Factors influencing incomplete fusion in automatic girth welding of oil and gas pipelines

In view of the incomplete fusion occurred in the automatic girth welding of oil and gas pipelines, the factors influencing the incomplete fusion were studied with the welding procedure test and numerical simulation in combination. The results show that the swing width of the welding torch gradually increases for welding within the range from 3:00 to 6:00 o'clock. During this process, the welding process has the welding current decreased and the welding speed slowed down if the heat input remains unchanged. In this case, a larger swing width is helpful to increase the welding pool depth on the groove wall, thus guaranteeing the stability of weld droplet transition and reducing the risk of incomplete fusion on the wall. Besides, the weld morphology at the position of 4:30-6:00 was very poor, and the "hump weld" in the current pass will increase the probability of incomplete fusion in the next pass. In addition, the welding temperature field is in a serrated shape during the swing welding, which can be effectively eliminated at the swing frequency of 5 times/s or above. The research results can provide reference for improving the quality and efficiency of pipeline automatic welding

Pore Changes in Purple Mudstone Based on the Analysis of Dry-Wet Cycles Using Nuclear Magnetic Resonance

The study on the change of rock pore structure during the weathering of purple mudstone is of guiding significance to the stability of the bank slope of the three gorges reservoir. In this paper, the pore changes in the wet and dry circulation of purple mudstone in the three gorges reservoir area are studied by means of nuclear magnetic resonance (NMR). The results show that the simulated weathering of wet and dry circulation has a great influence on the purple mudstone. With an increase in the number of dry-wet cycles, the purple mudstone pore volume ratio significantly changed. Originally, it consisted of a small pore structure with a single pore diameter of 0.01–0.1 µm and changed to a variety of pore structures with various pore diameters of 0.001–100 µm. With the increase in the number of dry-wet cycles, the micropores (0.001–0.1 µm) were transformed into macropores (0.1–1 µm). The area of the second peak of the three samples (large pores 0.1–1 µm) increased from 0.9413, 0.9974, and 0.6779 to 0.9871, 1.1498, and 0.9901, respectively.</jats:p

Research on the Effect of Stiffness Ratio Between Frame and Core Tube on Seismic Response of Super High-rise Building Under Frequent Earthquake

Abstract The stiffness ratio of frame to core tube has an important influence on the seismic behavior of frame-core tube hybrid structure which is a high-rise building structure system widely used in the world. In this paper, nine models of concrete-filled steel tubular frame-concrete core tube super-high-rise hybrid structures with different stiffness ratios are established by using finite element method, and the effect of stiffness ratio on inter-story displacement angle, top displacement and base shear force of super high-rise buildings under frequent earthquakes is studied. The results show that, with the increase of stiffness ratio, the inter-story displacement angle, the top displacement and the base shear force change complicatedly, the maximum base shear force increase, and the maximum inter-story displacement angle and the maximum top displacement first increase then peak, and that the strengthening layer with outrigger obviously improves the deficiency of lateral stiffness caused by height. This study provides a reference for reasonable determination of stiffness ratio and optimization of structural seismic design.</jats:p

Preparation of Nano-porous aerogels by supercritical drying

Abstract Nano-porous silica aerogels are synthesized by two steps by the supercritical condition. By synthesized process, tetra-ethyoxysilane is used as raw material, isopropanol and H2O which is distilled after ion exchange was used as solvent, HCl and NH4OH are used as hydrolysis and condensation catalysts, glycerol is used as drying control chemical agent. Silica aerogels are obtained by supercritical drying condition after aging, surface modification and exchanging solvent. The effect of water, PH, temperature, and so on, are analysed at supercritical drying condition. The resulting aerogels are characterized by means of X-ray diffraction and scanning electron microscopy. It is found that the aerogels made by this method have high porosity, specific surface area and the structure is sponge with narrow particle and pore size distribution.</jats:p

Pore Changes in Purple Mudstone Based on the Analysis of Dry-Wet Cycles Using Nuclear Magnetic Resonance

The study on the change of rock pore structure during the weathering of purple mudstone is of guiding significance to the stability of the bank slope of the three gorges reservoir. In this paper, the pore changes in the wet and dry circulation of purple mudstone in the three gorges reservoir area are studied by means of nuclear magnetic resonance (NMR). The results show that the simulated weathering of wet and dry circulation has a great influence on the purple mudstone. With an increase in the number of dry-wet cycles, the purple mudstone pore volume ratio significantly changed. Originally, it consisted of a small pore structure with a single pore diameter of 0.01–0.1 µm and changed to a variety of pore structures with various pore diameters of 0.001–100 µm. With the increase in the number of dry-wet cycles, the micropores (0.001–0.1 µm) were transformed into macropores (0.1–1 µm). The area of the second peak of the three samples (large pores 0.1–1 µm) increased from 0.9413, 0.9974, and 0.6779 to 0.9871, 1.1498, and 0.9901, respectively

Dynamic analysis and criterion evaluation on rockburst considering the fractured dissipative energy

As one of the dynamic disasters of deep mining, rockburst significantly affects the safety of underground environment especially at great depth. First, the elastic energy and dissipative energy are deduced to characterize rockburst process separately employing the theoretical analysis and test technique. Then, a series of split-Hopkinson pressure bar system tests are conducted. After calculation, the percentage of fractured dissipative energy occupied in total input dynamic energy is obtained. Subsequently, the dynamic mechanical parameters of rock specimens and dynamic impact factors are fitted. Finally, a three-dimensional model is developed using the mechanical property of the host rock, constitutive model, and in situ geostress. The contours of energy and the damage conditions of host rock are predicted, and the tendentiousness of rockburst is estimated. </jats:p

Research on the influence of frame-core tube stiffness ratio on dynamic characteristics of Super high-rise buildings

Abstract The frame-core tube hybrid structure is an important high-rise building structure system which is widely used in the world at present. The stiffness ratio of frame to core tube affects the dynamic characteristics of the structure. In this paper, nine models of concrete-filled steel tubular frame-concrete core tube super high-rise hybrid structure with different stiffness ratios are analyzed by subspace iteration method, and the analysis of the acceleration and displacement response spectrum value of each vibration mode under frequent earthquakes are carried out. The results show that the stiffness ratio has different effects on different modes, the fundamental frequency, natural period, acceleration and displacement response of the structure of the first mode increase with the stiffness ratio increasing, and it is feasible and significant to interpret the seismic response of structures from studying the dynamic characteristics of seismic waves and structures.</jats:p

Development of PMC Numerical Model for Soil and Stone Mixture

Soil and stone mixture is widely distributed in China, and its physical and mechanical properties are complex, which has a significant impact on geotechnical engineering. Usually soil and stone mixture shows anisotropic features along or perpendicular to the direction of settled layers, and the strength will be significantly affected by intermediate principal stress. True triaxial tests were carried on, Paul–Mohr–Coulomb (PMC) failure criterion was used for the strength analysis in soil-stone mixture, and related parameters of PMC model were obtained. A user-defined PMC numerical constitutive model was developed for FLAC3D. Composite failure criteria of shear failure and tension cut-off were applied for numerical analysis, and nonassociated flow rule was proposed based on the Mohr–Coulomb model. Verification modelling was applied as well, and deviation between analytical and numerical solutions in strains of X direction, Y direction, and Z direction was 1.0013, 1.0003, and 1.002, respectively

Determining Tensile Strength of Rock by the Direct Tensile, Brazilian Splitting, and Three-Point Bending Methods: A Comparative Study

To accurately obtain the tensile strength of rock and fully understand the evolution process of rock failure is one of the key issues to the research of rock mechanics theories and rock mass engineering applications. Using direct tensile, Brazilian splitting, and three-point bending test methods, we performed indoor and numerical simulation experiments on marble, granite, and diabase and investigated the tensile strength and damage evolution process of several typical rocks in the three different tests. Our experiments demonstrate that (1) the strength is about 10% greater in the Brazilian splitting than in the direct tensile, while the tensile modulus is lower; it is the highest in the three-point bending, which is actually subjected to the bending moment and suggested as one of the indexes to evaluate the tensile strength of rock; (2) the strength in splitting tests is strikingly different, while the strain law is basically similar; the direct tensile test with precut slits is more attainable than that with no-cut slits, with an uninfluenced strength; (3) the failure modes of rocks using different methods are featured by different lithology, while their final modes are basically the same under the same method; (4) PFC and RFPA numerical simulation tests are effective to analyze the internal crack multiplication and acoustic emission changes in the rock as well as the damage evolution process of rock in different tests