Strength Analysis on Brace Structure for Semi-Submersible in Consideration of Wave Slamming

Slamming on bracings of column stabilized units shall be considered as a possible limiting criterion under transit condition based on the requirements in DNV-OS-C103. However, the wave slamming loads under survival condition were ignored for the strength analysis of the brace structures in many semi-submersible projects. In this paper, a method of strength analysis of brace structure is proposed based on the reconstruction and extrapolation of numerical model. The full-scale mooring system, the wind, wave and current loads can be considered simultaneously. Firstly,the model tests of the semi-submersible platform in wind tunnel and wave tanker have been carried out. Secondly,the numerical models of the platform are reconstructed and extrapolated based on the results of model tests. Then, a nonlinear numerical analysis has been conducted to study the wave slamming load on brace in semi-submersible platform through the reconstructed and extrapolated numerical model. For the randomness of wave load, ten subcases under each condition have been carried out. The value of the 90% Gumble distribution values of the ten subcases are used. Finally, the strength on brace structure has been analyzed considering the wave slamming. The wave slamming loads have been compared between the survival condition and transit condition with the method. The results indicate that wave slamming under survival condition is more critical than that under transit condition.Meanwhile, the wave slamming is significant to the structural strength of the brace. It should be overall considered in the strength analysis of the brace structure.

Prediction of the Residual Strength for Durability Failure of Concrete Structure in Acidic Environments

According to the results of accelerated tests of acidification corrosion depth and compressive strength of concretes subjected to sulfuric acid environments,the acidification depth laws of concretes were predicted based on the grey system theory.Thus,the remaining compressive strength was calculated when the acidification depth reached the protection layer thickness of concrete structures,which indicates that the limit state of durability failure can be defined based on strength degradation,and the calculation process was illustrated by an example.The calculated results show that the remaining compressive strength values in the durability failure limit state for the concrete structures exposed to p H=2 and 3 sulfuric acid water environments and wet-dry cyclic sulfuric acid environment with p H=2 are 74%,72%,and 80% of initialstrength,respectively.The method provides references for the durability evaluation of concrete structure design under the acidic environments.

Reinforcement strength reduction in FEM for mechanically stabilized earth structures

The factor of safety of mechanically stabilized earth(MSE) structures can be analyzed either using limit equilibrium method(LEM) or strength reduction method(SRM) in finite element/difference method. In LEM, the strengths of the reinforcement members and soils are reduced with the same factor. While using the SRM, only soil strength is reduced during the calculation of the factor of safety. This causes inconsistence in calculating the factor of safety of the MSE structures. To overcome this, an iteration method is proposed to consider the strength reduction of the reinforcements in SRM. The method is demonstrated by using PLAXIS, a finite element software. The results show that the factor of safety converges after a few iterations. The reduction of strength has different effects on the factor of safety depending on the properties of the reinforcements and the soil, and failure modes.

Effect of Sand Content on Strength and Pore Structure of Cement Mortar

The effects of four sand contents on the compressive, flexural and splitting-tensile strength of cement mortars were evaluated. Moreover, we experimentally investigated the pore structure of cement mortar brought about by changing the sand content and water/cement ratio. The changes in the pore structure were quantified by measuring the porosity and pore size distribution obtained by using mercury intrusion porosimetry（MIP） technique. The test results show that the strengths of cement mortar increase with increasing sand content. It is also suggested that the traditional water/cement ratio law can be applied to cement mortar with different sand contents, provided that a slight modification is introduced. Sand content is an important parameter influencing the pore structure of cement mortar. Moreover, there is a good relationship between the pore structure and strength of cement mortar.

DUCTILE CRACK INITIATION AND STEADY-STATE PROPAGATION OF HIGH STRENGTH STRUCTURAL STEEL

The resistance to crack propagation at earlier stage for a high strength structural steel with certain ductility and its correlation to microstructures,stress states,deformation history and strain characteristics have been investigated.The resistance to crack propagation is mainly de- termined by the plastic constrain ahead of the crack tip,the elastic energy and plastic work absorbed in the stress-strain field.These are connected with the state function of triaxial stress.The deformation history and strain characteristic during deformation of material are described by the flow line in which the deformation history and strain characteristic restrain the crack initiation at stage Ⅱ and the crack propagation at stage Ⅲ.The strain hardening rate may sensitively reflect the stress distribution and micro-fracture mechanism in the interi- or of material.

Mesomechanics Finite-element Method for Determining the Shear Strength of Mudded Intercalation Materials

A new method regarding mesomechanics finite-element research is proposed to predict the peak shear strength of mudded intercalation materials on a mesoscopic scale. Based on geometric and mechanical parameters, along with the strain failure criteria obtained by sample＇s deformation characteristics, uniaxial compression tests on the sample were simulated through a finite-element model, which yielded values consistent with the data from the laboratory uniaxial compression tests, implying that the method is reasonable. Based on this model, a shear test was performed to calculate the peak shear strength of the mudded intercalation, consistent with values reported in the literature, thereby providing a new approach for investigating the mechanical properties of mudded intercalation materials.

Characteristics of structural loess strength and preliminary framework for joint strength formula

The strength of structural loess consists of the shear strength and tensile strength. In this study, the stress path, the failure envelope of principal stress （ Kf line）, and the strength failure envelope of structurally intact loess and remolded loess were analyzed through three kinds of tests： the tensile strength test, the uniaxial compressive strength test, and the conventional triaxial shear strength test. Then, in order to describe the tensile strength and shear strength of structural loess comprehensively and reasonably, a joint strength formula for structural loess was established. This formula comprehensively considers tensile and shear properties. Studies have shown that the tensile strength exhibits a decreasing trend with increasing water content. When the water content is constant, the tensile strength of the structurally intact soil is greater than that ofremolded soil. In the studies, no loss of the originally cured cohesion in the structurally intact soil samples was observed, given that the soil samples did not experience loading disturbance during the uniaxial compressive strength test, meaning there is a high initial structural strength. The results of the conventional triaxial shear strength test show that the water content is correlated with the strength of the structural loess. When the water content is low, the structural properties are strong, and when the water content is high, the structural properties are weak, which means that the water content and the ambient pressure have significant effects on the stress-strain relationship of structural loess. The established joint strength formula of structural loess effectively avoids overestimating the role of soil tensile strength in the traditional theory of Mohr-Coulomb strength.

An Integrated Structural Strength Analysis Method for Spar Type Floating Wind Turbine

An integrated structural strength analysis method for a Spar type floating wind turbine is proposed in this paper,and technical issues related to turbine structure modeling and stress combination are also addressed.The NREL-5MW ＂Hywind＂ Spar type wind turbine is adopted as study object.Time-domain dynamic coupled simulations are performed by a fully-coupled aero-hydro-servo-elastic tool,FAST,on the purpose of obtaining the dynamic characteristics of the floating wind turbine,and determining parameters for design load cases of finite element calculation.Then design load cases are identified,and finite element analyses are performed for these design load cases.The structural stresses due to wave-induced loads and wind-induced loads are calculated,and then combined to assess the structural strength of the floating wind turbine.The feasibility of the proposed structural strength analysis method for floating wind turbines is then validated.

Study on Adaptive Shape Optimization

Aim To introduce a new method of adaptive shape optimization (ASOP) based on three-dimensional structure boundary strength and optimize an engine bearing cap with the method. Methods Using the normal substance's property of thermal expansion and cooling shrinkage,the load which is proportional to the difference between the nodes' stress and their respective objective stress were applied to the corresponding variable nodes on the boundary.The thermal load made the nodes whose stress is greater than their objective stress expand along the boundary's normal direction and the nodes whose stress is less than objec- tive stress shrink in the opposite direction , This process would repeat until the stress on the boundary nodes was converge to the objective stress. Results The satisfied results have been obtained when optimizing an engine bearing cap.The mass of the bearing cap is reduced to 55 percent of the total. Conclusion ASOP is an efficient,practical and reliable method which is suitable for optimizing the shape of the continuous structures.

Structure improvement and strength finite element analysis of VHP welded rotor of 700℃ USC steam turbine

The optimized structure strength design and finite element analysis method for very high pressure （VHP） rotors of the 700℃ ultra-super-critical （USC） steam turbine are presented. The main parameters of steam and the steam thermal parameters of blade stages of VHP welded rotors as well as the start and shutdown curves of the steam turbine are determined. The structure design feature, the mechanical models and the typical position of stress analysis of the VHP welded rotors are introduced. The steady and transient finite element analysis are implemented for steady condition, start and shutdown process, including steady rated condition, 110% rated speed, 120% rated speed, cold start, warm start, hot start, very hot start, sliding-pressure shutdown, normal shutdown and emergency shutdown, to obtain the temperature and stress distribution as well as the stress ratio of the welded rotor. The strength design criteria and strength analysis results of the welded rotor are given. The results show that the strength design of improved structure of the VHP welded rotor of the 700℃ USC steam turbine is safe at the steady condition and during the transient start or shutdown process.

Effects of a Combined Silica-containing Additive on Structural and Rheological Properties of a Low-cement Silicon Carbide Castable

The use of a combined additive consisting of silica-containing additives“F”(thinning)and“S”(accelerating castable hardening)instead of the previously used silica-containing additive“A”and a mixture of dispersing additives based on polyethylene glycol in low-cement silicon carbide castable allows to improve the castable workability by increasing(in 5.4 times)the flowability of a freshly prepared castable,and increase by 1.2 and 1.1 times the cold crushing strength of heat-treated at temperatures of 110 and 1580°C,respectively,castable samples from low-cement silicon carbide castable with practically equal values of open porosity(15.8%and 16.0%).The petrographic studies of the castable sample microstructure after firing at a temperature of 1580°C showed that the investigated silica-containing additives“F”and“S”contribute to the denser and more uniform structure formation.As a result of the carried out research,the manufacturing technology of a low-cement silicon carbide castable was improved,of which the production was mastered at JSC“URIR named after A.S.Berezhnoy”.

Review of collapse triggering mechanism of collapsible soils due towetting

Loess soil deposits are widely distributed in arid and semi-arid regions and constitute about 10% of land area of the world.These soils typically have a loose honeycomb-type meta-stable structure that is susceptible to a large reduction in total volume or collapse upon wetting.Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils.For this reason,collapse triggering mechanism for loess soils has been of significant interest for researchers and practitioners all over the world.This paper aims at providing a state-of-the-art review on collapse mechanism with special reference to loess soil deposits.The collapse mechanism studies are summarized under three different categories,i.e.traditional approaches,microstructure approach,and soil mechanics-based approaches.The traditional and microstructure approaches for interpreting the collapse behavior are comprehensively summarized and critically reviewed based on the experimental results from the literature.The soil mechanics-based approaches proposed based on the experimental results of both compacted soils and natural loess soils are reviewed highlighting their strengths and limitations for estimating the collapse behavior.Simpler soil mechanics-based approaches with less parameters or parameters that are easy-to-determine from conventional tests are suggested for future research to better understand the collapse behavior of natural loess soils.Such studies would be more valuable for use in conventional geotechnical engineering practice applications.

Influence of expanded polystyrene size on deformation characteristics of light weight soil

Deformation characteristics of light weight soil with different EPS (expanded polystyrene) sizes were investigated by consolidation tests.The results show that the confined stress-strain relation curve is in S shape,which has a good homologous relation with e-p curve and e-lgp curve,and three types of curves reflect obvious structural characteristics of light weight soil.When cement mixed ratio and EPS volume ratio are the same for different specimens,structural strength decreases with the increase of EPS size,but compressibility indexes basically keep unchanged within the structural strength.The settlement of light weight soil can be divided into instantaneous settlement and primary consolidation settlement.It has no obvious rheology property,and 90% of total consolidation deformation can be finished in 1 min.Settlement-time relation of light weight soil can be predicted by the hyperbolic model.S-lgt curve of light weight soil is not in anti-S shape.It is proved that there is no secondary consolidation section,so consolidation coefficient cannot be obtained by time logarithm method.Structural strength and unit price decrease with the increase of EPS size,but the reducing rate of the structural strength is lower than that of the unit price,so the cost of mixed soil can be reduced by increasing the EPS size.The EPS beads with 3-5 mm in diameter are suggested to be used in the construction process,and the prescription of mixed soil can be optimized.

Finite element and experimental analysis of pinion bracket-assembly of three gorges project ship lift

The pinion bracket-assembly(PBA) is a major part of three gorges project(TGP) ship lift drive system. The static strength,fatigue strength and stress distribution of hinge pin of PBA were analyzed by ANSYS, and the structure of PBA was optimized. The results show that after the optimization, the maximum comprehensive stress is 259.59 MPa, the maximum fatigue cumulative damage of weld joints is 0.94 and the maximum vertical deformation of hinge pin is 0.14 mm. The elastic deformation, hydropneumatic spring cylinder(HSC) load response and the vibration characteristics of PBA were studied by the bearing test when PBA bore the load caused by different water level errors. The results indicate that when the water level of ship chamber ranges from 3.4 m to 3.6 m,the vertical elastic deformation of the pinion shaft is between-8.58 and 10.50 mm. When upward outage-load(1580 k N) is imposed by the test-rack, the vertical elastic deformation of the pinion shaft is 13.42 and 14.07 mm and HSC load response is 795.80-800.80 k N. In the process of imposing load on the pinion by the test-rack, the maximum vibration amplitude and acceleration of PBA internal components are 0.37° and 2.67 rad/s2, respectively; the maximum impact on the pin caused by vibration is 19.89 k N; the pinion shaft vertical displacement and HSC load response do not fluctuate. There is a great difference between the frequency of meshing force of the pinion and the rack(1.06 Hz) and first-order natural frequency of PBA(8.41 Hz), thus PBA will not resonate.From all above, PBA meets the static strength and fatigue strength requirements. The vibration of PBA internal components has no effect on the vertical displacement of the pinion shaft, HSC load response and smooth operation of PBA. There is a liner relationship in the ratio of 2:1 between the thrust imposed by the test-rack and HSC load, thus HSC can limit the load imposed on the pinion.

New filler metal systems for the brazing of titanium alloys

It＇ s well known welding takes the leading role in development of titanium structures. However, in number of cases technological processes of brazing are more appropriate and, sometimes, being the single possible, in particular, during production of multilayer thin-wall structures. It should be noted that brazing filler metals of Ti-Cu-Ni, Ti-Zr-Cu-Ni, Zr-Ti-Ni and Cu-Zr-Ti systems in a form of plastic foils, as well as in powder form are mainly used in world practice for brazing of titanium alloys. Present work provides the results of complex investigations of brazing filler metals of Ti-Zr-Fe, Ti-Zr-Mn and Ti-Zr-Co systems using differential thermal analysis, light and scanning microscopy, X-ray microspectrum analysis. Data on melting ranges of pilot alloys were obtained, and liquidas su^Caces of given systems using simplex-lattice method were build. Brazing filler metals covering brazing temperature range of current structural titanium materials based on solid solutions as well as intermetallics were proposed. Structure, chemical inhomogeniety and strength characteristics of brazed joints were studied. It is determined that brazing of solid solution based alloys （OT4, VT6 ） using indicated brazing fiUer metals ensures strength characteristics of joints, which are not inferior to that obtained with application of known brazing filler metals even if they are received at lower brazing temperature.

The effect of polyvinylpyrrolidone addition on microstructure,surface aspects,the glass transition temperature and structural strength of honey and coconut sugar powders

Deep knowledge of the microstructure and physicochemical properties of polymeric food systems,such as honey powders(HP)and coconut sugars(CS),has practical importance for industry and end users.This study investigated the effect of polyvinylpyrrolidone(PVP)addition on microstructure,roughness,glass transition,α-relaxation temperatures and structural strength(S)of anhydrous complex carbohydrates mixtures.The addition of PVP slightly increased the glass transition andα-relaxation temperature for HP and CS systems as high molecular weight components.Systems with PVP addition showed“stronger”behaviour according to the S approach.Polarized light,scanning electron and atomic force microscopies showed slight differences in transparency and shapes between controls and systems with PVP addition.Surface morphological changes and roughness were investigated in this study to provide insight into HP and CS particles’structural changes.Moreover,S-involved structural diagrams were built to determine S parameters for controlling the structural transformation of HP and CS systems with and without PVP addition.The results obtained in this work provide new information on polymer-carbohydrate interactions in complex food systems and structural transformations during their production and storage.

Improving hydro-mechanical behavior of loess by a bio-strategy

Loess is widely distributed all over the world,covering about 10%of the land surface on earth.China is one of the countries with the most serious loess soil erosion in the world,especially the loess plateau.This is mainly related to the poor water stability and mechanical properties of the loess.A new coupling method of bio-ce-mentation(Microbially Induced Calcite Precipitation:MICP)and sand additive to improve the hydro-mechanical behavior of loess was proposed.The feasibility,coupling improvement mechanism and the effects of sand content,bio-cement treatment cycle and cementation solution(cs)concentration were investigated through a series of tests.The results indicated that the proposed method was effective to improve the water stability and structure strength of loess.The coupling improvement performance were positively related to the sand content.When the sand content was 40%,compared to bio-cement treatment,the coupling treatment was 9 times deeper in treatment depth,3.5 times stronger in peak structure strength,and the sum slaking rate was less than half.The coupling improvement mechanism can be attributed to the form of the double layers including hard crust and cemented layer.With the addition of sand,the thickness,structure strength and water stability of the double layers increased.The main reason is that there were more interfacial voids between sand particles and loess particles,increasing the permeability of loess and treatment depth,forming more amount of calcium carbonates.Based on the experimental condition in this study,1.0 M of CS concentration was the optimal spaying strategy to improve the hydro-mechanical properties of loess.

Theory and applications of coupled fluid-structure interactions of ships in waves and ocean acoustic environment

Wave induced motions and structural distortions, and machinery or propeller excited vibrations and acoustic radiations of a ship are two kinds of important fluid-structure interaction problems. The branch of ship science that describes the coupled wave induced dynamic behavior of fluid-structure interaction system is referred to as hydroelasticity. During the past three decades the development of three-dimensional hydroelasticity theories and applications gained great progress. Recently the 3-D hydroelasticity theory was further extended to account for the fluid compressibility and the effect of the ocean acoustic environment with finite water depth. A three-dimensional sono-elasticity theory was then produced. In this paper, the 3-D hydroelasticity theory and the 3-D sono-elasticity theory of ships are briefly described. To illustrate the applicability and feasibility of these theories and the corre- sponding numerical approaches, several examples are presented including the predictions of wave loads, rigid-body and flexible- body responses, springing and fatigue behaviors, machinery or propeller excited coupled structural vibrations and acoustic radiations, as well as design optimizations for improving safety and acoustic behaviors of ships.

INVESTIGATIONS INTO THE DETACHMENT OF DIFFERENTLY STRUCTURED DUST LAYERS FROM SURFACES

A technique is presented for creating surface-adhering dust layers under defined conditions, and characterizing and stressing the layers created. The procedure described is shown to be suitable for the quantitative evaluation of the effects of different parameters such as particle size, porosity and surface roughness etc. on the stability of particle layers.