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1. Distributed Feedback Controllers for Stable Cooperative Locomotion of Quadrupedal Robots: A Virtual Constraint Approach*

   https://doi.org/10.23919/ACC45564.2020.9147673  

   Hamed, Kaveh Akbari; Kamidi, Vinay R.; Pandala, Abhishek; Ma, Wen-Loong; Ames, Aaron D. (July 2020, American Control Conference (ACC))

   This paper aims to develop distributed feedback control algorithms that allow cooperative locomotion of quadrupedal robots which are coupled to each other by holonomic constraints. These constraints can arise from collaborative manipulation of objects during locomotion. In addressing this problem, the complex hybrid dynamical models that describe collaborative legged locomotion are studied. The complex periodic orbits (i.e., gaits) of these sophisticated and high-dimensional hybrid systems are investigated. We consider a set of virtual constraints that stabilizes locomotion of a single agent. The paper then generates modified and local virtual constraints for each agent that allow stable collaborative locomotion. Optimal distributed feedback controllers, based on nonlinear control and quadratic programming, are developed to impose the local virtual constraints. To demonstrate the power of the analytical foundation, an extensive numerical simulation for cooperative locomotion of two quadrupedal robots with robotic manipulators is presented. The numerical complex hybrid model has 64 continuous-time domains, 192 discrete-time transitions, 96 state variables, and 36 control inputs. 

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2. Development of multi-directional real-time hybrid simulation for tall buildings subject to multi-natural hazards

   https://doi.org/10.1016/j.engstruct.2024.118348  

   Al-Subaihawi, Safwan; Ricles, James; Quiel, Spencer; Marullo, Thomas (September 2024, Engineering Structures)

   Real-time hybrid simulation (RTHS) divides a structural system into analytical and experimental substructures that are coupled through their common degrees of freedom. This paper introduces a framework to enable RTHS to be performed on 3D nonlinear models of tall buildings with rate dependent nonlinear response modification devices, where the structure is subjected to multi-directional wind and earthquake natural hazards. A 40-story tall building prototype with damped outriggers is selected as a case study. The analytical substructure for the RTHS consists of a 3-D nonlinear model of the structure, where each member in the building is discretely modeled in conjunction with the use of a super element. The experimental substructure for the RTHS consists of a full-scale rate-dependent nonlinear viscous damper that is physically tested in the lab, with the remaining dampers in the outrigger system modeled analytically. The analytically modeled dampers use a stable explicit non-iterative element with an online model updating algorithm, by which the covariance matrix of the damper model’s state variables does not become ill-conditioned. The damper model parameters can thereby be updated in real-time using measured data from the experimental substructure. The explicit MKR-α method is optimized and used in conjunction with the super element to efficiently integrate the condensed equations of motion of a large complex model having more than 1000 nonlinear elements, thus enabling multi-axis earthquake and wind hybrid nonlinear simulations to be performed in real-time. An adaptive servo-hydraulic actuator control scheme is used to enable precise real-time actuator displacements in the experimental substructure to be achieved that match the target displacements during a RTHS. The IT real-time architecture for integrating the components of the framework is described. To assess the framework, 3D RTHS of the 40-story structure were performed involving multi-axis translational and torsional response to multi-directional earthquake and wind natural hazards. The RTHS technique was applied to perform half-power tests to experimentally determine the amount of supplemental damping provided by the damped outrigger system for translational and torsional modes of vibration of the building. The results from the study presented herein demonstrate that RTHS can be applied to large nonlinear large structural systems involving multi-axis response to multi-directional excitation. 

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3. Improving the Seismic Performance of Structural Steel Systems Through Advanced Testing

   https://doi.org/10.1007/978-3-031-03811-2_6  

   James Ricles (May 2022, Lecture notes in civil engineering)

   Recent earthquakes in many parts of the world have resulted in damage to the civil infrastructure, resulting in fatalities and economic loss. This experience has resulted in stake holders demanding a more resilient infrastructure and the mitigation of earthquake hazards to minimize their impact on society. Researchers have developed concepts for structural steel systems to promote resilient performance. Real-time hybrid simulation (RTHS) provides an experimental technique to meet the need to validate new concepts. RTHS enables a complete structural system, including the soil and foundation to be considered in a simulation, interaction effects and rate dependency in component and system response to be accounted for, and realistic demand imposed onto the system for prescribed hazard levels. This paper presents the concept of RTHS and developments achieved at the Lehigh NHERI Experimental Facility that have advanced RTHS to enable accurate large-scale, multidirectional simulations involving multi-natural hazards to be performed. The role that hybrid simulation has played in these developments and how its use has enabled a deeper understanding of structural system behavior under seismic and wind loading will be discussed. Examples include self-centering steel moment resisting frame systems, braced frame systems with nonlinear viscous, and tall buildings with outriggers that are outfitted with nonlinear viscous. 

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4. A Unified Real-Time Motion Generation Algorithm for Approximate Position Analysis of Planar N-Bar Mechanisms

   https://doi.org/10.1115/1.4064132  

   Lyu, Zhijie; Purwar, Anurag; Liao, Wei (June 2024, Journal of Mechanical Design)

   Abstract This paper presents a novel real-time kinematic simulation algorithm for planar N-bar linkage mechanisms, both single- and multi-degrees-of-freedom, comprising revolute and/or prismatic joints and actuators. A key feature of this algorithm is a reinterpretation technique that transforms prismatic elements into a combination of revolute joint and links. This gives rise to a unified system of geometric constraints and a general-purpose solver which adapts to the complexity of the mechanism. The solver requires only two types of methods—fast dyadic decomposition and relatively slower optimization-based—to simulate all types of planar mechanisms. From an implementation point of view, this algorithm simplifies programming without requiring handling of different types of mechanisms. This versatile algorithm can handle serial, parallel, and hybrid planar mechanisms with varying degrees-of-freedom and joint types. Additionally, this paper presents an estimation of simulation time and structural complexity, shedding light on computational demands. Demonstrative examples showcase the practicality of this method. 

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5. Natural Hazards Research Summit 2022: Multi-Directional Cyber-Physical Experimental Testing to Establish Multi-natural Hazard Resiliency of Structural Systems and Building Content Hazard Mitigation

   https://doi.org/10.17603/ds2-fvgg-9h66  

   Harvey, Philip; Ricles, James; Villalobos Vega, Esteban; Al Subaihawi, Safwan; Cao, Liang; Marullo, Thomas; Briscoe, Terence (January 2023, Designsafe-CI)

   Protecting both the essential building contents and the structural system—as well as facilitating and accelerating the post-event functionality of business operations—is a major concern during natural hazards. Floor isolation systems (FIS) with rolling pendulum bearings along with nonlinear fluid viscous dampers (NFVD) have been proposed to mitigate damage and enhance the resiliency of non-structural and structural systems, respectively. These devices are designed to decrease vibrations under dynamic loading conditions. In this poster, we introduce research using tridimensional nonlinear cyber-physical experimental testing (i.e., real-time hybrid simulations) to validate the performance of these response modification devices placed in structural systems under wind and earthquake loading conditions. The effects of soil-structure-foundation and fluid-structure interactions were also accounted for. The novelty of the project is the use of multi-directional large-scale real-time hybrid simulations of complex nonlinear systems under wind and earthquake demands to combine experimental structural modification passive devices with analytical multi-story buildings considering soil-foundation interaction via neural network. Results show that the FIS and NFVD can significantly reduce the demand on non-structural and structural systems of buildings subjected to natural hazards whose response can be also significantly affected by soil-foundation-structure interaction. A product of this research is the data (which is linked in Related Works), which can be used to compare with new studies using the same experimental techniques and structural modification devices or with alternative approaches. Researchers interested in multi-natural hazards resilience and mitigation, state-of-the-art structural experimental techniques, and the use of machine learning as a tool to improve modeling efficiency will benefit from its results. Also, companies dedicated to the commercial development of structural response modification devices, as well as policymakers working or with interest in economic and social resilience. 

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