External Dynamic Forces Research Articles

The Role of Operational Factors in Shaping of Wear Properties of Alloyed Austempered Ductile Iron Part II. an Assessment of the Cumulative Effect of Abrasives Processes and the Dynamic Activity on the Wear Property of Ausferritic Ductile Iron/ Rola Czynników Eksploatacyjnych W Kształtowaniu Właściwości Zużyciowych Stopowych Żeliw Sferoidalnych Ausferrytycznych Część II. Ocena Skumulowanego Działania Scierniwa I Wymuszeń Dynamicznych Na Właściwości

Abstract The study presents results of the second part of wear tests of austempered ductile irons on a specially designed test rig that allows simulating the real operating conditions of chain wheels. The chain wheels subjected to testing were operated in conditions characterized by combined action of loose quartz abrasive and an external dynamic force. The studies involved the determination of the hardness, microstructure and linear wear of the ADIs in question considered as a function of the austempering temperature and the austenite content. Based on the results obtained, the following was observed: a decrease in the wear as a function of the austempering temperature and thus in the content of austenite in ADIs; a slight deformation of graphite after completing the wear test involving external dynamic forces; a negative linear dependence between the linear wear and the impact resistance. It was found that the increased wear of cast irons with a lower content of austenite may be caused by the propagation of cracks initiated by damage to graphite nodules, while in the conditions characterized by combined action of abrasive wear and dynamic load the cast irons with a higher content of austenite and higher impact resistance have better wear properties.

SELF-SUSTAINED TURBULENCE WITHOUT DYNAMICAL FORCING: A TWO-DIMENSIONAL STUDY OF A BISTABLE INTERSTELLAR MEDIUM

In this paper, the nonlinear evolution of a bistable interstellar medium is investigated using two-dimensional simulations with a realistic cooling rate, thermal conduction, and physical viscosity. The calculations are performed using periodic boundary conditions without any external dynamical forcing. As the initial condition, a spatially uniform unstable gas under thermal equilibrium is considered. At the initial stage, the unstable gas quickly segregates into two phases, or cold neutral medium (CNM) and warm neutral medium (WNM). Then, self-sustained turbulence with velocity dispersion of $0.1-0.2\;\mathrm{km\;s^{-1}}$ is observed in which the CNM moves around in the WNM. We find that the interfacial medium (IFM) between the CNM and WNM plays an important role in sustaining the turbulence. The self-sustaining mechanism can be divided into two steps. First, thermal conduction drives fast flows streaming into concave CNM surfaces towards the WNM. The kinetic energy of the fast flows in the IFM is incorporated into that of the CNM through the phase transition. Second, turbulence inside the CNM deforms interfaces and forms other concave CNM surfaces, leading to fast flows in the IFM. This drives the first step again and a cycle is established by which turbulent motions are self-sustained.

A Systematic Approach to Estimate the Impact of the Aerodynamic Force Induced by Rotating Stall in a Vaneless Diffuser on the Rotordynamic Behavior of Centrifugal Compressors

One of the main challenges of the present industrial research on centrifugal compressors is the need for extending the left margin of the operating range of the machines. As a result, interest is being paid to accurately evaluating the amplitude of the pressure fluctuations caused by rotating stall, which usually occurs prior to surge. The related aerodynamic force acting on the rotor can produce subsynchronous vibrations, which can prevent the machine's further operation, in case their amplitude is too high. These vibrations are often contained due to the stiffness of the oil journals. Centrifugal compressor design is, however, going towards alternative journal solutions having lower stiffness levels (e.g., active magnetic bearings or squeeze film dampers), which will be more sensitive to this kind of excitation: consequently, a more accurate estimation of the expected forces in the presence of dynamic external forces such as those connected to an aerodynamically unstable condition is needed to predict the vibration level and the compressor operability in similar conditions. Within this scenario, experimental tests were carried out on industrial impellers operating at high peripheral Mach numbers. The dedicated test rig was equipped with several dynamic pressure probes that were inserted in the gas flow path; moreover, the rotor vibrations were constantly monitored with typical vibration probes located near the journal bearings. The pressure field induced by the rotating stall in the vaneless diffuser was reconstructed by means of an ensemble average approach, thus defining the amplitude and frequency of the external force acting on the impeller. The calculated force value was then included in the rotordynamic model of the test rig: the predicted vibrations on the bearings were compared with the measurements, showing satisfactory agreement. Moreover, the procedure was applied to two real multistage compressors, showing notable prediction capabilities in the description of rotating stall effects on the machine rotordynamics. Finally, the prospects of the proposed approach are discussed by investigating the response of a real machine in high-pressure functioning when different choices of journal bearings are made.

Estimating dynamic external hand forces during manual materials handling based on ground reaction forces and body segment accelerations

Direct measurement of hand forces during assessment of manual materials handling is infeasible in most field studies and some laboratory studies (e.g., during patient handling). Therefore, this study proposed and evaluated the performance of a novel hand force estimation method based on ground reaction forces (GRFs) and body segment accelerations.Ten male subjects performed a manual lifting/carrying task while an optoelectronic motion tracking system measured 3D full body kinematics, a force plate measured 3D GRFs and an instrumented box measured 3D hand forces. The estimated 3D hand forces were calculated by taking the measured GRF vector and subtracting the force vectors due to weight and acceleration of all body segments.Root-mean-square difference (RMSD) between estimated and measured hand forces ranged from 11 to 27N. When ignoring the segment accelerations (just subtracting body weight from the GRFs), the hand force estimation errors were much higher, with RMSDs ranging from 21 to 101N. Future studies should verify the performance of the proposed hand force estimation method when using an ambulatory field measurement system.

Vibrational displacement of a spindle with static disequilibrium of the cutting tool

The geometric characteristics of the machined sur� face of a blank (slab) are mainly determined by the motion of the cutting system's components, which depend on the external dynamic forces due to the machining process. A key factor here is the highspeed spindle of the metalcutting machine, on which the tool is mounted. The spatial motion of the spindle's axis will depend on the structural imbalances of the mill, noncoaxiality of the mill and spindle after attach� ment, imbalances of the spindle, and changes in the cutting force due to the unstable properties and vari� able margin of the blank. The spindle is mounted in bearings 1 and 2 (Fig. 1a) and supports a complex mill 3 (by cantilever attachment). Longitudinal slots in mill 3 accommo� date cutting plates 4, made of tool material. Cutting plates 4 remove surface layer 7 and knots 5 randomly distributed in the material (Fig. 1b). The machined material of slab 6 is nonuniform, with variation in the hardness, the density, and the margin. The external working load on the cutting system consists of the cutting force, the unbalanced centrifu� gal force due to primary imbalance vector Dst of the spindle, and the bending torque M of the pair of iner� tial unbalanced centrifugal forces P1-P1 due to the presence of primary imbalance torque MD in the spin� dle. The increments in the cuttingforce components P z and P y are due to machining of the knots within the slab. In addition to these increments, an axial compo� nent P i appears in machining the knots. By x 1 , y 1 , x 2 , y2, respectively, we denote small displacements in the first and second bearings in the direction of the X and Y axes, with vibration of the mill's spindle in machining.

Experimental research on V-I characteristic of a novel cavity atomizing corona discharge device

In order to seek a new control method which can control the dust, SO2, NOx and other pollutants comprehensively, a novel atomizing corona discharge device without external dynamic force was invented. The voltage-current (V-I) characteristics in different electrode structures were studied. In the cavity-wire type discharge structure, the voltage-current characteristics of de-ionized water, tap water and saturated solution of Ca(OH)2 were compared and analyzed. The results showed that: the atomizing effect of cavity-wire type discharge structure was better than that of cavity-plate under the same electrode diameter and voltage. A better atomizing effect could be obtained when the curvature radius of the cavity atomizing electrode was reduced. Active ions in solution had damaging effect on hydrogen bond among water molecules, which is in favour of solution atomization. This work will provide theoretical basis and experimental supports for a new field that the electrostatic and the wet flue gas desulphurization (WFGD) are combined together at the same time.

Parametric resonance of steel bridges pylons due to periodic traffic loads

This paper deals with the parametric resonance of steel bridges pylons due to time-depended traffic loads. The analysis follows the basic lines of Bolotin’s technique for the solution of nonlinear problems of dynamic instability. In this work, the cases of forced vibrating pylons with and without damping subjected to periodic external dynamic forces acting axially are investigated. The effect of bridge vibration due to traffic loads has been also taken into account. Through the aforementioned technique, useful results regarding the dynamic stability of pylons are obtained, and illustrative examples for various cases of geometry and loading are presented in the form of plots and diagrams.

Nonlinear structural surface intensity: An application of contact acoustic nonlinearity to power flow based damage detection

The concept of structural surface intensity is extended to the nonlinear domain introducing a physical quantity denominated nonlinear structural surface intensity (NSSI). This quantity is formulated for mechanical systems whose dynamic response is governed by nonlinear harmonic frequencies due to contact nonlinearities. A specific experiment simulating a “loose joint” type of damage in a stiffened bolted aluminum panel was designed to validate the NSSI formulation. Damage was introduced in the form of loose bolts characterized by a contact nonlinear response. The nonlinear response resulted from separation and impact at closure of the joined structures due to active interrogation by an external dynamic force. The results prove that NSSI is a monotonic function of the damage size.

Effects of applied potential on SCC and HE for STS 316L in seawater

Offshore structures that are made of austenitic stainless steels are exposed to a severe corrosion environment, with fracturing of the passive film occurring by chloride ion intrusion, stress from dynamic external forces and fatigue due to wave and tidal forces.In this paper, we report our evaluation of the durability of STS 316L with respect to stress corrosion cracking and hydrogen embrittlement in natural seawater, which was carried out via electrochemical methods and slow strain rate tests (SSRTs). The effect of hydrogen on the material was assessed using a SSRT with an applied potential of −0.95 V (versus Ag/AgCl). In addition, potentials below an applied potential of −1.2 V indicate samples that are affected by atomic and molecular hydrogen. Theoretically, the optimum corrosion protection range possible without stress corrosion cracking and hydrogen embrittlement occurring is thought to be between−0.56 and −0.9 V.

Dynamic External Force Feedback Loop Control of a Robot Manipulator Using a Neural Compensator—Application to the Trajectory Following in an Unknown Environment

Dynamic External Force Feedback Loop Control of a Robot Manipulator Using a Neural Compensator—Application to the Trajectory Following in an Unknown EnvironmentForce/position control strategies provide an effective framework to deal with tasks involving interaction with the environment. One of these strategies proposed in the literature is external force feedback loop control. It fully employs the available sensor measurements by operating the control action in a full dimensional space without using selection matrices. The performance of this control strategy is affected by uncertainties in both the robot dynamic model and environment stiffness. The purpose of this paper is to improve controller robustness by applying a neural network technique in order to compensate the effect of uncertainties in the robot model. We show that this control strategy is robust with respect to payload uncertainties, position and environment stiffness, and dry and viscous friction. Simulation results for a three degrees-of-freedom manipulator and various types of environments and trajectories show the effectiveness of the suggested approach compared with classical external force feedback loop structures.

Cooperative Impedance Control of a Finger-Arm Robot by Regulating Finger's Manipulability

Algorithms of motion control for a 9-DOF finger-arm robot were proposed by using the finger's manipulability in a previous study. However, only the methods for completing an unconstrained motion of the finger-arm robot were discussed in the previous study. In this paper, the authors propose a novel method for a finger-arm robot to complete an impedance control by regulating finger's manipulability in a constrained task. Methods of combining the previous heuristic method to the passive impedance control and the active impedance control are firstly developed. Then, an impedance control combined with the steepest ascent method is also proposed. The features of the proposed methods are demonstrated through several experiments. The proposed impedance control method combing with the steepest ascent method shows a strong performance even when a dynamic external force was applied to the finger. By using the proposed method, the arm actively moves along a direction to effectively maintain the moving potential of the finger. As a result, the finger shows a robust performance to its singularity in both unconstrained and constrained tasks.

동적 특성을 고려한 휴머노이드 하체 부품의 구조최적설계

Abstract A humanoid is a robot with its overall appearance based on that of the human body. When the humanoid moves or walks, dynamic forces act on the body structure. Although the humanoid keeps the balance by using a precise control, the dynamic forces generate unexpected deformation or vibration and cause difficulties on the control. Generally, the structure of the humanoid is designed by the designer’s experience and intuition. Then the structure can be excessively heavy or fragile. A humanoid design scenario for a systematic design is proposed to reduce the weight of the structure while sufficient strength is kept. Lower parts of the humanoid are selected to apply the proposed design scenario. Multi-body dynamics is employed to calculate the external dynamic forces on the parts and structural optimization is carried out to design the lower parts. Because structural optimization using dynamic forces directly is fairly difficult, linear dynamic response structural optimization using equivalent static loads is utilized. Topology and shape optimizations are adopted for two steps of initial and detailed designs, respectively. Various commercial software systems are used for analysis and optimization. Improved designs are obtained and the design results are discussed.

Application of physical science analysis to strategic management monitoring and control systems

This article illustrates the potential for using mathematical reasoning and analogy from physical sciences to conceptualise and explore the effect of dynamic external forces on the response of a company. An example of a generalised second-order linear differential model is applied to study the dynamic response of a company or industry to an exogenous shock. In most systems, significantly over-damped or under-damped response characteristics are expected. However, strategic management monitoring and control systems can scan for external shocks in order to apply dynamic adaptive controls to optimise the company's response. Mathematical tools are used to predict conditions under which an efficient response to external shocks is expected. It is shown that active strategic management can provide superior response characteristics. Additional complementary mathematical modelling approaches are outlined to show how the model may be expanded to address inter-firm linkages, supply chain dynamics, and the propagation of shocks through an industry.

Noncontact Photo-Acoustic Defect Detection in Drug Tablets

Quality assurance monitoring is of great importance in the pharmaceutical industry for the reason that if defects such as coating layer irregularities, internal cracks, and delamination are present in a drug tablet, the desired dose delivery and bioavailability can be compromised. The U.S. Food and Drug Administration (FDA) established the Process Analytical Technology (PAT) initiative, in order to ensure efficient quality monitoring at each stage of the manufacturing process by the integration of analysis systems into the evaluation procedure. Improving consistency and predictability of tablet action by improving quality and uniformity of tablet coatings as well as ensuring core integrity is required. An ideal technique for quality monitoring would be noninvasive, nondestructive, have a short measurement time, intrinsically safe, and relatively inexpensive. In the proposed acoustic system, a pulsed laser is utilized to generate noncontact mechanical excitations and interferometric detection of transient vibrations of the drug tablets is employed for sensing. Two novel methods to excite vibrational modes in drug tablets are developed and employed: (i) a vibration plate excited by a pulsed-laser and (ii) pulsed laser-induced plasma generated shockwave expansion. Damage in coat and/or core of a tablet weakens its mechanical stiffness and, consequently, affects its acoustic response to an external dynamic force field. From the analysis of frequency spectra and the time-frequency spectrograms obtained under both mechanisms, it can be concluded that defective tablets can be effectively differentiated from the defect-free ones and the proposed proof-of-concept techniques have potential to provide a technology platform to be used in the greater PAT effort.

Dynamic directional gradient vector flow for snakes

Snakes, or active contour models, have been widely used in image segmentation. However, most present snake models do not discern between positive and negative step edges. In this paper, a new type of dynamic external force for snakes named dynamic directional gradient vector flow (DDGVF) is proposed that uses this information for better performance. It makes use of the gradients in both x and y directions and deals with the external force field for the two directions separately. In snake deformation, the DDGVF field is utilized dynamically according to the orientation of snake in each iteration. Experimental results demonstrate that the DDGVF snake provides a much better segmentation than GVF snake in situations when edges of different directions are present which pose confusion for segmentation.

Driving simulator experiment on the moving stability of an automobile under strong crosswind

In expanding expressway networks in Japan, various types of structures have been constructed, e.g., long span bridges and bridges with high piers. The expressway structures are well designed for the external dynamic forces, e.g., earthquakes and strong winds. However, for further safety promotion of the expressway networks, it is important to evaluate the drivers’ responses under strong dynamic disturbances. The present authors have investigated the moving stability of a vehicle under seismic motion based on both numerical simulation and virtual experiments using a driving simulator. Strong crosswind is considered as another factor that makes it difficult for drivers to control their vehicles. This study investigates the moving stability of a vehicle under strong crosswind based on numerical analyses and driving simulator experiments. To predict the future position of a moving vehicle including the reaction of a driver, the second-order predictable correction model is used in the numerical analyses. The results obtained from the numerical and experimental studies are compared and the validity of the driver model is discussed. It is expected that this research is helpful for the decision-making of expressway closure under strong wind and the design of wind barriers.

Robot-assisted evaluation of coordination between grasp and load forces in a power grasp in humans

A novel approach for evaluation of a grasp in humans is presented. The key novelty is combination of a haptic interface with force/torque transducers for measuring the grasp force. This paper presents results of grasp and load force coordination for quasi-static and dynamic external load force disturbances for a power grasp. An elevation of the grasp force is observed in a dynamic task. Elevation of the grasp force is needed for an additional safety margin to ensure a stable grasp.

Rolling resistance moment of microspheres on surfaces

In the current work, for the first time, the existence of a rolling moment of resistance of an adhesion bond between a microsphere and flat surface subjected to external dynamic force has been experimentally demonstrated. The rotational motion of spherical particles deposited on a wafer is excited in the 0–3.5 MHz range using a piezoelectric transducer. The approach is based on (i) the observation that the contribution of the rotational (rocking) motion to the axial displacement of the particle are few orders of magnitude higher than those of the purely axial motion and (ii) the existence of a relationship between the rotational natural frequency of the adhesion bond and the work of adhesion. The natural frequency of the rotational (rocking) motion is extracted from the low frequency components of the transient response of the particle in the axial direction, which is measured by a laser interferometer. The existing theoretical adhesion models for rolling resistance moment are evaluated using the experimental results. Good agreement between the theoretical predictions and experimental values is found.

Influence of thermal effects on street canyon circulations

A numerical study has been carried out to investigate the influence of large-scale thermal effects and strong local-scale temperature gradients near the ground on the circulation inside a street canyon. The results show that the dynamical forcing dominates the circulation inside a street canyon. But this forcing is influenced by the large-scale thermal stability. Thus, atmospheric stability indirectly controls the street canyon circulation. Small temperature gradients inside the street-canyon are neutralised by the external dynamical forcing. Strong temperature gradients inside the street-canyon show an impact on the street canyon circulation. While stable stratification reduces the circulation for the building configuration investigated, convective stratification seems to intensify it.

Multiple tuned liquid column dampers for reducing coupled lateral and torsional vibration of structures

This paper presents a theoretical investigation on the performance of multiple tuned liquid column dampers (MTLCD) for mitigating the coupled lateral and torsional vibration of a long span bridge which can be modelled as a two degrees-of-freedom structure. The cross section of the bridge has a vertical axis of symmetry but with the vertical offset between the elastic centre and the mass centre of the bridge. The external dynamic force and moment are applied at the elastic centre of the bridge. The proposed MTLCD consists of two sets of liquid column dampers with one tuned to the lateral frequency of the bridge and the other tuned to the torsional frequency of the bridge. The equations of motion for the coupled lateral and torsional vibration of the bridge with MTLCD are first presented. The nonlinear damping property of MTLCD is linearized using the equivalent linearisation technique. Extensive parametric studies are then carried out in the frequency domain to find beneficial parameters of the MTLCD for achieving maximum reduction of coupled lateral and torsional vibration of the bridge. The parameters investigated herein include water mass distribution between the two dampers, distance from the centre line of the MTLCD to the rotational axis of the bridge, ratio of horizontal length to total length of liquid column, head loss coefficient, and frequency tuning ratio. The performance of the MTLCD in reducing buffeting response of the bridge due to turbulent wind is finally investigated. This study shows that the performance of MTLCD in reducing the lateral and torsional displacements of the bridge depends on the head-loss coefficient and the frequency-tuning ratio significantly. It is also demonstrated that the aeroelastic effects due to the interaction between turbulent wind and bridge motion is a crucial factor affecting the performance of MTLCD in reducing buffeting responses of the bridge.