Initial Equilibrium Position Research Articles

Robust tracking control of a minimal realization model of an impaired human hand for anthropomorphic coordination

Objective Physiologically relevant optimal controllers better represent the decision-making process of the central nervous system (CNS) with proper neural inputs and proprioceptor feedback. A biomechanical mathematical framework in the human palm reference frame was simulated using physiological dynamics to explore the biomechanics of movement coordination of fingers in a human hand.Method Physiological state space models include multiple zero eigenvalues, representing a redundant system. A fingertip trajectory tracking control paradigm is created by reducing the model order through the H∞ control paradigm. The external disturbances and sensory noise are included in the 21-Degrees-of-Freedom biomechanical model.Main Results An analysis is conducted on the flexion movement of the robotic finger when it is disrupted from its initial equilibrium position. The controller administers feedback force at the joints to control the movement of the robotic finger. A full order H∞ robust controller was developed, and the results were compared with the reduced-order model. The model order was reduced from 21 to 18 states. A reference trajectory is followed by the index finger in the minimal realization model, which is derived from the joint angular position profile. It stabilizes at a flexion angle of 1 rad/sec within 2 sec. Studying the simpler form of a model first gives a realistic view of the more complex model. This study has the potential to enhance our comprehension of anthropomorphic movement coordination in hands with impairments in kinesiology, ergonomics, assistive technology, and prosthetic devices.

A unified approach to simulate thermal hydraulic instabilities and the mutual interactions using transient distributed model

In the present work, a 1-D thermal-hydraulic model is developed to simulate two phase flow boiling for a working coolant R134a circulating inside a single horizontal channel which includes a surge tank. The TH model is the first of its kind which solves the transient conservation equations based on distributive formulations without the incorporation of quasi-steady state approximation and still can simulate pure pressure drop oscillations (PDOs), Ledinegg excursion and density wave oscillations (DWOs), and the co-existence of those instabilities as well using a unified approach by employing appropriate external characteristic curves. The model is validated with the available experimental data and then, further used for intended purpose as mentioned above. Finally, the notable conclusions are drawn based on the simulations conducted. Results indicate that the initial equilibrium position in the negative slope region of the pressure drop vs. mass flux curve is unstable, leading to Ledinegg excursion or PDOs based on the steepness of the external pump characteristic curve. Increased surge tank volume extends PDOs. For Ledinegg excursion, the unstable position shifts to positive slope regions, and gets stabilized or destabilized depending on the occurrence of DWOs. DWOs are more likely at low mass flux and positive slope region. With a constant mass flow rate from an external pump, DWOs occur with a surge tank upstream of the heated section but not without it. Simulations demonstrate coexistence of PDOs, Ledinegg excursion, and DWOs in certain situations.

A Modal Derivatives Enhanced Kron’s Substructuring Method to Calculate Structural Responses and Response Sensitivities of Geometrically Nonlinear Systems

This paper develops a modal derivative enhanced Kron’s substructuring method to calculate the structural responses and response sensitivities of geometrically nonlinear systems. The proposed method divides the global structure into substructures, which are then assembled in a dual form. The substructural displacements are approximated around the initial linear equilibrium position by using a quadratic modal manifold governed by a few master modes only. A time-variant reduction basis augmented by the master modal derivatives is derived from the quadratic modal manifold, enabling the geometric nonlinearities to be accurately captured. With the reduction basis, the global system is transformed into a reduced one containing the master modes only. Subsequently, the master modal responses and response sensitivities are solved efficiently from the reduced system. The global structural responses and response sensitivities are finally recovered from the master modal solutions based on the quadratic modal manifold. The effectiveness of the proposed method is demonstrated through its application to a thin plate structure. The reduced system enjoys the merit of Kron’s substructuring method that does not contain the interface degrees of freedom. Besides, the proposed reduced system is formed from the quadratic modal manifold directly. Its size is equal to the number of master modes of the substructures and smaller than that of the conventional method, where its size grows quadratically with the number of master modes.

Drag reduction on a blunt body by self-adaption of rear flexibly hinged flaps

We study the aerodynamics of a blunt-based body with rear flexibly-hinged rigid flaps, subject to a turbulent flow of Reynolds number Re=12000, under aligned and cross flow conditions with yaw angle β=0° and β=4°. To that aim, different values of the equivalent torsional stiffness are considered, to cover the range of reduced velocity U∗=(0,3.48] in water tank experiments. The effect of the angular deflection of plates on the drag and near wake flow is analyzed, experimentally and numerically. The results show that, in the range of U∗ herein considered, the plates undergo an inwards quasi-static, self-adaptive deflection, which is symmetric for yaw angles β=0° and asymmetric for β=4°. In particular, the plates feature small mean deformation angles for values of U∗<1, whereas a sharp and monotonic increase of such deflection occurs for U∗>1, i.e. for lower values of the hinge’s stiffness, with an asymptotic trend towards the larger values of U∗. A critical value of reduced velocity of U∗≃0.96 is obtained as the instability threshold above which plates depart from their initial equilibrium position. The progressive streamlining of the trailing edge translates into significant reductions of the associated mean drag coefficients. Thus, reductions close to 19% with respect to reference static plates configurations are obtained for the most flexible case of U∗=3.48 for both β=0° and β=4°. A close inspection of the near wake reveals that the inwards progressive mean displacement of the plates yields a reduction in the recirculation bubble size. A symmetric evolution of the recirculating bubble is observed for β=0°, whereas the bubble becomes asymmetric for β=4°, with a larger leeward clockwise vortex. In both cases, the drag coefficient is shown to vary linearly with the global aspect ratio of the recirculating bubble. The analysis of the numerical results shows that the reduced extension of the recirculating bubble significantly alters the formation length and intensity of the eddies size and associated pressure. It is observed that despite the local pressure decrease in the vortices shed from the trailing edges, the plates self adaption reduces their size and prevents the eddies from entering the cavity, thus, creating a dead flow region with a consequent pressure increase at the body base.

Application of simulation methods on vibration analysis of a bus driver seat using the quarter car 3DOF model subjected under harmonic excitation

Vibration of bus driver's seat subjected under harmonic excitation, 3DOF (3 degrees of freedom) dynamic model is employed to carry out the calculation by 3 simulation methods. Mathematical model - numerical using Matlab programming language (Numerical model), Multi Body Dynamics (MBD) using Matlab Simmechanics tool (MBD model) and finite element model using Ansys APDL (FEM model) are employed. The strengths and limitations of each method are analyzed through the process of building models and retrieving the resulting data. The evaluation indexes include the response of driver's seat acceleration, response of the seat suspension's relative displacement and the seat suspension's vibration isolation ability according to two investigated cases of natural frequency and damping ratio. The obtained results from all 3 methods have no difference and the evaluation indexes are suitable according to the studies on vehicle vibration response. The Numerical model method requires the user to perform complex mathematical modeling. The MBD model method using Matlab Simmechanics is simpler, using built-in function blocks, requiring declarations to establish the exact initial equilibrium position of the mass elements. The FEM model method using Ansys APDL with keypoints and lines describing the model elements requires precise setting of the displacement of each keypoint. However, both the MBD and FEM model methods are only effective when investigating the response in the time domain for a particular instance of the excitation frequency. When analyzing the response in the frequency domain, which requires accessing and synthesizing data of many cases in the investigated frequency range, these two methods have many limitations in the calculation process, specifically, in performing complex computations with many loops and variables. Solving problems also takes longer than numerical method using mathematical model. The obtained results are analyzed in the time domain, frequency domain, and the value domain of the driver's seat suspension parameters. This result serves as a basis for developing the design of the driver's seat suspension system with nonlinear spring and shock absorber, and the selection of a calculation method suitable for each problem in the field of vehicle vibration.

Effect of Time and Frequency of Magnetic Field Application on MRF Pressure Performance.

This research was conducted to determine the effect of the time and frequency of magnetic field application on MRF pressure performance. It was carried out by placing magnetorheological fluid (MRF) in a U-shaped, glass tube and then repeatedly applying a magnetic field to it for a certain time period with a particular frequency set by the generator frequency. The length of the application period of the magnetic field, the frequency of the application of the magnetic field, and the magnitude of changes in fluid pressure that occurred and changes in pressure in the MRF were recorded with a data logger for a specific time, which was 60 s. From the field tests that were carried out, it was found that during the application of a continuous magnetic field, there was pressure on the MRF until it reached the maximum pressure; then, there was a gradual decrease in pressure when the magnetic field was turned off, but the pressure was intense. It was shown that the pressure decreased rapidly as the magnetism disappeared, even causing the pressure to drop below the initial pressure, which, in turn, gradually rose again toward the equilibrium pressure. Meanwhile, during the repeated application of a magnetic field, it appeared that the MRF effectively produced pressure in response to the presence of a magnetic field up to a frequency of 5 Hz. The higher the applied magnetic field frequency, the smaller the pressure change that occurred. Starting at a frequency of 10 Hz, the application of a magnetic field produced more minor pressure changes, and the resulting pressure continued to decrease as the liquid level decreased toward the initial equilibrium position.

A theory for bistable vibration isolators

Bistable structures have been widely used for vibrational energy harvesting, the corresponding potential vibration isolation application has also received attention recently. This paper presents a general theory for bistable vibration isolators (BVIs) and reveals the bistable vibration isolation mechanism. The nonlinear restoring force and potential energy are obtained through analyzing the general model of BVIs with “three-spring” quasi-zero stiffness (QZS) model. The generalized force and displacement transmissibilities of BVIs are deduced. The theoretical and numerical transmissibilities are calculated. A feasible model of BVIs is applied to quantitatively verify the advantages of BVIs in vibration isolation. The results demonstrate that BVIs can provide negative and softening stiffness characteristics to broaden the isolation band, and a shallower potential barrier and intrawell oscillation are beneficial to vibration isolation. BVIs should be carefully designed to avoid the interwall oscillation to ensure a considerable vibration isolation performance due to the effects of initial equilibrium position. This paper provides a guideline for the design, analysis, and optimization of BVIs.

Collision of two self-trapped atomic matter wave packets in an optical ring cavity.

The interaction between atomic Bose-Einstein condensate (BEC) and light field in an optical ring cavity gives rise to many interesting phenomena such as supersolid and movable self-trapped matter wave packets. Here we examined the collision of two self-trapped atomic matter wave packets in an optical ring cavity, and abundant colliding phenomena have been found in the system. Depending on the magnitude of colliding velocity, the collision dynamics exhibit very different features compared with the cavity-free case. When the initial colliding velocities of the two wave packets are small, they correlatedly oscillate around their initial equilibrium positions with a small amplitude. Increasing the collision velocity leads to severe scattering of the BEC atoms; after the collision, the two self-trapped wave packets usually break into small pieces. Interestingly, we found that such a medium velocity collision is of great phase sensitivity, which may make the system useful in precision matter wave interferometry. When the colliding velocity is further increased, in the bad cavity limit, the two wave packets collide phenomenally similar to two classical particles-they first approach each other, then separate with their shape virtually maintained. However, beyond the bad cavity limit, they experience severe spatial spreading.

Study on stability of cable-anchored underwater platform by parametric excitation

Aiming at the stability of the heaving–pitching coupling motion of the cable-anchored underwater platform in the nonlinear flow field, considering the change of its initial equilibrium position under the flow field, a coupled heaving–pitching motion equation is established; the transition curve of stability at frequency ratios of 0, 0.5, and 1 was obtained by using the virtual mass method and deformation parameter method. According to the Floquet theory, the stability characteristics under weak parameter excitation are studied. The stability and instability regions were identified and verified by time history response. The results show that the range of the stability region can be changed by adjusting the damping of the system. With the increase of damping, the range of stability gradually increases. Therefore, it is possible to take measures such as adding the helical damping side plate, changing the cross-sectional shape of the platform floating body, and increasing the cross-sectional diameter to suppress the heaving displacement and pitching range of the cable-anchored underwater platform.

ITER cold VDEs in the limit of perfectly conducting walls

Recently, it has been shown that a vertical displacement event (VDE) can occur in ITER even when the walls are perfect conductors, as a consequence of the current quench (CQ) [A. H. Boozer, Phys. Plasmas 26, 114501 (2019)]. We used the extended-MHD code M3D-C1 with an ITER-like equilibrium and induced a CQ to explore cold VDEs in the limit of perfectly conducting walls, using different wall geometries. In the case of a rectangular first wall with the side walls far away from the plasma, we obtained very good agreement with the analytical model developed by Boozer that considers a top/bottom flat-plates wall. We show that the solution in which the plasma remains at the initial equilibrium position is improved when bringing the side walls closer to the plasma. When approximating the ITER first wall as a perfect conductor, the plasma remains stable at the initial equilibrium position far beyond the value predicted by the flat-plates wall limit. When considering an opposite limit in which only the inner shell of the ITER vacuum vessel acts as a perfect conductor, the plasma is displaced during the CQ, but the edge safety factor remains above 2 longer in the current decay compared to the flat-plates wall limit. In all the simulated cases, the VDE is found to be strongly dependent on the plasma current, in agreement with a similar finding in the flat-plates wall limit, showing an important difference with hot VDEs in which the CQ is not a necessary condition.

Numerical Studies of Elastomeric Isolator Performance Under Seismic Influence

The article presents the studies of the elastomeric isolator performance under seismic influence. The solutions of the problems are obtained in the LS-Dyna software package. The calculations were performed by direct integration of the equations of motion using an implicit scheme. In the study of the elastomeric isolator, a three-dimensional finite element model was used. The diagrams of residual horizontal displacements of the support after the seismic influence are obtained. The inability of elastomeric isolators to self-return to the initial equilibrium position without additional devices is proved. The diagrams of acceleration of the support after the end of seismic influence are obtained. It is shown that the elastomeric isolators are an effective means of seismic isolation of buildings and structures. The dependence of the efficiency of the supports on the dominant frequency of external seismic influence is noted.

블록의 탑재 안전성을 위한 초기 평형 자세 탐색 방법 연구

블록의 탑재 안전성을 위한 초기 평형 자세 탐색 방법 연구

A viscosity model for ionic liquids based on the Eyring's theory and a cubic EoS

A thermodynamic model based on the combined use of the Eyring's activated state theory and a cubic equation of state was developed here to accurately represent the dynamic viscosity of pure ionic liquids (ILs). Within the Eyring's theory, the net viscous flow of a pure IL is assumed to be governed by four main variables: (1) the energy necessary for a molecule to jump from an initial equilibrium position to a new one, (2) the energy necessary to break the molecular bonds to create a hole (vacant sites) of molecular size in the liquid, (3) the availability of the vacant sites, and (4) the frequency or the mean residence time of the jumping molecules. The various activation-state variables were then related to well-known thermodynamic potentials that in turn were estimated from two simple cubic equations of state of the van der Waals type (Soave or Peng-Robinson). The resulting model was successfully validated during the representation of experimental dynamic viscosities of three families of imidazolium-based ILs ([CXmim][BF4], [CXmim][PF6] and [CXmim][Tf2N]), four pyridinium-based ILs ([bmpy][BF4], [empy][EtSO4], [Et2Nic][EtSO4] and [hemmpy][Tf2N]) and two ammonium-based ILs ([cpmam][MeSO4] and [4bam][doc]) within a temperature range varying from 0 to 80 °C and at pressures from 1 up to 3000 bar thus covering a wide viscosity range of 10–19,610 mPa-s.

Numerical studies of elastomeric isolator performance under static loads

The article presents the studies of the elastomeric isolator performance under static loads. The solutions of the problems have been obtained by means of a specialized software complex by direct integration of the motion equations according to the implicit scheme. For calculation of the elastomeric isolator, a 3D computational model comprised by solid finite elements has been used. Based on the results of the studies performed, the diagrams for displacement of the points of the top of the support have been plotted with the horizontal shear of the support. The possibility of formation of tilting in the upper plate of the elastomeric isolator has been proved. The diagram of residual horizontal displacements of the support after the horizontal load removal has been obtained. The inability of elastomeric isolators to return independently to the initial equilibrium position without additional devices has been proved.

Design of A Novel Passive Binary-Controlled Variable Stiffness Joint (BpVSJ) Towards Passive Haptic Interface Application

In this paper we present the design, development and experimental validation of a novel Binary-Controlled Variable Stiffness Joint (BpVSJ) towards haptic teleoperation and human interaction manipulators applications. The proposed actuator is a proof of concept of a passive revolute joint, where the working principle is based on the recruitment of series-parallel elastic elements. The novelty of the system lies in its design topology, including the capability to involve an (n) number of series-parallel elastic elements to achieve ( $2^{n}$ ) levels of stiffness, as compared to current approaches. Accordingly, the level of stiffness can be altered at any position without the need to revert to the initial equilibrium position. The BpVSJ has low energy consumption and short switching time, and is able to rotate freely at zero stiffness without limitations. Further smart features include scalability and relative compactness. This paper details the mathematical stiffness modeling of the proposed actuator mechanism, as well as the experimentally measured performance characteristics. The experimental results matched well with the physical-based modeling in terms of stiffness variation levels. Moreover, Psychophysical experiments were also conducted using (20) healthy subjects in order to evaluate the capability of the BpVSJ to display three different levels of stiffness that are cognitively realized by the users. The participants performed two tasks: a relative cognitive task and an absolute cognitive task. The results show that the BpVSJ is capable of rendering stiffness with high average relative accuracy (Relative Cognitive Task relative accuracy is 97.3%, and Absolute Cognitive Task relative accuracy is 83%).

Magnetic resonance force microscopy with a paramagnetic probe

We consider theoretically extension of magnetic resonance force microscopy (MRFM) replacing a ferromagnetic probe on a cantilever tip (CT) with a paramagnetic one (PMRFM). The dynamics of the interaction between the paramagnetic probe and a local magnetic moment in a sample is analyzed, using a quasi-classical approach. We show that the application of a proper sequence of electromagnetic pulses provides a significant deflection of the CT from the initial equilibrium position. Periodic application of these sequences of pulses results in quasi-periodic CT deflections from the equilibrium, which can be used for detection of the magnetic moment in a sample.

Ride responses of macpherson suspension systems

The main purpose of this study is to obtain more correct vehicle ride responses by using a nonlinear ride model considering the effect of Macpherson suspension geometry. Traditional ride model applied to analysis and controller design uses a two degree of freedom linear model, which includes sprung mass and unsprung mass and a spring and a damper vertically connect them. In fact, suspension components do not vertically position above the tire. The motions of body and tire are not going straight up and down. Therefore, the analysis results obtained by the simple model are often different from the experimental values of the actual vehicle. Because of the difference between simple model and actual vehicle, the control strategy almost cannot apply to actual vehicle. In order to understand the effect of suspension geometry on the vehicle ride responses and design a more practical control strategy, a nonlinear model including the geometric parameters of the suspension is constructed in this study. To estimate the initial equilibrium position of the suspension assembly under load, the static equilibrium analysis and mechanism motion analysis are synchronous implemented at the same time. The nonlinear model describes not only the relative position and velocity but also the force transmission between body and tire. Furthermore, by linearize this nonlinear model the development of control strategy for subsequent (semi) active suspension system could be expected.

Casimir and Optical Forces Acting on a Silicon NOEMS Device Based on Slot-Waveguide Structure

We investigate the effect of Casimir force on a silicon nano-opto-electro-mechanical system (NOEMS) device, based on a slot-waveguide structure and driven by optical forces. Light is strongly confined in the slot-waveguide, which enhances the optical force and reduces the optical power necessary to control the device. However, we predict that the Casimir force affects the device's critical points of stability, by reducing the critical optical power for the quasi-TE fundamental eigenmode, as well as imposing a critical power for the quasi-TM one. Casimir force also changes the initial NOEMS equilibrium position, pre-deforming the two sides of the slot-waveguide, even in the absence of optical forces; this establishes a minimal initial gap distance for the slot-waveguide, thus affecting the device's design parameters.

Dynamics of a Superconducting Linear Slider

In this paper, the dynamic behavior of a one degree-of-freedom (DOF) contactless linear slider based on superconducting magnetic levitation is experimentally analyzed. The device is intended for precision positioning of an optic mirror in cryogenic environments. Different prototypes of this device have been tested at cryogenic temperatures (77 K), and their mechanical behavior characterized in the sliding direction for forced and unforced oscillations. Experimental results reveal that the slider is self-stable at the initial equilibrium position and the dynamic behavior fits well an underdamped harmonic oscillator. Finally, the device showed great potential for horizontal vibration isolation, acting as a low-pass filter with a resonance at about 0.9 Hz.

Nonlinear Response of Carbon-Carbon Laminated Panels to Random Acoustic Excitation under a Gradient Temperature Field

Future missions for aircraft will expose structures to severe thermal and acoustic loads. Efficient analysis methods for predicting nonlinear random response and fatigue life are urgently important. This paper presents a finite element model for analyzing nonlinear random dynamic behaviors of Carbon-Carbon composite panels under temperature gradients and Guassian excitations. The temperature distribution over the plate follows double sine curve. A finite element formulation combined with the equivalent linearization approach and normal mode method is established. The global system of equations is reduced to a set of nonlinear, coupled modal equations. Examples are given for an orthotropic C/C composite laminated panel at various combinations of temperatures gradients and sound pressure levels. Numerical results include RMS values of maximum deflection, time histories of deflection response and stress response, power spectrum densities, probability distribution functions and higher statistical moments. Numerical results verified all three types of panel motions for a simply supported orthotropic laminated plate: small-deflection random vibration about the initial equilibrium positions, snap-through motions between the two buckled positions, and nonlinear random response about new equilibrium positions after post-buckling. Numerical results will provide the important reference basis to aero engine structural integrity design and improving the structure dynamic strength and working life.