The pressure distributions around a square cylinder in a crossflow were experimentally studied in a wind tunnel. The subject of study was conventional, but the results presented new findings. The experiments were performed by using a home-made linear pressure scanner. The ranges of Reynolds number and incidence angle were 2 × 104 - 9.4 × 104 and 0° - 45°, respectively. According to the topological flow patterns, the flows around the square cylinder at incidence showed three characteristic regimes: The subcritical, supercritical, and wedge flows. A critical incidence angle αcri = 15° separated the regimes of subcritical and supercritical modes. The results of current study provided information regarding the effects of the topological flow patterns on surface pressure distribution, drag, and lift characteristics. The pressure distributions, drag, and lift presented different characteristics in different characteristic flow regimes and had close correlations with the flows. At the critical incidence angle 15° which separated the subcritical and supercritical regimes, the surface-averaged pressure coefficient on each face displayed local extreme value—The drag coefficient attained a minimum of 1.6, the lateral force coefficient reached a maximum of 0.9. The appearance of the minimum drag at the critical incidence angle was attributed to the reduction of wake width which was induced by two surface flow phenomena: (1) reattachment of the separated boundary layer on the lateral surface facing windward at the critical incidence angle and (2) flow pattern change on the lateral surface facing leeward.

In this paper, the first-order ordinary differential constitutive equations of endochronic theory were combined with the principle of virtual work for simulating the response of creep (moment is kept constant for a period of time) or relaxation (curvature is kept constant for a period of time) of thin-walled tubes subjected to pure bending with different curvature-rates at the preloading stage. A group of Fourier series was used to describe the circumferential displacements of the tube. Thus, a system of nonlinear algebraic equations was determined. This system of equations can be solved by numerical method. Experimental data tested by Pan and Fan [1] were compared with the theoretical simulations in this study. It is shown that the theoretical formulations effectively simulate the experimental data.

The two dimensional punch problem for planar anisotropic elastic half-plane is revisited using the Lekhnitskii's formulation with aid of the Fourier transform and boundary integral equation. Four different conditions of contact problem for the rigid punch are analyzed in this study. From the combination of surface Green's function of half-plane and Hooke's law of anisotropic material, a set of Fredholm integral equations are obtained for mixed boundary value problems. After solving the integral equation according to specified contact condition, the explicit distributions of surface traction under the punch are obtained in closed-form. From the surface traction and Green's function of anisotropic half-plane, the full-field solutions of stresses are constructed. Numerical calculations of surface traction under the rigid punch are presented base on the analysis and are discussed in detail.

In this paper different failure mechanisms which yield cumulative damage are investigated through two types of hazard rate functions. They have been studied during the past two decades. Type A was developed early by assuming the hazard rate as a function of reliability. There are two kinds of trend, one follows the negative logistic decay model, the other the negative Gompertz decay. Some modifications are suggested according to the failure tendency and convenience of fittings. Type B is developed recently by assuming the hazard rate as a function of the expected operation time, T, which is defined as the integration of reliability over the time, normalized by the mean-time-between-failure. In both types the proposed hazard rates grow with the time monotonically. Typical examples are taken to examine these models, meanwhile the comparisons with the Weibull-typed distribution are also made. The results show that the most of proposed relations are successful in the expression of cumulative damage phenomenon, especially the Type B is a better choice even compared with the Weibull-typed description in some respects. The advantages of the models are discussed based on the physical meanings involved in the parameters.

In this paper, the development of a portable polymerase chain reaction (PCR) device is presented. Integrating electromagnetic mini-actuators for bi-directional fluid transport, the proposed device, whose dimension is 67mm × 66mm × 25mm, can be fully operated with a 5V DC voltage. The device consists of four major parts: A disposable channel chip in which PCR mixture is manipulated and reacted, a heater chip which generates different temperature zones for PCR reaction, a linear actuator array for pumping PCR mixture, and a circuit module for controlling and driving the system. The advantages of the device include the rapid temperature responses associated with continuous-flow-type PCR devices, as well as the programmable thermal cycling associated with chamber-type PCR devices. The thermal characteristics are measured and discussed. PCR amplification is successfully performed for the 122 bp segment of MCF-7/adr cell line. Due to its small footprint, this self-contained system potentially can be employed for point-of-care (POC) applications.

A body insonified by a sound field is known to experience a steady force that is called the acoustic radiation force. In this paper, the method of wave function expansion is adopted to study the scattering and the radiation force function caused by a plane normal harmonic acoustic wave incident upon an arbitrarily thick-walled functionally graded cylindrical shell submerged in and filled with compressible ideal fluids. A laminate approximate model and the so-called state space formulation in conjunction with the classical transfer matrix (T-matrix) approach are employed to present an analytical solution based on the two-dimensional exact equations of elasticity. Two typical models, representing the elastic properties of FGM interlayer, are considered. In both models, the mechanical properties of the graded shell are assumed to vary smoothly and continuously with the change of volume concentrations of the constituting materials across the thickness of the shell. In the first model, the simple rule of mixture governs. In the second, an elegant self-consistent micromechanical model which assumes an interconnected skeletal microstructure in the graded region is employed. Particular attention is paid on dynamical response of these models in a wide range of frequency and for different shell wall-thicknesses. In continue, by focusing on the second model, the normalized radiation force function and the form function amplitude are calculated and compared for different shell wall thicknesses and various profile of variations. Limiting cases are considered and good agreements with the solutions available in the literature are obtained.

A finite element method combined with three-dimensional anisotropic piezoelectric continuum damage mechanics is presented to simulate quasi-static crack propagation behavior in piezoelectric ceramics in this paper. In this method, the three-dimensional anisotropic piezoelectric damage constitutive model is utilized for characterizing the effects of mechanical and electrical damages on the fields near the crack tip, the combined-damage from the dominant mechanical and electrical damage components is regarded as the fracture criterion, and the gradient of combined-damage is assumed to control crack growth direction. A set of numerical simulations of the midspan crack propagation in a three-point bending PZT-4 beam are performed in various loading conditions. After the numerical results are validated by comparison with the corresponding experimental ones, the effects of mechanical and electrical loads on the cracking be havior are respectively evaluated. It is found from the obtained results that mechanical and electrical loads influence on the damage fields in the vicinity of the crack-tip, as well as the crack growth rate, in a significant way. With the increment in mechanical loading, the crack growth rate obviously increases. This means that positive and negative electric fields enhance and inhibit crack propagation, respectively.

In this study, a novel inflatable belt-type clamp is introduced and its performance is verified. Finite element simulations are performed to compare the performance of three different aorta clamping systems. In every case, the aorta is modeled as a simple hollow cylinder made of linearly elastic material. For a traditional surgical clamp in which the jaws remain inclined to one another as they close around the aorta, the maximum normal stress within the aorta wall is found to be 806kPa. It is shown that the numerical results are in good qualitative agreement with the experimental results obtained using a pressure sensitive film. The simulation results for a modified clamp in which the jaws remain parallel during the clamping operation show that the maximum normal stress is reduced to 222kPa. However, two regions of maximum stress are induced within the aorta wall. Finally, the numerical results for a novel inflatable belt-type clamp show that the maximum normal stress is equal to approximately 221kPa. In contrast to the modified clamp, the stress is uniformly distributed around the perimeter of the aorta, and thus the risk of aortic dissection is significantly reduced.

In this paper, the new concept of theory about Large Unified Symmetries for Hamilton systems are presented. The Large Unified Symmetries and conserved quantities for Hamilton systems are studied by the relation between the three kinds of symmetries and the three kinds of conserved quantities. We worked on the Large Unified Symmetries and conserved quantities by Noether symmetry, Lie symmetry and Mei symmetry, including the definition and criterion of the Large Unified Symmetries and the conserved quantities deduced from them. The Large Unified Symmetries are a intersection set among the Noether symmetries, the Lie symmetries and the Mei symmetries. The theory about Large Unified Symmetries will play an important role in the fields of modern theoretical physics.

A multi-cross-correlation method (MCCM) was developed in a particle image velocimetry (PIV) auto-processing system to reduce spurious vectors and improve accuracy of measurements. This technique is an improvement based on conventional cross-correlation method (CCM). Four typical neighboring interrogation windows were specified to be overlapped and calculated by MCCM. A high cross-correlation value is obtained in which many particle images match up with their corresponding spatially shifted partners, and small cross-correlation peaks due to interference of noises during experiments are reduced. Several parameters such as out-of-plane motions, particle size, and seeding density are considered for checking both MCCM and conventional PIV algorithms. The examination gives authenticity to the merits of MCCM for avoiding particles loss or mistaken velocity vectors.

Research on new techniques of multi-chamber mufflers equipped with a side inlet and internal nonperforated intruding tubes has been discussed in recent literature; however, the research work of multichamber mufflers in conjunction with side inlet and open-ended perforated intruding tubes which may efficiently increase the acoustical performance has been neglected. Therefore, the main purpose of this paper is to optimize the best design shape of multi-chamber side mufflers with open-ended perforated intruding tubes within a limited space.

In this paper, the four-pole system matrix in evaluating the acoustic performance is also deduced in conjunction with a simulated algorithm (SA). Results reveal that the maximum sound transmission loss (STL) is precisely located at the desired target tone. In addition, the acoustical performance of mufflers conjugated with perforated intruding tubes is superior to those equipped with non-perforated tubes. Additionally, the noise reduction ability for a three-chamber side muffler with a non-perforated intruding tube and a two-chamber side muffler with perforated intruding tubes are equivalent. Moreover, mufflers with more chambers will increase the acoustic performance for both pure tone and broadband noise.

In this paper, a new algorithm is proposed to solve the velocity and temperature fields in the thermal boundary layer flow over a semi-infinite flat plate. Both the flow and heat transfer solutions are calculated accurately by the Laplace Adomian decomposition method, Padé approximant and the optimal design concept. The Laplace Adomian decomposition method (LADM) is a combination of the numerical Laplace transform algorithm with the Adomian decomposition method (ADM). A hybrid method of the LADM combined with the Padé approximant, named the LADM-Padé approximant technique, is introduced to solve the thermal boundary layer problems directly without any small parameter assumptions, linearizatons or transformations of the boundary value problems to a pair of initial value problems. The LADM-Padé approximant solutions here in are given to show the accuracy in comparison with different method solutions.

This study predicts the failure behavior of an IM7/977-2 carbon epoxy composite material through a unified constitutive model. The traction-separation response and damage initiation and evolution behavior were studied by modeling a composite double cantilever beam subjected to a Mode I delamination. Damage within the composite panels was also taken into consideration through the use of the disturbed state concept (DSC). The finite element modeling software Abaqus was used to model the failure behavior of the composite using a unified constitutive modeling approach. The finite element model was validated by comparing the model results to referenced laboratory testing performed on IM7/977-2 carbon epoxy composite. The results of the finite element modeling performed in this study are in good agreement with the referenced laboratory testing. The damaged states associated with various stages of loading are presented in this study.

In proton exchange membrane fuel cells (PEMFCs), a low interfacial pressure between the bipolar plates and the membrane exchange assembly (MEA) results in a high contact resistance. Conversely, an excessive interfacial pressure reduces the porosity of the gas diffusion layer (GDLs) and may damage the proton exchange membrane (PEM). Consequently, the performance of a PEMFC is critically dependent upon the clamping method. Accordingly, this study emphasizes the development of a numerical methodology for analyzing clamping of a PEMFC and constructs a detailed three-dimensional (3D) full-scale finite element (FE) model of a PEMFC with the traditional and most popular point-load design as an example. The numerical method is first validated by experiments. A series of simulations are then performed on the example cases (i.e. 2-bolt, 4-bolt or 6-bolt) to analyze their behaviors on the contact pressure between the bipolar plates and the MEA and the corresponding effects on the GDL porosity and the contact resistance, under the constraints that the membrane and gaskets remain within their respective elastic limits and the porosity of the GDL has a value higher than 0.5. Overall, to complete the analysis procedures proposed in this paper, the results show that the six-bolt clamping mode with a tightening torque of 16 N-m achieves a uniform pressure distribution and a high interfacial pressure, and therefore represents the optimal clamping mode for the performed example cases.

A kinematics model of the ship wake in the presence of surface waves, generated by wind is presented. It was found that the stationary wave structure behind the ship covered a wedge region with the 16.9° half an angle at the top of the wake and only divergent waves are present in a ship wake for co propagating wind waves. Wind waves field directed at some nonzero angle to the ship motion can cause essential asymmetry of the wake and compressing of its windward half. The extension of Whitham-Lighthill kinematics theory of ship wake for the intermediate sea depth is also presented. The ship wake structure essentially depends from the Froude (Fr) number based on the value of the sea depth and ship velocity. For Froude number less than unit both longitudinal and cross waves are presented in the wake region and Kelvin wake angle increased with Fr. For Fr > 1 wake angle decreased with Froude number and finally only divergent waves are presented in the very narrow ship wake.

This study utilized a U-shape platform device to generate a single cavitation bubble for the detail analysis of the flow field characteristics and the cause of the counter jet during the process of bubble collapse induced by pressure wave. A series of bubble collapse flows induced by pressure waves of different strengths are investigated by positioning the cavitation bubble at different stand-off distances to the solid boundary. It is found that the Kelvin-Helmholtz vortices are formed when the liquid jet induced by the pressure wave penetrates the bubble surface. If the bubble center to the solid boundary is within one to three times the bubble's radius, a stagnation ring will form on the boundary when impacted by the penetrated jet. The liquid inside the stagnation ring is squeezed toward the center of the ring to form a counter jet after the bubble collapses. At the critical position, where the bubble center from the solid boundary is about three times the bubble's radius, the bubble collapse flows will vary. Depending on the strengths of the pressure waves applied, either just the Kelvin-Helmholtz vortices form around the penetrated jet or the penetrated jet impacts the boundary directly to generate the stagnation ring and the counter jet flow. This phenomenon used the particle image velocimetry method can be clearly revealed the flow field variation of the counter jet. If the bubble surface is in contact with the solid boundary, the liquid jet can only splash radially without producing the stagnation ring and the counter jet. The complex phenomenon of cavitation bubble collapse flows are clearly manifested in this study.

This paper has developed an accurate method for calculating the first and second derivatives of dynamic responses with respect to the design variables of structures subjected to dynamic loads. An efficient algorithm to calculate the dynamic responses, their first and second derivatives with respect to the design variables is formulated based on the Newmark-β method. The algorithm is achieved by direct differentiation and only a single dynamics analysis is required. An example is demonstrated with the new method proposed in this paper and the analytical method. The comparative numerical results show the new method is highly accurate compared to the analytical method.

In this paper, an evolution equation of cyclically internal damage in the intrinsic damage time scale after the threshold cycles N0 was extended by employing its damage parameters proposed to be dependent of frequency (v) and temperature (T) under cyclic fatigue loading. The resulting damage-coupled endochronic viscoplasticity can drive v and T modified power form equations of cyclic damage and its fatigue initiation life = N1 + N0. Under fatigue tests with T effect and N0 = 0, the power form equation of N1(T)/(Th), named as T-LCM (T modified Lee Coffin-Manson) equation for fatigue initiation life can bederived. The T modified factor (Th) depends on the T dependent material elastic modulus, the cyclicstress-strain response and the damage parameters. Theoretical predictions in the life data ofSn/3.8Ag/0.7Cu solder alloy under cyclic strain test with Tϵ [298,393] K were very well.

Also under fatigue tests with v effect only, the power form equation of /v-LCM (v modified Lee-Coffin-Manson) equation for fatigue initiation life can be derived. The v modified parameter depends on the v dependent cyclic stress-strain response and the damage parameters. Theoreticalpredictions in the life data of 96.5Sn/3.5Ag solder alloy with surface cracking effect i.e. N0 ≠ 0 during cyclicstrain tests with v ϵ [0.001,1] Hz were quite well.

Obviously, the values of power exponents C in the T-LCM and the v-LCM equations can not be determinedsimply by the least square method as in the Coffin-Manson empirical formulae. Also, they must bejustified by constrains imposed in the material parameters defining in the cyclic stress-strain response andthe accumulation behavior of cyclic damage.

The resultant equations derived here and the Δ-LCM equation derived under Δ angle proportional cyclicstrain tests can be combined together to form a T-v-ΔLCM equation for fatigue life studies in the solderalloys using bulk specimens or BGA solider joint specimens.

The effect of shape memory alloy (SMA) on the postbuckling behavior of rectangular cross-ply and angle-ply plates by varying the SMA fiber spacing was investigated using the Finite Element Method. The formulation of the location-dependent linear, nonlinear stiffness matrices due to non-homogeneous material properties and the temperature-dependent recovery stress stiffness matrix were derived. Numerical results show that the increase of SMA fiber volume fraction and prestrain may generate more recovery stress, and increase the stiffness of SMA reinforced composite laminate. Therefore, the postbuckling deflections of the plate may be decreased significantly. The buckling mode that plate will buckle into is dependent on the fiber orientation of the angle-ply laminates. When the SMA fibers are concentrated in the center of the plate, the postbuckling deflections of the plate will be decreased considerably.

The temporal/spatial evolution processes of the flow pattern, velocity distribution, and wall shear stress of pulsatile water flows in the arch of 180o turn-around tubes with/without stenosis were experimentally studied by using the particle image velocimetry (PIV). Three transparent tubes made of glass were used: A tube without stenosis in the arch, a tube with a 25% stenosis at the inner wall of arch, and a tube with a 50% stenosis at the inner wall of arch. Here the percentage of stensis denoted the ratio between the stenosis height to inner diameter of arch in the diametral cross section across mid-arch of the central plane. The flow was provided by a pump which approximately simulated the pulsatile pressure waves of human heart beats. The systole to diastole time period ratio is set at 35%:65%. The Womersley parameter, Dean number, and time-averaged Reynolds number were 14, 2348, and 3500, respectively. In the arch of the turn-around tube without stenosis, no boundary layer separation was found during the systolic phase. The reverse flow and recirculation bubble appeared in the arch only during the diastolic phase. The inner wall of the arch experienced lower wall shear stress during the diastolic phase due to the formation of recirculation bubble and secondary flow. In the arch with stenosis, the boundary layer separated from the inner wall and formed a recirculation bubble downstream the stenosis during the systolic phase. Lower stenosis (25%) did not cause drastic variation of the wall shear stresses. At higher stenosis (50%), however, the wall shear stress around the inner wall downstream the stenosis became extraordinarily low, whereas the wall shear stress around the upstream region of the outer wall of the downstream branch of the tube became anomalously large.