Continuous Force Research Articles

Finite-time stabilization with arbitrarily prescribed settling-time for uncertain nonlinear systems

This paper considers global finite-time stabilization with arbitrarily prescribed settling-time for nonlinear systems with unknown control directions and other serious uncertainties. In view of the challenge of the problem and the scarcity of available methods, several motivating facts are offered by elaborating examples and counterexamples. The facts disclose the potential obstructions in pursuing continuous controllers and force us to resort to powerful discontinuous feedbacks. By combining the method of adding a power integrator, homogeneous approach and desingularization technique, a state-feedback controller with design parameters is first proposed. Then a switching logic is proposed to tune the parameters online, wherein two types of switching sequences are involved to suppress serious uncertainties and to guarantee arbitrarily prescribed settling-time, respectively. Also, fixed-time stabilization is considered as a special case, aiming at the trade-off between arbitrary rapidness and high control cost. Two examples are provided to demonstrate the effectiveness of the proposed strategy.

A Continuous Contact Force Model for the Impact Analysis of Hard and Soft Materials

A Continuous Contact Force Model for the Impact Analysis of Hard and Soft Materials

Modeling rigid filament interaction under oscillatory flow using immersed boundary method

The thread-like biological filament structures can enhance many processes such as fluid transport, locomotion, defence against foreign bodies etc. Researchers have tried to mimic these filament movements to improve fluid transport, mixing, drug delivery for microfluidic applications. These biological filaments can be modelled as slender rigid filaments which can be either active or passive. Active filaments move on their own thus causing a disruption in the fluid domain in close vicinity while passive filaments undergo motion depending upon the fluid flow past them. The dynamics of both active and passive filaments in low Reynolds number flow has immense research potential. In the case of passive filament, the nature of the incoming flow field is an important factor that affects the flow physics around the filament. This paper studies the flow dynamics of vertical and inclined passive rigid filaments in an oscillatory flow. The effect of change in flow conditions is studied by varying the Reynolds and Strouhal numbers. The simulation involves fluid-structure interaction which is implemented with the help of continuous forcing based immersed boundary (IB) method using finite volume discretization. This is a preliminary work towards modelling active filaments under different fluid flow conditions in channel in the near future.

Post-Expansion and end of treatment outcomes of semi-rapid maxillary expansion with a modified removable appliance.

Maxillary expansion is the mainstay therapy for maxillary transverse deficiency. There has been a constant search for the most effective yet biologically friendly method of maxillary expansion, alternatives being, slow, rapid and semi rapid. The purpose of this study was to explore the outcome of palatal expansion achieved using a removable plate and low continuous forces brought about by a semi rapid screw activation protocol. Retrospective study. Plaster models of 56 consecutive patients treated for maxillary expansion were obtained pre-treatment (T0), post-expansion (T1), and post fixed appliance treatment (T2). The radiographic images of the models were traced using Image J software. Linear and angular measurements were evaluated to measure transverse change. Interclass Correlation Coefficient [ICC] and Dahlberg's formula were used for reliability test. The differences in the mean values between the three duration groups [T0, T1 and T2] were analysed using Analysis of Variance (ANOVA). For multiple comparisons, a post hoc Tukey honestly significant difference (HSD) test was performed. Significant increase in inter-molar, alveolar and palatal linear widths were observed from T0 to T1 with significant relapses from T1 to T2, with an overall net gain remaining at T2. Similarly, significant increases in all angular measurements were observed from T0 to T1 with significant relapses from T1 to T2 and an overall insignificant change at T2 as compared to T0. The appliance and protocol were effective in producing transverse expansion with minimal molar and alveolar tipping.

Sandwich Integration Technique for the Pressure Sensor Detection of Occlusal Force In Vitro.

Bite force measurement is an important parameter when checking the function and integrity of the masticatory system, whereas it is currently very difficult to measure bite force during functional movement. Hence, the purpose of this study is to explore the potential technique and device for the measurement and intervention of the continuous bite forces on functional and dynamic occlusal condition. A portable biosensor by sandwich technique was designed, and the validity, reliability, and sensitivity were determined by mechanical pressure loading tests; meanwhile, the pressure signal is acquired by, and transmitted to, voltage changes by the electrical measurements of the sensors. The result is that, when the mechanical stress detection device is thicker than 3.5 mm, it shows relatively ideal mechanical properties; however, when the thickness is less than 3.0 mm, there is a risk of cracking. Mechanical stress changing and voltage variation had a regularity and positive relationship in this study. The mechanical stress-measuring device made by medical and industrial cross has a good application prospect for the measurement of bite force during function.

Dynamics Investigation on Axial-Groove Gas Bearing-Rotor System with Rod-Fastened Structure

This research report discusses the dynamic behaviors of an axial-groove gas bearings-rotor system with rod-fastened structure. The time-based dependency-compressible Reynolds equation in the gas bearing nonlinear system is solved by the differential transformation method, and the continuous gas film forces of a three-axial-groove gas bearing are obtained. A dynamic mathematical model of the rotor system with rod-fastened structure supported in two- and three-axial-groove gas bearings with eight degrees of freedom is established. The dynamic motion equation of the rod-fastened rotor system is solved by the modified Newmark-β method based on disturbance compensation, which can reduce the computing error and improve computing stability. The dynamic characteristics of the rod-fastened rotor-gas bearing system are analyzed efficiently by the diversiform unbalance responses. The influence of the position angle of the pad on the nonlinear characteristics of the rod-fastened rotor system is also studied.

A continuous contact force model for impact analysis

Hunt and Crossley proposed a general expression of the contact force in 1975. The dissipative force term of the general expression has two exponents: the exponent of indentation depth and that of velocity. Because it is almost impossible to obtain an analytical solution based on the general expression, more than twenty continuous contact models have been developed based on the simplification of the general expression. In these studies, the exponent of the indentation depth was set as 0.25, 0.5, 0.65, 1.0 or 1.5, and the exponent of the velocity was set to 1.0. This paper proposes a new continuous contact force model with arbitrary values of the exponents of the indentation depth and velocity. The model is based on the general expression of the contact force. Considering the rule of energy equivalence, an approximatedynamic equation is developed by introducing the equivalent indentation and equivalent velocity. Subsequently, a new continuous contact force model is constructed based on the system dynamic equation and approximate dynamic equation. The influences of the two exponents on the performance of the continuous contact force models are investigated by analyzing the simulation results. Moreover, the validity of the new model is demonstrated by comparing the simulation results with two published experimental datasets. The comparison also indicates that the performance of the continuous contact model can be enhanced by selecting appropriate values of the two exponents.

Dimension-reduction of stochastic wave forces and probability density evolution analysis of wave-excited pile foundation

This paper discusses the reasonable description and simulation of the continuous stochastic wave force field at probabilistic level. Firstly, in order to overcome the challenge of high-dimensional random variables inherent in the conventional Monte Carlo sampling (MCS), the dimension-reduction (DR) simulations of stochastic processes are addressed based on both the non-deterministic spectral amplitude (NSA) method and the deterministic spectral amplitude (DSA) method. In the proposed method, merely one or two elementary random variables are required to describe the continuous stochastic wave force field at the level of probability density. Simultaneously, the simulation efficiency of the proposed scheme is significantly enhanced by employing the Fast Fourier Transform (FFT) algorithm. In addition, the DR simulations for continuous stochastic wave force field are conducted in accordance with the linear Morison's equation (LME) and the nonlinear Morison's equation (NLME). Finally, the stochastic wave force field acting on a single pile foundation is generated by the proposed method, followed by the refined linear dynamic analysis and reliability assessment of the employed single pile foundation combining the probability density evolution method (PDEM). The effectiveness, accuracy and engineering practicability of the DR methods are sufficiently illustrated by comparison with the MCS methods thereafter. The analysis results also show that the DR methods are of significance robustness in reliability assessment of offshore engineering structures.

Voluntary suppression of neck reflexes during passive head-on-trunk rotations: reflex gain control versus proprioceptive feedback.

Normal subjects can completely eliminate resistance upon imposed head-on-trunk rotations when they are asked to relax. It is not, however, clear how neck reflexes to stretch can be voluntarily suppressed. Reflexive responses might be modified by adjusting the gain of the reflex loop through descending control. Theoretically, necessary corrections upon interfering disturbances during coordinated motor performance requiring the interplay of relaxation/activation may be missing if muscle relaxation is taking place exclusively by this mechanism. It has been alternatively proposed that sensory information from the periphery may be allowed to "neutralize" neck reflexes if it is fed back with opposite sign to the structures driving the reflexes. Six healthy subjects were asked to relax while subjected to head-on-trunk rotations generated by a head motor. After any initial resistance had completely subsided, the head was unexpectedly exposed to "ramp-and-hold" perturbations of up to 2° amplitude and 0.7 s duration. Resistance to stretch consistently reappeared thereupon, suggesting that stretch reflex gain had not been set to zero during the previously achieved complete relaxation. Resistance to perturbations under these circumstances was compared with the forces generated when the same ramp-and-hold displacements were delivered unpredictably to the head held stationary. A quantitative model of neck proprioceptive reflexes suppression has been thus constructed. Gain scheduling or "motor set" cannot sufficiently account for the voluntary reflex suppression during slow passive head rotations. Instead, we propose as underlying mechanism, the "neutralization" of the controlling servo by means of continuous feedback tracking displacement and force signals from the periphery.NEW & NOTEWORTHY Head stabilizing neck reflexes can be voluntarily suppressed or activated depending on the task at hand. By applying brief perturbations unexpectedly, both during passive head-on-trunk movements and at rest, we investigated the mechanism of voluntary suppression of resistance to stretch. A physiologically plausible, neuromechanical model of voluntary/reflexive interactions was constructed favoring feedback over reflex gain adjustments. Accordingly, muscle relaxation during imposed head movements is based on sensory feedback similarly to muscle contractions during purposeful movements.

The effect of two different types of forces on possible root resorption in relation to dentin phosphoprotein levels: a single-blind, split-mouth, randomized controlled trial

BackgroundThe purpose of this 2-arm-parallel split-mouth trial was to evaluate and compare the extent of possible root resorption using dentin phosphoprotein levels in gingival crevicular fluid between controlled continuous and intermittent orthodontic force groups.Materials and methodsA sample of 16 maxillary first premolars from 8 patients requiring bilateral extractions of the upper first premolars as part of their orthodontic treatment were recruited. A buccally directed continuous force of 150 g, reactivated after 28 days, was applied to the upper first premolar on one side for 8 weeks. On the contralateral first premolar, a buccally directed intermittent force (21 days on, 7 days off) of the same magnitude was applied for the same period. Gingival crevicular fluid samples were collected at the beginning of the study, 1st, 3rd, 4th and 5th week, and at the end of the study to quantify and compare dentin phosphoprotein levels in both groups.ResultsDentin phosphoprotein levels showed a higher concentration in the continuous force group than the intermittent force group in week 4 and 8 of sample collection; where the differences were statistically significant (95% CI 0.007–0.14; P < .04) and (95% CI 0.02–0.17; P < .04) respectively. No harm was observed.ConclusionsDentin phosphoprotein was found to be a useful early biomarker to detect and monitor root resorption, showing that the application of an intermittent orthodontic force caused less root resorption than a continuous force.Trial registrationNCT04825665 ClinicalTrials.gov. Registered 1 April 2021—Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04825665.

An opinion dynamics model of meta-contrast with continuous social influence forces

Opinion dynamics is the study of how opinions in a group of individuals change over time and opinion dynamics models attempt to mathematically formulate this process. This research lays the foundations for, and develops the meta-contrast influence field model, a novel opinion dynamics model based on self-categorization theory. It improves on the existing meta-contrast model by providing a properly scaled, continuous influence basis while replicating key results of the original model. This influence basis is modular in nature, allowing future research to include other competing psychological forces in the mathematical formulation of influence. This flexibility is achieved while drastically reducing computational complexity, making feasible larger models of more psychologically complex agents.

Aquatic geochemistry of a major freshwater lake in the Kashmir Himalaya: solute acquisition and denudation process in the lacustrine system.

Lakes, the main entities of lacustrine environments, are a rich archive of environmental and geogenic changes in terms of compositional variation of water and sediment. Water and sediment samples (N = 173) were collected during 2013-2014 from the Wular Lake, one oftheimportant fresh lakeswithin the Indian landmass. The study provides insights on the solutes acquisition mechanism and provenance of ionic constituents within the lake water and the sediments. Besides, the impact of catchment attributes on the lake system was in addition assessed. The hydrochemical results suggest that the chemical weathering of silicate and carbonates within the catchment shapes the lake water chemistry and characterizes the facies pattern into a hybrid type. The geochemical results of the lake sediments demonstrate that the improved abrasion rates and ensuant settling of detritus into the lake are closely linked with the prominent physical weathering over chemical weathering. The new finding of the present study is that sediments represent an unweathered basalt compositional trend, plausible provenance from mafic rocks, experiencing low to moderate degree of chemical weathering. The study found that increased encroachment within the lake catchment due to continued anthropogenic forcing is the primary source contributing the organic matter (OM) as well as the higher levels of Cl, NO3, SO4, and P to the lake. These findings corroborate with the land use-land cover changes (from the last 50years) within the lake catchment in significantly deteriorating the lake system. The study recommends that the ongoing conversion of lake peripheral areas into urban settlement and agro-horticulture land by filling activities should be restricted.

C-CSF: Accurate, robust and efficient surface tension and contact angle models for single-phase flows using SPH

In this paper we propose some important improvements related to the single-phase Smoothed Particle Hydrodynamics (SPH) simulations and available for different SPH schemes (such as Riemann SPH or δ-SPH). This model is based on the Continuous Surface Force (CSF), a volumic description of the surface tension and relies on an accurate evaluation of the local normal and curvature at the interface. In particular we show that renormalized SPH operators are necessary to both improve the stability and the accuracy of the model. We also propose a solution aiming at imposing a desired equilibrium contact angle near the contact line for the Boundary Integral Method (BIM). The proposed model is called corrected CSF (C-CSF) and is validated through static and dynamic test cases, with and without solid boundaries, showing that the proposed corrections are necessary to obtained the expected solutions.

Space Closure Rate in Mandibular Canine Retraction by Ni-Ti Closed Coil Spring: A Clinical Trial

Introduction: In Majority of patients seeking orthodontic treatment, teeth must be extracted in order to obtain proper esthetics, occlusion, and stability as well as extraction of teeth is often a need to close residual space, after the initial decrowding and aligning. Pre adjusted fixed orthodontic appliances commonly utilize sliding mechanics for space closure with different types of force delivery systems. A variety of materials have been used as force delivery systems to close spaces between teeth as in the case of canine retraction after the extraction of premolars. Among all sliding or frictionless methods of canine retraction, super-elastic nickel titanium coil spring has a particular property in producing light continuous force at a long range of action, compared with previously available materials. Nickel-titanium closed coil spring, with a continuous action, might have some advantages in fixed appliance space closure mechanics. Materials and Methods: Over the period of one year from May 2015 to April 2016, this clinical trial was carried out and A total number of 20 patients (40 quadrants), who required canine retraction into first premolar extraction sites as part of their orthodontic treatment in the Department of Orthodontics of BSMMU selected as study population. The quadrants were affixed by nickel titanium closed coil springs (medium force, Ni-Ti extension spring, Ormco) with 200gm force measured by Correx Tension Gauge. Space closure was measured by means of direct measurement from the mesial surface of mesial wing of the 2nd premolar bracket and the distal surface of distal wing of the canine bracket with digital Vernier Calipers. Results: Mean space closer rate in mandibular canine retraction was 1.07 ± 0.12 mm/month by nickel-titanium (Ni-Ti) closed coil spring method with p value&lt;0.001. Conclusion: This study revealed that space closer rate in mandibular canine retraction by nickel-titanium (Ni-Ti) closed coil spring is 1.07 ± 0.12 mm/month. Medicine Today 2021 Vol.33(2): 90-93

Establishing Task-Relevant MVC Protocols for Modelling Sustained Isometric Force Variability: A Manual Control Study.

The present study examined how prevalent methods for determining maximal voluntary contraction (MVC) impact the experimentally derived functions of graded force-force variability. Thirty-two young healthy subjects performed continuous isometric force tracking (20 s trials) at 10 target percentages (5–95% MVC) normalized to a conventional discrete-point (n = 16), or sustained (n = 16) MVC calculation. Distinct rates and magnitudes of change were observed for absolute variability (standard deviation (SD), root mean squared error (RMSE)), tracking error (RMSE, constant error (CE)), and complexity (detrended fluctuation analysis (DFA)) (all p < 0.05) of graded force fluctuations between the MVC groups. Differential performance strategies were observed beyond ~65% MVC, with the discrete-point group minimizing their SD at force values below that of the criterion target (higher CE/RMSE). Moreover, the sustained group’s capacity to minimize SD/RMSE/CE corresponded to a more complex structure in their force fluctuations. These findings reveal that the time component of MVC estimation has a direct influence on the corrective strategies supporting near-maximal manual force control. While discrete MVC protocols predominate in the study of manual strength/endurance/precision, a 1:1 MVC-task mapping appears more to be ecologically valid if visuo-motor precision outcomes are of central importance.

A consistent and conservative Phase-Field model for thermo-gas-liquid-solid flows including liquid-solid phase change

In the present study, a consistent and conservative Phase-Field model is developed to study thermo-gas-liquid-solid flows with liquid-solid phase change. The proposed model is derived with the help of the consistency conditions and exactly reduces to the consistent and conservative Phase-Field method for incompressible two-phase flows, the fictitious domain Brinkman penalization (FD/BP) method for fluid-structure interactions, and the Phase-Field model of solidification of pure material. It honors the mass conservation, defines the volume fractions of individual phases unambiguously, and therefore captures the volume change due to phase change. The momentum is conserved when the solid phase is absent, but it changes when the solid phase appears due to the no-slip condition at the solid boundary. The proposed model also conserves the energy, preserves the temperature equilibrium, and is Galilean invariant. A novel continuous surface tension force to confine its contribution at the gas-liquid interface and a drag force modified from the Carman-Kozeny equation to reduce solid velocity to zero are proposed. The issue of initiating phase change in the original Phase-Field model of solidification is addressed by physically modifying the interpolation function. The corresponding consistent scheme is developed to solve the model, and the numerical results agree well with the analytical solutions and the existing experimental and numerical data. Two challenging problems having a wide range of material properties and complex dynamics are conducted to demonstrate the capability of the proposed model.

Influence of rheological behavior on wall thickness using low-melting alloy for sheet metal forming

The wrinkling-free forming method for sheet metal forming based on the low-melting alloy (LMA) is a novel sheet forming method. The LMA as a forming pressure medium to transfer loading force is utilized to prevent bulking and wrinkling occurrence in the sheet forming process due to the its controllable fluidity by adjusting the heating temperature. In the forming process, the upper and lower surface of blank were acted by continued loading force resulting from LMA flowing. In this study, the high-temperature mechanical properties of LMA were obtained by heating tensile test for preparation of simulation. The rheological behavior of LMA during the forming process was analyzed numerically. And the effect of LMA layer thickness, forming force and mold structure on the thinning of the formed parts was studied. With obtained results, the characteristic of wall thickness distribution and the effect of rheological behavior on thinning of formed part were comprehensively revealed. Moreover, the experimental results agree with those in numerical simulation by measuring the wall thickness of the formed specimen.

Influence of airflow movement on methane migration in coal mine goafs with spontaneous coal combustion

Spontaneous coal combustion was proved to cause methane accumulation and methane explosions in coal mine goafs. To avoid possible methane explosions, the empirical engineering measure, ventilation dilution, is proposed in coal mines though its disaster prevention mechanism has not been well understood. Through experimental and numerical simulations, the superposition effect of the air leakage and coal combustion-induced chimney effect was studied to reveal disaster prevention effect of ventilation dilution. Research results show that the high temperature area of coal combustion is steady and can provide continuous buoyancy force to form upward airflow even under ventilation dilution; the drifting methane accumulation is observed under the superposition effect of air leakage and upward airflow; ventilation dilution can weaken and even eliminate methane accumulation by overcoming chimney effect, but an increase in coal combustion temperature will enhance the upward airflow of chimney effect to cause methane accumulation again. The competitive relationship between the coal combustion-induced chimney effect and air leakage provides a new insight to study methane migration for the disaster formation and prevention mechanism.

Resolved CFD-DEM simulation of blood flow with a reduced-order RBC model

Mathematical modeling of the blood flow with a resolved description of biological cells mechanics such as red blood cell (RBC) has been a challenge in the past decades as it involves physical complexities and demands high computational costs. In the present study, we propose an approach for efficient simulation of blood flow with several suspended RBCs. In this approach, we employ our previously proposed reduced-order model for deformable particles (Nair et al. in Comput Part Mech 7:593–601, 2020) to mimic the mechanical behavior of an individual RBC as a cluster of overlapping spheres interconnected by flexible mathematical bonds. This discrete element method-based model is then coupled with a fluid flow solver using the immersed boundary method with continuous forcing in the context of computational fluid dynamics-discrete element method (CFD-DEM) coupling. The present computational method is tested with a couple of validation cases in which the single RBC dynamics, as well as the blood flow with several RBCs, were tested in comparison with existing literature date. First, the RBC deformation index in shear flow at different shear rates is studied with a good accuracy. Then, the blood flow in micro-tubes of different diameters and hematocrits was simulated. The key characteristics of blood flow such as cell-free layer (CFL) thickness, Fahraeus effect and the relative apparent viscosity are used as the validation metrics. The proposed approach can predict the formation of the migration of RBC toward the tube center-line and the CFL thickness in good agreement with previous measurement and simulations. Furthermore, the model is employed to study the CFL enhancement for plasma separation based on channel constriction. The simulation results compute the CFL thickness downstream of the channel constriction in good agreement with the experiments in a wide range of flow rates and constriction lengths. The original contribution of this study lies in proposing an efficient resolved CFD-DEM simulation method for blood flows with many RBCs which can be employed for numerical investigation of bio-microfluidic applications.

Insight on the structural changes of Glass-Ceramics during nanoindentation derived from Reactive Force-Field-Based molecular dynamic simulations

Glass-ceramics (GCs) are preferred over glass or ceramics in certain optical applications including those requiring lower porosity than ceramics and higher transition temperatures than glass. However, due to its material heterogeneity, it is difficult to precisely control the microstructure in GCs to meet specific property targets. The chemical mechanism behind the microstructural changes in the two-phase heterogeneity has not yet been clearly elucidated. In this work, the continuous Reactive Force Field molecular dynamics nanoindentation algorithm was developed and used to study the mechanism of structural evolution during nanoindentation. It was found that crystalline phases (CP) had the maximum load at the same indentation depth. The number of point defects of CP was more than glass-crystalline phase (GCP) at the end of loading. However, after total unloading, the opposite was observed with the number of point defects in GCP more than that in CP. The details in GCP bonding indicated that the formation of irreversible supersaturated bonds hindered the healing of defects while promoting the annihilation of pores. The evolution of pores and the typical chemical changes of GCP in the nanoindentation process had also been explored, which proves to be helpful in understanding the behaviors of two-phase heterogeneous materials at the nanoscale.