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To achieve the goal of 'carbon neutrality', it is of great significance to accelerate the process of dismantling high-carbon and high-pollution thin-walled cylinder structures such as chimneys and so on. A 183 m ultra-high coaxial thin-walled steel-inner-cylinder reinforced concrete chimney (UCTS-RCC) was successfully demolished for the first time. To successfully dismantle the UCTS-RCC by controlled blasting demolition technology, the necessary structural mechanics theoretical analysis and the critical blasting designs rationality verification were carried out. Based on the equilibrium equation of force and bending moment, a theoretical model of incision angle selection was established to determine the incision design of the steel inner cylinder (SIC). The stability of SIC under the designed incision parameters was verified based on FEM statics analysis. The cutting experimental on the target steel plate was completed with a linear shaped cutter to obtain the cutting effect. The cutting process and the overall collapse process of the UCTS-RCC were simulated by LS-DYNA. Based on the fixed axis rotation differential equation, the synchronous toppling theoretical model were established to study the motion of the UCTS-RCC. The results showed that the maximum stress at the position of the directional window and the stresses of the remaining supports were less than the yield limit of Q235B steel after that several pretreatment windows were carried out, the SIC could maintain the stability of remaining structures. The cutting experimental results of the target steel plate using linear shaped cutter were basically consistent with the cutting simulation and the cutting effect satisfied the design requirements of instantaneous cutting separation of the supports. According to the obvious difference of material properties between Q235B steel and reinforced concrete, the ignition delay time of the SIC was set 2 s earlier than that of the RCC. According to the synchronous collapse simulations, it could be known that the ignition delay time setting was reasonable and the collapse motion state of the UCTS-RCC was approximately fixed axis rotation, which was in line with the established synchronous toppling theory model. The SIC and RCC finally successfully collapsed synchronously. The blasting scheme and the rationality verification methods were applied successfully in this project, which was of great significance to provide a reliable reference for such ultra-high thin-walled cylinder complex structural chimney.

High-power diesel engine turbochargers predominantly utilize floating ring bearings as their primary supporting components. To further enhance their load capacity, multi-lobe noncircular bearings have been progressively employed. This study focuses on the investigation of noncircular three-lobe SFRBs (semi-floating ring-bearing structures) in marine turbochargers. Employing the half-step center Finite Difference Method (FDM) and the Newton–Raphson iterative procedure, the impact of operational parameters such as the journal speed, external load, oil supply pressure, and oil supply temperature on the static and dynamic characteristics of the inner oil film is analyzed. Subsequently, the accuracy of the theoretical model is validated through a comparative analysis of simulation results obtained from Dyrobes and Fluent. The findings indicate that as the oil supply pressure and temperature increase, the temperature rise and maximum oil film pressure of the three-lobe SFRBs gradually decrease, while the oil film thickness progressively increases, thereby significantly improving the lubrication state. The load capacity of the three-lobe SFRBs is primarily sustained by the bottom tile, where wall friction is most likely to occur. Additionally, within the actual speed range, the stiffness and damping of the three-lobe SFRBs exhibit noticeable nonlinear characteristics. [ABSTRACT FROM AUTHOR]

Based on MoC2 nanoribbons and poly-(terphenylene-butadiynylene) (PTB) molecules, we designed MoC2-PTB molecular spintronic devices and investigated their spin-dependent electron transport properties by using spin-polarized density functional theory and the non-equilibrium Green's function method. As a typical MXene material, it is found that the magnetic contribution of MoC2 nanoribbons mainly comes from the delocalized 3d electron of edge Mo atoms. Owing to the obvious spin-splitting near the Fermi level of the MoC2 nanoribbon electrode, the spin states can be effectively injected into the central scattering region under an external bias voltage. In addition, we also studied the effects of z-axis strain on the spin transport properties of the PTB molecular device, where the strain was controlled within the range of −9% to 9%. Under a compressed strain, spin current increases obviously, and the spin-filtering efficiency (SFE) decreases slightly. Nevertheless, under a tensile strain, we found that the SFE increases but spin current decreases. Moreover, z-axis strain can induce a negative differential resistance (NDR) effect at a high bias point. This work would expand the potential applications of new two-dimensional (2D) materials in the field of molecular spintronic devices. [ABSTRACT FROM AUTHOR]

For single-molecular junctions, the inherent energy mismatch between the central molecule and electrodes requires a delicate balance between electronic and phonon transport properties. Based on a combination of density functional theory and the non-equilibrium Green's function method, we have proposed a C8-BTBT molecule that is displaced by means of an intermediate layer, and it is demonstrated that the weak-coupling can dramatically suppress phonon transport, resulting in a low phonon thermal conductance. Furthermore, we also find that the p/n-type electrode doping tunes both the electronic and phononic transport properties effectively, leading to a more than one order of magnitude increase in both the power factor and thermoelectronic figure-of-merit over the undoped system, which is attributed to the enhancement of the electronic density of states from the hybrid orbital to increase the Seebeck coefficient. Moreover, it is found that reducing the mass mismatch in the electrode structure is one of the key factors to increase phonon thermal conductance, and an excellent thermoelectronic figure-of-merit of 3.8/7.2 has been obtained by boron/nitrogen doping. [ABSTRACT FROM AUTHOR]

A meso-finite element model with random voids in matrix is developed to simulate the tensile progressive damage of three-dimensional braided composites. A stiffness degradation method for generating the random void defect element in finite element method is presented. Proper criteria are adopted as initial damage of components, and stiffness degradation is implemented for damage propagation. The tensile strengths are predicted from calculated stress–strain curves. From simulation, void defects in matrix make the redistribution of micro-stress and accelerate the damage propagation of three-dimensional braided composites. Furthermore, void defects reduce the strength and ductility of the composites, but the reduction is not obvious if the porosity is controlled within a range. [ABSTRACT FROM AUTHOR]

In order to explore the micro-failure mechanism and predict tensile strength of three-dimensional braided composites, the three unit-cells models, namely interior cell, surface cell and corner cell, are established to simulate progressive damage of these materials. Macro model is firstly created and divided into three kinds of unit cells by their periodical distributions. A criterion is approached to determine damage and its pattern of each element, and stiffness degradation is implemented for the damaged elements with geometric damage theory. Periodical boundary conditions are applied on the models to calculate micro-stress and damage propagation is simulated with the increase of load. Each type of damage and its percentage is obtained by simulation and micro-failure mechanism is analyzed. Furthermore, the tensile strengths are predicted from calculated stress–strain curves. From simulation, composites with large braiding angle have more complicated micro-failure mechanism than composites with small braiding angle. It is also observed that there are more damages in surface cell than in interior cell and the damage types in the surface cell are various. The predicted results on the three unit-cells models agree well with the experimental data and are more accurate than only using an interior-cell model. [ABSTRACT FROM AUTHOR]

Based on MoC 2 nanoribbons and poly-(terphenylene-butadiynylene) (PTB) molecules, we designed MoC 2 -PTB molecular spintronic devices and investigated their spin-dependent electron transport properties by using spin-polarized density functional theory and the non-equilibrium Green's function method. As a typical MXene material, it is found that the magnetic contribution of MoC 2 nanoribbons mainly comes from the delocalized 3d electron of edge Mo atoms. Owing to the obvious spin-splitting near the Fermi level of the MoC 2 nanoribbon electrode, the spin states can be effectively injected into the central scattering region under an external bias voltage. In addition, we also studied the effects of z -axis strain on the spin transport properties of the PTB molecular device, where the strain was controlled within the range of -9% to 9%. Under a compressed strain, spin current increases obviously, and the spin-filtering efficiency (SFE) decreases slightly. Nevertheless, under a tensile strain, we found that the SFE increases but spin current decreases. Moreover, z -axis strain can induce a negative differential resistance (NDR) effect at a high bias point. This work would expand the potential applications of new two-dimensional (2D) materials in the field of molecular spintronic devices.