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A Systems Engineering Approach to Designing Complex Systems

A Systems Engineering Approach to Designing Complex Systems. Dr. Michael Winter, Mr. Randy Skelding, & Dr. Ravi Rajamani Pratt & Whitney, United Technologies Corporation. This document contains no technical data. United Technologies. Business units. commercial power solutions. aerospace

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A Systems Engineering Approach to Designing Complex Systems

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  1. A Systems Engineering Approach to Designing Complex Systems Dr. Michael Winter, Mr. Randy Skelding, & Dr. Ravi Rajamani Pratt & Whitney, United Technologies Corporation This document contains no technical data.

  2. United Technologies Business units commercial power solutions aerospace systems commercial building systems

  3. PRATT & WHITNEYLeading industry change P&W Canada P&W Rocketdyne Commercial Engines and Global Services Power Systems Military Engines

  4. System Engineering Process Driven by Product Needs Propulsion System Complexity Driving Need for More Robust Systems Engineering Process and Tools System of Systems

  5. Modern Gas Turbine Optimization is an Exercise in Managing Complexity ~ 80,000 PARTS ~5000 PART NUMBERS ~ 200 MAJOR PART NUMBERS REQUIRING 3D FEA/CFD ANALYSIS ~ 5000-10,000 PARAMETRIC CAD VARIABLES DEFINE MAJOR PART NUMBERS ~ 200 MAN-YEAR ANALYTICAL DESIGN EFFORT ~ 200 MAN-YEARS DRAFTING / ME EFFORT

  6. Requirements Management Program System Module Part Company Job Ticket Output SRD CRD PRD Requirements Flow to 3 Levels

  7. Program Job Ticket or Contract => Requirements Job Ticket measures compliance to requirements Product / Service Solution System Deliverables Roles System = Part I “Activities” Module Fan = Part II Part Fan Blade = Part III

  8. Simulation System Analysis & Optimization Execution Optimization CAD/CAM Computational Systems Engineering

  9. Complex Designs are Inherently Iterative & Bounded STANDARD WORK CAD MODEL PHYSICS MODEL DESIGN SPACE - NON LINEAR - MULTI MODAL - DISCONTINUOUS - NOISEY - HIGHLY CONSTRAINED WORK INSTRUCTIONS CRITERIA VALIDATED ANALYSIS PREFERRED CONFIGURATIONS DESIGN DECISION Manual Iteration 100s-1000s of Times

  10. Sophisticated Simulation Based DesignSystems

  11. …and Complex Designs are Iterated Across Disciplines & Organizations…

  12. . . . And Iterations Can Take Place Across the Globe • INTER-DIVISIONAL • CUSTOMERS • OUTSOURCING • PARTNERSHIPS

  13. Gains are Being Made by Shifting from “Human” to “Computer” Based MDO “HUMAN” BASED “COMPUTER” BASED WORKFLOW, RULES, And DESIGN ITERATIONS AUTOMATED WITHIN And ACROSS SYSTEMS & DISCIPLINES -- LABOR INTENSIVE -- SUB-SYSTEM B SUB-SYSTEM A SYSTEM MANUAL WORK FLOW per PROCESS MAPS MANUAL CAD/CAE MODEL BUILDING MANUAL EXPLORATION TO FIND OPTIMAL DESIGNS AUTOMATE WORKFLOW AUTOMATE MODEL BUILDING & EXECUTION AUTOMATE DESIGN EXPLORATION

  14. Large Scale Computer Based MDO is AlreadyPractical 3D Aero-Vibratory Shape Optimization Of A Cooled Turbine Airfoil (Single Row RANS CFD, Cooled UG Parametric Model, 3D ANSYS Vibes)

  15. Large Scale Computer Based MDO is AlreadyBecoming Practical 3D Shape Optimization Based On Hybrid Genetic Algorithm & Rule System (3D RANS Multi Row CFD, Population Size 80, Total Runs 2400, Run Time 48 hrs on 40CPUs) Discovered “bowed” rotor To control tip leakage Vortex

  16. Will Enable New Design Paradigms CUSTOMER NEEDS UNDERSTAND THE FUTURE CREATE TECHNOLOGY IMPROVE MODELS RE-FORMULATE PROBLEM UPGRADE COMPUTER BASED DESIGN “MACHINE” RUN 24/7 365 DAYS A YEAR CONTINUOUS DETAILED DESIGN SOLVE ALL POSSIBLE APPLICATIONS @ TECHNOLOGY READINESS LEVEL ENGINEERS COMPUTER BASED DESIGN CUSTOMER REQ. EXCEED TECHNOLOGY LESS TIME FEWER PEOPLE

  17. Tolerance Band Planned Profile) s ( ± x ) Actual Profile NTE (Not to Exceed) Goal Milestones Verification - Convergence to Requirements Technical Performance Measurement Tracking Chart Tolerance Band Planned Profile) s ( ± x ) Actual Profile NTE (Not to Exceed) Value (e.g.. Weight) Goal Milestones Time

  18. Convergence to Requirements Commitment 5400 lb Dry engine weight (lbs) -29 lb Entry Into Service >100 lbs Below Commitment

  19. Generic 2 Spool Gas Turbine Engine - Diagram Source: Wikipedia commons ITT PB N1 N2 EGT Putting Rigor into System Requirements with Requirements Modeling

  20. The classical “paper” based method for Systems Requirements Picture Source: Dr Peter Hoffman – IBM / Rational

  21. The classical “paper” based method for Systems Requirements Picture Source: Dr Peter Hoffman – IBM / Rational

  22. Requirements Requirements are explicit contracts between the system element that consumes a product feature and the system element that provides it. There are two major types of requirements. Product Requirements “the system shall” Statement of Work (SOW) Requirements “the contractor shall” Product Requirements specify something the product must door a quality the product must have. “The engine shall generate up to 20000 pounds of thrust during engine operation.” Focus on Product Requirements

  23. Product Requirements • Product Requirements further classified as: • Functional Requirements specify a task or activity the system must perform & its duty cycle. • Performance Requirements specify a constraint on how the system should perform a functional task. Performance Requirements linked to Functional Requirements

  24. Modeling Overview • Models are abstractions that allow us to focus on a solution to a particular problem. • Abstractions are essential to managing complexity. • Abstractions can be layered • accurately represent essential content • high fidelity and still remain simple. • The key to managing layers is to control the complexity of both the layer and its interfaces to other layers. • Push the details as low as possible but keep the essential meaning at all levels. Keep each layer simple & push the details down

  25. Models have different purposes • Functional Modeling • Logical relationships between activities and sequences in time • Parametric Modeling • Extends Functional Modeling to include equations or models of constraints on physical and functional elements. Data/Results may be collected by repeated computer runs in time-domain or thru a separate Monte Carlo analysis. • Dynamic Modeling • Focus is on mathematical representations of physical behavior of system or subsystem components. This may or may not be time domain. • Business / Economic Modeling • Focus is on cost and schedule Connect the network of models together

  26. Functional Modeling – Activity Diagrams / Tasks and Control Flow Activity Diagram Start, Stop, Operate Engine

  27. Functional Modeling • Requirements Modeling elucidate functional product requirements and their inter-relationships • It is designed to catch situations like the following • Page 257 states “The valve shall be on” when yyy. • Page 5205 states “The valve shall be off” when zzz • But the yyy and zzz conditions overlap, so the valve has to be both on and off at the same time. • State space of the system based on an analysis of the system requirements. ON or OFF but not both

  28. Modeling – Overview - Parametric Modeling Distiller - SYSML Parametric Model 28

  29. Modeling – Overview - Dynamic Modeling Rocket Engine – SIMULINK model 29

  30. Modeling – Form of model should match purpose • SYSML is ideal for functional modeling • UML is ideal for Software Architecture and Design • MATLAB / SIMULINK is ideal for Control System work. • NPSS is ideal for Aerodynamic simulations. • Mathmatica is ideal for symbolic calculations and mathematics. • Minitab is ideal for statistical calculations. • Microsoft Excel is also a modeling tool! Pick the model to match the problem

  31. What is SYSML? • SysML: • Reuses a subset of UML 2.0 • Uses UML 2.0 profile mechanisms to specify extensions for SysML • UML not required by SysML • UML reused by SysML SysML extensions to UML INCOSE slide – from tutorial by “The Aerospace Corporation” (Have no counterpart in UML or place UML constructs) 31 SysML tailored for Systems Engineering

  32. Example Drawings for a Functional Modeling using SYSML Use Case Diagram – captures system or subsystem scope Activity Diagram – captures tasks and control flow Internal Block Diagram – captures system structure and interfaces Sequence Diagram – captures details of interactions between system and external actors. State Diagram – details states and modes of system. To be shown in demo

  33. The Harmony Mini Cycle – as we use it Add parameters, attributes, and messaging Draw / Modify Use Case Diagram Generate/Modify Internal Block Diagram Annotate and finalize message sequences Draw High Level Activity Diagrams Create Ports, Interfaces, and Links Draw Detailed Activity Diagrams Draw State Charts Generate Sequences Animate and Execute To be shown in demo

  34. Family of use cases – highest level system description Use Case Diagram – Gas Turbine Engine – family of use cases What does the engine need to do?

  35. Lets zoom in so we can read the diagram Pick a particular use case – Operate Engine

  36. Engine Startup and Shutdown – Problem Overview To start a gas turbine engine: Turbine Rotation established by Air Starter Subsystem – driving generator for power and pressure for pumps Fuel flow is enabled. Proper Fuel / Air mix is established in combustion chamber. Electrical spark from Ignition - Subsystem starts combustion. Conditions monitored for automatic restart if necessary. Controlled ramp increases fuel flow per schedule to achieve stable idle Cockpit switch semantics rationalized with standard signals & start sequence

  37. Generic 2 Spool Gas Turbine Engine - Diagram Source: Wikipedia commons ITT PB N1 N2 EGT

  38. Use Case Diagram for “How to Start a Jet Engine” Hit a button and…

  39. Internal Block Diagram – formal system interfaces FADEC Control System Engineer draw connections

  40. Functional Modeling – Activity Diagrams / Tasks and Control Flow Level 1 Activity Diagram Start, Stop, Operate Engine

  41. Level 2 Activity Diagram – Start_Engine Draw flow chart

  42. Sequence Diagram – sequence and content of interactions Wizard reads flow chart and assists in developing sequence

  43. State Diagram – states, modes, detailed logic End-result is executable code* Formal Methods can be applied * Simulation or control logic

  44. Demo

  45. So… Where are the Requirements? Model firstfrom concept-of-operations information. the model becomes the requirements! The model then guides the writing of the requirements document. Key model elements – activities, dialogs, states, will trace to explicit requirements paragraphs.

  46. Next Step - Verification After creating an executable model, and writing requirements based on the model, the next step is to create formal test sequences One way to do this is to create another “actor”, and connect this actor to the external actors of the model. The test sequencer drives particular tests by setting states Animated sequence diagrams capture the results of the test Book keep your work, linking requirement to test

  47. Systems Engineering

  48. Requirements models start with pictures Parametric Structural Functional 48 SysML models are visual

  49. Details of “Control_Is_Active”

  50. Details of Engine Startup

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