Underground coal gasification technology is important in the context of China's energy crisis, for the efficient and clean utilization of coal resources, and for expanding the natural gas resources to realize the strategic resource replacement. Based on the investigation of underground coal gasification technology at home and abroad, this paper divides underground coal gasification technology into two categories, namely drilling technology and roadway technology, and focuses on the development mode of drilling underground coal gasification technology. The technology development of the well drilling UCG can be divided into four stages: (1) the basic theory research stage; (2) the borehole method technology development mode stage; (3) the linked vertical well development mode stage with different channel breakthrough methods; (4) the horizontal well development mode stage. This paper focuses on the key technology of three development modes in the UCG process, including the borehole mode, the vertical well drilling mode and the horizontal well drilling mode. By comparing different uses of these technology modes, the advantages and disadvantages are evaluated in detail. On the basis of summarizing the development process of underground coal gasification technology development mode, this paper points out the development trend of underground coal gasification technology, which has a positive guiding significance for the coming commercial development of underground coal gasification in China.

Composite materials are widely used in aerospace and other fields, and the lightweight design becomes a research focus. The quality optimization design of composite laminates can reduce the fiber consumption, the quality requirement and the cost of the laminates. Firstly, the deformation and stress diagrams of composite laminates under axial load are studied, and the failure prone parts are analyzed; taking the ply thickness as design variables, the maximum strain and the ply ratio as constraints, the optimization objective is to minimize the laminate quality, the ply thickness and other design variables of the carbon fiber composite laminates are optimized, and the optimization results are checked by the strength theory. The mechanical properties of the composite laminates before and after optimization are compared and analyzed by mechanical tests. The results show that the total weight of the carbon fiber composite laminates is reduced by about 16.7% after optimization. The optimized laminates can meet all requirements of the strength theory of composite materials. The experimental results are consistent with the software simulation, which shows that the optimization method is reasonable and reliable.

At the long-term service temperature (above 300℃), the pressure vessels and the pipelines are prone to thermal aging and high-temperature creep. The microstructure is characterized by the coarse second phase particles, the grain boundary coarsening and the creep cavities, so the microstructure heterogeneity of the material makes the micro-stress analysis very complicated. Firstly, the Eshelby's equivalent inclusion theory is elaborated in detail. In view of the microstructure change of the pressure bearing Steel SA508-III in service in the power plant, when an inclusion is contained in the matrix, the sparse material system (with a small number of inclusions) combines the first and in the early of the second stage of creep, and the non-sparse material system combines in the middle period of the second stage of creep. The microscopic stress and strain analysis of the inclusions is performed, and the stress and the transition strain are calculated when the temperature changes or an external load is applied. On this basis, combining the microstructure characteristics of the pressure bearing materials in the final period of the second stage and the third stage of creep, the transformation strain and elastic modulus of the two different inclusions in the matrix are obtained.

The limitations of the traditional one-dimensional Terzaghi consolidation theory are more and more felt. In this paper, the unified hardening (UH) constitutive model with consideration of the time effect is used, with the Hansbo's flow model coupled with the consolidation equation of the UH constitutive model, and the consolidation equations based on the UH model and the Hansbo's flow model under several typical cyclic loads are established. Numerical analysis is carried out by using the FlexPDE software, and the reliability of the algorithm is verified by comparing the calculation results with those in the literature. On this basis, the seepage consolidation characteristics of the saturated clay under several typical cyclic loads are studied, and the influence of the model parameters on the consolidation characteristics of the saturated clay is analyzed. The results show that: under the cyclic loading, the average consolidation degree and the settlement of the foundation are always in a cyclic state; the influence of the Hansbo's flow model parameters on the average consolidation degree is greater than that of the Darcy's flow parameters, and the secondary consolidation coefficient in the UH model has a greater influence on the consolidation process. In addition, the influence of the Hansbo's flow parameters and the soil rebound index and permeability index on the consolidation process is mainly reflected in the middle stage, and the later stage of the consolidation process will be in a stable circulation state.

In order to study the influence of the joint digital image processing (DIP) angle on the fracture mode and the fracture process of limestone, digital images are used to characterize the microscopic non-uniformity caused by the shape, the size and the distribution of the calcite in limestone. RFPA2D-DIP is used to simulate the fracture process and the failure mode of the jointed limestone with different dip angles. The results show that the meso structure has an important influence on the mechanical properties and the ultimate failure mode of the jointed specimens. The elastic modulus and the compressive strength of the jointed limestone have obvious anisotropy, and show shaped changes with the increase of the jointed dip angle. Under the action of the uniaxial compression, the jointed limestone is mainly subjected to the tensile failure accompanied with a small amount of shear failure on the mesoscale. The ultimate failure modes of the jointed limestone are shown in six forms depending on the jointed dip angle: the linear shape ($\alpha =45^\circ$, $\alpha =75^\circ$), the N shape ($\alpha=60^\circ$), the oblique Z shape ($\alpha =0^\circ$), the oblique N shape ($\alpha =90^\circ$), the M shape ($\alpha =15^\circ$), and the V shape ($\alpha =30^\circ$).

In order to investigate the effects of the recycled aggregate replacement ratio, the aggregate shape and distribution on the meso-cracks of the recycled aggregate concrete under the uniaxial compression loading, several 2-D random models of the circular and convex polygon aggregates by varying the replacement ratios of 0%, 30%, 50%, 70%, and 100% are established. The uniaxial compression test with a displacement load is simulated based on the potential base force element method (BFEM). The results show that the BFEM is a good method to study the meso-fracture damage of the recycled aggregate concrete. Generally, the cracks are always first formed in interfacial transition zones (ITZs), then the cracks are developed into isolated cracks around the aggregate. Finally, up to 2 cracks grow along the 45$^\circ$ direction through the aggregate-concentrated areas. For the circular aggregate, the continuous cracks are developed along the tangential direction of the aggregate and perpendicular to the aggregate diameter. For the convex aggregate, the continuous cracks are developed along the outer contour toward the tip direction of the aggregate parallel to the outer contour of the aggregates. With the increases of the replacement ratios, the compression strength decreases and stabilizes eventually. The compression strength of the convex polygon aggregate of the RAC is slightly higher than that of the circular aggregate.

Using the pseudo cohesive force formed by the capillary effect of the sand to prepare samples with different sedimentary directions, a series of the triaxial consolidation drainage shear tests are performed to study the influence of the granulometric composition on the mechanical properties of the initial anisotropic sand. The relationship among the granulometric composition, the sedimentary direction, the strength characteristics and the volume change is analyzed. The results show that the formation of the shear band is affected by the particle size distribution, which is the cause of the sharp drop stage in the stress-strain relationship. The sedimentation direction has an effect on the deviatoric stress peak strength of the coarse sand and the fine sand, and the effect on the residual strength is limited by the particle size distribution. When the sedimentary direction is close to the failure surface of the sample, the strength of the sample is low, the dilatancy deformation of the sample is small and it is easier to be damaged, and the granulometric composition has a more significant influence on the triaxial shear mechanical behavior of the sand.

A mechanical vibration system with a novel 2DOF nonlinear energy sink (NES) is studied. The nonlinear energy sink structure is constructed and the motion equation of the whole system is established. The nonlinear force acting on the second-order oscillator is approximately expressed by Taylor series and the numerical method is used to analyze the vibration reduction performance of the NES. The conditions of the targeted energy transfer in the NES are studied in terms of its structural parameters and the initial energy. It is shown that the NES can effectively reduce the energy of the main structure and the vibration suppression effect of the NES is better than that of the single degree of freedom NES.

In order to quantify the effect of the dead weight (hereinafter called the distributed axial force) of the beam, the rod and the column on the static instability and the transverse vibration, the mechanical and mathematical models of the instability and the transverse vibration are established with consideration of the distributed axial force. The finite difference method, the Galerkin method and the numerical integration method are used to obtain the numerical results. The results show that: the natural frequency of the rod with the axial distributed force decreases with the increase of the rod length, and the first order natural frequency is zero when the rod is unstable; the axial distributed force has a small impact on the critical load of the shorter rod, but has a greater impact for a longer rod; the Galerkin method is not suitable for calculating the buckling critical load of the super long rod.

The influence of the temperature on the galloping characteristics of iced conductor was often neglected in related studies. In this paper, the galloping governing equation with consideration of the temperature effect is derived. Based on the catenary method and the thermal stress theory, the partial differential galloping equation of iced conductor is derived, then the partial differential equation is transformed into the ordinary differential equation by Galerkin method. The aerodynamic load model is established and the aerodynamic loads are introduced into the galloping equation. Then the displacement response of the iced conductor is obtained by the multiple scale method. Finally, a parameter analysis and a numerical example analysis are carried out. The results show that the temperature has a significant effect on the in-plane and out-of-plane frequencies of the iced conductor, and also has a certain influence on the galloping amplitude of the iced conductor. It can be seen that the influence of the temperature on the galloping characteristics of the iced conductors must be considered when studying the galloping characteristics of the iced conductor.

For the plane triangular truss structure, the assumption of small deformation in materials mechanics can be used to simplify the solution process by replacing arcs with tangents, to meet the actual needs of the project to a certain extent. The knowledge for the application scope of this small deformation hypothesis is important for students. In this paper, taking the plane triangular truss structure as an example, the theoretical derivation and the finite element analysis are used to quantitatively analyze the applicable range of the small deformation hypothesis of the typical structure through a specific calculation example. The derivation process and the analysis are generalizable, which can help students understand the application of materials mechanics assumptions in engineering practice.

In the analytical mechanics, when two rigid surfaces with smooth shape keep contact at one point without friction or in the pure rolling state, two conditions are considered to deduce the ideal constraints for the contact. In the frictionless case, the possible infinitesimal displacements of the two contact points on the two surfaces are equal in the normal direction. In the pure rolling case, the relative velocity of the contact point is zero. In this paper, starting from the geometric conditions of taking the same position in space and in the tangent state, the preconditions are more clear and rigorous.

The collision of slider seems not relevant to Pi, but there is a certain connection between the two things really. In this paper, the collision dynamics of slider is studied. By using MATLAB, the connection between the number of collision of slider and Pi is established. The calculation results are proved theoretically.

In order to improve the teaching effect of materials mechanics and to cultivate students' ability to analyze and solve practical problems, the reform and the practice of the teaching method based on outcome based education (OBE) are carried out. Taking the college students majoring in mining as the teaching object, and with consideration of the latest developments in the roadway support technology, the roof bolts, the piers, the drilling bolt holes, the optimization of the roof anchor arrangement of roadway, the failure analysis of the steel tube concrete support and the stability analysis of the pier column are adopted as the examples of the axial tension, the axial compression, the torsion, the bending, the combined deformation, and the compression rod stability, respectively. Then, the cases are analyzed by using the knowledge of materials mechanics in related chapters. The OBE teaching method enables students to deeply understand the close relationship between materials mechanics and their majors. It can stimulate students' interest in learning and cultivate their scientific literacy and research thinking. In addition, it enables students to practice the skills of innovation and solving engineering problems. The teaching effect based on OBE is remarkable.

The fluid mechanics is a compulsory basic course for the undergraduate major of safety engineering category. Through innovating the teaching mode of safety engineering fluid mechanics theory, integrating professional disciplinary knowledge and reforming the practical teaching method, the overall teaching reform idea and plan are put forward. The core knowledge hierarchy of the safety engineering fuid mechanics is combed. A series of the seemingly isolated basics theoretic three formulas are linked. The knowledge points related to the safety engineering are extended. The ultimate goal of the teaching course is to make the student understand what to learn, how to learn and how to use the related knowledge in the safety engineering. In addition, the practice teaching link of the safety engineering is enriched. The self-made experiment is encouraged for students to conduct the exploratory discovery with an independent team formed. It is suggested to broaden the practice teaching form and method and guide students to carry out targeted virtual simulation experiments to improve the innovation ability of student.

With the integration of the information technology in the mechanics courses, the process assessment examination is practiced, which is student-centered and capacity-building oriented, meanwhile, focusing on students' ability in the whole learning process, such as the knowledge learning, the independent learning, the classroom learning, the team cooperation, the problem solving, the application and innovation ability, as far as possible to inspire every student all-around development,and to give a more comprehensive evaluation for students.

The teaching of experimentation is a key link between the theory and the practice, which is of great significance to cultivate and improve students' comprehensive quality. However, the traditional teaching model is not adequate to meet the requirement for innovative-oriented engineering talents. In this paper, the effect of developing the experimental equipment of fluid mechanics on improving undergraduates' innovation spirit and ability is discussed, combined with the experimental teaching reform practices of fluid mechanics. The innovative experimental teaching can stimulate the students' enthusiasm for doing experiments and enhance their innovative ability to solve complex practical problems with the knowledge they have learned.

Based on the textbook Elasticity by Wu Jialong, and the "trilemma" characteristics of the course, taking the common questions in the stress state theory as examples, the stress vector, the normal stress, the shear stress, the principal stress, the principal direction of the applied force and the maximum shear stress on any differential inclined plane are included. The Matlab-GUI module is used to compile the stress state theory solver, By processing the inputting physical parameters and displaying results, the thinking process of the elasticity is reproduced and the mathematical solution is verified, the complex abstract mechanical formulas and the differential slope results are clarified in graphic visualization, so that the students' abstract thinking and mechanical thinking are linked. The stress state theory solver of elasticity can provide a reference for students' mechanics learning and for mechanics teaching.

Although as a basic course, engineering, mechanics occupies a very important position in the professional course system, but the teaching effect of the mechanics course is not very good,. Limited by the teaching conditions and the student-level, many teaching methods are not adequate. This paper analyzes practical applications of the mechanics courses in the light of the contest and the three-stage teaching method of mechanics course is established, guided by National Structure Design Contest for College Students, with good results in practice. Key words engineering mechanics course, structure design contest, analyzed practical application, three-stage teaching method.

In the past years, the prosperous progress of additive manufacturing , promotes a rapid development of the mechanical architected metamaterials. In this paper, the design and the excellent mechanical properties of these metamaterials are introduced, including the following parts: the evolutional development of the unit cell design from beam-based, plated-based to shell-based structures in order to reduce the intrinsic stress concentration; the route to achieve the isotropic Hashin-Shtrikman stiffness limit; their applications in various fields of biological medicine, energy, environment, and others.