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## Effects of tension on vortex-induced vibration (VIV) responses of a long tensioned cylinder in uniform flows

### Acta Mechanica Sinica (2017-02-01) 33: 1-9 , February 01, 2017

The effects of tension on vortex-induced vibration (VIV) responses for a tension-dominated long cylinder with an aspect ratio of 550 in uniform flows are experimentally investigated in this paper. The results show that elevated tension suppresses fluctuations of maximum displacement with respect to flow velocity and makes chaotic VIV more likely to appear. With respect to periodic VIV, if elevated tension is applied, the dominant vibration frequency in the in-line (IL) direction will switch from a fundamental vibration frequency to twice the value of the fundamental vibration frequency, which results in a ratio of the dominant vibration frequency in the IL direction to that in the cross-flow direction of 2.0. The suppression of the elevated tension in the fluctuation of the maximum displacement causes the axial tension to become an active control parameter for the VIV maximum displacement of a tension-dominated long riser or tether of an engineering structure in deep oceans. However, the axial tension must be optimized before being used since the high dominant vibration frequency due to the elevated tension may unfavorably affect the fatigue life of the riser or tether.

## Large eddy simulation of fuel injection and mixing process in a diesel engine

### Acta Mechanica Sinica (2011-09-01) 27: 519-530 , September 01, 2011

The large eddy simulation (LES) approach implemented in the KIVA-3V code and based on one-equation sub-grid turbulent kinetic energy model are employed for numerical computation of diesel sprays in a constant volume vessel and in a Caterpillar 3400 series diesel engine. Computational results are compared with those obtained by an RANS (RNG *k*-*ɛ*) model as well as with experimental data. The sensitivity of the LES results to mesh resolution is also discussed. The results show that LES generally provides flow and spray characteristics in better agreement with experimental data than RANS; and that small-scale random vortical structures of the in-cylinder turbulent spray field can be captured by LES. Furthermore, the penetrations of fuel droplets and vapors calculated by LES are larger than the RANS result, and the sub-grid turbulent kinetic energy and sub-grid turbulent viscosity provided by the LES model are evidently less than those calculated by the RANS model. Finally, it is found that the initial swirl significantly affects the spray penetration and the distribution of fuel vapor within the combustion chamber.

## Numerical simulation of thermo-mechanical fatigue properties for particulate reinforced composites

### Acta Mechanica Sinica (2005-04-01) 21: 160-168 , April 01, 2005

### Abstract.

In this paper, a two dimensional Voronoi cell element, formulated with creep, thermal and plastic strain, is applied for the numerical simulation of thermo-mechanical fatigue behavior for particulate reinforced composites. The relation between mechanical fatigue phases and thermal fatigue phases influences the thermo-mechanical fatigue behavior and cyclic creep damage. The topological features of micro-structure in particulate reinforced composites, such as the orientation, depth-width ratio, distribution and volume fraction of inclusions, have a great influence on thermo-mechanical behavior. Some related conclusions are obtained by examples of numerical simulation.

## Oblique Perforation of Thick Metallic Plates by Rigid Projectiles

### Acta Mechanica Sinica (2006-08-01) 22: 367-376 , August 01, 2006

Oblique perforation of thick metallic plates by rigid projectiles with various nose shapes is studied in this paper. Two perforation mechanisms, i.e., the hole enlargement for a sharp projectile nose and the plugging formation for a blunt projectile nose, are considered in the proposed analytical model. It is shown that the perforation of a thick plate is dominated by several non-dimensional numbers, i.e., the impact function, the geometry function of projectile, the non-dimensional thickness of target and the impact obliquity. Explicit formulae are obtained to predict the ballistic limit, residual velocity and directional change for the oblique perforation of thick metallic plates. The proposed model is able to predict the critical condition for the occurrence of ricochet. The proposed model is validated by comparing the predictions with other existing models and independent experimental data.

## Validity ranges of interfacial wave theories in a two-layer fluid system

### Acta Mechanica Sinica (2007-12-01) 23: 597-607 , December 01, 2007

In the present paper, we endeavor to accomplish a diagram, which demarcates the validity ranges for interfacial wave theories in a two-layer system, to meet the needs of design in ocean engineering. On the basis of the available solutions of periodic and solitary waves, we propose a guideline as principle to identify the validity regions of the interfacial wave theories in terms of wave period *T*, wave height *H*, upper layer thickness *d*_{1}, and lower layer thickness *d*_{2}, instead of only one parameter–water depth *d* as in the water surface wave circumstance. The diagram proposed here happens to be Le Méhauté’s plot for free surface waves if water depth ratio *r* = *d*_{1}/*d*_{2} approaches to infinity and the upper layer water density *ρ*_{1} to zero. On the contrary, the diagram for water surface waves can be used for two-layer interfacial waves if gravity acceleration *g* in it is replaced by the reduced gravity defined in this study under the condition of *σ* = (*ρ*_{2} − *ρ*_{1})/*ρ*_{2} → 1.0 and *r* > 1.0. In the end, several figures of the validity ranges for various interfacial wave theories in the two-layer fluid are given and compared with the results for surface waves.

## Planning and control of 3-D nano-manipulation

### Acta Mechanica Sinica (2004-04-01) 20: 117-124 , April 01, 2004

The use of atomic force microscope (AFM) as a nanomanipulator has been evolving for various kinds of nano-manipulation tasks. Due to the bow effect of the piezo scanner of the AFM, the AFM space is different from the Cartesian space. Traditional nanomanipulation based on AFM is only a 2-D operation and does not consider the bow effect of the piezotube. In this paper, different 3-D nanomanipulation tasks using AFM such as nanolithography, pushing and cutting have been discussed. 3-D path planning is performed directly in the AFM space and the 3-D paths are generated based on the 3-D topography information of the surface represented in the AFM space. This approach can avoid the mappings between the AFM space and Cartesian space in planning. By following the generated motion paths, the tip can either follow the topography of the surface or move across the surface by avoiding collision with bumps. Nanomanipulation using this method can be considered as the “true” 3-D operations since the cantilever tip can be controlled to follow any desired 3-D trajectory within the range of AFM space. The experimental study shows the effectiveness of the planning and control scheme.

## Mechanical response of fabric sheets to three-dimensional bending, twisting, and stretching

### Acta Mechanica Sinica (2015-06-01) 31: 373-382 , June 01, 2015

A model for the mechanics of woven fabrics is developed in the framework of two-dimensional elastic surface theory. Thickness effects are modeled indirectly in terms of appropriate constitutive equations. The model accounts for the strain of the fabric and additional effects associated with the normal bending, geodesic bending, and twisting of the constituent fibers.

## Viscoelastic modeling of the diffusion of polymeric pollutants injected into a pipe flow

### Acta Mechanica Sinica (2013-04-01) 29: 166-178 , April 01, 2013

This study focuses on the transient analysis of nonlinear dispersion of a polymeric pollutant ejected by an external source into a laminar pipe flow of a Newtonian liquid under axi-symmetric conditions. The influence of density variation with pollutant concentration is approximated according to the Boussinesq approximation and the nonlinear governing equations of momentum, pollutant concentration are obtained together with and Oldroyd-B constitutive model for the polymer stress. The problem is solved numerically using a semi-implicit finite difference method. Solutions are presented in graphical form for various parameter values and given in terms of fluid velocity, pollutant concentration, polymer stress components, skin friction and wall mass transfer rate. The model can be a useful tool in understanding the dynamics of industrial pollution situations arising from improper discharge of hydrocarbon pollutants into, say, water bodies. The model can also be quite useful for available necessary early warning methods for detecting or predicting the scale of pollution and hence help mitigate related damage downstream by earlier instituting relevant decontamination measures.

## Effect of triaxial stress constraint on the deformation and fracture of polymers

### Acta Mechanica Sinica (2002-10-01) 18: 480-493 , October 01, 2002

One purpose of this paper is to give a brief overview on the research status of deformation, fracture and toughening mechanisms of polymers, including experimental, theoretical and numerical studies. Emphasis is on the more recent progresses of micromechanics of rubber particle cavitation and crazing, and the development of fracture criteria for ductile polymers.

The other purpose is to study the effect of triaxial stress constraint on the deformation and fracture behavior of polymers. Polycarbonate (PC), acrylonitrile-butadienestyrene (ABS) and PC/ABS alloy are considered in this investigation. A series of circumferentially blunt-notched bars are used to experimentally generate different triaxial stress fields. The fracture surfaces of specimens with different notch radius are examined by scanning electron microscope (SEM) to study the fracture and toughening mechanisms of polymer alloy. It is shown that the triaxial stress constraint has a significant effect on the deformation, fracture and toughening of PC, ABS and PC/ABS alloy. We will also discuss the extent to which a micromechanics criterion proposed by the first author can serve as a fracture criterion for ductile polymers. A new ductile fracture parameter is emphasized, which can be employed to evaluate the fracture ductility of polymers. Stress state independence of the parameter for the PC, ABS and PC/ABS alloy has been experimentally verified.

## A hyperbolic Lindstedt–Poincaré method for homoclinic motion of a kind of strongly nonlinear autonomous oscillators

### Acta Mechanica Sinica (2009-10-01) 25: 721-729 , October 01, 2009

A hyperbolic Lindstedt–Poincaré method is presented to determine the homoclinic solutions of a kind of nonlinear oscillators, in which critical value of the homoclinic bifurcation parameter can be determined. The generalized Liénard oscillator is studied in detail, and the present method’s predictions are compared with those of Runge– Kutta method to illustrate its accuracy.