Freedom Model Research Articles

Research on Interactive Product Design Based on User Behavior Data in Virtual Reality Environment

Abstract This paper designs an interactive product based on the virtual reality environment and related technologies and further optimizes the interactive product based on the user behavior data collected by the interactive product. Based on the ORB-SLAM algorithm, we construct a hand controller degree of freedom model for the interactive product to overcome the limitations of hand controller positioning. By constructing the ORB-SLAM3 jump perception model, the interactive product can be used more smoothly. The collected user interaction behavior data is downsized using PCA principal component analysis and interaction behavior characteristics of different users are classified using the LATM network. The average completion times of the camera proposed in this paper as a hand controller for tasks such as 3D pointing are 14.23, 12.29 and 13.68 seconds, respectively, which all perform well compared to other hand controllers. At the same time, the interactive products designed using the method of this paper have the least abnormalities detected by users during the use process, and the highest abnormal feeling rate is only 37.22%. There are significant differences in the behavioral characteristics of users during the use of interactive products, based on the distribution of feature data can be divided into three categories: virtual exploration, interactive experience, and traditional. Strategic directions for further optimizing interactive products can be provided through the behavioral analysis of users in different categories.

Noise analysis of interior structure under powertrain excitation

To accurately identify the structural noise problem caused by vibration in the cockpit, an experimental study was conducted on a certain type of SUV under uniform acceleration conditions. Based on the planning of the multi-body system dynamics model, a transfer path model with secondary contributions is constructed, and the load is identified using the single degree of freedom model and multi-frequency bandwidth model under the OPAX method based on this path. The results indicate that the second-order vibration of the powertrain is transmitted to the entire suspension system through the X direction of the right suspension. The second-order vibration of the suspension system is then transmitted to the Z direction of the right rear bolt of the subframe, causing the entire subframe vibration and ultimately reaching the target point. This structural path has the greatest impact on the interior noise of the vehicle. This path research method can more accurately determine the main excitation points that cause interior noise problems on a certain path and better understand the overall energy transfer characteristics along the transmission path.

Investigation of field scenarios using a 4n degrees of freedom transient torque and drag model

A coupled drill string dynamics model presents an opportunity to understand, replicate and potentially control the vibrations occurring along a drill string in a deep well. This paper describes a 4n degrees of freedom (4nDOF) model of the axial, torsional and lateral dynamics, consisting of coupled wave equations and lumped elements, which include modeling of the contact between the drill string and wellbore with a stiff string assumption. The model accounts for the bit-rock interaction, structural damping, and hydraulic forces acting on the lumped elements. The 4nDOF model is compared with three field scenarios from a drilling operation in the North Sea: a three-stage top drive start-up procedure, a drilling sequence starting from off-bottom conditions, and a backreaming operation at low rotational speed. The selected cases include instances of stick–slip and higher modes of torsional vibrations, which persist despite the use of a surface vibration mitigation system. High-frequency data recorded by a downhole measurement sub placed near the drill bit are used to verify the simulated downhole rotational speed and triaxial accelerations. The model is useful for analyzing torsional stick–slip events, which are replicated with a similar period and amplitude as in the downhole measurements. Furthermore, the model accurately reproduces the transition between first and second mode torsional oscillations upon the activation of a tuned top drive vibration mitigation system. The model can also be used to analyze lateral deformations and whirling of the drill string at various depths. The field case simulations show that the lateral dynamics can undergo significant changes at certain points in the drill string during torsional stick–slip and higher-mode torsional oscillations. The proposed model can be used to run simulations in close to real-time on a standard personal workstation, thus making it a valuable tool for devising and testing new drill string vibration mitigation solutions.

City-scale buildings damage estimation based on broadband physics-based ground motion simulation of 2021 Ms 6.4 Yangbi, China, earthquake

This article proposed a computational workflow for city-scale building damage estimation based on broadband physics-based ground motion simulation. The dynamic stiffness matrix method in frequency-wavenumber domain is employed for broadband physics-based ground motion simulation of finite fault along with site response correction using equivalent-linear site response analysis approach. With simulated ground motion, seismic response of buildings, using multi-degree of freedom model, is simulated using nonlinear time history analysis, and building damage is evaluated based on a trilinear backbone curve of story’s nonlinear force-drift model. Main advantage of the framework lies in the employed dynamic stiffness matrix method for ground motion simulation, which can efficiently generate broadband ground motions in perfect parallel and naturally capture the physics of finite fault source, propagation path, and spatial variability characteristics of ground motion. To demonstrate the salient features of proposed workflow, the 2021 Ms 6.4 Yangbi earthquake is simulated with frequency resolution up to 20 Hz, and seismic damage of buildings in Yangbi county are estimated. Results show that most traditional wood-adobe structures suffer moderate to severe damage, and engineered seismic buildings (mostly RC frame) in Yangbi county suffer minor damage, which agrees with field investigation results.

Finite element modeling of piezoelectric cantilever-beam energy harvester

Piezoelectric energy harvesting from mechanical vibrations has attracted considerable attention during the last decade. The homogeneous harvesters were studied experimentally or numerically by various models such as single degree of freedom (SDOF) modeling, finite element (FE) modeling as well as using analytical solutions. In this work, FE models for simulating a piezoelectric beam bimorph power harvester consisting of a laminated piezoelectric beam, a proof mass, and an electrical load (series or parallel connections) configurations are developed. The effects of the material and size of the substrate, the proof mass have been studied on the resonance frequencies and the output parameters of the piezoelectric generator (PEG). Numerical results obtained using the proposed procedure for piezoelectric bimorph power harvesters are in good agreement with the experimental data available in the literature. The proposed method can be used for modeling accurately this class of energy harvesting devices.

Learning Latent Dynamics for Autonomous Shape Control of Deformable Object

In recent years, the methods of loading and transporting rigid objects have become more and more perfect. However, in the process of transportation, the shape control of deformable objects has attracted extensive attention because deformable objects have been widely used in intelligent tasks such as packing and sorting cables before transportation. Restricted by the super-degrees of freedom and nonlinear dynamic models of deformable objects, planning the action trajectories to control the shape of deformable objects is a challenging task. In this work, we use contrastive learning to solve the shape control problem of deformable objects. The method jointly optimizes the visual representation model and dynamic model of deformable objects, maps the target nonlinear state to linear latent space which avoids model inference for deformable objects in infinite-dimensional configuration spaces. Furthermore, to extract effective information in the latent space, we construct an encoder with a multi-branch topology to improve the representation ability of the model. Experimentally, we collect dynamic trajectory data for random shape control task involving cloth or rope in a simulated environment. Then we apply it to train the proposed offline method to obtain latent dynamic models for shape control of deformable objects. In comparison with other baseline methods, our proposed method achieves substantial performance improvements.

Evaluation of equivalent linearization methods of MDOF isolated structures in response spectrum analysis

In the seismic design of isolated structures, equivalent linearization of the hysteretic isolators is normally considered. There exist many equivalent linearization methods and evaluation of these methods has been widely studied. However, most of the previous studies concern a single degree of freedom system only, and the used analysis method is time history analysis. In such a case, the evaluation heavily depends on the ground motions selected. Note that the response spectrum analysis is a commonly used method for seismic design of structures. Therefore, it is more valuable to evaluate these equivalent linearization methods based on the response spectrum analysis. In this study, a multiple degree of freedom model is adopted due to the contribution of higher modes of the superstructure to the seismic responses, and the procedure of the response spectrum analysis in conjunction with the equivalent linearization method is presented in detail. Then, considering a series of parameters of isolators, a statistical study is performed to evaluate the accuracy of these equivalent linearization methods by comparing with the nonlinear time history analysis. Moreover, the effect of the damping reduction factor for the response spectrum on the accuracy of the equivalent linearization methods is discussed in terms of probability in a desirable error range. The analytical results show that the accuracy of the equivalent linearization methods is associated with the earthquake intensity. Meanwhile, for different response quantities the accuracy of each equivalent linearization method varies significantly. In addition, to estimate the seismic responses with a better accuracy in the response spectrum analysis, a suitable damping reduction factor should be considered.

A compatible uniaxial Bouc–Wen model for accurate estimation of residual deformation of seismically isolated structures

Bouc–Wen (BW) model is commonly used to model lead rubber bearings (LRBs) in seismically isolated buildings. However, the original BW model violates the Drucker’s or Ilyushin’s postulate of plasticity by displaying the displacement drift, force relaxation, and non-closure of hysteretic loops. These deficiencies can significantly impact the seismic performance of the isolated structures, leading to unrealistic evaluation of residual deformation concentrated in the isolation layer. To address these issues, a step-by-step amendment algorithm is proposed to develop a compatible uniaxial BW (CBW) model that conforms to the basic physical rules. The proposed algorithm involves adding a reinforcement factor to the short-path reloading branches, defining reversal and reloading points to identify reloading behavior. Furthermore, it develops an adaptive limit to distinguish between the short-path and full-path reloading branches. The proposed algorithm was validated using various short unloading–reloading scenarios. Subsequently, a simplified single degree of freedom (SDOF) model representing a seismically isolated building was defined. Incremental dynamic analysis was performed to evaluate the seismic responses of the isolated building designed with the original BW, CBW, and bilinear models. Results indicate that although the peak displacement and seismic force of the isolation layer induced by the three models produce small deviations, considerable errors in residual displacement are observed. Compared with the original BW model, the bilinear model produces unrealistic sharp yielding transition and overestimates the residual displacement. However, it can reduce displacement drift and force relaxation. By contrast, the proposed CBW with the improved algorithm can effectively correct the defects of the original BW and bilinear models. The CBW model can be used to accurately estimate the residual deformation of the seismically isolated buildings.

NN-based reinforcement-learning optimal sliding mode control for drag-free and attitude of spacecraft with state constraints

This paper investigates a tracking control issue for a class of drag-free spacecraft with state constraints caused by the optical assembly. Firstly, a nonlinear kinematics and dynamics relative equation of coupling system of position and attitude is devised by a 6-degree of freedom (DOF) model of rigid body. Secondly, an optimal control method with a terminal functional is designed to meet state constraints. To solve the Hamilton-Jacobi-Bellman (HJB) equation generated by the optimal control of the nonlinear model, a policy iteration ideal is presented and the final numerical solution of the iteration is obtained by a critic neural network (NN). Thirdly, to enhance the robustness of the closed-loop system, an optimal sliding mode control is proposed, which can ensure the optimal and robustness performance simultaneously. At last, the simulation results demonstrate the performance of the proposed methods and the contrast of precision and robustness of two methods are showcased.

Lip-valve interactions with the resonant bore of a trombone

Players of brass instruments usually play at a pitch close to one of the strong resonances of the instrument bore, but can easily play either above or below a resonance. Simple one-degree-of freedom models having aperture in phase with longitudinal lip displacement do not readily explain auto-oscillationwith realistic values of lip losses and cannot explain oscillation at frequencies below resonance. Experimental measurements of lip motion, pressures and flows show that the lips’ longitudinal motion leads the transverse: the lips move downstream closed, then open, then retract while open. Because of the forward sweeping motion, flow starts before the lips open. The sweeping motion has two important effects: first, it allows a range of phases between pressure and flow. Second, it means that the DC pressure acts on a larger area in the forward motion than during retraction. Both have consequences for oscillation energetics. A simple calculation of the PdV work done on the longitudinal component of motion, using measured quantities, indicates that it could provide a substantial fraction of the energy necessary for auto-oscillation with lossy lips. These mechanisms might have implications for other auto-oscillatory systems such as the vocal folds.

New six degree of freedom model for ice throw simulations

Icing and thus ice throw from wind turbines is currently unavoidable in cold climates. Therefore, the associated risk requires adequate quantification and assessment. In this study, a new six degree of freedom model with increased accuracy is introduced, which aims to overcome limitations of currently used approaches. This is achieved by taking into account translation and rotation of the thrown fragments and thus allowing to represent more complex trajectories. To limit the necessary numerical effort, look-up tables for forces and moments are pre-calculated with the help of CFD simulations. Validation of the model was achieved by comparison to real life experiments. For these, artificial ice fragments based on collected real fragments were produced and released from wind turbines under partially controlled conditions. This showed a significantly improved agreement between simulated and observed values when compared to the state-of-the-art model. Since the distribution patterns of the presented model differ significantly from those of the established model, these consequences must be taken into account in future risk assessments.

The Sensitivity of Global Structural Parameters for Unreinforced Masonry Buildings Subjected to Simulated Ground Motions

This research performs a parametric study based on Equivalent Single Degree of Freedom (ESDOF) models for simplified seismic analysis of unreinforced masonry (URM) structures. This is a necessary action due to the fact that it is not affordable to model and analyze populations of masonry buildings by using detailed continuum-based models during regional seismic damage and loss estimation studies. Hence, this study focuses on the sensitivity of major structural parameters of a selected idealized hysteretic model for URM buildings. The numerical models are subjected to region-specific simulated ground motion time histories generated using validated seismological parameters. The variations in dynamic analysis results are evaluated using statistical tools for major structural and seismological parameters. The results reveal that the strength factor is the most influential structural parameter, whereas magnitude and distance have a significant impact on the response of idealized URM models as seismological parameters. Furthermore, the specific seismic performance exhibiting limited ductility capacity and the narrow margin of safety between the initial state of inelastic behavior and the ultimate (collapse) state for URM buildings is verified by the statistical approaches employed in this study.

Modeling of Piezo Stack Actuators and Their Application in Active Vibration Control

This paper presents the vibration control of a highly simplified two degree of freedom model of a helicopter. The vibration control study has been performed using both active and passive vibration control schemes. In the case of active vibration control, the feedback mechanism affects the stiffness of the system; whereas in passive vibration control, the absorber mass affects the inertia of the system. The active control is achieved using a combination of piezo stack sensor and actuator mechanism. A finite element model for the piezo stack mechanism has been developed to obtain a relation between deformation, applied/induced potential and externally applied mechanical load. The results of this study indicate that inclusion of sensor and actuator units increases the natural frequency of the system due to increase in stiffness of the system. It is observed that in the case of active vibration control, the frequency response of acceleration of the system is highly sensitive to small variations in the magnitude of gain around its optimum value and insensitive to changes in excitation frequency; whereas in passive vibration control, the frequency response does not exhibit any significant change in the characteristics with respect to the variation in the absorber mass, while it is highly sensitive to changes in operating frequency.

The virtuous, the caring, and the free: ethical theory to understand the ethics of the teacher as a role model in engineering education

ABSTRACT In this paper, we discuss the ethical responsibilities of being a role model as an engineering teacher in higher education. We draw on virtue ethics, care ethics, ethics of freedom and role modeling theory, using Grande's framework for engineering education. We argue that the three ethical theories give different views on the ethics of role modeling as a teacher. Virtue ethics implies that the teacher should behave as virtuously as possible to encourage students to emulate character traits. Care ethics implies that the ethics of role modeling is fundamentally about care practices, emphazising relationships and values such as attentiveness and responsibility. Ethics of freedom urges the teacher to grant individuals opportunities to develop and be free from the control of others. By using role modeling and ethical theory, we aim to show how theory has an impact on both teaching practices and could underpin empirical research in engineering education.

Interacting effects of AFO stiffness, neutral angle and footplate stiffness on gait in case of plantarflexor weakness: A predictive simulation study

To maximize effects of dorsal leaf ankle foot orthoses (AFOs) on gait in people with bilateral plantarflexor weakness, the AFO properties should be matched to the individual. However, how AFO properties interact regarding their effect on gait function is unknown. We studied the interaction of AFO bending stiffness with neutral angle and footplate stiffness on the effect of bending stiffness on walking energy cost, gait kinematics and kinetics in people with plantarflexor weakness by employing predictive simulations.Our simulation framework consisted of a planar 11 degrees of freedom model, containing 11 muscles activated by a reflex-based neuromuscular controller. The controller was optimized by a comprehensive cost function, predominantly minimizing walking energy cost. The AFO bending and footplate stiffness were modelled as torsional springs around the ankle and metatarsal joint. The neutral angle of the AFO was defined as the angle in the sagittal plane at which the moment of the ankle torsional spring was zero. Simulations without AFO and with AFO for 9 bending stiffnesses (0–14 Nm/degree), 3 neutral angles (0–3-6 degrees dorsiflexion) and 3 footplate stiffnesses (0–0.5–2.0 Nm/degree) were performed.When changing neutral angle towards dorsiflexion, a higher AFO bending stiffness minimized energy cost of walking and normalized joint kinematics and kinetics. Footplate stiffness mainly affected MTP joint kinematics and kinetics, while no systematic and only marginal effects on energy cost were found.In conclusion, the interaction of the AFO bending stiffness and neutral angle in bilateral plantarflexor weakness, suggests that these should both be considered together when matching AFO properties to the individual patient.

Direct loss‐based seismic design of reinforced concrete frame and wall structures

AbstractThis paper presents a procedure to design reinforced concrete (RC) buildings to achieve an acceptable target level of earthquake‐induced loss (e.g., deaths, dollars, downtime) under a site‐specific hazard profile. The procedure is called “direct” since the target loss level is specified at the first step of the process, and virtually no iteration is required. The procedure is based on a simplified loss assessment involving a surrogate model for the seismic demand (i.e., probability distribution of peak horizontal deformation given ground‐motion intensity) and simplified loss models for direct and indirect losses. For an arbitrarily‐selected target loss level and structural geometry, the procedure provides the force‐displacement curve of the corresponding equivalent single degree of freedom system. The principles of displacement‐based design are adopted to provide member detailings (beams, columns, walls) consistent with such force‐displacement curve. The procedure is applied to 16 realistic RC case studies with a lateral resisting system composed of frames in one direction and cantilever walls in the perpendicular one. They show different geometries, hazard profiles, and target values of direct economic expected annual loss. A benchmark loss estimation is obtained using cloud‐based non‐linear time‐history analyses of multi‐degree of freedom models. The procedure is conservative since the benchmark loss levels are always smaller than the targets. Such discrepancy is within 10% for 12 out of 32 case studies, between 10% and 20% for 13, between 20% and 31% for the remaining six. Therefore, the proposed procedure is deemed dependable for preliminary design.

A single degree of freedom model for cracked beam

This paper presents a simplified model of cracked beam by single-degree-of-freedom system. Equivalence between the beam and SDOF models means that they have the same fundamental natural frequency and similar frequency response functions (FRFs). Similarity of FRFs is checked by using the frequency-domain assurance criterion acknowledged herein as spectral similarity index (SSI). Finally, FRFs of both the cracked beam and its simplified SDOF model have been examined versus crack location and depth using the so-called spectral damage index (SDI). Numerical results show that SDI is significantly sensitive to crack and could be used as a novel indicator for crack detection in beam by measurements of frequency response functions.

Event-trigger NMPC for 3-D trajectory tracking of UUV with external disturbances

In this paper, a novel Three-Dimensional (3-D) trajectory tracking method based on Event-triggered Nonlinear Model Predictive Control (ENMPC) is designed for an Underwater Unmanned Vehicle (UUV) with external disturbances. Firstly, the 5-Degrees of Freedom (5-DoF) model of UUV is represented by both kinematics and dynamics. After that, a Nonlinear Model Predictive Control (NMPC) algorithm is designed for the 3-D trajectory tracking of UUV, and the feasibility of the control method and the stability of the closed-loop system are proved, which are further verified by simulation experiments. Then, an event-triggered mechanism is introduced on the basis of NMPC algorithm, which reduces the amount of calculation iterations without affecting the 3-D trajectory tracking performance. Finally, the simulation results verify the feasibility and effectiveness of the proposed algorithm. Compared with the Traditional Model Predictive Control (TMPC) and NMPC algorithm, the ENMPC strategy can effectively reduce the amount of calculation iterations and improve the tracking efficiency.

Source contribution analysis of vehicle pass-by noise using a moving multi-band model based OPAX method

The conventional operational path analysis with eXogeneous inputs (OPAX) method has been widely used to investigate the vibration transfer paths. However, the single degree of freedom model is not available for the load identification of acoustic sources due to their unknown source behavior. And the alternative multi-band (MB) model can only offer a deterministic estimation to the load parameters. To assess the acoustic source contribution of vehicle pass-by noise (PBN), this paper develops the OPAX method by introducing a moving multi-band model (MMB). In this method, the vehicle acoustic sources are simplified as a combination of a series of point sources. The source loads are firstly parametrically modelled by MB models. Then the load parameters are solved several times in the MMB and estimated by the index of coefficient of variation, which suppresses the effect of nonlinear random noise and improves the load identification accuracy of acoustic sources. Finally, the source contributions to PBN at receivers can be derived. Both numerical studies and experimental validations are implemented to examine the performance of the proposed method. Results show that compared to the conventional OPAX method, the proposed method can provide a higher accuracy for the source contribution analysis of PBN.

Theoretical and Experimental Investigation of Using Multidegree of Freedom Electrostatically Actuated Microstructures in Performing Classification Problems

This paper demonstrates the use of micro-electromechanical systems to perform an efficient classification problem. Classification using digital computers is inefficient due to its power requirement and the separation between memory and processing units. As a proof of concept, basic signal classification has been performed using a network of only three mechanically coupled devices. The classification occurred at the hardware level rather than using a digital computer. The classification problem involves distinguishing between a ramp signal versus a step input signal. In this demonstration, a three-degree of freedom model was built for the proposed network in MATLAB. Detailed simulation results were extracted to validate the network operation and sensitivity to operating conditions. Next, the device network hardware was fabricated and tested to perform the required classification problem. Good agreement between simulation and experiment is demonstrated.