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The simple expansion chamber muffler is a base control device whose use is to attenuate sound power, and has been known for a long time. Some of the most compelling research has focused on the mufflers with a straight inlet and outlet. To date, a muffler with a right angle inlet has never been studied. Therefore, the purpose of this work is to analyze the simple expansion chamber muffler with a right angle inlet. The numerical results show a comparable agreement between the experiment and other numerical approaches. A discussion is also presented in this work on the muffler with a different radius to that of the inlet/outlet pipe, a different inlet part, etc. The result clearly shows that the attenuation of the muffler with a right angle inlet is better than that with a straight inlet at particular frequencies. In addition, the mufflers do not have any absorbent linings attached to the inside of them, unlike the right angle-inlets which do. However, the propagation of sound in the muffler with a right angle inlet can lead its sound power to be attenuated about 10 ∼ 40dB at those particular frequencies.
In this study, the mechanical properties of graphene and single walled carbon nanotubes (SWCNTs) were investigated based on molecular dynamics (MD) simulation. During the characterization of the mechanical properties, the atomistic interactions of the carbon atoms were described using the bonded and non-bonded energies. The bonded energy consists of four different interactions: Bond stretching, bond angle bending, dihedral angle torsion, and inversion. On the other hand, the non-bonded interaction between the carbon atoms within the cut-off ranges was regarded as the van der Waals (vdW) force. The effect of vdW force on the mechanical properties of graphene and SWCNTs would be mainly of concern. Simulation results indicated that the Young's modulus of the graphene with vdW force included is 15% higher than that without considering any vdW interaction. The same tendency also was observed in the armchair and zig-zag SWCNTs. Furthermore, it was revealed that the increment of moduli caused by the vdW force could be primarily attributed to the 1-4 vdW interaction. The influence of the vdW interactions on the mechanical properties of graphene and SWCNTs was then elucidated using the parallel spring concept.
Vibration-based structural damage detection has been the focus of attention by many researchers over the last few decades. However, most methods proposed for this purpose utilize extracted modal parameters or some indices constructed based on these parameters. A literature review revealed that few papers have employed Frequency Response Functions (FRFs) for detecting structural damage. In this paper, a technique is presented for damage detection which is based on measured FRFs. Proper Orthogonal Decomposition (POD) has been implemented on spatiotemporal responses in each frequency in order to reduce the dimension of the data. This is based on the concept that the forced harmonic response of a linear vibrating system can be fully captured utilizing a single basis vector. A different approach is also presented in this paper in which POD is applied to the frequency domain data. Operational Deflection Shapes (ODSs) have been decomposed using POD to localize the damage. The efficiency of the method is demonstrated through some numerical and experimental case studies.
Pavement roughness causes pavement stress fluctuation along the road. However, the dynamic effects were not taken into account in most pavement design and studies. To investigate the influences of roadway roughness on pavement stresses, this study developed a coupled system consisting of a quarter-car model and an equivalent lump pavement model. The coupled system also incorporated measured road profiles. By means of transfer function in frequency domain, the deflections and stresses of pavements were computed in seconds. The results were validated with Westergaard's solutions satisfactorily. It was found that the critical roughness, which might cause extreme responses, is related to the vehicle speed and suspension of vehicles. The maximum tension at the bottom of pavements also depends on the size of bump. In addition, the study demonstrates the correlation between roughness index, IRI, and ISO roughness classifications. It was also found that disturbance due to model boundary affects simulation results significantly.
Flat heat pipes having mesh capillaries were investigated experimentally in this study. An apparatus was designed to test thermal performance of plate type copper water heat pipe having one or two layers of #50 or #80 mesh capillary structures with 5 to 50 W heat input. The working fluid, water, is charged in volumes equivalent to 25%, 33%, or 50% of the internal space. In addition to horizontal orientation, heat pipes were tested with the evaporator section elevated up to 40 degree inclination angle. Temperature distribution of the heat pipe was measured, and the evaporator, adiabatic and condensation resistances were calculated separately. The effects of mesh size, charge volume fraction, and inclination angle on thermal resistance were discussed. In general, the #80 mesh yielded lower thermal resistance than the #50 mesh. Inclination angle has a more significant effect on condenser than evaporator. Analysis of evaporation and condensation in flat heat pipes was conducted and semi-empirical correlations were derived. The present evaporation correlation predicts evaporation resistance between −20% and +30%, and the condensation correlation predicts most condensation resistance data within ±30% for 25% and 33% charge volume fraction.
This study presents an innovative fuzzy inverse method with the finite-element scheme for estimating the unknown time-varying load inputs on a three-dimensional (3D) spatial truss structural system. The finite-element scheme is employed to discretize the problem in space, allowing multidimensional problems of various geometries to be treated. This method is based on the fuzzy Kalman Filter (FKF) technology and the fuzzy weighting recursive least square method (FWRLSM). The fuzzy Kalman filter measures the system responses at two distinct nodes in the 3D spatial truss structure. The fuzzy weighting recursive least square method is derived using the residual innovation sequence to compute the input loads. The proposed method's superiority is demonstrated using several typical simulation cases that vary with different estimator and the distinct levels of the initial process noise covariance and the measurement noise covariance. The results show that this method has great stability and accuracy.
Shock absorption is one of the fundamental biomechanical functions of disc. The knowledge of the effect of fatigue loading, impact energy and contact period on the disc shock attenuation is important in clarifying the risk factors of back pain and evaluating the efficacy of novel disc prosthesis. The purpose of this study is to find the changes of shock attenuation of motion segment after fatigue loading, and the effect of impact energy and contact period on the disc shock attenuation pre and post fatigue loading.
The 3-unit porcine spinal motion segment was used for testing. The impact test was applied pre and post fatigue loading. Impact energy and contact period were controlled in the experiment. Shock attenuation properties, including the acceleration attenuation (AA) of disc, force transmissibility (FT) and phase delay of force (PDF) of motion segment, were calculated from the acceleration and force responses.
The results showed that the shock attenuation properties (acceleration attenuation and force transmissibility) decreased post fatigue. The disc acceleration attenuation was independent of impact energy and contact period. The disc acceleration attenuation was 0.78 (−1.06dB) pre fatigue and 1.04 (0.14dB) post fatigue. The force transmissibility of motion segment decreased post fatigue only during short contact period. The phase delay of force did not change significantly post fatigue.
We found that the fatigue loading decreased the disc shock attenuation. The disc was at higher risk of injury following fatigue loading even at a mild impact loading. The disc acceleration attenuation was invariant of impact energy and contact period, but decreased post fatigue. The disc acceleration attenuation is a good index to evaluate the degree of fatigue injury.
In this study, the failure response of two serial bolted joints in composite laminates was investigated. The composite material was consisted of epoxy matrix and glass fibers. To find out the effects of joint geometry and stacking sequences on the failure response, parametric studies were performed experimentally. Three different geometrical parameters that were the edge distance-to-hole diameter ratio (E/D), plate width-to-hole diameter ratio (W/D) and the distance between two serial holes-to-hole diameter ratio (K/D) were investigated. Hence, E/D, W/D and K/D ratios were considered from 1 to 5, 2 to 5 and 3 to 5, respectively. In addition, the failure tests were carried out for a range of preload moments as 2, 3, 4, 5 Nm and without any preload moments as 0Nm. Tested composite laminates were oriented two different stacking sequences as [0°]8 and [0°/0°/90°/90°]s. Experimental results point out that failure response of two serial bolted composite joints are firmly effected from material parameters, geometrical parameters and the magnitudes of applied preload moments.
As inspired by studies of fish schooling in literature, this work investigates hydrodynamic performance of a two-dimensional undulating-foil triad in viscous flows via numerical simulation. The chord of foil oscillates in the form of a streamwise traveling wave. The triad is in triangular formation, i.e., two foils followed by one. A series of triad configuration are computed assuming the same wave speed, amplitude, and frequency of chord traveling wave for each foil. The results show that, to achieve highest thrust efficiency, the two leading foils should separate from each other by 0.4 chord length, perform antiphase undulating motion, and the leading edge of the trailing foil stay 0.2 chord length in front of the trailing edges of the leading foils. An underlining mechanism, vortex pair shedding from the leading foil interacting with boundary-layer vorticity field of the trailing foil, has been identified to explain the efficiency enhancement. This optimal triad configuration is different from that obtained in a previous potential flow analysiss.
Anterior Lumbar Interbody Fusion (ALIF) has been widely used to treat internal disc degeneration. However, different cage positions and their orientations may affect the initial stability leading to different fusion results. The purpose of the present study is to investigate the optimum cage position and orientation for aiding an ALIF having a transfacet pedicle screw fixation (TFPS). A three-dimensional finite element model (ALIF with TFPS) has been developed to simulate the stability of the L4/L5 fusion segment under five different loading conditions. The Taguchi method was used to evaluate the optimized placement of the cages. Three control factors and two noise factors were included in the parameter design. The control factors included the anterior-posterior position, the medio-lateral position, and the convergent-divergent angle between the two cages. The compressive preload and the strengths of the cancellous bone were set as noise factors. From the results of the FEA and the Taguchi method, we suggest that the optimal cage positioning has a wide anterior placement, and a diverging angle between the two cages. The results show that the optimum cage position simultaneously contributes to a stronger support of the anterior column and lowers the risk of TFPS loosening.
The effects of distinct properties during phase change on mass, momentum, energy, species, and magnetic field intensity transport in workpieces and electrodes in the course of heating, melting, cooling and freezing periods in AC (alternative current) resistance spot welding are realistically and extensively investigated. Resistance spot welding has been widely used in joining thin workpieces due to its light weight and easy manufacturing. This study accounts for electromagnetic force, heat generations at the electrode-workpiece interface and faying surface between workpieces, and dynamic electrical resistance taking the sum of temperature-dependent bulk resistance of the workpieces and contact resistances at the faying surface and electrode-workpiece interface. The contact resistance is a function of hardness, temperature, electrode force, and surface condition. Instead of dealing with specific materials, this work is a general dimensionless investigation of resistance spot welding of materials with different specific heat and thermal conductivity ratios subject to realistic working parameters. The computed results show that nugget formation is delayed and heat transfer is reduced by increasing solid-to-liquid thermal conductivity and liquid-to-solid specific heat ratio. The corresponding thermal fields and flow patterns are also presented.
Many kinds of mechanical systems can be modeled as spatial rigid multibody systems (SR-MBS), which consist of a set of rigid bodies interconnected by joints, springs and dampers. Vibration calculation of SR-MBS is conventionally conducted by approximately linearizing the nonlinear equations of motion and constraint, which is very complicated and inconvenient for sensitivity analysis. A new algorithm based on constraint-topology transformation is presented to derive the oscillatory differential equations in three steps, that is, vibration equations for free SR-MBS are derived using Lagrangian method at first; then, an open-loop constraint matrix is derived to obtain the vibration equations for open-loop SR-MBS via quadric transformation; finally, a cut-joint constraint matrix is derived to obtain the vibration equations for closed-loop SR-MBS via quadric transformation. Through mentioned above, the vibration calculation can be significantly simplified and the sensitivity analysis can be conducted conveniently. The correctness of the proposed method has been verified by numerical experiments in comparison with the traditional approaches.
In this paper, cyclic damage behavior of cyclically load drop curves and their fatigue initiation life of Sn/3.5 Ag/0.75Cu BGA solder joint specimens under oblique displacement cyclic tests were investigated by the theory of damage — coupled endochronic viscoplasticity.
By linearly unloading with damage elastic modulus and the linearly damage-free behavior of grip system, the damage loops of force-Φ angle oblique displacement of BGA solder joint specimen were converted successfully into damage loops of the representative solder ball under cyclically proportional straining, which can be predicted by the endochronic constitutive equations. These results established the relationship of the BGA oblique displacement amplitudes da(Φ) and the effective inelastic strain amplitudes of solder ball: da (Φ)= . Based on the phenomena of cyclic damage and its fatigue life, a Φ dependent degree of damage in the evolution equation of damage under proportional strain path was proposed to depend positively on and N cycles. Using this parameter in the damage per cycle computed by the endochronic theory, a Φ modified cycles N(Φ)/β(Φ) can be defined and then derive the Φ modified Lee-Coffin-Manson (Φ-LCM) equation for the fatigue initiation life of solder ball:
Finally, a Φ modified Lee's BGA (Φ LBGA) equation for BGA solder joint specimens can be derived:
This equation can predict quite well the life data of Sn/3.5Ag/0.75Cu solder joint specimens under Φ ϵ [0π/2]. As a consequence, a vehicle to study the fatigue initiation life of BGA solder joint specimens is constructed completely by the workable methodology and the theory discussed in the paper.
In this paper, analytical particular solutions of the augmented polyharmonic spline (APS) associated with Reissner plate model are explicitly derived in order to apply the dual reciprocity method. In the derivations of the particular solutions, a coupled system of three second-ordered partial differential equations (PDEs), which governs problems of Reissner plates, is initially transformed into a single six-ordered PDE by the Hörmander operator decomposition technique. Then the particular solutions of the coupled system can be found by using the particular solution of the six-ordered PDE derived in the first author's previous study. These formulas are further implemented for solving problems of Reissner plates under arbitrary loadings. In the solution procedure, an arbitrary loading measured at some scattered points is first interpolated by the APS and a corresponding particular solution can then be approximated by using the prescribed formulas. After that the complementary homogeneous problem is formally solved by the method of fundamental solutions (MFS). Numerical experiments are carried out to validate these particular solutions.
The influence of both the Rossby number and the Hartmann number on the hydromagnetic stability of a thin liquid film flowing down along the surface of a vertical cylinder is investigated. The long-wave perturbation method is employed to solve for generalized nonlinear kinematic equations with a free film interface. The normal mode approach is used to compute the stability solution for the film flow. The modeling results indicate that the stability of the liquid film is enhanced by increasing the strength of the magnetic field or reducing the speed at which the cylinder rotates. By contrast, the flow becomes relatively more unstable as the cylinder radius is increased at larger values of the Rossby number. Notably, this finding is the opposite of that observed for film flows along a stationary vertical cylinder.
Research on new techniques of side-inlet/outlet mufflers equipped with internal
non-perforated intruding tubes has been discussed in recent literature; however, the
research work of multi-chamber sideinlet/outlet mufflers in conjunction with cross-flow
tubes and open-ended perforated intruding tubes which may efficiently increase the
acoustical performance is rare. Therefore, the main purpose of this paper is not only to
analyze the sound transmission loss (STL) of three kinds of
side-inlet/outlet mufflers (a three-chamber muffler with cross-flow tubes, a five-chamber
muffler with cross-flow tubes and a nonperforated tube, and a five-chamber muffler with
cross-flow tubes and a perforated tube) but also to optimize their best design shape
within a limited space.
In this paper, both the generalized decoupling technique and plane wave theory in solving
the coupled acoustical problem are used. A four-pole system matrix in evaluating the
acoustic performance is also deduced in conjunction with a simulated algorithm
(SA). A numerical case in finding the optimal STL of
mufflers, which is constrained within a basement with a side-inlet/outlet, at targeted
tones has been introduced. Before the optimization is carried out, an accuracy check of
the mathematical model is performed. Results reveal that the maximal STL
is precisely located at the desired target tone. Moreover, it has been seen that mufflers
with more chambers will increase the acoustic performance for both pure tone and broadband
noise. Additionally, the acoustical performance of mufflers conjugated with perforated
intruding tubes is superior to those equipped with non-perforated tubes.
Consequently, the approach used for seeking the optimal design of the STL
proposed in this study is indeed easy and quite effective.
Though the total stress undrained analysis approach in geotechnical engineering is widely utilized by practicing engineers, it has some intrinsic imperfections that cause the obtained parameters to have unavoidable empirical correlations. In this study, an undrained soft clay model is developed, which overcomes the imperfections of the conventional total stress undrained approach. In addition, the high soil stiffness at small strain and the concept of yield surface are employed to realistically simulate actual soil behavior. The model parameters can be obtainable directly from conventional laboratory tests. The model is validated through different laboratory stress path tests and strength tests in this paper.
This paper characterizes the mass transfer and replenishment of glucose and oxygen in tissue engineered cartilage constructs by a numerical approach. Cell population growth modulated by glucose and oxygen is incorporated in the mathematic model. The distribution of synthesized type II collagen and its influence on mediating the chondrocyte growth over scaffold are also investigated. Results from simulation are compared with the experiments in literature to verify the formulation and predictions. It is found that, under static culture, the oftentimes observed phenomenon that the overall cell number densities in thick scaffolds are smaller than in thin scaffolds is mainly due to depletion of glucose rather than oxygen. Cell growth is found to be more sensitive to the change in glucose concentration for thick scaffolds, whereas to be more sensitive to the change in oxygen concentration for thin scaffolds. Results also demonstrate the modulation of chondrocyte growth by type II collagen, presenting the biphasic impact of type II collagen which promotes chondrocyte growth in the initial phase of cultivation, while inhibits cell growth in the long term. The numerical model provides a useful reference for developing cartilaginous constructs in tissue engineering.
Miniature synthetic jet actuators are low operating power, zero-net-mass-flux and very compact devices which have demonstrated their capability in modifying the subsonic flow characteristics for boundary layer flow control. In order to improve the design active flow control systems, the present study aims to examine the formation and interaction of unsteady flowfield of a synthetic jet with external crossflow. In view of a single synthetic jet emitting into a turbulent boundary layer crossflow via a circular orifice, the theoretical model utilized the transient three-dimensional conservation equations of mass and momentum for compressible, turbulent flows with a negligible temperature variation over the computational domain. The motion of a movable membrane plate was also treated as the moving boundary by prescribing the displacement on the plate surface. The predictions by the computational fluid dynamics (CFD) software ACE+® were compared with the measured transient phase-averaged velocities in literature for code validation. The predictions showed the time evolution of the large vortical structure originating from the jet orifice and its successive interaction with the crossflow to change the flow structure inside the boundary layer.
Green's function and complex function methods are used here to investigate the problem of the scattering of SH-wave by a cylindrical inclusion near interface in bi-material half-space. Firstly, Green's function was constructed which was an essential solution of displacement field for an elastic right-angle space possessing a cylindrical inclusion while bearing out-of-plane harmonic line source load at any point of its vertical boundary. Secondly, the bi-material media was divided into two parts along the vertical interface using the idea of interface “conjunction”, then undetermined anti-plane forces were loaded at the linking sections respectively to satisfy continuity conditions, and a series of Fredholm integral equations of first kind for determining the unknown forces could be set up through continuity conditions on surface. Finally, some examples for dynamic stress concentration factor of the cylindrical elastic inclusion are given. Numerical results show that dynamic stress concentration factor is influenced by interfaces, free boundary and combination of different media parameters.