Application of GNSS-PPP on Dynamic Deformation Monitoring of Offshore Platforms

The real-time dynamic deformation monitoring of offshore platforms under environmental excitation is crucial to their safe operation.Although Global Navigation Satellite System-Precise Point Positioning(GNSS-PPP)has been considered for this purpose,its monitoring accuracy is relatively low.Moreover,the influence of background noise on the dynamic monitoring accuracy of GNSS-PPP remains unclear.Hence,it is imperative to further validate the feasibility of GNSS-PPP for deformation monitoring of offshore platforms.To address these concerns,vibration table tests with different amplitudes and frequencies are conducted.The results demonstrate that GNSS-PPP can effectively monitor horizontal vibration displacement as low as±30 mm,which is consistent with GNSS-RTK.Furthermore,the spectral characteristic of background noise in GNSS-PPP is similar to that of GNSS-RTK(Real Time Kinematic).Building on this observation,an improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise(CEEMDAN)has been proposed to de-noise the data and enhance the dynamic monitoring accuracy of GNSS-PPP.Field monitoring application research is also undertaken,successfully extracting and analyzing the dynamic deformation of an offshore platform structure under environmental excitation using GNSS-PPP monitoring in conjunction with improved CEEMDAN de-noising.By comparing the de-noised dynamic deformation trajectories of the offshore platform during different periods,it is observed that the platform exhibits reversible alternating vibration responses under environmental excitation,with more pronounced displacement deformation in the direction of load action.The research results confirm the feasibility and potential of GNSS-PPP for dynamic deformation monitoring of offshore platforms.

Characteristics of Saturated Soft Clay in Dynamic Deformation

-This paper presents the research results of dynamic pore water pressure and the characteristics of dynamic deformation of saturated soft clay and the factors affecting the dynamic pore water pressure and dynamic deformation. Dynamic triaxial compression tests are carried out and the soil samples used in the tests are remoulded clay from the seabed of the Bohai Bay. The paper also deals with the dynamic deformation mechanism of saturated soft clay foundation without drain. A calculation model for permanent dynamic deformation of saturated soft clay foundation has been established.

Mirror-assisted multi-view high-speed digital image correlation for dual-surface dynamic deformation measurement

Based on the recently proposed mirror-assisted multi-view digital image correlation(MV-DIC),we establish a cost-effective and easy-to-implement mirror-assisted multi-view high-speed digital image correlation(MVHS-DIC)method and explore its applications for dual-surface full-field dynamic deformation measurement.In contrast to the general requirement of four expensive high-speed cameras for dual-surface dynamic deformation field measurement,the established mirror-assisted MVHS-DIC halves the cost by involving only two synchronized high-speed cameras and two planar mirrors.The two synchronized high-speed cameras can dynamically measure the front and rear surfaces of a sheet sample simultaneously through the reflection of the two mirrors.The results on the two surfaces are then transformed into the same coordinate system,leading to the required dual-surface 3D dynamical deformation fields.The effectiveness and accuracy of the established system are validated through modal tests of a cantilever aluminum sheet.The vibration measurement of a drum and dual-surface transient deformation measurement of a smartphone in the drop-collision process further prove its practicability.Benefiting from the attractive advantages of multi-view dynamic deformation measurement in a cost-efficient way,the established mirror-assisted MVHS-DIC is expected to encourage more comprehensive dynamic mechanical behavior characterization of regular-sized materials and structures in vibration and impact engineering fields.

Liquefaction susceptibility and deformation characteristics of saturated coral sandy soils subjected to cyclic loadings-a critical review

Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and responses of these soils subjected to monotonic and cyclic loadings have been a subject of intense interest among the geotechnical and earthquake engineering communities.This paper critically reviews the progress of experimental investigations on the undrained behavior of coral sandy soils under monotonic and cyclic loadings over the last three decades.The focus of coverage includes the contractive-dilative behavior,the pattern of excess pore-water pressure(EPWP)generation and the liquefaction mechanism and liquefaction resistance,the small-strain shear modulus and strain-dependent shear modulus and damping,the cyclic softening feature,and the anisotropic characteristics of undrained responses of saturated coral sandy soils.In particular,the advances made in the past decades are reviewed from the following aspects:(1)the characterization of factors that impact the mechanism and patterns of EPWP build-up;(2)the identification of liquefaction triggering in terms of the apparent viscosity and the average flow coefficient;(3)the establishment of the invariable form of strain-based,stress-based,or energy-based EPWP ratio formulas and the unique relationship between the new proxy of liquefaction resistance and the number of cycles required to reach liquefaction;(4)the establishment of the invariable form of the predictive formulas of small strain modulus and strain-dependent shear modulus;and(5)the investigation on the effects of stress-induced anisotropy on liquefaction susceptibility and dynamic deformation characteristics.Insights gained through the critical review of these advances in the past decades offer a perspective for future research to further resolve the fundamental issues concerning the liquefaction mechanism and responses of coral sandy sites subjected to cyclic loadings associated with seismic events in marine environments.

Effects of strain rates on dynamic deformation behavior of Cu-20Ag alloy

Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electrical conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a complex service condition,which widely exists in the field of national defense,military and industrial application.Therefore,the dynamic deformation behavior of the Cu-20Ag alloy was investigated by Split Hopkinson Pressure Bar(SHPB)with the strain rates of 1000-25000 s^(-1),high-speed hydraulic servo material testing machine with the strain rates of 1-500 s^(-1).The effect of strain rate on flow stress and adiabatic shear sensitivity was analyzed.The results show that the increase of strain rate will increase the flow stress and critical strain,that is to say,the increase of strain rate will reduce the adiabatic shear sensitivity of the Cu-20Ag alloy.The Cu-Ag interface has obvious orientation relationship with;(111)_(Cu)//(111)_(Ag):(^(-)111)_(Cu)//(^(-)111)_(Ag):(^(-)200)_(Cu)//(^(-)200)_(Ag) and [0^(-)11]_(Cu)//[0^(-)11]_(Ag) with the increase of strain rate.The increase of strain rate promotes the precipitation of Ag and increases the number of interfaces in the microstructure,which hinders the movement of dislocations and improves the stress and yield strength of the Cu-20Ag alloy.The concentration and distribution density of dislocations and the precipitation of Ag were the main reasons improve the flow stress and yield strength of the Cu-20Ag alloy.

Dynamic Deformation Behavior of Dual Phase Ferritic-Martensitic Steel at Strain Rates From 10^(-4)to 2000 s^(-1)

The deformation behavior of the dual phase steel （DP1000 steel） was studied by the quasi-static tensile ex-periment and the dynamic tensile experiment. The experiments were carried out at strain rates ranging from 10^-4 to 2 000 s^-1 at room temperature. Then the stress-strain curves of DP1000 steel in the strain rate range of 10^-4-2000 s^-1 were measured. By introducing the strain rate sensitivity factor m, Zerilli Armstrong model was optimized. The con- stitutive equation parameters which formulate the mechanical behavior of DP1000 steel were fitted based on the John-son-Cook （JC） constitutive model and the optimized Zerilli-Armstrong （ZA） constitutive model, respectively. By comparing indicators of ＂accuracy-of-fit＂, Rz terms, for the two models, the optimized Zerilli-Armstrong constitu-tive model can reflect plastic deformation behavior both at the low and high strain rates more accurately. The reasons why the optimized Zerilli-Armstrong constitutive model is more advantageous than the Johnson Cook model were discussed by using the yield strength and ultimate tensile strength （UTS） versus strain rates, and strain hardening rate versus effective plastic strain analytical methods.

Effects of dynamic deformation of pendant water drops on the electric field between hollow porcelain insulator sheds under extreme rainfall

Hollow porcelain insulators in substations are frequently confronted with rain flashovers under extreme rainfall.This study aims to investigate the spatial and temporal variation of electric fields between hollow porcelain insulator sheds affected by dynamic deformation of pendant water drops and effects of the dimensionless number of fluids,the Weber number(We)and the electric Bond number(BoE),on it for influencing factors'analysis.Flow‐electric field coupling simulations were carried out to compute the magnitude and the position of AC electric fields between the sheds.The results show that the maximum electric field at a point in time(Etmax)increases significantly after the breakup of the pendant water drop,and its position alters accordingly.For low We and BoE,the global maximum electric field(Egmax)increases with increasing We and BoE,respectively.It is much closer to the adjacent sheds and occurs later than Etmax at the breakup of the pendant water drop(Ebmax).By contrast,Egmax decreases in different degrees at high We and BoE,respectively.There is little difference between Egmax and Ebmax in the position and the occurring time.The influence mechanism on the maximum electric field and discharges and the relationship between discharges induced by the pendant water drop and rain flashover are discussed.

A Model of Dynamic Recrystallization in Alloys during High Strain Plastic Deformation

Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization

Field of vertical crustal deformation in North China and the feature of its dynamic evolution

Based on the data of precise leveling surveys for 30-odd years and using unified adjustment method unified starting point of calculation and unified network,contour maps of the vertical crustal deformation rate in North China during the periods of 1965-1975,1975-1979,1979-1983 and 1983 1988 have been drawn.Meanwhile,the evolution of vertical crustal deformations has also been studied from a dynamic viewpoint. The results of analysis show that there is an obvious correspondence between the regular variations of the vertical crustal deformation field and the seismic cycles.Furthermore,the paper has also inferred that this correspondence might be related to the micro-variations of the regional stress/strain field. Finally,some problems related to the vertical deformation field and earthquake prediction have been discussed.

Research on dynamics patterns and parameter characters of crustal deformation field before and after strong earthquake

Based on the dynamic monitoring data of crustal deformation, the parameter evolution for the dynamics pattern and fractal dimension of crustal deformation field and the integral activity level of many faults etc. before and after the Tangshan (1976) and Lijiang (1996) strong earthquakes and others are studied by using the method of pattern dynamics. It is exposed that two time space characters, the ordered dimension drop of the deformation field and the accelerated motion of multi fault before an earthquake, are probably caused by the deformation localization and fault softening after the seismogenic process enters the nonlinear stage. They could be an important seismic precursor if they occurred repeatedly before strong earthquakes.

Evaluation of the biodegradation product layer on Mg-1Zn alloy during dynamical strain

Magnesium(Mg)alloys are attractive biodegradable implant materials.The degradation products on Mg alloys play a critical role in the stability of the interface between implant and surrounding tissue.In the present study,the effects of dynamic deformation on the interface layer of biomedical Mg-1Zn alloy were investigated using the constant extension rate tensile tests(CERT)coupled with electrochemical impedance spectroscopy(EIS).The deformation of the Mg-1Zn alloy had an adverse influence on the impedance of the surface degradation layer formed in simulated body fluid that only containing inorganic compounds.However,the surface degradation layer with improved corrosion resistance was obtained for the strained samples tested in protein-containing simulated body fluid.The spontaneous or enhanced adsorption of protein into the degradation product led to a flexible and stable hybrid anti-corrosive layer.A relationship between the dynamic deformation of Mg alloy and the impendence of the degradation layer was established,which demonstrates the necessity for in situ characterisation of the evolution of the surface layer under dynamic condition.

Theoretical Research and Experimental Validation of Elastic Dynamic Load Spectra on Bogie Frame of High-speed Train

When a train runs at high speeds, the external exciting frequencies approach the natural frequencies of bogie critical components, thereby inducing strong elastic vibrations. The present international reliability test evaluation standard and design criteria of bogie frames are all based on the quasi-static deformation hypothesis. Structural fatigue damage generated by structural elastic vibrations has not yet been included. In this paper, theoretical research and experimental validation are done on elastic dynamic load spectra on bogie frame of high-speed train. The construction of the load series that correspond to elastic dynamic deformation modes is studied. The simplified form of the load series is obtained. A theory of simplified dynamic load–time histories is then deduced. Measured data from the Beijing–Shanghai Dedicated Passenger Line are introduced to derive the simplified dynamic load–time histories. The simplified dynamic discrete load spectra of bogie frame are established. Based on the damage consistency criterion and a genetic algorithm, damage consistency calibration of the simplified dynamic load spectra is finally performed. The computed result proves that the simplified load series is reasonable. The calibrated damage that corresponds to the elastic dynamic discrete load spectra can cover the actual damage at the operating conditions. The calibrated damage satisfies the safety requirement of damage consistency criterion for bogie frame. This research is helpful for investigating the standardized load spectra of bogie frame of high-speed train.

Hot Deformation Behavior and Processing Maps of As-cast Mn18Cr18N Steel

Hot deformation behavior of as-cast Mn18Cr18 N austenitic stainless steel was studied in the temperature range of 950-1200 ℃ and strain rate range of 0.001-1 s^（-1） using isothermal hot compression tests. The true stress-strain curves of the steel were characterized by hardening and subsequent softening and varied with temperatures and strain rates. The hot deformation activation energy of the steel was calculated to be 657.4 k J/mol, which was higher than that of the corresponding wrought steel due to its as-cast coarse columnar grains and heterogeneous structure. Hot processing maps were developed at different plastic strains, which exhibited two domains with peak power dissipation efficiencies at 1150 ℃/0.001 s^（-1） and 1200 ℃/1 s^（-1）, respectively. The corresponding microstructures were analyzed by optical microscopy（OM）, scanning electron microscopy（SEM）, and electron backscatter diffraction（EBSD）. It has been confirmed that dynamic recrystallization（DRX） controlled by dislocation slipping and climbing mechanism occurs in the temperature and strain rate range of 1050-1200 ℃ and 0.001-0.01 s^（-1）; And DRX controlled by twinning mechanism occurs in the temperature and strain rate range of 1100-1200 ℃, 0.1-1 s^（-1）. These two DRX domains can serve as the hot working windows of the as-cast steel at lower strain rates and at higher strain rates, respectively. The processing maps at different strains also exhibit that the instability region decreases with increasing strain. The corresponding microstructures and the less tensile ductility in the instability region imply that the flow instability is attributed to flow localization accelerated by a few layers of very fine recrystallized grains along the original grain boundaries.

DYNAMICAL FORMATION OF CAVITY IN A COMPOSED HYPER-ELASTIC SPHERE

The dynamical formation of cavity in a hyper_elastic sphere composed of two materials with the incompressible strain energy function, subjected to a suddenly applied uniform radial tensile boundary dead_load, was studied following the theory of finite deformation dynamics. Besides a trivial solution corresponding to the homogeneous static state, a cavity forms at the center of the sphere when the tensile load is larger than its critical value. An exact differential relation between the cavity radius and the tensile land was obtained. It is proved that the evolution of cavity radius with time displays nonlinear periodic oscillations. The phase diagram for oscillation, the maximum amplitude, the approximate period and the critical load were all discussed.

“Rigid-elastic chimera” pore skeleton model and overpressure porosity measurement method for shale: A case study of the deep overpressure siliceous shale of Silurian Longmaxi Formation in southern Sichuan Basin, SW China

Based on analysis of pore features and pore skeleton composition of shale,a“rigid elastic chimeric”pore skeleton model of shale gas reservoir was built.Pore deformation mechanisms leading to increase of shale porosity due to the pore skeleton deformation under overpressure were sorted out through analysis of stress on the shale pore and skeleton.After reviewing the difficulties and defects of existent porosity measurement methods,a dynamic deformed porosity measurement method was worked out and used to measure the porosity of overpressure Silurian Longmaxi Formation shale under real formation conditions in southern Sichuan Basin.The results show:(1)The shale reservoir is a mixture of inorganic rock particles and organic matter,which contains inorganic pores supported by rigid skeleton particles and organic pores supported by elastic-plastic particles,and thus has a special“rigid elastic chimeric”pore structure.(2)Under the action of formation overpressure,the inorganic pores have tiny changes that can be assumed that they don’t change in porosity,while the organic pores may have large deformation due to skeleton compression,leading to the increase of radius,connectivity and ultimately porosity of these pores.(3)The“dynamic”deformation porosity measurement method combining high injection pressure helium porosity measurement and kerosene porosity measurement method under ultra-high variable pressure can accurately measure porosity of unconnected micro-pores under normal pressure conditions,and also the porosity increment caused by plastic skeleton compression deformation.(4)The pore deformation mechanism of shale may result in the"abnormal"phenomenon that the shale under formation conditions has higher porosity than that under normal pressure,so the overpressure shale reservoir is not necessarily“ultra-low in porosity”,and can have porosity over 10%.Application of this method in Well L210 in southern Sichuan has confirmed its practicality and reliability.

Experimental Investigation of the Dynamic Deformation of LY12 Aluminum Plate Heated by Strong Electrical Current

The moire interferometry method was used with holographic gratings for high temperature and high speed photography to measure the dynamic deformation of LY12 aluminum plate with a central hole under tensile loading condition and heated by a strong current. Transient fullfield fringe patterns were acquired during the heating process. Transient temperature of the specimen was simultaneously recorded by a temperature measurement system. The experimental results show that dynamic moire fringe patterns can be measured during high heating rate conditions using high speed photography.

Dislocation me diate d dynamic tension-compression asymmetry of a Ni_(2)CoFeV_(0.5)Mo_(0.2) medium entropy alloy

Although tension-compression(T-C)asymmetry in yield strength was rarely documented in coarse-grained face centered cubic(FCC)metals as critical resolved shear stress(CRSS)for dislocation slip differs little between tension and compression,the T-C asymmetry in strength,i.e.,higher strength when loaded in compression than in tension,was reported in some FCC high entropy alloys(HEAs)due to twinning and phase transitions activated at high strain regimes in compression.In this paper,we demonstrate a reversed and atypical tension-compression asymmetry(tensile strength markedly exceeds compressive strength)in a non-equiatomic FCC Ni_(2)CoFeV_(0.5)Mo_(0.2) medium entropy alloy(MEA)under dynamic loading,wherein dislocation slip governs dynamic deformation without twins or phase transitions.The asymme-try can be primarily interpreted as higher CRSS and more hard slip modes(lower average Schmid factor)activated in grains under dynamic tension than compression.Besides,larger strain rate sensitivity in dy-namic tension overwhelmingly contributes to the higher flow stress,thanks to the occurrence of more immobile Lomer-locks,narrower spacing of planar slip bands and higher dislocation density.This finding may provide some insights into designing MEAs/HEAs with desired properties under extreme conditions such as blast,impact and crash.

Quantifying the Microstructures of Pure Cu Subjected to Dynamic Plastic Deformation at Cryogenic Temperature

A pure Cu （99.995 wt%） has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy （TEM） assisted by convergent beam electron diffraction （CBED） analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries （〈15°） that are spaced in the nanometer scale, whereas most deformation twins are deviated from the perfect ∑3 coincidence （60°/〈111〉） up to the maximum angle of 9°. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship.

Annealing-induced Hardening in a Nanostructured Low-carbon Steel Prepared by Using Dynamic Plastic Deformation

Lamellar nanostructures were induced in a plain martensitic low-carbon steel by using dynamic plastic deformation at room temperature.The nanostructured steel was hardened after annealing at 673 K for20 min,with a tensile strength increased from 1.2 GPa to 1.6 GPa.Both the remained nanostructures and annealing-induced precipitates in nano-scale play key roles in the hardening.