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Select the common mooring system-soft yoke mooring system as the research object. The soft yoke mooring system is regarded as a structure composed of multiple rigid bodies, and the theoretical analysis of multi-body dynamics is used to discuss the interaction of multi-rigid bodies. The classical HYSY113 FPSO is selected as an example, for the soft yoke mooring system, the stiffness characteristics and static restoring force curved compared with those of software OrcaFlex, and they are in good agreement, which verify the reliability of the formula derived, and it is a prerequisite for the accurate simulations in further steps. Coupled analysis to the whole system in time domain is also carried out both in OrcaFlex and AQWA, and the representative response of the FPSO under different environmental conditions is compared, the results are consistent well with each other. It is a good reference for the future study in this field. Good static characteristics are a prerequisite for accurate analysis of time-domain motion. By comparing the results in the time domain, it is found that under the same working conditions, the analysis results calculated by different commercial software (AQWA and OrcaFlex) may be different. We need to perform design analysis based on the characteristics of the software.

In the present work, a novel computational fluid dynamics (CFD) methodology was developed to simulate full-scale non-premixed rotating detonation engines (RDEs). A unique feature of the modeling approach was the incorporation of adaptive mesh refinement (AMR) to achieve a good trade-off between model accuracy and computational expense. Unsteady Reynolds-averaged Navier–Stokes (RANS) simulations were performed for an Air Force Research Laboratory (AFRL) non-premixed RDE configuration with hydrogen as fuel and air as the oxidizer. The finite-rate chemistry model, along with a ten-species detailed kinetic mechanism, was employed to describe the H2-Air combustion chemistry. Three distinct operating conditions were simulated, corresponding to the same global equivalence ratio of unity but different fuel/air mass flowrates. For all conditions, the capability of the model to capture essential detonation wave dynamics was assessed. An exhaustive verification and validation study was performed against experimental data in terms of a number of waves, wave frequency, wave height, reactant fill height, oblique shock angle, axial pressure distribution in the channel, and fuel/air plenum pressure. The CFD model was demonstrated to accurately predict the sensitivity of these wave characteristics to the operating conditions, both qualitatively and quantitatively. A comprehensive heat release analysis was also conducted to quantify detonative versus deflagrative burning for the three simulated cases. The present CFD model offers a potential capability to perform rapid design space exploration and/or performance optimization studies for realistic full-scale RDE configurations.

Falling backward can lead to injuries including hip fracture, back injury, and traumatic brain impact among older adults. A loss of consciousness is associated with falling backward and accounts for about 13% of all falls among older adults. Little is known about the dynamics of backward falls, such as the falling duration, the impact severity, and how the fall dynamics are affected by the biomechanical properties of the lower limb joints, particularly the rotational stiffness. The purpose of this study was to investigate the influence of the stiffness of individual leg joints on the dynamics of backward falls after losing consciousness in terms of the falling duration and impact velocities. Based on a 15-segment human model, we simulated the process of falling backward by sweeping the parameter space of ankle, knee, and hip's stiffnesses varying from 0 to 8.73 N·m·deg−1 (or 500 N·m·rad−1). The results revealed that the falling duration and impact speeds of the head and hip ranged from 0.27 to 0.63 s, 2.65 to 7.88 m·s−1, and 0.35 to 3.36 m·s−1, respectively, when the stiffness of the leg joints changed within their limits. Overall, the influence of the joint stiffness on the falling dynamics (falling duration and impact speed) is comparable between hip and knee joints, whereas ankle stiffness showed little influence on the backward falling dynamics. Our findings could provide references for designing protective devices to prevent impact-induced injuries after a backward fall.

Foot slip is one of the major causes of falls in human locomotion. Analytical bipedal models provide an insight into the complex slip dynamics and reactive control strategies for slip-induced fall prevention. Most of the existing bipedal dynamics models are built on no foot slip assumption and cannot be used directly for such analysis. We relax the no-slip assumption and present a new bipedal model to capture and predict human walking locomotion under slip. We first validate the proposed slip walking dynamic model by tuning and optimizing the model parameters to match the experimental results. The results demonstrate that the model successfully predicts both the human walking and recovery gaits with slip. Then, we extend the hybrid zero dynamics (HZD) model and properties to capture human walking with slip. We present the closed-form of the HZD for human walking and discuss the transition between the nonslip and slip states through slip recovery control design. The analysis and design are illustrated through human walking experiments. The models and analysis can be further used to design and control wearable robotic assistive devices to prevent slip-and-fall.

The arterial input function (AIF)—time-density curve (TDC) of contrast at the coronary ostia—plays a central role in contrast enhanced computed tomography angiography (CTA). This study employs computational modeling in a patient-specific aorta to investigate mixing and dispersion of contrast in the aortic arch (AA) and to compare the TDCs in the coronary ostium and the descending aorta. Here, we examine the validity of the use of TDC in the descending aorta as a surrogate for the AIF. Computational fluid dynamics (CFD) was used to study hemodynamics and contrast dispersion in a CTA-based patient model of the aorta. Variations in TDC between the aortic root, through the AA and at the descending aorta and the effect of flow patterns on contrast dispersion was studied via postprocessing of the results. Simulations showed complex unsteady patterns of contrast mixing and dispersion in the AA that are driven by the pulsatile flow. However, despite the relatively long intra-aortic distance between the coronary ostia and the descending aorta, the TDCs at these two locations were similar in terms of rise-time and up-slope, and the time lag between the two TDCs was 0.19 s. TDC in the descending aorta is an accurate analog of the AIF. Methods that use quantitative metrics such as rise-time and slope of the AIF to estimate coronary flowrate and myocardial ischemia can continue with the current practice of using the TDC at the descending aorta as a surrogate for the AIF.

The effects of the race surface waviness on the cage dynamics, including cage slip ratios, cage instabilities, and time-averaged cage wear rates, in high-speed ball bearings are investigated. A dynamic model of high-speed ball bearings considering the cage effect and the race surface waviness is proposed. Based on the proposed dynamic model, the effects of the maximum wave amplitude (MWA) and the wave order (WO) of race surface waviness on cage slip ratio, cage instability, and time-averaged cage wear rate are investigated. The results show that the race surface waviness has a great effect on the cage dynamics. The waviness would increase the random impacts between balls and cage pockets and thus cause more instable motion of the cage. Although the ball skidding and the cage slip ratio decrease with the increase of MWA, the cage instability and the cage wear rate become severe when MWA increases. In addition, the effect of WO on cage dynamics is nonlinear. The current investigation could provide a theoretical tool for an in-depth understanding of the dynamics in a high-speed ball bearing.

Exhaust gas recirculation (EGR) is one of the most promising methods of improving the performance of power-generating gas turbines. CO2 is known to have the largest impact on flame behavior of any major exhaust species, but few studies have specified its thermal, kinetic, and transport effects on turbulent flames. Therefore, in this study, methane/air mixtures diluted with CO2 are experimentally investigated in a reactor-assisted turbulent slot (RATS) burner using OH planar laser-induced fluorescence (PLIF) measurements. CO2 addition is tested under both constant adiabatic flame temperature and variable adiabatic flame temperature conditions in order to elucidate its thermal, kinetic, and transport effects. Particular attention is paid to CO2's effects on the flame surface density, progress variable, turbulent burning velocity, and flame wrinkling. The experimental measurements reveal that CO2's thermal effects are the dominant factor in elongating the turbulent flame brush and decreasing the turbulent burning velocity. When thermal effects are removed by holding the adiabatic flame temperature constant, CO2's kinetic effects are the next most important factor, producing an approximately 5% decrease in the global consumption speed for each 5% of CO2 addition. The transport effects of CO2, however, tend to increase the global consumption speed, counteracting 30–50% of the kinetic effects when the adiabatic flame temperature is fixed. It is also seen that CO2 addition increases the normalized global consumption speed primarily through an enhancement of the stretch factor.

In this work, vibration characteristic diagnosis of misalignment rotor in loosely fitted bearing is investigated using dimensional analysis (DA) approach. A comprehensive empirical model (EM) using nondimensional parameters is developed to diagnose the rotor-bearing system, and EM model has been validated through an experimental setup developed in-house. Experiments are performed for various defects such as misalignment and bearing looseness. The EM results can be used to monitor the real-time conditions of the rotor-bearing system. This work also presents the effect of misalignment and bearing looseness under various load and speed conditions. Further, work has been extended to predict the combined effect of bearing looseness and misalignment. It has been found that EM model predictions of the vibration amplitude are better when compared to experimental results.

This paper introduces the design of a specific landing gear retraction system presenting a mechanism with four redundant side stays and examines its dynamic behavior during the folding and unfolding processes. First, a concept design of a four-side-stay landing gear retraction system is presented. To get the particular motion during folding and unfolding, the main kinematics parameters are given. Then, the influence of the side stay's kinematic redundancy on the mechanism parameters is examined. Because the mechanism is overconstrained, the allowable parameters belong to a specific region of the space called feasible region. Finally, a dynamic analysis of the over-constrained system is executed by using the Newton–Euler approach and compliant equations. Numerical simulations indicate that this kind of landing gear retraction system equitably share the loads between different side stays, and therefore, the total load at one side stay is greatly reduced.

This paper focuses on the implementation of a Hamiltonian model of multi-unit hydropower systems (MUHSs). First, a nonlinear mathematical model of the MUHS is established considering the occurrence of water hammer during the transient process. From the point of view of the energy transmission and dissipation of the system, a novel Hamiltonian model of the MUHS is proposed. Moreover, numerical simulations are carried out to further investigate the effectiveness and consistency of the implemented model. Finally, a comparative analysis is performed to validate the proposed approach against existing methods. The results demonstrate that the proposed Hamiltonian function not only reflects the energy change but also describes the complex dynamic evolution of MUHSs in transient processes. It is also found that the transient dynamic behavior of the system is influenced by the coupled effect of common penstock and the interaction of basic system variables. This study provides theoretical basis for the safe and stable operation of hydropower stations during transient processes.

The early detection of a kick and mitigation with appropriate well control actions can minimize the risk of a blowout. This paper proposes a downhole monitoring system, and presents a dynamic numerical simulation of a compressible two-phase flow to study the kick dynamics at downhole during drilling operation. This approach enables early kick detection and could lead to the development of potential blowout prevention strategies. A pressure cell that mimics a scaled-down version of a downhole is used to study the dynamics of a compressible two-phase flow. The setup is simulated under boundary conditions that resemble realistic scenarios; special attention is given to the transient period after injecting the influx. The main parameters studied include pressure gradient, raising speed of a gas kick, and volumetric behavior of the gas kick with respect to time. Simulation results exhibit a sudden increase of pressure while the kick enters and volumetric expansion of gas as it flows upward. This improved understanding helps to develop effective well control and blowout prevention strategies. This study confirms the feasibility and usability of an intelligent drill pipe as a tool to monitor well conditions and develop blowout risk management strategies.

This paper introduces a new parallel co-simulation method to study vehicle-track dynamic interactions. The new method uses the transmission control protocol/internet protocol (TCP/IP) to enable co-simulation between a detailed in-house track dynamics simulation package and a commercial vehicle system dynamics simulation package. The exchanged information are wheel-rail contact forces and rail kinematics. Then, the message passing interface (MPI) technique is used to enable the model to process track dynamics simulations and vehicle dynamics simulations in parallel. The parallel co-simulation technique has multiple advantages: (1) access to the advantages of both in-house and commercial simulation packages; (2) new model parts can be easily added in as new parallel processes; and (3) saving of computing time. The original track model used in this paper was significantly improved in terms of computing speed. The improved model is now more than ten times faster than the original model. Two simulations were conducted to model a locomotive negotiating a section of track with and without unsupported sleepers. The results show that the vertical rail deflections, wheel-rail contact forces and vehicle suspension forces are evidently larger when unsupported sleepers are present. The simulations have demonstrated the effectiveness of the proposed parallel co-simulation method for vehicle-track dynamic interaction studies.

Lie-theoretic methods provide an elegant way to formulate many problems in robotics, and the tutorial by Park et al. (2018, “Geometric Algorithms for Robot Dynamics: A Tutorial Review,” ASME Appl. Mech. Rev., 70(1), p. 010803) is simultaneously a complete and concise introduction to these methods as they pertain to robot dynamics. The central reason why Lie groups are a natural mathematical tool for robotics is that rigid-body motions and pose changes can be described as Lie groups, and allow phenomena including robot kinematics and dynamics to be formulated in elegant notation without introducing superfluous coordinates. The emphasis of the tutorial by Park et al. (2018, “Geometric Algorithms for Robot Dynamics: A Tutorial Review,” ASME Appl. Mech. Rev., 70(1), p. 010803) is robot dynamics from a Lie-theoretic point of view. Newton–Euler and Lagrangian formulation of robot dynamics algorithms with O(n) complexity were formulated more than 35 years ago using recurrence relations that use the serial structure of manipulator arms. This was done without using the knowledge of Lie theory. But issues such as why the ω× terms in rigid-body dynamics appear can be more easily understood in the context of this theory. The authors take great efforts to be understandable by nonexperts and present extensive references to the differential-geometric and Lie-group-centric formulations of manipulator dynamics. In the discussion presented here, connections are made to complementary methods that have been developed in other bodies of literature. This includes the multibody dynamics, geometric mechanics, spacecraft dynamics, and polymer physics literature, as well as robotics works that present non-Lie-theoretic formulations in the context of highly parallelizable algorithms.

The complex architecture of aircraft engines requires demanding computational efforts when the dynamic coupling of their components has to be predicted. For this reason, numerically efficient reduced-order models (ROM) have been developed with the aim of performing modal analyses and forced response computations on complex multistage assemblies being computationally fast. In this paper, the flange joint connecting two turbine disks of a multistage assembly is studied as a source of nonlinearities due to friction damping occurring at the joint contact interface. An analytic contact model is proposed to calculate the local microslip based on the different deformations that the two flanges in contact take during vibration. The model is first introduced using a simple geometry representing two flanges in contact, and then, it is applied to a reduced finite element model in order to calculate the nonlinear forced response.

In this paper, we propose a new coupled dynamical model of a horizontal axis wind turbine (HAWT). The proposed model takes into consideration the dynamic coupling of the flexible tower with both bending and torsion of the flexible blades. This model also accounts for the dynamics of an additional point mass located in one of the blades to simulate a crack. In addition, a finite element model (FEM) analysis along with an experimental study is conducted in this research to validate the modal analysis of a HAWT prototype. Data from the analytical, numerical, and experimental investigations were collected and showed comparable findings. Using the analytical model, the modal analysis and the steady-state response of the HAWT prototype are performed for two configurations: with and without a crack. In this paper, we also propose a new model-based technique for the detection of cracks in the HAWT.

Catastrophic chaotic and hyperchaotic dynamical behaviors have been experimentally observed in the so-called “smart valves” network, given certain critical parameters and initial conditions. The centralized network-based control of these coupled systems may effectively mitigate the harmful dynamics of the valve-actuator configuration which can be potentially caused by a remote set and would gradually affect the whole network. In this work, we address the centralized control of two bi-directional solenoid actuated butterfly valves dynamically coupled in series subject to the chaotic and hyperchaotic dynamics. An interconnected adaptive scheme is developed and examined to vanish both the chaotic and hyperchaotic dynamics and return the coupled network to its safe domain of operation.

Developing a flywheel energy storage system (FESS) with permanent magnetic bearing (PMB) and spiral groove bearing (SGB) brings a great challenge to dynamic control for the rotor system. In this paper, a pendulum-tuned mass damper is developed for 100 kg-class FESS to suppress low-frequency vibration of the system; the dynamic model with four degrees-of-freedom is built for the FESS using Lagrange's theorem; mode characteristics, critical speeds, and unbalance responses of the system are analyzed via theory and experiment. A comparison between the theoretical results and the experiment ones shows that the pendulum-tuned mass damper is effective, the dynamic model is appropriate, and the FESS can run smoothly within the working speed range.

This paper proposes a novel computationally efficient dynamics modeling approach for down-hole well drilling system. The existing drilling modeling methods are either computationally intensive such as those using finite element method (FEM) or weak in fidelity for complex geometry such as those using transfer matrix method (TMM). To take advantage of the benefits of FEM and TMM and avoid their drawbacks, this paper presents a new hybrid method integrating both of the aforementioned modeling approaches, enabled by the unique structural geometry of the drilling system. The new method is then applied to the down-hole well drilling system modeling, incorporating the dynamics of top drive, drill-string, bottom-hole-assembly (BHA), and bit–rock interaction. The hybrid integration approaches for both the axial and torsional dimensions are explicitly derived, and we also give directions on how to resolve those for flexural dimension. To this end, numerical simulation results are presented to demonstrate the effectiveness of the proposed hybrid modeling approach.

The structural dynamics of thin-walled parts vary as the material is removed during machining. This paper presents a new, computationally efficient reduced order dynamic substructuring method to predict the frequency response function (FRF) of the workpiece as the material is removed along the toolpath. The contribution of the removed mass to the dynamics of the workpiece is canceled by adding a fictitious substructure having the opposite dynamics of the removed material. The equations of motion of the workpiece are updated, and workpiece FRFs are evaluated by solving the hybrid set of assembled equations of motion in frequency domain as the tool removes the material between two consecutive dynamics update steps. The orders of the initial workpiece structure and the removed substructures are reduced using a model order reduction method with a newly introduced automatic master set selection criterion. The reduced order FRF update model is validated with peripheral milling tests and FRF measurements on a plate-shaped workpiece. It is shown that the proposed model provides ∼20 times faster FRF predictions than the full order finite element (FE) model.

This paper considers the inherent unsteady behavior of the three dimensional separation in the corner region of a subsonic linear compressor cascade equipped of thirteen NACA 65-009 profile blades. Detailed experimental measurements were carried out at different sections in spanwise direction achieving, simultaneously, unsteady wall pressure signals on the surface of the blade and velocity fields by time-resolved PIV measurements. Two configurations of the cascade were investigated with an incidence of 4° and 7°, both at Re = 3.8 * 105 and Ma = 0.12 at the inlet of the facility. The intermittent switch between the two statistical preferred sizes of separation, large and almost suppressed, is called bimodal behaviour. The existence of such oscillation, reported at first in previous experimental and numerical works on the same test rig, is confirmed for both incidences. Additionally, the present PIV measurements provide, for the first time, time-resolved flow visualizations of the size switch of the separation with an extended field of view covering the entire blade section. The interaction of random large structures of the incoming boundary layer with the blade is found to be a predominant element that destabilizes the separation boundary. The recirculation region enlarges when these high vorticity perturbations blend with larger eddies situated in the aft part of the blade. Such massive separation persists until the blockage in the passage causes the breakdown of the largest structures in the aft part of the blade. The flow starts again to accelerate and the separation is almost suppressed. Finally, POD analysis is carried out to decompose flow modes and to contribute to the clarification of underlying cause-effect-relations, which predominate the dynamics of the present flow scenario.

In differential drive robots, wheel slip severely affects the ability to track a desired motion trajectory and the problem is exacerbated when differential drive robots are used in applications involving coordination of multiple robots. This problem is investigated and, based on the wheel–ground traction forces, a simple slip avoidance control strategy is discussed. Differential drive robots with two driven wheels and one or more ball-type caster wheels are considered. The traction forces between the wheels and the ground surface are determined by assuming rigid wheel, rigid ground interaction. These traction forces are used to determine the maximum value of the input wheel torque that can be applied on the wheel before it slips. To avoid wheel slip, this limiting torque value is used to set a saturation limit for the input torque computed by a trajectory tracking controller. Stability of the closed-loop system with the slip avoidance strategy is shown. Experiments are conducted with this strategy using a single robot as well as multiple robots in a platoon. A representative sample of the experimental results is presented and discussed.

The objectives of this investigation were to develop a coupled dynamic model for turbocharger ball bearing rotor systems, correlate the simulated shaft motion with experimental results, and analyze the corresponding bearing dynamics. A high-speed turbocharger test rig was designed and developed in order to measure the dynamic response of a rotor under various operating conditions. Displacement sensors were used to record shaft motion over a range of operating speeds. To achieve the objectives of the analytical investigation, a discrete element angular contact ball bearing cartridge model was coupled with an explicit finite element shaft to simulate the dynamics of the turbocharger test rig. The bearing cartridge consists of a common outer ring, a pair of split inner races, and a row of balls on each end of the cartridge. The dynamic cartridge model utilizes the discrete element method in which each of the bearing components (i.e., races, balls, and cages) has six degrees-of-freedom. The rotor is modeled using the explicit finite element method. The cartridge and rotor models are coupled such that the motion of the flexible rotor is transmitted to the inner races of the cartridge with the corresponding reaction forces and moments from the bearings being applied to the rotor. The coupled rotor–cartridge model was used to investigate the shaft motion and bearing dynamics as the system traverses critical speeds. A comparison of the analytical and experimental shaft motion results resulted in minimal correlation but showed similarity through the critical speeds. The cartridge model allowed for thorough investigation of bearing component dynamics. Effects of ball material properties were found to have a significant impact on turbocharger rotor and bearing dynamics.

In this paper, based on the nonlinear strain–deformation relationship, the dynamics equation of a spatial curved beam undergoing large displacement and small deformation is deduced using the finite-element method of floating frame of reference (FEMFFR) and Hamiltonian variation principle. The stress-stiffening effect, which is also called geometric stiffening effect, is accounted for in the dynamics equation, which makes it possible for the dynamics simulation of the spatial curved beam with high rotational speed. A numerical example is carried out by using the deduced dynamics equation to analyze the stress-stiffening effect of the curved beam and then verified by abaqus software. Then, the modal synthesis methods, which result in much fewer numbers of coordinates, are employed to improve the computational efficiency.

The governing linear equations of transverse motion of a spinning disk with a splined inner radius and constrained from lateral motion by guide pads are derived. The disk is driven by a matching spline arbor that offers no restraint to the disk in the lateral direction. Rigid body translational and tilting degrees-of-freedom are included in the analysis of total motion of the spinning disk. The disk is subjected to lateral constraints and loads. Also considered are applied conservative in-plane edge loads at the outer and inner boundaries. The numerical solution of these equations is used to investigate the effect of the loads and constraints on the natural frequencies, critical speeds, and stability of a spinning disk. The sensitivity of eigenvalues of spline spinning disk to the in-plane edge loads is analyzed by taking the derivative of the spinning disk's eigenvalues with respect to the loads. An expression for the energy induced in the spinning disk by the in-plane loads, and their interaction at the inner radius, is derived by computation of the rate of work done by the lateral component of the edge loads. Experimental idling and cutting tests for a guided spline saw are conducted at the critical speed, super critical speeds, and at the flutter instability speed. The cutting results at different speeds are compared to show that the idling results of a guided spline disk can be used to predict stable operation speeds of the system during cutting.

High-speed machine tools have parts with both stationary and rotating dynamics. While spindle housing, column, and table have stationary dynamics, rotating parts may have both symmetric (i.e., spindle shaft and tool holder) and asymmetric dynamics (i.e., two-fluted end mill) due to uneven geometry in two principal directions. This paper presents a stability model of dynamic milling operations with combined stationary and rotating dynamics. The stationary modes are superposed to two orthogonal directions in rotating frame by considering the time- and speed-dependent, periodic dynamic milling system. The stability of the system is solved in both frequency and semidiscrete time domain. It is shown that the stability pockets differ significantly when the rotating dynamics of the asymmetric tools are considered. The proposed stability model has been experimentally validated in high-speed milling of an aluminum alloy with a two-fluted, asymmetric helical end mill.

The objective of this study is to investigate the hydrodynamics and heat transfer phenomena due to high frequency droplet train impingement on a pre-wetted solid surface for electronic cooling applications. The effects of crown propagation dynamics and surface heat transfer were investigated experimentally and numerically. Experimentally, a single stream of mono-dispersed HFE-7100 droplets was generated using a piezo-electric droplet generator at a frequency ( f ) of 6000 Hz with a droplet Weber number (We) of 280. Droplet-induced crater and crown were imaged using a high speed camera system. Numerically, the ANSYS Fluent CFD tool was used to simulate the droplet train impingement process. A reasonable agreement was reached between experimental and numerical data in terms of crown propagation dynamics. Numerical simulations reveal that at the instant of initial spot formation, the magnitude of droplet velocity is almost identical to the crown's radial velocity. The instantaneous temperature field obtained by numerical simulations shows that heat transfer was most effective within the crown propagation region due to the radial momentum generated by the droplets, which leads to a large velocity gradient within the liquid film. A significant increase in surface temperature was observed beyond a radial position of 500 μm. In summary, high frequency droplet impingement leads to a very small temperature gradient in the radial direction within the droplet-induced impact crater. This study will benefit in understanding the relationship between the droplet parameters and surface heat transfer for different cooling applications involving impinging droplets.

The dynamic properties of machine tools are frequently calculated by means of finite-element (FE) models. Usually, in a first step, the structural components, such as machine bed, slides, columns, spindle housing, spindle, and work piece, are meshed. In a second step, these components are positioned relatively to each other and are connected by joints. Usually, the joints comprise a three-dimensional spring–damper element (SDE) and constraints that connect the SDE to adjacent structural components. Commercial FE programs do rarely offer insight into the underlying constraint equations. Rather, the constraints are realized by selecting the faces or nodes to connect and the type of constraint over a graphical user interface. Moreover, when insight into the underlying equations is offered, it is normally difficult to implement user-defined constraint equations. So far, literature lacks a coherent and in-depth description of constraints that are used for assembly of machine tool FE components. This drawback is addressed here. Different common constraints are revisited while particular focus is put on simulating moving machine axes. Common multipoint constraints (MPC) are supplemented by a shape function based node weighting. Thus, two new MPC are introduced, which improve model quality for ball screw joints (named node-to-beam (NB)-constraint) and linear guides (named RBE4-constraint). A three-axis milling machine serves as an application example for the different constraints. Simulation results are compared to experimentally derived results. Both, frequency response functions (FRF) and time-domain forced responses are considered. Showing reasonable correlation, the comparison of simulation and experiment indicates the validity of the constraints that have been introduced.

Arm-free paraplegic standing via functional electrical stimulation (FES) has drawn much attention in the biomechanical field as it might allow a paraplegic to stand and simultaneously use both arms to perform daily activities. However, current FES systems for standing require that the individual actively regulates balance using one or both arms, thus limiting the practical use of these systems. The purpose of the present study was to show that actuating only six out of 12 degrees of freedom (12-DOFs) in the lower limbs to allow paraplegics to stand freely is theoretically feasible with respect to multibody stability and physiological torque limitations of the lower limb DOF. Specifically, the goal was to determine the optimal combination of the minimum DOF that can be realistically actuated using FES while ensuring stability and able-bodied kinematics during perturbed arm-free standing. The human body was represented by a three-dimensional dynamics model with 12-DOFs in the lower limbs. Nakamura’s method (Nakamura, Y., and Ghodoussi, U., 1989, “Dynamics Computation of Closed-Link Robot Mechanisms With Nonredundant and Redundant Actuators,” IEEE Trans. Rob. Autom., 5(3), pp. 294–302) was applied to estimate the joint torques of the system using experimental motion data from four healthy subjects. The torques were estimated by applying our previous finding that only 6 (6-DOFs) out of 12-DOFs in the lower limbs need to be actuated to facilitate stable standing. Furthermore, it was shown that six cases of 6-DOFs exist, which facilitate stable standing. In order to characterize each of these cases in terms of the torque generation patterns and to identify a potential optimal 6-DOF combination, the joint torques during perturbations in eight different directions were estimated for all six cases of 6-DOFs. The results suggest that the actuation of both ankle flexion∕extension, both knee flexion∕extension, one hip flexion∕extension, and one hip abduction∕adduction DOF will result in the minimum torque requirements to regulate balance during perturbed standing. To facilitate unsupported FES-assisted standing, it is sufficient to actuate only 6-DOFs. An optimal combination of 6-DOFs exists, for which this system can generate able-bodied kinematics while requiring lower limb joint torques that are producible using contemporary FES technology. These findings suggest that FES-assisted arm-free standing of paraplegics is theoretically feasible, even when limited by the fact that muscles actuating specific DOFs are often denervated or difficult to access.

The influence of the spherical joint with clearance caused by wear on the dynamics performance of spatial multibody system is predicted based on the Archard's wear model and equations of motion of multibody systems. First, the function of contact deformation and load acting on the spherical joint with clearance is derived based on the improved Winkler elastic foundation model and Hertz quadratic pressure distribution assumption. On this basis, considering the influence of clearance size and wear state on the contact stiffness between spherical joint elements, an improved contact force model is proposed by Lankarani–Nikravesh contact force model and improved stiffness coefficient that is the slope of the function of contact deformation and load. Second, due to the complexity for that wear impacts on the surface topography of contact bodies, an approximate calculation method of contact area with respect to the clearance spherical joint is provided for simplifying the computational process of contact pressure in the Archard's wear model. Subsequently, the contact pressure between contact bodies is calculated by the improved contact force model and approximate contact area (ICFM–ACA), which is verified via finite element method (FEM). Moreover, the dynamics model of spatial four bar mechanism considering spherical joint with clearance caused by wear is formulated using equations of motion of multibody systems. Finally, the wear depth of spherical joint with clearance is predicted via two different kinds of contact pressure based on the Archard's wear model (one is from the ICFM–ACA and the other is from FEM), respectively. The numerical simulation results show that the improved contact force model and proposed approximate contact area are correctness and validity for predicting wear in the spherical joint with clearance. Simultaneously, the effect of the spherical joint with clearance caused by wear on the dynamics performance of spatial four bar mechanism is analyzed.

This paper presents the analysis, design, and simulation of a novel microrobotic platform that is able to perform translational and rotational sliding with submicrometer positioning accuracy and develop velocities up to 1.5 mm/s. The platform actuation system is novel and based on centripetal forces generated by vibration micromotors. The motion principle is discussed in detail, and the dynamic model of the platform and of its actuation system is developed. Analytical expressions for the distinct modes of operation of the platform are derived and used to provide system design guidelines. Simulations are performed that verify the analytical results, demonstrate the platform capabilities, and examine its transient response. The microrobot design is simple, compact, and of low cost. In addition, the energy supply of the mechanism can be accomplished in an untethered mode using simple means, such as single-cell batteries. DOI: 10.1115/1.2168472

Floating breakwaters have potential applications in protecting minor ports and harbors such as fisheries and recreational harbors, where-in stringent tranquillity requirements are not warranted. In field applications of the existing floating breakwaters, limitations are imposed due to their large relative width (ratio between breakwater width and wave length) requirements to achieve desirable tranquillity level. This relative width requirement is greater than 0.3 for the existing floating breakwaters. To overcome the above drawback associated with the existing system a new configuration for a floating breakwater is derived, which could yield the desired performance with minimum relative width requirement. The floating breakwater comprises of two pontoons rigidly connected together and each of the pontoons having a row of cylinders attached beneath, for improved performance characteristics. The laboratory tests were conducted in both regular and random wave flumes to study the dynamic behavior of the breakwater. Transmission and reflection coefficients, water surface elevations and velocities inside the cage like area provided in between the pontoons, rigid body motions floating breakwater and mooring forces were studied under regular and random waves and under the regular waves followed by a uniform current. The results proved the suitability of the floating breakwater to the field conditions even for large wave periods. In addition the variations in water particle kinematics, rigid body motion and mooring forces show nominal magnitudes when compared to the existing systems indicating the rigidness of the breakwater. Copyright ? 2005 by ASME.

Electrically driven impact microactuators generate nanoscale displacements without large driving distances and high voltages. These systems exhibit complex dynamics because of inherent nonlinearities due to impacts, friction, and electric forces. As a result, dramatic changes in system behavior, associated with so-called grazing bifurcations, may occur during the transition between impacting and nonimpacting dynamics, including the presence of robust chaos. For successful open-loop operating conditions, the system design is limited to certain parameter regions, where desired system responses reside. The objective of this paper is to overcome this limitation to allow for a more precise displacement manipulation using impact microactuators. This is achieved through a closed-loop feedback scheme that successfully controls the system dynamics in the near-grazing region.

The vibratory energy of a moving cable in an elevator increases in general during upward movement. A control method is presented to dissipate the energy associated with the lateral vibration of the cable. A novel experimental method is developed to validate the theoretical predictions for the uncontrolled and controlled lateral responses of a moving cable in a high-rise elevator. This includes the design and fabrication of a scaled elevator, experimental setup, and development of measurement and parameter estimation techniques. Experimental results show good agreement with the theoretical predictions.

This paper presents a time-domain dynamic model, which simulates cylindrical plunge grinding processes under general grinding conditions. The model focuses on the prediction of grinding chatter boundaries and growth rates. Critical issues are considered in the model including: the distributed nonlinear force along the contact length, the geometrical interaction between the wheel and workpiece based on their surface profiles, the structure dynamics with multiple degrees of freedom for both the wheel and workpiece, the response delay due to spindle nonlinearities and other effects, and the effect of the motion perpendicular to the normal direction. A simulation program has been developed using the model to predict regenerative forces, dynamic responses, surface profiles, stability regions, and chatter growth rates. The model is validated using existing numerical and experimental results.

A new experimental approach to identify the cutting dynamics in turning operations is presented. This method treats the problem as a closed-loop gray-box identification problem and is based upon spectral analysis and least squares estimation techniques. An active magnetic bearing is employed both to excite the system and to increase the tool’s damping. The inherent time delay of the cutting process is “removed” in identification by limiting the observation period to less than one revolution period of the workpiece. The coefficients of several cutting tests were identified. The methodology was validated by predicting the critical depth of cut from the identification results and comparing with the experiment result measured from a cutting test. DOI: 10.1115/1.2034509

It is believed that nurses risk the development of back pain as a consequence of sudden loadings during tasks in which they are handling patients. Forward dynamics simulations of sudden loads (applied to the arms) during dynamic lifting tasks were performed on a two-dimensional whole-body model. Loads were in the range of −80kg to 80 kg, with the initial load being 20 kg. Loading the arm downwards with less than that which equals a mass of 20 kg did not change the compressive forces on the spine when compared to a normal lifting motion with a 20 kg mass in the hands. However, when larger loads (40 kg to 80 kg extra in the hands) were simulated, the compressive forces exceeded 13 000 N (above 3 400 N is generally considered a risk factor). Loading upwards led to a decrease in the compressive forces but to a larger backwards velocity at the end of the movement. In the present study, it was possible to simulate a fast lifting motion. The results showed that when loading the arms downwards with a force that equals 40 kg or more, the spine was severely compressed. When loading in the opposite direction (unloading), the spine was not compressed more than during a normal lifting motion. In practical terms, this indicates that if a nursing aide tries to catch a patient who is falling, large compressive forces are applied to the spine.

In this paper we consider a sinusoidal arch with one end pinned in space while the other end attached to a mass and supported by a spring. The supporting wall of the spring is moved a distance quasi-statically to initiate preload in the arch and the spring. The assembly is then set in motion by an impact at the attached mass. The condition under which the arch may snap to the other side dynamically depends on the initial speed of the attached mass due to impact. Sufficient condition on the initial speed against dynamic snap-through is formulated based on the concept of minimum energy barrier. The effects of damping on the transient response of the assembly are also discussed. An experimental setup is designed to measure the transient response of the arch following the impact and the critical initial speed of the attached mass. The experimental results are in good agreement with theoretical predictions.

In this paper the tripod dynamics and its inertia effect is studied. The tripod design is becoming popular for the development of parallel kinematic machines (PKMs). The combination of a tripod with a gantry system forms a hybrid machine that offers the advantages from both serial and parallel structures. The tripod dynamics under study includes the mass of the moving platform as well as those of the legs. The natural orthogonal complement method is applied to derive the dynamic equations. The inertia effect of the moving platform and the legs is investigated in terms of two parameters, namely, the ratio of the total leg mass to the mass of the moving platform, and the velocity of the moving platform. The dynamic equations are separated by three terms, inertia, coupling, and gravity. Quantitative studies are carried out by simulation to examine how the two parameters affect the three respective terms. Based on the simulation results, the dynamic equations can be simplified by retaining the dominant terms while neglecting less significant ones. The simplified dynamic equations provide an efficient model for design and control of tripods.

The effects of slowly varying wave drift forces on the nonlinear dynamics of mooring systems have been studied extensively in the past 30 years. It has been concluded that slowly varying wave drift may resonate with mooring system natural frequencies. In recent work, we have shown that this resonance phenomenon is only one of several possible nonlinear dynamic responses of mooring systems to slowly varying wave drift excitation. We were able to reveal new phenomena based on the design methodology developed at the University of Michigan for autonomous mooring systems and treating slowly varying drift as an external time-varying force. In this paper, the U of M methodology is used systematically to reveal seven phenomena induced by mean and slowly varying drift forces; one of those is resonance. Conceptually, numerous qualitatively different behaviors may be induced. The next step toward the comprehensive identification of such phenomena is taken by introducing the method of harmonic balance to study nonautonomous mooring systems.

A six-degree-of-freedom model was developed and used to simulate the motion of all elements in a cylindrical roller bearing. Cage instability has been studied as a function of the roller-race and roller-cage pocket clearances for light-load and high-speed conditions. The effects of variation in inner race speed, misalignment, cage asymmetry, and varying size of one of the rollers have been investigated. In addition, three different roller profiles have been used to study their impact on cage dynamics. The results indicate that the cage exhibits stable motion for small values of roller-race and roller-cage pocket clearances. A rise in instability leads to discrete cage-race collisions with high force magnitudes. Race misalignment leads to a rise in instability for small roller-cage pocket clearances since skew control is provided by the sides of the cage pocket. One roller of larger size than the others causes inner race whirl and leads to stable cage motion for small roller-race clearances without any variation in roller-cage pocket clearance. Cage asymmetry and different roller profiles have a negligible impact on cage motion.

In this paper, we study numerically the effects of discontinuity in elasticity and damping on the dynamics of an electromechanical transducer. Frequency-response curves of oscillatory states are obtained. Bifurcation structures and transitions to nonperiodic or chaotic motion are found.

The dynamics of pico sliders is investigated during scratch impact using laser Doppler vibrometry. Air-bearing frequencies and damping of the pitch-2 frequency are studied as a function of disk velocity for lubricant thickness values of 1.6 nm, 1.0 nm and 2.0 nm. Time-frequency analysis is performed to study the instantaneous air-bearing frequencies. System identification methods are used to model the response of the slider after a scratch impact. The results indicate that the slider dynamics and the damping coefficients are affected by the disk velocity and lubricant thickness and also possibly by disk micro-waviness. @DOI: 10.1115/1.1695568#

A procedure for determining the cooperative system nominal motion whereby the system’s desired motion belongs to a set of nominal motions, is proposed. The procedure originates from the solution of the elastic structure cooperative motion taking into account all specific properties of the cooperative manipulation. The starting basis of the procedure is determined by some essential properties of the mathematical model of the dynamics of the cooperative manipulation of the object by the nonredundant manipulators with 6 degrees of freedom (DOFs), whereby the problem of the force indefiniteness is solved by introducing elastic properties for a part of the cooperative system.

The paper deals with a dynamic analysis of a non-contacting seal with two flexibly mounted rotating rings. The kinematics of motion is described and the equations of dynamics derived. Hydromechanical forces and moments containing coupling elements of the equation of motion are also determined. Selected results of digital calculations show the influence of the coupling elements on the axial and angular vibrations of a flexibly mounted ring.

Traditionally, cam-follower systems are designed by assuming a constant camshaft speed. Nevertheless, all cam-follower systems, especially high-speed systems, exhibit some camshaft speed fluctuation (despite the presence of a flywheel) which causes the follower motions to be inaccurate. This paper therefore proposes a novel design procedure that explicitly takes into account the camshaft speed variation. The design procedure assumes that (i) the cam-follower system is conservative and (ii) all forces are inertial. The design procedure is based on a single design choice, i.e., the amount of camshaft speed variation, and yields (i) cams that compensate for the inertial dynamics for any period of motion and (ii) a camshaft flywheel whose (small) inertia is independent of the period of motion. A design example shows that the cams designed in this way offer the following advantages, even for non-conservative, non-purely inertial cam-follower systems: (i) more accurate camshaft motion despite a smaller flywheel, (ii) lower motor torques, (iii) more accurate follower motions, with fewer undesired harmonics, and (iv) a camshaft motion spectrum that is easily and robustly predictable.

This literature review focuses mainly on geometrically nonlinear (finite amplitude) free and forced vibrations of circular cylindrical shells and panels, with and without fluid-structure interaction. Work on shells and curved panels of different geometries is but briefly discussed. In addition, studies dealing with particular dynamical problems involving finite deformations, eg, dynamic buckling, stability, and flutter of shells coupled to flowing fluids, are also discussed. This review is structured as follows: after a short introduction on some of the fundamentals of geometrically nonlinear theory of shells, vibrations of shells and panels in vacuo are discussed. Free and forced vibrations under radial harmonic excitation (Section 2.2), parametric excitation (axial tension or compression and pressure-induced excitations) (Section 2.3), and response to radial transient loads (Section 2.4) are reviewed separately. Studies on shells and panels in contact with dense fluids (liquids) follow; some of these studies present very interesting results using methods also suitable for shells and panels in vacuo. Then, in Section 4, shells and panels in contact with light fluids (gases) are treated, including the problem of stability (divergence and flutter) of circular cylindrical panels and shells coupled to flowing fluid. For shells coupled to flowing fluid, only the case of axial flow is reviewed in this paper. Finally, papers dealing with experiments are reviewed in Section 5. There are 356 references cited in this article.

Sliding friction between meshing teeth is one of the primary excitations for noise and vibration in geared systems. Yet, there exist very limited studies on this topic. This paper proposes new modeling strategies for incorporating friction in the dynamic analysis of a gear pair. First, some tribological issues are discussed for estimation of the friction forces under different operating conditions. Second, modeling procedures and results are compared for linear time-invariant, linear time-varying and non-linear time-varying formulations. Criteria such as energy balance, system complexity and desired solution methodology are discussed. Finally, sample results from the various analyses along with their benefits and limitations are examined.

A dynamic deflection model that incorporates the effect of the alignment errors that arise when a drill is held in the spindle assembly has been developed. The drill is modeled as an Euler-Bernoulli beam with clamped-free end conditions. Thrust and radial forces were applied at the free end of the beam. The mechanistic model used to predict these forces has been enhanced to incorporate the effect of the alignment errors and drill vibrations. A method has been outlined to measure these alignment errors. The mechanistic model demonstrates the ability to predict the drill vibrations and the radial forces within 6 percent of the measured vibrations and forces. The effect of these alignment errors on the drill vibrations and the radial forces has also been studied.

A numerical and analytic study of film formation and evolution during spray impingement is presented. For the part of the film which excludes drop impact locations, the governing equations reduce to a convenient form that can be exploited using a Lagrangian particle method. At impingement points the source terms for mass and energy are calculated based on conservation principles and phenomenological results. It is shown that during the period where most of the film evolution takes place, the effect of gas shear and surface tension are negligible. Numerical testing is performed to ensure convergence. Comparisons to spray impingement experiments consisting of film extension and thickness measurements yield reasonable agreement with the exception of the shallow angle impingement case where it is suspected that the total mass deposited is overpredicted.