Theoretical and Numerical Studies on the Coupling Deformation of Global Lateral Buckling and Walking of Submarine Pipeline

Buckling initiation devices/techniques,including sleepers,distributed buoyancy,snake lay,and residual curvature method(RCM),have recently been widely applied in engineering.These initiated buckles may induce a long pipeline to transform into multiple short pipeline segments,which promote the occurrence of pipeline walking.Thus,a pipeline,which is designed to buckle laterally,may laterally and axially displace over time when subjected to repeated heating and cooling cycles.This study aims to reveal the coupling mechanism of pipeline walking and global lateral buckling.First,an analytic solution is proposed to estimate the walking of pipeline segments between two adjacent buckles.Then,the sensitivity of this method to heating and cooling cycles is analyzed.Results show the applicability of the proposed walking analytical solution of buckling pipelines.Subsequently,an influence analysis of walking on global buckling,including the capacity of buckling initiation,buckling amplitude,buckling mode,and failure assessment of the buckling pipeline,is performed.The results reveal that the effect of walking on the buckling axial force is negligible.However,pipeline walking will aggravate the asymmetry of the pipeline buckling and the failure parameters of the pipeline during the post-buckling.

Investigation into the deformation of a large span roadway in soft seams and its support technology

We investigated the deformation failure mechanism of surrounding rock from the aspect of engineering support for a roadway in seams with soft roofs and soft floors and observed the large displacement of the roadway in these soft seams.The result shows that the deformation area is quite large,and settlement of the roof is evident and displacement of the side walls is also obvious.We considered rock bolt-cable coupling for roadway support in seams with soft roofs and floors,in which the cable should be fixed at key positions.As well,we designed an optimal scheme to support a roadway in soft seams of the Shizuishan Second Mine in Ningxia,China.Field monitoring results show that bolt-cable coupling support has achieved the aims of roadway stability control and minimizes deformation.

Deformation failure and countermeasures of deep tertiary extremely soft rock roadway in Liuhai coal mine

In view of failure phenomena with nonlinear large deformation including extensive damage,whole section destruction in short time,high rate of repair,most destruction forms occurred in the tertiary roadway of soft rocks engineering in Liuhai mine,according to the methods of geological survey,theoretical analysis,numerical calculation and in-situ test,the composite failure mechanism of molecular expansion,tectonic stress,gravity stress and engineering deviatoric stress,faults and random joint in this area is analyzed deeply,then an coupling support of double-layer-truss is proposed.The research results show that the first wave of deformation energy was released by bolt-mesh-cable fixed into the roof,floor and two sides of the roadway.While the second wave of deformation energy was released through the interface function between double-layer-truss and the surrounding rock.The double-layer-truss that characterized by high strength,good integrity can absorb high deformation energy of surrounding rocks,which led to the uniform distribution of the stress.Engineering practice shows this technology has been successfully applied to control the deformation failure of the tertiary extremely soft rock roadway.

A study of support strategies in deep soft rock:The horsehead crossing roadway in Daqiang Coal Mine

Geomechanics in deep mines becomes more complex and structural support in soft rock can be very difficult.Highly stressed soft rock subject to expansion deformation is particularly difficult to control.The Tiefa Coal Industry Group Daqiang Coal Mine is used as an example.A ventilation shaft,à550 horsehead,is located in tertiary soft rock.Analysis of the reasons for deformation shows an intumescent rock,which is easily damaged.Field observations and theoretical analysis led to a design capable of stabilizing the rock.A combination of spray,anchors,anchor bolts,and soft corner coupled truss supports allowed the deformation to be controlled.This provides a model for similar designs when support of a horsehead roadway is required.

Nonlinearity analysis of piezoelectric micromachined ultrasonic transducers based on couple stress theory

This paper studies the static deformation behavior of a piezoelectric micromachined ultrasonic transducer （PMUT） actuated by a strong external electric field. The transducer membrane consists of a piezoelectric layer, a passive layer and two electrode layers. The nonlinearities of the piezoelectric layer caused by electrostriction under a strong electric field are analyzed. Because the thickness of the transducer membrane is on the microscale, the size dependence of the deformation behavior is evaluated using the couple stress theory. The results show that the optimal ratio of the top electrode diameter and the membrane diameter is around 0.674. It is also found that this optimal value does not depend on any other parameters if the thicknesses of the two electrodes are negligible compared with those of the piezo- electric and passive layers. In addition, the nonlinearities of the piezoelectric layer will become stronger along with the increase of the electric field, which means that softening of the membrane stiffness occurs when a strong external electric field is applied. Meanwhile, the optimal thickness ratio for the passive layer and the piezoelectric layer is not equal to 1.0 which is usually adopted by previous researchers. Because there exists size dependence of membrane deforma-tion, the optimal value of this thickness ratio needs to be greater than 1.0 on the microscale.

A new finite element of spatial thin-walled beams

Based on the theories of Timoshenko＇s beams and Vlasov＇s thin-walled members, a new spatial thin-walled beam element with an interior node is developed. By independently interpolating bending angles and warp, factors such as transverse shear deformation, torsional shear deformation and their Coupling, coupling of flexure and torsion, and second shear stress are considered. According to the generalized variational theory of Hellinger-Reissner, the element stiffness matrix is derived. Examples show that the developed model is accurate and can be applied in the finite element analysis of thinwalled structures.

Numerical Analysis of Settlement Response of Shallow Footing Subjected to Heavy Rainfall and Flood Events

The US and many parts around the world have experienced prolonged periods of heavy rainfall, severe floods, and droughts over the past 50 years. This study investigates the impacts of extreme hydrological events such as heavy rainfall and flood on the settlement behavior of continuous footing installed in unsaturated soil using a coupled Geotechnical-Hydrological finite element software, PLAXIS 2D. Initially, the effect of different degrees of saturation on the settlement behavior of the continuous footing of widths 1.5 m, 3.0 m, and 4.5 m was analyzed by applying a mechanical load. Then the settlement behavior of the footing was analyzed by applying heavy rainfall of intensity 102 mm/day for six days. Finally, the settlement behavior of the footing was analyzed by applying a flood head of 2.5 meters for seven days. The results indicated that the wetting front movement during heavy rainfall and flooding led to the weakening of soil strength and stiffness and induced additional settlements. The additional settlement induced by the flood was significantly higher than the heavy rainfall. The differential settlement was higher when the rainfall was applied on one side of the footing. The rebound of the elastic settlement was uniquely noticed when the flood head receded with time. The results indicated that not all the settlements were induced by the soil saturation but also due to the hydrostatic loading due to the flood head. The settlements induced by the flooding exceeded the allowable settlement of 25 mm, resulting in failure. These additional settlements caused by heavy rainfall and flood will lead to poor serviceability of the structures and cause the failure of the footing.

SECTIONAL FINITE ELEMENT ANALYSIS OF COUPLED DEFORMATION BETWEEN ELASTOPLASTIC SHEET METAL AND VISCO-ELASTOPLASTIC BODY

The present paper is devoted to developing a new numerical simulation method for the analysis of viscous pressure forming （VPF）, which is a sheet flexible-die forming （FDF） process. The pressure-carrying medium used in VPF is one kind of semisolid, flowable and viscous material and its deformation behavior can be described by the visco-elastoplastic constitutive model. A sectional finite element model for the coupled deformation analysis between the viscoelastoplastic pressure-carrying medium and the elastoplastic sheet metal is proposed. The resolution of the Updated Lagrangian （UL） formulation is based on a static explicit approach. The frictional contact between sheet metal and visco-elastoplastic pressure-carrying medium is treated by the penalty function method. Coupled deformation between sheet metal and visco-elastoplastic pressure-carrying medium with large slip is analyzed to validate the developed algorithm. Finally, the viscous pressure bulging （VPB） process of DC06 sheet metal is simulated. Good agreement between numerical simulation results and experimental measurements shows the validity of the developed algorithm.

A New Dynamic Model for a Flexible Hub-Beam System

In this paper,a new dynamic model for the flexible hub-beam system is proposed by using the principle of continuum medium mechanics and the finite element discretization method.In the proposed model,the coupling deformation of any element of the beam is only related with the nodal coordinates of this element.So this model is suitable to the rotating beam in an arbitrary shape.Numerical examples of slender beams in straight and irregular shapes are carried out to demonstrate the validation of the proposed model.Simulation results indicate that the proposed model can be used valid for dynamic description of flexible rotating beam in irregular shape, and for both low and high rotation speeds.

A Thermo-Magneto-Mechanically Coupled Constitutive Model of Magnetic Shape Memory Alloys

A macroscopic phenomenological constitutive model considering the martensite transformation and its reverse is constructed in this work to describe the thermo-magneto- mechanically coupled deformation of polycrystalline magnetic shape memory alloys （MSMAs） by referring to the existing experimental results. The proposed model is established in the frame- work of thermodynamics by introducing internal state variables. The driving force of martensite transformation, the internal heat production and the thermodynamic constraints on constitutive equations are obtained by Clausius dissipative inequality and constructed Gibbs free energy. The spatiotemporal evolution equation of temperature is deduced from the first law of thermodynam- ics. The demagnetization effect occurring in the process of magnetization is also addressed. The proposed model is verified by comparing the predictions with the corresponding experiments. It is concluded that the thermo-magneto-mechanically coupled deformation of MSMAs including the magnetostrietive and magnetocaloric effects at various temperatures can be reasonably described by the proposed model, and the magnetocaloric effect can be significantly improved over a wide range of temperature by introducing an additional applied stress.

Tensile behaviors of filaments with misfit of chirality

Slender chiral filaments are ubiquitous in both artificial and biological materials.Due to their chiral microstructures,chiral filaments usually exhibit favorable properties such as superior elasticity and unusual stretch-twist coupling deformation.However,how these chiral microstructures affect the elastic behavior of filaments remains unclear.In this paper,a refined Cosserat rod model with misfit or mismatching of chirality induced by inhomogeneous arrangement of chiral microstructures incorporated is developed.Using the refined rod model,the force-displacement relationships and variation of structural chirality during the tensile processes of two typical helical structures,i.e.,single-strand helix and double-strand helix,are investigated.The results show that the misfit of chirality can lead to a bend-twist deformation with a high coupling degree,which makes the rod much“soft”when stretched.The chiral filaments undergo an unusual twist when stretched,corresponding to an obviously nonlinear variation of structural chirality.The work suggests that the misfit of chirality can be used to tune the elastic behavior of chiral filaments,which is helpful in guiding the design of flexible actuators and soft devices.