Instantaneous Force Research Articles

Novelty in Intelligent Controlled Oscillations in Smart Structures

Structural control techniques can be used to protect engineering structures. By computing instantaneous control forces based on the input from the observed reactions and adhering to a strong control strategy, intelligent control in structural engineering can be achieved. In this study, we employed intelligent piezoelectric patches to reduce vibrations in structures. The actuators and sensors were implemented using piezoelectric patches. We reduced structural oscillations by employing sophisticated intelligent control methods. Examples of such control methods include H-infinity and H2. An advantage of this study is that the results are presented for both static and dynamic loading, as well as for the frequency domain. Oscillation suppression must be achieved over the entire frequency range. In this study, advanced programming was used to solve this problem and complete oscillation suppression was achieved. This study explored in detail the methods and control strategies that can be used to address the problem of oscillations. These techniques have been thoroughly described and analyzed, offering valuable insights into their effective applications. The ability to reduce oscillations has significant implications for applications that extend to various structures and systems such as airplanes, metal bridges, and large metallic structures.

Selection criteria for rotor number and rotational direction in arrays of closely spaced Darrieus turbines

Abstract The efficiency gains observed in a pair of closely spaced Darrieus turbines suggest the deployment of multiple turbines as an appealing solution for wind and, particularly, hydrokinetic applications, where the inflow direction is constant. The present study develops some design guidelines for closely spaced hydrokinetic Darrieus turbines by analyzing the trends of both power augmentation and wake development within arrays of multiple rotors, including not only an even number of rotors, which is the usual case in literature, but also an odd one. The analysis is carried out by means of two-dimensional Computational Fluid Dynamics simulations and includes not only the assessment of instantaneous blade forces but also locally sampled flow fields past each blade that allowed the reconstruction of dynamic polar data, contributing to a more comprehensive understanding of the physical mechanisms at play in such compact setups. The study demonstrates a consistent power augmentation mechanism across different layouts, even in the case of an odd number of rotors. This enhancement originates from flow blockage in the mutual interaction areas, favorably altering the inflow angle and subsequently increasing the angle of attack and lift generation. While this mechanism aligns with previous observations on arrays of counter-rotating pairs, its application to multiple turbines introduces complexities due to potential asymmetries in inflow, leading to an uneven power enhancement across turbines within the array. The identified efficiency improvement pattern suggests that maximizing leeward mutual interactions within an array of multiple Darrieus turbines would enhance the overall efficiency of the setup.

Dynamic Modeling of Angular Contact Ball Bearing with Local Defects under EHL Considering Impact Force

In order to analyze the operating status of angular contact ball bearings(ACBBs) with local defects in more detail, a dynamic model of ACBB with local defects considering impact force under elastohydrodynamic lubrication conditions is proposed. Firstly, an elastohydrodynamic lubrication model for defective bearings considering spin is established, the film thickness and film stiffness of the defective bearings are calculated, and then time-varying displacement excitation model and time-varying stiffness model for local defects in angular contact ball bearings is presented. Based on this, an instantaneous impact force function related to defect size and bearing speed is established. Secondly, based on Hertz contact theory and impact force function, a dynamic calculation method for ACBBs with local defects on the outer ring is proposed. Finally, the vibration characteristics of ball bearings with faults are investigated, and the influence of different parameters on the dynamic response of the bearings is analyzed. The calculation results show that under lubrication conditions, the impact force on the vibration of the bearing is significantly weakened. With the increase of defect size and load, the frequency of bearing fault characteristics remain unchanged, but its amplitude increases. As the bearing speed increases, the characteristic frequency and amplitude of bearing faults increase.

Impact of the Source Material Gradation on the Disaster Mechanism of Underground Debris Flows in Mines

In mines where the natural caving method is used, the frequent occurrence of underground debris flows and the complex mine environments make it difficult to prevent and control underground debris flows. The source is one of the critical conditions for the formation of debris flows, and studying the impact of source material gradation on underground debris-flow disasters can effectively help prevent and control these occurrences. This paper describes a multiscale study of underground debris flows using physical model experiments and the discrete-element method (PFC3D) to understand the impact of the source material gradation on the disaster mechanism of underground debris flows from macroscopic and microscopic perspectives. Macroscopically, an increase in content of medium and large particles in the gradation will enhance the instantaneous destructive force. Large particles can more easily cause disasters than medium and fine particles with the same content, but the disaster-causing ability is minimized when the contents of medium and large particles exceed 50% and 60%, respectively. With increasing fine particle content, the long-distance disaster-causing ability and duration is increased. On the microscopic level, the source-level pairs affect the initial flow mode, concentration area of the force chain, average velocity, average runout distance, and change in energy of the underground debris flow. Among them, the proportion of large particles in the gradation significantly affects the change in kinetic energy, change in dissipative energy, time to reach the peak kinetic energy, and time of coincidence of dissipative energy and gravitational potential energy. The process of underground debris flow can be divided into a “sudden stage”, a “continuous impact stage”, and a “convergence and accumulation stage”. This work reveals the close relationship between source material gradation and the disaster mechanism of underground debris flows and highlights the necessity of considering the source material gradation in the prevention and control of underground debris flows. It can provide an important basic theory for the study of environmental and urban sustainable development.

Crushing behavior of GFRP composite-reinforced PVC tubes: Experimental testing and numerical simulation

This paper introduces glass fiber reinforced polymer (GFRP)-reinforced Polyvinyl Chloride (PVC) tubes, both corrugated and non-corrugated, designed as energy absorber devices. The PVC tubes were externally and internally reinforced with GFRP composite oriented at ±45∘ and subjected to quasi-static axial compression tests. Results indicated that all reinforced tubes exhibited significantly higher load-bearing capacity, energy absorption capability, and crushing force efficiency compared to standard PVC tubes. Among the tested specimens, externally reinforced corrugated tubes demonstrated the highest specific energy absorption (SEA), surpassing other configurations by 17.5 kJ/kg when considering both pre- and post-crushing stages combined. However, these corrugated specimens showed instability during crushing, reflected in poor instantaneous crush force efficiency (iCFE) and the lowest iCFE among the composite tubes, with an average decrease of 43.59%.The corrugation notably increased the initial peak load, enhancing energy absorption in the pre-crushing stage without compromising the stability of crush force efficiency (CFE). Additionally, the combination of external and internal reinforcement significantly improved CFE and iCFE. Consequently, the PVC tubes combining corrugation with both external and internal reinforcement emerged as the best-performing configuration among all tested tubes.Furthermore, a 3D Finite Element (FE) model was developed using ABAQUS FE code with user-defined subroutines to simulate the crushing process. The constitutive models and numerical procedures employed are detailed. The FE model’s predictions showed a satisfactory correlation with experimental results, providing valuable insights into the crushing mechanics and offering a predictive tool for future design optimizations.

Two independent mechanisms with distinct laws for the generation of drag force on accelerating plates

Acceleration of objects in fluids widely exists in biological propulsions and contains rich unsteady fluid mechanisms. In this paper, the instantaneous drag force on accelerating normal flat plates (circular, elliptical, square, and rectangular plates) in a wide range of dimensionless acceleration (a*=16∼2) is measured, and the underlying mechanism for force generation is investigated. At first, we find that the drag force coefficient generally scales with the square root of a* when a*<1.0, coinciding with the scaling law given by Reijtenbagh et al. (PRL. 2023,130,174001). However, the drag force coefficient more linearly scales with a* rather than a* when a*>1.0, thereby indicating acceleration plays two distinct roles on the force generation depending on a*. Moreover, two scaling laws are built to quantitatively describe the two distinct roles of a* on the drag force generation. Based on fluid impulse, the drag force is largely contributed by the added mass of the accelerating plates (added mass force) and vorticity generation fed by the shear layer on the edge of the plates (vortex creation force). When a*<1.0, the vortex creation force scales with a* and almost contributes to the total drag force. When a*>1.0, the added mass force scaling with a* contributes to most of the drag force. Furthermore, the two force generation mechanisms associated with acceleration (a*) are independent, and a criterion based on the energy ratio is proposed to identify the transition of the two force generation mechanisms. The present results uncover the role of acceleration in force generation and explain the inconsistencies of using one quasi-steady model in describing the force on accelerating plates.

Direct Instantaneous Torque and Axial Force Control Method for Linear-Rotary Switched Reluctance Motor With Two Radial Windings

Direct Instantaneous Torque and Axial Force Control Method for Linear-Rotary Switched Reluctance Motor With Two Radial Windings

Effect of instantaneous local solid volume fraction on hydrodynamic forces in freely evolving particle suspensions

Particle Resolved Simulations (PRS) for freely evolving sphere suspensions at solid volume fractions (φ) between 0.1 and 0.4, Reynolds number Re from 10 to 300 and particle-fluid density ratios ρsρf of 2, 10 and 100 are used to investigate the effect of Voronoi tessellation based particle local solid volume fraction (φv)on particle drag and lateral forces. Findings reveal the instantaneous suspension mean drag force is positively correlated with the variance of φv among particles in the suspension. It is also shown that using the conditioned instantaneous φv of each particle in existing mean drag force correlations can significantly improve the prediction accuracy. Suspension mean lateral force ranges up to 60 % of the drag force while individual particles exhibit values as high as 90 % of the drag force. An instantaneous lateral force correlation is proposed based on suspension-averaged flow variables and φv.

Investigation on the unsteady aerodynamic performance of the Drela AG 08 and Boeing B29 airfoils subjected to heaving motion

This article aims to investigate the unsteady flow characteristics of Drela AG08 and Boeing B29 airfoils when subjected to heaving motion. The influence of heave amplitude, heave frequency in terms of instantaneous force coefficients of the airfoil is investigated at Re = 5 × 104. Furthermore, the flow field investigations were carried out to analyze the Leading Edge Vortex (LEV) formation and its convection airfoil’s suction side. From the findings, a variation in the oscillation amplitude of force coefficients was observed and a non-sinusoidal behavior was also noticed. Additionally, a remarkable change in the instantaneous force coefficients (both qualitatively and quantitatively) is also observed with respect to the slight change in aforementioned parameters. A transition in the wake pattern from drag inducing to thrust producing is observed under certain conditions. It is observed that the flow separates at the leading edge by forming LEV on both airfoil’s suction side and pressure side. It is also noticed that whenever the flow departs the trailing edge, these vortices convect downstream of the airfoil and form alternating pattern of coherent vortices. With the increase in number of cycles, these vortices interfere with the previously shed vortices and affects the airfoil’s aerodynamic characteristics. From the investigations, it is observed that, by controlling the system parameters, the adverse effects of the LEV can be minimized.

Numerical analysis of dynamic behaviors of underwater towed system with hydrofoil manipulations

This paper addresses the dynamic characteristics of an underwater towed system under manipulations of synchronous hydrofoils, considering the coupling of instantaneous fluid forces on the complete systems and hydrofoil control, which is usually difficult to solve with existing methods. A hydrodynamic model coupled with hydrofoil control algorithms is presented, wherein the hydrodynamic forces on the hydrofoils and Underwater Towed Vehicle (UTV) are simulated using the Computational Fluid Dynamics (CFD) method, and the fluid forces on the Towing Cable (TC) are described using a flexible cable dynamic model. The dynamic behaviors of the underwater towed system under depth-undulating, depth-tracking, and depth-keeping controls of hydrofoils are analyzed using the proposed model. The results show that the towing speed has a significant effect on the control efficiency of the hydrofoils. The dynamic responses of the underwater towed system increase or decrease more significantly in submerged depth control operations than in freely towing operations. The hydrofoils can achieve satisfactory effects in submerged depth control for the UTV at an appropriate towing speed, whereas it fails at a lower towing speed and noticeable dynamic response oscillations occur simultaneously. This study is expected to provide guidance on both hydrodynamic and control issues of underwater towed systems.

Nonlinear dynamic analysis of high-speed precision grinding considering multi-effect coupling

The aerostatic spindle is widely used in the field of precision grinding because of its excellent machining stability and machining accuracy. The spindle is jointly affected by multiple excitation effects in the high-speed grinding process. In order to study the dynamic characteristics of the aerostatic spindle under high-speed precision machining, it is necessary to analyse the nonlinear response of the aerostatic spindle with multi-physical field coupling. In this paper, the nonlinear dynamic model of the aerostatic spindle system under multi-effect coupling is established by considering three aspects: fluid-structure coupling, mass eccentricity excitation coupling, and vibration-grinding force coupling. Firstly, the instantaneous nonlinear air film force excitation is calculated by the derivation of the dynamic air film thickness model with multi-degree-of-freedom vibration responses coupling. The mass eccentricity excitation considering dynamic deflection angle is derived through the eccentric-load relationship. Afterwards, the dynamic precision grinding force model under the full surface of the tool is established based on judging the material removal mode, which considers the grain-workpiece interaction relationship under the influence of the nonlinear vibration. Finally, the accuracy and effectiveness of the coupled model is verified by high-speed precision grinding experiments, and the nonlinear dynamic behaviour under different operating parameters is analysed.

Propulsive performance of a heaving and pitching foil with large amplitudes in unsteady ground effect

To reveal the effect of ground on the force behavior, propulsion performance, and vortex dynamics of a flapping foil, we numerically study a flapping foil actuated by combined heaving and pitching motions with large amplitudes near a solid ground surface. The instantaneous forces in both streamwise and cross-stream directions undergo a sudden drop during upstroke in close ground effect. The time-averaged thrust is enhanced by the ground but varies non-monotonically with ground distance at high foil oscillating frequencies. Three force regimes are identified in lift production, giving rise to two equilibrium altitudes of zero lift, one stable and another unstable. Moreover, we propose a simple scaling law model by a path-length-based Strouhal number and ground effect for thrust and power performance of a large-amplitude flapping foil. The results of the model are consistent with numerical results and previous experimental studies. The vortex dynamics in the wake structure are largely affected by ground proximity; in particular, the formed vortex pairs and their orientations are sensitive to their initial relative positions. Different sources and mechanisms of satellite vortex formation are then discussed. The ground exerts little effect on the phase angles that optimize the propulsive efficiency. This study is expected to provide new insights into the development and maneuvering of flapping foil-based propulsive systems.

Momentum induced by steam injection into a subcooled pool

Boiling Water Reactors (BWR) and Advanced Pressurized Water Reactors (APWR) often use spargers to release steam from the primary coolant system into a pool with subcooled water to prevent containment overpressure. Direct contact Condensation (DCC) creates sources of mass, heat, and momentum determined by the condensation regimes in a subcooled pool. Thermal stratification can develop in the pool if buoyancy forces created by the heat source dominate the momentum source. Only part of the stratified pool volume can be used as the heat sink which is a safety concern. Modeling of steam injection and its effect on a large pool is computationally expensive due to the considerable spatial and temporal scale differences between the steam-water interface dynamics and global pool circulation. To enable the prediction of realistic plant transients, Effective Heat Source (EHS) and Effective Momentum Source (EMS) models were proposed. These models aim to calculate the time-averaged integral effects of the steam injection on the pool without resolving the dynamics of the interface and DCC phenomena.This work aims to develop the empirical correlations that predict the time-averaged effective momentum induced by steam injection into a subcooled pool. The experimental data were collected in a Separate Effect Facility (SEF-POOL) at LUT, Finland. The force acting on the injection pipe was measured in SEF-POOL to estimate the effective momentum rate created by steam injection. The condensation regime coefficient C, defined as the ratio of effective momentum rate to the theoretical momentum rate of injected steam, is presented as a function of Jakob and Mach numbers. We found that the pitch-to-diameter ratios (P/D) had a significant effect on both the effective (time averaged) momentum rate and instantaneous forces measured in the low Jakob number region, which might be attributed to the interactions between neighboring nozzles.

A Fast and Strong Microactuator Powered by Internal Combustion of Hydrogen and Oxygen

AbstractThe development of fast and strong microactuators that can be integrated in microdevices is an essential challenge due to a lack of appropriate driving principles. A membrane actuator powered by internal combustion of hydrogen and oxygen in a chamber with a volume of 3.1 nanoliters is demonstrated. The combustion in such a small volume is possible only for an extremely high surface‐to‐volume ratio on the order of 107 m−1. The fuel with this ratio is prepared electrochemically in a special regime that produces only nanobubbles. A cloud of nanobubbles merges, forming a microbubble, which explodes, increasing the volume 500× in 10 µs. The actuator generates an instantaneous force up to 0.5 N and is able to move bodies 11 000× more massive than itself. The natural response time of ≈10 ms is defined by the incubation time needed to produce an exploding bubble. The device demonstrates reliable cyclic actuation at a frequency of 1 Hz restricted by the effect of electrolyte aging. After 40 000 explosions, no significant wear in the chamber is observed. Due to a record‐breaking acceleration and standard microfabrication techniques, the actuator can be used as a universal engine for various microdevices including microelectromechanical systems, microfluidics, microrobotics, wearable and implantable devices.

Excitation of the Secondary Modes by the Broad Spectrum Sound in a Liquid with Relaxation Losses

Features of nonlinear phenomena and, in particular, acoustic excitation of the entropy and relaxation modes in a liquid electrolyte with a chemical reaction are examined. The total range of frequencies of an exciter is considered, and the instantaneous dynamic equations are derived which govern perturbations in the secondary modes. The instantaneous leading-order acoustic forces of the secondary modes are evaluated. Examples of harmonic and nearly harmonic acoustic exciter are considered in detail. The difference in the nonlinear acoustic phenomena in an electrolyte and gases with relaxation mechanisms are specified and discussed.

On the water entry impact characteristics of high-speed vehicle with an Arbitrary Lagrangian-Eulerian method

This paper investigates the fluid-structure interaction process of high-speed vehicles during water entry using the Arbitrary Lagrangian-Eulerian method. Through mesh independence verification and comparison of numerical simulation results with experimental data and empirical formulas, the reliability and accuracy of the computational method are confirmed. The study comprehensively analyzes flow field pressure distribution, cavity evolution characteristics, and vehicle force features, evaluating the impact of water-entry angle, Froude number (Fr), and cavitator dimension. The results indicate that during water entry, the instantaneous impact forces are mainly concentrated on the wetted surface at the bottom of the vehicle and the plane at the head. The peak stress at the entry point is significantly higher than at other locations, and stress waves propagate along the vehicle body, concentrating at the hollow structure due to the structural characteristics. The change in water-entry angle does not significantly affect the decay of Fr for the vehicle, but increasing the water-entry angle leads to an earlier and larger peak stress at the mid-point monitoring location of the vehicle. In addition, the study also found that the stress level increases with the increase of the Froude number, resulting in larger high-stress areas and peak stresses. However, the cavity evolution at the same water-entry depth is essentially independent of the variation in Fr. With the increase in cavitator dimension, the water-entry load and cavity profile will also significantly increase, and vehicles with larger cavitator dimension will generate larger stress waves upon impact.

Examining basic theorems and plane waves in the context of thermoelastic diffusion using a multi-phase-lag model with temperature dependence

This study employs a novel mathematical formulation of temperature-dependent thermoelastic diffusion with multi-phase delays (TDMT). The TDMT model, which is assumed, is obtained by converting the fundamental rules of Fourier’s and Fick’s laws into higher order time derivatives of the heat flow vector, the temperature gradient, diffusing mass flux, and the chemical potential gradient. Fundamental theorems such as energy, uniqueness, reciprocity theorems, and variational criterion are established using the fundamental equations for the assumed model TDMT. The reciprocity theorem is applied to a particular scenario by using instantaneous concentrated body forces, heat sources, chemical potential sources, and moving heat sources as examples. It is noted that both the variational criterion and these theorems depend on the field variables’ susceptibility as well as the fluctuations in the higher order temporal derivatives’ parameters. Additionally, the assumed model’s two-dimensional (2D) plane wave propagation is described. Three longitudinal waves are identified: the longitudinal (P) wave, the thermal (T) wave, the chemical potential (CP) wave, and the linked transverse (SV) wave. Wave properties (phase velocity and attenuation coefficient) are calculated numerically and shown visually. A few special examples are also investigated and compared with the established findings. The framework for additional research into basic issues in thermoelastic continua under various physical field variables is provided by this work. Numerous applications in material science, geomechanics, soil dynamics, and the electronic sector can be made of the current findings.

Repacking in Compacting Mushes at Intermediate Melt Fractions: Constraints From Numerical Modeling and Phase Separation Experiments on Granular Media

AbstractBefore large volumes of crystal poor rhyolites are mobilized as melt, they are extracted through the reduction of pore space within their corresponding crystal matrix (compaction). Petrological and mechanical models suggest that a significant fraction of this process occurs at intermediate melt fractions (ca. 0.3–0.6). The timescales associated with such extraction processes have important ramifications for volcanic hazards. However, it remains unclear how melt is redistributed at the grain‐scale and whether using continuum scale models for compaction is suitable to estimate extraction timescales at these melt fractions. To explore these issues, we develop and apply a two‐phase continuum model of compaction to two suites of analog phase separation experiments—one conducted at low and the other at high temperatures, T, and pressures, P. We characterize the ability of the crystal matrix to resist porosity change using parameterizations of granular phenomena and find that repacking explains both data sets well. A transition between compaction by repacking to melt‐enhanced grain boundary diffusion‐controlled creep near the maximum packing fraction of the mush may explain the difference in compaction rates inferred from high T + P experiments and measured in previous deformation experiments. When upscaling results to magmatic systems at intermediate melt fractions, repacking may provide an efficient mechanism to redistribute melt. Finally, outside nearly instantaneous force chain disruption events occasionally recorded in the low T + P experiments, melt loss is continuous, and two‐phase dynamics can be solved at the continuum scale with an effective matrix viscosity.

Optimal Gearing of Musculoskeletal Systems.

Movement is integral to animal life, and most animal movement is actuated by the same engine: striated muscle. Muscle input is typically mediated by skeletal elements, resulting in musculoskeletal systems that are geared: at any instant, the muscle force and velocity are related to the output force and velocity only via a proportionality constant G, the "mechanical advantage". The functional analysis of such "simple machines" has traditionally centered around this instantaneous interpretation, such that a small vs large G is thought to reflect a fast vs forceful system, respectively. But evidence is mounting that a comprehensive analysis ought to also consider the mechanical energy output of a complete contraction. Here, we approach this task systematically, and deploy the theory of physiological similarity to study how gearing affects the flow of mechanical energy in a minimalist model of a musculoskeletal system. Gearing influences the flow of mechanical energy in two key ways: it can curtail muscle work output, because it determines the ratio between the characteristic muscle kinetic energy and work capacity; and it defines how each unit of muscle work is partitioned into different system energies, that is, into kinetic vs "parasitic" energy such as heat. As a consequence of both effects, delivering maximum work in minimum time and with maximum output speed generally requires a mechanical advantage of intermediate magnitude. This optimality condition can be expressed in terms of two dimensionless numbers that reflect the key geometric, physiological, and physical properties of the interrogated musculoskeletal system, and the environment in which the contraction takes place. Illustrative application to exemplar musculoskeletal systems predicts plausible mechanical advantages in disparate biomechanical scenarios, yields a speculative explanation for why gearing is typically used to attenuate the instantaneous force output ($G_{\text{opt}} \lt 1)$, and predicts how G needs to vary systematically with animal size to optimize the delivery of mechanical energy, in superficial agreement with empirical observations. A many-to-one mapping from musculoskeletal geometry to mechanical performance is identified, such that differences in G alone do not provide a reliable indicator for specialization for force vs speed-neither instantaneously, nor in terms of mechanical energy output. The energy framework presented here can be used to estimate an optimal mechanical advantage across variable muscle physiology, anatomy, mechanical environment, and animal size, and so facilitates investigation of the extent to which selection has made efficient use of gearing as a degree of freedom in musculoskeletal "design."

Biomechanics of Insect Flight Stability and Perturbation Response.

Insects must fly in highly variable natural environments filled with gusts, vortices, and other transient aerodynamic phenomena that challenge flight stability. Furthermore, the aerodynamic forces that support insect flight are produced from rapidly oscillating wings of time-varying orientation and configuration. The instantaneous flight forces produced by these wings are large relative to the average forces supporting body weight. The magnitude of these forces and their time-varying direction add another challenge to flight stability, because even proportionally small asymmetries in timing or magnitude between the left and right wings may be sufficient to produce large changes in body orientation. However, these same large-magnitude oscillating forces also offer an opportunity for unexpected flight stability through nonlinear interactions between body orientation, body oscillation in response to time-varying inertial and aerodynamic forces, and the oscillating wings themselves. Understanding the emergent stability properties of flying insects is a crucial step toward understanding the requirements for evolution of flapping flight and decoding the role of sensory feedback in flight control. Here, we provide a brief review of insect flight stability, with some emphasis on stability effects brought about by oscillating wings, and present some preliminary experimental data probing some aspects of flight stability in free-flying insects.