Logistics Modeling and Simulation (M&S)

Classes of Modeling and Simulation

The Defense Science Board in 1992 defined an appropriate classification of models and simulations: Constructive, Virtual, and Live.

1. Constructive Models and Simulations

This class of M&S represents, or simulates, a totally synthetic world. In other words, this category of M&S only replicates the “real” world, and has no “real” components; it portrays numerous entities interacting in a simulated environment. However, it is important to understand that a constructive model is subject to real people inserting real data, but the real people are not involved in the simulation itself. To a large extent, a constructive model is either driven by mathematical equations representing the simulated universe being modeled, or supported by fabricated, or derived, data inserted into the model which is intended to represent what is conceived to be a validly projected scenario. For this reason, multiple iterations are usually run when using a constructive simulation in order to provide statistical confidence in the outcome. An example is the Air Force’s Logistics Composite Model (LCOM), a large-scale computer simulation used to model manpower and other logistical requirements. It considers employment of a myriad of alternative support resources to help the user decide the best mix to support a given requirement.

2. The Virtual Simulation

Virtual models are based upon real people interacting with synthetic, or virtual, environments. In a virtual simulation, the system being modeled may include portions of actual hardware, which can be driven, or stimulated, by the output derived from a computer simulation. For example, a weapon system simulator might employ a “near-real” crew compartment imitating its actual environment relative to equipment, controls and display panels. Operators are thus immersed in an environment which is driven by a simulator, and that for them has the look and feel of the real thing. The principal advantage of virtual prototyping is that it permits the design engineer, operators and crews, maintenance and manufacturing personnel, and other key members of the development team to interact simultaneously with the same realistic three-dimensional representation.

3. Live Simulations

Everything is simulated except combat. Troops are allowed to use the equipment under actual environmental conditions approaching real-life combat. The live simulation provides a testing ground to provide live data on actual hardware, software and human performance in an actual operational environment. Of course, the real advantage that a live simulation provides management is the opportunity to subject a system to “real data” and to “real environmental” stresses. Given the high cost of live simulations, the use of less resource-intensive forms of M&S, such as constructive and virtual simulations, is often a more optimal analytical approach.

M&S Support Across the Life Cycle

M&S can be an effective tool in the supportability analysis and evaluation process in implementing life-cycle management principles because all the sustainment/materiel readiness driver metrics can be considered in parallel. Consequently, the sustainment M&S objective should be to use validated models to consider materiel availability/readiness implications when assessing the merits of alternatives throughout the life cycle. M&S should be used in assessing the alternatives for major decisions affecting the design and deployment of both the end item and its support system. Properly applied M&S encourages collaboration and integration among the varied stakeholders (including the test and transportation communities) facilitating materiel availability and system effectiveness.

The models should be used throughout the life cycle and should include the multiple materiel availability stakeholder contribution and funding streams for the supply chain components. (The level of detail used varies based on several factors including, but not limited to, the system's complexity, criticality to the user, program phase, and risk.) In all cases, M&S efforts should consistently and credibly look at/trade off life-cycle alternatives in a repeatable fashion. In addition, the underlying assumptions and drivers for the values of each of the sustainment metrics should be documented as thresholds, objectives, and estimates evolve through the life cycle.

Technology Maturation and Risk Reduction (TMMR) Phase

M&S should be used to refine sustainment objectives and identify any constraints based on technology assessments. The technology demonstration results should be modeled to project likely support capabilities and the associated confidence levels that enabling technologies (i.e. prognostics and health management, Item Unique Identification, etc.) will allow the achievement of those support capabilities. M&S should also be used to develop initial/notional system level product sustainment strategy and maintenance concepts for major sub-system. As the design evolves, M&S can be used to help keep the product support elements in balance between and within system hardware elements.

Engineering and Manufacturing Development (EMD) Phase

Modeling and simulation combined with supportability analysis are important best practices to design and develop the individual product support elements required to implement the support strategy. During this phase they are applied to lower and lower levels of detail as the design matures. The supportability analysis should continue to be used to determine the relative cost vs. benefits of different support strategies (including the source of support decisions). The data should be refined and the results included in the Life Cycle Sustainment Plan and used to support contract negotiations.

Once Integrated Product Support (IPS) are developed and prototyped, modeling and simulation can also be used to provide confidence the sustainment metrics will mature to sufficient levels when the system and supply chain are deployed. This is accomplished with the use of models that take test results and predict likely capabilities. The same concepts are applied to provide confidence levels of what the enabling technologies will be able to achieve in the operational environment and identify any anticipated constraints. All of these factors are then used to project the mature sustainment metric values and their associated confidence levels for the projected Concept of Operations.

Production and Deployment (P&D) Phase

M&S continues to support the program improvement efforts by analyzing the impact of proposed design refinement, maintenance processes, and budget alternatives on the sustainment metrics/mission effectiveness. M&S should be used in assessing the alternatives of both the system and its support system (especially the enabling technologies), ensuring all critical metrics are considered in parallel and not at the expense one another. In addition, taking early operational results and predicting likely trends (with confidence levels) can be used to proactively anticipate problems so corrective actions can be taken as the system is fielded to minimize adverse impacts on the users. This also helps to provide confidence the critical sustainment metrics will mature to sufficient levels when the system and supply chain are fully deployed and to identify any anticipated constraints or limitations.

Operations and Support (O&S) Phase

During this phase M&S supports the program improvement efforts by analyzing the impact of proposed continuous process improvements, Engineering Change Proposals, and budget alternatives on the sustainment metrics as well as mission effectiveness. M&S can be used in assessing the alternatives affecting the design and deployment of both the end item and its support system. In addition, it can be used in a proactive mode to anticipate problems by taking use data and user feedback to (a) project trends (with confidence levels) so actions are taken as conditions deteriorate to minimize adverse impacts on the users, (b) identify areas in the supply chain where performance is adversely affecting materiel availability, increasing Life Cycle Costs, or where there are opportunities for savings/improvements, and (c) identify specific risk areas and ways to address/resolve root causes and reduce risk.

Validation, Verification, and Accreditations (VV&A)

It is DoD policy that (a) models, simulations, and associated data used to support DoD processes, products, and decisions shall undergo verification and validation (V&V) throughout their lifecycles and (b) models, simulations, and associated data used to support DoD processes, products, and decisions shall be accredited for an intended use. The last thing any manager wants to do is to take a recommendation up the line to a decision maker and be asked, “Why should I believe this analysis?”, and then not be able to substantiate the credibility of the underlying methodology.

Validation is defined as the process of determining the degree to which a model or simulation is an accurate representation of the real-world from the perspective of the intended uses of the model or simulation. In other words, the functional expert should be asking if the model or simulation indeed represents the real thing. Verification, on the other hand, is the process of determining that a model or simulation implementation accurately represents the developer's conceptual description and specifications. The developer should be asking if the model or simulation works as expected. Finally, accreditation is the official certification that a model or simulation is acceptable for use for a specific purpose. In this case, the model or simulation is tested to see if it meets the user’s needs.

Conclusion

M&S capabilities and limitations are often inadequately understood, and M&S is sometimes not planned and/or managed with sufficient rigor. Although one can credibly model many things that are understood well (e.g., physical capabilities, natural phenomena, and physics-based interactions), it is much more difficult to reliably represent things not fully understand (e.g., human behavior, reliability, and emergent behaviors of complex systems). M&S capability involves not only the software tools themselves, but the data that feeds them; the computing platforms that execute them; the standards, middleware and networks that may interconnect them; the encryption capabilities and security constraints that protect them; and, most importantly, the people that plan, develop, integrate, verify, validate, accredit and use them. Deficiencies in any of these present a risk to a program. Thus acquisition managers should approach the use of M&S wisely and plan carefully.