Terms Of Forces Research Articles

Effect of amplitudes and frequencies on Virtual Planar Motion Mechanism of AUVs, Part I: Forces, moments and hydrodynamic derivatives

Planar motion mechanism tests have been widely used in the virtual form for ocean craft, especially for underwater vehicles. These tests involve a pre-determined sinusoidal trajectory for the AUV. While there are general guidelines for the choice of amplitude and frequency for such trajectories in existing literature, there are minimal to none for smaller submerged ocean craft such as autonomous underwater vehicles. This series of articles analyzes VPMM from the perspective of AUVs and the significance of variation in these parameters. The results in Part I of this series are discussed in terms of forces and moments reconstructed using hydrodynamic derivatives obtained through RANSE. This includes variation in forces and moments, and the possible non-linear effects that cause such variation. The resultant hydrodynamic damping derivatives show upto 50% variation based on parameters that signify pure sway and pure yaw simulations. The resultant added mass derivatives do not vary much among the various VPMM simulations attempted (<2%). The inflow angle to the craft is found to be significant in characterizing pure sway simulations.The results in Part II are discussed in terms of implemented dynamic maneuvers through RANSE and in field.

Label free and high-throughput discrimination of cells at a bipolar electrode array using the AC electrodynamics

BackgroundCell characterization and manipulation play an important role in biological and medical applications. Cell viability evaluation is of significant importance for cell toxicology assay, dose test of anticancer drugs, and other biochemical stimulations. The electrical properties of cells change when cells transform from healthy to a pathological state. Current methods for evaluating cell viability usually requires a complicated chip and the throughput is limited. ResultsIn this paper, a bipolar electrode (BPE) array based microfluidic device for assessing cell viability is exploited using AC electrodynamics. The viability of various cells including yeast cells and K562 cells, can be evaluated by analyzing the electro-rotation (ROT) speed and direction of cells, as well as the dielectrophoresis (DEP) responses of cells. Firstly, the cell viability can be identified by the position of the cell captured on the BPE electrode in terms of DEP force. Besides, cell viability can also be evaluated based on both the cell rotation speed and direction using ROT. Under the action of travelling wave dielectric electrophoresis force, the cell viability can also be distinguished by the rotational motion of cells on bipolar electrode edges. SignificanceThis study demonstrates the utility of BPEs to enable scalable and high-throughput AC electrodynamics platforms by imparting a flexibility in chip design that is unparalleled by using traditional electrodes. By using BPEs, our proposed new technique owns wide application for cell characterization and viability assessment in situ detection and analysis.

Review of Wind-Induced Effects Estimation through Nonlinear Analysis of Tall Buildings, High-Rise Structures, Flexible Bridges and Transmission Lines

The nonlinear effects exhibited by structures under the action of wind loads have gradually stepped into the vision of wind-resistant researchers. By summarizing the prominent wind-induced nonlinear problems of four types of wind-sensitive structures, namely tall buildings, high-rise structures, flexible bridges, and transmission lines, the occurrence mechanism of their nonlinear effects is revealed, providing cutting-edge research progress in theoretical studies, experimental methods and vibration control. Aerodynamic admittance provides insights into the aerodynamic nonlinearity (AN) between the wind pressure spectrum and wind speed spectrum of tall building surfaces. The equivalent nonlinear equation method is used to solve nonlinear vibration equations with generalized van-der-Pol-type aerodynamic damping terms. The elastic–plastic finite element method and multiscale modeling method are widely employed to analyze the effects of geometric nonlinearity (GN) and material nonlinearity (MN) at local nodes on the wind-induced response of latticed tall structures. The AN in blunt sections of bridges arises from the amplitude dependence of the aerodynamic derivative and the higher-order term of the self-excited force. Volterra series aerodynamic models are more suitable for the nonlinear aerodynamic modeling of bridges than the polynomial models studied more in the past. The improved Lindstedt–Poincare perturbation method, which considers the strong GN in the response of ice-covered transmission lines, offers high accuracy. The complex numerical calculations and nonlinear analyses involved in wind-induced nonlinear effects continue to consume significant computational resources and time, especially for complex wind field conditions and flexible and variable structural forms. It is necessary to further develop analytical, modeling and identification tools to facilitate the modeling of nonlinear features in the future.

NEMOH: Open-source boundary element solver for computation of first- and second-order hydrodynamic loads in the frequency domain

NEMOH is developed to solve potential flow problems using the boundary element method for computing wave loads on offshore structures. The solver solves the first-order problem in the frequency domain. An extended module enables computation of the second-order loads on a structure in bi-chromatic bi-directional waves. NEMOH is released as open-source, developed, and distributed under the terms of GNU General Public License (GPLv3). Along with the source code, a user manual is available which facilitates the compilation and execution of the source files. In this new release, NEMOH v3.0 has new features; irregular frequencies removal method, new linear system solvers for enhancing computational efficiency, and a new module for computing the full quadratic transfer function (QTF) of drift forces. Verification cases are shown for a truncated cylinder, a truncated cylinder with a thin heave plate, a spar buoy platform (SOFTWIND), and a semi-submersible platform (OC4). The results are compared with reference data from commercial software, WAMIT, DIODORE, and HYDROSTAR, and the comparison showed that NEMOH v3.0 is accurate and efficient. Program summaryProgram Title: NEMOHCPC Library link to program files:https://doi.org/10.17632/k9v4hjb5xj.1Developer's repository link:https://gitlab.com/lheea/NemohCode Ocean capsule:https://codeocean.com/capsule/9256007Licensing provisions: GPLv3Programming language: FortranExternal libraries and programs: BLAS [1], LAPACK [2]Nature of problem: NEMOH solves the potential flow problems of diffraction and radiation in wave-structure interactions. Typical use is the estimation of the dynamic response of floating structures, e.g. floating offshore wind turbine platforms, or wave-energy converters.Solution method: The linear potential flow problems, diffraction and radiation, are expressed in the boundary integral of the source distribution formulation. The equations are solved in the frequency domain and implemented using the boundary element method with quadrilateral panels. The source distribution on the body panels is obtained by solving the linear system. The hydrodynamic coefficients are computed with the known source distribution. The second-order potential flow problem is not solved directly; the Green formulation is used with an assisting function which is the instantaneous radiation potential, that allows the computation of second-order force for given first-order hydrodynamic quantities.Additional comments including restrictions and unusual features:•The previous version, NEMOH v2.0 [3], was available only for computing first-order hydrodynamic coefficients without the irregular frequency removal method. NEMOH v3.0 has new features, the extended boundary integral method is implemented for removing the irregular frequencies, new linear system solvers are added for enhancing computational efficiency, and a new module is added for computing second-order wave loads. NEMOH v3.0 has better accuracy than v2.0 due to finer interpolation points of the free-surface Green function and a better integration method for constructing the influence coefficients.•For the free-surface piercing bodies problem, it is known that non-unique solutions exist in the boundary integral equation at certain frequencies. In NEMOH, the extended boundary integral equation is applied to remove the irregular frequencies by providing the lid panels on the body waterplane. The second-order loads require the computation of the free-surface forcing terms in the integral forms. These free-surface integrals are essential for the sum-frequency wave loads but may be negligible in the difference-frequency loads. For now, it is suggested not to apply the lid panels when the free-surface integrals are computed.

Application of immersed boundary methods to non-Newtonian yield-pseudoplastic flows

The interaction force between fluid and particles in particulate flows is highly dependent on the rheology of fluid. In some engineering applications, like mineral processing, the rheological behaviour of the carrier fluid is characterized by a yield-pseudoplastic non-Newtonian model. The immersed boundary method (IBM) is a numerical strategy to simulate the interaction between phases in the particulate systems using a Cartesian fixed grid. It imposes the solid boundary condition in the computational domain through a modification (e.g. a forcing term) in the governing equations. However, there is still little study in the literature discussing the applicability of different IBMs to yield-pseudoplastic flows. In this paper, the numerical methodology in several versions of immersed boundary methods, including the Volume Penalization IBM (VP-IBM), Indirect Imposition of Discrete Forcing IBM (ID-IBM), and Direct Imposition of Discrete Forcing (DD-IBM), is described. The numerical implementation of the methods is first validated using Newtonian benchmark cases. Then the solvers are utilized for the simulation of yield-pseudoplastic cases with stationary or moving particles. The investigation shows that in the explicit forcing methods, like VP-IBM and ID-IBM, the forcing procedure is conducted using an intermediate solution over the entire computational domain. The dependence of viscosity to strain rate in non-Newtonian cases leads to an inevitable sharp change in viscosity near the solid surface, giving rise to stiffness of the intermediate solution in the interface region. This makes the explicit forcing approaches based on intermediate solution incompatible with the flows with non-Newtonian yield-pseudoplastic rheology. On the other hand, the implicit forcing used in DD-IBM directly implements the boundary conditions on the boundary cells, making this method free from the perturbations related to the highly viscous solid region. In this regard, the simulation with the Direct Imposition IBMs like ghost-cell shows a good agreement between the predicted results and the experimental measurements for the stationary/moving cases. Therefore, it is shown that the DD-IBM is a reliable approach to modelling non-Newtonian flows.

Seismic performance of buffer-equipped anchored piles considering end restraints

During seismic events, slopes buttressed by anchored piles can experience instability when piles convert to perilous cantilever systems upon anchor cables failure. Implementing buffer devices in anchoring structures has the potential to reduce the seismic forces in the anchors and consequently improve the seismic performance of the supported structures. Taking advantage of the excellent ductility of flexible piles, this study investigates a buffer device installed in series with the anchored piles. Shaking table tests were conducted on a slope stabilized by buffer-equipped anchored piles considering two typical pile tip conditions: either hinged or free end restraints. Three ground motions with different characteristics were applied to the model slopes fitted with springs with varying stiffness and its seismic response was evaluated in terms of soil accelerations, pile displacements, earth pressures, and anchor-cable forces. In addition, the cable loading reduction mechanism was investigated through the force Fourier spectrum. The results indicated that the system dominant frequency decreased for anchor with hinge support and the pile displacement increased and the dynamic earth pressure decreased as the spring stiffness decreased. Most importantly, implementing the buffer device (i.e., the spring) reduced the response energy significantly over the whole frequency range, especially in the middle range, which resulted in a marked reduction in the anchor cable stress and fatigue damage. The reduction of anchor force was found to be inversely correlated with the spring stiffness. Based on the maximum pile displacement and spring stroke, a stiffness optimization strategy was proposed considering the foundation conditions and seismic excitations. For major earthquakes, stiff springs are advisable to mitigate load effects and to help maintain pile displacement within permissible bounds, while the spring stiffness can be reduced appropriately by implementing a hinge support. Meanwhile, the design should focus on critical displacement rather than loading reduction for seismic hazard characterized by near field earthquakes or high peak ground acceleration.

The Regional Aerosol Model Intercomparison Project (RAMIP)

Abstract. Changes in anthropogenic aerosol emissions have strongly contributed to global and regional trends in temperature, precipitation, and other climate characteristics and have been one of the dominant drivers of decadal trends in Asian and African precipitation. These and other influences on regional climate from changes in aerosol emissions are expected to continue and potentially strengthen in the coming decades. However, a combination of large uncertainties in emission pathways, radiative forcing, and the dynamical response to forcing makes anthropogenic aerosol a key factor in the spread of near-term climate projections, particularly on regional scales, and therefore an important one to constrain. For example, in terms of future emission pathways, the uncertainty in future global aerosol and precursor gas emissions by 2050 is as large as the total increase in emissions since 1850. In terms of aerosol effective radiative forcing, which remains the largest source of uncertainty in future climate change projections, CMIP6 models span a factor of 5, from −0.3 to −1.5 W m−2. Both of these sources of uncertainty are exacerbated on regional scales. The Regional Aerosol Model Intercomparison Project (RAMIP) will deliver experiments designed to quantify the role of regional aerosol emissions changes in near-term projections. This is unlike any prior MIP, where the focus has been on changes in global emissions and/or very idealised aerosol experiments. Perturbing regional emissions makes RAMIP novel from a scientific standpoint and links the intended analyses more directly to mitigation and adaptation policy issues. From a science perspective, there is limited information on how realistic regional aerosol emissions impact local as well as remote climate conditions. Here, RAMIP will enable an evaluation of the full range of potential influences of realistic and regionally varied aerosol emission changes on near-future climate. From the policy perspective, RAMIP addresses the burning question of how local and remote decisions affecting emissions of aerosols influence climate change in any given region. Here, RAMIP will provide the information needed to make direct links between regional climate policies and regional climate change. RAMIP experiments are designed to explore sensitivities to aerosol type and location and provide improved constraints on uncertainties driven by aerosol radiative forcing and the dynamical response to aerosol changes. The core experiments will assess the effects of differences in future global and regional (Africa and the Middle East, East Asia, North America and Europe, and South Asia) aerosol emission trajectories through 2051, while optional experiments will test the nonlinear effects of varying emission locations and aerosol types along this future trajectory. All experiments are based on the shared socioeconomic pathways and are intended to be performed with 6th Climate Model Intercomparison Project (CMIP6) generation models, initialised from the CMIP6 historical experiments, to facilitate comparisons with existing projections. Requested outputs will enable the analysis of the role of aerosol in near-future changes in, for example, temperature and precipitation means and extremes, storms, and air quality.

Optimization of a coupled launching process considering hydrodynamic interaction effects

Crane-assisted launching and recovering of small boats from a large vessel is common in a wide range of operational scenarios and may be required during research missions or in emergency situations for rescue boats. As the mothership moves in natural irregular seas, the resulting accelerations and motions of the small boat can lead to dangerous situations, such as a collision between the mothership and the small boat or a slamming of the small boat onto the free water surface can occur, posing a great danger to the people involved. In the paper, the development of a coupled simulation method for the motions of the mothership and the small boat during the launching in the time-domain is described. The developed simulation method is based on the impulse response function. The implementation of the suspension on a crane is realised by a holonomic constraint and a Lagrange’s equation. The parameter influencing the launching operation include the current sea state, the stationary wave field induced by the motherships forward speed, at which the small boat is launched and the initial position of the small boat relative to the water surface. By varying the above mentioned parameters, the process can be optimised for different sea states in terms of forces and accelerations. In considering the forward speed of the mother boat during the launching process, it can be observed that in many cases the small boat is operated at high Froude numbers of greater than 0.4. This leads to an exceedance of the operational limits of the programmes used in this paper.

The Krylov–Bogoliubov–Mitropolsky method for modeling a forced damped quadratic pendulum oscillator

In the present investigation, a quadratically forced damped pendulum-type equation is solved analytically using several effective and highly accurate approaches. Some different types of pendulum oscillators linked to the forced and damped terms, in addition to the power of the damping term, are analyzed. In the first part, the Krylov–Bogoliubov–Mitropolsky (KBM) technique and the ansatz method are carried out for analyzing the quadratically damped pendulum oscillator. In the second part, the two variants of the KBM technique are implemented for investigating the quadratically forced damped pendulum oscillator. Some symmetric approximations are derived and compared with the fourth-order Runge–Kutta numerical approximation. In addition, the maximum distance error is estimated in the whole study domain for ensuring that all obtained approximations are accurate. The obtained results are illustrated through concrete examples.

A Study of Chan-Vese Model with the Introduction of Edge Information

In image segmentation, the image edge information and the selection of edge-stopping function have a extremely important influence on the segmentation effect. As a classical geometric active contour model, Chan-Vese model completely utilizes image global information for segmentation, which has the problems of inability to handle grayscale uneven images and slow curve evolution. This paper introduces edge information into the Chan-Vese model, chooses a new edge stopping function and simplifies the driving force term to build a new image segmentation model. The new model can detect the target fast, displaying better detection effect on the targets of images with uneven grayscale and the detection effect of the target in the uneven gray image is better

An investigation of the transient electrophoresis of conducting colloidal particles in porous media using a cell model

A comprehensive analytical study of the electrophoresis of a suspension of charged spherical particles in an arbitrary electrolyte solution through a porous medium is analyzed using a unit cell model. The unsteady Brinkman equation with the term of the electric force governing the fluid velocity fields is solved by means of the Laplace transform. The porous medium is uniformly charged by fixed charge density Q, and the embedded spherical particle is conductive and charged with constant zeta potential. Two different accurate concepts of the boundary conditions at the outer virtual surface, are presented to solve the governing equations for the flow field. Steady-state electrophoretic velocity is obtained analytically and displayed graphically for different physical parameters. Also, a closed form of the transient electrophoretic velocity versus the dimensionless elapsed time is plotted and discussed for different values of the Debye length parameter, particle volume fraction, density ratio, permeability of the porous medium, and for highly- and non-conducting particles. The steady/ transient electrophoretic velocity is a monotonic decreasing function of the permeability parameter, the particle-to-fluid density ratio, and the particle volume fraction, but it increases with an increase in the Debye length parameter with constant zeta potential. In general, the Kuwabara cell model predicts a smaller value for the electrophoresis velocity than the Happel model, but the difference is not significant. On the other hand, when the transient velocity is normalized by its steady state, the Happel model has smaller values than the Kuwabara model. The effects of the relevant parameters on the transient starting electrokinetic flow in the porous medium are interesting and significant. The results are found to be in excellent agreement with the exact numerical results obtained by Lai and Keh.

A discrete Boltzmann model with symmetric velocity discretization for compressible flow

A discrete Boltzmann model (DBM) with symmetric velocity discretization is constructed for compressible systems with an adjustable specific heat ratio in the external force field. The proposed two-dimensional (2D) nine-velocity scheme has better spatial symmetry and numerical accuracy than the discretized velocity model in literature [Acta Aerodyn. Sin. 40 98108 (2022)] and owns higher computational efficiency than the one in literature [Phys. Rev. E 99 012142 (2019)]. In addition, the matrix inversion method is adopted to calculate the discrete equilibrium distribution function and force term, both of which satisfy nine independent kinetic moment relations. Moreover, the DBM could be used to study a few thermodynamic nonequilibrium effects beyond the Euler equations that are recovered from the kinetic model in the hydrodynamic limit via the Chapman–Enskog expansion. Finally, the present method is verified through typical numerical simulations, including the free-falling process, Sod’s shock tube, sound wave, compressible Rayleigh–Taylor instability, and translational motion of a 2D fluid system.

High-order modeling of multiphase flows: Based on discrete Boltzmann method

The high-order kinetic model for compressible multiphase flow is presented within the framework of the discrete Boltzmann method (DBM). Based on the Carnahan–Starling state equation, this model can describe the phase transition by introducing a source term of molecular interaction on the right-hand side of the Boltzmann equation. Meanwhile, the force term is incorporated to describe the external force. Through Hermite polynomial expansion, the equilibrium distribution function is expressed. Compared to the Navier–Stokes equations, the DBM provides more detailed and accurate information on both hydrodynamic and thermodynamic non-equilibrium effects. Finally, the model is verified through several typical benchmarks, including the liquid–vapor coexistence curve, free-falling process, shock wave, sound wave, thermal phase separation, and two-bubble oblique collision.

Influence of seabed profile on the seismic response of monopile-supported offshore wind turbines including dynamic soil-structure interaction

In this article, the seismic response of four different Offshore Wind Turbines (OWTs) from 5 to 15 MW, founded on monopiles embedded in homogeneous and non-homogeneous soil profiles with equivalent shear-wave velocities from 100 to 300 m/s is analysed. Two types of variable soil profiles with a semi-parabolic variation of the shear-wave velocity as depth increases are considered. The system seismic response under ten different accelerograms is computed through a finite element substructuring model in frequency domain. The foundation behaviour is obtained by a continuum model including kinematic and inertial interaction. Several models, in addition to that of rigid base condition, are considered to determine the influence of soil-structure interaction (SSI), as well as the contribution of each kinematic interaction (KI) factor. The seismic response of the OWTs is obtained in terms of maximum shear forces and bending moments at mudline level, as well as the acceleration amplification factor at hub level. It is found that the maximum response is produced when SSI is considered, including both the inertial and kinematic interaction. The differences arising due to the soil profile definition are shown to be mainly related to the rotational KI factor, which significantly affects the second vibration mode of the system. The largest responses are obtained for the homogeneous equivalent profile.

Performance of CFST members internally strengthened with I-shaped CFRP under impact load

This study presents experimental and numerical research on the dynamic behaviors and resistances of square concrete-filled steel tubular members internally strengthened by I-shaped CFRP profile (SCFST-CFRP) with fixed boundary conditions subjected to lateral impact loads. Dynamic impact tests were conducted on five SCFST-CFRP specimens and a traditional concrete-filled steel tubular (SCFST) specimen, examining their dynamic responses with respect to deformation modes, impact force, displacement, and strain distribution at different levels of impact energies and impact momentums. The test results indicated that the deformation of the specimens was concentrated in the impact region, approximately 0.38 L above the base, due to the transient localized characteristics of the lateral impact load. In terms of displacement and impact force, the SCFST-CFRP member exhibited better impact resistance compared to the SCFST member. Finite element models of the SCFST-CFRP members were created using LS-DYNA and validated against the impact tests. These validated models were then utilized to explore the damage patterns, dynamic bending moment, and load transfer mechanism of the SCFST-CFRP member under lateral impact loading. Additionally, a parametric study was conducted to evaluate the effects of load and structural parameters, including CFRP profile, impact energy, and impact momentum, on the impact resistance and dynamic flexural capacity of the SCFST-CFRP member. The results demonstrate that the enhancement in impact resistance caused by the inner CFRP profile was more significant under higher impact energy. Based on the parametric analysis results, empirical equations were proposed to predict the dynamic flexural capacity of lateral impact-loaded SCFST-CFRP members.

Glass Fiber Reinforced Acrylonitrile Butadiene Styrene Composite Gears by FDM 3D Printing

Abstract3D printing of gears via fused deposition modeling (FDM) has been recently introduced as a low‐cost efficient manufacturing method. Different materials have been 3D printed and Acrylonitrile Butadiene Styrene (ABS) with excellent mechanical properties has been found to be promising. However, 3D printed ABS gears possess a high level of abrasion rate. This paper introduces a new class of ABS‐based gears reinforced by different amounts of milled E‐glass fibers and 3D printed by FDM with acceptable thermo‐mechanical properties and performance. A set of thermo‐mechanical tests is carried out to provide an insight into the influence of adding glass fibers on the glass transition temperature (Tg), hardness and teeth bending strength, teeth failure force, weight lost, abrasion resistance, mechanical wear, and performance of composite gears. The mechanical behaviors of driving and driven gears are examined in high and room temperatures with or without lubrication. Microstructure and gear profile analysis of 3D printed layers, worn surfaces, and fracture locations are also conducted by SEM images and profile projector. The newly developed glass fiber reinforced ABS gears reveal a high level of thermo‐mechanical performance in terms of hardness, mechanical strength, bending force, abrasion and wear resistance compared to pure 3D printed ABS gears.

Unexpected low CO2 emission from highly disturbed urban inland waters

Constituents and functionality of urban inland waters are significantly perturbed by municipal sewage inputs and tailwater discharge from wastewater treatment plants. However, large knowledge gaps persist in understanding greenhouse gas dynamics in urban inland waters due to a lack of in situ measurements. Herein, via a 3-year field campaign (2018–2020), we report river and lake CO2 emission and related aquatic factors regulating the emission in the municipality of Beijing. Mean pCO2 (546 ± 481 μatm) in the two urban lakes was lower than global non-tropical freshwater lakes and CO2 flux in 47% of the lake observations was negative. Though average pCO2 in urban rivers (3124 ± 3846 μatm) was among the higher range of global rivers (1300–4300 μatm), average CO2 flux was much lower than the global river average (99.7 ± 147.5 versus 358.4 mmol m−2 d−1). The high pCO2 cannot release to the atmosphere due to the low gas exchange rate in urban rivers (average k600 of 1.3 ± 1.3 m d−1), resulting in low CO2 flux in urban rivers. Additionally, eutrophication promotes photosynthetic uptake and aquatic organic substrate production, leading to no clear relationships observed between pCO2 and phytoplankton photosynthesis or dissolved organic carbon. In consistence with the findings, CO2 emission accounted for only 32% of the total greenhouse gas (GHG) emission equivalence (CO2, CH4 and N2O) in Beijing waters, in contrast to a major role of anthropogenic CO2 to anthropogenic GHG in the atmosphere in terms of radiative forcing (66%). These results pointed to unique GHG emission profiles and the need for a special account of urban inland waters in terms of aquatic GHG emissions.

Comparative Analysis of Soft Pneumatic Actuator Designs for Effective Human Finger Movement: A Study on Continuous and Non-Continuous Chamber Configurations

Soft actuators show immense potential in various fields, such as wearable medical devices and the rehabilitation of stroke patients. This study aims to design and fabricate a soft pneumatic actuator (SPA) that effectively mimics human finger movements, with specific focus on post-stroke rehabilitation. Two SPA designs, referred to as M1 and M2, were developed and compared. M1 featured segmented chambers to mimic finger joints, while M2 had continuous chambers. The performance of the SPAs was evaluated based on curvature, generated force, and similarity to natural finger movement. Results showed that M1 exhibited superior curvature and achieved greater bending angles compared to M2 at the same pressure levels. This makes M1 well-suited for applications requiring high bending angles such as gripping. Additionally, M2 demonstrated the ability to mimic specific angles associated with picking-like movements. The findings highlight the potential for further research to explore the customization of SPAs for specialized tasks by modifying the number of sections and chambers. In terms of force, M2 generated slightly higher forces than M1, although the difference was not statistically significant. Overall, it is expected that this research contributes to the development of soft actuators and wearable medical devices, particularly in the field of post-stroke rehabilitation.

Whether contact time can evaluate the anti-icing properties of superhydrophobic surface - A research based on the MDPDE method

Impact freezing of droplets on a cold surface has attracted the attention of scholars. This process is vital for practical problems such as the anti-icing of aircraft wings and cables. Researchers have found that superhydrophobic surfaces can reduce the contact time of droplets and delay nucleation. However, whether contact time can evaluate the anti-icing properties of superhydrophobic surface needs further study. Considering the change in droplet temperature, we vary the dissipative force term of the conservative force in the many-body dissipative particle dynamics with the energy conservation (MDPDE) method. Then combined with the experimental results, a nucleation model of the recalescence rate related to the degree of undercooling is achieved. Finally, we obtain a droplet impact freezing model based on the MDPDE method for the first time, and the impact processes of supercooled droplets on the superhydrophobic surface with three different topological microstructures are explored. Effect of Weber number We on the critical adhesion temperature T* of micropillar surface is reversed when the solid fraction φ is different, and φ is the main factor affecting T*of the microcavity surface. When other conditions are the same, T* of the microridge surface is the lowest. And surprisingly, we observed that the contact time of droplets did not fully measure the anti-icing ability of the superhydrophobic surface.

Mechanics of superelastic tensegrity braces for timber frames equipped with buckling-restrained devices

This work studies tensegrity bracing systems to be used as energy dissipation devices in next generation, earthquake-proof timber buildings. The examined lightweight and high-strength structures with re-centering capabilities are formed by timber members and pretensioned elements with a superelastic response, which may consist of shape memory alloy wires, cables or bars with energy dissipation capacity. In the case of bars, we assume that such members can be protected against buckling through their encasement in buckling-restrained devices, so as to respond both in tension and in compression. The work on the analyzed bracing systems presents novel results on this type of bi-directional response and the effects derived from the pretension of the superelastic elements, within an analytic formulation of the mechanical response of the structure. It includes an example dealing with a full-scale glued laminated timber frame, which compares the responses of different bracing systems in terms of the lateral force vs. drift ratio curve and ductility factor. The beneficial effects deriving from the use of buckling-restrained devices in an inverted V-braced timber frame are discussed. The presented results highlight the high potential of superelastic braces with tensegrity architecture for the design of timber frames exhibiting markedly high ductility ratios, which considerably surpass those of full-timber or timber-steel systems.