基于磁偶极子的磁场梯度张量局部缩并及试验验证

基于磁偶极子的磁场梯度张量缩并理论虽然可较好地描述磁源,不受测量系统的朝向的影响,但在实际的磁场梯度张量测量中通常仅可测得部分磁场梯度参数,没有获得磁场梯度张量中的所有张量分量,如何有效利用这些部分磁场梯度参量,已成为目前磁场梯度张量缩并理论及在磁场定位的应用中亟需解决的问题。基于磁偶极子理论提出磁场梯度张量局部缩并的方法,给出磁场梯度张量的局部模量的概念,分析了磁场梯度张量的局部模量及相关参数的三维空间分布规律,结果表明:局部模量CXY及kXY值随着g先增大后减小,在g=39°时取最大值,在g=90°时取最小值;局部模量C_Z及k_Z值随着g先减小后增大,在g=63°时取最小值,在g=0°时取最大值。提出磁场梯度张量局部模量中重要参数的近似计算公式,并通过试验进行验证。试验结果表明,试验值与理论计算值基本一致,可为磁场梯度张量局部缩并理论的应用提供依据和参考。     

Theoretical and experimental study of the isothermal mechanical behaviour of alloys in the semi-solid state

An isothermal constitutive model for semi-solid alloys based on the concepts of mechanics of continuous media and the theory of mixtures is presented. The model is applicable to semi-solid states obtained either by solidification from liquid state or partial remelting from solid state in which each of the solid and the liquid phases is contiguous. During deformation their behaviours are coupled: the densification of the solid matrix considered as a porous viscoplastic medium saturated with a liquid drives the fluid flow behaviour, and the resulting pressure distribution in the liquid affects in turn the stresses and the densification of the solid. The identification procedure of the model uses two types of mechanical tests: uniaxial compression and drained die pressing (filtration) carried out with A356 alloy. The identification results are then validated using drained triaxial compression.     

Fracture-mode map of brittle coatings: Theoretical development and experimental verification

Brittle coatings, upon sufficiently high indentation load, tend to fracture through either ring cracking or radial cracking. In this paper, we systematically study the factors determining the fracture modes of bilayer material under indentation. By analyzing the stress field developed in a coating/substrate bilayer under indentation in combination with the application of the maximum-tensile-stress fracture criterion, we show that the fracture mode of brittle coatings due to indentation is determined synergistically by two dimensionless parameters being functions of the mechanical properties of coating and substrate, coating thickness and indenter tip radius. Such dependence can be graphically depicted by a diagram called ‘fracture-mode map’, whereby the fracture modes can be directly predicated based on these two dimensionless parameters. Experimental verification of the fracture-mode map is carried out by examining the fracture modes of fused quartz/cement bilayer materials under indentation. The experimental observation exhibits good agreement with the prediction by the fracture-mode map. Our finding in this paper may not only shed light on the mechanics accounting for the fracture modes of brittle coatings in bilayer structures but also pave a new avenue to combating catastrophic damage through fracture mode control.     

Basins and bifurcations of a delayed feedback control system and its experimental verification for a DC bus circuit

Nonlinear Dynamics - Stochastic synchrony, also known as noise-induced synchronization that leads to phase coherence, arises when a set of uncoupled neurons synchronizes to a common white noise...     

Theoretical and experimental study of waves propagating along the edge of a wedge

The properties of a surface acoustic wave moving along the edge of an elastic wedge are studied. The equations defining the character of the wave motion under consideration are obtained. A method is proposed to determine field parameters that adequately describe the experimentally confirmed acoustic phenomena taking into account the characteristics of wave propagation in the wedge-shaped region. The results of the theoretical study are compared with experimental data obtained on an original device used to determine displacements in small surface areas.     

The experimental study on the contact process of passive walking

The passive dynamic walking is a new concept of biped walking. Researchers have been working on this area with both theoretical analysis and experimental analysis ever since McGeer. This paper presents our compass-like passive walking model with a new set of testing system. Two gyroscopes are used for measuring the angles of two legs, and ten FlexiForce sensors are used for measuring the contact forces on the feet. We got the experimental data on the passive walking process with the validated testing system. A great emphasis was put on the contact process between the feet and the slope. The contact process of the stance leg was divided into four sections, and differences between the real testing contact process and the classic analytical contact process with no bouncing and slipping were summarized.     

A comprehensive experimental study of the rheological behaviour of HDPE

Die-swell data have been obtained for six high-density-polyethylene (HDPE) samples. The data are presented in the form of generalized relationships taking into account both molecular and operational parameters. Data obtained from annealed samples have been used to calculate the first normal-stress difference by using Tanner's approach. An analytical expression has been found correlating the normal-stress difference with the shear-stress taking into account the molecular characteristics.     

Theoretical and experimental study of convection in a liquid layer with local heating

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 53–57, March–April, 1990.     

Contact force prediction and experimental verification on an OHC finger-follower-type cam-valuve system

In this work, contact forces acting on a finger-follower-type cam-valve system are predicted with a lumped mass-spring-damper dynamic model and predicted values verified experimentally. Since it is extremely difficult to measure contact forces directly, an indirect method is suggested and tested. Dynamic strain at a specified point of the finger-follower was calculated when the predicted contact forces act on the finger-follower. Then the actually measured strain at the specified point is compared with the calculated dynamic strain. It was found that the measured and calculated dynamic strain agreed with each other very well for a wide range of cam-valve system operation speeds. That means the indirect method suggested is very effective and reliable to predict contact forces in a cam-valve system.     

某型飞机机翼前缘抗鸟撞结构设计与试验验证

针对某型飞机机翼前缘抗鸟撞性能不满足适航要求的问题,采用"数值仿真-试验验证-再仿真"的研究思路,对该结构进行了抗鸟撞优化设计。首先,通过有限元数值仿真,分别对具有三角板结构和前墙结构的两种新型前缘结构抗鸟撞能力进行了分析。仿真结果表明:具有前墙结构的机翼前缘抗鸟撞能力优于原始结构和带三角板结构的机翼前缘;在鸟撞过程中,这种具有前墙结构的机翼前缘通过利用破损蒙皮继续变形吸能的方式提高了结构的抗鸟撞性能。基于此,对带前墙结构的机翼前缘进行了抗鸟撞试验,一方面验证了数值模拟方法的准确性,另一方面验证了前墙结构的抗鸟撞效果。最后,采用数值仿真方法对带前墙结构的机翼前缘结构进行了参数分析,得到了前缘蒙皮厚度和前墙厚度与结构抗鸟撞性能的关系,并基于结构承载和抗鸟撞能力的综合要求,确定了最终结构参数。分析表明,优化后的机翼前缘结构不仅满足抗鸟撞要求,而且实现结构减重30%。     

A comprehensive experimental study of the rheological behaviour of HDPE.

Extensional properties of four high density polyethylenes with different molecular weights and molecular weight distributions are presented. The samples have already been well characterized in shear and non-isothermal extensional flow. The data were collected at 180 °C for elongational rates between 3 · 10^–1 and 10^–4s^–1. Some qualitative and quantitative generalizations of the results are given.     

Theoretical and experimental study of an enhanced nonlinear energy sink

Nonlinear Dynamics - Based on theoretical and experimental investigations, this paper proposes a nonlinear energy sink (NES) with piecewise linear springs to enhance vibration suppression effects....     

The vibro-impact capsule system in millimetre scale: numerical optimisation and experimental verification

Meccanica - The vibro-impact capsule system has been studied extensively in the past decade because of its research challenges as a piecewise-smooth dynamical system and broad applications in...     

Experimental study of unsteady forced convection in a duct with and without arrays of block-like electronic components

An experimental apparatus was designed, built and used to study the behavior of transient forced convection in a rectangular duct with and without barriers due to a sinusoidal heat input at the inlet, to simulate the electric heating and cooling inside the computer. A wide range of Reynolds number (400 ≤Re ≤ 20,000) and inlet frequencies (0.01 Hz ≤ β ≤ 0.08 Hz) was covered in this experimental study for both laminar and turbulent flow. The experiments are carried out in the thermal entrance region with the fully developed velocity profile. The temperature variation at several locations along the duct was measured and recorded, and the experiment results showed that the oscillation at different locations are the sine variation with the same period as the heat input, while its amplitude decayed exponentially along the duct. The decay indexes are obtained from the experimental investigation under different conditions and presented in tabular and graphical forms.     

Parametric study of the cyclic behaviour of a hygroscopic matrix in a desiccant airflow system

The study of the transport phenomena in desiccant airflow systems has been addressed in numerous research works, some of them concerning combined processes of cooling, dehumidification and energy recovery. In this paper a detailed numerical model is used to simulate the behaviour of a parallel-plate channel, cyclically exposed to two airflows with different inlet conditions, the plate being composed by a substrate and a desiccant porous layer. The modelled channel is considered to be representative of a real channel of a hygroscopic matrix that is operating at steady state regime, like it occurs in desiccant or enthalpy rotors. The numerical results are treated in order to represent the global behaviour of the hygroscopic rotor under steady state conditions. Results of a parametric study are presented as maps of isovalues of the heat and mass transfer rates and of the outlet states of both airflows, considering channels of distinct wall thickness, of different thickness of the desiccant and the subtract layers, together with wide ranges of the rotation speed and of the wheel partition. The mapped results presented provide an overview of the operation characteristics of hygroscopic rotors, allowing a quick determination of the optimum range of values for relevant parameters, such as the rotation speed and the wheel partition. The model is thus an interesting tool for design and manufacture purposes of enthalpy and desiccant wheels.     

Theoretical analysis and experimental study of Coriolis mass flow sensor sensitivity

The measuring tube is the core sensitive unit of the Coriolis mass flow sensor. Its design parameters directly influence natural frequency and sensitivity, such as shape and structure dimensions. In this study, we obtained under concentrated force the equivalent elastic coefficient of the measuring tube by adopting static analysis and calculating static deflection curves, including the respective U-shape, slightly curved, and straight tubes. We then obtained the resonant frequency from the second-order vibration equation. Additionally, the maximum sensitivity and position coordinates were obtained by calculating the torsional displacement curve of the measuring tube under the distribution of Coriolis force during a rated flow. Sensor models with different measuring tube shapes were designed by applying this theoretical analysis. Calibration tests for sensors were performed using a static gravimetric method. Theoretical analysis and test results show that the resonant frequency and sensitivity of the sensors calculated by applying static mechanical analysis and Coriolis distributing force align with the experimental results, thereby proving the validity of the theoretical method. Furthermore, the proposed method simultaneously obtained the relation curve of the measuring tube structure dimensions and natural frequency and sensitivity. It therefore provides theoretical evidence for the sensor design and detector installation position.