Reliability-Based Design for Jacket Platform Under Extreme Loads

In this paper, reliability analysis for the offshore jacket platform with the interaction of structure- pile- soil under extreme environmental loads is carried out. The inherent uncertainties of the environmental load, foundation soil, platform itself, and calculating models are evaluated. The action of extreme loads on the offshore platform is modeled as a function of extreme wave height. The system capacity of the whole platform is determined by nonlinear pushover analysis, and the relevant probability property is obtained by the simulation method. The reliability model for the whole jacket platform is described as the relationship between the load and resistance based on the offshore design codes. The reliability of whole platform is calculated by the analytical method and the importance sampling method on the basis of a case study for a tripod jacket platform.

Anti-slip security assessment between main cable and saddle of the middle pylon under extreme vehicle loads

The traffic condition of Taizhou Yangtze River Bridge is obtained to a certain extent, according to the traffic investigation nearby Taizhou Bridge. The statistical characteristics of the traffic conditions are acquired by statistical analysis. Simulation of the extreme vehicle loads and the sensitive analysis of load parameters are carried out based on these data complemented, which would guide the determination of the frictional coefficient between the main cables and the saddle.

Extreme mechanics

With the development of cutting-edge sciences and new technologies,we have to consider the size,the density,the hardness,the stiffness and other properties of engineering materials and structures beyond the conventional ranges,as well as their mechanical behavior in extreme environments,such as ultra-conventional temperature,speed,physical and chemical fields,and severe weather,and more effective theories and methods of mechanics are required.This paper first gives the fundamental definition and the scientific connotation of extreme mechanics,then reviews the studies of extreme mechanics from three aspects:the extreme properties,the extreme loads,and the discipline development,as well as major engineering and scientific challenges.The characteristics of extreme mechanics and major challenges in the aspects of mechanical theory,computational methods and experimental techniques are discussed.Prospectivei developments of extreme mechanics are suggested.

Analysis of Wave Loads on A Semi-Submersible Platform

For the global and structural fatigue strength analysis of a semi-submersible platform, wave loads under design conditions are calculated by use of the three-dimensional boundary element method. Methods for calculating the forward-speed free-surface Green function are discussed and a computer program with this Green function is developed. According to the special rules, the wave loads under several typical design conditions of the platform are calculated. The maximum vertical bending moment, torsion moment and horizontal split force are determined from a series of contour maps of wave loads for the wave period of 5 to 18 seconds at a certain interval and the wave phase of 0degrees to 360degrees at a certain interval. The wave height is determined by the function of wave period with a given exceedance probability. The maximum wave loads under the combination of wave parameters are used as the input of hydrodynamic pressure in the three-dimensional finite element analysis process. The transfer functions of wave loads on the platform are used for the fatigue strength analysis of the K-tubular joint and the sub-model of the structure.

Large Chip Production Mechanism under the Extreme Load Cutting Conditions

There has existed a great deal of theory researches in term of chip production and chip breaking characteristics under conventional cutting and high speed cutting conditions,however,there isn＇t sufficient research on chip formation mechanism as well as its influence on cutting state regarding large workpieces under extreme load cutting.This paper presents a model of large saw-tooth chip through applying finite element simulation method,which gives a profound analysis about the characteristics of the extreme load cutting as well as morphology and removal of the large chip.In the meantime,a calculation formula that gives a quantitative description of the saw-tooth level regarding the large chip is established on the basis of cutting experiments on high temperature and high strength steel2.25Cr-lMo-0.25V.The cutting experiments are carried out by using the scanning electron microscope and super depth of field electron microscope to measure and calculate the large chip produced under different cutting parameters,which can verify the validity of the established model.The calculating results show that the large saw-toothed chip is produced under the squeezing action between workpiece and cutting tools.In the meanwhile,the chip develops a hardened layer where contacts the cutting tool and the saw-tooth of the chip tend to form in transverse direction.This research creates the theoretical model for large chip and performs the cutting experiments under the extreme load cutting condition,as well as analyzes the production mechanism of the large chip in the macro and micro conditions.Therefore,the proposed research could provide theoretical guidance and technical support in improving productivity and cutting technology research.

Improving the damage potential of W-Zr reactive structure material under extreme loading condition

Projectiles made of reactive structure materials(RSM)can damage the target with not only kinetic but also chemical energy,but the enhanced damage potential of RSM may become compromised if extreme loading condition disintegrates the projectile before the target is reached.In this work,a ductile coating of Ni was introduced to a tungsten-zirconium(W-Zr)alloy,a typical brittle RSM,to preserve the damage potential of the projectile.Detonation driving tests were carried out with X-ray photography and gunpowder deflagration driving tests were carried out with high-speed photography for the coated and uncoated RSM samples,respectively.The craters on the witness target were analyzed by scanning electron microscopy and X-ray diffraction.The Ni coating was found to effectively preserve the damage potential of the W-Zr alloy under extreme loading conditions,whereas the uncoated sample fractured and ignited before impacting the target in both detonation and deflagration driving.The crack propagation between the reactively brittle core and the ductile coating was analyzed based on the crack arrest theory to mechanistically demonstrate how the coating improves the structural integrity and preserves the damage potential of the projectile.Specifically,the Ni coating envelops theW-Zr core until the coated sphere penetrates the target,and the coating is then eroded and worn to release the reactive core for the projectile to damage the target more intensively.

Effects of corner modifications on wind loads and local pressures on walls of tall buildings

In this study, the aerodynamic characteristics of tall buildings with corner modifications (e.g., local wind force coefficients, mean pressure distributions, normalized power spectrum density, and extreme local pressure) were examined. Wind tunnel experiments were conducted to measure the wind pressures on building models with different heights and recessed corners of different ratios. At a wind direction of a = 0° (i.e., wind blowing on the front of a building), corner modifications effectively reduced wind forces in all cases. Specifically, small corner modification ratios reduced wind forces more effectively than their larger counterparts. However, corner modifications resulted in extreme local pressure on building surfaces. In addition, for small corner modification ratios, the probability of extreme local pressure occurring at a = 0° was high. This probability was also high for large corner modification ratios at a = 15° (i.e., wind blowing slightly obliquely on the front of a building) because wind blowing obliquely creates substantial vortex shedding on one side surface and extreme negative pressure over one building side surface. Results of computational fluid dynamic modeling were adopted to determine details of the aerodynamic characteristics of tall buildings with corner modifications.

Numerical analysis and experimental investigation of wind turbine blades with innovative features:Structural response and characteristics

Innovative features of wind turbine blades with flatback at inboard region,thick airfoils at inboard as well as mid-span region and transversely stepped thickness in spar caps have been proposed by Institute of Engineering Thermophysics,Chinese Academy of Sciences(IET-Wind)in order to improve both aerodynamic and structural efficiency of rotor blades.To verify the proposed design concepts,this study first presented numerical analysis using finite element method to clarify the effect of flatback on local buckling strength of the inboard region.Blade models with various loading cases,inboard configurations,and core materials were comparatively studied.Furthermore,a prototype blade incorporated with innovative features was manufactured and tested under static bending loads to investigate its structural response and characteristics.It was found that rotor blades with flatback exhibited favorable local buckling strength at the inboard region compared with those with conventional sharp trailing edge when low-density PVC foam was used.The prototype blade showed linear behavior under extreme loads in spar caps,aft panels,shear web and flatback near the maximum chord which is usually susceptible to buckling in the blades according to traditional designs.The inboard region of the blade showed exceptional load-carrying capacity as it survived420%extreme loads in the experiment.Through this study,potential structural advantages by applying proposed structural features to large composite blades of multi-megawatt wind turbines were addressed.

Dynamically compressive behaviors and plastic mechanisms of a CrCoNi medium entropy alloy at various temperatures

As an attractive class of metallic materials,single-phase CrCoNi medium-entropy alloy(MEA)has drawn much attention recently regarding their deformation behaviors,but the dynamically mechanical responses of this alloy at high strain rates remain less studied,especially coupled with extremely low temperatures.In this study,the dynamic deformation behaviors of this CrCoNi MEA were systematically investigated at room temperature(RT)of 298 K and liquid nitrogen temperature(LNT)of 77 K using the split Hopkinson pressure bar(SHPB).This alloy exhibited a combination of higher yield strength and stronger hardening rate upon dynamic compressive deformation when the loading conditions become much harsher(higher strain rate or lower temperature).Detailed microstructure analyses indicated that the strong strain hardening ability during dynamic deformation was mainly attributed to the continuous formation of nanoscale deformation twins.Furthermore,as loaded at LNT,multi-directional deformation twins were activated.Meanwhile,due to the interaction between Shockley partial dislocations and twin boundaries,large-sized deformation-induced FCC-HCP phase transformations at a micrometer scale were also observed within the grains,which not only accommodated the plasticity but also played an important role in improving the hardening capability owing to the appearance of newly generated interfaces.