Symmetric Displacement Research Articles

Instability of imperfect non-uniform shallow arch under uniform radial pressure for pinned and fixed boundary conditions

The instability of imperfect non-uniform circular shallow arch under radial pressure for both pinned-pinned and fixed-fixed boundary conditions is discussed in the article. The imperfection includes the symmetric initial displacement inducing no stress and the non-uniformity which represented by three piecewise constant-stiffness segments. Analytical theoretical formulation is derived by the least potential energy principle. Through mathematical analysis, it's shown rigorously that the effect of imperfection still doesn’t vanish as the mode number of imperfection approaching to infinity. The stiffer end case and stiffer center case are discussed concerning equal potential energy load and snap-through criterion. Distinct snap-through behavior is observed for stiffer end case with fixed boundary condition by a proposed index plot. Moreover the two limiting cases including rigid end case and rigid center case are investigated by employing the augmented potential energy with Lagrangian multipliers considering the imperfection effect. Snap-through criteria are obtained in a closed form for rigid center case. And for the rigid end case with pinned BC, when the center segment's size is tending to zero, an asymptotical solution is derived and by this solution, the importance of multiplicity of roots of some equations governing the snap-through behavior is illustrated clearly. Besides, the equal potential energy load of two limiting cases is analyzed in detail with emphasis on imperfection effect. This paper aims to extend the understanding of imperfect non-uniform circular shallow arch under radial pressure.

A novel analytical approach for predicting the noncylindrical pile penetration‐induced soil displacement in undrained soil by combining use of cavity expansion and strain path methods

SummarySince development of cavity expansion theory and strain path method, almost all the conventional analyses of pile penetration problem have been based on circular cross section penetrometer. However, noncylindrical pile (with noncircular cross section) is also required in geotechnical engineering such as rectangular cross‐sectional pile, X‐sectional cast‐in‐place concrete pile, H‐shaped steel pile, prefabricated vertical drains, and flat dilatometer. This paper presents a novel and general analytical approach for capturing the soil deformation mechanism around the pile with arbitrary cross section. The penetration problem is simulated by a new 2‐dimensional (radial and circumferential) cavity expansion model. Based on the theoretical framework of strain path method, the kinematics (velocity field) of the noncylindrical cavity expansion is reduced to solve the Laplace equation with arbitrary velocity boundary conditions by using the conformal mapping technique. Then, solutions for the strain and displacement, which could consider the large deformation effect, are obtained by the integration of the strain rate and velocity along the streamline. The analytical solution is validated by comparing the degenerate solution of this study with conventional circular (cylindrical) cavity expansion theory. Subsequently, typical numerical examples for the deformation mechanism of elliptical and rectangular cavity expansion are presented to prove the advantage of the proposed new solution particularly in capturing the noncylindrical symmetric displacement field. A brief application of the proposed new analytical solution to the interpretation of the smear effect of prefabricated vertical drain installation confirms its useful in geotechnical engineering.

Two-dimensional thermo-elastic analysis of FG-CNTRC cylindrical pressure vessels

This paper focuses on the application of the first-order shear deformation theory (FSDT) to thermo-elastic static problems of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) cylindrical pressure vessels. A symmetric displacement field is considered as unknown function along the longitudinal direction, whereas a linear distribution is assumed along the thickness direction. The cylindrical pressure vessels are subjected to an inner and outer pressure under a temperature increase. Different patterns of reinforcement are applied as distribution of CNTs. The effective material properties of FG-CNTRC cylindrical pressure vessels are measured based on the rule of mixture, whereas the governing equations of the problem are here derived through the principle of virtual works. A large parametric investigation studies the effect of some significant parameters, such as the pattern and volume fraction of CNTs, on the longitudinal distribution of deformation, strain and stress components, as useful tool for practical engineering applications.

Experimental performance of RC moment frame beams with rectangular openings

A large-scale experimental case study was carried out to investigate the cyclic behavior of T-shaped, moment-resisting frame (MRF) beams with openings. The beams are located in an existing structure in the western U.S., which was designed according to ACI 31-95 and UBC97. Limited availability of test data in current literature and lack of guidance in existing design standards motivated the construction of four replica cantilever test specimens with lengths of 3.8–5.3m. All other specimen dimensions were scaled to 80%, resulting in cross-sections of 0.61 in width and 0.98m in height. Three beam specimens had openings with dimensions of 0.98m×0.37m; the control specimen did not have openings. Each beam replica was instrumented with internal and external instrumentation consisting of strain gauges, linear voltage differential transducers (LVDTs) and string potentiometers, and tested to complete structural failure under quasi-static symmetric displacement reversals. The cyclic performance of all beams was evaluated in terms of failure progression and plastic hinge development, strength and stiffness degradation, and energy dissipation capacity. In addition, the contribution of shear and flexural deformations to the overall displacement profile was studied. Simple monotonic strut and tie modeling was utilized to estimate and compare the beams’ capacities in the elastic range. A discussion of deficient and successful test results highlights the suitability of introducing openings in moment frame beams.

Longitudinal resistance performance of granular ballast beds under cyclic symmetric displacement loading

The longitudinal resistance performance of a granular ballast bed under cyclic symmetric displacement loading was studied based on a full-scale test model of ballast track structures. The change law of the longitudinal resistance characteristics of the ballast bed under variable displacement amplitudes was analyzed. The results show that: the resistance-displacement curves of a granular ballast bed are a set of closed hysteretic curves, indicating obvious energy consumption; a granular ballast bed softens gradually during the cyclic process with constant displacement amplitude, and the residual deformation rate increases nonlinearly with increasing cycle number; the peak value of the longitudinal resistance of lines decreases with increasing cycle number; the cyclic softening of a granular ballast bed is dependent on the displacement amplitude–the higher the displacement, the more severe the cyclic softening will become; after cyclic displacement loading is applied several times, the longitudinal resistance of the bed will degenerate obviously, and the higher the displacement amplitude, the higher the longitudinal resistance attenuation rate of the ballast bed will become.

Transapical Coaptation Plate for Functional Mitral Regurgitation: An In Vitro Study.

A novel transapical coaptation plate (TCP) device was developed and anchored by sutures in the mitral valve to treat functional mitral regurgitation. The objective of this study was to test efficacy of the TCP in an in vitro model. Eight fresh porcine mitral valves were mounted in a left heart simulator to simulate functional mitral regurgitation by means of annular dilatation and asymmetrical or symmetrical papillary muscle (PM) displacement. Six polyurethane TCPs in thickness of 6.4(#1), 4.8(#2), 3.2(#3) mm and hardness of durometer 30 A (H) and 30 OO(S),were fabricated and labeled as H1, H2, H3 and S1, S2, S3, respectively. These TCPs were anchored by the sutures in the mitral annulus and left ventricle apex, and tested. Steady backward flow leakage in a hydrostatic condition and regurgitant volume in a pulsatile flow were measured before and after implantation of the TCPs. Mean regurgitant volume fractions in the asymmetric PM displacement were reduced significantly from 59.1 to 37.2% for H1, 43.2% for H2, 35.9% for S1 and 34.2% for S2 (p<0.021), after implantation of the TCPs. No significant reduction in mitral regurgitation was seen for H3 and S3 (p>0.067). Mitral regurgitation was mild in the symmetric PM displacement, and was not significantly reduced after implantation of the TCPs. In conclusion, the TCP anchored by the sutures in the mitral annulus and left ventricle apex functions successfully as a plug in the mitral valve leaflet gap. The TCP with thickness equal to or greater than 4.8mm is effective to reduce functional mitral regurgitation. The TCP hardness has no effect on difference in reduction of functional mitral regurgitation.

Accurate phase-shift velocimetry in rock

Spatially resolved Pulsed Field Gradient (PFG) velocimetry techniques can provide precious information concerning flow through opaque systems, including rocks. This velocimetry data is used to enhance flow models in a wide range of systems, from oil behaviour in reservoir rocks to contaminant transport in aquifers. Phase-shift velocimetry is the fastest way to produce velocity maps but critical issues have been reported when studying flow through rocks and porous media, leading to inaccurate results. Combining PFG measurements for flow through Bentheimer sandstone with simulations, we demonstrate that asymmetries in the molecular displacement distributions within each voxel are the main source of phase-shift velocimetry errors. We show that when flow-related average molecular displacements are negligible compared to self-diffusion ones, symmetric displacement distributions can be obtained while phase measurement noise is minimised. We elaborate a complete method for the production of accurate phase-shift velocimetry maps in rocks and low porosity media and demonstrate its validity for a range of flow rates. This development of accurate phase-shift velocimetry now enables more rapid and accurate velocity analysis, potentially helping to inform both industrial applications and theoretical models.

High-precision method for submicron-aperture fiber point-diffraction wavefront measurement.

It is a key issue to measure the point-diffraction wavefront error, which determines the achievable accuracy of point-diffraction interferometer (PDI). A high-precision method based on shearing interferometry is proposed to measure submicron-aperture fiber point-diffraction wavefront with high numerical aperture (NA). To obtain the true shearing point-diffraction wavefront, a double-step calibration method based on three-dimensional coordinate reconstruction and symmetric lateral displacement compensation is proposed to calibrate the geometric aberration in the case of high NA and large lateral wavefront displacement. The calibration can be carried out without any prior knowledge about the system configuration parameters. With the true shearing wavefront, the differential Zernike polynomials fitting method is applied to reconstruct the point-diffraction wavefront. Numerical simulation and experiments have been carried out to demonstrate the accuracy and feasibility of the proposed measurement method, and a good measurement accuracy is achieved.

양방향 스털링엔진/발전기의 효율 특성 연구

This paper describes generating efficiency characteristics of the double acting Stirling engine/generator for domestic small-scale CHP (Combined Heat and Power) system. In small distributed generation applications, Stirling engine has competition from fuel cell, microturbine and etc. In order to be economical in the applications, a long life with minimum maintenance is generally required. Free piston Stirling engine (FPSE) has no crank and rotating parts to generate lateral forces and require lubrication. Double acting Stirling engine/generator has one displacer and two power piston which are supported by flexure springs. Two power pistons oscillate with symmetric displacement and are connected with moving magnet type linear generators for power generation from PV work. In experiments, 1 kW class double acting free piston Stirling engine/generator is fabricated and tested. Heat is supplied to hot end of engine by the combustion of natural gas and converted to electric power by linear generators which are assembled with power pistons. The electric parameters such as voltage, current and phase are measured with for variable flow rate of fuel gas. Especially, generating efficiency of FPSE is measured with three different measurement methods. Generating efficiency of the double acting Stirling engine/alternator is about 24%.

Design and Implementation of a Multi-Phase Induction Machine Operating in generating Mode for Power Generation

Self-excited induction generators are increasingly being used in remote areas to generate electrical power from both conventional and nonconventional energy sources. This paper investigates a multi-phase self excited induction generator designed for its six-phase operation. Evaluations were made out on the basis of the machine performance which includes voltage and current characteristics at different conditions. The model used for analyzing the machine behavior has two three phase winding sets. In this paper the analytical modeling of a self excited induction generator operating in six phase mode has been made and the analysis of the machine has been carried out with symmetrical phase displacement between the six stator windings. The dynamics of the self excitation process of the six phase self-excited induction generator has been made which was simulated and analyzed.

Effects of Heat Transfer, Magnetic Field and Space Porosity on Peristaltic Flow of a Newtonian Fluid in a Tapered Channel

In this paper, the influences of magnetic field and porous space of peristaltic flow of a Newtonian fluid in the tapered channel are studied. Flow analysis is also discussed in the presence of heat transfer. A model of wall-induced fluid flow within an infinite tapered channel having symmetric wall displacements and phase difference is developed. Expressions of dimensionless stream function and temperature are obtained analytically by employing long wavelength and low Reynolds number assumptions. The effects of various emerging parameters on the flow characteristics are shown and discussed with the help of graphs. It has been found that The geometric parameters likes, non-uniform parameter, amplitudes and phase difference control the fluid transport phenomena.

Development of highly accurate approximate scheme for computing the charge transfer integral.

The charge transfer integral is a key parameter required by various theoretical models to describe charge transport properties, e.g., in organic semiconductors. The accuracy of this important property depends on several factors, which include the level of electronic structure theory and internal simplifications of the applied formalism. The goal of this paper is to identify the performance of various approximate approaches of the latter category, while using the high level equation-of-motion coupled cluster theory for the electronic structure. The calculations have been performed on the ethylene dimer as one of the simplest model systems. By studying different spatial perturbations, it was shown that while both energy split in dimer and fragment charge difference methods are equivalent with the exact formulation for symmetrical displacements, they are less efficient when describing transfer integral along the asymmetric alteration coordinate. Since the "exact" scheme was found computationally expensive, we examine the possibility to obtain the asymmetric fluctuation of the transfer integral by a Taylor expansion along the coordinate space. By exploring the efficiency of this novel approach, we show that the Taylor expansion scheme represents an attractive alternative to the "exact" calculations due to a substantial reduction of computational costs, when a considerably large region of the potential energy surface is of interest. Moreover, we show that the Taylor expansion scheme, irrespective of the dimer symmetry, is very accurate for the entire range of geometry fluctuations that cover the space the molecule accesses at room temperature.

Vincenzo Quercioli (1876-1939), researcher and pioneer of the atlas fracture.

A review of early 20th century literature regarding fractures of the atlas led the authors to discover a paper written in Italian by Professor Vincenzo Quercioli in 1908, at that time an assistant surgeon at the University of Siena. The work was published in the journal Il Policlinico, which at that time was directed by Professor Francesco Durante. The paper described the first case of a quadripartite fracture of the atlas, and it accurately reported the mechanism of injury, symptoms, neurological examination, treatment, complications, and cause of death of the patient. Quercioli performed an autopsy on the patient and gave a detailed description of anatomopathological features. In particular, he identified the 4 symmetrical fracture lines related to the arches of the atlas and the substantial integrity of the atlantoaxial ligaments, particularly the transverse ligament. Based on those findings, Quercioli concluded that the mechanism of trauma was an axial force. This force passed through the center of the vertebral ring and caused symmetrical displacement and compression of the articular masses. These concepts of dynamic physics led Quercioli to conclude that, because the atlas is wedge shaped, the masses of the atlas reacted to stress by moving away from the center. This reaction resulted in stretching the front and rear arches, which then fractured at their 4 points of weakness. The integrity of the spinal cord was intact, based on a negative neurological examination for CNS lesions. Thus, he concluded that these injuries were not fatal and could be cured by appropriate treatment with a Minerva cast and, in the presence of swallowing disorders, with a nasogastric tube. The case described by Quercioli was later mentioned in two classic works on atlas fractures by Sir Geoffrey Jefferson, published in 1920 and 1927. In those works, Jefferson proposed his classification of 5 different anatomopathological classes; this work is widely cited in the literature and should be considered a classic. The patterns and deductions that Jefferson reported on these fractures appeared to draw upon the scientific experience of Quercioli and his description of the quadripartite atlas fracture, which appeared to be unique, even in Jefferson's review. Therefore, the authors believe that they have identified another scientist and pioneer of the atlas fracture in Professor Vincenzo Quercioli. With his brilliant insights, which remain useful and valid, Quercioli led the way to further research on the subject.

Ultrahigh-Q modes in anisotropic 2D photonic crystal

In this work, we design a two-dimensional photonic crystal cavity made with a substrate of an anisotropic material. We consider triangular lattice photonic crystal made from air holes in tellurium. The cavity itself is then created by three missing holes in the centre. Using the three-dimensional finite-difference time-domain simulation and optimization of the geometrical parameters and the symmetric displacement of the edge air holes on the quality factor, the cavity’s structural parameters yield an ultrahigh-Q mode cavity with quality factor Q = 2.95 × 1011 for a filling factor r/a = 0.45 and lateral displacement of 10 nm. This shows great enhancement compared with previous studies in which silicon material has been used. The designed structure can be helpful in a number of applications associated with photonic crystal cavities, including quantum information processing, filters, and nanoscale sensors.

A novel coaptation plate device for functional mitral regurgitation: an in vitro study.

A novel mitral valve repair device, coaptation plate (CP), was proposed to treat functional mitral regurgitation. The objective of this study was to test efficacy of the CP in an in vitro model of functional mitral regurgitation. Ten fresh porcine mitral valves were mounted in a left heart simulator, Mitral regurgitation was emulated by means of annular dilatation, and the asymmetrical or symmetrical papillary muscles (PM) displacement. A rigid and an elastic CPs were fabricated and mounted in the orifice of regurgitant mitral valves. Steady flow leakage in a hydrostatic condition and regurgitant volume in a pulsatile flow were measured before and after implantation of the CPs. The rigid and elastic CPs reduced mitral valve regurgitant volume fraction from 60.5 ± 11.4 to 35 ± 11.6 and 36.5 ± 9.9%, respectively, in the asymmetric PM displacement. Mitral regurgitation was much lower in the symmetric PM displacement than in the asymmetric PM displacement, and was not significantly reduced after implantation of either CP. In conclusion, both the rigid and elastic CPs are effective and have no difference in reduction of functional mitral regurgitation. The CP does not aggravate mitral valve coaptation and may be used as a preventive way.

Electric field induced ultra-high actuation in a bulk carbon nanotube structure

Electric-field induced nonlinear actuation behavior is demonstrated in a bulk nanotube (CNT) structure under ambient conditions. Completely recoverable and non-degradable actuation over several cycles of electric-field is measured in these structures. A symmetric and polarity independent displacement corresponding up to an axial strain of 14% is measured upon application of a low strength electric field of 4.2kV/m in the axial direction. However, a much lower strain of ∼1% is measured in the radial (or, transverse) direction. Furthermore, the electric field induced actuation increases by more than a factor of 2 upon impregnating the CNT cellular structure with copper oxide nano-particles. An electrostriction mechanism, based on the electric-field induced polarization of CNT strands, is proposed to account for the reported actuation behavior.

Isolated effect of geometry on mitral valve function for in silico model development

Computational models for the heart's mitral valve (MV) exhibit several uncertainties that may be reduced by further developing these models using ground-truth data-sets. This study generated a ground-truth data-set by quantifying the effects of isolated mitral annular flattening, symmetric annular dilatation, symmetric papillary muscle (PM) displacement and asymmetric PM displacement on leaflet coaptation, mitral regurgitation (MR) and anterior leaflet strain. MVs were mounted in an in vitro left heart simulator and tested under pulsatile haemodynamics. Mitral leaflet coaptation length, coaptation depth, tenting area, MR volume, MR jet direction and anterior leaflet strain in the radial and circumferential directions were successfully quantified at increasing levels of geometric distortion. From these data, increase in the levels of isolated PM displacement resulted in the greatest mean change in coaptation depth (70% increase), tenting area (150% increase) and radial leaflet strain (37% increase) while annular dilatation resulted in the largest mean change in coaptation length (50% decrease) and regurgitation volume (134% increase). Regurgitant jets were centrally located for symmetric annular dilatation and symmetric PM displacement. Asymmetric PM displacement resulted in asymmetrically directed jets. Peak changes in anterior leaflet strain in the circumferential direction were smaller and exhibited non-significant differences across the tested conditions. When used together, this ground-truth data-set may be used to parametrically evaluate and develop modelling assumptions for both the MV leaflets and subvalvular apparatus. This novel data may improve MV computational models and provide a platform for the development of future surgical planning tools.

Long-Term 3-Dimensional Stability of Mandibular Advancement Surgery

To evaluate 3-dimensional changes in the position of the condyles, rami, and chin from 1 to 3 years after mandibular advancement surgery. This prospective observational study used pre- and postoperative cone-beam computed tomograms of 27 subjects with skeletal Class II jaw relation and normal or deep overbite. An automatic technique of cranial base superimposition was used to assess positional and bone remodeling changes that were visually displayed and quantified using 3-dimensional color maps. Analysis of covariance with presence of genioplasty, age at time of surgery, and gender as explanatory variables was used to estimate and test adjusted mean changes for each region of interest. The chin rotated downward and backward 1 to 3 years after surgery. Changes of at least 2 mm were observed in 17% of cases. Mandibular condyles presented with displacements or bone remodeling of at least 2 mm on the anterior surface (21% of cases on the left side and 13% on the right), superior surface (8% on right and left sides), and lateral poles (17% on left side and 4% on right). Posterior borders of the rami exhibited symmetric lateral or rotational displacements in 4% of cases. In the hierarchy of surgical stability, mandibular advancement surgery is considered one of the most stable surgical procedures. However, 1 to 3 years after surgery, approximately 20% of patients had 2- to 4-mm changes in horizontal and vertical chin positions or changes in condylar position and adaptive bone remodeling.

Empirical investigation and characterization of surface subsidence related to block cave mining

For guidance on relationships between caving depth and surface subsidence, a comprehensive database was developed after an exhaustive search of published data from cave mining operations from around the world. The distribution of data was found to largely focus on caving angles and macro deformations; very little empirical data exists on the extent and magnitudes of smaller surface displacements. The data clearly show that caving-induced surface deformations tend to be discontinuous and asymmetric due to large movements around the cave controlled by geologic structures, rock mass heterogeneity and topographic effects. The data also show that as undercut depth increases for a given extraction volume, the magnitude and extent of the caved zone on surface decreases. However, numerical modeling indicates that this is only the case for macro deformations and the extent of smaller displacements actually increases as a function of undercut depth. The results presented caution against relying on existing empirical design charts for estimates of caving-induced subsidence where small strain subsidence is of concern, as the data being relied upon does not properly extrapolate beyond the macro deformations (i.e., caving angles) that make up the majority of the observations. The findings also suggest that the extent and magnitudes of subsidence may be underestimated if the analysis adopted neglects the influence of geological structures and assumes symmetrical surface displacements above the undercut.

Simulation Research on Defects Detection in Straight Pipes Using Guided Waves

Ultrasonic guided wave provides a suitable fast screening technique that enables the localization of the defects and offers a rough estimation of the defect size in pipes. Using the ANSYS, the entity model of a pipe with defects such as cracks and holes was established in this paper. Then the L(0,2) mode guided wave was excited by exerting symmetric displacement loads on an end of the pipe model. By analyzing the incident wave and the reflected wave of defects, the axial location and circumferential location of the defects can be reached. Besides, by fitting the data with some certain formulas, the relationships between reflection coefficient and the defects extent can be acquired. This new technique is of great significance in nondestructive detection.