Center Of Mass Research Articles

Preliminary CFD simulations of a lab-scale novel design of a particle receiver for CSP applications

In the present work, a preliminary CFD analysis of a novel design of particle receiver for CSP applications was performed. The particle receiver is a new lab-scale prototype consisting in a thin fluidized bed in which the walls are made of glass to permit thermal radiation to pass through. The working fluid is air and the thermal performance has been studied for the case in which i) only gas flows through the receiver (no particles) and ii) particles are placed in the receiver. The addition of the particles enhances the heating process by increasing the heat transfer coefficient from the heated wall to both the bed of particles and the gas resulting in an increase of more than 55% in the air temperature at the outlet of the receiver. Then, the bed dynamics have been studied in detailed as a function of the superficial gas velocity and the static bed height of the system. The analysis comprises the time evolution of the temperature of the gas and solid phases, the position of the centre of mass (that can be increased by more than 25% during the heating process) and the bubble characteristics. It has been found that when the gas velocity is increased by 66% the average temperature of the solids is only decreased 10%; while, for the static bed height, when the number of particles is increased 3 times the average temperature of the particles is increased by 18%.

Walking kinematics of ants carrying food in the mandibles vs. gaster

The locomotor behavior of an animal strongly depends on the distribution of its body mass. Whenever changes occur in this distribution, the displacement of the body center of mass (CoM) may lead to a loss of balance. Ants are an interesting biological model to investigate how an animal copes with such changes because, when they transport food, their CoM may be displaced from its usual position. We studied the ant Formica rufa whose diet consists mainly in liquid food, stored in the abdomen, but which also includes prey transported in the mandibles. We investigated the kinematics of locomotion of the same individuals while walking unloaded and while transporting food internally or externally. We found that the kinematics of locomotion slightly differed in the two types of transport. Ants transporting food in their mandibles adopted a more erect posture and tended to be more often in static instability than ants transporting food internally. In addition, the amplitude of the vertical oscillations of their CoM was higher, which led to a jerky locomotion. However, due to their erect position, the position of their overall CoM was actually not different from that of unloaded ants. Finally, the mechanical work achieved by ants to rise and accelerate their CoM was smaller in ants transporting food internally than in ants transporting food externally or in unloaded ants. This suggests that the morphology of F. rufa could make the transport of food in the gaster more mechanically efficient than the transport of food in the mandibles.

Exploring optimal sensitivity of lepton flavor violating effective couplings at the e+e− colliders

We analyze lepton flavor violation (LFV) using the Standard Model effective field theory (SMEFT) framework at the future lepton colliders. Our focus is on the associated production of tau lepton with electron/muon at the electron-positron (e+e−) colliders, related to four-Fermi SMEFT effective operators. In accordance with the upper limits on effective couplings from lepton flavor violating tau decays, we conduct a cut-based analysis to achieve sufficient signal significance. We utilize the optimal observable technique (OOT) to estimate the optimal sensitivity of the effective couplings. The impact of electron beam polarization and the interplay of signal and background in enhancing the optimal sensitivity of the effective couplings are discussed in detail. We find that the sensitivity of flavor-violating effective couplings is enhanced by order of one for 3 TeV center-of-mass (CM) energy and 1000 fb−1 integrated luminosity at the e+e− colliders. Published by the American Physical Society 2024

Pitching kinematics have direct and indirect effects on pitch location in NCAA baseball.

Kinematics and release parameters are important factors of throw location, yet an understanding of their relationship has yet to be achieved. This study sought to explore this relationship. Kinematic data were collected for seventy-seven collegiate pitchers. Fifty-seven kinematic parameters were included in path analyses for horizontal (HPL) and vertical plate locations (VPL). Release angles were set as mediating variables (MED) between independent (IV) and dependent (DV) variables. Eleven kinematic variables directly (13 indirectly) affected VPL, while 23 directly affected HPL (10 indirectly). Linear mixed models revealed that lateral trunk flexion at ball release (BR) (R2=.908, BIC=-598, ICC=.528) best explained VPL. Trunk flexion at foot contact (FC) (R2=.944, BIC=-607, ICC=.776), mediolateral centre of mass (COM) displacement at FC (R2=.974, BIC=-573, ICC=.918), and BR (R2=.967, BIC=-593, ICC=.865), and pelvis rotation at BR (R2=.965, BIC=-588, ICC=.895) models were identified for HPL. Results indicate the relationship between pitching kinematics, release conditions, and throw location is complex. Biomechanics can influence release parameters, which in turn impacts throw location. This work may serve to understand better how biomechanics influence performance.

Decreased Knee Extensor Torque During Single-Limb Stance: A Computer Simulation Study of Compensations and Consequences

Background/Objectives: For over 50 years, it has been suggested that the plantar flexors and hip extensors can compensate for weak knee extensors and prevent collapse of the leg during a single-limb stance. However, the effects of these compensations have not been studied thoroughly. The purpose of this computer simulation study was to determine, for a given posture, the hip and ankle net joint torque (NJT) required to prevent leg collapse due to systematic decreases in knee NJT and to determine the effect of these compensations on the horizontal ground reaction force. Methods: Single-limb stance was simulated using a static, multisegmented model in eight different postures. For each posture, the knee NJT was systematically decreased. The ankle and knee NJT necessary to prevent lower extremity collapse, along with any net horizontal ground reaction forces, were then calculated. Results: Decreases in knee NJT required linear increases in ankle and hip NJT to prevent the limb from collapsing. There were greater increases in ankle NJT compared to hip NJT, resulting in posteriorly-directed horizontal ground reaction forces. While the magnitudes were different, these findings applied to all postures simulated. Conclusions: For a given posture, ankle and hip NJTs can compensate for a decrease in knee NJT. However, this resulted in a horizontal ground reaction force, which was in the posterior direction for all the postures examined. This horizontal ground reaction force would induce an acceleration on the body’s center of mass that, if not accounted for, could have deleterious effects on achieving a task objective.

STABILOMETRY AS A METHOD FOR DIAGNOSIS AND TRAINING OF THE HUMAN POSTURAL BALANCE

Introduction. Posture is intrinsically linked to balance and the maintenance of an upright body position. Achieving stable posture and upright movement relies on the body’s complex neuromuscular regulation system. In clinical practice, stabilometry is employed to assess balance function and postural control. This study aims to synthesize data on the effectiveness of stabilometry as a diagnostic tool for evaluating postural balance and as a training method to enhance it. Materials and Methods. An analysis of 45 sources from databases including Academia.edu, PubMed, ResearchGate, and Google Scholar over the past decade was conducted using Keywords: posture, stabilometry, and postural balance. Results. Stabilometry is a contemporary technique for tracking the projection of the body’s center of mass on the support plane, as well as its fluctuations while standing or performing diagnostic tests and medical procedures. This review examines the application of stabilometry both for diagnosing balance and as a supplementary training method to improve postural balance in athletes and individuals with musculoskeletal disorders. Stabilometry results have highlighted correlations between stomatognathic system dysfunctions and musculoskeletal issues and demonstrated the positive impact of occlusal adjustments on body balance. As such, stabilometry can serve as an effective diagnostic tool for assessing posture in a dental clinic, useful for both diagnostic assessments and evaluating preventive or treatment outcomes. Conclusions. Training that combines myogymnastic exercises with stabilometric platform exercises significantly improved balance and functional efficiency in patients, as shown through stabilometric analysis. A key area of ongoing research is the interplay between posture and other bodily systems, particularly the stomatognathic system, which may be pivotal in treating temporomandibular joint dysfunction.

Experimental Study on the Acceleration Amplification Ratio of Cable Terminations for Electric Power Facilities

Among national infrastructure facilities, electric power facilities are very important sites that must maintain their functions properly even during a natural disaster or during social crises. Therefore, seismic design is required when necessary for major electric power facilities that have a significant impact when damaged in the event of an earthquake. In electric power facilities, bushings are generally installed in devices or structures. Therefore, ground acceleration can be amplified through devices, such as transformers, or sub-structures. Among various electric power facilities, cable terminations are representative cantilever-type substation facilities consisting of a bushing, a sub-structure, and support insulators. The bushings of cable terminations are generally made of porcelain or fiber-reinforced plastic (FRP) materials, and they may have different dynamic characteristics. This study attempted to estimate the acceleration amplification ratio in the main positions of cable terminations considering the materials of bushings. For two cable terminations with different specifications and bushing materials, three-axis shake table tests were conducted in accordance with IEEE 693, which includes a seismic performance evaluation method for a power substation facility. The acceleration amplification ratios at the top of the bushing, mass center, and top of the support structure were estimated using the acceleration responses of each cable termination. They were then compared with the acceleration amplification factors presented in design standards. Consequently, the acceleration amplification ratio of cable termination with an FRP bushing was lower than that of the cable termination with a porcelain bushing.

Nonequilibrium Molecular Dynamics Method to Generate Poiseuille-Like Flow between Lipid Bilayers.

There are various flows inside and outside cells in vivo. Nonequilibrium molecular dynamics (NEMD) simulation is a useful tool for understanding the effects of these flows on the dynamics of biomolecules. We propose an NEMD method to generate a Poiseuille-like flow between lipid bilayers. We extended the conventional equilibrium MD method to produce a flow by adding constant external force terms to the water molecules. Using the Lagrange multiplier method, the center of mass of the lipid bilayer is constrained so that the flow does not sweep away the lipid bilayer, but the individual lipid molecules fluctuate. The temperature of the system is controlled properly in the solution and membrane by using the Nosé-Hoover thermostat. We found that the flow velocity increases linearly as the applied external force term increases. It is possible to estimate the appropriate value of acceleration to generate a flow with an arbitrary velocity using this proportional relation once a single short MD simulation is performed. We also found that the flow between two lipid bilayers is slower than the analytical solution of the Navier-Stokes equations between rigid parallel plates due to the interactions between water molecules and the membrane. This method can be applied not only to a flow on lipid membranes but also to a flow on soft surfaces generally.

Use of the Brief-BESTest partially instrumented with accelerometry to detect balance deterioration in middle-age

BackgroundMost standardized balance tests cannot detect subtle balance deterioration in middle age, or identify those at higher risk for accelerated balance decline due to a ceiling effect.AimsTo determine whether the Brief Balance Evaluation Systems Test (Brief-BESTest), partially instrumented with accelerometry, can detect balance deterioration in middle age and identify individuals with poor balance.MethodsWe studied young (25.3 ± 2.3 years), early middle-aged (47.7 ± 2.6 years), and late middle-aged adults (60.6 ± 3.6 years), with 25 participants in each age group. Subjects wore an accelerometer on their lower back while performing the Brief-BESTest. Balance measurements included the Brief-BESTest total and sub-measures scores, and postural sway during the Brief-BESTest standing tasks, calculated by the 95% confidence ellipse trajectory of the center of mass (COM-95% ellipse).ResultsCompared to the two middle-aged groups, young adults had better total Brief-BESTest and sub-measures scores, apart from the Stability-in-Gait sub-measure, and less postural sway during the Sensory-Orientation sub-measure. The total Brief-BESTest scores as well as the Biomechanical-Constraints and Sensory-Orientation sub-measures differed also between early and late middle-aged adults. Both the Brief-BESTest total scores and the Sensory-Orientation postural sway values demonstrated increased variation with age, allowing to identify subjects with poor balance. A moderate negative correlation (r = -0.43) was found between the Brief-BESTest total score and the COM-95% ellipse size, and a moderate agreement (k = 0.56) in identifying subjects with poor performance in the early but not the late middle age group.ConclusionsThe Brief-BESTest test combined with accelerometry could be a suitable screening tool to identify middle-aged people with early balance deterioration and potentially identify those with poor balance and a possible higher risk for falls. Clinicians and policymakers can use our findings to implement balance assessment programs in patients < 65 years, leading to preventive strategies before the risk increases.

Mechanical attributes of fractal dragons

Fractals are ubiquitous natural emergences that have gained increased attention in engineering applications, thanks to recent technological advancements enabling the fabrication of structures spanning across many spatial scales. We show how the geometries of fractals can be exploited to determine their important mechanical properties, such as the first and second moments, which physically correspond to the center of mass and the moment of inertia, using a family of complex fractals known as the dragons.

Spindle vibration induced optical performance deterioration and its trans-scale characterization for diamond turned large-aperture optics

In ultra-precision diamond turning of large-aperture optics, the spindle vibration (SV) would cause a deterioration of optical performance. To discuss this issue, the spindle vibration was first excited by a series of designed mass center errors for diamond turning of large-aperture optics. Then, a trans-scale characterization was developed to reveal its dynamic behaviors by combining a white light interferometer and laser interferometer. Next, the amplitude variations were quantitatively evaluated by surface texture parameters and the scale bandwidth was revealed through power spectrum density (PSD). Finally, the point spread function (PSF), encircled energy ratio (EER), and modulation transfer function (MTF) were analyzed and compared. The results indicated that, with the increased SV, Sq and Sz increased and Ssk and Sku showed a transition from skew to normal height distribution. PSD showed that spindle vibration mainly affected the large-scale components rather than the small-scale components. The shape of PSF changed from a standard ring to a dispersed half ring. At the 1 µm radius of the Airy disk, the EER decreased from 82.0% (no SV) to 27.5% (high SV). At the scale of 200mm−1, the MTF decreased from 0.84 (no SV) to 0.44 (high SV). The work provides a fundamental understanding of the evolutionary mechanism of spindle vibration induced optical performance deterioration.

Orbital motion control of an electrically charged spacecraft

In this paper, the orbital motion of an electrically charged spacecraft in the gravitational and magnetic fields of the Earth is investigated. The “direct magnetic dipole” is considered as a model of the geomagnetic field. The nonlinear non-autonomous system of differential equations of motion of the spacecraft center of mass in the Cartesian and spherical coordinate systems is derived. The analytical study of the influence of the Lorentz force on the orbital motion of a charged spacecraft is carried out. The approximate solution of the differential system is found. The results of numerical simulation of the spacecraft orbital motion based on the derived system of differential equations are presented. The analytical and numerical solutions are compared. The problem of stabilizing the spacecraft’s center of mass in the orbital plane is considered. Feedback control methods based on the use of jet engines are proposed. The technical justification of the proposed control methods is carried out. As a result, stabilization of an electrically charged spacecraft in a small neighborhood of the plane of the initial orbit is achieved. The motion of a spacecraft with a variable electric charge is considered. Methods of controlling orbital motion due to low thrust as a result of the Lorentz force effect are proposed.

Benchmarking the non-flow contributions to the elliptic flow parameter (v2) in proton-proton collisions

Abstract This manuscript reports on the elliptic flow parameter, v 2 , in proton-proton (p–p) collisions using PYTHIA8 event generator simulations. The typical event plane (EP) method v 2 (EP) as the one used for the real data analysis has been adopted to measure the v 2 of particles composed of different quark flavors, and produced at mid-pseudorapidity ∣η∣≤1 at center-of-mass energy s = 200 GeV and s = 13 TeV. The event plane has been constructed using the soft-charged particles with transverse momentum ( p T &lt; 2 GeV/c) produced in various η ranges. The pseudorapidity gap technique (Δη) between the particle of interest and the soft charged particles contributed to the event plane constructions has been utilized to benchmark the non-flow contributions. The v 2 π ± , π 0 , v 2 J ∕ ψ , ϒ , K , D , B , and the v 2 γ dir show similar pattern dependence on the transverse momentum for the same Δη, at both s = 200 GeV and s = 13 TeV. At each center-of-mass energy, the measured v 2 shows obvious dependence on the quark flavor contents where v 2 γ dir ≤ v 2 J ∕ ψ , ϒ , K , D , B ≤ v 2 π ± , π 0 for similar Δη gap. The measured v 2 shows slightly higher values at smaller s for particles of similar values of Δη gaps, particularly at small Δη gap. The measured v 2 for all particles shows systematic decreases with increasing the Δη gap as expected from the previous experimental results. Because PYTHIA8 simulations do not incorporate final state interactions, the v 2 ( EP ) values reported here primarily reflect the non-flow contributions and its dependence on the quark contents, pseudorapidity gap as a function on p T at each center of mass–energy. These contributions should be carefully subtracted from the signal in real data analysis that employs the same event plane determination algorithm.

Dynamic Simulation Model of Miniature Tracked Forestry Tractor for Overturning and Rollover Safety Evaluation

This study proposes a method to construct a dynamic simulation model to implement the lateral overturning and backward rollover characteristics of an actual tractor. Based on theoretical analysis, factors affecting these characteristics are identified, which include tractor weight, track width, wheelbase, location of mass center, weight distribution, heights of front and rear axles, and geometric shapes. The location of the mass center of the actual tractor is measured based on the standard test procedure set by the International Organization for Standardization, and the remaining influencing factors are derived through measurements. A three-dimensional (3D) model of the tractor is constructed to reflect all these factors. Additionally, a simulation model utilizing this 3D model is developed using a commercial dynamic simulation software program. The ability of the model to simulate the overturning and rollover characteristics of the actual tractor is verified by comparing the static sidelong falling angle and minimum turning radius with those of the actual tractor. The errors between the characteristics of the actual tractor and those of the 3D model and dynamic simulations are shown to be less than 5%, thus indicating that the proposed method can effectively simulate the overturning and rollover characteristics of the actual tractor.

Center of mass kinematic reconstruction during steady-state walking using optimized template models.

Template models, such as the Bipedal Spring-Loaded Inverted Pendulum and the Virtual Pivot Point, have been widely used as low-dimensional representations of the complex dynamics in legged locomotion. Despite their ability to qualitatively match human walking characteristics like M-shaped ground reaction force (GRF) profiles, they often exhibit discrepancies when compared to experimental data, notably in overestimating vertical center of mass (CoM) displacement and underestimating gait event timings (touchdown/ liftoff). This paper hypothesizes that the constant leg stiffness of these models explains the majority of these discrepancies. The study systematically investigates the impact of stiffness variations on the fidelity of model fittings to human data, where an optimization framework is employed to identify optimal leg stiffness trajectories. The study also quantifies the effects of stiffness variations on salient characteristics of human walking (GRF profiles and gait event timing). The optimization framework was applied to 24 subjects walking at 40% to 145% preferred walking speed (PWS). The findings reveal that despite only modifying ground forces in one direction, variable leg stiffness models exhibited a >80% reduction in CoM error across both the B-SLIP and VPP models, while also improving prediction of human GRF profiles. However, the accuracy of gait event timing did not consistently show improvement across all conditions. The resulting stiffness profiles mimic walking characteristics of ankle push-off during double support and reduced CoM vaulting during single support.

Controller design and experimental validation of walking for a musculoskeletal bipedal lower limb robot based on the spring-loaded inverted pendulum model

In the study of PAM (McKibben-type pneumatic artificial muscle)-driven bipedal robots, it is essential to investigate whether the intrinsic properties of the PAM contribute to achieving stable robot motion. Furthermore, it is crucial to determine if this contribution can be achieved through the interaction between the robot’s mechanical structure and the PAM. In previous research, a PAM-driven bipedal musculoskeletal robot was designed based on the principles of the spring-loaded inverted pendulum (SLIP) model. The robot features low leg inertia and concentrated mass near the hip joint. However, it is important to note that for this robot, only the design principles were based on the SLIP model, and no specialized controller was specifically designed based on the model. To address this issue, based on the characteristics of the developed robot, a PAM controller designed also based on the SLIP model is developed in this study. This model-based controller regulates ankle flexion PAM to adjust the direction of the ground reaction force during robot walking motion. The results indicate that the proposed controller effectively directs the leg ground reaction force towards the center of mass during walking.

Accounting for intensity variation within pixels of Shack-Hartmann wavefront sensors

The accuracy of centroiding algorithms in Shack-Hartmann wavefront sensing is limited by the implicit approximation of uniform pixel illumination. Iterative centroiding algorithms are further limited by the consideration of full pixels to define the image domain for centroiding. Here, we demonstrate two practical and complementary approaches to mitigate both these sources of error. First, we consider partial or ‘fractional’ pixels to maintain centroiding area symmetry around the center of mass. Secondly, we propose methods to perform piece-wise polynomial interpolation to calculate intensity distribution within pixels, which is then used to estimate the centroid within each pixel area. This approach that accounts for intensity non-uniformity across pixels notably reduces centroid errors up to a factor of 5 across lenslet image widths ranging from 1.33 to 3.10 pixels full-width-half-maximum (FWHM). Consequently, wavefront sensing errors decrease from 14 % to 4 %, on average, for FWHM = 1.35 pixels, demonstrating a substantial benefit when the number of pixels per lenslet is minimized to enhance the signal-to-noise ratio or increase frame rate.

Control of the Motion of an Inverted Spherical Pendulum on a Moving Base. Hybrid Impact Approach

A new hybrid method for the construction of control actions of a linear control system with constant coefficients is considered in this paper. It is assumed in this paper that a part of the discussed system meets some conditions. Some states of the main system are considered to be control actions for a subsystem for which and LQR stabilizer is acquired. Then, those control actions of the subsystem are used to construct the control actions for the main system. In the problem of controlling the motion of a complex linear system of an inverted spherical pendulum on a moving base, a new approach to the construction of control actions (hybrid action method) was used. It is assumed that a component of the complex system under discussion satisfies certain conditions. The inertial forces at the center of mass of the base of the composite system are considered to be the controlling influences on the inversion of the pendulum, for which the LQR stabilizer was purchased. The determined internal control actions on the inverted pendulum are then used to construct external control actions on the base of the composite system. In the end, a numerical analysis was carried out.

On the dynamics of transporting rolling cylinders

AbstractA common, yet hazardous, method of transporting cylindrical tanks used to carry compressed gas involves rolling both tanks at opposite angles of inclination to the vertical. By propelling one of the tanks while maintaining point contact between the tanks, both tanks can be moved such that their centers of mass move in a straight line. The purpose of this paper is to explore this locomotion mechanism. First, the problem of supporting an inclined cylinder in point contact with a rough surface is examined. The analysis shows that dependent on the geometry of the cylinder and the coefficient of static friction, a wide range of angles of inclination are feasible. The presence of non-integrable constraints on the motion of the rolling cylinder is explored using the concept of a holonomy. The problem of transporting two cylinders using the aforementioned mechanism is then analyzed with the help of Frobenius’ integrability criterion for constraints and numerical simulations. The results show the mechanical advantage of transporting a pair of cylinders, the range of possible angles of inclination, and the forces needed to sustain the motion.

Optomechanical motions of gold dimer’s spin, rotation and revolution manipulated by bessel beam

The optomechanical motion of a gold nanoparticle (GNP) dimer—a pair of optically bound GNPs—in fluid, manipulated by a Bessel beam, is theoretically studied using the multiple multipole (MMP) method. Since a Bessel beam possesses orbital angular momentum (OAM) and spin angular momentum (SAM) simultaneously, complicated rigid-body motions of the dimer can be induced. The mechanism involves the equilibrium between the optical force with the reactive drag force exerted by the fluid. Our results demonstrate that the dimer rotates around its center of mass (COM), while the COM performs an orbital revolution around the optical axis. Additionally, each individual GNP undergoes spinning. The directions of the GNPs’ spin and the orbital revolution of COM depend on the handedness and the order (topological charge) of Bessel beam, respectively. Nevertheless, the rotation direction of the dimer depends on the size of GNP. In the case of a smaller dimer, the direction of dimer’s rotation with respect to the COM is consistent with the handedness of the light. Conversely, a larger dimer performs a reverse rotation, accompanied by a precession during the orbital revolution. There are multiple turning points in the radius of the GNP for the alternating rotation of the dimer caused by positive or negative optical torque. Our finding may provide an insight to the optomechanical manipulation of optical vortexes on the motions of GNP clusters.