Investigation Of Scale Effects Research Articles

Investigation of Scale Effects on Linear Vertical Maneuvering Derivatives of a Submarine

Investigation of Scale Effects on Linear Vertical Maneuvering Derivatives of a Submarine

An investigation of scale effects on the self-propulsion characteristics of a submarine

This study's main objective is to investigate the scale effect on the benchmark DARPA Suboff submarine hull form's resistance and self-propulsion characteristics. The study's secondary objective is to explore the feasibility of the 1978 ITTC performance prediction method for submarines' power prediction. In achieving both objectives, the CFD solver is utilised. Hence, the flow around the three different scales of the DARPA submarine forms and its propellers, including a full-scale one, is first solved using the steady RANS method with the k-ω SST turbulence model. Verification studies are conducted to determine the uncertainty level of the numerical computations for each scale. The hull resistance, propeller open water and self-propulsion performances are validated with the available experimental data and other numerical studies in the literature for the widely used benchmark submarine model. In the self-propulsion simulations, the propeller flow is modelled using the discretised propeller geometry with the Moving Reference Frame (MRF) approach. Also, the Proportional Integral (PI) controller is adopted to find the self-propulsion point efficiently. The scale effects on the hull resistance and its components, nominal wake fraction and self-propulsion characteristics, are explored at two different velocities. The extrapolated numerical results obtained by the 1978 ITTC procedure show that the scale ratio decrease enables better prediction of the self-propulsion characteristics compared to the full-scale CFD predictions. As well as this, the extrapolated self-propulsion characteristics using the model scale results, which are obtained by the CFD computations, are found to be in good agreement with those of the full-scale CFD results. The study, therefore, suggests that the 1978 ITTC performance prediction method can be used in some confidence to extrapolate the performance results from the model to full-scale for the submerged bodies, similar to the surface ships. This study also presents the full-scale self-propulsion characteristics of the benchmark DARPA Suboff form for the first time in the literature using the CFD tool over a realistic range of submarine forward speeds.

An investigation of scale effects on marine propeller under cavitating and non-cavitating conditions

ABSTRACT In this study, scale effects on the hydrodynamic performance of DTMB 4119 propeller have been investigated in uniform flow under non-cavitating and cavitating conditions by a simple practical method based on OpenFOAM. A potential based Lifting Surface Method has also been applied. A verification study of non-cavitating simulations has been carried out by Grid Convergence Index method at one scale ratio. Then the results have been validated with experiments. Schnerr-Sauer cavitation model of OpenFOAM has been used for the phase change between vapor and liquid. Cavitation simulations have been performed as a time-dependent with dynamic mesh while non-cavitating simulations have been carried out as a steady-state with static mesh. Effects of the scale ratio and cavitation simulations have been investigated and a simple fitting procedure on the thrust and torque values based on logarithm of Reynolds number have been applied. Results have also been compared with ITTC corrections.

An investigation of scale effect and applicability of compact light sources in microchannel reactors applied to pollutant abatement.

In this work, the performance of microreactors irradiated with conventional (fluorescent) and UV-LED light was evaluated. For this purpose, a microfluidic reactor with an equivalent diameter of 133.5 μm was used. In addition, the effect of scale variation on the performance of photochemical reactors was assessed using reactors with three internal diameters (600, 1200, and 2300 μm), 2 residence times (30 and 60 s), and two sources of UVA radiation (A with irradiance of 115 W m-2 and B with irradiance of 44 W m-2). Also, the relationship between the configuration of the photocatalyst film and the effect of the scale on the performance of photochemical reactors was experimentally and theoretically investigated. For both cases, methylene blue dye was used as a model pollutant and titanium dioxide (TiO2) as a photocatalyst deposited on the inner wall of the photocatalytic reactors. For the residence time of 30 s, the smaller the reactor diameter, the greater was the degradation (22, 18, and 6%, respectively, for lamp A and 17, 16, and 8 %, respectively, for lamp B). The influence of the diameter of the reactor was also observed for the residence time of 60 s, but only for the reactor with a 2300-μm internal diameter. The reactors with diameters 600 and 1200 μm only showed different results when illuminated with lamp B (33 and 28% of methylene blue conversion, respectively). Moreover, computational simulation results suggested higher efficiency as the reactor's diameter is decreased and an optimum thickness of photocatalyst film to maximize the performance of devices in which photocatalytic reactions are carried out.

Investigation of scaling effect on power factor of permanent magnet Vernier machines for wind power application

This study investigates the scaling effect on power factor of surface mounted permanent magnet Vernier (SPM-V) machines with power ratings ranging from 3 kW, 500 kW, 3 MW to 10 MW. For each power rating, different slot/pole number combinations have been considered to study the influence of key parameters including inter-pole magnet leakage and stator slot leakage on power factor. A detailed analytical modelling, incorporating these key parameters, is presented and validated with two-dimensional finite-element analysis for different power ratings and slot/pole number combinations. The study has revealed that with scaling (increasing power level), significant increase in electrical loading combined with the increased leakage fluxes, i.e. (i) magnet leakage flux due to large coil pitch to rotor pole pitch ratio, (ii) magnet inter-pole leakage flux and (iii) stator slot leakage flux, reduces the ratio of armature flux linkage to permanent magnet flux linkage and thereby has a detrimental effect on the power factor. Therefore, unlike conventional SPM machines, the power factor of SPM-V machines is found to be significantly reduced at high power ratings.

Scale Effect on Impact Performance of Unidirectional Glass Fiber Reinforced Epoxy Composite Laminates.

As a result of the increasing use of glass fiber reinforced plastic (GFRP) composites in engineering fields, the investigation of scale effect on impact performance for this kind of composite is essential for large scale structure design. The effects of scaling on the impact response of simply supported unidirectional GFRP were investigated through drop weight impact (DWI) tests in this study. Impact tests were undertaken over a wide range of energies to generate damages between barely visible and initiated penetration on four scale size GFRP laminates. The main impact responses including impact force, contact duration, displacement, energy absorption and damage area of scaled specimens were normalized to compare with the full-size specimen. It was found that the impact response of large sample with elastic deformation and small area of delamination can be predicted accurately according to a geometrical similar scaling law. Scale effect was found in the damage threshold force and absorbed energy of the laminates when significant internal damage occurs due to the microstructural effect becoming important in resisting impact force and absorbing impact energy. Moreover, the energy partition and effective stiffness were calculated according to the energy balance model to reveal the contribution of different modes of deformations on energy absorption for the GFRP laminates.

The influence of scale on the air flow and pressure in the modelling of Oscillating Water Column Wave Energy Converters

In this work, air compressibility effects are investigated during wave interaction with an Oscillating Water Column (OWC) Wave Energy Converter (WEC). Mathematical modelling includes a thermodynamic equation for the air phase and potential flow equations for the water phase. A simple three dimensional OWC geometry with a linear Power Take Off (PTO) response is considered and both the thermodynamic and potential flow equations are linearised. Analysis of the linearised system of equations reveals a nondimensional coefficient which we name “compression number”. The flow potential is decomposed into scattering and radiation components, using an analogue of spring-dashpot response and taking into account the additional effects of air compressibility to wave interaction processes. We use these concepts to characterise the relative importance of the air compressibility effects inside the OWC and to derive novel scaling relations for further investigation of scaling effects in OWC physical modelling. The predictions of the methodology are validated against large scale experimental data, where compressibility effects are evident and further application of the methodology to a realistic OWC geometry is used to demonstrate the importance of these effects to prototype scale.

Statistical analysis of scale effect on equivalent elastic modulus of jointed rock masses

The study of scale effects plays an important role in the evaluation of mechanical properties of rock masses. There have been many studies on this topic; however, few have been able to effectively analyze relationships between size and deformation properties analytically. This paper presents an investigation of scale effects on deformation properties of jointed rock masses by using analytical and statistical methods. First, the analytical formula for E eq (equivalent elastic modulus) of jointed rock with a parallel joint set was derived. This derivation is related to a geometrical parameter ρ’, defined as joint trace length per unit area. Second, model of a half-space rock with a parallel joint set was constructed and subsequently sampled to specimens with different locations and lengths. The expectation and standard deviation of the ρ’ of rock samples were derived to statistically describe scale effect of ρ’. Then, the scale effect of 1/E eq (equivalent elastic compliance) was analyzed. The investigation shows that expectation of 1/E eq is a constant with varying size and standard deviation of 1/E eq decreases and periodically fluctuates with increasing size. The applicability of the conclusions was discussed, and some extended studies on stochastic jointed rock masses were made. Finally, representative elementary volumes of the rock model were determined according to the analytical solutions.

Study of Scale Effect in a Starved Elastohydrodynamically Lubricated Contact

The article describes an experimental investigation of scale effect in a starved elastohydrodynamically lubricated contact on lubricant film thickness. Lubricant film thickness and its distribution is one of the most important parameters determining the performance and life of machine parts. Current experimental and numerical studies are mostly connected with oil lubrication. However, greases are used in more than 80 % of all rolling bearings where the starvation phenomenon occurs most frequently. The aim of this work is to compare two approaches to measuring film thickness of different greases. The use of multiple contacts optical test rig based on thin film colorimetric interferometry for film thickness measurement has enables to obtain film thickness of starved contact and the film distribution. The experimental observation of full-scale model of bearing will help to understand better the behavior of real bearing. The evaluation of the experiment was made by chromatic interferometry. This method is used to measure thin lubrication films.

Investigation of scaling effects on fiber metal laminates under tensile and flexural loading

In this study, scaling effects on fiber metal laminates under tensile and three-point bending tests were investigated numerically and experimentally. The fiber metal laminate specimens were made of aluminum 1050 and unidirectional glass–epoxy. Two scaled sizes of specimens were prepared based on [Formula: see text]. Some specified mechanical properties of these samples were investigated and results showed that fiber metal laminates obey scaling law under quasi-static loading. Explicit finite element code LS-DYNA was utilized for numerical simulation. After validating numerical simulation with experiments, scaling law was studied numerically for four different sample sizes. Finite element analysis demonstrated that scaling law is valid for fiber metal laminates. In final part, hole size effect in FML specimen was investigated numerically.

Investigation of scale effect for the computation of turbulent flow around a circular cylinder

In order to investigate the scale effect of turbulent flow around a circular cylinder, two similarity numbers (criteria) based on turbulent kinetic and dissipation rates associated with the fluctuation characteristics of turbulence wake are deduced by analyzing the Reynolds averaged Navier-Stokes equations (RANS). The RNG k-ɛ models and finite volume method are used to solve the governing equations and the second-order implicit time and upwind space discretization algorithms are used to discrete the governing equations. A numerical computation of flow parameters around a two-dimensional circular cylinder with Reynolds numbers ranging from 102 to 107 is accomplished and the result indicates that the fluctuation of turbulence flow along the center line in the wake of circular cylinder can never be changed with increasing Reynolds numbers when Re ⩾ 3 × 106. This conclusion is useful for controlling the scale of numerical calculations and for applying model test data to engineering practice.

An investigation of scale effects in family substance abuse treatment programs

This short report investigates scale effects in family substance abuse treatment programs. In Massachusetts, the family substance abuse treatment programs were much more costly than other adult residential treatment models. State officials were concerned that the "scale" or size of these programs (averaging just eight families) was too small to be economical. Although the sample size (just nine programs) was too small to permit reliable inference, the data clearly signalled the importance of "scale effects" in these family substance abuse treatment programs. To further investigate scale effects in family substance abuse treatment programs, data from the Center for Substance Abuse Treatment's (CSAT's) Residential Women and Children and Pregnant and Postpartum Women (RWC-PPW) Demonstration were re-analyzed, focusing on the relationship between cost per family-day and the estimated average family census. This analysis indicates strong economies of scale up until an average family census of about 14, and less apparent scale effects beyond that point. In consideration of these and other study findings, a multidisciplinary interagency team redesigned the Massachusetts' family treatment program model. The new programs are larger than the former family treatment programs, with each new program having capacity to treat 11 to 15 families depending on family makeup.

Experimental Investigation of Scaling Effect on Thermal Transport in Nanoscale Hot Spots

This article reports experimental investigation of the scaling effect on thermal transport in platinum nanoheaters deposited on a single crystalline silicon substrate. The size dependency of the thermal resistances of nanoheaters with dimensions from 5 μm down to 100 nm was experimentally obtained. Additional joule heating and electrical resistance thermometry in heater/sensor pairs of various dimensions and spacing (100 to 400 nm) were carried out in order to study the temperature distribution in the vicinity of these nanoheaters. The results of these two sets of measurements confirm that the thermal resistances of smaller nanoheaters are dominated by the interface resistance between the platinum and silicon substrate. Furthermore, analytical solutions of the BTE around a hot spot were used to evaluate and examine the significance of the localized heating or subcontinuum transport around a hot spot.

Deformation behavior of silver submicrometer-pillars prepared by nanoimprinting

Scaling in material properties is of great importance in microsystems and microelectronics where the device dimensions continuously shrink. Recently, compression tests of micron-sized pillars produced using a focused-ion beam (FIB) have become standard in the investigation of scaling effects. The influence of the fabrication process on the mechanical properties of the samples has, however, not been conclusively resolved. In this study, 130 silver pillars were fabricated using a novel embossing technique that does not pose the issues associated with FIB milling, i.e. surface amorphization and gallium contamination. Displacement-controlled compression tests on pillars with diameters of 130–3000 nm reveal for submicrometer samples an inverse proportionality of flow strength to diameter, which is associated with a wide strength distribution and a deformation taking place in large discrete strain bursts. The largest pillars show instead near bulk-like behavior. Unlike studies on other fcc materials, mechanical twinning is also an important deformation mechanism in Ag due to its very low stacking fault energy. In addition, occasional preexisting twin boundaries constituted preferential planes for localized deformation if favorably sloped. Despite the absence of ion-induced artifacts, scaling laws and absolute values of strength are comparable to those obtained via FIB milling.

Investigation of Scaling Effects in Fiber—Metal Laminates

The results of a series of quasi-static and impact tests on four scale-model sizes of fiber—metal laminate (FML) are compared to a scaling law that predicts response parameters based on a simple geometrical relationship of the input parameters. The FMLs consist of an aluminum alloy and a self-reinforced thermoplastic composite based on polypropylene fibers in a polypropylene matrix. The scaled FML laminates were arranged in a 2/1 configuration, and ply-level scaling of the FML constituent materials was employed to yield specimens with a nominally constant composite volume fraction, as well as correctly scaled in-plane and bending stiffness properties. In the initial part of this experimental program, the tensile and flexural properties of these hybrid materials were investigated at quasi-static rates of loading. Here, no significant scaling effects were observed in the mechanical response of the laminates. Following this, simply-supported scaled beams and plates were subjected to low-velocity impact loading in order to investigate scaling effects in the processes of damage development and target perforation. Here, response parameters such as the target deflection, the impact force, and the damage threshold energy were found to obey the scaling law. It is believed that experimental data of this nature will give greater confidence to engineers involved in the design of components based on hybrid materials such as fiber—metal laminates.

Investigation of scale effects and directionality dependence on friction and adhesion of human hair using AFM and macroscale friction test apparatus

Macroscale testing of human hair tribological properties has been widely used to aid in the development of better shampoos and conditioners. Recently, literature has focused on using the atomic force microscope (AFM) to study surface roughness, coefficient of friction, adhesive force, and wear (tribological properties) on the nanoscale in order to increase understanding about how shampoos and conditioners interact with the hair cuticle. Since there are both similarities and differences when comparing the tribological trends at both scales, it is thus recognized that scale effects are an important aspect of studying the tribology of hair. However, no microscale tribological data for hair exists in literature. This is unfortunate because many interactions between hair–skin, hair–comb, and hair–hair contact takes place at microasperities ranging from a few μm to hundreds of μm. Thus, to bridge the gap between the macro- and nanoscale data, as well as to gain a full understanding of the mechanisms behind the trends, it is now worthwhile to look at hair tribology on the microscale. Presented in this paper are coefficient of friction and adhesive force data on various scales for virgin and chemically damaged hair, both with and without conditioner treatment. Macroscale coefficient of friction was determined using a traditional friction test apparatus. Microscale and nanoscale tribological characterization was performed with AFM tips of various radii. The nano-, micro-, and macroscale trends are compared and the mechanisms behind the scale effects are discussed. Since the coefficient of friction changes drastically (on any scale) depending on whether the direction of motion is along or against the cuticle scales, the directionality dependence and responsible mechanisms are discussed.

Adhesion and Friction Studies of Silicon and Hydrophobic and Low Friction Films and Investigation of Scale Effects

Tribological properties are crucial to the reliability of microelectromechanical systems/nanoelectromechanical systems (MEMS/NEMS). In this study, adhesion and friction measurements are made at micro and nanoscales on single-crystal silicon (commonly used in MEMS/NEMS) and hydrophobic and low friction films. These include diamondlike carbon (DLC), chemically bonded perfluoropolyether (PFPE), and self-assembled monolayer (SAM) films. Since MEMS/NEMS devices are expected to be used in various environments, measurements are made at a range of velocities, humidities, and temperatures. The relevant adhesion and friction mechanisms are discussed. It is found that solid films of DLC, PFPE, and SAM can reduce the adhesion and friction of silicon. These films can be used as anti-adhesion films for MEMS/NEMS components under different environments and operating conditions. Finally, the adhesion and friction data clearly show scale dependence. The scale effects on adhesion and friction are also discussed in the paper.

A Full‐Bayesian Approach to parameter inference from tracer travel time moments and investigation of scale effects at the Cape Cod Experimental Site

A method for inverting the travel time moments of solutes in heterogeneous aquifers is presented and is based on peak concentration arrival times as measured at various samplers in an aquifer. The approach combines a Lagrangian [Rubin and Dagan, 1992] solute transport framework with full‐Bayesian hydrogeological parameter inference. In the full‐Bayesian approach the noise values in the observed data are treated as hyperparameters, and their effects are removed by marginalization. The prior probability density functions (pdfs) for the model parameters (horizontal integral scale, velocity, and log K variance) and noise values are represented by prior pdfs developed from minimum relative entropy considerations. Analysis of the Cape Cod (Massachusetts) field experiment is presented. Inverse results for the hydraulic parameters indicate an expected value for the velocity, variance of log hydraulic conductivity, and horizontal integral scale of 0.42 m/d, 0.26, and 3.0 m, respectively. While these results are consistent with various direct‐field determinations, the importance of the findings is in the reduction of confidence range about the various expected values. On selected control planes we compare observed travel time frequency histograms with the theoretical pdf, conditioned on the observed travel time moments. We observe a positive skew in the travel time pdf which tends to decrease as the travel time distance grows. We also test the hypothesis that there is no scale dependence of the integral scale λ with the scale of the experiment at Cape Cod. We adopt two strategies. The first strategy is to use subsets of the full data set and then to see if the resulting parameter fits are different as we use different data from control planes at expanding distances from the source. The second approach is from the viewpoint of entropy concentration. No increase in integral scale with distance is inferred from either approach over the range of the Cape Cod tracer experiment.

Investigation of Scaling Effects in Elastic-Plastic Ductile Fracture Using the Local Approach

This paper investigates the ability of a simple ductile local fracture model to predict the fracture initiation conditions for geometrically similar specimens of different sizes containing either sharp cracks or blunt notches. The material considered is the high strength, low hardening HY 130 steel. We simulated fracture tests on fatigue-precracked compact tension specimens and three-point bend bars containing blunt notches, using the local fracture model to control crack initiation in the finite element analyses. We compared the results of the simulations with experimental results. The comparison indicates that the model qualitatively predicts the right scaling effects for cracked specimens when a characteristic material length is adequately introduced. However, the model failed to predict the fracture initiation conditions and the scaling behavior of notched specimens. The discrepancy arises because the actual micromechanism leading to fracture initiation at the notch (void growth in a band of localized shear) is different from the mechanism underlying the model (quasi-isotropic void growth). Therefore, new or improved models capable of handling ductile failure by void growth under predominantly shear deformation must be developed to predict ductile fracture initiation conditions and scaling laws for generalized loading and geometric configurations.

Investigation of scaling effects in the aggregation of dilute kaolinite suspensions by quasi-elastic light scattering

Kaolinite in acidic solution is known to have negatively charged faces and positively charged edges [l]. One of the consequences of this dual charge character is the possibility of heteroflocculation between the edges and the faces forming three-dimensional voluminous “card-house” structures [Z-4]. Face-face aggregation, however, results in densely packed flake-like aggregates. In the past decade it has been shown that colloidal aggregates are fractal objects and their radius R is therefore related to the mass of the aggregate m by the following expression [5-61