Parallel Force Research Articles

Formation mechanism of tearing defects in machining Nomex honeycomb core

Nomex honeycomb core has been widely applied in aerospace industries due to its superior strength and rigidity. However, the machining defects of honeycomb core can deteriorate the bonding strength between honeycomb core and connective face sheet. This paper investigates the tearing defects formatted in milling process of Nomex honeycomb core. Firstly, a cutting force model is proposed to predict the milling forces under various tool entrance angles. Then, finite element simulation for machining honeycomb wall is conducted to reveal the formation mechanism of tearing defects. The accuracy of the model is verified by a group of experiments under different entrance angles and the relative error is below 25% in 1-direction and 20% in 2-direction. It is found that the formation of tearing defects is closely related to the deformation of honeycomb wall and the component of cutting force in direction parallel to wall. The tool entrance angle can be thus optimized based on the reduction of tearing defects. The optimized entrance angle of double wall is among 40° and 70°.

Measuring colloid-surface interaction forces in parallel using fluorescence centrifuge force microscopy.

Interactions between colloidal-scale structures govern the physical properties of soft and biological materials, and knowledge of the forces associated with these interactions is critical for understanding and controlling these materials. A common approach to quantify colloidal interactions is to measure the interaction forces between colloids and a fixed surface. The centrifuge force microscope (CFM), a miniaturized microscope inside a centrifuge, is capable of performing hundreds of force measurements in parallel over a wide force range (10-2 to 104 pN), but CFM instruments are not widely used to measure colloid-surface interaction forces. In addition, current CFM instruments rely on brightfield illumination and are not capable of fluorescence microscopy. Here we present a fluorescence CFM (F-CFM) that combines both fluorescence and brightfield microscopy and demonstrate its use for measuring microscale colloidal-surface interaction forces. The F-CFM operates at speeds up to 5000 RPM, 2.5× faster than those previously reported, yielding a 6.25× greater maximum force than previous instruments. A battery-powered GoPro video camera enables real-time viewing of the microscopy video on a mobile device, and frequency analysis of the audio signal correlates centrifuge rotational speed with the video signal. To demonstrate the capability of the F-CFM, we measure the force required to detach hundreds of electrostatically stabilized colloidal microspheres attached to a charged glass surface as a function of ionic strength and compare the resulting force distributions with an approximated DLVO theory. The F-CFM will enable microscale force measurements to be correlated with fluorescence imaging in soft and biological systems.

Investigation of the effect of a 15-degree tilt-in-space on the fluctuation of shear forces exerted on the buttocks when the back support is reclined.

[Purpose] This study aimed to investigate the effect of the combination of 15° tilt-in-space and recline angles on the fluctuation of shear forces exerted on the buttocks. [Participants and Methods] The participants were 11 healthy adult males. The parameters of the shear forces were the parallel and perpendicular forces exerted on the buttocks as measured by a force plate. The two conditions tested were T0R100-130 and T15R100-130. The tilt-in-space angles were set to 0° and 15° in the T0R100-130 and T15R100-130 conditions, respectively. The reclining angles were determined to be 100° to 130° in both conditions. [Results] Upon comparing the two conditions, the parallel and the perpendicular forces exerted on the buttocks in the T15R100-130 condition were significantly lower than those in the T0R100-130 condition in all positions of back support. Upon comparing the fluctuation values of the parallel and perpendicular forces, those applied in the T15R100-130 condition were significantly higher than those in the T0R100-130 condition. [Conclusion] These results suggest that the fluctuation of shear forces exerted on the buttocks could be decreased by using a combination of 15° tilt-in-space and reclining functions.

Design and Multi-Objective Optimization of a Dexterous Mobile Parallel Mechanism for Fusion Reactor Vacuum Vessel Assembly

The present paper proposed a newly designed dexterous mobile parallel mechanism for fusion reactor vacuum vessel assembly, the robot system has advantages in terms of compact design, the capability to carry out heavy-duty machining tasks, is easy to evacuate, and has less space occupation than other robot systems in existence. Despite different robot systems having been studied in the fusion reactor, there is still a lack of research on mechanism development for vacuum vessel assembly, which is attractive to future fusion reactors. In the fusion reactor, the robot systems will carry out different tasks, such as welding and machining. The assembly tasks of the vacuum vessel will be performed from inside of the vacuum vessel on-site. Then the paper introduced the single-objective and multi-objective optimization design of the proposed mechanism, the optimized objective was considered to be a combination of parallel mechanism dynamic machining force, dexterity, stiffness and workspace volume. The design variables were derived from the geometry of the fixed and movable platforms, which include mass, inertia, the sizes of the platforms, and distances between universal joints located on the platforms. In the multi-objective optimization, non-dominated sorting genetic algorithm II was adopted and different trajectories were designed to simulate the machining process, which further turns the local optimization problem into a global optimization problem. Finally, the optimized results were extracted and analyzed. Simulation results indicated the effectiveness of the proposed multi-objective optimization approaches and multi-objective optimization was found to be more reliable than single-objective optimization.

Particle actuation by rotating magnetic fields in microchannels: a numerical study.

Magnetic particles confined in microchannels can be actuated to perform translation motion using a rotating magnetic field, but their actuation in such a situation is not yet well understood. Here, the actuation of a ferromagnetic particle confined in square microchannels is studied using immersed-boundary lattice Boltzmann simulations. In wide channels, when a sphere is positioned close to a side wall but away from channel corners, it experiences a modest hydrodynamic actuation force parallel to the channel walls. This force decreases as the sphere is shifted toward the bottom wall but the opposite trend is found when the channel is narrow. When the sphere is positioned midway between the top and bottom channel walls, the actuation force decreases as the channel width decreases and can reverse its direction. These phenomena are elucidated by studying the flow and pressure fields in the channel-particle system and by analyzing the viscous and pressure components of the hydrodynamic force acting on different parts of the sphere.

Predicting Orbital Resonance of 2867 Šteins Using the Yarkovsky Effect

While gravitational forces have the largest impact on asteroid orbit determination, thermal forces such as the Yarkovsky and YORP effects also perturb asteroid orbits. We analyzed the impact of these thermal effects on the orbit of asteroid 2867 Šteins, an E-type asteroid measuring five kilometers in diameter. The orbit of Šteins lies within the range of a Kirkwood Gap, a region devoid of asteroids because of Jupiter’s gravitational pull. Given that thermal effects can perturb asteroids of similar properties, we sought to determine whether the Yarkovsky effect would push Šteins into a Kirkwood Gap within 50,000 years. Based on Šteins’ location and size, we hypothesized that the Yarkovsky effect will push Šteins into a Kirkwood gap. We computationally generated a thermal map of Šteins to approximate the Yarkovsky force and YORP torque. Analysis of the thermal map yielded an average Yarkovsky force parallel to velocity of -0.714 N and acceleration of -5.22 x 10-15 m/s2. The torque parallel to the angular velocity due to the YORP effect was 4.680 N m, with an angular acceleration of 1.217 x 10-20 rad/s2. We inputted the calculated Yarkovsky force into NASA’s GMAT to model the resulting change to Šteins’ orbit and found that the Yarkovsky force decays the semi-major axis of Šteins by 16.4 km in 242.2 years, and up to 5,365 km in 50,000 years within 95% confidence. This perturbation is unlikely to transfer Šteins into a Kirkwood Gap.

The influence of laser treatment of aluminum-magnesium alloy surface on the ”self-assembly” of nanoparticles during the evaporation of colloidal solution

Establishing the characteristics of the self-assembly of micron and sub-micron particles when colloidal solution droplets evaporate from solid surfaces is an urgent problem. This is explained by the possibility of using these structures obtained by droplet technologies to create and optimize the production of direct and indirect liquid cooling devices, electronic and sensor working boards, current-conducting coatings, optical crystals, and chemo sensors. The method used in this study for processing of metals and alloys by laser radiation is prospective for controlling the processes at the liquid/gas/solid interface. This article aims to analyze the effect of laser processing of the widely used in the industry aluminum-magnesium alloy on the formation of a layer of particles during the droplet evaporation of colloidal solutions. The samples’ surfaces were processed by two methods: polished by tumbling and nanosecond laser pulses. The geometric parameters of the droplets of colloidal solutions evaporating from the samples’ surfaces were determined by the shadow method. To process the obtained shadow images, the Young — Laplace method was used. Using a scanning electron microscope, the authors have received the images of the particles’ layers formed due to the droplet evaporation of colloidal solutions. The experimental studies reveal the effect of texture formed on aluminum-magnesium alloy sample on the morphology of the layer of polystyrene nanoparticles during the droplet evaporation of colloidal solutions. Due to the self-assembly of particles, solid ring-like sediments are formed, which are elongated under the action of the capillary force parallel to the motion vector of the laser beam (when creating the texture). When the solvent evaporated from the solution droplet on the textured surface, in addition to the rings, a homogeneous layer of polystyrene particles was formed. This refers to the droplet evaporation of the solution. The results show that with an increase in the concentration of particles in the solution, the sizes of radial cracks on the rings formed due to particle deposition increase. There were no cracks on the rings at a relatively low volume concentration of particles.

Nanomechanics of self-assembled DNA building blocks

DNA has become a powerful platform to design functional nanodevices. DNA nanodevices are often composed of self-assembled DNA building blocks that differ significantly from the structure of native DNA. In this study, we present Flow Force Microscopy as a massively parallel approach to study the nanomechanics of DNA self-assemblies on the single-molecular level. The high-throughput experiments performed in a simple microfluidic channel enable statistically meaningful studies with nanometer scale precision in a time frame of several minutes. A surprisingly high flexibility was observed for a typical construct used in DNA origami, reflected in a persistence length of 10.2 nm, a factor of five smaller than for native DNA. The enhanced flexibility is attributed to the discontinuous backbone of DNA self-assemblies that facilitate base pair opening by thermal fluctuations at the end of hybridized oligomers. We believe that the results will contribute to the fundamental understanding of DNA nanomechanics and help to improve the design of DNA nanodevices with applications in biological analysis and clinical research.

Impact of ion temperature anisotropy on 2D edge-plasma transport

Abstract A model of ion temperature anisotropy for 2D plasma transport in the scrape-off layer (SOL) of tokamaks is described and implemented in the UEDGE fluid transport code. Two ion energy equations are used to describe the evolution of the separate parallel and perpendicular ion temperatures. The temperature anisotropy generates viscous forces in both parallel and perpendicular directions that modify the parallel force balance equation and add an additional cross-magnetic-field drift velocity. Using the full set of UEDGE plasma and neutral equations (particle continuity, momentum, and energy), simulations are performed for both a 1D poloidal case and a 2D (radial and poloidal) single-null tokamak geometry case to highlight the 2D effects. The results show that ion parallel flows near the magnetic X-point in a comparatively low collisionality regime can be overestimated by the standard isotropic Braginskii model. The 2D ion temperature anisotropy varies substantially near the X-point and also near the divertor target plates, due to ionization sources. Moving radially outwards at the outer midplane, the anisotropy decreases between the core boundary and the magnetic separatrix and then it increases while moving across the SOL to the chamber wall.

A solar regenerated liquid desiccant evaporative cooling system for office building application in hot and humid climate

In this paper, we provide the thermal analysis and design methodology of a liquid desiccant assisted dew point indirect evaporative cooling system. The purpose of the system is to serve as an alternative for conventional vapour-compression based building air conditioning systems in providing satisfactory human thermal comfort conditions in the hot and humid climatic regions. The main features of the study are the following: i) novel incorporation of a forced parallel flow direct solar regenerator and a dew point indirect evaporative cooler within the same air conditioning unit; ii) detailed thermal modelling of each of the system components with fewer simplifying assumptions compared to earlier works; iii) large cooling capacity (~18.8 TR) under harsh climate; and, iv) a comprehensive year-round case study for system operation in a hot and humid location (Kolkata, India). Our thermal model is validated with a reference model study. The maximum room air temperature predicted by the current system for year-long analysis is 26.7 °C. The thermal COP of the system for diurnal operation in the most humid month of a calendar year (July) varied between 0.40 and 0.96. The cooling system can prevent overheating of the conditioned space, as specified by ASHRAE Standard 55–2017, throughout the year.

Mixed Convective Flow of Unsteady Hydromagnetic Couple Stress Fluid Through a Vertical Channel Filled with Porous Medium

In this paper, the mixed convective flow of an electrically conducting, viscous incompressible couple stress fluid through a vertical channel filled with a saturated porous medium has been investigated. The fluid is assumed to be driven by both buoyancy force and oscillatory pressure gradient parallel to the channel plates. A uniform magnetic field of strength <i>B0</i> is imposed transverse to the channel boundaries. The temperature of the right channel plate is assumed to vary periodically, and the temperature difference between the plates is high enough to induce radiative heat transfer. Under these assumptions, the equations governing the two-dimensional couple stress fluid flow are formulated and exact solutions of the velocity and the temperature fields are obtained. The effects of radiation, Hall current, porous medium permeability and other various flow parameters on the flow and heat transfer are presented graphically and discussed extensively.

Comparison between Rafidhiya and Shuaiba Domes within the properties of Mishrif Formation in Zubair Field; the implication of structural Geology and petrophysical analyses

The current study combined both concepts of structural geology and petrophysical to understand the structural feature of Mishrif Formation and its implication on the petrophysical characterization of the formation in Shuaiba and Rafidhiya Domes (or culminations) in Zubair Field. Shuaiba and Rafidhiya are adjacent domes and these domes belong to the same Field but the domes separated by saddle may related to Basra – Zubair basement fault.
 The domes have different petrophysical properties of Mishrif Formation; consequently, influenced in water and oil saturation. Therefore, the study tries to understand the structural and petrophysical position of Mishrif Formation of the domes. The structural analysis included geometric and genetic analysis, whereas petrophysical analysis used open hole logs interpretation to determine the petrophysical characteristics (especially the distribution of porosity, permeability, and water saturation.
 It was concluded that may a variation in porosity and permeability of Mishrif Formation for Shuaiba and Rafidhiya domes because each dome was formed by a different folding mechanism effected on the petrophysical properties. The structural geology analysis detects that may be Shuaiba dome formed by bending fold mechanism (vertical force of salt structure), while Rafidhiya dome by buckling fold mechanism (parallel force of collision of Arabian and Eurasian plate). These mechanisms may directly be affected in permeability distribution, and consequently on oil and water saturation of Mishrif Formation. Thus, Shuaiba Dome has thinning in hinge area and extensional force leads to create fractures and karst phenomena, and as a result, high permeability in upper Mishrif. On the contrary, Rafidhiya Dome has a thickening feature and there is no indication of karst phenomena and low permeability. Therefore, the Mishrif of Shuaiba dome permeable and oil-saturated, while, it flooded with water in Rafidhiya Dome. The disconnection in reservoir pressure confirmed by difference in initial reservoir pressure of Mishrif Formation of Shuaiba Dome and recent reservoir pressure of Mishrif Formation of Rafidhiya Dome

Correction of height-fluctuation-induced systematic errors in polymers by AFM-based nanomechanical measurements

AFM-based nanomechanical measurements are powerful tools for the characterization of polymer composites. However, a flat surface of the samples is usually required, which restricts the wide applications of nanomechanical measurements. In this work, the height-fluctuation induced systematic errors were investigated taking polystyrene beads as the model sample. Corrections were further made based on the assumption that the components of force and deformation parallel to the sample surface can be approximately ignored. Results show the deviations of force and deformation due to height-fluctuations can be well corrected by the proposed method. Moreover, the reliability of the corrected force curves was further verified in the calculation of the mechanical properties. Young's moduli value without height-gradient dependency can be obtained by applying both Johson-Kendall-Roberts (JKR) model and Derjaguin-Muller-Toporov (DMT) model. The correction method proposed in this work can broaden the applications of AFM-based nanomechanical measurements on polymers without strict restrictions on the surface flatness.

Nucleation properties of isolated shear bands.

Shear banding, or localization of intense strains along narrow bands, is a plastic instability in solids with important implications for material failure in a wide range of materials and across length scales. In this article, we report on a series of experiments on the nucleation of single isolated shear bands in three model alloys. Nucleation kinetics of isolated bands and characteristic stresses are studied using high-speed in situ imaging and parallel force measurements. The results demonstrate the existence of a critical shear stress required for band nucleation. The nucleation stress bears little dependence on the normal stress and is proportional to the shear modulus. These properties are quite akin to those governing the onset of dislocation slip in crystalline solids. A change in the flow mode from shear banding to homogeneous plastic flow occurs at stress levels below the nucleation stress. Phase diagrams delineating the strain, strain rate and temperature domains where these two contrasting flow modes occur are presented. Our work enables interpretation of shear band nucleation as a crystal lattice instability due to (stress-assisted) breakdown of dislocation barriers, with quantitative experimental support in terms of stresses and the activation energy.

A simple analytic model of impurity leakage from the divertor and accumulation in the main scrape-off layer

Edge codes such as SOLPS-ITER find distributions of impurity ions, e.g. of C, N, Ne and Ar, in the divertor and SOL which are quite non-uniform spatially, both poloidally and radially. Poloidally, impurity ion density distributions often have strong peaks near the targets as well as a peak on/near the separatrix in the main SOL near the outside midplane. A high density of low-Z impurities near the targets is quite desirable since cold, dense divertor plasma conditions there result in very efficient radiative dissipation of power. By contrast, impurity concentration near the outside midplane separatrix is often quite undesirable since the impurity density there is essentially the boundary value for impurity levels in the confined plasma. In order to better understand the poloidal distribution of impurities in the edge plasma, a simple analytic 1D impurity fluid model, 1DImpFM, has been developed for the transport along open field lines of impurity ions in a specified fuel-plasma background. Often, the strongest parallel forces acting on impurity ions in the edge plasma are (i) FiG, the (fuel) ion temperature parallel-gradient force (‘thermal force’), and (ii) FF, the friction force between fuel and impurity ions (‘friction force’). Recently, Senichenkov et al (2019 Plasma Phys. Control. Fusion 61 045013) reported the extremely useful and informative result that the impurity ion parallel velocity calculated by the SOLPS-ITER code can be remarkably well reproduced by assuming the simple force balance FF + FiG = 0. In the present paper the basis for, and a number of basic predictions of, the 1DImpFM are reported including an assessment of the circumstances under which FF + FiG = 0 can be expected to be a good approximation. The 1DImpFM is used to elucidate the competing roles of thermal and friction forces, as they control three key features of edge impurity behavior: (a) leakage of impurity ions from the divertor, (b) the peaking of impurity density near the targets, and (c) impurity ion accumulation near the midplane separatrix; the model provides simple analytic expressions for estimating the divertor leakage rate (ions/m2/s) and impurity density peaking/accumulation (ions/m3). A subsequent paper will report comparisons of results from the 1DImpFM and from SOLPS-ITER modeling of some ITER cases with neon impurities.

The deformation characteristics and flow field around knotless polyethylene netting based on fluid structure interaction (FSI) one-way coupling

Knotless polyethylene (PE) netting is widely used in fisheries because of its excellent hydrodynamic performance and low cost. Netting deformation and the surrounding flow field distribution play an important role in determining the hydrodynamic characteristics of netting in moving water. In order to investigate the effect of solidity ratio and attack angle on drag, netting deformation, and flow field distribution through the netting, a fluid-structure interaction (FSI) model based on a one-way coupling combining the shear stress turbulent (SST) k-omega model and the large deformation nonlinear structural finite element model was evaluated. Our results showed the difference between the parallel and normal drag forces found in the present numerical model and experimental flume tank data were 9.17% and 11.58%, respectively. The mean relative error in the inclined hydrodynamic drag for different flow velocities and attack angles was 8.35%, 6.69%, and 5.37% for the nettings 1, 2, and 3, respectively. These results show that the present numerical simulation based on FSI one-way coupling can be used to examine hydrodynamic forces on netting. The flow simulation results show that there is a noticeable flow velocity decrease through the netting and a rather large velocity reduction region downstream from the netting for different attack angles. These results reveal the existence of turbulent flow due to the netting wake. It was found that the equivalent stress and total deformation increase as the flow velocity increases and solidity ratio decreases.

Derivation of the friction and thermal force for SOLPS-ITER multicomponent plasma modeling

SOLPS-ITER is a code package for tokamak plasma boundary modeling comprising the B2.5 plasma fluid code and the EIRENE neutral kinetic code. The form of the momentum balance equation, used in the SOLPS-ITER code before version 3.0.6 (and in all previous versions of SOLPS codes), was simplified due to numerical reasons—the electric field term was replaced by the electron gradient pressure term; friction and thermal force terms were derived using the trace impurity assumption. It has now been decided to switch back to the general Braginskii version of this equation. Derivation of the new form of the parallel friction and thermal force terms has been required to allow the use of the general form of the equation and allow more accurate modeling of multicomponent plasmas. The new form is based on the theoretical description of multicomponent plasma derived by V. M. Zhdanov [Plasma Phys. Controlled Fusion 44(10), 2283 (2002)]. In the present paper, a detailed derivation of these terms is presented, and their implementation into the SOLPS-ITER code package is discussed.

COMPARING METHODS FOR 3D INVERSE DYNAMICS ANALYSIS OF SQUAT LIFTING USING A FULL BODY LINKED SEGMENT MODEL

Objective: The main objective of this study was to assess the accuracy of bottom-up solution for three-dimensional (3D) inverse dynamics analysis of squat lifting using a 3D full body linked segment model. Least squares solution was used in this study as reference for assessment of the accuracy of bottom-up solution. Findings of this study may clarify how much the bottom-up solution can be reliable for calculating the joint kinetics in 3D inverse dynamics problems. Methods: Ten healthy males volunteered to perform squat lifting of a box with a load of one-tenth of their body weights. The joint moments were calculated using 110 reflective passive markers (46 anatomical markers and 64 tracking markers) and a 3D full body linked segment model. Ground reaction forces and kinematics data were recorded using a Vicon system with two parallel Kistler force plates. Three-dimensional Newton–Euler equations of motion with bottom-up and least squares solutions were applied to calculate joint moments. The peak and mean values of the joint moments were determined to check the quantitative differences as well as the time-to-peak value of the moment curves was determined to check the temporal differences between the two inverse dynamics solutions. Results: Significant differences (all [Formula: see text]-[Formula: see text]) between the two inverse dynamics solutions were detected for the peak values of the hip (right and left sides) and L5–S1 joint moments in the lateral anatomical direction as well significant differences (all [Formula: see text]-[Formula: see text]) were detected for the peak and mean values of the L5–S1 joint moment in all anatomical directions. Moreover, small differences (all [Formula: see text]) were detected between the two inverse dynamic solutions for the calculated lower body joint moments. Conclusions: The findings of this study clarified the disadvantages of the straightforward solutions and demonstrated that the bottom-up solution may not be accurate for more distal measures from the force plate (for hip and S1–L5) but it may be accurate for more proximal joints (ankle and knee) in 3D inverse dynamics analysis.

Stiffness modeling and force mapping analysis of hybrid-limb six-axis force sensor

To meet the needs of large load and high reliability measurement under complex working conditions and downsize the outline of six-axis force sensor as much as possible, the design concept of hybrid limb is proposed to the design of parallel six-axis force sensor. A kind of heavy-load-bearing flexible integrated six-axis force sensor with hybrid limbs is proposed. The proposed force sensor adopts a hybrid-limb configuration integrating eight measuring redundant limbs and four load-bearing limbs. It is capable of measuring 5500 N vertical force, 3000 N horizontal force, 160 N·m moment about the vertical axis, and 130 N·m moment about the horizontal axis. Based on the superposition principle under small deformation, the whole stiffness matrix of force sensor and the analytical mapping relation are constructed, respectively. The accuracy of the theoretical modeling is verified by the stress analysis of the designed sensor using finite element method software ANSYS. Finally, the prototype is calibrated, and the results show that it has good linearity.

Influence of Impact Velocity on the Residual Stress, Tensile Strength, and Structural Properties of an Explosively Welded Composite Plate.

This study aimed to analyze the effect of the impact velocity of a Zr 700 flyer plate explosively welded to a Ti Gr. 1/P265GH bimetallic composite on the residual stress formation, structural properties, and tensile strength. The residual stresses were determined by the orbital hole-drilling strain-gauge method in a surface layer of Zr 700 in as-received and as-welded conditions. The analysis of the tensile test results based on a force parallel to interfaces was used to propose a model for predicting the yield force of composite plates. Compressive residual stresses found in the initial state of the Zr 700 plate were transformed to tensile stresses on the surface layer of the welded Zr 700 plate. A higher impact velocity resulted in higher tensile stresses in the Zr 700 surface layer. To increase the resistance of the composite plate to stress-based corrosion cracking, a lower value of impact velocity is recommended in the welding process.