bluuebunny/crossref_metadata_2025 huggingface dataset:
Orientation Workspace and Stiffness Optimization of Cable-Driven Parallel Manipulators With Base Mobility
Authors: Anson Michael , Alamdari Aliakbar , Krovi Venkat
Published: February 2017

Cable-driven parallel manipulators (CDPM) potentially offer many advantages over serial manipulators, including greater structural rigidity, greater accuracy, and higher payload-to-weight ratios. However, CDPMs possess limited moment resisting/exerting capabilities and relatively small orientation workspaces. Various methods have been contemplated for overcoming these limitations, each with its own advantages and disadvantages. The focus of this paper is on one such method: the addition of base mobility to the system. Such base mobility gives rise to kinematic redundancy, which needs to be resolved carefully in order to control the system. However, this redundancy can also be exploited in order to optimize some secondary criteria, e.g., maximizing the size and quality of the wrench-closure workspace with the addition of base mobility. In this work, the quality of the wrench-closure workspace is examined using a tension-factor index. Two planar mobile base configurations are investigated, and their results are compared with a traditional fixed-base system. In the rectangular configuration, each base is constrained to move along its own linear rail, with each rail forming right angles with the two adjacent rails. In the circular configuration, the bases are constrained to move along one circular rail. While a rectangular configuration enhances the size and quality of the orientation workspace in a particular rotational direction, the circular configuration allows for the platform to obtain any position and orientation within the boundary of the base circle. Furthermore, if the bases are configured in such a way that the cables are fully symmetric with respect to the platform, a maximum possible tension-factor of one is guaranteed. This fully symmetric configuration is shown to offer a variety of additional advantages: it eliminates the need to perform computationally expensive nonlinear optimization by providing a closed-form solution to the inverse kinematics problem, and it results in a convergence between kinematic singularities and wrench-closure singularities of the system. Finally, we discuss a particular limitation of this fully symmetric configuration: the inability of the cables to obtain an even tension distribution in a loaded configuration. For this reason, it may be useful to relax the fully symmetric cable requirement in order to yield reasonable tensions of equal magnitude.
Improving Prediction of Flapping-Wing Motion By Incorporating Actuator Constraints With Models of Aerodynamic Loads Using In-Flight Data
Authors: Gerdes John W. , Bruck Hugh A. , Gupta Satyandra K.
Published: February 2017

Flapping-wing flight is a challenging system integration problem for designers due to tight coupling between propulsion and flexible wing subsystems with variable kinematics. High fidelity models that capture all the subsystem interactions are computationally expensive and too complex for design space exploration and optimization studies. A combination of simplified modeling and validation with experimental data offers a more tractable approach to system design and integration, which maintains acceptable accuracy. However, experimental data on flapping-wing aerial vehicles which are collected in a static laboratory test or a wind tunnel test are limited because of the rigid mounting of the vehicle, which alters the natural body response to flapping forces generated. In this study, a flapping-wing aerial vehicle is instrumented to provide in-flight data collection that is unhindered by rigid mounting strategies. The sensor suite includes measurements of attitude, heading, altitude, airspeed, position, wing angle, and voltage and current supplied to the drive motors. This in-flight data are used to setup a modified strip theory aerodynamic model with physically realistic flight conditions. A coupled model that predicts wing motions is then constructed by combining the aerodynamic model with a model of flexible wing twist dynamics and enforcing motor torque and speed bandwidth constraints. Finally, the results of experimental testing are compared to the coupled modeling framework to establish the effectiveness of the proposed approach for improving predictive accuracy by reducing errors in wing motion specification.
Hybrid Active and Semi-Active Control for Vibration Suppression in Flexible Structures
Authors: Khan Irfan Ullah , Wagg David , Sims Neil D.
Published: February 2017

A new hybrid control methodology is presented for vibration suppression in flexible structures, where an active actuator is used to assist a nearby semi-active device to achieve a control performance close to that of a fully active system. The clipping phenomenon, typical of semi-active control, is reduced to a large extent by the proposed hybrid controller. The immersion and invariance methodology along with sliding mode control is used to create the hybrid controller. The result is that as the semi-active controller switches off in the hybrid controller, the active actuator injects the required energy into the system. A two degree of freedom system with cubic stiffness is used as an example system. Both simulation and experiment data are presented to demonstrate the usefulness of the proposed idea. The proposed hybrid controller shows robust results as compared to just using a semi-active controller.
Segregation of Heterogeneous Robotics Swarms via Convex Optimization
Authors: Edwards Victoria , Rezeck Paulo , Chaimowicz Luiz , Hsieh M. Ani
Published: February 2017

The division of labor amongst a heterogeneous swarm of robots increases the range and sophistication of the tasks the swarm can accomplish. To efficiently execute a task the swarm of robots must have some starting organization. Over the past decade segregation of robotic swarms has grown as a field of research drawing inspiration from natural phenomena such as cellular segregation. A variety of different approaches have been undertaken to devise control methods to organize a heterogeneous swarm of robots. In this work, we present a convex optimization approach to segregate a heterogeneous swarm into a set of homogeneous collectives. We present theoretical results that show our approach is guaranteed to achieve complete segregation and validate our strategy in simulation and experiments.
Robust Composite Nonlinear Feedback Control for Path Following of Underactuated Surface Vessels With Desired-Heading Amendment
Authors: Hu Chuan , Wang Rongrong , Yan Fengjun
Published: February 2017

This paper studies the transient performance improvement problem for path following control of underactuated surface vessels (USVs) in the presence of oceanic disturbances. The traditional practice that chooses the tangent direction of the desired path as the desired heading may deteriorate the tracking performance in the curve-path following. That is because the sideslip angle is not zero in turnings, which unavoidably makes the lateral offset hard to converge to zero. Also, the disturbances in wave filed greatly affect the transient control of the path following errors. To this end, this paper makes two contributions: 1) An amendment on the choice of the desired heading is presented to consider the sideslip angle in turnings and then achieve a more accurate path-following maneuver; 2) A novel robust composite nonlinear feedback (CNF) technique is proposed based on a multiple-disturbances observer to improve the transient performance for path following control in seaway environment considering the input saturation. Comparative simulations verify the reasonability of the amendment on the desired heading direction and the effectiveness of the CNF approach in improving the transient performance for the path following control of USVs.
Minimum Backpressure Wastegate Control for a Boosted Gasoline Engine With Low Pressure External EGR
Authors: Nazari Shima , Stefanopoulou Anna , Martz Jason
Published: February 2017

Turbocharging and downsizing (TRBDS) a gasoline direct injection (GDI) engine can reduce fuel consumption but with increased drivability challenges compared to larger displacement engines. This tradeoff between efficiency and drivability is influenced by the throttle-wastegate control strategy. A more severe tradeoff between efficiency and drivability is shown with the introduction of Low-Pressure Exhaust Gas Recirculation (LP-EGR). This paper investigates and quantifies these trade-offs by designing and implementing in a one-dimensional (1D) engine simulation two prototypical throttle-wastegate strategies that bound the achievable engine performance with respect to efficiency and torque response. Specifically, a closed-wastegate (WGC) strategy for the fastest achievable response and a throttle-wastegate strategy that minimizes engine backp-pressure (MBWG) for the best fuel efficiency, are evaluated and compared based on closed loop response. The simulation of an aggressive tip-in (the driver’s request for torque increase) shows that the wastegate strategy can negotiate a 0.8% efficiency gain at the expense of 160 ms slower torque response both with and without LP-EGR. The LP-EGR strategy, however offers a substantial 5% efficiency improvement followed by an undesirable 1 second increase in torque time response, clarifying the opportunities and challenges associated with LP-EGR.
Dynamic Modeling of a 2-DOF Cable Driven Powered Ankle-Foot Prosthesis
Authors: Dallali Houman , Ficanha Evandro , Rastgaar Aagaah Mohammad
Published: February 2017

The first step to study and develop a two Degrees of Freedom (DOF) prosthesis is to derive a dynamic model for simulation and control design. In this paper, the ankle-foot prosthesis has controllable Dorsi-Plantarflexion (DP) and Inversion-Eversion (IE) DOF. We derive a compliant dynamic model for a recently developed ankle-foot prosthesis followed by identification of the actuators, transmission, and prosthetic foot parameters. The resulting model is then verified experimentally and in simulation. Dynamic decoupling of the actuators to the ankle’s DP and IE DOF is also investigated using Bode plots. The code used for simulating the prosthesis is provided on GitHub for the community.
Design and Control Framework for Selecting Wind Turbine Gear Ratios Based on Optimal Power Generation and Blade Stress
Authors: Lall Amrita , Khakpour Nejadkhaki Hamid , Hall John
Published: February 2017

A variable ratio gearbox (VRG) can enable small wind turbines to operate at discrete variable rotor speeds. This reliable, low-cost, alternative does not require power conversion equipment, as is the case with conventional variable speed. Previous work conducted by the author has demonstrated that a VRG can increase the power production for a fixed-speed system with passive blades. The current study characterizes the performance of a wind turbine equipped with a VRG and active blades. The contribution of this work is an integrative framework that optimizes power production with blade root stress. It works by defining a set of control rules that specify the VRG gear ratio and pitch angle that will be used in relation to wind speed. Three ratios are selected through the proposed procedure. A case study based on the simulation of a 300-kW wind turbine model is performed to demonstrate the proposed technique. The model is constructed with aerodynamic, mechanical, and electrical submodels. These drivetrain components work together to simulate the conversion of moving air to electrical power. The blade element momentum (BEM) technique is used here to compute the blade loading. The resulting torque and rotor speed are reduced and increased, respectively, through the mechanical system gearbox. The output from this is then applied to the electrical generator. The BEM technique is also used here to determine the bending and thrust and loads that are applied to the blade. The stress in the root of the blade is then determined based on these loads, and that caused by centrifugal force and gravity. The proposed method devises a VRG design and control algorithm based on the unique wind conditions at a given installation site. Two case studies are conducted using wind data sets provided by the National Renewable Energy Laboratory (NREL). Low and high-speed data set are selected as inputs to demonstrate the versatility of the proposed method. Dynamic programming is used to reduce the computational expense. This enables the simulation of an exhaustive set of potential VRG combinations over each set of recorded wind data. Each possible combination is evaluated in terms of the total energy production and blade-root stress produced over the simulation period. A set of weights is applied to a multi-objective function that computes the cost associated with each combination. A Pareto analysis is then used to identify the VRG combination and establish the control algorithm for both systems. The results suggest that the VRG can improve energy production in the partial-load region by roughly 10% in both cases. Although stress increases in Region 2, it decreases in Region 3, and overall, through the optimal selection of gear combinations.
Robust Control Design for Load Reduction on a Liberty Wind Turbine
Authors: Ossmann Daniel , Theis Julian , Seiler Peter
Published: February 2017

The increasing size of modern wind turbines also increases the structural loads on the turbine caused by effects like turbulence or asymmetries in the inflowing wind field. Consequently, the use of advanced control algorithms for active load reduction has become a relevant part of current wind turbine control systems. In this paper, an H∞-norm optimal multivariable control design approach for an individual blade-pitch control law is presented. It reduces the structural loads both on the rotating and non-rotating parts of the turbine. Classical individual blade-pitch control strategies rely on single control loops with low bandwidth. The proposed approach makes it possible to use a higher bandwidth since it takes into account coupling at higher frequencies. A controller is designed for the utility-scale 2.5 MW Liberty research turbine operated by the University of Minnesota. Stability and performance are verified using a high-fidelity nonlinear benchmark model.
Simulation Based Design of a Pediatric-Sized Hydraulic Ankle-Foot Orthosis
Authors: Neubauer Brett Cullen , Durfee William K.
Published: February 2017

Cerebral palsy can cause gait impairments in children that require the prescription of passive ankle-foot orthoses. This project aims to develop a pediatric-sized hydraulic active ankle-foot orthosis with computer-controlled stiffness. The orthosis will allow a clinician to investigate a range of AFO stiffnesses while collecting gait performance metrics to determine the optimal stiffness value for the AFO prescription. The ankle-foot orthosis uses hydraulic technology to generate the large required torques in a light, compact package. The preliminary design uses additive manufacturing to further reduce the weight of the manifolds on the medial and lateral sides of the ankle. The simulation prototype of the design illustrated that the orthosis should be capable of generating 91 Nm of ankle torque and a maximum angular velocity of 483 °/sec. The device will be a valuable resource in the clinic, saving time and resources in the AFO prescription process while improving the healthcare of the patient.
An Insect Tether System Using Magnetic Levitation: Development, Analysis and Feedback Control
Authors: Hsu Shih-Jung , Bayiz Yagız Efe , Liu Pan , Cheng Bo
Published: February 2017

Insect flight has gained wide interests in both biology and engineering communities in the past decades regarding its aerodynamics, sensing and flight control. However, studying insect flight experimentally remains a challenge in both free-flight and tethered-flight settings. In free flight experiments, due to highly unpredictable and fast flight behavior of flying insects, it is difficult to apply controlled sensory inputs to their flight system for system identification and modeling analyses. In tethered flight experiments, constrained whole body movement results in silenced proprioceptive feedback therefore breaks the flight control loop and does not reveal any flight dynamics. Therefore, this work aims to develop a novel insect tether system using magnetic levitation. Such a system magnetically fixes an insect in space but allows it to rotate freely about yaw axis with minimal interference from mechanical constraints. This paper presents the development, analysis and feedback control of this system and finally test its performance using a hawkmoth (Manduca Sexta). In addition, a system identification of the magnetic levitation system and detailed analysis in closed-loop stability and performance are provided. In the future, the insect tether system will be applied to study the insect flight aerodynamics, sensing and control.
Triple-Stage Track-Following Servo Design for Hard Disk Drives
Authors: Pan Jinwen , Bagherieh Omid , Shahsavari Behrooz , Horowitz Roberto
Published: February 2017

This paper studies possible robust control design methods in triple-stage actuation settings for achieving minimum position error signal (PES) while maintaining enough stability margins. Firstly, the sensitivity-decoupling design technique, is utilized to estimate the resulting increase in low frequency disturbance attenuation and servo bandwidth. A systematic tuning methodology based on μ-synthesis is then proposed for track-following servo design of triple-stage actuation systems. In this approach, the objective is to minimize the PES, by considering all constraints and uncertainties explicitly in the design. We describe a step by step Multi-Input Single-Output (MISO) controller design methodology which includes system modeling, noise characterization, control objective determination and controller synthesis and verification. In this methodology, servo bandwidth is not the only performance metric. Rather, the control objective will be to minimize the closed-loop system H∞ norm directly, while all stroke and control constraints are satisfied and enough stability margin is ensured. The proposed method is applied to design track-following feedback controllers for single-, dual- and triple-stage actuation systems. Simulation results show that compared to dual-stage actuation, triple-stage actuation enhances low frequency disturbance rejection by 6 dB at around 100Hz and increases servo bandwidth from ∼3kHz to ∼5kHz.
Active Sensing on a Bicycle for Accurate Tracking of Rear Vehicle Maneuvers
Authors: Jeon Woongsun , Rajamani Rajesh
Published: February 2017

This paper focuses on development of an active sensing system for a bicycle to accurately track rear vehicles. Cost, size and power constraints highly limit the type of sensor that can be used on a bicycle for measurement of distances to vehicles. A single beam laser sensor mounted on a rotationally controlled platform is proposed for this sensing mission. The rotational orientation of the laser sensor needs to be controlled in real-time in order to focus on a target point on the vehicle, as the vehicle’s lateral and longitudinal distances change. This tracking problem involves two challenges: Controlling the real-time angular position of the laser sensor based on very limited information and tracking the vehicle’s position for different types of maneuvers. The first challenge is addressed by developing an algorithm to detect whether a reflection is from the front or side of the target vehicle and then controlling sensor orientation to alternately obtain both lateral and longitudinal distance measurements. The second challenge is addressed by using an interacting multiple model observer that incorporates straight and turning vehicle motion models. Simulation results are presented to show the advantages of the developed tracking control system compared to simpler alternatives.
The Effects of Cutaneous Haptic Feedback on EMG-Based Motion Control of a Transfemoral Prosthesis
Authors: Canino J. Miles , Fite Kevin B.
Published: February 2017

This paper builds on prior investigations of the electromyogram (EMG) control of a single degree-of-freedom (DOF) transfemoral prosthetic limb, but augmented with mechanical haptic feedback of prosthetic limb state. Preliminary studies were conducted where quasi-static and vibratory cutaneous haptic feedback was provided to subjects performing nonweight-bearing motion tracking tasks with the EMG controlled transfemoral prosthesis. The results of these studies showed that the subjects exhibited improved tracking performance when following pseudo-random step commands under EMG control augmented with static and vibratory haptic feedback cues. The work to be discussed in this paper augments the EMG control architecture to foster improved co-contraction of the instrumented antagonist muscle pair. Using the modified EMG control architecture, experimental studies were conducted to investigate the efficacy of two haptic feedback modalities in conveying information pertinent to single-DOF nonweight-bearing sinusoidal motion tracking tasks. The two haptic feedback modalities investigated were quasi-static pressure feedback provided with pneumatic actuation and vibratory feedback provided by a vibrotactile motor array. Able-bodied test subjects were asked to control the prosthetic knee to follow sinusoidal trajectories with and without visual and haptic feedback. Experimental results show that EMG-control performance in tracking sinusoidal trajectories significantly improves in visually devoid environments when haptic feedback in the form of error-based and pacemaking stimulation patterns are presented to the user.
A Generalized Compressor Power Model for Turbocharged Internal Combustion Engines With Reduced Complexity
Authors: Zeng Tao , Upadhyay Devesh , Sun Harold , Zhu Guoming G.
Published: February 2017

Control-oriented models of automotive turbocharger compressors typically describe the compressor power assumming an isentropic thermodynamic process with a fixed isentropic efficiency and a fixed mechanical efficiency for power transmission between the turbine and compressor. Although these simplifications make the control model tractable, they also introduce additional errors due to unmodeled dynamics, especially when the turbocharger is operated outside its normal operational region. This is also true for map-based approaches, since these supplier-provided maps tend to be sparse or incomplete at the boundary operational regions and often ad-hoc extrapolation is required, leading to large modeling error. Furthermore, these compressor maps are obtained from the steady flow bench tests, which introduce additional errors under pulsating flow conditions in the context of internal combustion engines. In this paper, a physics-based model of compressor power is developed using Euler equations for turbomachinery, where the mass flow rate and compressor rotational speed are used as model inputs. Two new coefficients, speed and power coefficients are defined. This makes it possible to directly estimate the compressor power over the entire compressor operating range based on a single analytic relationship. The proposed modeling approach is validated against test data from standard turbocharger flow bench, steady state engine dynamometer as well as transient simulation tests. The validation results show that the proposed model has adequate accuracy for model-based control design and also reduces the dimension of the parameter space typically needed to model the compressor dynamics.
Analysis of Performance Resilience for Discrete-Time Systems With Both Multiplicative and Additive Control Gain Perturbations
Authors: Feng Fan , Schneider Susan C. , Yaz Edwin E.
Published: February 2017

In this work, a procedure is presented for performance analysis of the resilience property of discrete-time systems with perturbed controller and observer gains. The resilience property is defined in terms of both multiplicative and additive perturbations on the gains so that the closed loop eigenvalues do not leave a specified region in the complex plane. In this work, this region is chosen as a disk in the unit circle. Maximum gain perturbation bounds can be obtained based on the designer’s choices of controller eigenvalue region. The linear matrix inequality technique is used throughout the analysis process. Illustrative examples are included to demonstrate the effectiveness of the proposed methodology. The observer counterpart of the results is also provided in an appendix.
Robust Sliding Mode Control of Buck-Boost DC-DC Converters
Authors: Reitz Max A. , Wang Xin
Published: February 2017

DC-DC converters are an efficient way to convert a source voltage from one to level to another and have found extensive applications in many areas such as portable electronics, solar and wind energy systems. This paper presents a comparison of first order and higher order sliding mode control of buck-boost converters. Sliding mode control is ideal for controlling non-linear systems like switched voltage regulators as a result of its robustness to internal parameter uncertainties and external disturbances. First order sliding mode control is subject to a phenomenon known as chattering, which causes an undesirable oscillation about the desired output. Computer simulation studies are presented and show that the higher order controller reduces this problem.
Investigation of Factors Affecting Steering Feel of Column Assist Electric Power Steering
Authors: Li Yijun , Shim Taehyun , Wang Dexin , Offerle Timothy
Published: February 2017

An application of electric power assist steering (EPAS) system has rapidly grown and overtaken hydraulic power assist steering (HPAS) system in recent automotive industry. The EPAS system has better fuel efficiency and potential application on vehicle dynamic control compared to HPAS. However, it is widely believed that the steering feel of EPAS system is inferior to HPAS system due to its mechanical construction.

This paper first presents a comprehensive model of column electric power assist steering (CEPAS) system consisting of steering wheel, worm gear, assist motor, intermediate shaft, and rack and pinion. In this model, the friction in steering system is modeled by LuGre friction model and basic control strategies are also implemented. Using the proposed CEPAS model, the steering feel responses have been investigated with varying system parameters through simulation, and important factors affecting the steering feel response have been identified. This result gives insights on how the steering feel is affected by various factors and can be useful to improve the steering feel control algorithm design.
Classification of Muscular Nonfatigue and Fatigue Conditions Using Surface EMG Signals and Fractal Algorithms
Authors: Marri Kiran , Swaminathan Ramakrishnan
Published: February 2017

The application of surface electromyography (sEMG) technique for muscle fatigue studies is gaining importance in the field of clinical rehabilitation and sports medicine. These sEMG signals are highly nonstationary and exhibit scale-invariant self-similarity structure. The fractal analysis can estimate the scale invariance in the form of fractal dimension (FD) using monofractal (global single FD) or multifractal (local varying FD) algorithms. A comprehensive study of sEMG signal for muscle fatigue using both multifractal and monofractal FD features have not been established in the literature. In this work, an attempt has been made to differentiate sEMG signals recorded nonfatigue and fatigue conditions using monofractal and multifractal algorithms, and machine learning methods. For this purpose, sEMG signals have been recorded from biceps brachii muscles of fifty eight healthy subjects using a standard protocol. The signals of nonfatigue and fatigue region were subjected to eight monofractal (Higuchi, Katz, Petrosian, Sevcik, box counting, multi-resolution length, Hurst and power spectrum density) and two multifractal (detrended fluctuating and detrended moving average) algorithms and 28 FD features were extracted. The features were ranked using conventional and genetic algorithms, and a subset of FD features were further subjected to Naïve Bayes (NB), Logistic Regression (LR) and Multilayer Perceptron (MLP) classifiers. The results show that all fractal features are statistically significant. The classification accuracy using feature subset of conventional method is observed to be from 83% to 88%. The highest accuracy of 93.96% was achieved using genetic algorithm and LR classifier combination. The result demonstrated that the performance of multifractal FD features to be more suitable for sEMG signals as compared to monofractal FD features. The fractal analysis of sEMG signals appears to be a very promising biomarker for muscle fatigue classification and can be extended to detection of fatigue onset in varied neuromuscular conditions.
Discrete-Time H-Infinity Synthesis of Frequency-Shaped Sliding Mode Control for Suppression of Vibration With Multiple Peak Frequencies
Authors: Zheng Minghui , Tomizuka Masayoshi
Published: February 2017

Vibration with multiple large peaks at high frequencies may cause significant performance degradation and have become a major concern in modern high precision control systems. To deal with such high-frequency peaks, it is proposed to design a frequency-shaped sliding mode controller based on H∞ synthesis. It obtains an ‘optimal’ filter to shape the sliding surface, and thus provides frequency-dependent control allocation. The proposed frequency-shaping method assures the stability in the presence of multiple-peak vibration sources, and minimizes the weighted H∞ norm of the sliding surface dynamics. The evaluation is performed on a simulated hard disk drive with actual vibration sources from experiments, and the effectiveness of large vibration peak suppression is demonstrated.
Unscented MPC Design for Turbocharged EGR System in Diesel Engines
Authors: Samokhin Sergey , Zenger Kai
Published: February 2017

Exhaust gas recirculation (EGR) has become an integral part of the NOx emission reduction mechanisms utilized in modern combustion engines. However, capabilities to recirculate the processed gas are oftentimes compromised by the inability to surmount the pressure differential between the intake and exhaust manifolds. The issue is dealt with successfully by the turbocharged EGR system discussed in this article. The increased complexity of such an EGR system requires a multivariable control system in order to achieve the EGR set-point tracking across the desired operating range. In this work, model predictive control is used to naturally incorporate the information about system internal couplings and constraints via the prediction model. The states of the partially observed EGR system required for the feedback control are recovered by using the unscented Kalman filter. Finally, the designed unscented MPC (UMPC) system is validated by numerical simulations.
Optimal Robust Time-Varying Safety-Critical Control With Application to Dynamic Walking on Moving Stepping Stones
Authors: Nguyen Quan , Sreenath Koushil
Published: February 2017

This paper presents a novel methodology to handle time-varying safety-critical constraints under high level of model uncertainty with application to dynamic bipedal walking with strict foot-placement constraints. This paper builds off recent work on optimal robust control through quadratic programs that can handle stability, input / state dependent constraints, as well as safety-critical constraints, in the presence of high level of model uncertainty. Under the assumption of bounded uncertainty, the proposed controller strictly guarantees time-varying constraints without violating them. We evaluate our proposed control design for achieving dynamic walking of an underactuated bipedal robot subject to (a) torque saturation constraints (input constraints), (b) contact force constraints (state constraints), and (c) precise time-varying footstep placements (time-varying and safety-critical constraints). We present numerical results on RABBIT, a five-link planar bipedal robot, subject to a large unknown load on its torso. Our proposed controller is able to demonstrate walking while strictly enforcing the above constraints with an unknown load of up to 15 Kg (47% of the robot mass).
Safety-Critical Control of a 3D Quadrotor With Range-Limited Sensing
Authors: Wu Guofan , Sreenath Koushil
Published: February 2017

Enforcing safety is critical for aerial robotics. In this paper we consider the safety control problem for a 3D quadrotor with limited sensing range subject to avoiding collisions with time-varying obstacles. By using the concepts of Control Lyapunov Functions (CLFs) and Control Barrier functions (CBFs), we propose a control algorithm that explicitly considers the nonlinear and underactuated dynamics of a quadrotor to strictly guarantee time-varying safety-critical constraints. We demonstrate the feasibility of our proposed control design through numerical validation of (a) aerial flight through a region of dense cluttered obstacles, and (b) aerial flight through a dense time-varying obstacle field.
Model Predictive Control of a Tail-Actuated Robotic Fish
Authors: Castaño Maria L. , Tan Xiaobo
Published: February 2017

The increase of potential threats to the integrity of our aquatic ecosystems has caused global concerns which have led to interest in the use autonomous aquatic robots to monitor such environments. In recent years, underwater robots that propel and maneuver themselves like real fish, often called robotic fish, have emerged as mobile sensing platforms for freshwater and marine environments. These robots achieve locomotion via actively controlled fins, and actuation is often achieved via oscillatory inputs. Given these types of applications, accuracy and energy-saving in trajectory control is of importance for mission successes. In this work, we propose a nonlinear model predictive control (NMPC) approach to path following of a tail-actuated robotic fish. In this design, we use bias and amplitude of the tail-beat as the input to be determined by the NMPC. The effectiveness of the proposed approach is demonstrated via simulation.
Analysis of a Compact Heat Exchanger Using Porous Media Cooling for Use in a SCO2 Rankine Cycle
Authors: Anderson Kevin R. , Gross Thomas , McNamara Christopher , Shafahi Maryam
Published: February 2017

This paper presents the analysis of a compact heat exchanger design for application to a supercritical CO2 (SCO2) Rankine cycle waste energy conversion cycle. In this paper a compact heat exchanger using a multi-pass wavy channel configuration with surface area density β = 1222 m2/m3 and overall surface efficiency of 50% is analyzed using the NTU-ε method. Due to the high pressures used in the SCO2 Rankine cycle (high side of 20 MPa low side of 12.4 MPa) the variability of the specific heat of SCO2 leads to thermal pinch which must be accounted for in the modeling. Heat transfer augmentation is accomplished using porous media Silica particles on the low-side (12.4 MPa, a.k.a. hot fluid stream) of the SCO2 heat exchanger. Results for heat transfer area versus duty, temperature approach versus heat transfer area, and, effectiveness versus duty are presented. Parametric results for entropy generation and Second Law considerations are presented in order to place a realistic bound on the analysis. Effects of porous flow on exit temperature, temperature approach and effectiveness are summarized. Results of this study can be used to guide design and development of compact heat exchanger selection for renewable energy waste heat recovery applications.
Boundary Value Problems in the Theory of Thermoelasticity for Triple Porosity Materials
Authors: Svanadze Merab
Published: February 2017

This paper concerns with the quasi static linear theory of thermoelasticity for triple porosity materials. The system of governing equations based on the equilibrium equations, conservation of fluid mass, the constitutive equations, Darcy’s law for materials with triple porosity and Fourier’s law of heat conduction. The cross-coupled terms are included in the equations of conservation of mass for the fluids of the three levels of porosity (macro-, meso- and micropores) and in the Darcy’s law for materials with triple porosity. The system of general governing equations is expressed in terms of the displacement vector field, the pressures in the three pore systems and the temperature. The basic internal and external boundary value problems (BVPs) are formulated and on the basis of Green’s identities the uniqueness theorems for the regular (classical) solutions of the BVPs are proved. The surface (single-layer and double-layer) and volume potentials are constructed and their basic properties are established. Finally, the existence theorems for classical solutions of the BVPs are proved by means of the potential method and the theory of singular integral equations.
Evaluation of a Residential Scale Hybrid Co-Generation System
Authors: Mao Shuni , Kowalski Gregory J. , Zenouzi Mansour
Published: February 2017

The performance and thermoeconomics of a residential co-generation with fuel cell system were simulated and demonstrated that there is a significant energy, exergy and cost advantage to it over the base solution. Three different operational strategies were investigated. The thermoeconomic value of electricity production and the thermal load is $0.081, $0.2613 and $0.085/KWh for strategies a), b) and c), respectively, as compared to that for the baseline solution of purchasing from the utility, $0.2615. All three strategies significantly outperformed the utility based solution. At the present time only few people are using onsite cogeneration system. Even though this project has economic competitiveness, people may not be willing to use it, because of the complexity of the system itself, the maintenance time and the site location. The issue is a tradeoff of the above disadvantages and the cost factors and independence of operating off grid.
Combined Finite Element and Multi-Body Dynamics Analysis of Effects of Hydraulic Cylinder Movement on Ploughbreast of Horizontally Reversible Plough
Authors: Lin Zhu , Peng Shuang-Shuang , Cheng Xi , Jen Tien-Chien
Published: February 2017

Hydraulic Cylinder (HC), one of the key components of Horizontally Reversible Plough (HRP), takes the responsibilities for the commuting tillage of Horizontally Reversible Plough (HRP). The dynamic behaviors of HC surely affect the tillage performances. Based on our previously related work, this paper further addresses the effects of HC movements on plough-breast of HRP, especially on plough-shank, due to too much wear on it. For HC, uniform motion was considered in this study. A combined finite element analysis (FEA) and multi-body dynamics analysis (MDA) was implemented to assess both tillage kinematics and kinetics of the plough-breast. These predictions were separately focused on five different HC movement scenarios and two actual HRP tilling conditions at the maximum operation depth, i.e. 0.36m. The loading data due to the HC movements were obtained from an MDA and applied to load a finite element modal of the plough-breast. Our results show that HC movements result in the maximum stress and strain at the plough-shank. Our findings demonstrate that the movements cannot have adverse effects on the service life of the plough-breast.
The Effect of Gas Evolution on Hydrodynamic Characteristics of Fluid Flow in Pipeline
Authors: Panakhov Geylani M. , Abbasov Eldar M. , Bakhtiyarov Sayavur I. , Siginer Dennis A.
Published: February 2017

A relative motion of different phases leads to formation of certain forces at the interface of transported fluid and pipe walls. In the non-isothermal flow case a thermal interaction between the phases will affect the flow velocity, the pressure and the temperature distributions in variable cross section pipes. Laboratory experiments were conducted in order to study the effects of the gas generation at the pipe walls on the hydrodynamic characteristics of the two-phase oil/gas flow. It is shown that a throughput capacity of the pipe is affected by the temperature difference between the oil and the pipe walls. At certain temperature difference value (∼3°C) the pipe capacity reached a maximum value.
Exergy Study of Air-Conditioned Space of a Prototype Scale of a River Vessel Room
Authors: Fajardo J. , Sarria B. , Alvarez Guerra M. , Cruz O.
Published: February 2017

The study was conducted on a scale prototype, which simulates one of the rooms in the real vessel air conditioning system. The main results are as follows: the higher the thermal load, the higher the exergy destruction, and increasing the average temperature in the room increases the exergetic efficiency and reduces the exergy destruction. There is an optimal thermal load per unit area of 214.074 W/m2. The highest exergetic efficiencies and lowest values of the exergy destruction indices occur when the average temperature of the room is in the comfort range recommended by ASHRAE, from 22 to 24°C.
Sensitivity Analysis of Planar Piezoresistive Sensors for MEMS Applications
Authors: Hossain A. , Mian A.
Published: February 2017

In this study, the sensitivity of two-dimensional four-terminal piezoresistive sensors commonly referred to as “van der Pauw (VDP)” structure is investigated and analyzed. VDP sensors have the potential to obviate some of the limitations of resistor based sensors such as size and temperature effects. In this study, we will consider the VDP sensor to be fabricated on (100) silicon due to its potential application in MEMS pressure sensors or electronic packaging stress measurements. The sensitivity of the VDP sensor may be affected by misalignment (i.e., orientation) during the etching/diffusion process, the size of the sensor relative to the size of the underlying diaphragm, pad size where the current and voltage are determined, and on their global positions. In this study, we have presented how the VDP stress sensitivity is affected by variations in pad size and sensor orientation with respect to the wafer flat direction. First, a 3D finite element analysis (FEA) model is developed representing a piezoresistive VDP sensor fabricated on (100) silicon diaphragm. Then, the FEA model is validated with the closed form analytical solution for different bi-axial loads. Once the FEA model is validated, additional simulations are conducted to understand the influence of different parameters on the resistance measurements. The change in resistivity of the VDP will then be analyzed to predict its sensitivity under a certain set of sensor parameters.
Analysis of Cassowary Casques for Shock Absorption
Authors: Widholm Scott , Jawaharlal Mariappan
Published: February 2017

The cassowary, a large flightless bird native to Australia, is best known for the helmet-like casque on its head. This casque looks like a large bony fin, but actually is a hollow structure made of keratin. Because the cassowary uses this casque to ram trees to knock down fruit, it is thought that the structure might provide much of the shock-absorbing qualities needed to keep the head safe. This analysis is a first look into this possibility.
Strain Localization in Determining the Constitutive Response of Polymers
Authors: Kweon Soondo , Benzerga Ahmed Amine
Published: February 2017

The constitutive response of glassy polymers is characterized by their complex thermo-mechanical behavior such as strain rate and temperature sensitive yielding, softening at small strains and re-hardening at large strains. These complex behaviors trigger strain localization in the deformation of polymers. Since localization can be induced by both structural and material instabilities, careful analysis needs to be performed to investigate the localization behavior of polymer specimen testing. Localization such as neck formation and propagation that typically occurs in the tensile and compressive testing of polymers and plastics makes it difficult for experimentalists to extract their intrinsic constitutive response. This problem is exacerbated when localization occurs with shear bands. In this study, a macromolecular constitutive model for polymers showing small-strain softening and large-strain directional hardening is employed to investigate the effect of localization in tension onto the constitutive identification process. Considering the complex interplay between the structural and constitutive instabilities, a method based on direct, real-time measurement of area reduction at the neck section has been proposed to extract the intrinsic constitutive response of polymer materials.
Mass Burning Rate of Syngas/Air Mixtures and Gas to Liquid Fuel Auto-Ignition at High Temperatures and Pressures
Authors: Elia Mimmo , Ferrari Matthew , Askari Omid , Metghalchi Hameed
Published: February 2017

Mass burning speed and onset of auto-ignition of premixed syngas/air and gas to liquid (GTL)/air mixtures respectively, have been determined at high temperatures and pressures over a wide range of fuel-air equivalence ratios. The experimental facilities consist of two spherical and cylindrical vessels. The spherical vessel was used to collect pressure data to measure the burning speed, mass burning rate and determine the onset of auto-ignition and cylindrical vessel was used to take pictures of flame propagation with a high speed CMOS camera up to 40,000 frame per second located in a Schlieren system. Effect of cellular flames on mass burning rate have been determined. Critical pressures and temperature for different fuel air equivalence ratios at which auto-ignition takes place have been measured. In this paper, mass burning rate of syngas is calculated for a wide range of equivalence ratio from 0.6 to 2, unburned temperature from 400 to 680 K and initial pressure from 2 to 25 atm. A power law correlation has been developed as a function of equivalence ratio, temperature and pressure. The onset of auto-ignition for GTL/air mixture has been identified for equivalence ratio of 0.8 to 1.2.
Study of Liquid Motion and Pressure Forces Applied on the Walls of Partially Filled Moving Tank
Authors: Noui O. , Bouazara M. , Richard M. J.
Published: February 2017

Various analytical, numerical and experimental studies have been developed to investigate the effect of liquid sloshing on the dynamic behavior of tank-trucks. However, this type of studies is still complex and expensive. Mechanical models are used to simulate complex phenomena. Using these models in the simulation of deformable bodies provides both geometrical and physical aspects. In this study, a new 3D mechanical model is applied to simulate liquid motion in partially filled tank. This model, which is developed in previous study, is able to simulate lateral, longitudinal and vertical displacements. It may also evaluate pressure forces applied on the tank walls. The main idea of this model is to represent the liquid as a mesh of spring-mass systems. The liquid was divided in multiple masses along each axis. The movement of each mass is simulated by displacement of its mass center; this constitutes the mesh nodes. Each adjacent two nodes are linked by flexible edges having a parallel spring and damper. The discretizing method of the liquid is applied; it is followed by computing of masses and initial coordinates of each node. We show, in detail, the method to obtain stiffness of the springs and damping coefficient of the dampers. Afterwards, equations of dynamic liquid motion are obtained. The system of equations is solved for some examples in order to compare results to the literature.