Displacement Mode Research Articles

Analytical Studies on Mode III Fracture in Flexoelectric Solids

Abstract Due to the stress concentration near crack tips, strong flexoelectric effect would be observed there, which might lead to new applications of flexoelectricity in material science and devices. However, different from the flexoelectric effect in cantilever beams or truncated pyramids, at the crack tip, multiple components of strain gradients with nonuniform distribution contribute to the flexoelectric effect, which makes the problem extremely complex. In this paper, with the consideration of both direct and converse flexoelectricity, the electromechanical coupling effect around the tip of a Mode III crack is studied analytically. Based on the Williams’ expansion method, the displacement field, polarization field, strain gradient field along with the actual physical stresses field are solved. A path-independent J-integral for Mode III cracks in flexoelectric solids is presented. Our results indicate that the existence of flexoelectricity leads to a decrease of both the J-integral and the out-of-plane displacement in Mode III cracks, which means that the flexoelectric effect around the tip of Mode III cracks enhances the local strength of materials.

Research on Shear Lag Warping Displacement Modes of Frame-Tube Structures Based on the Hamiltonian Mechanics

Based on the equivalent continuity method, the accuracy of the shear lag warping displacement functions for frame-tube structures was studied under the Hamiltonian mechanics. Different types of functions were selected to describe the shear lag warping displacement of the flange plate, and the shear deformation and longitudinal warping of the equivalent plate were considered. The total potential energy of the structure and the corresponding Lagrangian function under different displacement modes were obtained. Not with the traditional variational methods, the problem was studied under the Hamiltonian mechanics system. The Hamiltonian canonical equation for the frame-tube structure was derived and solved with the precise integration method, then the column axial force was calculated and the accuracy was analyzed. The verification results of the calculation examples show that, this method is simple and feasible to analyze the shear lag effects of the frame-tube structures. The choice of different warping displacement functions has little effect on the lateral displacement calculation results, but has great influence on the axial force solution, and the quadratic parabola can best reflect the actual warping displacement distribution of the flange. Comparison of the stress distributions in the equivalent flange under different types of loads indicate that, with the increase of the position of the external load resultant force, the negative shear-lag effect on the top gradually weakens to disappear.

Adaptive Learning for Maximum Takeoff Efficiency of High-Speed Sailboats

This paper presents an optimal takeoff maneuver for an AC75 foiling sailboat competing in the America's Cup. The innovative sailboat design introduces extra degrees of freedom and articulations in the boat that result in nonlinear, high-dimensional, and unstable dynamics. The optimal maneuvers were achieved by exploring out-of-the-box solutions through adaptive control and optimization. We used a high-fidelity sailboat simulator for the data generation process and an adaptive control approach (Jacobian Learning (JL)) to optimize the sailing maneuver. Takeoff is a dynamic sailboat maneuver that involves transitioning the boat from a low-speed in-water status (displacement mode) to a high-speed out-of-water status (foiling mode) via actuation of the sailboat's inputs. We optimized the time for the boat's transitions from displacement mode to foiling mode while maximizing the projection of the velocity (Velocity Made Good (VMG)) in the desired target direction (True Wind Angle (TWA)). Furthermore, we optimized the sailboat's upwind steady-state performance (closed-haul VMG) for varying sailing directions (TWA) and used the optimal TWA to formulate the takeoff. The optimal solution is subject to physical/actuator constraints and the ones enforced to ensure the feasibility of the maneuvers by humans (sailors). The optimal takeoff achieved an average VMG of 7.42 m/s. This maneuver serves as a performance benchmark for the sailors and provides insightful information about the underlying dynamics of the boat.

Design of core thermocouple adaptive plug-and-pull device

In the process of change and maintenance material of nuclear power plants, due to the uncontrollable driving force of the existing core thermocouple insertion and removal tools, it is easy to cause the thermocouple to be installed in place, the thermocouple to be easily damaged, or even to have poor sealing, and the pressure boundary of the primary circuit is incomplete and other issues. Aiming at the above problems, this paper takes FPGA as the core controller, and adopts a closed-loop control method with multiple modes of force, speed and displacement, and develops a set of automatic insertion and removal device for nuclear power plant core thermocouple. The device has the advantages of safety and reliability, high control precision, and online observation of multiple parameters.

Numerical Investigation of Enhanced Oil Recovery from various Rocks by Nanosuspensions Flooding

This work is devoted to the systematic numerical simulation of oil displacement using nanosuspension with silicon oxide particles with concentration of up to 1 wt% and particle sizes of 5 nm. The influence of such factors as core wettability, concentration of nanoparticles, capillary number, and oil viscosity on the enhanced oil recovery by nanosuspension has been systematically investigated using the VOF method for 2D-dimensional micromodels. Various rocks were considered: dolomite, metabasalt and sandstone. It is shown that the oil recovery coefficient improves for all considered types of rock with increasing nanoparticle concentration. The most effective application of nanosuspension for enhanced oil recovery is observed at a low capillary number, corresponding to the capillary displacement mode. The addition of nanoparticles facilitates increasing oil recovery factor in a wide range of viscosity ratios between oil and displacement fluid.

Microwave Resonance-Based Reflective Mode Displacement Sensor With Wide Dynamic Range

A wide dynamic range reflective mode displacement sensor is designed in this article based on the resonance frequency shift. The linearity of the sensor is enhanced using a tapered metallic patch that forms the capacitance of the sensor, leading to a better dynamic range. The sensor is designed using a coplanar waveguide (CPW) terminated with a series <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$RLC$ </tex-math></inline-formula> resonator with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R=50\,\,\Omega $ </tex-math></inline-formula> . A movable dielectric slab is placed above the capacitive patch of the resonator, where displacing the dielectric slab modifies the overall capacitance of the resonator causing a shift in the resonance frequency. The sensing principle is analyzed in detail, using an accurate circuit model and full-wave electromagnetic simulations. The proposed sensing method is capable of detecting the displacement direction. Furthermore, the sensing concept can be extended to a 2-D displacement sensor as well. The sensing approach and the design concept are verified through the fabrication and measurement of a sensor prototype.

Joint modelling in advanced thin-walled beam models

A methodology for thin-walled frame analysis using displacement modes of beams at joint interfaces has recently been proposed. This paper introduces an implementation that uses a specific advanced beam element based on semi-analytical beam mode solutions of a generalised beam theory. The end cross-sections of the beam elements consist of wall elements with displacement degrees of freedom that can be joined to conventional finite shell element models of the joints. However, before joining the beam element and joint model at the interface, both beam and joint model are transformed into cross-section displacement mode degrees of freedom. This transformation enables the use of a reduced mode space at the interface as well as in the beam. The quadratic nature of the beam mode equations of the beam element leads to a non-unique number of beam displacement modes. However, this paper introduces an exact mode selection technique that leads to a unique set of modes. Necessary details of the beam element formulation are included in order to make a self-contained description of the mode selection technique. Mode reduction through a length scale dependent choice of the number of exponentially decaying distortional modes is investigated and discussed for three types of joint design in four examples. The three joint design types investigated are based on in-plane membrane action, flexural out-of-plane action and a combination of both membrane and flexural action.

Estimation of earth pressure against retaining walls with different limited displacement modes based on elastic theory

Estimation of earth pressure against retaining walls with different limited displacement modes based on elastic theory

Seismic design of plane steel MRFS, EBFS and BRBFS by improved direct displacement-based design method

An improved direct displacement-based design (DDBD) method for the seismic design of three types of plane steel frames, i.e., moment-resisting frames (MRFs), steel eccentrically braced frames (EBFs), and buckling-restrained braced frames (BRBFs) is developed. The improvement lies in the fact that it uses a MDOF equivalent system instead of a SDOF one used by the original DDBD method. Thus, higher modes and P-Δ effects are considered more rationally and with higher accuracy than in the conventional method. The proposed method employs deformation-dependent equivalent modal damping ratios and design modal displacements for the first few modes significantly contributing to the response, as functions of target inter-storey drift ratios representing various performance levels. Employment of a displacement design spectrum for high amounts of damping in conjunction with the equivalent modal damping ratios and design modal displacements can provide the required modal periods, the modal stiffness values, and the modal base shear forces. The design base shear force is obtained by a modal combination rule, such as the SRSS rule, and is distributed to the stories of the frame for member dimensioning. Numerical examples illustrate the method and demonstrate its advantages over the original DDBD method.

Guided waves in a functionally graded 1-D hexagonal quasi-crystal plate with piezoelectric effect

For the purpose of design and optimization for piezoelectric quasi-crystal transducers, guided waves in a functionally graded 1-D hexagonal piezoelectric quasi-crystal plate are investigated. In this paper, a model combined with the Bak’s and elastohydrodynamic models is utilized to derive governing equations of wave motion, and real, pure imaginary, and complex roots of governing equations are calculated by using the modified Legendre polynomial method. Subsequently, dispersion curves and displacements of phonon and phason modes are illustrated. Then, guided waves in functionally graded 1-D hexagonal piezoelectric quasi-crystal plates with different quasi-periodic directions are studied. And the phonon-phason coupling effect on Lamb and SH waves are analyzed. Accordingly, some interesting results are obtained: The phonon-phason coupling just affects Lamb waves in the x- and z-direction quasi-crystal plates, and SH waves in the y-direction quasi-crystal plate. Besides, frequencies of propagative phason modes decrease as phonon-phason coupling coefficients Ri increase. Furthermore, a variation in the polarization has a more significant influence on phonon modes, and a variation in the quasi-periodic direction has a more significant influence on phason modes.

Modal Kinematic Analysis of a Parallel Kinematic Robot with Low-Stiffness Transmissions

Several industrial robotic applications that require high speed or high stiffness-to-inertia ratios use parallel kinematic robots. In the cases where the critical point of the application is the speed, the compliance of the main mechanical transmissions placed between the actuators and the parallel kinematic structure can be significantly higher than that of the parallel kinematic structure itself. This paper deals with this kind of system, where the overall performance depends on the maximum speed and on the dynamic behavior. Our research proposes a new approach for the investigation of the modes of vibration of the end-effector placed on the robot structure for a system where the transmission’s compliance is not negligible in relation to the flexibility of the parallel kinematic structure. The approach considers the kinematic and dynamic coupling due to the parallel kinematic structure, the system’s mass distribution and the transmission’s stiffness. In the literature, several papers deal with the dynamic vibration analysis of parallel robots. Some of these also consider the transmissions between the motors and the actuated joints. However, these works mainly deal with the modal analysis of the robot’s mechanical structure or the displacement analysis of the transmission’s effects on the positioning error of the end-effector. The discussion of the proposed approach takes into consideration a linear delta robot. The results show that the system’s natural frequencies and the directions of the end-effector’s modal displacements strongly depend on its position in the working space.

Experimental Study on the Behavior of Steel–Concrete Composite Decks with Different Shear Span-to-Depth Ratios

This paper presents the results of an experimental study on the mechanical behaviors of steel‒concrete composite decks with different shear span-to-depth ratios. Herein, four composite decks categorized into two types with shear span-to-depth ratios of 2.5 and 4.6 are designed for an experimental program. The decks then undergo the four-point bending tests until failure to investigate the structural responses, such as the load, displacement, crack mechanism, and failure mode. Conventional section analysis is used to derive the flexural strength of composite decks in comparison with the test results. Additionally, the ductility of the composite decks is assessed based on the displacement indices. The analysis results demonstrate that the stiffness and capacity of the composite deck increase with the decrease in the shear span length. However, the ductility of the composite slabs increases with the shear span length. The flexural strengths predicted by section analysis overestimate the actual test results. The shear span-to-depth ratio affects the crack mechanism of the composite decks.

Theoretical and experimental investigation of MWCNT dispersion effect on the elastic modulus of flexible PDMS/MWCNT nanocomposites

Abstract In this article, Young’s modulus of a flexible piezoresistive nanocomposite made of a certain amount of multiwalled carbon nanotube (MWCNT) contents dispersed in polydimethylsiloxane (PDMS) has been investigated using theoretical and experimental approaches. The PDMS/MWCNT nanocomposites with the governing factor of MWCNT weight fraction (e.g., 0.1, 0.25, and 0.5 wt%) were synthesized by the solution casting fabrication method. The nanocomposite samples were subjected to a standard compression test to measure their elastic modulus using Instron Universal testing machine under force control displacement mode. Due to the costs and limitations of experimental tests, theoretical predictions on the elasticity modulus of such flexible nanocomposites have also been performed using Eshelby–Mori–Tanaka (EMT) and Halpin–Tsai (HT) approaches. The theoretical results showed that HT’s approach at lower MWCNT contents and EMT’s approach at higher MWCNT contents have a better agreement to experimental results in predicting the elastic modulus of PDMS/MWCNT nanocomposites. The experimental results indicated that the inclusion of MWCNT in the PDMS matrix resulted in a noticeable improvement in Young’s modulus of PDMS/MWCNT nanocomposite at small values of MWCNT contents (up to w f = 0.25%); however, exceeding this nanofiller content did not elevate Young’s modulus due to the emergence of MWCNT agglomerations in the nanocomposite structure.

Water Hammer and Harmonic Excitation Response With Fluid-Structure Interaction in Elbow Piping

Abstract This study focuses on the numerical analysis of a piping structure subjected to the water-hammer event caused by a rapid valve closure that is combined with external harmonic loading representing an idealized machine excitation. The fluid–structure interaction procedure applied to solutions involves the method of characteristic for the fluid equations with the finite element method for pipe structures, which are modeled as beams. Junction coupling at the pipe elbow governs the two-way coupled fluid–structure interaction, and both the friction and Poisson couplings are incorporated as well. There is an application on a piping structure that consists of a valve, tank, and elbow that are defined as boundary conditions. The solved result quantities include pressure and bending stress responses as well as dynamic displacement modes of the piping structure. Comparisons of the results show that water hammer loading combined with the mechanical excitation load induces significantly increased displacements and higher stress peaks when frequencies of the harmonic load and the acoustic natural mode of the piping system coincide. Additionally, the resulting mode of lateral structural vibration of the piping member closely resembles an analytically solved eigenmode of the beam. The conclusion is that dynamically changing flows due to a water hammer event can solely excite natural frequencies of the piping structure causing resonance in the system.

Deformation mechanisms of sidewall in layered rock strata dipping steeply against the inner space of large underground powerhouse cavern

In low to moderate stress regions, deformations of the high sidewall dominated by bedding planes dipping against the cavern space, often pose an unpredictable threat to local stability of underground powerhouse. In this study, detailed field surveys, in-situ tests, beam theory, and the discrete element method (DEM) are used to critically investigate the deformation mechanisms of high sidewall in layered rock strata steeply inclined against the inner space of the underground powerhouse cavern. First, an approach integrating in-situ surveys, deformation monitoring and acoustic wave tests, is adopted to analyse the evolutionary features of displacements of a high sidewall in layered strata steeply dipping against cavern space. Differences of deformation behaviours and their relationships with excavating activities in low to moderate and high geo-stress regions, were distinguished. Second, two zones with different deformation mechanisms in layered strata involved are presented, which could be evidenced by the presence of various displacement modes near the top area of a high sidewall. Then, based on the conceptual beam models, mechanisms of displacements controlled by bedding planes in two zones are investigated. Synergistic effects arising from two zones promoting the overall deformation profile are presented. Third, combining with DEM simulations, the mechanical influences of bedding thickness on the excessive deformation modes near the top of sidewall, are revealed. Displacements of a sidewall partly affected by an intersecting chamber are described in detail. Finally, suggestions for applicable supports of the high sidewall with bedding planes dipping steeply toward the internal area of surrounding rocks during cavern excavation are presented. The aforementioned investigations can provide valuable guidelines for the construction of similar underground powerhouse caverns.

A numerical method to determine the displacement spectrum of micro-plates in viscous fluids

In this paper, we present a semi-numerical method for determining the dynamics of micro-resonators with finite width immersed in incompressible viscous fluids. The micro-resonator is modeled using Kirchhoff plate theory, and the hydrodynamic force acting on the plate is determined from a boundary integral formulation of the Stokes equations. The resulting equation of motion is solved with a continuous/discontinuous finite element method in which an interior penalty term imposes C1-continuity to the plate’s deflection. Numerical investigations show the method to be convergent with an exponent of the convergence rate equals 2. Examples demonstrate that the proposed method overcomes the limitations of existing semi-analytic methods, only applicable to beam geometries, considering arbitrary plate modes in the structure’s dynamics and their effects on the fluid flow. Different resonator geometries are investigated for which displacement spectrum, mode shapes, and quality factors are not determinable with existent semi-analytic methods. Moreover, we find excellent agreement between simulated and experimental data, which has not been achieved even with purely numerical methods. The present method will allow the understanding of high quality factors of wide micro-resonators in viscous fluids and facilitate new applications in liquid atomic force microscopy and gas sensing in ambient and low-pressure conditions.

Nanoobject mass measurement using the node displacement of the second mode of the nanomechanical resonator

This work suggests a new approach to weighting the nanoscale objects placed at the tip of cantilever vibrating inside the camera of scanning electron microscope. In contrast to traditional approach to mass determination, we suggest tracing the shift of the node of the second vibration mode as an alternative to frequency shift measurement. We demonstrate the applicability of our approach to carbon nanowhisker cantilevers grown on tungsten needles by focused electron beam induced deposition. We compare experimentally the performance of the suggested approach with the traditional frequency shift-based method.

Carcerality and the legacies of settler colonial punishment in Nairobi

From the beginning of its colonial settlement in Kenya, the British administration criminalized Kenyans. Even now, colonial modes of punishment, incarceration, closure, interrogation, curfew, confiscation, separation, displacement, and detention without trial are deeply embedded in the spatial and ideological arrangements of post-colonial Kenya. Initially assumed to herald a rupture from colonial modes of criminalization and punishment, the post-colonial period instead normalized them. Through ethnographic, scholarly, and visual encounters, the paper engages five interconnecting structures that engendered the legacy of a seamless system of control, containment, and punishment evident in the ‘afterlives’ of empire. These are settler colonialism, violence, racism, colonial corporeality, and capitalism. The paper attends to the violence and brutality that endures in the very geographies that were the urban targets of colonial siege and links the carceral practices of settler colonialism and the everyday post-colonial governance of Nairobi’s poor neighbourhoods, encounters with the debris and ruination of empire found in the material and spatial fabric of Mathare. We take up a critical encounter with colonial files to both discern the continuity and lineage of carceral practices and to disrupt the authorial totality and continuity the colonial archive files assembled. The paper includes archival and authored photographs:

Two-wave laser displacement meter

A two-wave laser displacement meter based on Michelson interferometer has been developed for measurements at an unknown temperature profile at the measurement trace. The requirements for meteorological parameters support during displacement measurements using the offered laser interferometer are less strict compared to using an one-wave interferometer. The article describes the optical schematic of the device. The results for the measurements of the developed laser interferometer for realization of the displacement unit within the limits of 60 m are presented. The weather condition influence on measurements was estimated. The application of pseudorandom displacement of the interferometer’s reference arm with accumulation made possible the reflector position resolution down to 0.01 μm the stoped-displacement mode, and down to 0.05 μm at the displacement mode. It was shown that such resolution allows to measure displacements at trace up to 60 m with inaccuracies less than 10 μm at the temperature profile amplitude up to 1 °C.

Wettability effect on the invasion patterns during immiscible displacement in heterogeneous porous media under dynamic conditions: A numerical study

This paper investigates the wettability effect on the characteristics of two-phase immiscible flows in porous media at different capillary numbers. This issue presents both applied results useful to engineering disciplines and explores the fundamentals of displacement mechanisms, especially in the mode of compact displacement. The main findings of this study are based on numerical flow simulations in a digital model of heterogeneous porous structure, for which the lattice Boltzmann equations are used in combination with the multi-relaxation time and color-gradient models. This work is one of the few which studies the wettability effect in porous structures with a random arrangement of particles. The influence of the contact angle and the capillary number is presented in the form of images of the fluid distribution at various contact angles and capillary numbers, which were associated with the phase-diagrams for displacement efficiency and fractal dimension, as well as fluid-fluid interfacial length and finger width. It was found that increasing capillary number suppresses the wettability effect on displacement characteristics. This article first identifies four crossover zones between capillary and viscous fingering and compact displacement. It was shown that the critical contact angle, which determines the appearance of compact displacement, increases with the capillary number. Particular attention is paid to the displacement mechanisms for compact displacement. Analysis of the pressure signature at various contact angles and capillary numbers clarifies the role of touches and overlaps that stabilize interfacial front during compact displacement and determines the real driving force for this invasion pattern. This article is the first to establish a relationship between pore-filling events and fluctuations in the pressure signature during compact displacement. It was found that an increase in the pressure signature is characterized by a uniform displacement of all menisci along with the entire fluid-fluid interface, while invasion with a sharp decrease in pressure is determined by the burst-like displacement of a concave meniscus in narrowly localized areas of the pore space.