Study Of Scale Effects Research Articles

Comparative Study of Mechanical Scaling Effects of Origami-Inspired Motion Generation Mechanisms with Multi-Degree Vertices

Origami exhibits the remarkable ability to transform into diverse shapes, including quadrilaterals, triangles, and more complex polygons. This unique property has inspired the integration of origami principles into engineering design, particularly in the development of foldable mechanisms. In the field of robotics, when combined with actuators, these foldable mechanisms are referred to as active origami. Origami-based mechanisms play a pivotal role as versatile end effectors or grippers, enabling them to accurately trace desired trajectories. The performance of these mechanisms heavily relies on their specific fold patterns. To shed light on their capabilities, this study focuses on five representative structures using spherical mechanisms: oriceps, Miura ori, MACIOR, and two hexagonal structures. To assess their potential, a comparative analysis is conducted, evaluating their kinematic and scaling performances. The analysis employs the “scaling factor” as a metric, which quantifies the mechanical advantage of these mechanisms. This metric aids in the selection of appropriate structures for various applications.

SPH study of scale effects of perforated caissons

The hydrodynamic characteristics of perforated caissons are significantly influenced by the viscous fluid motion near the perforations on the front wall. Consequently, models designed in accordance with the Froude similarity suffer from the scale effects. To investigate the scale effects, a Smoothed Particle Hydrodynamics (SPH) model is established, in which fluid motion is governed by the continuity and Navier-Stokes equations, and the solid boundaries are represented by the dynamic boundary particles. The convergence and reliability of the SPH model are examined by employing it to replicate two laboratory experiments. Subsequently, the SPH model is applied to the study of interactions between regular waves and perforated caissons with different length scales, porosities, and chamber length to wavelength ratios. This enables an analysis of the scale effects on the vorticity and velocity fields, wave reflection, and wave force. The findings indicate that a scaled-down model tends to underestimate flow field intensity and wave force amplitude, while overestimate the wave reflection coefficient.

Spatial difference on nitrogen removal in the water based on different resolutions for Sanhuanpao wetland, Northeast China.

The research on the deviations caused by different resolutions is relevant to the study of spatial scale effects. In 2018, spatial interpolations were performed using the removal ratios of the TN, NH4-N, and NO3-N of the layers of different resolutions, respectively. Based on the mean and the standard deviation, the area, shape, and position were obtained for four levels related to the removal ratios of the three nitrogen forms. The linear and 6th function fitting methods were used to reveal the differences in nitrogen removal in wetland water at different spatial resolutions. The results showed that a resolution of 25 times the original was the key scale of the spatial effects. Due to the fact that 52 of the 72 functions did not reach a significant level (P < 0.05), the spatial scale effect of the nitrogen removal was mainly characterized by disorderly fluctuations. The results have a certain extrapolation value for the analysis of spatial scale effects. PRACTITIONER POINTS: The resolution difference was not sufficient to change the spatial pattern of the geographic phenomena. The resolution of 25 times the original was the important scale for determining spatial effects. When studying the spatial scale effects caused by differences in resolution, it was necessary to comprehensively consider various resolutions.

Mechanical behavior of bio‐inspired composites made of co‐continuous geopolymer and 3D‐printed polymer

AbstractGeopolymers (GPs) are emerging, low‐density ceramic materials that are simple to manufacture, with high elastic modulus and strength, albeit with low toughness. Fiber reinforcements have been used to achieve varied ductile behaviors, but little is known about the GP addition to polymeric frame structures. Thus, drawing inspiration from the nanostructure of bones, this paper investigated an interpenetrating, co‐continuous composite consisting of a GP as the stiff but brittle phase, and a 3D‐printed polymer (PA12 White) as the soft and deformable phase. The composite mechanical properties and failure modes were studied experimentally using uniaxial compression and four‐point bending tests. The co‐continuous network constrained brittle cracking within the GP and reduced strain localization in the polymer. The results showed that the composite had higher strength (56.11 ± 2.12 MPa) and elastic modulus (6.08 ± 1.37 GPa) than the 3D‐printed polymer and had higher toughness (5.98 ± 0.24 MJ/mm3) than the GP for the specific geometries examined. The shape effect study demonstrated that cubic structures had higher elastic modulus and strength but at the expense of lower toughness when compared to rectangular prism structures. The study of scale effects indicated that increasing the number of periodic unit cells while maintaining consistent bulk dimensions led to augmented strength and toughness, albeit without statistically significant alterations in elastic modulus. Thus, this paper presents an experimental realization of a novel, bio‐inspired, interpenetrating, GP–polymer composite design, offering improved strength and toughness. It also provides valuable insights into the shape and size effects on the mechanical properties of this new composite.

Numerical study of scale effects on the open water performance of a rim-driven thruster

This paper presents the study of scale effects on the open water performance of a rim-driven thruster (RDT) based on Computational Fluid Dynamics (CFD) simulations. For marine propellers, the effects of viscosity are often significant when there is a dramatic change in Reynolds number, which occurs when the results from model scale tests are extrapolated to propellers at full scale. Reynolds-Averaged Navier–Stokes (RANS) simulations with the Moving Reference Frame (MRF) approach are carried out in ANSYS Fluent for the RDTs under different working conditions. Considering the potential transitional flow on the propeller at model scale, the γ−Reθ transition model is adopted which can better resolve the boundary layer and yield more accurate results for transitional flows. From the simulations, it is observed that the duct and rim are more affected by the scale effects than the propeller. When the Reynolds number increases, there is a small amount of increment in the total thrust coefficient but a significant decrease in the total torque coefficient, resulting in a substantial improvement in hydrodynamic efficiency of the full scale RDT compared to the model scale.

DEM study of particle scale effect on plain and rotary jacked pile behaviour in granular materials

The capacity of open-ended piles strongly depends on the potential plugging occurring during installation. The Discrete Element Method (DEM) is particularly suitable to the study of pile plugging, as it can model large soil deformation. However, DEM simulation of the 3D boundary value problems is computationally expensive, and particle upscaling is usually used to reduce the number of particles modelled. In this paper, two granular beds were created with the same average porosity, initial stress field and contact parameters, but different particle scales. Two pile geometries were installed by plain and rotary jacking. Normalised results show that the pile penetration mechanism is strongly affected by the particle scale. Larger particles lead to earlier pile plugging, higher shaft resistance and require a greater force to penetrate the ground. This effect can be linked to a modified penetration mechanism, with larger shear zones and less well defined “nose cone” under the pile tip for larger particles. Changing particle scaling has a neutral effect on the total penetration resistance of a rotary jacked pile, but reduces the base penetration and increases the plug resistance. Maximising the ratio of particle scale to wall thickness is key to adequately capturing the pile coring mechanism.

Experimental Study of Scale Effect in Tunnel Fires at Different Sealing Ratios

Fully or partially sealing the openings of tunnels to accelerate the self-extinction of fires provides a promising firefighting tactic to beat large fires in a long tunnel. So far, most experimental studies on the characteristics of fire with different sealing ratios have been conducted in reduced-scale tunnels. However, whether the findings in a reduced-scale tunnel can be converted to its full-scale prototype tunnel based on scaling laws has not yet been adequately studied. A series of experiments with heat-release rates of 15.8, 31.6 and 63.2 kW were conducted with sealing ratios ranging from 0% to 100% in a prototype tunnel measuring 20 m long, 0.9 m wide and 0.46 m high. The experimental results were compared with those from a 1/2 reduced-scale tunnel measuring 10 m long, 0.45 m wide and 0.23 m high. It showed that temperature rise along the tunnel in the 1/2 reduced-tunnel could be significantly underestimated. The differences in temperature rise increased monotonously with distance away from the fire seat, and they were as high as 70% at the tunnel portals, irrespective of the heat-release rates and sealing ratios. The study showed that the scale effect of fires was not sensitive to the Reynolds number of flows in tunnels. The minimal sealing ratio for the self-extinction of fires in the prototype tunnel was 85%, whilst it was 75% in the 1/2 reduced-scale tunnel, and the study revealed that the fires were much easier to extinguish in the 1/2 reduced-scale tunnel than those in the prototype tunnel, where the fires can sustain in a lower oxygen concentration. The study demonstrated that scaling laws could be invalid for tunnel fires with different sealing ratios and that results observed in reduced-scale tunnels should be further verified when applied to full-scale prototypes.

A study of scale effects in experiments of monopile scour protection stability

Small scale hydraulic experiments are widely used to model the stability of a scour protection around an offshore monopile foundation. Knowing the associated scale effects is important for evaluating the validity of the obtained experimental and design results. This paper provides a quantification analysis of scale effects that exist in monopile scour protection experiments, with a focus on the shear damage of a dynamically stable scour protection. Large scale models (scale ratio 1:8.33 and 1:16.67) and similar small scale models (scale ratio 1:50) have been adopted in the experiments with waves against current hydrodynamic conditions applied. For the waves and current conditions, the Froude scaling rule is used; for the armour stones, the so-called Best Model scaling rule suggested by Hughes (1993) is used. The scaling scheme achieves similarities between large and small scale models with regard to Shields number, relative density, geometry and settling velocity of particle. The scour protection damage patterns are measured and the three dimensional damage numbers are analysed. For better comparing the small and large scale test results, the small scale tests are performed repeatedly to obtain reliable damage results with associated range of deviation. Visual assessment of the damage patterns shows some agreements between small and large scale tests with regard to the damage and accretion locations. However, detailed analysis shows that the small scale tests introduce higher global and subarea damage numbers compared to large scale tests. The damage areas in small scale tests are larger than that in large scale tests. Significant lee-side damage due to the presence of lee-wake vortices is found in small scale tests. The dissimilarities of pile Reynolds number ( R e , D P ), ratio between Shields numbers ( θ m a x / θ c r ) and vortex shedding frequency in the different scaled models are believed to be the primary reasons of obtained scale effects. • Scale effects in monopile scour protection experiments are investigated quantitatively. • Large scale (1:8.33 and 1:16.67) and small scale (1:50) experiments are performed under wave opposing current conditions. • Repeated small scale experiments are carried out to obtain reliable mean damage numbers and 95% confidence intervals. • Scour protection damages are analyzed and compared between small and large scale experiments. • Time scale of scour protection progressive damage development is investigated. • Different Reynolds numbers ( R e , D P ) and ratios between Shields numbers ( θ m a x / θ c r ) are the main reasons for the scale effects.

Study of scaling effect of ferroelectric gate stack in planar InGaAs MOSFET

AbstractNegative capacitance field effect transistors is found to be a promising option for low power VLSI devices in the advanced technology node. In this article, through extensive numerical simulation, we report the scaling effect of ferroelectric gate stack, channel thickness and gate length on electrostatic integrity, DC, analog and RF performance of InGaAs quantum well MOS transistor. The different DC and analog figure of merits such as on current (), switching ratio (), threshold voltage roll‐off, sub‐threshold swing (SS), trans‐conductance (), transconductance efficiency () of the test device has been analyzed for different ferroelectric layer thicknesses and compared with the baseline device. We have investigated RF performance such as gate capacitance, unity‐gain cut‐off frequency and small signal voltage gain of the device. Improvement in DC and analog figure of merits is proportional to the ferroelectric layer thickness. However, for higher values of ferroelectric thickness, the hysteresis effect gradually became prominent. MOS transistor with optimum ferroelectric layer thickness shows the negligible amount of threshold voltage roll‐off and improved transconductance‐frequency product compared to the baseline device. In presence of ferroelectric layer, the effect of channel thickness variation on device performance is reduced. The role of ferroelectric gate stack is found to be more prominent at shorter gate length.

Comparative study of scale effect in concrete fracturing via Lattice Discrete Particle and Finite Discrete Element Models

We study the structural response of concrete weight coating of offshore pipelines subject to various loading conditions by utilizing the Lattice Discrete Particle Model and Finite Discrete Element Method in a comparative manner. We use laboratory experiments to validate our numerical simulations. We discuss the framework in detail, experiment setups, and outline the capabilities and limitations of both methods. A parametric study with a correlation to the size effect is also presented. We simulate Uniaxial Compressive Strength, Brazilian Disk and a three-point bending of a beam with a notch in both methods. We observe that strength and macroscopic fracture patterns fit well between numerical and experimental methods. We discuss the effectiveness of the methods concerning the transition of size effect, as well as comparing to the size effect law. Our statistical analysis quantifies the capability of capturing the size effect in both models. Capturing the size effect helps to increase the accuracy of predicting the structure response and performance which in turn a key factor in durability of concrete structures.

A nanoscale study of size scale, strain rate, temperature, and stress state effects on damage and fracture of polyethylene

The mechanical properties and damage behavior of amorphous polyethylene are investigated using Molecular Dynamics (MD) simulations. The influence of time, temperature, size scale, and stress state are extensively studied to gather insights into the complex nature of glassy polymers and the related damage process of void formation during dynamic loading conditions. The Modified Embedded Atom Method (MEAM) is employed to model interatomic interactions, balancing computational efficiency with a superior description of free surfaces and void formation to provide a detailed analysis of the progression of damage in the form of nucleation, growth, and coalescence of voids. The MD simulations capture the evolution of the number and size of voids and are shown to correlate to specific regimes of the stress-strain response. Particular attention is given to the quantification of void coalescence and the influence coalescence has on the growth and nucleation rates of voids. A nanoscale parameter, the critical Inter-void Ligament Distance (ILD), is defined for the initiation of void coalescence, and is found to be about 0.75 void diameters resulting in the enhancement of void growth and the restriction of void nucleation once the critical ILD is achieved. This study provides important insight into the damage progression of glassy polymers that cannot be defined through current experimental techniques.

Numerical prediction of scale effect on propeller bearing force of a four-screw ship

In case of a four-screw ship, the propellers show different hydrodynamics performance due to the asymmetric distribution of the wake. And the particularity of the scale effect on wake field for this type of ship would make a more complicated characteristics on propeller bearing force. In this paper, a numerical simulation study of scale effect on propeller unsteady bearing force of a four-screw ship was performed by employing RANS method. The load variation of the single-blade is analyzed to understand the fluid mechanism of the interaction between the propeller blade and wake flow. The larger wake field difference between inside and outside propeller disk aggravates the unbalanced load distribution for the full-scale ship. The results of propeller bearing force highlight that the fluctuation values of full-scale ship are smaller than those of model one. Moreover, the scale effect of outside propeller is strong with respect to the inside one. The above findings can provide theoretical guidance for load balancing and vibration reduction of the four-screw ships.

A Study of Scale Effects in Discrete Scaled Dynamic Systems

Scaled experimentation is an important experimental approach for the investigation of complex systems. Unfortunately, scaling suffers scale effects, where changes in behaviour with scale can be so significant to undermine any scaled investigation. The state-of-the-art in scaled experimentation remains dimensional analysis, which unfortunately offers no solution to scale effects and consequently scaled experiments although important provide only limited usefulness at the present time.This paper is concerned with a new approach to scaled experimentation founded on the theory of finite similitude applied to discrete mechanical systems. The new theory applies the metaphysical concept of space scaling, where objects, prototypes, systems, experimental apparatus and facilities are scaled by the means of space contraction or expansion. Although space scaling is clearly practically impossible, what is possible is an assessment of the effects of space scaling on the governing physics and a comparison with real experimental behaviours.It is shown in the paper how the new theory accounts for all scale dependencies and unlike dimensional analysis is able to accommodate known scale effects. It provides also alternative scale-invariances that cater for the situation where scale effects are present but unknown. This aspect is the focus here with application of first-order finite similitude to simple mechanical-dynamic systems, an approach that requires two scaled experiments at two distinct scales. It is demonstrated how it is possible by means of two scaled experiments to represent behaviours at the full scaled that hitherto would have been deemed impossible with traditional dimensional analysis.

Numerical study of scale effects on self-heating ignition of lithium-ion batteries stored in boxes, shelves and racks

Abstract The fire safety of Lithium-ion batteries (LIBs) during their storage and transport is becoming of prime importance for the industry, with a number of such fires reported in recent years. It is crucial to understand the mechanisms and causes of these fires to provide insights for prevention. Previous studies mostly focused on small ensembles with a few cells and the chemistry involved. The possibility of ignition resulting from heat transfer within a large-size ensemble of LIBs had received little attention before. Focusing on the fire safety of large-scale stored LIBs, we discuss the risk and likelihood of self-heating ignition, which is a known cause of fires in other industries (e.g. chemical storage). Taking LiCoO2 type of battery as a base case and using its chemical kinetics reported in the literature, we build a transient heat transfer model with multi-step reactions to analyze the self-heating behaviour of ensembles of LIBs. Four typical storage sizes, from a single cell to racks containing around 2 million cells, are simulated using COMSOL Multiphysics. The results show that the critical ambient temperature for self-heating ignition is significantly lower for a large-scale LIB ensemble (e.g. 60 °C for the rack), indicating spontaneous side reactions are not negligible heat sources in large LIB ensembles and self-heating poses potential fire hazards in storage. Effects of size and heat transfer in LIB ignition should therefore not be ignored. This work provides insights into the fire safety of Li-ion batteries and additional means of protection during storage and transport.

Concluding Notes and Future Directions

The articles in this issue include experimental research and clinical studies on the bidirectional process of connecting experience and words, which we term the Referential Process (RP). These concluding notes focus on new questions and new directions for research. Studies now under way include characterization and measurement of the Arousal function of the referential process, which involves how people talk when the connection to specific ideas is not yet fully developed, and new research on paralinguistic features of interpersonal communication. Further work in these areas will involve automatic transcription technology to incorporate pitch, rate of speech and loudness, as well as development of a Time-DAAP program to enable such assessment. Research is also needed to investigate the relationship between language and underlying physiological and neurological mechanisms. These relationships can be examined using physiological measures such as galvanic skin response (GSR) and changes in heart rate and respiration. While fMRI scans are not compatible with tasks requiring speech production, fMRI compatible tablet systems are available for writing tasks. Participants may also be scanned while reading literary passages that show differences in RP functions. A major goal of our research program is the application of RP measures in large scale treatment efficacy and effectiveness studies evaluating particular treatment forms. The computerized referential process procedures have the potential to study whole trajectories of large numbers of treatments; and also to identify important turning points within treatments and within sessions. The interpretation of these measures in the context of a systematic theory of treatment process has the value of enabling results that are not only statistically powerful but clinically significant as well. Other potential areas of study include application of the language measures in large scale studies of political, religious and literary discourse.

Scale and size effects on the mechanical properties of bioinspired 3D printed two-phase composites

Multi-material 3D printing offers design flexibility for the manufacture of new architectured composite materials and has been increasingly used to explore the mechanical properties of bioinspired composites. In this study, the influence of scale and size on mechanical properties of periodic two-phase composites with various architectures of a stiff and a soft phase are explored. The studied composites include an interpenetrating phase composite with two continuous phases (inspired by bone), a matrix-inclusion composite with a continuous and a discontinuous phase, and a discontinuous phase composite where both phases are discontinuous. These composites are fabricated by additive manufacturing, and their mechanical properties are evaluated experimentally using a compression test complemented by digital image correlation, and numerically through finite element analysis. Overall trends show that the elastic moduli and yield strengths decrease as the scale is increased. Our results on size effects reveal an increase in elastic modulus and yield strength with increasing size of the sample. Our investigation outcomes help to better understand some of the challenges in studying and applications of additively manufactured composites and shed light on scale and size effects on mechanical properties of 3D printed two-phase composites. This paper illustrates a need for further studies of scale and size effects in additively manufactured materials.

An experimental study of scaling effects in notched quasi-isotropic carbon/epoxy laminates under compressive loads

The size effects in centre-notched quasi-isotropic carbon/epoxy laminates under compression were investigated. The in-plane dimensions of the baseline specimen were scaled up by a factor of up to 14. The centre-notched specimens were compared to open-hole specimens of the same dimensions. It was found that compressive strength of the small centre-notched specimen is similar to that of the open-hole specimen. However, as the in-plane dimensions increase, the centre notches are weaker than the open holes, and start to follow a Linear Elastic Fracture Mechanics (LEFM) scaling line. These trends were well captured by a Composite Compressive Strength Modeller (CCSM) using the fracture toughness measured in the current study. Fibre micro-buckling was confirmed to be the dominant failure mechanism under compression. The failure mechanisms under compression were also compared against those under tension. Matrix splitting under compression was observed through X-ray Computed Tomography but was less extensive than under tensile loading.

Jurisdiction size and local government effectiveness: Assessing the effects of municipal amalgamations on performance

AbstractThe optimal jurisdiction size has been debated since Plato and Aristotle. A large literature has studied economic and democratic scale effects, but we have almost no knowledge of the effects of jurisdiction size on the effectiveness of local services. This is due to two methodological problems. First, selection bias and reverse causality often render change in jurisdiction size an endogenous variable. Second, there is a lack of empirical indicators of effectiveness, and most studies therefore focus on spending measures. Extant research thus studies economies of scale, leaving effectiveness of scale unexamined. We address both problems in a quasi‐experimental study of public schools. Our findings from the school area indicate that jurisdiction size does not have systematic effects on effectiveness. Our analysis therefore supports recent studies of economic and democratic scale effects that indicate that the search for the optimal jurisdiction size is futile.

A Numerical Study of Roughness Scale Effects on Ocean Radar Scattering Using the Second-Order SSA and the Moment Method

The roughness scale effects on ocean radar scattering are studied using the second-order small slope approximation (SSA-II) and the method of moments (MoM). The KHCC03 spectrum is employed to represent 2-D and 1-D sea surfaces in the above two scattering methods, respectively. Criteria of full spectrum truncation are proposed for the numerical simulations of ocean scattering. Numerical results are illustrated in fully bistatic configuration at L- and C-bands. It is found that scattering at higher frequency is relatively more sensitive to the small-scale roughness but less sensitive to the large-scale roughness. At L- and C-bands, short waves with wavenumber larger than 316 rad/m have little effect on ocean scattering. The large-scale waves put more impacts on scattering in the forward directions, especially for large incidence angles. Other than the specular direction, the effects of large-scale roughness on ocean scattering are in general smaller at VV-pol than HH-pol. The bistatic scattering at cross polarizations is less sensitive to the roughness scale as compared to the copolarizations. For numerical simulations of ocean scattering with incidence angle less than 60°, using small surface profiles with size about 1/6 of those accounting for full spectrum yields results with errors less than 2 dB. Results also indicate that the incoherent parts dominate the scattered power from ocean surfaces with large-scale roughness.

Numerical study of scale effect on the wake dynamics of a propeller

In this study, the effects of the scale on the evolution of propeller wake is simulated and analyzed under open water conditions. The simulation is conducted using numerical techniques based on the detached eddy simulation method. The open water performance such as thrust and torque are analyzed for validation, and the instantaneous flow field, vortical structure and the kinetic energy spectra are investigated for the scale effect on the wake dynamics of a propeller. The results indicated that the influence of scale effect on load and wake dynamics of a propeller can differ significantly under different conditions. Under lighter loading condition, the average spanwise circulation at full-scale are considerably larger than those at model-scale at the range of inner radius, and the full-scale propeller exhibits a stronger blade shed vortex. Analysis of vortical structure shows that the transition-to-instability position of vortices vary under different conditions. Power spectral density analysis of the kinetic energy demonstrates that the kinetic energy of full-scale propellers is generally proportionally larger than that of model-scale propellers.