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Directed fuzzing, as an efficient method to focus on a specific set of targets in the program, often works better than random fuzzing when combined with a researcher’s empirical judgment. However, the current directed fuzzing work is not efficient enough. In previous studies, some have generated closer seed inputs by guiding the execution path through the distance from the target region, but the distance guided algorithm is less robust. Some studies used selective symbolic execution for directed testing to alleviate the path explosion problem, but it brings a higher false-positive rate. In this paper, we propose a keypoint coverage-based fuzzing (KCFuzz) method, which extracts the keypoint list using a control flow graph, obtains the keypoint list coverage information through runtime instrumentation, calculates the test priority of the seeds based on the overall coverage and keypoint coverage using an energy scheduling algorithm, and continuously generates test inputs closer to the target according to the specified mutation strategy. On this basis, a hybrid testing framework is implemented, using keypoint coverage directed fuzzing to generate a seed queue covering keypoints, using offspring generation strategies and hybrid execution technology, and further exploring the new state of the program according to changes in overall and keypoint coverage. The experimental results show that the KCFuzz method can efficiently induce the generation of seed queues to reach the target region, and at the same time, the depth and validity of the exploration paths are higher than those of the most advanced directed fuzzing methods such as AFLGo.

Development cycles in Advanced Driver Assistance Systems (ADAS) and Autonomous Driving (AD) technologies pose various challenges even at the development stages, since they require extensive calibration, testing, and validation before they can be commissioned. Specifically, testing and verifying the expected vehicle behavior for ADAS/AD functions in various traffic scenarios is a major challenge. Unfortunately, the extent of real-life tests is often quite limited due to associated high costs. Therefore, it is a common practice to employ simulations for this. However, simulation-only verification also has limitations due to un-modeled dynamics. It is therefore in the interest of the developers and OEMs alike to ensure that ADAS/AD systems conform to reliability, compliance, and performance requirements in a cost-effective and efficient manner. Motivated by these, we introduce in this chapter two alternative testing/verification methods combining real-world testing with simulation for ADAS/AD development. The first concept involves a novel steerable chassis dynamometer and real-time camera stimulation in a co-simulation framework. The second involves a generalization of the co-simulation framework with a vehicle-in-the-loop concept and is named “hybrid testing” that was developed in the scope of the EU-H2020 funded project INFRAMIX, where a real vehicle can be combined with a virtual traffic scenario.

A digital twin is a powerful new concept in computational modelling that aims to produces a one-to-one mapping of a physical structure, operating in a specific context, into the digital domain. This technology could therefore provide improved and robust decision making for asset management. Although the applications of digital twins vary, this paper focuses on digital twins for structural dynamic systems. A key consideration in developing a digital twin is in the construction of a workflow that defines decisions and interactions within the modelling framework. This process will generally be bespoke to specific applications, however key principles will apply. Furthermore, a workflow will provide a methodology for identifying poor predictive performance and systematically improving predictions via optimal decision making. In this paper a three storey building structure is introduced as a case study in order to motivate the challenges and technologies required of a digital twin. The context of this case study is to develop a digital twin of the building structure that consistently predicts the acceleration response of the three floors given an unknown structural state, caused by a contact nonlinearity between two floors. This reflects realistic challenges for a digital twin in that the physical twin will degrade with age, and its response may change under various loading scenarios, unforeseen in the initial model development phase. Key elements within a potential workflow for this application are discussed. These include indicating when model updating schemes become problematic and how augmenting physics-based models with a data-based component can provide information about poor predictive performance. These techniques are linked to hybrid testing, as a potential method for improving model development based on the physical structure in a controlled offline manner. Finally, the impact of these procedures are discussed for model based control methods in terms of vibration attenuation performance, but also robustness against model uncertainties and external disturbances. The workflow and key technologies investigated in this specific case study are expected to outline the general processes that apply to digital twins more broadly, and provide a clearer understanding of how a digital twin should be implemented.

Future applications of mechatronic systems will be characterized by a high degree of digitization enabling the integration of numerous innovative functions. The validation and reliability analysis of such complex systems often requires the realization of cost intensive full system prototypes and the evaluation of field tests. Innovative technologies are therefore integrated slowly in industrial sectors that focus on system reliability. Hence, there is a strong interest in a reliability orientated development and test process for complex mechatronic systems.

Hybrid simulation techniques, which combine real physical models with virtual simulation models, have developed significantly in the last decades. Continuing scientific work and steady progress in simulation and modeling techniques together with powerful automatic code generation tools have pushed this development. For an engineer, this technology offers the possibility of significant savings, faster product development, reduced design uncertainties and reliable component testing without any risk. Due to these advantages there is an increased industrial acceptance and consequently the integration in engineering education is required. From a scientific point of view, hybrid testing demands advanced knowledge in the fields of modeling and simulation, real-time integration, model-order reduction, measurement and signal processing. Furthermore, since coupled systems generally result in a closed loop structure, profound understanding of control theory as well as sensors and actuators is essential. In order to manage this diversity of requirements, several experiments of varying complexity have been developed for illustration of the theoretical background. The laboratory experiments presented comprise dynamic absorber testing and hybrid testing of mechatronic systems like a quadcopter during complex flight operations. The aim is a basic understanding of hybrid testing, its challenges and potentials, and the ability recognize and implement possible application in science and industry.

Hybrid simulation is an innovative experimental method currently being tested and utilized for the simulation of earthquake loads on structures. The reliability of this experimental method will be achieved as more research targeting realistic conditions of structures (e.g. subassemblages and structures at larger scales) with more complex configurations are conducted. Furthermore, these studies need to address the efficacy of hybrid testing to simulate the collapse of structures. The University of Puerto Rico at Mayaguez (UPRM) is developing a hybrid simulation facility with its first-stage consisting of a two channel MTS Flex Test 60 control system with quasi-static hybrid simulation capabilities. The main objective of the UPRM hybrid simulation facility is testing of more realistic models of prototypes subjected to dynamic loads. The research is also focused on substructuring techniques: development, implementation and error measurement. At first, the hybrid facility will be calibrated with the analysis and hybrid testing of a 3-story 2-bay moment resisting steel frame subjected to the Canoga Park time history. Hybrid simulation with substructuring allows the modeling of parts of the structure we can predict analytically and testing other parts of interest at the laboratory. In this case, only the exterior column of the first and second story column of our prototype will be tested at a 1:3 scale while the rest of the structure will be modeled analytically using the software OpenSees and OpenFresco. Coupled numerical simulations were conducted of current partitioning strategies including the conventional and pinned substructuring techniques. These numerical studies showed that there is a need for better partitioning methods. The problem with the studied substructuring techniques is that they approximate the response of the prototype when they do not fully enforce compatibility and/or equilibrium in all degrees of freedom at the boundaries of the partitioned structures trying to simplify the experimental substructure.

International experience from the effects of past earthquakes on the existing reinforced-concrete (RC) structures with limited-ductility has shown that many behave poorly and some possess very low levels of safety, to the extent that they are at risk of collapse. While the seriously damaged RC frames may be demolished and reconstructed, a large number of earthquake-damaged RC frames can be repaired and operative again. The primary objective of this paper is to evaluate the capability of carbon-fibre reinforced polymer (CFRP) repair on rehabilitating the earthquake-damaged columns to their initial collapse resistance capacity. A state-of-the-art hybrid testing facility, referred to as the Multi-Axis Substructure Testing (MAST) system, was used to simulate complex time-varying six-degrees-of-freedom (6-DOF) boundary effects on the physical specimens using mixed load/deformation modes. Based on the experimental results, a comparative collapse risk assessment of the column before and after repair was conducted, which illustrates the effectiveness of using CFRP-repair to restore and improve the collapse resistance of earthquake-damaged RC structures.

Nowadays, many of the proposed solutions to improve automotive vehicle efficiency, such as downsized engines and advanced torque lock-up strategies (for automatic transmissions), can lead to worse noise and vibration characteristics. A typical phenomenon that occurs in such situations is low-frequency booming noise, which happens because of the irregular torque vibrations that are transferred through the flexible driveline elements. This paper presents a combined test and 1D modelling approach used to analyze and predict driveline torsional oscillations and their effect on low frequency booming noise and vibration. In this context, Model Based System Testing (MBST) can be defined as the framework that combines physical testing and simulation with the objective of validating and improving the behavior of 1D multiphysical models. Tests are carried out to obtain insight in the dynamical system behavior, as well as to obtain specific component parameters. This data is then used to create and improve 1D models of the full vehicle driveline, and to predict booming noise characteristics.

Control-based continuation is a relatively new technique for tracking the orbits and bifurcations in a physical experiment under parameter variations. It leverages ideas from the dynamical systems community, particularly from numerical continuation, and combines them with feedback control. A related idea is that of hybrid testing, whereby a physical system is substructured into two parts: one physical and one numerical. The two substructures are connected in real-time via actuators and sensors to form a closed system. This methodology enables the testing of large-scale structures without needing to build everything. In this paper, we will present initial results from combining these two methodologies and we show how the nonlinear dynamics and bifurcations of a particular coupled system can be explored systematically even though a model for the full system is not available. The principal benefit of combining these two methods is that parameter studies become much more straightforward—the numerical model contains numerous parameters that can be adjusted programmatically allowing for an extensive investigation of the full system.

Approaches for structural health monitoring of civil infrastructure using vibration-based damage detection methods have progressed significantly over the past decade as a result of extensive experimentation on both full-scale and laboratory-scale structures. However, the field instrumentation of in-service structures involving well-characterized damage scenarios is a complex, costly, and high-risk investment. In contrast, the use of numerical simulations to generate synthetic data for structural health monitoring research is restricted by challenges associated with modeling experimental uncertainties associated with measurement devices and ambient disturbances. In both cases, the faithful representation of meaningful damage progression is often a technical limitation. Recently, hybrid simulation has been explored as a novel alternative for experimental structural health monitoring research that alleviates the expense and logistics associated with full structural testing, yet retains the empirical nature of experimentation by combining an experimental substructure with an analytical model. In this paper, the use of pseudo-dynamic hybrid simulation for exploration of vibration-based structural health monitoring techniques is demonstrated using a truss structure where a single member and bolted gusset plate connection are incorporated in the experimental model. Hybrid simulations are performed in the baseline state and following introduction of localized damage developed at a limit state of the bolted connection. The results correlate strongly with predictions obtained from a fully analytical model and support the further exploration of hybrid simulation as a tool for vibration-based structural health monitoring research.

Cyber Physical Testing or Real Time Hybrid Testing is a Hardware-In-The-Loop approach allowing for tests of structural components of complex machines with realistic boundary conditions by coupling virtual components. The need to actuate the physical interface makes the tests on structural systems challenging. In order to deal with stability and accuracy issues, we propose the use of an Adaptive Feed-Forward Cancellation approach with a Recursive Least Squares (RLS) adaption law for interface synchronization of harmonically excited systems. The interface forces are generated from multiple harmonic components of the excitation force. A RLS adaption law sets the amplitudes and phases of the harmonic interface force components and minimizes the interface gap. One major practical advantage of using a RLS adaption law is that only one forgetting factor has to be chosen compared to other adaption algorithms with various tuning parameters. As a consequence, it is possible to test systems with multiple interface DoF. In order to illustrate the performance and robustness of the proposed testing algorithm, the contribution includes a numerical investigation on a lumped mass system.

Experimental modal analysis is commonly associated with the use of simulation models for validation, correlation and model updating. However, this interaction between simulation and test is constantly evolving, not in the least because it can be applied to model-based design engineering in the broad sense. Over time, new simulation methods have emerged and consequently, new approaches combining experimental and numerical methodologies are needed and possible. Model Based System Testing (MBST) is an innovative paradigm that allows to structure this process and, in particular, to investigate how the well-established modal testing and analysis procedures and ways of working can be adopted to the multiphysical nature of mechatronic systems. As a result, many possibilities arise: test data can be used to validate multiphysical models, models help gaining insights into test conditions, hybrid approaches allow combining testing and simulation on hardware-in-the-loop and system-in-the-loop test benches, where physical systems can be combined with simulation models to apply loads and more realistic test conditions, as well as the use of data coming from feedback control system information for testing purposes. In this paper, the context and concepts of MBST will be introduced, and application examples will be shown, highlighting the advantages of such a methodology.

Distributed hybrid testing offers a promising approach to use resources from geographically separate laboratories in a highly efficient way, to perform more complex, larger-scale tests than are possible in most individual laboratories. The method involves splitting a structure into a set of substructures (some tested physically, some modelled numerically) located in different laboratories. Simulation of the full structural response involves simultaneous testing of the substructures with feedback of data between them, requiring fast communication through computer networks. To handle systems involving rate dependence, there is a desire for test speed to approach real time. In addition to the increased difficulty of tracing errors caused by the distributed environment, organizing and planning distributed experiments creates much more complexity than in single-laboratory hybrid tests. This points to the importance of a platform to support the testing activities. This platform has been achieved by means of a specification called Celestina, created at the University of Oxford. Celestina provides a framework for conducting the experiment workflow. It provides a specification for the services to be implemented under three main headings of networking, test definition and experiment execution, and supports to data exchange during a test. It does not force any particular implementation, which can be independently developed and implemented under this framework, nor does it restrict the actual method of data exchange. In this article we discuss the design and conception of the specification as well as one implementation that has been validated through a series of substructured “numerical experiments” in partnership with the University of Kassel.

The practical and inexpensive nature of ambient vibration testing has contributed to this approach being widely used by researchers and practitioners for identifying the dynamic characteristics of a wide range of laboratory and full-scale structures. The dynamic characteristics identified from such testing can be used for validating and calibrating analytical models, for quantifying and evaluating actual operating or performance characteristics, or for identifying damage and structural health monitoring. Although ambient vibration testing has been used extensively, it remains subject to a number of assumptions and limitations that are not always readily apparent in the results and that can reduce the reliability and utility of these results for many structures and applications. The authors believe that a pseudo ambient vibration testing approach using controlled excitation from a spatially distributed network of low-cost excitation devices could provide more consistent and reliable dynamic characterizations while maintaining many of the desirable attributes of ambient vibration testing. The writers conducted a study of the proposed testing approach using a large-scale laboratory model. The dynamic properties of the structure were identified by ambient vibration testing and by different implementations of the proposed pseudo ambient vibration testing approach. The results obtained from the testing are compared and discussed.

This paper presents a hybrid test method that enables the investigation of contact-impact scenarios in complex systems using kinematically versatile, off-the-shelf industrial robots. Based on the pseudo-dynamic test method, the technique conducts tests on an enlarged time scale, thereby circumventing control rate and response time limitations of the transfer system. An initial exploratory study of a drop test demonstrates that non-rate dependant effects including non-linear stiffness and structural hysteresis can be captured accurately while limitations result from the neglect of rate- and time-dependant effects such as viscous damping and creep. Future work will apply the new method to contact scenarios in air-to-air refuelling.

Hybrid simulation method in earthquake engineering, which combines physical testing and numerical simulation, was developed to evaluate seismic performance of civil structural systems. Thus, instead of constructing a full sized structural specimen, hybrid simulation allows researchers to build a complex experimental substructure tested experimentally while the relatively simple part of the structure is numerically simulated to economically obtain the full structural responses. Recently a versatile hybrid testing system was built at the Laboratory of Earthquake and Structural Simulation (LESS) at Western Michigan University. The major equipment consists of a seismic simulator (often called shake table), an actuator/reaction system and an advanced hybrid testing controller. Such testing system is capable of conducting various hybrid simulation experiments such as displacement-based pseudodynamic substructure testing as well as force-based real time dynamic hybrid testing. The benchmark scale testing system at LESS is particularly suitable for development of hybrid simulation techniques and earthquake engineering education and outreach activities. The development of this testing system including both hardware and software integration is presented. Example hybrid simulation methods that can be conducted using the developed testing system as well as its applications in the hybrid simulation method development of two NEESR projects are discussed.

This study presents an experimental study comparing the testing quality of a Hybrid Testing (HT) process with the commonly used approaches in industry: Scripted Testing (ST) and Exploratory Testing (ET). The study was conducted in an international IT service company in Sweden with the involvement of six experienced testers. Two measures were used for comparison: 1) defect detection effectiveness (DDE) and 2) functionality coverage (FC). The results indicated that HT performed better in terms of DDE than ST and worse than ET. In terms of FC, HT performed better than ET, while no significant differences were observed between the HT and ST. Furthermore, HT performed best for experienced testers, but worse with less experienced testers.

Hybrid testing is an emergent technology encompassing a variety of contemporary methods such as hardware-in-the-loop, pseudo-dynamic, and real-time dynamic testing. A system to be tested is split into two or more subsystems, with some of the components represented by numerical models and the remainder being comprised of real, physical hardware. Forces and displacements are transmitted between subsystems via actuators and sensors. This paper is concerned with the challenges that emerge when trying to accommodate real-time simulations with highly nonlinear force characteristics in the physical substructure. A brief review of hybrid testing considerations is provided, including actuation hardware, controllers, and numerical time-integration schemes. An new approach is then proposed which unites novel methods in the numerical model, the integration scheme and the actuator control to achieve high performance levels independent of the physical component being tested, specifically for the case of highly nonlinear components and relatively coarse timesteps in the numerical substructure. Simulation results are provided to substantiate the projected benefits.