According to the International Council on Systems Engineering (INCOSE), “Systems Engineering is a transdisciplinary and integrative approach to enable the successful realization, use, and retirement of engineered systems, using systems principles and concepts, and scientific, technological, and management methods” [1]. Model Based Systems Engineering (MBSE) focuses on formalized applications of modeling to support systems engineering artifacts development from the conceptual design phase throughout the end of the system of interest (SOI) lifecycle [2]. In his 1993 book, “Model Based Systems Engineering”, Dr. Wayne Wymore first introduced the term “MBSE” [3]. Systems engineers are living in a generation wherein modern systems are growing in complexity ^[4][5][4,5]. MBSE is the proposed solution by the researchers to cope with system complexity in a variety of SOI ^[6][7][6,7]. Various MBSE methodologies have been developed in recent years. The most notable ones are Object Oriented Systems Engineering Method (OOSEM), Object Process Methodology (OPM), State Analysis, IBM Harmony and Arcadia-Capella ^[8][9][8,9]. Among these, OOSEM-based SysML has better tool support than any other MBSE methodologies available ^[10][11][10,11]. In fact, SysML has emerged as the de facto standard system modeling language for MBSE ^[12][13][12,13]. According to Friedenthal, Moore, and Steiner, “SysML is a general-purpose graphical modeling language that supports the analysis, specification, design, verification, and validation for complex systems” [14]. SysML is owned and published by the Object Management Group, Inc. (OMG) [15]. SysML is a derivation of UML, developed in the 1990s as a general-purpose language for software engineering [16]. SysML consists of nine diagram types, namely Package Diagram, Requirements Diagram, Block Definition Diagram (BDD), Internal Block Diagram (IBD), Use Case Diagram, Activity Diagram, State Machine Diagram, Sequence Diagram, and Parametric Diagram (see Figure 1) [15].

VR is one of the major technologies with the utmost anticipated potential for growth, especially in the fields of engineering, education, gaming, cinematography and healthcare ^{[18][19][20][21][22][23][24][25]}[18,19,20,21,22,23,24,25]. For example, different engineering fields leveraged VR technologies to accomplish various tasks, such as VR based Civil Engineering training, Industry 4.0 implementation, and Aerospace training ^{[26][27][28][29][30][31][32]}[26,27,28,29,30,31,32]. Coates et al. defined VR as an electronic simulation of environments with head mounted display and wired outfit, which allows the end user to interact with lifelike 3D environments [33]. A typical VR system consists of the following key components: VR implementation software, Head Mounted Display (HMD), base station, tracking sensors, feedback devices, on board/external computers and users ^[34][35][36][34,35,36].

Though SysML application has been widespread in recent years, it has not been fully adopted by organizations. In addition, stakeholders may not have knowledge of SysML [37]. External product suppliers do not have SysML software knowledge and often ask for Excel/Word documents for data exchanges. Hence, system engineers still need to generate documents from the SysML system model to present the work in front of non-technical audiences. Therefore, there is a need for automatic data extraction from SysML models to facilitate model demonstration to technical and non-technical stakeholders alike.

To date, SysML models have mostly been used to define requirements, use cases, system architectures, system behaviors, and task sequences through static viewpoints and elements. In recent years, researchers have incorporated simulation analysis within SysML models to enable system requirements verification and design evaluation ^[38][39][38,39]. However, very few studies have focused on the integration of VR tools with SysML models. Recent studies indicate that VR-supported immersive design review allows participants to identify more issues/faults in design, improve collaborative engagement, focus and presence as compared to non-immersive methods ^[40][41][40,41]. Moreover, VR environments are beneficial for visualizing complex structures and provide higher levels of understanding and knowledge retention than the conventional approaches ^[42][43][44][42,43,44]. Recent case studies/evaluations by the researchers showed that VR environment translation of visual formalisms (similar to SysML) resulted in enhanced collaboration, learning and understanding among the users/stakeholders. For example, multiple studies have confirmed that 3D VR environments significantly increase the processes of knowledge retention and the collaborative process modeling experience of Business Process Model and Notation (BPMN) ^[45][46][47][45,46,47]. Similarly, modeling 3D UML diagrams in a virtual environment resulted in faster model comprehension and a more enjoyable modeling experience than 2D diagrams ^[48][49][48,49]. Based on the above study results, it can be elicited that visualization of 2D SysML diagrams in a 3D VR environment can improve model understanding, especially of complex systems, and facilitate a better collaborative environment among users and stakeholders.

VR technology can help visualize the system architecture, facilitate virtual storytelling, verify system requirements and evaluate product/service performance early in the lifecycle of a SOI. For example, a system engineer can evaluate system architecture (e.g., Telescope Mount System) in a 3D virtual environment and, based on their understanding of the system, modify/refine the architecture early in the design phase. In addition, external stakeholders with minimal technical knowledge can be immersed into a 3D virtual environment and experience use case scenarios of proposed designs. As a result, there is a need for interoperability between 3D VR models and SysML models to enable data exchange and review to systems engineering artifacts such as use cases, requirements, operational concepts, system architecture, etc.

In addition, use of Digital Twin (DT) technologies in systems engineering projects have been increasing in recent years. DT as a concept was first introduced by Michael Grieves as a virtual representation of an actual component that can be used to emulate the same behavior as that of its real world counterpart [50]. However, the term “Digital Twin” first appeared in National Aeronautics and Space Administration’s (NASA) draft technological roadmap published in 2010 [51]. Over the last two decades, literature and research in the field has evolved to produce a wide variety of DT definitions and methodologies [52]. To simplify the ambiguity, a DT can be defined as a digital or virtual model of a real-world object (system, component, part, process, human, etc.) representative of the exact or future state of its physical twin via real time data exchange as well as keeping records of historical data [53]. Virtual models can be developed using a variety of methods, including VR, Augmented Reality (AR), Mixed Reality (MR), dashboard technologies and 2D simulations, etc. ^{[54][55][56][57][58][59]}[54,55,56,57,58,59]. For example, developers can fabricate an entire machine in a digital environment and test their high-level control mechanism in a VR environment; manufacturing engineers can utilize dashboards to analyze the production process in real time and make necessary adjustments. Data exchanges between real and virtual counterparts of a DT infrastructure are achieved through internal/external sensors connected to physical systems and communication networks [58]. Recently, few DT frameworks have emerged where VR environments co-exist with other DT infrastructure and support validation of the digital/virtual configurations before the physical twin implementation ^[60][61][60,61]. The integration of MBSE tools and DT infrastructure can present several opportunities for systems engineers to test and visualize large models ^[62][63][62,63]. Both the physical and virtual models can be integrated with a shared MBSE repository (e.g., SysML model), which will act as a communication hub between DT infrastructure and systems engineering activities [63]. Moreover, MBSE efforts can introduce early DT development in a program’s lifecycle [64]. Therefore, integration of SysML models with VR tools is one of the key steps in establishing synergy between DT and MBSE.

2. Integration of SysML and Virtual Reality Environment

The authors believe there are limited studies available in MBSE research which emphasize integration of VR environments with SysML tools. In his thesis paper, Kande proposed an integration methodology of Virtual Engineering (VE) suite with the SysML model, providing a graphical interface to demonstrate the system of interest and operations [65]. He created a fermenter analysis model using Computer Aided Design (CAD) data and analyzed the effects of changes in design parameters on system performance. To enable effective communication of systems engineering artifacts to the non-engineering disciplines, Madni mapped systems engineering (SE) artifacts modeled in SysML to virtual worlds, within which different storylines can unfold [66]. In addition, he combined MBSE + frameworks (MBSE and storytelling in VR) and Experimental Design Language (EDL) to enable early participation and collaboration of the stakeholders in the system design [67]. Abidi et al. proposed an interactive VR simulation to encompass real time simulation of production flows in a lean manufacturing industry through communication between ARENA and Virtual Environment by utilizing SysML based transformation and Real Time Infrastructure (RTI) [68]. Mahboob et al. proposed a concept for a user- and task-centric model for product development in the VR environment. In that research proposal, SysML was used to separate isolated model components into products, actors and behaviors of a specific use case, and then those model components were combined to build the use case-specific scenario in VR [69]. Sanvordenker visualized a self-driving truck’s SysML model in a VR environment by extracting SysML model diagrams, representing them in a browser, and finally embedding the web browser inside a Unity scene through a custom plugin [70]. Oberhauser demonstrated a solution concept for visualizing and interacting with SysML models as stacked hyperplanes in a VR environment [71]. However, in the above research there are some limitations. Namely, requiring extensive manual effort to set up each of the simulation components and frequent changes in the interface files (e.g., dynamic link library) to enable seamless data exchange. Furthermore, the VR diagrams used in these studies were more complex (e.g., stacked hyperplanes) instead of being easily comprehendible and their methodologies involved far-reaching conversions of models (XMI conversion, MASCARET, etc.). Those complex design techniques may hinder the mass use of VR-enabled SysML due to the time and effort needed to set up those systems.