bluuebunny/crossref_metadata_2025 huggingface dataset:
Robust Maneuvering Control for Marine Vehicles Under Uncertain Ocean Currents
Authors: Huang Qingmin , Chen Ye-Hwa , Nie Xin
Published: February 2014

We consider the problem of tracking a desired trajectory with a desired velocity for a marine vehicle. There are possibly fast time-varying uncertainties which may exist in the model, the inputs, the ocean currents, as well as environment disturbances. Based on the possible bound of the uncertainties and some structure properties the marine vehicle are met, a state transformation is made to the dynamics of error of the marine vehicle. A robust control scheme is proposed which renders the transformed system practically stable. A proof shows that the original uncertain marine vehicle under this control will also be practically stable. Furthermore, the uniform ultimate boundedness ball and uniform stability ball of the marine vehicle can be made arbitrarily small by suitable choice of the design parameters.
Computer-Aided Customized Shape Design of an N95 Filtering Facepiece Respirator
Authors: Lei Zhipeng , Yang James
Published: February 2014

A respirator protects its user by sealing the user’s face and filtering hazardous particles from environment. However, faceseal leakages of users-respirators always happen. First, this study investigated a computer-aided technique for designing a well fitted N95 filtering facepiece respirator (FFR) for a subject. The customized N95 FFR includes a customized contact area, a center filtering area, two straps and a nasal clip. Five base contact areas of National Institution for Occupational Safety and Health (NIOSH) headforms were created and the customized contact area was modeled using the mapping relationship between the subject and a NIOSH headform. The center filtering area was designed by considering constraints of N95 FFR shape. Second, this study used simulation-based approaches, including the FE method and computational fluid dynamics (CFD) method, to assess the performance of the customized N95 FFR on the subject. The contact pressure and the faceseal leakage from the subject-customized N95 FFR combination were compared with the results from the subject-existing N95 FFRs combinations. The comparison showed that the customized N95 FFR provided the subject an optimized contact pressure distribution and no faceseal leakage.
Consideration of Assistive Devices in the Gait Analysis of Spinal Cord–Injured Subjects
Authors: Lugrís Urbano , Carlín Jairo , Luaces Alberto , Cuadrado Javier
Published: February 2014

The gait of spinal cord–injured subjects can be improved by means of properly designed active orthoses. Since the gait pattern varies greatly among different patients, the orthoses and their corresponding controllers must be carefully customized, and the joint motor torques obtained from inverse dynamic analysis constitute a useful input for this task.

Nowadays, the analysis of standard gait by using motion capture data is a mature discipline. However, the problem becomes more complex in the case of spinal cord–injured subjects wearing active orthoses: in addition to the presence of the orthoses, these patients always require the help of supplementary assistive devices, such as crutches, in order to stabilize their gait.

In this work, the gait analysis of a subject walking with the aid of crutches and active knee–ankle–foot orthoses is performed, by introducing the assistive devices both at the experimental and computational levels. The required sensors and actuators are incorporated to the system, and the measurements are used to solve the inverse dynamics problem in order to calculate the joint motor torques produced by the subject during gait.
Analytical Conditions for Impacts and Stuck Motions in a Constrained Cantilever Beam
Authors: Luo Albert C. J. , George Richard
Published: February 2014

This paper discusses the forced vibration of a constrained cantilever beam with impact and stuck interactions using any number of modes of vibration. Impacting chatter and stuck phenomena are investigated for the cantilever beam with the constraints at the free end, and analytical conditions for motion switching at the boundary are developed. From the analytical conditions, numerical simulations of periodic motions with motion switching are performed.
An Intelligent Process Planning System Based on Formal Manufacturing Capability Models
Authors: Sadeghi Samira , Ameri Farhad
Published: February 2014

This paper presents an intelligent process planning system for generating machining instructions for prismatic parts. The generated instruction includes machine tool information, machining sequence, tool and setup information, machining parameters, and tool path. In the proposed system, part information is received as a STEP AP224 feature model. One novel aspect of the proposed system is implementation of a formal OWL ontology for representation of machine tool and cutting tool capability knowledge as well as part information. OWL-based ontology enables automated ontological reasoning during process planning. Also, SWRL rule modeling approach is adopted for identifying feasible machine tools and cutting tools and also specifying process parameters. A proof-of-concept implementation is presented as well in this paper.
Avian-Inspired Grasping for Quadrotor Micro UAVs
Authors: Thomas Justin , Polin Joe , Sreenath Koushil , Kumar Vijay
Published: February 2014

Micro Unmanned Aerial Vehicles (MAVs) have been used in a wide range of applications [1, 2, 3]. However, there are few papers addressing high-speed grasping and transportation of pay-loads using MAVs. Drawing inspiration from aerial hunting by birds of prey, we design and equip a quadrotor MAV with an actuated appendage enabling grasping and object retrieval at high speeds. We develop a nonlinear dynamic model of the system, demonstrate that the system is differentially flat, plan dynamic trajectories using the flatness property, and present experimental results with pick-up velocities at 2 m/s (6 body lengths / second) and 3 m/s (9 body lengths / second). Finally, the experimental results are compared with observations derived from video footage of a bald eagle swooping down and snatching a fish out of water.
Efficient Approach for Constraint Enforcement in Constrained Multibody System Dynamics
Authors: Mukherjee Rudranarayan , Malczyk Pawel
Published: February 2014

We present an efficient and robust approach for enforcing the loop closure constraint at acceleration, velocity and position level in modeling multi-rigid body system dynamics. Our approach builds on the seminal ideas of the Divide and Conquer Algorithm (DCA) and the Augmented Lagrangian Method (ALM). The order-independent hierarchic assembly-disassembly process of the DCA provides an excellent opportunity for modularizing the system topology such that the loop closure constraints can be elegantly handled using constraint enforcement ideas motivated by the ALM. We present a non-iterative, user controlled constraint enforcement approach that enables robust constraint enforcement within the DCA. This approach eliminates the need for the iterative scheme found in many ALM motivated approaches. Similarly, it enables the use of relative or internal coordinates to model kinematic joint constraints not involved in the loop closure, thereby enforcing the constraints exactly for these joints. The approach also enables computationally very efficient serial and parallel implementations. Results from a number of test cases with single and couple closed loops are presented to demonstrate verification of the algorithm.
Enhanced Targeted Initial Populations for Multiobjective Product Line Optimization
Authors: Foster Garrett , Ferguson Scott
Published: February 2014

Initial populations for genetic algorithms are often created using randomly generated designs in an effort to maximize the genetic diversity in the design space. However, research indicates that the inclusion of solutions generated based on domain knowledge (i.e. non-random solutions) can notably improve the performance of the genetic algorithm with respect to solution performance and/or computational cost for convergence. This performance increase is extremely valuable for computationally expensive problems, such as product line optimization. In prior research, the authors demonstrated these improvements for product line design problems where market share of preference was the performance objective. Initial product line solutions were constructed from products that had the largest product-level utility for individual respondents. However, this simple product identification strategy did not adequately scale to accommodate the richer design problem associated with multiple objectives. This paper extends the creation of targeted initial populations to multiobjective product line design problems by using the objectives of the problem, instead of product level utility, to identify candidate designs. A MP3 player and vehicle feature packaging product line design problems are used to demonstrate this approach and assess the improvement of this modification.
Enhancing Range of Transport in Optical Tweezers Assisted Microfluidic Chambers Using Automated Stage Motion
Authors: Chowdhury Sagar , Švec Petr , Thakur Atul , Wang Chenlu , Losert Wolfgang , Gupta Satyandra K.
Published: February 2014

In this paper, we present a planning approach for automated high-speed transport of cells over large distances inside an Optical Tweezers (OT) assisted microfluidic chamber. The transport is performed in three steps that combine the optical trap and motorized stage motions. This includes optical trapping and transporting the cells to form a desired cell-ensemble that is suitable for a long distance transport, automatically moving the motorized stage to transport the cell-ensemble over a large distance while avoiding static obstacles, and distributing the cells from the ensemble to the desired locations using OT. The speeds of optical traps and the motorized stage are determined by modeling the motion of the particle under the influence of optical trap. The desired cell-ensemble is automatically determined based on the geometry of the microfluidic chamber. We have developed a greedy heuristic method for optimal selection of the initial and the final location of the cell-ensemble to minimize the overall transport time while satisfying the constraints of the OT workspace. We have discussed the computational complexity of the developed method and compared it with exhaustive combinatorial search. The approach is particularly useful in applications where cells are needed to be rapidly distributed inside a microfluidic chamber. We show the capability of our planning approach using physical experiments.
Online Implementation of the Delta Design Game for Analyzing Collaborative Team Practices
Authors: Oberoi Sharad , Finger Susan , Rosé Eric
Published: February 2014

Over the past four years the authors have developed an online version of the Delta Design game, a board game which was developed by Bucciarelli (1) to teach students design collaboration skills. In the online version, players move tiles on a shared virtual board and communicate only through text chat. In addition, the objective functions are computed automatically each time a tile is moved, so the focus of the game changes from rapid number-crunching to negotiation. Since every state of the board, along with micro-level team performance and chat data, are captured, the resulting corpus from 38 four-player team games provides a rich resource to explore different aspects of collaborative team practices.

This paper gives an overview of the online implementation of Delta Design and discusses the findings from user studies including several undergraduate capstone design classes. Observations of the board-moving tactics show that teams planning a strategy before starting the game or players sharing details about their role’s constraints with other team members do not have much effect on the game’s outcome. Finally, this paper demonstrates that the complex rules of the Delta Design game make it a suitable candidate for analyzing collaboration strategies in team-based design projects.
Predicting Reliability of Structural Systems Using Classification Method
Authors: Gorguluarslan Recep M. , Choi Seung-Kyum
Published: February 2014

This research examines classification approaches for estimating the reliability of structural systems. To validate the accuracy and efficiency of the classification methods, a practical engineering problem; namely, a spider assembly of a washing machine, has been considered. For the spider assembly, fatigue life test, finite element analysis, physical experimentation, and a classification processes are conducted in order to establish the analytical certification of its current design. Specifically, the finite element analysis and fatigue life analysis are performed and their results are validated compared to physical experimental results. The classification process is developed to estimate the probability of failure of the spider assembly in terms of stress and fatigue life. The relationship between the random quantities and structural responses of the spider assembly is established using probabilistic neural network and the support vector machine classifiers. The performance margin of the spider assembly is fully identified based on the estimated failure probability and structural analysis results from the fatigue life analysis and classifications.
Control of Hand Prostheses: A Literature Review
Authors: Cloutier Aimee , Yang James
Published: February 2014

In recent years, there has been a steep rise in the quality of prostheses for patients with upper limb amputations. One common control method, using electromyographic (EMG) signals generated by muscle contractions, has allowed for an increase in the degrees of freedom (DOFs) of hand designs and a larger number of available grip patterns with little added complexity for the wearer. However, it provides little sensory feedback and requires non-natural control which must be learned by the user. Another recent improvement in prosthetic hand design instead employs electroneurographic (ENG) signals, requiring an interface directly with the peripheral nervous system (PNS) or the central nervous system (CNS) to control a prosthetic hand. While ENG methods are more invasive than using surface EMG for control, an interface with the PNS has the potential to provide more natural control and creates an avenue for both efferent and afferent sensory feedback. Despite the recent progress in design and control strategies, however, prosthetic hands are still far more limited than the actual human hand. This review outlines the recent progress in the development of EMG and ENG controlled prosthetic hands, discussing advancements in the areas of sensory feedback and control. The potential benefits and limitations of both control strategies, in terms of signal classification, invasiveness, and sensory feedback, are examined. A brief overview of interfaces with the CNS is provided, and potential future developments for these control methods are discussed.
Coupled Field Dynamic Model of Fatigue Evolution in Structures
Authors: Nguyen Son Hai , Chelidze David
Published: February 2014

A new dynamic model of fatigue evolution in structures is presented. The analytical model is derived for an Euler-Bernoulli beam with a fatigue crack. This model captures the coupling between the crack propagation dynamics and the beam oscillations. Hamilton’s Principle and Paris’ Law are used to advance the coupled field model in which a new characteristic of the beam motion is introduced as a loading parameter to fatigue model. The resulting fatigue damage model is validated by experimental data.
An M-Shaped Asymmetric Nonlinear Oscillator for Broadband Energy Harvesting
Authors: Leadenham S. , Erturk A.
Published: February 2014

Nonlinear oscillators have been given growing attention due to their ability to enhance the performance of energy harvesting devices by increasing the frequency bandwidth. Duffing oscillators are a typical type of nonlinear oscillator characterized by a symmetric hardening or softening cubic restoring force. In order to realize the cubic nonlinearity in a cantilever at reasonable excitation levels, often an external magnetic field or mechanical load is imposed, since the inherent geometric nonlinearity would otherwise require impractically high excitation levels to be pronounced. As an alternative to magnetoelastic structures and other forms of symmetric Duffing oscillators, in this paper, an M-shaped bent beam with clamped end conditions is investigated for bandwidth enhancement under base excitation. The M-shaped beam geometry can exhibit significantly asymmetric spring behavior: hardening in one direction and softening in the other. A particular advantage of the M-shaped structure is its well-pronounced nonlinear characteristics without needing an external component to create hardening or softening. The force-displacement relationship of the M-shaped beam with a central lumped mass attachment is experimentally identified and asymmetric nonlinear behavior is verified. The purely elastic system parameters (such as the linear and nonlinear stiffness components) identified from the experiments are used in numerical simulations and compared with the experimental results. A quadratic damping term is included to account for nonlinear dissipative effects. Bandwidth enhancement with increasing base excitation is investigated experimentally and numerically. Very good agreement is observed between the simulated frequency response curves and experimental measurements.
Sensitivity of Vehicle Market Share Predictions to Alternative Discrete Choice Model Specifications
Authors: Heckmann C. Grace , Michalek Jeremy J. , Morrow W. Ross , Liu Yimin
Published: February 2014

When design decisions are informed by consumer choice models, uncertainty in the choice model and its share predictions creates uncertainty for the designer. We take a first step in investigating the variation in and accuracy of market share predictions by characterizing fit and forecast accuracy of multinomial logit, mixed logit, and nested logit models over a variety of utility function specifications for the US light duty new vehicle market. Using revealed preference data for years 2004–2006, we estimate a multinomial logit model for each combination of a chosen set of utility function covariates found in the literature. We then use each of the models to predict vehicle shares for the 2007 market and examine several metrics to measure fit and predictive accuracy. We find that the best models selected using any of the proposed metrics outperform random guessing yet retain substantial error in fit and prediction for individual vehicle models. For example, with no information (random guessing) 30% of share predictions are within 0.2% absolute share error in a market with an average share of ∼0.4%, whereas for the best models 70% are within 0.2% (for the 2007 vehicle market this translates to an error of ∼33,000 units sold). Share predictions are sensitive to the presence of utility covariates but less sensitive to the form. Models that perform well on one metric tend to perform well on the other metrics as well. In particular, models selected for best fit have comparable forecast error to those with the best forecasts, and residual error in model fit is a major source of forecast error.
Advanced Folding Approaches for Deployable Spacecraft Payloads
Authors: Reynolds Whitney D. , Jeon Sungeun K. , Banik Jeremy A. , Murphey Thomas W.
Published: February 2014

Radio communications apertures for spacecraft have long been implemented using deployable architectures in order to fit within the allowable launch vehicle volume. Apertures for optics missions have traditionally not been segmented because of the tight requirements on the deployed surface. By the nature of the problem, larger apertures are generally better, but complicate orbital delivery. While there are several reflectors commercially available, high packing ratios come at very high cost due to the extremely complex nature of the designs. Researchers at the Space Vehicles Directorate have been investigating ways to enable high packing ratios while reducing the design, integration, and testing complexity of deployable systems, thereby driving down cost and enabling greater mission capabilities. Recent advances in flexible composites have opened up the possibilities of packaging apertures using either distributed or concentrated strain. This paper offers an overview of recent work done to enable lower complexity deployable apertures. Several origami-inspired designs are presented including a flat spiral folding membrane, a parabolic antenna reflector, and a phased array structure.
Using Geared Cardanic Motion to Generate Metamorphic Linkages
Authors: Nelson Carl A.
Published: February 2014

Cardanic motion profiles are a special case of the general epicycloids, hypocycloids, epitrochoids, and hypotrochoids. Under certain geometric constraints, circles, ellipses, and straight lines can be generated. In this paper we explore the use of the geared Cardan mechanism as a component generating metamorphic effects, or equivalent topology changes, in planar linkages by capitalizing on this change from linear to circular motion. The concept of instantaneous Grashof criterion in these mechanisms is also explored. The theory is detailed and example applications are described.
Magnetic Actuation of Meso-Scale Mechanisms
Authors: Moore P. M. , Modica F. , Wiens G. J. , Fassi I.
Published: February 2014

This paper discusses the applications and development of magnetic actuators for meso-scale mechanisms. Due to their small sizes, meso-scale parts cannot be actuated using techniques typical of macro-scale mechanisms, such as servos or ball screws. Similarly, the techniques used in micro-actuation, such as the use of electrostatic force in MEMS devices, cannot be easily scaled up to the meso-scale. As a result, the use of magnetic forces for actuating meso-scale mechanisms may be capable of filling this void of actuation methods.

A case study of a fixturing mechanism meant for meso-scale end-milling was analyzed. This mechanism uses two fixed-fixed beams in order to actively tune the harmonic modes of the machining operation in order to improve the stability of the cutting. It also uses magnetic forces to actuate the fixturing platform in order to provide close-loop feedback of cutting force.
Parametric Instability in a Gear Train System Due to Stiffness Variation
Authors: Wang S. Y. , Sinha S. C.
Published: February 2014

The excitation from mesh stiffness variation in a tunnel gear driving system can cause excessive noise and vibrations. Since the stiffness variation may induce parametric instability, the system could be damaged on a permanent-basis. Therefore, the study of parametric instability in such system is of paramount importance. In this work, a rigid-elastic model is developed using the energy method, where the ring gear is treated as a rotating thin ring having radial and tangential deflections, whereas the pinions are assumed to be rigid bodies having translational motion relative to the radial directions of the ring gear as well as rotational motions around their centers. All gear meshes are modeled as interactions caused by time-varying springs, and the supports of the pinions are modeled as linear springs in the radial direction relative to the ring gear. The modeling leads to a set of partial-ordinary linear differential equations with time-varying coefficients. For an N planet system, the discretization process yields 2N+2 ordinary differential equations. Stability boundaries are determined using Floque’t theory for a wide range of parameter values. Specifically, the effects of mesh stiffness on the parametric instability are examined. The results show that the instability behaviors are closely related to the basic parameters when considering the time-varying excitation. This could be a serious consideration in the preliminary design of such systems.
Improvement of RFID Accuracy for a Product Tracking System
Authors: Bian Chao , Peng Qingjin , Zhang Gong
Published: February 2014

Radio Frequency Identification (RFID), as the name suggests, is technology that makes use of radio frequency electromagnetic wave to automatically identify objects. In spite of its broad applications, a RFID system might inherently produce some false and duplicate readings. Such reading data would affect the accuracy of the RFID system and might result in an unreliable performance or even complete unavailability of the system. In this paper, a reading rate-based algorithm is proposed to efficiently clean RFID data for a local business in product tracking. The method takes advantage of the proportional relationship between reading rate of a RFID tag and its distance to the reader to filter among raw data sets. Using the proposed reading rate-based algorithm, the reading accuracy of the RFID system in the local business is greatly improved.
Simultaneous Identification of the Human Tibio-Talar and Talo-Calcaneal Joint Rotation Axes by the Burmester Theory
Authors: Sancisi Nicola , Parenti-Castelli Vincenzo
Published: February 2014

In several applications, such as the design and setting of prostheses, orthoses and exoskeletons, and the multibody modelling of the lower limb, it is sometimes necessary to approximate the spatial motion of human joints to a rotation about a fixed axis. The identification of these axes can be particularly difficult at the ankle joint, where two different articulations are observed, namely the tibio-talar joint (connecting the tibia and talus) and the talo-calcaneal joint (connecting the talus and calcaneus). Thus, the ankle requires two distinct axes to be identified in order to correctly describe the joint motion. A new technique is proposed here for the identification of the tibio-talar and talo-calcaneal rotation axes. The technique is based on a particular use of the Burmester theory and exhibits several advantages: the talus motion is not required, and only the tibia-calcaneus motion is needed; the identification of both rotation axes is simultaneous and thus the identification accuracy of both axes is independent; the method is not based on optimization techniques and thus it does not require the definition of an objective function; it is robust with respect to experimental inaccuracies; it makes it possible to obtain the talus motion, even if it could not be measured during the experimental session. The technique reveals particularly useful during in vivo measurements based on skin markers or other non-invasive measures, since the talus motion cannot be obtained from skin measurements. An application example is shown by means of experimental data measured on an ankle specimen.
Dynamic Simulation of Autonomous Boats for Cooperative Skimming and Cleanup
Authors: Kim Soonkyum , Bhattacharya Subhrajit , Kumar Vijay
Published: February 2014

We consider the use of autonomous boats for oil skimming and clean up of surface debris by operating two boats with a boom cooperatively. A boom, or a cable as considered in this paper, attached to two robots at each end can be used to efficiently manipulate multiple objects on the surface of the water. In our previous work, Bhattacharya, et al. (ICRA 2011), we showed the feasibility of this concept with an experimental testbed using two autonomous boats and a towed cable. This work showed that an accurate dynamic simulation of the system is indispensable in analysis and development of efficient control schemes. For the purpose of manipulating objects in such a way, not only do we need to model the drag forces, but we also need to model the interaction between the cable and the objects. In this paper we model the boom or the cable as a chain with a discrete number of rigid links connected by passive revolute joints and model the interaction of the cable with the water (drag) as well as the contacts with objects on the surfaces. We derive the equations governing the cable and object dynamics and model the contact interactions as linear complementarity constraints. The boats are driven by simple controllers that only require knowledge of positions and velocities at the both ends of the cable. Several examples are used to illustrate the performance of the numerical simulation.
Simulation-Based Design of a Self-Folding Smart Material System
Authors: Peraza-Hernandez Edwin , Hartl Darren , Malak Richard
Published: February 2014

Origami engineering — the practice of creating useful three-dimensional structures through folding operations on two-dimensional building-blocks — is receiving increased attention from the science, mathematics, and engineering communities. The topic of this paper is a new concept for a self-folding material system. It consists of an active, self-morphing laminate that includes two meshes of thermally-actuated shape memory alloy (SMA) separated by a compliant passive layer. The goal of this paper is to analyze several of the key engineering tradeoffs associated with the proposed self-folding material system. In particular, we examine how key design variables affect folding behavior in an SMA mesh-based folding sheet. The design parameters we consider in this study are wire thickness, mesh wire spacing, thickness of the insulating elastomer layer, and heating power. The output parameters are maximum von Mises stress in the SMA, maximum temperature in the SMA, and minimum folding angle. The results show that maximum temperature in the SMA is mostly dependent on the total heating power per unit width of SMA. The results also indicate that through-heating — heat transfer from one SMA layer to the other through the insulating elastomer — can impede folding for some physical configurations. However, we also find that one can mitigate this effect using a staggered mesh configuration in which the SMA wires on different layers are not aligned. Based on our results, we conclude that the new staggered mesh design can be effective in preventing unintended transformation of the non-actuated layer.
Cognitive-Based Terminal State Prediction for Human Motion Planning
Authors: Howard Brad , Yang James , Yang Guolai
Published: February 2014

Every day, people are presented with tasks that are completed with very little mechanical effort such as turning a door knob, turning a screw driver, and grabbing a cup to move it to a new location and/or orientation. These tasks are often overlooked in the mechanical study of human movement due to the fact they carry with them very little biomechanical costs or effort. However, from a cognitive standpoint, these tasks carry high complexity. For example, the simple task of grabbing a cup and flipping it over is very easy mechanically and can be effortlessly achieved by a two year old. However, it is impossible to predict or simulate this motion without major intervention in the form of explicit constraints defining the task. The model itself cannot decide in which orientation the hand should assume in order to grasp the object. Also, it cannot decide where on the object the hand should be placed. These aspects must be assumed by the researcher and constrained in the formulation. In other words, digital human models, such as optimization-based motion prediction models, are unable to plan actions. This implies that for each task, a unique optimization formulation is needed in order to predict the motion/posture needed to complete each task. This paper presents a new method for task planning prediction within optimization based posture and motion prediction. It provides a new single optimization formulation that allows for the prediction of multiple unique manual manipulation tasks. The method is based on observations made from experimental studies on cognitive motor planning.
Handling Overruns and Underruns of Real-Time Processes With Precedence and Exclusion Relations Using a Pre-Run-Time Schedule
Authors: Xu Jia
Published: February 2014

Many embedded systems applications have hard timing requirements where real-time processes with precedence and exclusion relations must be completed before specified deadlines. This requires that the worst-case computation times of the real-time processes be estimated with sufficient precision during system design, which sometimes can be difficult in practice. If the actual computation time of a real-time process during run-time exceeds the estimated worst-case computation time, an overrun will occur, which may cause the real-time process to not only miss its own deadline, but also cause a cascade of other real-time processes to also miss their deadline, possibly resulting in total system failure. However, if the actual computation time of a real-time process during run-time is less than the estimated worst-case computation time, an underrun will occur, which may result in under-utilization of system resources. This paper describes a method for handling underruns and overruns when scheduling a set of real-time processes with precedence and exclusion relations using a pre-run-time schedule. The technique effectively tracks and utilizes unused processor time resources to reduce the chances of missing real-time process deadlines, thereby providing the capability to significantly increase both system utilization and system robustness in the presence of inaccurate estimates of the worst-case computation times of real-time processes.
Computer Aided Design of Useful Spherical Watt I Six-Bar Linkages
Authors: Sonawale Kaustubh H. , Arredondo Alex , McCarthy J. Michael
Published: February 2014

This paper presents a software system for the kinematic synthesis of useful spherical Watt I six-bar linkages that can guide a body through five task positions. The design procedure begins with the specification of a spherical 3R open chain that reaches five specified task positions. The six-bar linkage is designed by constraining the 3R spherical chain to the topology of a Watt I spherical six-bar linkage. The CAD software SolidWorks is used to specify the 3R chain and the five spherical task positions. We describe the SolidWorks Add-In MechGen that reads the SolidWorks data and generates candidate linkages. Included in the task specification are tolerance zones that allow random adjustments to the task positions to search for defect-free linkages. An example is provided that demonstrates the five position synthesis of a useful spherical Watt I six-bar linkage.
Contact Model Between Superelements in Dynamic Multibody Systems
Authors: Virlez Geoffrey , Brüls Olivier , Sonneville Valentin , Tromme Emmanuel , Duysinx Pierre , Géradin Michel
Published: February 2014

In this paper, a new contact formulation defined between flexible bodies modeled as superelements is investigated. Unlike rigid contact models, this approach enables to study the deformation and vibration phenomena induced by hard contacts. Compared with full-scale finite element models of flexible bodies, the proposed method is computationally more efficient, especially in case of a large number of bodies and contact conditions. The compliance of each body is described using a reduced-order elastic model which is defined in a corotational frame that follows the gross motion of the body. The basis used to reduce the initial finite element model relies on the Craig-Bampton method which uses both static boundary modes and internal vibration modes. The formulation of the contact condition couples all degrees of freedom of the reduced model in a nonlinear way. The relevance of the approach is demonstrated by simulation results first on a simple example, and then on a gear pair model.
Pseudo Compressible Mixed Interpolation Finite Element Method for Solving Three Dimensional Navier-Stokes Equations
Authors: Apte Shrinivas G. , Dennis Brian H.
Published: February 2014

A pseudo compressible finite element method for solving three dimensional incompressible Navier-Stokes equations is presented. A physical problem discretized using tetrahedral elements with linear and quadratic interpolation functions for pressure and velocity variables respectively is then marched in time by using implicit time marching scheme based on finite differencing. The possible formation of indefinite matrix due to incompressibility constraint is avoided by inserting an artificial/pseudo time dependent term (Chorin, 1974) into the continuity equation that is eliminated when steady state is reached. This definite matrix system can then be solved using standard pre-conditioners and iterative solvers. Solutions for pressure driven flows obtained using this method are validated with the ones obtained from a standard problem of flow over a cylinder and also with numerical benchmark case of a 3-D laminar flow around an obstacle. An object oriented C++ program was developed which uses exact integrals of shape functions in its calculations rather than numerical integrations. This program was tested with different values of artificial compressibility factor (β), Reynolds numbers (Re) and grid sizes (number of Elements) and time steps (dt). The effect of these parameters on the the number of linear solver iterations required for convergence is studied efficiently using the non-dimensional numbers Pseudo Compressibility Number (PCN) and Elemental Reynolds Number (ERe). Although the relationship between the linear solver performance and these two non dimensional numbers remain complicated, it is found that there exists an optimum range of PCN as a function of ERe for which the solution convergence can be obtained with the minimum number of iterations.
Experimental Validation of a Volumetric Planetary Rover Wheel/Soil Interaction Model
Authors: Petersen Willem , McPhee John
Published: February 2014

For the multibody simulation of planetary rover operations, a wheel-soil contact model is necessary to represent the forces and moments between the tire and the soft soil. A novel nonlinear contact modelling approach based on the properties of the hypervolume of interpenetration is validated in this paper. This normal contact force model is based on the Winkler foundation model with nonlinear spring properties. To fully define the proposed normal contact force model for this application, seven parameters are required. Besides the geometry parameters that can be easily measured, three soil parameters representing the hyperelastic and plastic properties of the soil have to be identified. Since it is very difficult to directly measure the latter set of soil parameters, they are identified by comparing computer simulations with experimental results of drawbar pull tests performed under different slip conditions on the Juno rover of the Canadian Space Agency (CSA). A multibody dynamics model of the Juno rover including the new wheel/soil interaction model was developed and simulated in MapleSim. To identify the wheel/soil contact model parameters, the cost function of the model residuals of the kinematic data is minimized. The volumetric contact model is then tested by using the identified contact model parameters in a forward dynamics simulation of the rover on an irregular 3-dimensional terrain and compared against experiments.
High-Fidelity Modeling of a Power-Split Plug-In Hybrid Electric Powertrain for Control Performance Evaluation
Authors: Taghavipour Amir , Masoudi Ramin , L. Azad Nasser , McPhee John
Published: February 2014

Plug-in hybrid electric vehicle (PHEV) development seems to be essential for a sustainable transportation system along with electric vehicles. An appropriate power management strategy for a PHEV determines how to blend the engine and the battery power in such a way that leads to significant fuel economy improvement and environmental footprint reduction. To evaluate and validate the controls design, software and hardware-in-the-loop (SIL/HIL) simulations are useful approaches, especially at the early stages of controls design. To conduct SIL/HIL tests, an accurate and relatively fast mathematical model of the real powertrain is required which solely contains the essential dynamics of the plant. In this paper, a physics-based model of a power-split plug-in powertrain is developed and implemented using MapleSim software. This model contains a chemistry-based lithium-ion battery pack, which can distinguish it from other models used in the literature, since the performance of a PHEV greatly depends on its battery. The symbolic computation power of MapleSim makes the model very suitable for real-time SIL/HIL tests.
A Novel Origami Crash Box With Varying Profiles
Authors: Ma Jiayao , You Zhong
Published: February 2014

Crash boxes in automobiles are often made from thin-walled tubes. They are designed to absorb energy when subjected to axial crushing. In this paper we present a novel crash box known as the origami crash box. It is produced by pre-folding the surface of a thin-walled tube according to a developable origami pattern. The pre-folded surface serves both as a type of geometric imperfection to lower the initial peak force, and as a mode inducer to trigger a collapse mode that is more efficient in terms of energy absorption. Numerical simulation of quasi-static axial crushing of the origami crash box has shown that a new collapse mode deemed the completed diamond mode can be triggered in tubes with square, rectangular, and polygonal cross sections and tapered shapes, leading to both a substantial gain in overall energy absorption, while at the same time, a reduction in initial peak force.
Nonlinear Response of CNT Cantilever Based Nano-Resonators
Authors: Kim Il Kwang , Lee Soo Il
Published: February 2014

This paper presents nonlinear dynamic response of carbon nanotube (CNT) cantilevers incorporating electrostatic forces and van der Waals interactions between the CNT and the conducting plane. The CNT cantilever models including geometric and inertial nonlinearities for predicting unexpected phenomena when the deflection of the CNT is increased. As a result, the CNT cantilever shows complex dynamic responses due to the applied voltage. At the low voltages, the cantilever has only linear response at fundamental resonance except the superharmonic response due to the harmonic excitation of electrostatic field. The secondary resonance response branches off through period-doubling (PD) bifurcation, and becomes softened through saddle-node (SN) bifurcation when the applied voltage is increased. After SN bifurcation, the lower branch of the solution near resonance loses its stability and becomes unstable. This theoretical finding can help the prediction of complex response of the nano-resonators.
Dynamic Analysis of Hula Hoop Motion and Optimized Energy Harvest Circuit
Authors: Huang T.-C. , Chen W.-D. , Lu C. X. , Chao Paul C.-P. , Tsai C.-H. , Sung C. K.
Published: February 2014

The nonlinear dynamics of hula hoop motion is deciphered in this study by nonlinear dynamic modeling techniques to find solution and stability analysis. This is different from the previous study [1], where a homotopy method is employed. The analysis results are capable of transforming linear reciprocating motion into rotational motion. The dynamic governing equations of the system are first successfully derived by force balance. The non-linear dynamic analysis is next applied to derive approximate, asymptotic solutions. Stabilities associated with all solution are determined by subsequent analysis on the derived asymptotic solutions. In addition, the transformer could be integrated with coils, magnets, and electric circuits to form a portable energy scavenging device. A novel front-end circuit is proposed in this work for harvesting human’s energy. The situation of human’s walking and running is simulated by a shaker. And the ac-like energy is processed by the novel energy harvesting circuit, transformed as a DC voltage suitable for devices successfully. The efficiency of the entire circuit is proven up to 60%, and is an input-powered circuit with no standby power. A complete experimental system is also designed and successfully confirm the existence of the stable nonlinear solutions found by analytical and numerical analysis.
Displacement and Stress Constrained Topology Optimization
Authors: Takalloozadeh Meisam , Suresh Krishnan
Published: February 2014

The objective of this paper is to demonstrate a topology optimization method subject to displacement and stress constraints. The method does not rely on pseudo-densities; instead it exploits the concept of topological level-set where ‘partial’ elements are avoided. Consequently: (1) the stresses are well-defined at all points within the evolving topology, and (2) the finite-element analysis is robust and efficient. Further, in the proposed method, a series of topologies of decreasing volume fractions are generated in a single optimization run. The method is illustrated through numerical experiments in 2D.
A Simple Model for Body Pitching Stabilization
Authors: Che Yuhang , Shen Zhuohua , Seipel Justin
Published: February 2014

Pitching dynamics are an important component of the dynamics of legged locomotion. We develop an energy-open pitching stabilization model to achieve full asymptotic stability of locomotion. This model is called the pitched-actuated Spring-Loaded Inverted Pendulum (pitched-actuated SLIP) model. It extends the conservative SLIP model to include a trunk as well as net nonzero hip torque and leg damping. The hip torque is governed by a proportional and derivative controller which uses only the angle between body and leg as feedback during stance. During the swing phase of the leg, inertial frame feedback is used to reset the leg to a fixed angle in space. The use of body-frame feedback in stance is thought to be relevant to biology and robotic control, as time delays and uncertainty in inertial frame feedback could be challenging in stance. Further, this method of control during stance could be implemented in a neural feedforward manner using antagonistic pairs of muscle or muscle-like actuators around the hip joint. This model of pitching dynamics exhibits full asymptotic stability over a range of model parameters. Further, derivative control significantly impacts disturbance mitigation. Periodic locomotion solutions of the model with large energy cost tend to be unstable. Whereas, the most energy efficient locomotion solutions found tend to be within the stable region of the parameter space. The correlation between energy efficiency and stability found in this model may have significant implications for locomotion with pitching.