bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Error Prediction and Compensation of Coordinate Measuring Machines
Authors: Dong Chensong , Zhang Chuck , Wang Ben , Zhang Guoxiong
Published: November 2021

Coordinate measuring machines (CMMs) are already widely used as a measuring tool in the manufacturing industry. Fast probing is now the trend for next generation CMMs. However, increases in the measuring velocity of CMMs are limited by dynamic errors that occur in CMMs.

In this paper, theoretical analysis and experimental research is used to create a systematic approach for modeling the dynamic errors of a touch-trigger probe CMM. First, an overall analysis of the dynamic errors of CMMs is given, and methods to improve the stiffness of air bearings are presented. Weak elements of the CMM are identified with a laser interferometer. The probing process, as conducted with a touch-trigger probe, is analyzed and dynamic errors are measured. Based on these analyses, the dynamic errors in touch-trigger probing are modeled using neural networks. In turn, dynamic errors are predicted. An approach to achieving software error compensation is discussed. Finally, the method and results from this study illustrate that it is possible to compensate for dynamic errors of CMMs.
Fixture Configuration Design Using a Computer Experiment
Authors: Xie L. Shelley , Hu S. Jack , Li Wei , Sudjianto A.
Published: November 2021

A new approach to fixture configuration design is developed based on the design and analysis of computer experiments (DACE). In the past, fixture configuration design undergoes three steps in an iterative manner: locator position design, clamp position design, and clamping force design. The fixture and workpiece were generally assumed to be rigid bodies. In this study, a sampled computer experiment is conducted with a finite element analysis (FEA). Surrogate models are developed based on the responses of this experiment. The purpose of building these models is to represent complex physical relations among the design variables in a simple functional form such that design analysis can be conducted efficiently. The surrogate response models can be used to provide a directional guidance in optimization, to identify feasible fixture configuration designs for flexible workpieces, and more importantly to enable a simultaneous design of locator/clamp positions and clamping forces. In the surrogate models workpiece deflections and locator reaction forces are used as variables. Distance-based Latin Hypercube Sampling Design (LHD) is used to increase the number of the sample points and to evenly spread them in the design space. Multivariate Adaptive Regression Splines (MARS) and Gaussian Stochastic Kriging (GSK) models are employed to capture nonlinear relationship among the design variables. The proposed approach is illustrated with examples.
On the Numerical Solutions of Nonlinear Machine-Tool Chatter With Multiple Delays
Authors: Fofana M. S. , Ryba Pamela B.
Published: November 2021

Stable and unstable machining during chatter and the occurring nonlinear phenomenon have been identified numerically. The corresponding governing equations for the machining model are nonlinear differential equations with multiple time delays. A characteristic equation for the linearized stability about equilibrium machining is analyzed. From this it is readily seen that stable machining increases as the feed rate factor increases. The change in character of nonlinear chatter is viewed as a phase portrait trajectory in a phase plane.
Automatic Defects Measurement on Silicon Wafer Surface by Laser Scattered Defect Pattern
Authors: Takahashi Satoru , Miyoshi Takashi , Takaya Yasuhiro
Published: November 2021

A new optical measurement method for evaluating the defects on silicon wafer surfaces quantitatively, applicable to in-process measurement, is presented. The experimental system for measuring the defects consists of a Fourier transform optical system using a high-power objective lens. In order to verify the feasibility of the applications of this method to automatic in-process measurement, a two-stage measurement for detecting and evaluating small particles, which are typical defects on silicon wafer surfaces, was carried out. The results showed that the proposed two-stage measurement method is effective for measuring small defects in the sub-micro meter scale size.
Refrigerative Stereolithography Using Sol-Gel Transformable Photopolymer Resin and Direct Masking
Authors: Murakami Tamotsu , Kamimura Akiya , Nakajima Naomasa
Published: November 2021

The authors have been studying a new fabrication method termed “refrigerative stereolithography” which uses a gel resin layer instead of a liquid layer used in conventional stereolithography. In this paper, we propose the “direct masking method” in which a masking pattern is drawn directly on a gel layer surface to block harmful light exposure of photopolymer resin. With such masks, we can avoid surplus growth only in the regions where it is unnecessary to improve height direction accuracy and resolution. The possibility of surplus growth in the width direction caused by light reflection from the mask surface is pointed out, and the effect is analyzed and confirmed by simulation and experiment. This new surplus growth is termed “reflective surplus growth”. Also, we can solidify the required section shape selectively using the masks and a lamp instead of laser scan patterns. The effectiveness of refrigerative stereolithography with the direct masking method is discussed and confirmed by some experimental results.
A Finite Element Based Die Design Algorithm for Sheet Metal Forming on Reconfigurable Tools
Authors: Socrate Simona , Boyce Mary C.
Published: November 2021

Tooling cost is a major contributor to the total cost of small-lot production of sheet metal components. Within the framework of an academic/industrial/ government partnership devoted to the development of a reconfigurable tool for stretch forming, we have implemented a Finite Element-based procedure to determine optimal die shape. In the reconfigurable forming tool [1], the die surface is created by the ends of an array of square pins, which can be individually repositioned by computer driven servo-mechanisms. An interpolating polymer layer is interposed between the part and the die surface to attain a smooth pressure distribution. The objective of the die design/algorithm is to determine optimal positions for the pin array, which will result in the desired part shape. The proposed “spring-forward” method was originally developed for matched-die forming [2, 3] and it is here extended and adapted to the reconfigurable tool geometry and stretch forming loading conditions. An essential prerequisite to the implementation of the die design procedure is the availability of an accurate FE model of the entire forming operation. The particular nature of the discrete die and issues related to the behavior of the interpolating layer introduce additional challenges. We have first simulated the process using a model which reproduces, as closely as possible, the actual geometry of the discrete tool. In order to optimize the delicate balance between model accuracy and computational requirements, we have then used the information gathered from the detailed analyses to develop an equivalent die model. An automated algorithm to construct the equivalent die model based on the discrete tool geometry (pin-positions) is integrated with the spring-forward method, to generate an iterative die design procedure that can be easily interfaced with the reconfiguring tool. The success of the proposed procedure in selecting an optimal die configuration is confirmed by comparison with experimental results.
Optimum Process Design in Sheet Metal Forming With Finite Element Analysis
Authors: Huh Hoon , Kim Se-Ho
Published: November 2021

Process optimization is carried out to determine process parameters which satisfy the given design requirements and constraint conditions in sheet metal forming processes. The scheme incorporates with a rigid-plastic finite element method for calculation of the final shape and the strain distribution. The optimization scheme adopts a direct differentiation method and a response surface methodology in order to seek for the optimum condition of process parameters. The algorithm developed is applied to design of the draw bead force and the die shapes in deep drawing processes. Results show that design of process parameters is well performed to increase the amount of strain for increasing the strength or to decrease the amount of strain for preventing fracture by tearing. The present algorithm also enhances the stable optimum solution with small number of iterations for optimization.
Stretch Forming Process Modeling: The Role of Modern Stretch Forming Machinery Design and Performance
Authors: Widmann James M.
Published: November 2021

Extrusion stretch forming is used extensively in the aerospace and architectural industries to add contour to extrusions and roll formed sections. Frame members, stringers, wing spars, curtain tracks and many other important aircraft parts are formed with this process. Forming is achieved by pulling an initially straight part in the tensile direction above the material’s yield point and then wrapping the section around a die to add contour. Local buckling and wrinkling that might appear in a pure bending operation can be avoided. There is current interest in improving the process for greater repeatability and less part rework to reduce cost while achieving tighter tolerances (e.g. [1,2]). The stretch forming die plays a significant role in the process. To this end researchers are interested in quicker die development techniques using non-linear beam theory and non-linear finite element modeling of the forming process. For a complete analytical picture of the process, a close look at the stretch forming machine’s performance must be included in the process model. Two major areas of machine performance are important; machine deflections and hydraulic control system performance. This paper provides a brief overview of the extrusion stretch forming process and then focuses on the structural and control system design of the modern stretch forming machine. Analytical models of the machine deflection as well as its hydraulic control system are developed. A short discussion concerning the difference between traditional “pressure forming” and modern CNC position forming is also included. Insight into the limitations of traditional PID control for the stretch forming machine can be seen from the analysis. It is evident that these machine models must be used to complete the process model to effectively create die designs for close tolerance and highly repetitive part production.
Aluminum Tailored Blank Welding Using Laser Beam Shaping and Twin-Spot Optics
Authors: Hsu Rey , Fliss Stefan , Heinemann Stefan
Published: November 2021

The use of aluminum tailor welded blanks in the automotive industry continues to grow due to the fact that aluminum is lightweight and the characteristics of the tailor welded blanks. It has been found that welding of aluminum blanks with a CO2 laser is difficult but doable in a production environment. By using a high power CW Nd:YAG (Neodynium dopped Yittrium Aluminum Garnet) laser. It is possible to obtain sound results with a much wider process parameter window. However, currently, high power CO2 lasers (in the range of 8 kW) are still the dominate laser source in North America steel tailor welded blank companies. Will these lasers be able to weld aluminum tailored blanks if the demand for aluminum tailor welded blanks increases? This study employed twin spot and beam shaping methods to weld 1mm and 2 mm tailored blanks together using a high power (9 kW maximum) CO2 laser for both 5754-O and 6111-T4 alloys. The results show that high power CO2 lasers can be used to weld 5754-O and 6111-T4 aluminum alloys with very precise parameter settings. However, using beam shaping is more critical than using twin spot for 1 mm thick aluminum blanks. Once the correct parameters are applied for using beam shaping, the cup test results are better than using twin spot.
Measurement and Analysis of Tip Growth
Authors: Steele Charles R. , Dumais Jacques , Shaw Sidney L.
Published: November 2021

Tip growth is basic and deceptively simple. A single cell has a wall that is cylindrical with a prolate spheroid as an end cap. The growth takes place in the end cap. The mechanical loading which drives the growth consists of turgor pressure of magnitude 5–10 atmospheres. We report recent measurements on the geometry of the growth that provide detail of the shape of the end cap. In addition, fluorescent beads were placed at points on the cap, whose positions with time were recorded.

A Lagrangian formulation provides the kinematics of the growth process, and indicates that for steady-state, axisymmetric growth, the current velocity of a bead depends on only the geometry and the stretch ratio. The ratio of current mean strain rate to mean stress provides a coefficient of growth rate. This depends on position, which can be interpreted as a dependence on the stretch ratio, i.e., the past history of the wall element. Thus a simple mechanical description appears to be appropriate. However, the stability of the process has not yet been considered.
Tensegrity and the Emergence of Complex Mechanical Behavior in Living Cells
Authors: Ingber Donald E.
Published: November 2021

Existing engineering models of cell mechanics fail to incorporate current knowledge of the molecular intricacy of living cells. An alternative model of cell structure based on tensegrity architecture suggests that complex mechanical behaviors emerge in cells from collective interactions among different cytoskeletal filaments which are organized within hierarchical networks that are tensionally prestressed to ensure shape stability. This discrete network model has been controversial because it goes against prevailing views. In this article, I will review the concept behind cellular tensegrity, explain how it has become translated into mathematical terms over time, and provide reference to recent studies which provide experimental verification of predictions that have arisen from this theoretical model. Taken together, these findings suggest that tensegrity represents a robust and unified model of cell mechanics which, in contrast to alternative approaches, may facilitate future understanding of the link between mechanics and biochemistry.
Mechanics of Angioplasty: Wall, Balloon and Stent
Authors: Holzapfel Gerhard A. , Schulze-Bauer Christian A. J. , Stadler Michael
Published: November 2021

Studying the solid mechanics of angioplasty provides essential insight in the mechanisms of angioplasty such as overstretching the disease-free tissue, plaque disruption or dissection, redistribution inside the wall and lipid extrusion etc. We desribe our current understanding of the mechanics of angioplasty based on the example of a human iliac artery with an eccentric stenosis. We outline a new approach which has the potential to improve interventional treatment planning, to predict the balloon and stent-induced wall stresses as well as the dilation success. In particular, we use MRI to obtain accurate geometrical data for the vessel wall and plaque architecture and to identify their different types of soft (biological) tissues and calcifications. One issue is to characterize the quasistatic stress-strain response of these components in both axial and circumferential directions. We present new experimental results showing strong nonlinearity and anisotropy. Another issue is to identify predominant directions of each component by analyzing orientations of cellular nuclei. The morphological and mechanical information is used for the elastoplastic constitutive model designed to capture the finite strains of the stenotic artery during angioplasty. The three-dimensional model is fitted to the experimental data. Associated material parameters, corresponding to the different tissues of the stenosis, are presented. The numerical part outlines briefly the concept of the finite element model and, based on a computational structural analysis, discusses the mechanism of angioplasty for the considered type of stenosis.
Friction Effects in Pipe Flow of Phan-Thien-Tanner Fluids
Authors: Letelier Mario F. , Siginer Dennis A.
Published: November 2021

An analytical study of the friction law for rectilinear flow a Phan-Thien-Tanner fluid is presented. The flow is assumed steady and the pipe circular. The equations of motion are solved and the velocity, rate of flow, and friction factor are determined. Friction effects are related to the Reynolds number and to other flow parameters, such as the Deborah number.
Appraisal of an ESF Radial Plate Clutch With Cooling Flow Using a NNF CFD Solver
Authors: Ellam Darren J. , Atkin Raymond J. , Bullough William A.
Published: November 2021

To aid the application of electro-structured fluid (ESF) devices, a virtual two plate radial clutch is examined in a pre-prototyping exercise to estimate the effect of a radial cooling flow on pre-set torque transmission. A throughflow of ESF will act to keep the fluid temperature under control making such devices more reliable over a wider operating range.

The ESF is treated as a Bingham viscoplastic material and clutch behaviour is investigated under steady state isothermal conditions. The resulting two-dimensional non-Newtonian fluid (NNF) model is solved using a computational fluid dynamics (CFD) package. The results are partially verified using analytical analysis and compared with sparse experimental data. This work is expected to lead to a more complex CFD model for which analytical methods will not be available.

Indications are that, for realistic rates of throughflow, torque transmission should not be overtly affected. Hence the cooling of slipping ESF clutches by throughflow can be contemplated.
Symmetry Breaking in ER and MR Fluids Under Shear
Authors: Tao R. , Zhang J. , Shiroyanagi Y. , Tang X. , Zhang X.
Published: November 2021

The behavior of an electtorheological (ER) chain under a shear force is investigated theoretically and experimentally. Contrary to the conventional assumption that the ER chain under a shear force becomes slanted and breaks at the middle, we have found that there is symmetry breaking. When the shear strain is small, the chain becomes slanted with a space gap between the first and second particles (or between the last and next last particles). As the shear strain increases, the gap becomes wider and wider. When the shear strain exceeds a critical value, the chain breaks at the gap. The experiment also confirms that an ER chain under the shear breaks at either end, not at the middle. This symmetry breaking reflects the space’s anisotropy, which is the result of the applied electric field.
The Control of Impulsive Forces Using Electrorheological and Magnetorheological Fluids
Authors: El Wahed Ali K. , Sproston John L.
Published: November 2021

This paper is concerned with an experimental assessment of the application of both Electrorheological (ER) and Magnetorheological (MR) fluids in the control of impulsively applied loads. The ER device was built as a squeeze cell incorporating a chemically simple ER fluid, consisting of a suspension of a polymeric compound in a dielectric liquid carrier, sandwiched between two electrodes which, during impact, move towards each other, whilst the MR device was a commercially available vibration absorber. Each device was mounted in an experimental drop-hammer rig, which was capable of determining the instantaneous responses of the fluids for a range of applied loads.

The transient characteristics of the devices were assessed for various mechanical force levels and, for the ER device, under DC excitation of the fluid in conjunction with a digital controller to provide a constant applied electrical field.

Input and output force levels were monitored using a dedicated data acquisition system in conjunction with a PC enabling the dynamic response of the devices to be determined using a combination of displacement, force, velocity and acceleration measurements.
A Novel Design for Producing Fine-Celled Foams of Plastic/Wood-Fiber Composites
Authors: Rizvi Ghaus M. , Park Chul B.
Published: November 2021

This paper presents an innovative system design for production of plastic/wood-fiber composite foams based on a chemical blowing agent (CBA). Wood-fiber inherently contains moisture, which adversely affects the foam processing and the resultant cell morphology. To improve the cell morphology, the moisture content in the final foam should be minimized. A novel system design is presented for achieving this goal. Undried wood-fibers were processed together with HDPE, CBA and a coupling agent (CA) in a tandem extrusion system. At the interconnection of the two extruders, a vent was provided to purge the moisture into the atmosphere. HDPE/wood-fiber composite foams were produced on this system and on a single extruder without the vent, for comparison. The cellular morphology and volume expansion ratios of the foamed composites were characterized. The foams produced on the newly developed tandem system exhibited significantly improved cell morphology and surface quality.
Failure Analysis of Hybrid Armor Under High Velocity Impact
Authors: Mahfuz Hassan , Zhu Yuehui , Mamun Wahid A. , Haque Anwarul , Jeelani Shaik
Published: November 2021

Failure analysis of hybrid integral armor has been performed using finite element method. LS-DYNA3D code has been employed to investigate the response of an integral armor under high velocity impact. A 3-D FE model consisting of the various layers of the armor has been developed and subjected to transient dynamic loading. The analysis is based on actual experiments conducted in a gas gun set up. V50 velocity for a Fragment Simulating Projectile (FSP) has been considered, and the corresponding responses have been investigated to assess the failure of the armor at the ballistic limit. The investigation consisted of three successive studies; first, a base model was developed to have preliminary ideas about the energy absorption and the depth of penetration. Second, interface gap elements were introduced at the rubber interfaces, as the delamination across the rubber layer seemed critical in the failure of the armor. Third, a user defined material model has been introduced to account for the fracture behavior of ceramic. Details of the development of the models, and the analysis of failure are presented in this paper.
Control of a Hydraulically Driven Flexible Manipulator Using Sliding Mode
Authors: Liu Y. , Handroos H.
Published: November 2021

A class of multi-link, structurally flexible and hydraulically powered manipulators are considered for an application of using sliding mode control to track a trajectory of end-tip. Due to the particularity of dynamic model of system and for the purpose of control synthesis, it is required to a modification mapping from the generalized coordinate to the task space, and position of end tip is defined as output of system for the tracking target in the task space. The control based on the model is developed to exploit the full potential of flexible hydraulic manipulator. In the paper, the control performance is demonstrated by simulation on PATU 655 log crane, that is a three flexible links manipulator with the actuation of the lift and jib hydraulic servo systems in the presence of considerable uncertainty.
Pneumatic Pipe Modeling: Theory and Experimental Approach—Part II
Authors: Bideaux E. , Scavarda S.
Published: November 2021

In fluid power systems, lines or pipes can have a predominant effect on dynamics. Although many studies have been carried out on hydraulic pipe modeling, there are only a few existing approaches for such problems in pneumatics. This paper proposes an experimental work in modeling of pneumatic pipes. A short state of the art situation, the nature of this problem, and different approaches of modeling pneumatic pipes are presented in Pneumatic Pipe Modeling: Theory and Experimental Approach (PART I). As the simulation of system with pipes may need an important computing time, it is crucial to use the adequate model. While it is not difficult to develop theoretical models, we need to tune them by adjusting the unknown parameters such friction factor and the thermal exchange parameter. We introduce then an experimental method to evaluate these parameters. The robustness of the models is proved through several examples and in order to validate our propositions, we compare experimental trails to the results given by the simulation.
A PDF Formulation on Turbulence Modeling
Authors: Tao L. , Chen G. Q.
Published: November 2021

We propose a framework to develop turbulence models based on single-point closure through a probability distribution function. The evolution equation for the characteristic function is formed and the possible way of constructing specific models is addressed.
On the Response of Modulated Doublet Modes to Traveling Wave Excitation
Authors: Chang J. Y. , Wickert J. A.
Published: November 2021

The forced vibration of arotationally periodic structure when subjected to traveling wave excitation is discussed, with emphasis placed on the steady-state response of doublet modes having either repeated or split frequencies. Such vibration modes have spatially modulated shapes defined by (i) the numbers of nodal diameters present in the limiting case of axisymmetry, and (ii) certain additional, superposed, contaminating Fourier harmonics which distort their appearances. The natural frequency and mode structure of a model periodic structure is discussed in the context of an otherwise axisymmetric disk having evenly-spaced, sector-shaped, line distributions of stiffness and inertia. Through a perturbation analysis, the contamination wavenumbers present in a doublet having repeated frequency are shown to comprise two subsets, the members of which have sine and cosine coefficients of the same, or of differing, signs for each wavenumber present in the mode shape’s Fourier expansion. That structure for the wavenumber content is explored further with respect to the response of repeated and split doublets to a harmonic traveling wave excitation. The individual Fourier components comprising a modulated doublet mode shape can propagate in the same direction as the excitation, or opposite to it, depending on the wavenumber of the excitation and the subset to which the contamination wavenumber belongs. The response of the split frequency doublets and the circumstances under which traveling or standing wave responses, or a blend of the two, can occur in the structure’s reference frame are examined and discussed in the context of the model periodic structure. The qualitative character of the response, the forward or backward propagation direction of each mode’s constituent wavenumber components, and the phase speeds of those components are discussed in illustrative case studies.
Modal Control of Flexible Systems Using Distributed Sensing
Authors: Nagarkatti Siddharth P. , Rahn Christopher O. , Dawson Darren M. , Zergeroglu Erkan , Malatpure Aniket A.
Published: November 2021

In this paper, we design a modal controller for conservative flexible systems that uses distributed sensing. Spatial filtering of the distributed displacement and velocity measurements based on the system eigenfunctions prevents spillover instabilities in the closed-loop system. The proposed control is proven to stabilize a discrete set of controlled modes without destabilizing the remaining, residual modes. We then apply the theory to a single flexible link robot arm and experimentally demonstrate the feasibility of the proposed control strategy. The experiments use high speed video feedback with image processing to determine the spatial beam curve. The controller quickly damps the first modal response without causing instability in the remaining modes.
Design Curves for 3D Reinforced Composite Laminated Double Cantilever Beams
Authors: Mabson Gerald E. , Deobald Lyle R.
Published: November 2021

Design curves for 3D reinforced composite laminated double cantilever beams (DCB) are developed and presented. Z-pin and stitch reinforcements are considered. These curves may be used by designers and analysts in specifying Z-pin and stitch fields for preliminary design to arrest the progression of delaminations in laminated composite structures.
Stability of Sandwich Cylindrical Shells and Panels With Rib-Reinforced Facings
Authors: Birman Victor , Simitses George J. , Shen Liang
Published: November 2021

A new concept in sandwich structures, considered in the paper, employs composite facings with internal ribs. The advantage of this approach is related to enhanced local stiffness and strength of the facings. In particular, the material of facings can be redistributed making the facings thinner, while using the released material for internal ribs. Obviously, this means that the weight of the structure remains without change, while local strength and stiffness increase. The penalty for using this approach is a potential decrease of global stability and global strength as well as lower natural frequencies. The present paper addresses the stability problem for cylindrical shells and panels subjected to axial compression. Buckling loads are calculated for short, complete, cylindrical shells. Based on the numerical results discussed below, it is obvious that ribs should be symmetrically located with respect to the middle surface of the shell. Then a decrease of global stability is relatively small and the proposed design is justified and feasible in practical applications.
Failure Behavior of Closed Cell Foams
Authors: Christensen Richard M. , DeTeresa Steven J.
Published: November 2021

A two-parameter theory of failure is developed for materials for which the uniaxial compressive stress failure magnitude is less than that for uniaxial tension. The theory is compared with data for a closed cell foam material under combined shear and normal stresses. Although the theory shows the correct general behavior, it probably omits certain finer scale features seen in the data. A more refined theory is now being developed, along with further experimental data.
Behavior of Unidirectional Sandwich Panels With a Bi-Linear “Soft” Core: High Order Approach
Authors: Schwarts-Givli Hilla , Frostig Yeoshua
Published: November 2021

A closed-form high-order theory for the analysis of a sandwich panel with a core made of a material characterized by a bi-linear constitutive relation is presented. The non-linearities in the core are a result of bi-linear constitutive relations of the shear and vertical normal stresses. The governing equations are non-linear in the longitudinal and in the vertical coordinates in general. The solution procedure adopted is an iterative one along with convergence criteria. The numerical examples include two types of core material behaviors; where the first one deals with a bi-linear constitutive relation for the shear stress only; and the second one with a bi-linear constitutive relation for vertical normal stresses only. The results demonstrate the relaxation of the stress concentration involves as the load level increase beyond the yielding level as the secant modulus decrease. In the sequel, a summary and conclusions are presented.
On the Choice of Shear Correction Factor in Sandwich Structures
Authors: Birman Victor , Bert Charles W.
Published: November 2021

The first-order shear deformation theory (FSDT) is a relatively simple tool that has been found to yield accurate results in the non-local problems of sandwich structures, such as buckling and free vibration. However, a key factor in practical application of the theory is determination of the transverse shear correction factor (K), which appears as a coefficient in the expression for the transverse shear stress resultant. The physical basis for this factor is that it is supposed to compensate for the FSDT assumption that the shear strain is uniform through the depth of the cross section. In the present paper, the philosophies and results of K determination for homogeneous rectangular cross sections are first reviewed, followed by a review and discussion for the case of sandwich structures.
Drag Coefficients of Viscous Drops
Authors: Feng Zhigang , Michaelides Efstathios E.
Published: November 2021

We have used a finite-difference scheme to solve the Navier-Stokes equations for the steady flow inside and outside viscous spheres in a fluid of different properties. Hence, we obtained the hydrodynamic forces and the steady-state drag coefficient of the spheres. The computational technique we have used enables us to extend the results to Reynolds numbers between 0 and 1,000. The viscosity ratio of the computations ranges between 0 (inviscid bubble) and infinity (solid particle). The method presented here makes use of a two-layer concept for the computational domain outside the sphere. The first layer is a very thin one [O(Re−1/2)] and is positioned at the interface of the sphere. The second layer is based on an exponential function and covers the rest of the domain. The computations yield the friction and the form drag of the sphere. It is observed that both the Reynolds number and the viscosity ratio play a major role on the value of the hydrodynamic force and the drag coefficient. If all other conditions are the same, there is a negligible effect of the density ratio on the drag coefficient of viscous spheres.
Transient Heat Transfer in the Case of Fast Starting Process for Small Steam-Generator
Authors: Bai Bofeng , Guo Liejin
Published: November 2021

The present paper deals with the results of an experimental investigation on transient heat transfer of helical coil steam generator during transient caused by two types of starting processes, which were named lag-start-up and synchro-start-up. The lag-start-up in this paper was referred to as that the working fluid keeps actionless in the initial stages and the pump is started after the heat loading. The synchro-start-up was referred to as that the pump and the heat load were started synchronously from zero to one certain high level. The investigation was conducted to provide one optimal operation. Some correlation to calculate the transient forced convective heat transfer coefficients of single-phase water flow and boiling flow were proposed, and a criterion of critical heat flux for the safety evaluations of starting processes were also obtained. The influence on the starting time was investigated as well.
Cycle-Induced Flow and Transport in a Model of Alveolar Liquid Lining
Authors: Benintendi Steven W. , Grotberg James B. , Halpern David
Published: November 2021

A simplified model of alveolar liquid lining dynamics is developed using a stretchable two-dimensional slot and an insoluble surfactant. Using lubrication theory, a coupled set of evolution equations is derived that describes the film height and interfacial surfactant distribution during the oscillation cycle. This system is solved asymptotically in the limit of small stretching amplitudes. The unsteady flow field is characterized by vortices at the end positions of the oscillation cycle. The cycle-averaged flow field also contains vortical structures, whose number and size vary over parameter space. For large molecular species, like proteins and surfactants, the bulk Peclet numbers can be large, indicating the importance of this liquid layer in the transport process. This may have an impact on the effectiveness and optimization of several medical treatment modalities. Also, since the liquid lining covers many cells within an alveolus, the predicted flow/transport patterns can allow a communication pathway among cells of the same alveolus.
Cavitation Bubble Field at Low Frequency: Simulations and Experiments
Authors: Laborde J.-L. , Servant G. , Hita A. , Caltagirone J.-P. , Gerard A.
Published: November 2021

Power ultrasound is becoming a generally recognized tool in small-scale laboratory. It has considerable potential for industrial use. Actually, propagation of ultrasound wave (from 20 to 800 kHz) through a liquid inside a cylindrical reactor initiates acoustic cavitation and fluid dynamics phenomena. Acoustic cavitation is the formation and activity of bubbles in a liquid due local negative pressures. Spectacular effects including: erosion, sonoluminescence, molecular damage and chemical effects occur. Traveling power ultrasound also initiates fluid dynamics phenomena such as free surface deformations (aerosol formation), convection (macro-mixing), acoustic streaming (micro-mixing), … Characterization of the wave field formation is of significant importance for understanding phenomena and designing and optimizing industrial reactors. Mathematical modeling is here of a great interest, because the scale-up difficulties of ultrasound-based processes. Then, two-phase models (bubbles in liquid) are shown necessary, because bubble clouds interact directly with ultrasound propagation and modify the pressure field establishment. The cavitation field is so dense that it could play the role of an acoustic screen. Bubbles dynamic is considered and simple models are derived. Results show the influence of a homogeneous density distribution of bubbles on the wave attenuation and the agreement between the transient bubble motion induced by pressure gradients and visualizations.
Application of Wavelet Packet to Particle Image Velocimetry Technique
Authors: Li Hui , Takei Masahiro , Saito Yoshifuru , Horii Kiyoshi
Published: November 2021

Our motive of this study is to develop an application of the wavelet packet to PIV image compression processing in order to improve the spatial resolution and reliability furthermore. It was found that the reconstructed PIV image with a lower compression ratio may emphasize particle edges at a relatively high spatial resolution, and the reconstructed PIV image with a higher compression ratio may display the large-scale motion of particles and may deduce noisy. In this study, the relative error of the wavelet packet image compression technique was lower than that of the standard wavelet image compression technique. The higher compression ratio of 64:1 can be realized without losing significant flow information in PIV processing. It could say that the wavelet packet could provide a better compression performance than the standard wavelet image compression technique when compressing PIV images.
Computation of the Vortical Flow in Human Aorta
Authors: Liu Hao
Published: November 2021

Blood flow in aorta cannot spiral as a single helical flow according to conventional fluid dynamic theories. Most in vivo studies, however, show a helical flow in the aorta and such a rotational flow is seen even in the descending aorta. Through a series of stepwise parametrical computational fluid dynamic studies we here show that a swirl secondary flow imposed at inlet can create the helical flow in the aorta. We built an aortic arch model which has realistic geometry of the aorta being reconstructed based on MRI images and a computer-aided method. Our results demonstrate that, rather than geometric influence of the curvature and torsion of the aorta, the swirl inflow condition at inlet plays a key role in the generation of the helical flow. This also implies that the secondary inflow conditions can affect the flows downstream significantly at high Reynolds numbers and we may need to reinvestigate and restudy some fluid dynamic phenomena with application to the physiological fluid dynamics.
Scheduling Algorithms With Application to Parallel Computing of Aeroacoustics
Authors: Povitsky Alex
Published: November 2021

In this study we consider one method of parallelization of implicit numerical schemes on multiprocessor systems. Then, the parallel high-order compact numerical algorithm is applied to physics of amplification of sound waves in a non-uniform mean flow. Due to the pipelined nature of this algorithm, its efficient parallelization is based on scheduling of processors for other computational tasks while otherwise the processors stay idle. In turn, the proposed scheduling algorithm is taken as a special case of the general shop scheduling problem and possible extentions and generalizations of the proposed scheduling methodology are discussed.

Numerical results are discussed in terms of baroclinic generation of wave-associated vorticity that appear to be a key process in energy transfer between a non-uniform mean flow and a propagating disturbance. The discovered phenomenon leads to significant amplification of sound waves and controls the direction of sound propagation.
Analysis of a Novel DCB Specimen for Stitched Texile Composites
Authors: Chen Leishan , Sankar Bhavani V. , Ifju Peter G.
Published: November 2021

Laminated composites, such as graphite-epoxy, are vulnerable to delamination. Through-the-thickness stitching can dramatically improve the interlaminar strength and fracture toughness of laminated composites. In some instances the fracture toughness is so high that conventional DCB tests cannot propagate the crack, instead the specimen fails in flexure. Recently a novel fixture has been developed and used successfully to measure Mode I fracture toughness of such stitched composites. Due to the stable propagation, the location of the crack front and the corresponding load can be precisely measured. The nonlinear differential equations of equilibrium of the new specimen were solved using an iterative procedure to obtain the strain energy release rate as a function of load and crack length. Results include, bending moment, transverse deflection and slope as a function of crack length. The analytical method in conjunction with experimental measurements has been successfully used to determine the instantaneous GIC of the specimen. It was found that the apparent fracture toughness of the specimens tested was roughly constant along the stitched zone, and was about sixty times that of unstitched specimen.
Evaluation of Progressive Failure Simulation Based on Continuum Damage Approximations
Authors: Whitcomb John , Noh Jae , Chapman Clint
Published: November 2021

Discrete modeling of individual damage sites in composites is generally impractical using finite element analysis. A popular alternative is reduction of material properties at those integration points where the stress state exceeds the allowable. This selective reduction of properties results in inhomogeneous properties within an element. Using ordinary finite element interpolation results in severe violation of equilibrium. This paper examines the behavior of the the simplest element, a uniaxial rod element, when selective property reduction is used. Both exact and numerically integrated forms were examined. The results show that errors can be reduced significanly if a robust technique can be developed for representing the damage with a smooth function.
Decoupling the Design Sampling Region From the Trust Region in Approximate Optimization
Authors: Pérez Victor M. , Renaud John E.
Published: November 2021

Response Surface Approximations (RSA’s) are widely used in the design community to provide designers with an approximate representation of a system. The use of RSA’s allow designers to query the system while avoiding the high computational costs associated with today’s advanced simulation codes. Sequential Approximate Optimization (SAO) methodologies have proved to be effective in managing the optimization of multi-disciplinary design problems. In SAO the sampling required to build the RSA’s often takes place within the same bounds as imposed on the current optimization iterate. This assures a good representation of the system in the region where it will be optimized. However it may restrict the approximation from extrapolating beyond the design space, and therefore improve the convergence rate of the algorithm. In this research a decoupling of the sampling region from the trust region is proposed.
Multi-Junction, Multi-Branch Torsional Vibration in a Geared Rotating System
Authors: Yuan Qing Ke , Yao David Y.
Published: November 2021

A multi-junction, multi-branch torsional vibration system is often found in a geared rotating system. This is an important part in many types of machinery, such as mining machinery, petroleum machinery, steel rolling machinery and automobiles. If the design parameters of the system are improper, there will be serious torsional vibration, which will cause noticeable sound disturbances, severe shakings, and component fatigue problems. Analyzing and pre-estimating critical speeds or torsional natural frequencies and mode shapes of the vibration systems in the design stage is very important to avoid future disastrous and costly repairs of the machinery. In this paper, a radical and effective method for calculating natural frequencies and mode shapes of multi-junction, multi-branch torsional vibration systems, has been put forward, a program named MJBTVAP (Multi-Junction, multi-Branch Torsional Vibration Analysis Program) based on this method has been developed, actual problems have been solved.
Dynamics of Two Time-Delay Coupled Relaxation Oscillators of the van der Pol Type
Authors: Sen Asok K. , Rand Richard H.
Published: November 2021

In this paper we examine the dynamics of two time-delay coupled relaxation oscillators of the van der Pol type. By integrating the governing differential-delay equations numerically, we find the various phase-locked motions including the in-phase and out-of-phase modes. Our computations reveal that depending on the strength of coupling (α) and the amount of time delay (τ), the in-phase (out-of-phase) mode may be stable or unstable. There are also values of α and τ for which the in-phase and out-of-phase modes are both stable leading to birhythmicity. The results are illustrated in the α-τ parameter plane. Near the boundaries of stability and instability of the in-phase (out-of-phase) mode, many other types of phase-locked motions can occur. Several examples of these phase-locked states are presented.
Design Optimization of a Special Mounting System: Floating Raft for Ship Power Equipment Vibration Isolation
Authors: Wang Yu , Hua HongXing , Shen Rongying
Published: November 2021

Design optimization of ship power equipment mount system for vibration isolation is presented. The power equipment is modeled as nearly rigid body supported by a set of rubber mounts, called upper level mounts. The upper level mounts are mounted on a middle flexible structure, which is supported by another set of rubber mounts, the lower level mounts. This whole mount system is called floating raft system, which is mounted on elastic bases. This paper, at first explained that the transmissibility, which is defined as the ratio of power equipment vibration response to the transmitted vibration response of the base, can be expressed by frequency response functions. Then based on the frequency response sensitivity analysis, a new design optimization scheme is presented in which the transmissibility is the optimization objective. Finally, an example is used to demonstrate its feasibility.
Dynamics of a Nonlinear System Under Combined Parametric and Quasiperiodic Excitation
Authors: Tan Chin An , Kang Bongsu
Published: November 2021

The forced response of a Duffing oscillator under combined parametric and quasiperiodic excitation with two frequencies is studied. Numerical results are obtained by the spectral balance method. Characteristics of the motion as a frequency parameter is tuned are investigated in terms of the response time histories, frequency spectra, Poincaré sections and Lyapuov exponents. It is found that routes to chaotic motions are different at the primary and parametric resonances.