilated state and the partially ventilated state occurs at a larger speed coefficient, and the transverse force coefficient and the open water efficiency increases.
The calculation of multiscale elastic parameters of cementitious materials based on micromechanical tests and the composite material theory is one of the key theoretical bases for precise design of cementitious materials performance. In this paper, grid nanoindentation tests of microscopic elastic modulus and the mercury intrusion test were conducted on hardened cement paste specimens at different water-cement ratios, to establish a multiscale homogenization calculation method for the elastic modulus of cement paste considering the influence of pores. Besides, the applicability of the dilute method, the self-consistent method, the Mori-Tanaka method, the interaction direct derivation (IDD) method, and the multilevel homogenization method was compared. The results show that the multi-phase and multi-scale calculations considering the effect of pores is in good agreement with experimental values. Except the multi-level homogenization method, the calculation results of several commonly used composite homogenization methods are similar.
To study the dynamic mechanical characteristic of steam cured concrete and self-compacting concrete bonding interface, a split Hopkinson pressure bar (SHPB) test was used to evaluate the dynamic properties of concrete with a bonding interface. The failure pattern and the characteristics of stress-strain curves and a constitutive model of concrete with a bonding interface were discussed. The results show that the impact destructions are associated with two forms of failures, i.e., the interface separation failure and concrete crushed failure. In interface separation failure, the peak stress, dynamic increase factor (DIF), peak strain, and impact toughness of concrete with a bonding interface increase with the increase of strain rate, and the concrete with a bonding interface shows a stronger strain rate sensitivity. In concrete crushed failure, there exist debonding deformation and crush deformation exist simultaneously. With the increase of strain rate, the accumulation and development of crack at the interface could make the interface zone play an energy relieving role in concrete with a bonding interface. The peak stress and the DIF of concrete with a bonding interface remain unchanged, while the peak strain and impact toughness both increase. The calculated data by the established dynamic constitutive model are similar to the experimental results, especially before the ultimate state of strain stress curves.
Because of the particularity and complexity of Jinan spring area, the quaternary sedimentary layer is mainly composed of clay and silty clay, which has the characteristics of a strong permeability. In the construction of excavation, a series of problems such as the precipitation abnormal difficulties and the serious structural water seepage would occur. In order to reveal the causes of the strong permeability of Jinan red clay, a study from the perspective of micropore structure of Jinan red clay was conducted. First, the basic physical properties of the undisturbed red clay were tested, and the micro particle arrangement of the red clay was obtained by the scanning electron microscope (SEM). Then, a soil seepage device based on computed tomography (CT) was developed. The three-dimensional pore structure and the water flow visualization of the red clay in different seepage stages were obtained through CT scanning. Finally, a pore network model (PNM) was established to quantitatively analyze the number and the volume proportion of the pores and throats in the soil during the seepage process. The results show that the overlapping of particles in the horizontal section of Jinan red clay is more loose, and the pore structure is mainly developed vertically, with the existence of large connected channels. Water flows preferentially along the existing connected pore channel of the red clay, which leads to the expansion of the seepage channel. The connected channel with a large pore diameter is the main factor affecting the permeability of the soil.
The excavation of foundation pit above the existing metro tunnel inevitably leads to the uplift of the tunnel. As an anti-uplift measure, the anti-uplift portal frame is still lack of research. Based on a foundation pit excavation project colinear with tunnel for long-distance, the excavation influence on the underlying shield tunnel during the construction process of anti-uplift portal frame and the foundation pit excavation was studied via numerical simulation. The interaction mechanism between the anti-uplift portal frame and ground as well as the anti-uplift effect were analyzed. Finally, a structural optimization design was proposed based on the simulation. The results show that the tunnel may be uplifted due to the shaft excavation during the construction of the anti-uplift portal frame and the uplift can be effectively restricted by backfilling and sectional excavation. Compared to the excavation without the anti-uplift portal frame, the uplift value of the tunnel decreases from 19.5 mm to 15 mm because of the restriction of the anti-uplift portal frame. The connection between the slabs and piles are weak positions of the structure due to the stress concentration and it is necessary to do a local reinforcement treatment in the connection.
Taking the damping layer as the research object, first, by using the dynamic mechanical test, based on the high-order fractional derivative FVMP model, and in combination with the temperature-frequency equivalent principle, the temperature and frequency dependent properties of the damping layer was characterized. Then, the model was applied to the vehicle-CRTSIII slab ballastless track coupled system. Finally, the effect of the temperature and frequency dependent properties of the damping layer on track structure vibration response was analyzed. The results show that the temperature and the loading frequency have a significant impact on the dynamic mechanical properties on the damping layer and the high-order fractional derivative FVMP model can accurately characterize this property. In the time domain response, the peak values of the slab track displacement and the acceleration on the FVMP model are significantly larger than those on the K-V model. At each reference temperature point, the displacement response of the slab track on the FVMP model decreases with the decrease of temperature, while the acceleration of the slab track shows an opposite trend. In the middle and high frequency band, the frequency domain response of the slab track on the FVMP model are greater than those on the K-V model. At each reference temperature point, the response of the slab track on the FVMP model decreases with the decrease of the temperature. Therefore, in order to improve the accuracy of the track structure prediction, it is necessary to consider the temperature and frequency dependent properties of the damping layer.
Unbonded flexible risers are widely applied to transport oil and gas resources from seabed to platform, and composite cylindrical layers are sometimes contained due to design requirements. Based on an 8-layer unbonded flexible riser model, the bending properties of the unbonded flexible risers with composite cylindrical layers are studied. A theoretical method of combining axisymmetric and bending loads acting on unbonded flexible risers is proposed, and a numerical method with detailed geometric characteristics taken into account is established for verification. The influence of two typical composite materials as well as the fibre volume fraction on the bending properties of the unbonded flexible risers is analyzed. The theoretical and the numerical results are in good agreement, which shows that the bending properties of the unbonded flexible risers are greatly affected by the axial Young’s modulus of the composite cylindrical layers, and composite material with larger axial Young’s modulus would greatly enhance the bending stiffness of the unbonded flexible risers, expecially in the full-slipping stage. In addition, the axial tensile stiffness and bending stiffness of full-slipping stage are proportional to the fibre volume fraction of the composite cylindrical layers.
Finite strip method (FSM) is a classical method to analyze the buckling of thin-walled members. The traditional FSM adopting trigonometric functions longitudinally can hardly analyze the members with spaced ribs along the longitudinal direction, while the compound strip method (CSM) can compensate for this shortcoming. Based on the CSM, the influence of utilizing plane elements and shell elements to respectively imitate stiffeners on buckling is investigated. Compared with the shell-element ribs, the plane-element ribs are prone to assembling the stiffener matrices with fewer degrees of freedom. But the shell-element ribs are more comprehensive as the out-plane displacement of ribs are taken into consideration. It is found that plane element ribs and shell element ribs have little difference on the buckling capacity of members. The buckling capacity has a small difference of mean absolute error (MAE) underneath 0.75% between the two types of CSMs, and the buckling capacity and modes are in good agreement with the finite element results. The buckling loads of the two types of CSMs are close to the FEM with a MEA less than 5%. The accuracy of the plane elements satisfies the predicted requirements, which helps to reduce the program computation and simplify the analysis complexity. The efficiency of analysis can be dramatically improved for fine meshing elements.
An adjacent excavation model based on the hardening soil-small strain (HSS) constitutive model was established by using the numerical method, which was compared with the single excavation model and the adjacent excavation model without considering the wall-soil friction. The stress deformation characteristics of adjacent excavation implemented simultaneously were obtained, and the interaction mechanism of adjacent excavations were revealed. The results show that two kinds of arching effects exist in the confined soil. One is the arching effect caused by uneven deformation of walls, and the other is the arching effect caused by the wall-soil friction, both of which affect the lateral earth pressure acting on the retaining walls. With the decrease of the excavation spacing, the former is weakened, resulting in the weakening of the transfer of lateral earth pressure between the soil near the excavation face to bracing soil, while the latter is enhanced, leading to the decrease of magnitude of the lateral earth pressure acting on adjacent retaining walls. Under the action of the arching effects, the curve of lateral earth pressure develops from an R-shaped distribution to a linear distribution and then returns to an R-shaped distribution with the decrease of the spacing. The maximum horizontal displacement of non-adjacent walls increases, and the maximum horizontal displacement of adjacent walls increases primarily and then decreases.
A numerical model to analyze the response of the membrane surface under ponding load is propesed which combines the smoothed particle hydrodynamics (SPH) method and the non-linear constitutive model of the membrane material. According to the stress-strain response surface of the membrane material based on the biaxial tensile test with different stress ratios, a nonlinear constitutive model is established. SPH particles are used to simulate water, and a numerical model of the fluid-solid coupling between the membrane surface and ponding load is established. The mesh size adopted in this paper is determined by verifying the mesh convergence, and the influence of the loading time on the calculation results is analyzed. At the same time, the distribution law of stress and strain of the membrane surface are analyzed. The results show that the loading process becomes increasingly stable with the increase of the loading time, and 100 s can meet the analysis requirements.The numerical simulation results are compared with those of the flat membrane ponding test. It is found that the maximum vertical deformation of the membrane surface is in good agreement, which verifies the reliability of the method proposed in this paper.
Rainfall infiltration analysis is one of the important methods for predicting engineering disasters. In order to effectively analyze the infiltration process of slope under heavy rainfall, based on the classical Green-Ampt model, a slope rainfall infiltration model considering the effect of saturated zone seepage and air pressure under the condition of non-uniform distribution of initial water content was established, and the corresponding expression of landslide stability coefficient was derived. The results show that the influence of slope size on rainfall infiltration is obvious. On the one hand, the expansion rate of wetting front increases with the increase of slope length, on the other hand, when considering the effect of air pressure, the smaller the slope length, the longer it takes to reach the same wet front. When the slope length increases to a certain extent, the difference is not obvious. In addition, the influence of seepage force on slope stability is greater than that of air pressure. Because the former gradually increases during the rainfall process while the latter is basically unchanged, the influence of seepage force increases, and the influence of air pressure decreases.
Transport time lag is a crucial characteristic of fire spreading in fire early stage, which determines the activation time of the fire detector. To clarify the quantitative relationship between the delay behavior and the quasi-steady state of smoke transmission in a long-narrow space, a time-varying spreadsheet is theoretically proposed to calculate the delay time of fire smoke transmission based on the theory of weak plume and the existing achievements concerned. Moreover, a theoretical model concerning the critical time for quasi-steady state assumption applicability is developed, where the method of calculating the critical time is also presented. The results of the case study show that due to the difference of smoke spreading velocity in long-narrow spaces and unconfined spaces for a case with the same conditions, the critical time for the smoke transmission to reach the quasi-steady state at a given radial distance on the ceiling in a long-narrow space is larger than that in the open space. For the open case, the thin ceiling plume, the small volume of entrained air, and the relatively high velocity of smoke lead to the longer delay time of smoke transmission in a long-narrow space than that in the open space under the same situations.
Based on the unified strength theory and the Terzaghi limit equilibrium theory, the ultimate bearing capacity of screw pile has been deduced. The method to determine the critical pitch and calculate the ultimate bearing capacity of the screw pile in two failure modes including the independent bearing failure mode and the cylinder shear failure mode has been proposed. The influence of the unified strength theoretical parameter b and the key parameters of concrete screw pile on the ultimate bearing capacity has been analyzed. The results show that the ultimate bearing capacity of the screw pile is 1.5—2 times that of the round pile with the same outer diameter. The ultimate bearing capacity of the screw teeth is mainly determined by the cohesion, the internal friction angle, and the buried depth of the soil. As b increases from 0 to 1, the theoretical value of the ultimate bearing capacity of the screw pile increases by nearly 48%. As the influence of the medium principal stress on the soil strength is considered, the theoretical calculation results of the bearing capacity of the concrete screw pile will be more accurate. Of the parameters of the concrete screw pile, the screw height bh has the greatest influence on the ultimate bearing capacity, while the screw thickness t has little influence on the bearing capacity. When designing threaded pile, the height of screw can be increased to some extent to improve the ultimate bearing capacity of the screw pile.
This paper aims to solve the problem of the oxygen cylinder contribution to the overall scattering intensity of the open breathing diver, which is the basis for mastering the accurate prediction and identification of the diver. A two-dimensional finite element axisymmetric model of 3D-object with non-axisymmetric excitation is constructed. The numerical solution to the far-field frequency characteristics of the acoustic scattering by the object with different azimuths is obtained by using the acoustic-solid coupling multi-physical interface in frequency domain. The reason and the estimation formula of the bright fringe at the resonance frequency are given. Under the assumption of the linear acoustics, the numerical solution to finite element method (FEM) is taken as the system function, and the linear frequency modulation signal with the same bandwidth is taken as the input signal of the system. The echo simulation in time domain can be obtained based on the convolution theorem. Combining the bright spot model and the elastic circumferential wave theory, the precise prediction model of the distance-angle echo in time domain is proposed. The results show that the main factors that affect the strength of the echo include the mirror reflection and the angular reflection. The additional bright spots and circumferential waves generated by the fine structures such as valves and spherical cap have a non-negligible influence on the frequency response characteristics in different azimuths. The validity of the echo prediction and resonance frequency characteristics is verified by the lake experiment in monostatic mode.
The local scour around a circular array of cylindrical piles through physical model was studied under the live-bed condition, concerning the effect of porosity of the structure on the local scour development. The porosity of the model was achieved by varying the number of single piles, while the outer diameter of pile groups was kept as a constant. The effect of porosity on the equilibrium scour depth, the scour extent, and the time scale of scour was examined. It is found that the scour around the pile group is significantly affected by the porosity of the structure. As p>0.7, the resultant scour is mainly determined by the scour around each individual pile. As p<0.5, the scour is characterized by the pattern of one single pile with the same outer diameter as the pile group. As 0.5<p<0.7, the scour shows a pattern of transition from local scour to global scour. It is also found that the normalized equilibrium scour depth is a power function of p, with a power of approximately 0.67.
In order to transiently solve the transient movement of sediment particles in dredge pumps, a modified algorithm is realized based on the discrete phase model in ANSYS Fluent. The granular phase volume fraction solved by using the Eulerian (granular)-Eulerian (liquid) two phases flow method and the Huilin-Gidaspow drag force laws are introduced for tracking particles with the Lagrangian method in dense flow. The solution process that solves particle motion after updating the impeller grid is changed to a process that solves particle relative motion after rotating synchronously the impeller grid with the particles. Under the situations of moving wall, the modified algorithm avoids the calculation error on collision identification and rebounded velocity of the particles. A comparison of numerical results shows that the modified algorithm can significantly improve the accuracy of particle motions in the dredge pump with similar time cost. The erosive wear predicted by the modified algorithm mainly appears on the front edges of the blades and the peak of erosion rate is about 7×10-5 kg/(m2∙s), which is similar to the actual situations, supporting the effectiveness of the modified algorithm.
The difference in the water migration and the deformation characteristics of silty sand and clay in the freezing process cannot be ignored when the artificial ground freezing method is used in coastal complex strata consisting of clay and silty sand, and is also the root cause of current engineering accidents caused by freezing. In order to find out the difference of the water migration and the deformation characteristics between the silty sand and clay, a self-made single side freezing instrument was used to conduct a series of freezing tests of original silty sand of ②3 layer and the remodeled clay of ④ layer in Shanghai at a freezing temperature of -20 ℃, -15 ℃, and -10 ℃. The results show that the deformation curves can be divided into steep curve I(silty sand) and gradual curve II(clay). The deformation curves of different layers of clay soil sample fluctuated greatly with time. The results indicate that water migration is fully developed inside the clay during the freezing process, while most of the water inside the silty sand freeze quickly and thus water migration is not developed as obvious as that inside the clay. In addition, the deformation curves of the two types of soils is consistent with the distribution changes of water inside the silty sand and clay after freezing. Based on the research results, specific suggestions can be made for the relevant measures to deal with engineering problems such as frost heave in the practice of the freezing method for coastal complex strata consisted of silty sand and clay.
The overburden of rockfill dams has complex soil types, loose structures, and sometimes lenses, which make the material parameters of the overburden have spatial variability, and the impact of earthquakes on the stress and deformation of the dam foundation cut-off wall cannot be ignored. Under the framework of Monte Carlo, by using the Gaussian spatial random field discrete method of Cholesky decomposition, the secondary development of Abaqus with Python is used to realize the “non-invasive” stochastic finite element analysis of the spatial variability of the overburden material. The research results show that considering the spatial variability of the cover material, the stress and deformation of the different parts of the cut-off wall have different degrees of excess, and the coefficient of variation of dynamic stress is greater than that of the dynamic displacement, indicating the variability of the material parameters of the cover is more sensitive to the stress changes of the impervious wall under the action of earthquake. Therefore, this uncertainty should be considered in the design stage to ensure the safe operation of the dam foundation impervious wall.
A yield criterion for the steel-concrete-steel (SCS) unit panel subjected to in-plane membrane forces is proposed, which is expressed in the in-plane (principal) stress space and follows the Tresca yielding principle for steel plates. This yield criterion for the SCS unit panel is based on the Navier’s three principles (equilibrium conditions, strain compatibility, and the constitutive laws of materials). A calculation method for determining the yield load of the SCS unit in combination with the test data is proposed, and the method is applied to the bidirectional tensile and compression test of the SCS unit. By using this method, nine SCS tested panels with different steel ratios and different tension compression ratios are analyzed, and the yield criterion of the SCS unit is compared with the test results. In addition, seven SCS shear specimens tested by Ozaki are used for further verification. The results derived from the yield criterion of the SCS panel elements are found in good agreement with the test results.
In order to directly solve the horizontal dynamic response of a single pile under the condition that the shear modulus of the soil around the pile varies linearly with the depth, a method for solving the horizontal dynamic response of piles in nonhomogenous foundation is proposed based on the layered generalized Gibson foundation and the Adomian decomposition method. Compared with the initial parameter method and the transfer matrix method, the proposed method does not need to discretize the nonhomogeneous foundation. Compared with the numerical method, it has the advantages of low computational cost, high accuracy, and fast convergence speed. The correctness and rationality of this method are verified by comparing it with the calculation results of the layered method, the analytical method of homogeneous foundation, and the numerical method. The influence of boundary conditions on the pile bottom, soil parameters, and pile slenderness on the horizontal dynamic response of the pile is investigated. The result show that in nonhomogeneous foundation, the pile-soil elastic modulus ratio is an important factor affecting the horizontal dynamic response of pile. As the shear modulus of soil increases, the amplitude of horizontal displacement of the pile decreases, and the distribution tends to be gentle. In addition, compared with other parameters, Poisson’s ratio and damping ratio of soil have less influence on the horizontal dynamic response of pile.
In order to study the one-dimensional (1-D) consolidation behavior of double-layered saturated porous-fissured clay foundation, the governing consolidation equations of saturated porous-fissured media were developed based on the mixture theory under the condition of one-dimensional complete confinement. The finite element program for 1-D consolidation of saturated porous-fissured clay was compiled by Fortran language, and the results of single-layered foundation research were used to verify the correctness of this model and program. The influences of compression modulus, permeability coefficient, and soil thickness on the consolidation behavior of double-layered saturated porous-fissured clay foundation were analyzed by using the finite element program. The results show that the consolidation rate of the foundation can be significantly accelerated by increasing the compression modulus and permeability coefficient of the softer topsoil, and the dissipation laws of excess pore water pressure and excess fissure water pressure were different. The dissipation of excess pore water pressure at the base of the foundation would lag behind that of excess fissure water pressure, and the lag would increase with the increase of the permeability coefficient of topsoil. For double-layered saturated porous-fissured clay foundation, improving the softer porous-fissured clay properties of the upper layer can better improve the consolidation behavior of the foundation.
The acceleration and deceleration movement of the metro near the metro station have a certain impact on the foundation soil. After the soil has been sloped and sampled, a dynamic three-axis undrained dynamic test is conducted to study the influence of the distance of the metro station, acceleration, dynamic stress amplitude, and consolidation confining pressure on the cumulative plastic deformation of saturated soft clay. The results show that the cumulative plastic strain curve of soft clay at variable frequency cyclic loading in and out of the station can be roughly divided into three stages: explosive growth, rapid growth, and gradual stability. The increase in the distance from the metro station, the increase in the amplitude of the dynamic stress, and the decrease in the consolidation confining pressure can reduce the number of entry and exit times required for the soil to enter the gradual stabilization phase, increase the vertical deformation of the soil, and reduce the shear deformation. As the acceleration value in and out of the station increases, the vertical deformation of the soil decreases but the shear deformation increases. For the actual project, the initial stage of metro operation, the settlement deformation of the soil in the inbound section, the horizontal displacement of the soil in the outbound section, the horizontal displacement under the larger acceleration condition, the settlement under the smaller acceleration condition, the high dynamic stress amplitude, and the soil area with a low consolidation stress are the focus of engineering geological disaster prevention.
In order to study the movement mechanisms of plain weave fabric yarns, the numerical simulation of behavior of yarn pull-out and movement under various loading conditions was carried out on a typical plain-woven fabric. The effects of friction coefficients, model size, and pre-stress levels on yarn movement responses were analyzed in detail, and the coupling relation among pull-out length, pull-out fractured strength, and model parameter conditions, including friction coefficients and pre-stress levels were shown. The results indicate that positive correlations exist between peak pull-out loads and those main model parameters of plain weave fabrics, including the friction coefficients, model size, and pre-stress levels. As the pre-stress level rises from 200 MPa to 700 MPa, the peak pull-out load increases by 34.49%, and the existence of yarn crimps could lead to improvement of the pull-out loads. The pull-out fractured strength of yarns gradually increases with the growths of pre-stress levels and friction coefficients in the plain weave fabrics. Specifically, the pull-out fractured strength of yarns increases by 16.48% as the friction coefficient grow from 0.1 to 0.2. In addition, the pull-out fractured length of yarns of the plain-woven fabrics is highly dependent on the actual stress state, and the homogenization of the stress state is an important factor that influences the pull-out fractured length.
The soil unloading effect caused by the adjacent excavation will influence both the uplift and the deformation of the adjacent existing tunnel, and even interfere with the normal operation of the tunnel. A simplified calculation method for the longitudinal deformation of the underlying tunnel caused by foundation pit excavation is proposed. The tunnel is simplified into an infinitely long Euler-Bernoulli beam resting on a three-parameter Kerr foundation model. The difference method is combined with the boundary conditions at both ends of the tunnel to obtain the longitudinal deformation difference decomposition of the tunnel. The accuracy of the proposed method is proved by comparing it with the finite element simulation method and some cases study. Compared with the tunnel simplified as the Euler-Bernoulli beam which is placed upon the existing Pasternak foundation model, the Kerr foundation model has more advantages. As the elastic modulus of soil mass and the depth of tunnel axis increase, the longitudinal deflection and the inner force of the tunnel will decrease. The inner force of the tunnel will increase with the increment of the stiffness of the tunnel.
The superstructures of offshore platforms are usually complex in shape, and wind tunnel test is the most reliable method to obtain the wind loads. Few researches about the procedures of uncertainty analysis (UA) and key points have been conducted, and the influences of error sources are not clear. The UA of an offshore platform wind load tests is first performed based on the International Towing Tank Conference (ITTC) recommended procedures. According to the wind load test procedure of the offshore platform, the uncertainties due to many error sources are analyzed. In order to obtain the remark of all error sources and propose the approach of reducing uncertainties, error sources are evaluated and graded. The results show that the wind profile, the accuracy of the model, the air pressure measurement, and the balance measuring state have a great influence on wind load coefficients, which contribute to 96.13% of the combined uncertainty. The uncertainties can be effectively reduced by model simplification, high quality wind profile, high precision air pressure measurement, and stable measurement state.
In order to study the application characteristics of the peridynamics (PD) method in the field of ice mechanical behavior and the sensitivity analysis of parameter changes in the numerical prediction of ice failure, the ordinary state-based peridynamic method is employed to systematically analyze the impact failure process of cylindrical ice in the present work. The results show that the simulated ice impact process by the proposed method is basically consistent with the test results, and the calculation results converge under the selected time step and particle spacing. The impact velocity, Poisson’s ratio, and the elastic modulus of the ice have remarkable effects on the impact process of ice cylinder, while the size and fracture toughness of the ice only have little influence. The innovation of this paper lies in the fact that the state-based PD method is applied to study the ice impact problem, which compensate for the shortcomings of the bond-based PD method that limits the Poisson’s ratio of the ice.
Large-scale marine equipment will overheat if it works for a long time and a cooling system is necessary to be established to ensure that the equipment works in a safe range of temperature. To meet the cooling requirements of a large-scale marine equipment, a model of seawater cooling system is established in FloMaster, and simulations under dynamic conditions are conducted. According to the temperature of the coolant (glycol solution) in the front or back of the room of the heat exchanger, the pump speed or valve opening is changed to realize automatic control of seawater flow. Three control schemes are proposed, and the control effects are evaluated by the response characteristics and operating characteristics of the system under variable working conditions using the FloMaster-Simulink co-simulation method. The results show that when the pump speed is controlled by both the open loop and closed loop, the best control effect and lower energy consumption can be achieved.
Ocean resource exploration expands into deep and ultra-deep waters, which has posed great challenges to the 6-DOF parallel platform that requires to finish the long-span and high-velocity wave compensation task with high precision and anti-interference ability. The control strategy employed in the asymmetric hydraulic system of large aspect ratio requires more careful considerations when operating in the harsh and severe environment. An adaptive feedback linearization control strategy was proposed by employing the radial basis function neural network (RBFNN) for identification. First, a nonlinear model of the asymmetric hydraulic system was established. Then, an adaptive controller was designed based on RBFNN and feedback linearization. Finally, simulations were performed by using MATLAB/Simulink under the five-stage wave environment at a 90° wave encounter angle and under the external interference condition. The result shows that this method has a good traceability and robustness compared to classic PID and sliding mode control methods, which is more suitable in control of the wave compensation platform in complex sea conditions. The new controller can significantly increase the compensation accuracy and anti-interference ability, and provide a workbench for the 6-DOF parallel platform operation in deep waters.
