NEW PRINCIPLES OF WORK AND ENERGY AS WELLAS POWER AND ENERGY RATE FORCONTINUUM FIELD THEORIES

New principles of work and energy as well as power and energy rate with cross terms for polar and nonlocal polar continuum field theories were presented and from them all corresponding equations of motion and boundary conditions as well as complete equations of energy and energy rate with the help of generalized Piola's theorems were naturally derived in all and without any additional requirement. Finally, some new balance laws of energy and energy rate for generalized continuum mechanics were established. The new principles of work and energy as well as power and energy rate with cross terms presented in this paper are believed to be new and they have corrected the incompleteness of all existing corresponding principles and laws without cross terms in literatures of generalized continuum field theories.

Consistency and Validity of the Mathematical Models and the Solution Methods for BVPs and IVPs Based on Energy Methods and Principle of Virtual Work for Homogeneous Isotropic and Non-Homogeneous Non-Isotropic Solid Continua

Energy methods and the principle of virtual work are commonly used for obtaining solutions of boundary value problems (BVPs) and initial value problems (IVPs) associated with homogeneous, isotropic and non-homogeneous, non-isotropic matter without using (or in the absence of) the mathematical models of the BVPs and the IVPs. These methods are also used for deriving mathematical models for BVPs and IVPs associated with isotropic, homogeneous as well as non-homogeneous, non-isotropic continuous matter. In energy methods when applied to IVPs, one constructs energy functional (I) consisting of kinetic energy, strain energy and the potential energy of loads. The first variation of this energy functional (δI) set to zero is a necessary condition for an extremum of I. In this approach one could use δI = 0 directly in constructing computational processes such as the finite element method or could derive Euler’s equations (differential or partial differential equations) from δI = 0, which is also satisfied by a solution obtained from δI = 0. The Euler’s equations obtained from δI = 0 indeed are the mathematical model associated with the energy functional I. In case of BVPs we follow the same approach except in this case, the energy functional I consists of strain energy and the potential energy of loads. In using the principle of virtual work for BVPs and the IVPs, we can also accomplish the same as described above using energy methods. In this paper we investigate consistency and validity of the mathematical models for isotropic, homogeneous and non-isotropic, non-homogeneous continuous matter for BVPs that are derived using energy functional consisting of strain energy and the potential energy of loads. Similar investigation is also presented for IVPs using energy functional consisting of kinetic energy, strain energy and the potential energy of loads. The computational approaches for BVPs and the IVPs designed using energy functional and principle of virtual work, their consistency and validity are also investigated. Classical continuum mechanics (CCM) principles i.e. conservation and balance laws of CCM with consistent constitutive theories and the elements of calculus of variations are employed in the investigations presented in this paper.

On complete and micropolar-based incomplete strain gradient theories for periodic lattice structures

The micropolar(MP) and strain gradient(SG) continua have been generally adopted to investigate the relations between the macroscopic elastic constants and the microstructural geometric parameters. Owing to the fact that the microrotation in the MP theory can be expressed in terms of the displacement gradient components, we may regard the MP theory as a particular incomplete SG theory called the MPSG theory,compared with the existing SG theories which are deemed complete since all the SGs are included. Taking the triangular lattice comprising zigzag beams as an example, it is found that as the angle of the zigzag beams increases, the bending of the beams plays a more important role in the total strain energy, and the difference between the results by the two theories gradually decreases. Finally, the models are verified with the pure bending and simple shear of lattices by comparing with the results obtained by the finite element method(FEM)-based structure analyses.

Mechanical stress and deformation analyses of pressurized cylindrical shells based on a higher-order modeling

In this research,mechanical stress,static strain and deformation analyses of a cylindrical pressure vessel subjected to mechanical loads are presented.The kinematic relations are developed based on higherorder sinusoidal shear deformation theory.Thickness stretching formulation is accounted for more accurate analysis.The total transverse deflection is divided into bending,shear and thickness stretching parts in which the third term is responsible for change of deflection along the thickness direction.The axisymmetric formulations are derived through principle of virtual work.A parametric study is presented to investigate variation of stress and strain components along the thickness and longitudinal directions.To explore effect of thickness stretching model on the static results,a comparison between the present results with the available results of literature is presented.As an important output,effect of micro-scale parameter is studied on the static stress and strain distribution.

Instability criterion for the system composed of elastic beam and strain-softening pillar based on gradient-dependent plasticity

A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear slips of multiple shear bands, the pillar is divided into several narrow slices where compressive deformation is treated as uniformity. In the light of the compatibility condition of deformation, the total compressive displacement of the pillar is equal to the displacement of the beam in the middle span. An instability criterion is derived analytically based on the energy principle using a known size of localization band according to gradient dependent plasticity. The main advantage of the present model is that the effects of the constitutive parameters of rock and the geometrical size of structure are reflected in the criterion. The condition that the derivative of distributed load with respect to the deflection of the beam in the middle span is less than zero is not only equivalent to, but also even more concise in form than the instability criterion. To study the influences of constitutive parameters and geometrical size on stability, some examples are presented.

The Minimum Energy Principle in Description of Nonlinear Properties of Orthotropic Material

In this paper the conception of theoretical determine the relations between material experimental characteristics is presented. On the base of stress-strain relations for nonlinear elastic anisotropic material and geometrical interpretation of deformation state, the general form of strain energy density function was introduced. Using this function and variational methods the relations between material characteristics were achieved. All considerations are illustrated by a short theoretical example.

Virtual Principle for Determination Initial Displacements of Reinforced Concrete and Prestressed Concrete (Overtop) Members

Theoretical approach with analytical and numerical procedure for determination initial displacement of a reinforced and prestressed concrete members, simple and cantilever beams, loaded by axial forces and bending moments is proposed. It is based on the principle of minimum potential energy with equality of internal and external forces. The equations for strain internal energy have been derived, including compressed and tensile concrete and reinforcement. The energy equations of the external forces with axial flexural displacement effects have been derived from the assumed sinusoidal curve. The trapezoid rule is applied to integrate the segment strain energy. The proposed method uses a non-linear stress-strain curve for the concrete and bilinear elastic-plastic relationship for reinforcement;equilibrium conditions at a sectional level to generate the strain energies along the beam. At the end of this article are shown three specific numerical examples with comparative, experimental (two tests) results with the excellent agreement and one calculation result with a great disagreement, by obtaining results of virtual principle method. With this method is avoiding the adoption of an unsure (EJ), as in the case of underestimating or overestimate initial flexural rigidity.

Stability and electronic structure of InN nanotubes from first-principles study

The stability and electronic structure of hypothetical InN nanotubes were studied by first-principles density functional theory. It, was found that the strain energies of InN nanotubes are smaller than those of carbon nanotubes of the same radius. Single-wall zigzag InN nanotubes were found to be semiconductors with a direct band gap while the armchair counterparts have an indirect band gap. The band gaps of nanotubes decrease with increasing diameter, similar to the case of carbon nanotubes.

Thermodynamic Consistency of Plate and Shell Mathematical Models in the Context of Classical and Non-Classical Continuum Mechanics and a Thermodynamically Consistent New Thermoelastic Formulation

Inclusion of dissipation and memory mechanisms, non-classical elasticity and thermal effects in the currently used plate/shell mathematical models require that we establish if these mathematical models can be derived using the conservation and balance laws of continuum mechanics in conjunction with the corresponding kinematic assumptions. This is referred to as thermodynamic consistency of the mathematical models. Thermodynamic consistency ensures thermodynamic equilibrium during the evolution of the deformation. When the mathematical models are thermodynamically consistent, the second law of thermodynamics facilitates consistent derivations of constitutive theories in the presence of dissipation and memory mechanisms. This is the main motivation for the work presented in this paper. In the currently used mathematical models for plates/shells based on the assumed kinematic relations, energy functional is constructed over the volume consisting of kinetic energy, strain energy and the potential energy of the loads. The Euler’s equations derived from the first variation of the energy functional for arbitrary length when set to zero yield the mathematical model(s) for the deforming plates/shells. Alternatively, principle of virtual work can also be used to derive the same mathematical model(s). For linear elastic reversible deformation physics with small deformation and small strain, these two approaches, based on energy functional and the principle of virtual work, yield the same mathematical models. These mathematical models hold for reversible mechanical deformation. In this paper, we examine whether the currently used plate/shell mathematical models with the corresponding kinematic assumptions can be derived using the conservation and balance laws of classical or non-classical continuum mechanics. The mathematical models based on Kirchhoff hypothesis (classical plate theory, CPT) and first order shear deformation theory (FSDT) that are representative of most mathematical models for plates/shells are investigated in this paper for their thermodynamic consistency. This is followed by the details of a general and higher order thermodynamically consistent plate/shell thermoelastic mathematical model that is free of a priori consideration of kinematic assumptions and remains valid for very thin as well as thick plates/shells with comprehensive nonlinear constitutive theories based on integrity. Model problem studies are presented for small deformation behavior of linear elastic plates in the absence of thermal effects and the results are compared with CPT and FSDT mathematical models.

Some Ideas of James Watt in Contemporary Energy Conversion Thermodynamics

James Watt contributed significantly to the development of the thermodynamics of energy conversion as a science. Several of his ideas are now integral part of thermodynamics, but Watt as their creator is not mentioned. This paper presents some of Watt’s concepts of energy conversion, including his thermodynamic analysis of the Newcomen steam engine that marks the beginning of thermal engineering. The analysis illuminated the causes of the enormously high heat losses in the installation and showed the ways for their reduction. This led him to a new conception of the steam engine with a separate condenser. Not less important was Watt’s determination of some physical properties of water and steam used as the working substance. In the experiments he observed the decrease of the latent heat of steam with increasing temperature and its disappearance at very high temperature led him to postulate the existence of a thermodynamic critical state of water. He introduced the work associated with volume change into thermodynamics and illustrated it graphically. Several of Watt’s numerous ideas deserve to be included into the history of the thermodynamics of energy conversion but they are rarely mentioned in the scientific literature. Arguably the most important is the First Law of Thermodynamics, which he introduced in his 1769 patent and related works in 1774 and 1778.

稀土X(X=La、Ce、Pr、Nd)修饰单层h-MoS_(2)的NO气敏性

为提高h-MoS_(2)对NO的气敏性,采用第一性原理研究了X(X=La、Ce、Pr和Nd)对h-MoS_(2)的稳定性、吸附特性、功函数和伏安特性的影响.研究结果表明:X(X=La、Ce、Pr和Nd)取代Mo原子后得到的形成能均为负,说明掺杂体系容易形成且稳定存在.同时X掺杂后的h-MoS_(2)布居数相比于未掺杂前的大,也说明掺杂有利于体系稳定.NO吸附在La、Ce原子顶部位置的吸附能为-1.215 eV、-1.225 eV,吸附距离分别为2.475?、2.854?,具有明显的化学吸附特征.同时Hirshfeld转移电荷分别为0.213e和0.325e,具有明显的受体特征,提高了气敏性.La和Ce掺杂后能明显改变功函数的大小,也说明La和Ce能提高h-MoS_(2)对NO的气敏性.施加电场后能有效提高Pr掺杂体系的吸附强度,增大Hirshfeld转移电荷,对功函数的改变最大,所以电场对Pr掺杂体系的影响非常明显.通过分析掺杂体系的伏安特性曲线,La、Ce两掺杂体系的电流分别由0增大到5.3μA和4.8μA,而Pr、Nd两掺杂体系的电流分别由0增大到2.2μA和1.2μA,所以La、Ce掺杂对于体系敏感性的影响比较明显.

吉利帝豪EV450交流充电故障检修

随着我国各地区环保要求不断提升,人们的环境保护意识也不断增强,新能源产业随即成为主流,新能源汽车潮流也被广泛推广、应用。在新能源汽车中交流充电系统不仅是纯电动汽车主要的组成部分,也是纯电动汽车上一种非常重要的充电装置之一。同时根据交流充电系统常见故障现象,通过原理分析法、文献参考法、技术和经验分析法,对此类故障进行深入探索、分析和排除;问题的解决和技术、经验的交流更有利于促进新能源汽车产业更好地发展。

真空断路器弹簧操动机构分闸弹簧的优化设计方法

操动机构分闸弹簧设计时,为解决分闸弹簧出力特性和负载特性不匹配带来的分闸保持不住、分闸速度过大或过小等问题,提出一种分闸弹簧的优化设计方法。首先计算出分闸过程中的力矩与功,然后根据功能原理计算出各位移点的分闸速度,最后根据分闸速度和能量要求等因素对分闸弹簧进行优化。结果表明,优化后的分闸弹簧可使分闸过程中的出力特性和负载特性合理匹配,保证机构可靠分闸的同时,得到满足要求的分闸速度。通过理论计算和试验验证证明了所提优化方法的可行性,为真空断路器弹簧操动机构的分闸弹簧优化设计提供了有益指导。

液力传动装置工作原理及其在轨道交通上的应用

现代轨道交通系统建设需要兼顾运力、绿色化、安全性,一些传统的技术方法经优化后仍可发挥作用,包括液力传动装置在内。文章首先对该装置的构成、工作原理、特点进行分析,在此基础上分析其应用的具体形式和不足,最后展望轨道交通中液力传动装置应用优化思路,为后续轨道交通建设、液力传动装置的应用提供少许参考。

螺旋卸煤机在散货码头中的应用分析

螺旋卸煤机是一种常见的散货码头装卸设备,具有高效、可靠、节能等优势。通过分析螺旋卸煤机在散货码头作业中的应用情况,包括工作原理、优势和限制,提出相关改进建议,旨在提高散货码头的作业效率,实现可持续发展。

Rockburst mechanism in soft coal seam within deep coal mines

A number of rockburst accidents occurring in soft coal seams have shown that the rockburst mechanism involved in soft coal seams is significantly different from that involved in hard coal seams. Therefore, the method used to evaluate rockburst in hard coal seams is not applicable to soft coal seams. This paper established an energy integral model for the rockburst-inducing area and a friction work calculation model for the plastic area. If the remaining energy after the coal seam is broken in the rockburstinducing area is greater than the friction work required for the coal to burst out, then a rockburst accident will occur. Mechanisms of ‘‘quaking without bursting" and ‘‘quaking and bursting" are clarified for soft coal seams and corresponding control measures are proposed as the optimization of roadway layouts and use of ‘‘three strong systems"(strong de-stressing, strong supporting, and strong monitoring).

Growth of a Void in a Rubber Rectangular Plate under Uniaxial Extension

The finite deformation and stress analyses for a rectangular plate with a center void and made of rubber with the Yeoh elastic strain energy function under uniaxial extension were studied in this paper. An approximation solution was obtained from the minimum potential energy principle. The numerical results for the growth of the cavitation and stresses along the edge of the cavitation were discussed. In addition, the stress concentration phenomenon was considered.

Improvement for New Energy Vehicle within UI—Case Study on Han EV

New energy vehicle (NEV) refers to a vehicle which is fully or partially powered by electricity instead of petrol. Since petrol price grows constantly and people become more environmentally conscious, people have shown their numerous interests on the NEV. A lot of previous studies have paid more attention on vehicle itself, such as the high technology of the in-car assistance systems, and the pros and cons of electricity as a new energy for vehicle. However, the quality of vehicle should not only be limited to these aspects. Therefore, in this study, author focus more on the relationship between the vehicle and users and gives a brief introduction of some user interface problems through investigating one of the top selling types of NEV, Han EV belonging to BYD company, in terms of Standardize symbol, Gestalt grouping principles, Design of Visual display, Working memory and attention. In addition, corresponding improvement advice will also be provided in the later part of this work.

三阶屈服屈曲约束支撑耗能机理及设计方法研究

屈曲约束支撑(BRB)在拉压荷载作用下受力基本对称,其滞回曲线饱满,是一种耗能效果优良且广泛在工程中应用的耗能构件。传统屈曲约束支撑在多遇地震作用下不发生屈服,无法为结构提供耗能,且无法兼顾不同强度地震作用的使用需求。基于此,提出一种能够三阶屈服的屈曲约束支撑(TYBRB),并通过理论和模拟相结合对其工作原理及力学性能进行了系统的研究。介绍了TYBRB的构造组成及工作机理;在力学分析的基础上,建立了TYBRB的刚度方程,给出了各阶屈服力和屈服位移的计算方法;并采用ABAQUS有限元软件进行数值模拟,分析了TYBRB受力性能和抗震优越性。研究结果表明:TYBRB可以在较小变形情况实现一阶、二阶屈服进行耗能,具有明显的三阶屈服效果,可兼顾不同强度地震作用实现分阶段屈服耗能,且耗能性能优越。

海洋波浪能发电装置PTO系统研究进展

从波浪能发电能量转换过程出发,梳理动力输出系统与波浪能发电装置及其各部分的协同作用关系,并通过不同类型动力输出系统基本结构和工作过程归纳技术特点,列举对应的典型波浪能发电装置实例,探讨动力输出系统及波浪能发电装置存在的问题并展望未来发展趋势。