The changes in the status parameters of the thermal system reflect the operating status of the system in real time. The forecast results of the trend extraction and time series prediction of the current equipment status parameters can be used as a reference for the next operation management strategy and equipment maintenance, which can be used for the long-term system safe and stable operation. In this paper, a method which is described as MWSA, based on the midpoint and regression based empirical mode decomposition (MREMD), the wavelet threshold denoising (WTD) and midpoint and techniques, the singular value decomposition (SVD) and optimized parameter permutation entropy (PE), and an auto regressive integrated moving average model (ARIMA), is applied to the single-parameter time series prediction of thermal systems. First, the MREMD is used to decompose the monitored operating state parameters into a number of intrinsic mode functions (IMF) and residual components. Next, the components that do not meet the screening conditions are subjected to wavelet thresholding. The denoised components and the components that originally meet the filtering conditions are recomposed into new IMF components. Finally, the K-means clustering algorithm based on SVD and PE is used to classify the recomposed IMF components, the component with a lower entropy value is selected and reconstructed into a trend item, and ARIMA is used to predict. An actual case verifies that this method can effectively overcome the interference of high-frequency noise in the original parameter timing, and the prediction accuracy is higher than that of similar methods without noise reduction treatment.
Electric heat tracing is often used for cold protection in polar ocean engineering equipment. Heat balance is the key problem of convective heat transfer. In this paper, the circular tube structure is taken as the research object. Numerical simulations using Fluent and model experiment are conducted to analyze the change of the convective heat transfer coefficient of the circular tube component under the polar environment with a wind speed range of 0—40 m/s and a temperature range of -40—0 ℃. Based on the numerical simulation data, the prediction model of the convective heat transfer coefficient of the electric heating tube is obtained. The results show that the convective heat transfer coefficient increases with the increase of wind speed and the decrease of temperature. When the temperature is below -30 ℃, or when the wind speed is greater than 25 m/s and the temperature is lower than -20 ℃, the influence of temperature on the convective heat transfer coefficient increases. The rationality of the model is verified by experimental test.
Ship block transfer is important to the orderly flow of blocks between crafts, which is costly. Shipyard managers have to monitor the actual transfers, especially the unproductive transfers that occur when blocks are obstructed or reworked. A high-load shipyard, called S, often uses one site for multiple purposes, and the difficulties in obtaining the state of ship blocks through the time-site data of blocks provided by the existing monitoring technology make it difficult to monitor two types of unproductive transfers. To address this problem, four hidden Markov models whose parameters are calculated by a supervised approach are proposed, and a Viterbi algorithm based method is proposed to identify the state of blocks, achieving an accuracy of up to 93.5% on the test dataset. One of the hidden Markov models is applied to the time-site data of blocks to monitor two types of unproductive transfers in shipyards. Preliminary suggestions for improving the blocks transfer process based on monitoring results are proposed.
By establishing a quantitative analysis method of relative humidity, pore solution saturation, and corrosion reaction rate of concrete, the influence of environmental relative humidity on the mechanical properties of glass fiber reinforced polymer (GFRP) in seawater sea-sand concrete environment has been studied. Based on the pore size distribution of concrete and the surface tension formula of pore solution, the relationship between the relative humidity and pore solution saturation of seawater sea-sand concrete is established. It is assumed that the pore solution is uniformly smeared in concrete. Therefore, the concentration of corrosive ion OH- can be obtained. The corrosion rate and strength retention rate of GFRP bars under the action of OH- are evaluated using the etching model. The accuracy of the current method is verified by experimental results. Based on the climate statistics of some coastal cities in China, the influence of relative humidity on the strength retention rate of GFRP bars in seawater and sea sand concrete environment is predicted under the conditions of representative ambient temperature and water-cement ratio. The increase of relative humidity promotes the performance degradation of GFRP bars. According to relevant standards, the relations between relative humidity and service life of GFRP bars in seawater sea-sand concrete environment have been predicted.
There is a strong real-time coupling between seabed topography and wave field, current field and wind field in shallow water area. The existing analysis model cannot directly consider the influence factors of seabed, and it is more difficult to explain the unsteady evolution mechanism of the coupling field between typical seabed topography and wave, shear flow and gradient wind. Based on the secondary development of STAR-CCM+platform, the shallow sea wind-wave-current numerical pool is constructed under four typical seabed landform conditions: seabed plain, seabed slope, trough, and flat landform. The multi-layer particle velocity coupling method is proposed and the multi-layer wind-wave-current coupling model is established. The wind-wave-current decoupling is realized at the initial time. The temporal and spatial evolution laws of wave field, current field, and wind field in different seabed topographies are compared and analyzed. The principal component analysis method is introduced to evaluate the unsteady effect of wind-wave-current in various typical seabed topographies, and the unsteady evaluation index of the whole life cycle of the wind-wave-current-seabed coupling field is established. The results show that the multi-layer wind-wave-current coupling model can more truly reflect the influence of vertical wind speed and uneven velocity distribution on wave field. The seabed topography can lead to a multi-stage time-history distribution of wave field in the evolution process. The flat topography, submarine slope, and trough conditions are divided into wave surface surge, attenuation, and stability stages. The submarine plain conditions are divided into external breaking wave, internal breaking wave, and climbing stage. The evolution of the current field presents a multi-stage spatial distribution, and the seabed leads to the formation of multi-vortex accumulation or multi-vortex coexistence in the current field. The coupling evolution of wind-wave-current-seabed has an amplification effect on the wind profile index, and positive relationship between seabed height and wind profile coefficient. The end-stage unsteady evaluation indices of flat landform, submarine plain, submarine slope, and trough are 0.268, 4.612, 0.672, and 0.926, respectively.
An experimental investigation is conducted to study the hydrodynamic responses of cylinder floating production storage and offloading (FPSO) subjected to heading short-crested waves of different spreading parameters. The motion response and mooring dynamics of cylinder FPSO are analyzed and the results are compared with those from the long-crested waves. The simulation experiment shows that the short-crested waves induce smaller surge motions and mooring tensions, but generate bigger sways and roll motions compared with those of the long-crested waves. There are statistically significant differences in hydrodynamics of cylinder FPSO between short-crested and long-crested waves. The research results provide important references for further study of short-crested waves and their interaction with ocean engineering structures.
Fenders play an important protective role in ship collisions, but there are few studies related to the collision simulation methods and the protection mechanism of composite fenders. First, aimed at the new composite fender design scheme proposed in this paper and based on the material properties exhibited in the test, low-density foam and hyperelastic models are selected to simulate the inner foam and outer polyurethane of the fender, respectively. Subsequently, for the hull-fender-quay collision problem, a multi-body geometry model is established and a collision simulation method is formed to analyze the fender protection mechanism from the perspective of energy conversion. It is proved that the composite material has a better protection effect on the hull structure than the rubber fender. Finally, the inner foam strength, hull stiffness, outer polyurethane thickness, and tensile strength of composite materials are varied to analyze the protection mechanism of composite materials respectively. The results show that the relative stiffness of the fender and the structure is the main factor affecting the protection performance. The inner foam of the composite fender is the main energy-absorbing structure, absorbing the kinetic energy of the hull through compression deformation to reduce the response of the structure, while the outer polyurethane mainly plays the role of protecting the core.
A novel method for optimal design of hydrodynamic performance of bionic propeller with a deformable leading edge is proposed. Based on the bionics principle and method of parameterized modeling, the fore-fin concave-convex structure of humpback whales is applied to the propeller leading edge, the leading edge in the propeller to meet flow region according to the exponential decay curve and the standard sine curve smooth leading edge for similar humpback fins protuberant structure of concave and convex deformation, and the leading edge of concave and convex bionic propeller. The hydrodynamic performance, the cavitation performance, and the noise performance of the exponential decay bionic propeller and the sinusoidal function bionic propeller were simulated respectively. The propeller with a better performance is selected, and the simulation based design (SBD) technology is introduced into the optimization design of the new bionic propeller. The parameters controlling the shape of the exponential attenuation curve of the guide edge deformation are taken as optimization design variables, the torque of the parent propeller is taken as the constraint condition, the open water efficiency is selected as the objective function, and the optimization algorithm of Sobol and T-Search is adopted. A bionic propeller optimization system based on the exponential decay curve is constructed. The results show that the application of the concave and convex structure of the humpback whale fore-fin to the guide edge of the propeller improves the cavitation performance and noise performance of the propeller, but the improvement of the open water performance of the propeller is not particularly significant. It is verified that the hydrodynamic performance optimization design method of the bionic propeller established in this paper is effective and reliable, which provides a certain theoretical basis and technical guidance for the performance numerical calculation and configuration optimization design of the bionic propeller.
Based on the nonlinear geometric relationship of the bulging angle and the bending angle, and the principle of virtual work and nonlinear constitutive relationship of Neo-Hookean incompressible hyperelastic material, a quasi-static mechanical model for pneumatic toothed soft actuator was established, considering the strain energy of the bottom, side walls, and front and rear walls. Considering the geometric nonlinearity and material nonlinearity, the proposed model could solve the configuration of the soft actuator at different driving pressures and terminal loads precisely and efficiently. The finite element simulation of the cantilevered-free soft actuator was conducted by Abaqus, and the corresponding experimental device was established. The simulation analysis and experimental investigation were performed at different driving pressures. A comparison of the results show that there is a positive linear correlation between the driving pressure and the bending angle of the soft actuator, and the prediction of the theoretical model agrees well with the simulation and experimental results. In addition, the distribution of the strain energy was analyzed. Based on the equal-curvature model, the configuration results of the soft actuator at terminal loads are basically consistent with those obtained by Abaqus. The proposed quasi-static mechanical modeling method provides a theoretical basis for the structural optimization design, performance improvement, and motion control of similar soft actuators.
Aimed at the short-term extreme value prediction of ship motion, a sliding window method based on motion spectrum information is proposed to extract feature data, based on which, a series prediction model of convolutional neural networks (CNN) and long short-term memory (LSTM) is built. The CNN module aims at the local correlation characteristics of the input data, and the LSTM module aims at the time dimension characteristics of the data. The simulation test results of S175 ship show that the model has a good prediction effect on the motion extremum information in the next 1 and 2 cycles, and the evaluation indexes are significantly better than those of LSTM and gate recurrent unit (GRU) models, which has an important application value.
Based on the immersed boundary method, a resolved CFD-DEM algorithm is proposed to tackle fluid-solid interaction problems which widely exist. In the proposed method, the fluid filed is described by the computational fluid dynamics in the Eulerian framework, while the movement and collision of the solids are simulated by the discrete element method in the Lagrangian framework. In order to deal with the moving interfaces between the fluid and the solids, several immersed boundary points are allocated on the boundaries of the solids. Two classic test cases are calculated to verify the accuracy of the proposed method, including the vortex-induced vibration of a cylinder and the rotational galloping of a rectangular rigid body. Good agreements are achieved between the current results and those in previous references and the reliability of the present method in modelling the fluid-solid interaction problems are proved. Finally, the sedimentation of multiple solids is simulated and the ability of the proposed CFD-DEM method in solving the complex fluid field and the collision among the solids with arbitrary shapes are verified.
In order to solve the problem of graphics processing unit (GPU) memory access conflicts possibly caused by the disorder of particles and enhance the computation efficiency, an improved GPU acceleration strategy is proposed by establishing particle reorder technology. The acceleration strategy is applied to the smoothed particle hydrodynamics (SPH) method to simulate the dam breaking with obstacles in three dimensions, and the algorithm is verified by comparing with the experimental results, which obtained a high calculation accuracy. Based on this benchmark example of the SPH, the studies on the effect of particle renumbering and the solution efficiency of the algorithm are conducted by comparing the simulations of different hardware facilities. The results indicate that the particle reorder technology can ensure a stable single-step running time, and can effectively solve the problem of graphic card memory access conflicts that commonly exist in the GPU-SPH algorithm. Furthermore, the GPU parallel algorithm can greatly improve the solution efficiency of the SPH method, and with the increase of particle number, the advantage of drastically reducing the computation time becomes more obvious. The method proposed in this paper provides the possibility to expand the application of the SPH method to solve 3D numerical simulations.
Pile-supported wharf (PSW) is widely used in the deep-water port engineering construction, most of which are located in liquefiable ground. The effect of wave action on the working performance of PSW in liquefiable ground cannot be ignored, but few studies have been reported. This study performs the wave flume test of PSW in liquefiable ground considering the soil-structure-wave interaction. This test really reproduces the operating condition of PSW, and explores the internal response difference of wharf structure under wave. The influence of wave height on dynamic response of the PSW system is discussed systematically. The result shows that the acceleration and displacement of the PSW deck gradually increase first and finally remain relatively stable with the increase of wave action. The hydrodynamic pressure and deformation of each pile in pile group are obviously different, and the response variation is related to the pile position. The pore pressure of the soil layer in the free field and around the pile decreases with the increase of depth, and the existence of the pile group can reduce the pore pressure in the soil layer around the pile, and increase the acceleration of the soil layer. The effect of wave height on the soil layer decreases with the increase of depth. The above results can provide reference for the similar PSW test under wave and the support for the design and wave protection of PSW.
In recent years, offshore wind turbines show the trend of large-scale development, the installation area of which has been expanding to the deep and far-reaching ocean. However, due to the harsh environmental conditions in the far-reaching ocean region, the traditional rotor-lifting method is facing many limitations. In contrast, the single blade installation technology has significant advantages in installation efficiency and safety, and has gradually become a new research hotspot. Based on the characteristics and difficulties of the offshore single blade installation technology, this paper investigates and summarizes the lifting equipment and key technologies involved in single blade installation section, including blade yokes, the single blade installation dynamic simulation model, and the active control technology. Among them, the research and development of novel single blade installation equipment and methods with active control technology are essential for large-scale offshore wind turbine installation in the far-reaching ocean region. Additionally, based on the development trend and prospect of offshore blade installation and the docking technology, it introduces some technical ideas, including single blade yoke with dynamic positioning function, and double hoop blade vertical installation auxiliary device, which are expected to solve the installation problem of large-scale offshore wind turbines.
Considering the nonlinear changes of compressibility and permeability of soft soil around the tunnel, a two-dimensional nonlinear seepage consolidation control equation is established, which is solved by an alternating implicit difference method, and the development law of the average degree of consolidation with time under the three conditions of complete permeability, complete impermeability, and semi permeability of the tunnel is obtained. By comparing the degenerate solution with the existing analytical solution, the correctness of the difference solution is verified. In addition, the effects of compression index Cc and permeability index Ck on the consolidation degree of soft soil around the tunnel are analyzed. The results show that the permeability of tunnel is an important factor affecting the development and change of consolidation degree. The influence of compression index Cc on the development of degree of consolidation is less than that of permeability index Ck. Seepage consolidation will change the effective stress field of the soil around the tunnel, and the average degree of consolidation decreases with the increase of permeability index Ck. If the nonlinearity of soil is not considered, there will be a large error in the calculation of degree of consolidation.
The cavity expansion theory is widely used in the analysis and prediction of cone resistance and lateral displacements in cone penetration test (CPT) and pile installation. Nowadays, the existing theoretical solutions for cavity expansion in structured clay cannot consider the influences of structure degradation on the mechanical behaviors of soil during the expanding process, which limits its applications in practical engineering to some extent. Therefore, taking the penetration of cone or pile tip as a spherical cavity expansion process in soil, based on the structured Cam-Clay (SCC) model and the large strain theory in plastic zone, the undrained spherical cavity expansion problem could be attributed to a boundary value problem of a system of ordinary differential equations about effective stress components. The equations then could be solved with stresses on the elastic-plastic boundary serving as boundary conditions. The results show that, with strengthening of soil structure, the plastic and critical state zones narrow, the internal cavity stresses increased, and the softening behavior and dilatancy of over-consolidated soil become more significant. For structured clay with the same initial stresses, the effective stress components adjacent to cavity wall overlap with that of the corresponding reconstituted soil, which indicates that the degradation of soil structure occurs during the soil-disruption accompanied expansion process. Finally, the internal cavity stresses derived from the proposed solution were used for theoretical calculation of cone resistance and pore pressure in CPT. A comparison of the existing solution with the results calculated indicates that the results obtained with consideration of soil structure are closer to the measured values.
When pumping in confined aquifers, vertical leakage could be found in the multi-aquifer system in soft deposits, and the responses of groundwater flow and strata deformation are complicated. Based on pumping tests in an ultra-deep underground project, this study performs a 3D finite-difference modeling to investigate the responses of groundwater and strata to pumping in the second and third confined aquifers. It considers the hydro-mechanical coupled and small strain stiffness characteristics of soils in the analysis, and discusses and compares the spatiotemporal distribution characteristics of drawdown and deformation induced by pumping in different confined aquifers. The results indicate that the ground settlement induced by pumping in the second confined aquifer is greater though the groundwater drawdown is smaller, and the compression of dewatering aquifers caused by dewatering in the second and third aquifers accounts for 56.18% and 77.69% of the settlement, respectively. It could be attributed to the connectivity between the second confined aquifer and its overlying aquitards, which results in a greater influential depth. In addition, the compressibility of shallow strata is significantly greater than that of deep strata. The study is significant for the dewatering construction and environmental deformation control of ultra-deep excavations.
Wave run-up and air-gap are key issues for the safety of semi-submersible platforms. Real-time wave run-up prediction is helpful to ensure the safety of offshore activities. Based on the long short-term memory (LSTM) network, the extreme short term online prediction method is developed for predicting the wave run-up of semi-submersible platforms using wave and motion sequences. With the help of large sets of data from the model test, the LSTM model is trained and tested. The study shows that when the forecast durations are 6 s and 12 s, the average accuracy of the prediction results are 92.90% and 84.09%, and the relative errors of the maximum wave run-up height are lower than or equal to 19.69% and 30.66%, respectively. In addition, the model has a stable and exact prediction of extreme values of wave run-up height when the forecast duration is within 6 s, which confirms its ability to provide valid technical support for the early warning of wave slamming and overtopping during the operation of offshore platforms.
The hydrodynamic characteristics of a propeller under the crashback condition are closely related to the crash stopping ability of a ship, which directly affect the ship navigational safety. In this paper, a numerical study on the hydrodynamic characteristics of a propeller and the flow field around the propeller under the crashback condition is conducted based on the Reynolds-averaged Navier-Stokes solver in the open source computational fluid dynamics platform OpenFOAM. Taking the 5-blade propeller DTMB4381 model as the study object, the ahead and crashback conditions are numerically simulated. The numerical results are compared with international open model test data to validate the effectiveness of the numerical method in the prediction of the hydrodynamic characteristics of the propeller under different conditions. Based on the obtained hydrodynamic loads and flow field details, the local flow field characteristics changing with the advance velocity and the relation between the local flow fields and the global hydrodynamic forces are explored, which provides theoretical basis for the evaluation of ship crash stopping ability.
In order to improve the accuracy of velocity formulation in a Boussinesq-type wave model, with a two-layer Boussinesq-type model with the highest spatial derivative of 2 being chosen as the research object, a third-order term with constant coefficient is proposed to modify the velocity formulation. The coefficient is optimized by minimizing the error between the summation of the integration of horizontal and vertical velocities of the equation and that of the analytical linear Stokes wave velocity components in the range of 0<kh< 8 (where k is wave number, h is still water depth). At a 1% tolerance error, the applicable water depths of the modified formulations for horizontal and vertical velocities are up to kh=7.34 and kh=7.83, respectively, which are larger than those of the original formulations. The evolution of the steady-state wave and the focused wave is numerically simulated by using the numerical model. The horizontal velocity under the maximum surface elevation crest is in good agreements with the analytical solution of stream function and published experimental data, which verifies the effectiveness of the modified formulations. The studies show that the velocity accuracy of the improved equation is greatly improved. This method provides an important reference for the improvement of velocity field of other Boussinesq-type models.
The research on large-scale offshore vertical axis wind turbine is of great significance to the development of ocean wind energy. For the safety of wind power, it is very important to study the reasonable supporting structure of the large-scale wind turbine. In this paper, an supporting structure optimization of a large-scale vertical axis wind turbine based on the variable deletion rate bidirectional evolutionary structural optimization (BESO) algorithm is proposed, and the reliability of structural optimization is verified by analyzing the dynamic response. The results show that this inverse proportional BESO algorithm can effectively improve the optimization iteration rate, and has a wide applicability to the optimal design of vertical axis wind turbine supporting structure. Compared with the initial structure, the wind-induced dynamic response of the topological new structure model under wind load is significantly reduced. The findings can be used to optimize the structural design of vertical axis wind turbine.
In order to explore the wake characteristics of non-ducted and ducted propellers in oblique inflow with a large drift angle, based on the delayed detached eddy simulation, a numerical simulation of non-ducted and ducted propellers in oblique inflow is conducted with an advance coefficient (J=0.4) and a large drift angle (β=45°, 60°). It is found that the deflection degree of the non-ducted propeller wake is higher than that of the ducted propeller. However, the overall distribution area of the wake vortex behind the ducted propeller is kinked. The wake field in the oblique flow shows its complexity, and the evolution process of vortices on the windward side differs from that on the leeward side. The above characteristic of the non-ducted propeller is more prominent. At the same time, the leading edge of the nozzle on the leeward side will produce local shedding vortices and transmit to the downstream due to flow separation. Part of the kinetic energy of the ducted propeller is converted into the nozzle thrust, which makes the turbulence kinetic energy of the wake lower than that of the non-ducted propeller. This phenomenon is more evident with the increase in the drift angle. Compared with the non-ducted propeller, the ducted propeller can maintain a better handling stability in large-angle oblique flow. This paper analyzes the influence of large-angle oblique inflow on the non-ducted and ducted propellers from the perspective of wake field characteristics and explores the theoretical basis for the ducted propeller to maintain a better handling stability in oblique flow.
A marine drilling riser at normal operation condition is required to disconnect the lower marine riser package (LMRP) and blow-out preventer (BOP) in case of severe weather. When the weather gets fine, it must reconnect the LMRP and the BOP. This process is called riser reentry. Marine drilling operations have been driven into extreme deep-waters characterized by severe weather which inevitably leads to a much higher incidence of disconnection. In addition, it requires to accomplish the reentry in a fast way owing to the capricious ocean environment. This study tries to develop a novel reentry control system based on model predictive control (MPC). First, the transverse governing equation of the hanging-off riser system with an end-mass is established based on the modified Hamilton’s principle. The optimization function and constraints in MPC are designed by use of the riser prediction model and the target location. A nonlinear disturbance observer is established for compensation of the model uncertainties and ocean environment disturbances. Finally, simulations are conducted after introducing the dynamic position system (DPS). The riser dynamics employing MPC are compared with that when adopting proportional-integral-derivative (PID) controller. It has found that the drilling riser system based on MPC has a higher response speed, which can complete the reentry process in a faster and more stable manner. It can handle the hydrodynamic force model uncertainties well and has a good robustness for current velocity disturbances. As the flexibility of the riser system is notably enhanced with the significant increase of aspect ratio, the higher-order mode of the flexible hanging-off riser can be triggered in the fast reentry process subjected to the excitations of the mother vessel and ocean environment.
Low power efficiency is a critical factor that restricts the engineering application of the vertical axis wind turbine (VAWT). In order to improve the efficiency of VAWT and reduce aerodynamic load, an improved aerodynamic performance optimization model for a large VAWT with trailing edge flaps at a medium tip speed ratio (TSR=2.65) is proposed. A numerical simulation is conducted using the SST k-ω turbulence model. The results indicate that compared with the base model, the power coefficient of the model under the synergic motion of pitch and flap can be increased by 12.2%. In addition, the synergic motion of pitch and flap can significantly reduce the thrust and lateral force on the VAWT, which are reduced by 12.4% and 7.5% respectively compared with the base model. The load fluctuation of thrust and lateral force is also significantly lower than that of the base model, which is helpful to reduce the fatigue load on wind turbine. This model is expected to be applied to MW-level VAWT.
The wavy deformed cross-section cylindrical structure has excellent properties of drag reduction in fluid flow, but the flow-induced vibration characteristics of flexible structure with such variable cross-section are still unclear. In this paper, based on the high-performance spectral element method, a fluid-structure coupled mechanistic model and a numerical algorithm for slender structures are established. The wake characteristics, structural dynamic responses, energy transfers, and spanwise variations of vortex shedding frequencies are discussed. The numerical simulation results show that slender structure with the wavy-deformed cross-section can greatly suppress the vortex-induced vibration response at an appropriate cross-section disturbance wave height, and the special vortex structure formed on both sides of the wavy-shaped slender structure can stabilize the flow around the shear layer and elongate the vortex formation length, thereby reducing the fluid-structure coupling effect between the wake structure and the slender structure, and suppressing the vortex-induced vibration response.
In order to study the effects of deep-sea complex and severe working conditions on the power device of deep-sea wading equipment, taking the contacting mechanical seal for deep-sea propeller as the research object, a two-dimensional axisymmetric finite element model is established. The influence of alternating conditions on the temperature rise of seal face is explored. The pseudo-real condition test of the mechanical seal is conducted on a self-built test rig, and the temperature rise of seal face is monitored. The surface morphology and wear characteristics are measured and analyzed. The results show that the alternating conditions have a significant influence on the temperature field of the seal ring, and the temperature rise of seal face shows an obvious alternating transient characteristic. After the alternating condition test, the end face roughness of the rotating ring increases significantly. The transient working condition makes the contact state between the seal faces unstable. Abrasive wear occurs on the end face, with obvious pits and densely distributed furrows of different depths. The alternating speed has a greater influence on the temperature rise and wear of the end face than that of the alternating medium pressure. The numerical simulation results are in good agreement with the experimental results, which provides a necessary theoretical guidance and experimental basis for the structural design of the mechanical seal of the deep-sea propeller.
The study of reliable support structure is of great significance to the safety of large-scaled horizontal axis wind turbine (HAWT) system. In this paper, for cap-supported HAWT with high pile, the bidirectional evolutional structure optimization (BESO) algorithm based on inversely proportional deletion rate was used to optimize its support structure. Using computational fluid dynamics (CFD) and the principle of pile-soil interaction, the finite element model of HAWT was established, where the wind load and pile-soil interaction were taken into consideration. The reliability of the structural optimization method was verified through the comparison of the dynamic response characteristics between the initial and the optimized model. The results show that the current BESO algorithm can effectively generate a novel support structure form for high-pile HAWT, whose dynamic response is significantly reduced. The results can provide useful references for HAWTs designs.
The membrane structure roof is widely used in large-span buildings such as stadiums and gymnasiums because of its full use of natural light sources and flexible forms. In order to solve the prominent problems such as poor thermal insulation performance and prone to external environmental factors, the multi-layer membrane structure design, laying of insulation layers, and other schemes are applied to engineering practice. However, there is still a gap in the relevant research of thermal environment monitoring and analysis. In order to study the thermal environment of the double-layer PTFE (polytetrafluoroethylene)-aerogel roof, multi-point thermometers were uniformly arranged to monitor, and the overall temperature field was constructed using the measured data. A thermophysical model which could accurately reflect the change of temperature field was established, whose average error was less than 5%. With the laying of roof insulation layer as the variable, three working conditions, i.e., no insulation layer, only rock wool insulation layer, and all aerogel insulation layer were constructed based on the model. The comparison indicates that the laying of aerogel reduces the average temperature of indoor space by 2.0 ℃, the original working condition has the best thermal insulation effect, and the average temperature difference between indoor and outdoor is 9.6 ℃. This paper can provide reference for the thermal insulation design of membrane structure roofs.
As a novel scour protection measure, the fluidized solidified slurry is pumped into the developed scour holes around the pile foundation for scour repair as the fluidized material solidifies gradually. In the process of pumping operation, the fluidized solidified slurry will have a negative effect on the pile. However, there is still a lack of comprehensive study on the force acting on the pile in this process. The CFD model is adopted to simulate the flow and diffusion of the solidified slurry pumped into the scour pit around the monopile. The effects of pumping velocity, current velocity, and material property of solidified slurry on the force acting on the pile are systematically investigated, of which, current velocity is the most sensitive factor. A simplified analysis method for force of fluidized solidified slurry acting on the monopile is proposed, providing basis for the design and construction of the pumping operation.
Based on the field measured data of a double-line parallel power pipe jacking upper span subway shield tunnel, the environmental impact of a short-distance double-line pipe jacking in sandy silt stratum in the process of crossing over the existing subway tunnel was analyzed in detail, including the transverse surface settlement distribution, the development of settlement with time, and the floating of subway tunnels. The results show that the horizontal surface settlement curve of single pipe jacking presents a “V” shape, while the horizontal surface settlement curve of double line pipe jacking is an asymmetric “W” shape. The settlement of ground surface above the axis of the later pipe jacking is larger than that of the first pipe jacking. During the construction of the later pipe jacking, the settlement above the axis of the first pipe jacking is also obvious. The Peck formula has a good applicability in predicting surface settlement curve caused by pipe-jacking construction. For single-line pipe-jacking, the width parameter of settlement trough is 0.79, and the ground loss ratio is 1.6%. For double-line pipe jacking, the width parameter of settlement trough of the first and later pipe jacking are 0.74 and 0.58 respectively, and the former is 1.28 times of the latter. The soil loss ratio of the first and the second pipe jacking are 2.41% and 3.11% respectively, and the latter is 1.29 times of the former. Pipe jacking causes the vertical displacement distribution curve of the “W” shape in the longitudinal direction of the underlying subway tunnel. There is a lag in the up-floating of the tunnel after the completion of pipe jacking crossing. The longitudinal influence range of the parallel pipe jacking construction on the subway shield tunnel is about 4~6 times the pipe jacking diameter. The instantaneous settlement generated by the later pipe jacking across the monitoring section is greater than that generated by the first pipe jacking. The permeability of the undisturbed soil is reduced when the silty soil above the tunnel is pre-reinforced by the metro jet system (MJS). The ground settlement will continue for a period of time after the pipe jacking crossing. The exponential function can be used to describe the development of the settlement with time after the instantaneous settlement occurs.
This paper investigates the ultimate capacities of domestic cold-formed stainless steel square and rectangular hollow sections (SHS and RHS) undergoing web crippling. The finite element (FE) software Abaqus was employed during the investigation. It verifies the validity of FE models against experimental results available in the literature and performs an extensive parametric study comprised of 224 FE analyses to obtain the web crippling capacities of cold-formed stainless steel SHS and RHS, considering various materials, cross-sectional dimensions, bearing lengths and loading conditions in the parametric study. Based on the obtained FE results, the applicability of existing web crippling design provisions to domestic cold-formed stainless steel SHS and RHS is evaluated. The results indicate that the technical code of cold-formed steel structures (exposure draft) cannot be used for the studied cold-formed stainless steel SHS and RHS. On the other hand, it is shown that the American Specification SEI/ASCE 8-22 and proposed direct strength method (DSM) can lead to safe and accurate design predictions. Therefore, the SEI/ASCE 8-22 and DSM can be used to predict the capacities of domestic cold-formed stainless steel SHS and RHS undergoing web crippling.
Aimed at the phenomenon of modal confusion and lack of practical significance of instantaneous frequency caused by Hilbert-Huang transform (HHT) noisy vibration signal time-frequency analysis, complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) is obtained by improving empirical mode decomposition (EMD), and in combination with multiscale permutation entropy (MPE) to suppress EMD modal confusion. At the same time, improved normalized Hilbert transform(INHT) is obtained by improving Hilbert transform, and finally the CEEMDAN·MPE-INHT time-frequency analysis algorithm is formed. In order to verify the accuracy of time-frequency analysis of CEEMDAN·MPE-INHT noisy vibration signals, a comparative study of time-frequency analysis of EMD-HT, EEMD-NHT, CEEMDAN-INHT and CEEMDAN·MPE-INHT noisy simulation vibration signals is conducted. The results show that CEEMDAN can control low frequency noise; MPE can suppress high frequency noise; INHT can make Hilbert transform not constrained by Bedrosian theorem. Finally, CEEMDAN·MPE-INHT algorithm is applied to the time-frequency analysis of noisy vibration signals in practical engineering. The time spectrum of intrinsic mode function (IMF) decomposed by CEEMDAN·MPE after INHT processing has a high resolution in time domain and frequency domain, which can improve the extraction accuracy of time-frequency characteristic parameters and help control the harm of vibration signals.
The slamming process of two-dimensional structures under free fall condition with arbitrary symmetrical shapes is investigated by combining various analytical models for slamming and the precise integration method in the time domain. By closely analyzing the mathematical expression of analytical models, the total slamming force acting on the body can be decomposed into two terms which are dependent on the velocity and the acceleration respectively. The developed model proposed in this paper is validated against the results from experiments and other numerical methods. Moreover, it is found that if the gravity of body is ignored, which is a reasonable assumption for situations such as structures with light weight or large entry velocity, the maximum acceleration (or the peak slamming force) for a free fall body will always occur at the certain penetration depth for a particular shape and mass, regardless of the initial slamming velocity.
Accurate evaluation of the vertical bearing capacity of the mat foundation on the clay seabed is of great significance for the safe operation of the mat-supported jack-up platform in the marine environment. Combining the centrifuge test and the coupled Eulerian-Lagrangin (CEL) large deformation numerical calculation method, the vertical bearing characteristics of mat foundation on horizontal and sloping clay seabed were studied. First, the distribution law of undrained shear strength of soil along the depth was obtained through the T-bar penetration test. Then, the vertical bearing characteristics of two kinds of bottom mat foundations on soft clay seabed were tested. Finally, the vertical bearing characteristics of the mat foundation were discussed in combination with the numerical method of CEL large deformation, and the bearing capacity and soil displacement changes of the foundation on different inclination seabed were analyzed. The results show that the foundation load displacement curve has no obvious peak value, and the bearing capacity of the square foundation is slightly higher than that of the rectangular foundation. The development law of soil excess pore pressure is basically consistent with the change law of bearing capacity in the process of foundation entering the sea bead, and most of the vertical stress is borne by the excess pore pressure. The foundation bearing capacity gradually decreases as the slope of the seabed increases, and the soil below the foundation tends to slip in the direction of the slope angle, which may lead to slip damage of the seabed. Therefore, operation in the seabed area with a large slope should be avoided in actual practice.
Efficient and accurate extreme short-term prediction is of great significance for the safety of ship and marine structures in actual sea waves. Due to the stochastic of actual sea waves, short-term prediction always uses time series analysis. The neural networks, particularly long short-term memory (LSTM) neural networks, have received increasing attention for their powerful forecasting capability in time series analysis. Based on this, an improved form of LSTM combining generative adversarial ideas is proposed, in which the frequency domain characteristics are embedded in the neural network to achieve coupled time-frequency domain information forecasting. The experimental test shows that the forecasting accuracy of this method is better than the results of traditional time series analysis methods and the LSTM neural network, and it is suitable for extreme short-term time series prediction for better ship maneuvering.
Based on the Foshan-Dongguan Intercity Line Changlong Tunnel Project, indoor tests and numerical simulations were conducted to study the instability and progressive failure process of the cutter replacement ground at atmospheric pressure. The fast Lagrangian analysis of continua method was adopted to establish the numerical model. The safety factor of the cutter replacement ground was analyzed, and the effect of the steel pipe pile-grouting method on the control effect of release and displacement was studied. The results show that the excavation face becomes unstable at atmospheric pressure, which causes soil loss and earth pressure release. As the cutter head moves backward, a large-scale vertical displacement of cutter replacement ground is gradually induced, and finally goes through to the surface. With the steel pipe pile-grouting reinforcement, the safety factor of the cutter replacement ground is significantly improved, and the ground stress release and displacement is effectively controlled. Compared with the grouting reinforcement, the steel pipe pile-grouting reinforcement has the advantages of short construction period and less pollution. Moreover, the steel pipe pile could be recycled without affecting the subsequent use of the soil, which provides a new ground reinforcement idea for the project.
