A Simple Model to Predict Critical Ricochet Angle in Long-Rod Penetration by Kamran Daneshjou and Majid Shahravi was published in Journal of Mechanics in the March issue of 2009 (Vol. 25, No. 1, pp. 117-128).

Double-walled carbon nanotubes (DWNTs) are expected to be useful as elements in improving conventional polymer-based fibers and films. An extensive molecular dynamics simulation and continuum analyses are carried out to estimate the influence of matrix stiffness and the intertube radial displacements on free vibration of an individual DWNT. The effects of nanotube length and chirality are also taken into account. The continuum analyses are based on both Euler-Bernoulli and Timoshenko beam theories which considers shear deformation and rotary inertia and for both concentric and non-concentric assumptions considering intertube radial displacements and the related internal degrees of freedom. New intertube resonant frequencies are calculated. Detailed results are demonstrated for the dependence of resonant frequencies on the matrix stiffness. The results indicate that internal radial displacement and surrounding matrix stiffness could substantially affect resonant frequencies especially for longer doublewalled carbon nanotubes of larger innermost radius at higher resonant frequencies, and thus the latter does not keep the otherwise concentric structure at ultrahigh frequencies.

This study designs, fabricates and characterizes three valveless impedance pumps, namely a symmetrical pump with a circular cross-section, an asymmetrical pump with a circular cross-section, and an asymmetrical pump with a rectangular cross-section. The pressure head and flow rate characteristics of the three pumps are investigated as a function of the compression location, the compression frequency and the compression amplitude. The experimental results show that the flow is reversible in every case. Moreover, the pressure head is found to be significantly dependent on the actuating frequency, the compression location and the compression amplitude. However, no pressure head is produced when the pinching effect is applied at the center of channel configuration for the symmetrical pump. In the symmetrical pump, a maximum pressure head of 590mm is obtained at a frequency of 26Hz, and results in a flow rate of 0.581/min in the positive direction (i.e. from the left-hand reservoir of the pump to the righthand reservoir). Meanwhile, in the asymmetrical pumps with circular and rectangular cross-sections, respectively, maximum pressure heads of −620mm and −570mm are developed at frequencies of 36Hz and 32Hz, respectively. The corresponding flow rates are determined to be 0.641/min and 0.531/min, respectively. In both cases, the fluid moves in the negative direction (i.e. from the right-hand reservoir of the pump to the left-hand reservoir). Overall, the valveless impedance pumps developed in this study generate a high pumping rate, are easily fabricated and have no moving mechanical valves. As a result, they are eminently suitable for pumping applications in such diverse systems as biomedical devices, fuel cells, PC cooling systems, and so forth.

In this work, we introduced an innovative technique that enables simultaneous measurement of the 3D kinematics and 2D–3 Components fluid velocities of the induced flow of a swimming fish, which greatly advanced the experimental technique for research in fish biomechanics. This technique was theoretically based on the combined use of new reconstruction formulas of position and the calibration polynomials of stereo-DPIV, employing only two cameras in the imaging system. Both kinematic and hydrodynamic characteristics of a fish executing three-dimensional and complicated locomotion are readily and accurately revealed. Measuring simultaneously 3D kinematics and hydrodynamics is significantly important for an accurate investigation of fish biomechanics because fish motions are three-dimensional. We demonstrate results of 3D kinematics and fluid velocity fields measured in the wake of a maneuvering pectoral fin of a fish, which proves the effectiveness and usefulness of this technique. The application of this technique is extendable to biomechanics research concerning locomotion of both swimming and flying animals.

The objective of the present study is to explore pressure-driven flows with the presence of electric double layer (EDL) in nanochannels of various wall lattice planes. Three face-centered cubic (fcc) lattice planes, i.e. fcc(111), fcc(100), and fcc(110), of the channel wall are considered. The structure of diffuse EDL and electrokinetic flow characteristics are dealt with in an atomistic view. Fluid and charge density layering phenomena and their influences on the Stern layer are investigated with the molecular dynamic simulation results. In most of the simulations, a monatomic molecule, W, is used as the solvent model and the charged particles W+ and W− of the same size as the ions. To examine behaviors of the dissimilar particles, a simulation with the aqueous model W for fluid, Na+ for cation and Cl− for anion is also performed. Effects of ion concentrations, wall-fluid interaction energy, and surface charge density on the electro-hydrodynamics are studied. In addition, based on the continuum theory, two analytic expressions for zeta potential with the presence of fluid slippage are derived and analyzed. The present results disclose interesting physics about the influences of wall lattice-fluid interactions, which are significant in further understanding and applications of the nanoscale electrokinetic flows.

A fiber Bragg grating (FBG) sensor system which can simultaneously measure the point-wise, out-of-plane and in-plane dynamic displacements is proposed. A demodulation system based on the fiber Bragg grating filter is used. The steady-state responses of particle motions of a piezoceramic plate measured by the FBG out-of-plane and in-plane displacement sensors are simultaneously compared with those obtained by a laser Doppler vibrometer (LDV) and a surface-mounted FBG strain sensor, respectively. The integration of the FBG displacement sensor with a dynamic signal analyzer (FBG-DSA) forms a measurement system which has the ability to acquire the frequency response of a piezoceramic plate. An LDV-DSA system and an impedance analyzer are used to compare the results obtained from the dynamic signal analyzer combined with the out-of-plane FBG sensor (OFBG-DSA) and the in-plane FBG sensor (IFBG-DSA), respectively. The experimental results of the impulse excitation as well as the random excitation of the piezoceramic plate are also presented. To explain the experimental results, an optical full-field measurement technique called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) and FEM numerical calculations are also used to provide full-field vibration mode shapes of the piezoceramic plate. These results indicate that the proposed displacement sensor system has the multiplexing capability to measure the dynamic displacements up to 45kHz.

In Taipei, many pile proof load tests were not conducted to failures but only to a multiple (e.g., 2) of the design load. This leads a difficulty of incomplete information: For these test results, the ultimate bearing capacities of the test piles are unknown. This paper addresses the issue of calibrating resistance factors of piles for the axial ultimate bearing capacities based on the incomplete information from these tests. A simplified probabilistic method is proposed to resolve this issue. A local pile test database of Taipei is presented, and the analysis results show that the inclusion of the incomplete pile load test data helps in calibrating the resistance factors. Moreover, it is found that the calibrated resistance factors for the axial ultimate bearing capacities are consistent to the safety factors that are adopted in the current Taiwan design code. This paper also addresses another important issue for the pile design in Taipei: the end bearing capacity in the sandstone layer is very uncertain. A maximum likelihood method is taken to identify the best estimate for this end bearing capacity. The conclusion of this paper may be useful for reliability-based designs for the axial ultimate bearing capacities of single bored piles in the Taipei region.

Some analytical formulas are presented for torsional analysis of homogeneous hollow tubes. The cross section is supposed to consist of straight and circular segments. Thicknesses of segments of the cross section can be different. The problem is formulated in terms of Prandtl's stress function. The derived approximate formulas are so simple that computations can be carried out by a simple calculator. Several examples are presented to validate the formulation. The accuracy of formulas is verified by accurate finite element method solutions. It is seen that the error of the formulation is small and the formulas can be used for analysis of thin to moderately thick-walled hollow tubes.

The scattering of plane SH-wave from a partially debonded shallow cylindrical elastic inclusion in half space is investigated in this paper by complex function method and expansion method of wave function. The debonding regions are considered as multiple arc-shaped interface cracks with non-contacting faces. Firstly, in the inclusion district, the standing wave function in the elastic inclusion with unknown coefficients which satisfies the boundary condition is constructed and generated into the Fourier series; in the half space, the stress and displacement boundary condition around the elastic inclusion can be modeled as the same as the standing wave function in the elastic inclusion. Then, a set of infinite algebraic equations can be obtained around the same boundary and the solution of problem can be gained. In the end, numerical examples of the surface displacement are provided and discussed. It is found that the interface cracks can raise the surface displacement amplitudes to a certain degree.

An evolution equation for the Cauchy stress tensor is proposed, taking into account the elastic, viscous and plastic characteristics of complex fluids. Hypoplasticity, in particular, is incorporated to model the plastic features. The model is applied to investigate time-dependent Poiseuille flows between two parallel plates to simulate non-Newtonian behavior of complex rheological fluids. Results show that while different degrees of elastic and viscous features can be indexed by varying the values of the model parameters, hypoplasticity is capable of simulating the plastic characteristics. The fluid tends to be divided into different parallel layers as hypoplastic effects enhance gradually. Applications of the model may be found in geomorphic fluid motions involved granular materials.

The main aims of this research are, at first, combustion instability study based on equivalence ratio oscillation, and, secondly, investigation various frequency modes of combustion instability, taking combustion chamber geometry into account. Considering the configuration of the simulated combustion chamber, excitation probability of the longitudinal modes is higher than that of transversal modes. The reason of this fact is that the resonance frequency values of the longitudinal modes are less than those of transversal modes. So, the most important frequency mode, during combustion instability, is the first longitudinal mode. In this paper thermo-acoustic instability model is utilized for pre-mixed gas turbines combustion chamber, founded on equivalence ratio oscillation. For this purpose Lieuwen method is developed in order to attain the phase difference between pressure and heat release oscillations. Results concluded from combustion instability simulation for the first longitudinal mode, considering its importance, are compared with experimental data and good agreement is observed.

Most of finite element (FE) models used to study single tooth dental implants consider only an isolated implant. It is of course more realistic to model also the adjacent teeth of the implant. However, including the adjacent teeth significantly increases the complexity of the model and necessitates the complex contact analysis. The main difference between the FE models with and without the adjacent teeth is that the model without the adjacent teeth cannot capture the effect of the contact forces that are transferred between the implant-retained crown and the adjacent teeth. In this study, the hypothesis that the contact forces are not important is verified by the FE contact analysis. Realistic 3D FE models of a mandible and a single tooth implant with and without adjacent teeth are constructed and analyzed. It is found from the results that the difference between the maximum bone stresses of the two models is very small when various loading directions are considered. The obtained results, therefore, indicate that the effect of contact forces between a dental implant and its adjacent teeth is not significant. Consequently, the adjacent teeth can be excluded from FE models if various loading directions are considered.

The transonic tail flutter and flap buzz under the wing-flap-tail configurations are analyzed utilizing a dynamic grid capability of unstructured Euler solver coupled with an appropriate aeroelastic solver. From the results, the presence of a forewing, either stationary or oscillating, has significant effect on the tail flutter characteristics. In particular, the tail motion may be in resonance with the oscillating wing before the onset of flutter, which is dangerous to the tail structure because of the large amplitude oscillations. Besides, a complicated aerodynamic and aeroelastic interference of the tail have been found due to the unsteady disturbance which is a strong variability of flow structure induced by the buzz of the flap. In the high transonic flow regime, the flap buzz with limit-cycle oscillations does occur, and the influence induced by the tail is not important. The increasing restoring force at the pivot where the flap joints with the wing will reduce the flap oscillations that improves the effect of the flap buzz.

In this paper, a direct boundary element method (DBEM) is formulated numerically for the problems of the unbounded potential flows past supercavitating bodies of revolution (cones and also disks which are special case of cones with tip vertex angle of 180 degree) at zero degree angle of attack. In the analysis of potential flows past supercavitating cones and disks, a cavity closure model must be employed in order to make the mathematical formulation close and the solution unique. In the present study, we employ Riabouchinsky closure model. Since the location of the cavity surface is unknown at prior, an iterative scheme is used. Where, for the first stage, an arbitrary cavity surface is assumed. The flow field is then solved and by an iterative process, the location of the cavity surface is corrected. Upon convergence, the exact boundary conditions are satisfied on the body-cavity boundary. For this work, powerful software, based on CFD code, is developed in CAE center of IUST. The predictions of the software are compared with those generated by analytical solution and with the experimental data. The predictions of software for supercavitating cones and disks are seen to be excellent. Using the obtained data from software, we investigate the mathematical behavior of axisymmetric supercavitating flow parameters including drag coefficients of supercavitating cones and disks, cavitation number and maximum cavity width for a wide range of cone and disk diameters, cone tip angles and cavity lengths. The main objective of this study is to propose appropriate mathematical functions describing the behavior of these parameters. As a result, among all available functions such as linear, polynomial, logarithmic, power and exponential, only power functions can describe the behavior of mentioned parameters, very well.

Blood flow rheology is a very complex phenomenon. Hemodynamics owns Newtonian or non-Newtonian characteristic is still debatable. Recently, studies related to blood tend to classify blood as non-Newtonian fluid. In this research, power law, Casson and Carreau which are being the most popular non-Newtonian models are applied to investigate the hemodynamics variables that influence formation of thrombosis and predict damageability to blood cell. The branched arterial system is simplified as T-junction geometry and the computational fluid dynamics software Fluent 6.2 with finite volume method is utilized to analyze the blood flow rheology in cases of continuous and pulsatile flow. The analysis results are compared with that of Newtonian model and give out very interesting hemodynamics predictions for each model. The size of recirculation zone is different from each model that is observed significantly. The wall shear stress of Carreau model gets the highest value, 14% in case of continuous flow and around 17% in pulsatile case bigger than that of Newtonian model. The results of pulsatile flow show that the Newtonian model is closed to power law model while the Casson model is similar to the Carreau model.

This study attempts to examine convection caused by the combined effects of temperature and concentration gradients in an annular enclosure with steps. An experimental study of thermosolutal convection of a CuSO4+ H2SO4+ H2O solution in a horizontal annular enclosure with steps is conducted using an electrochemical system that enables either opposing or cooperating in temperature and concentration gradients to be imposed. The shadowgraph recording technique is utilized to visualize and analyze the flow field phenomenon. The large difference between the thermal and solutal diffusion rates causes the flow to exhibit double-diffusive characteristics. In both cooperating and opposing cases, some finger-type flow can be visualized in the layered flow structure. Furthermore, Sh (mass transfer rate) increased with increasing Grt for fixed Grm and S*. Sh is larger in the cooperating case than in the opposing case for given Grt and Grm values.