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Evaluation and Design of Advanced Navy Topside Communication Systems Using EIGER - A DOD HPCMO Challenge Project

Dr. Charles W. Manry Jr., Dr. John R. Rockway, John Strauch, Darlene T. Wentworth

Space and Naval Warfare Systems Center San Diego San Diego, CA 92152-5001

30th Plasmadynamics and Lasers Conference

28 June - 1 July 1999 Norfolk, VA

For permission to copy or to republish, contact the American Institute of Aeronautics and Astronautics, 1801 Alexander Bell Drive, Suite 500, Reston, VA, 20191-4344.

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EVALUATION AND DESIGN OF ADVANCED NAVY TOPSIDE COMMUNICATION SYSTEMS USING EIGER - A DOD HPCMO CHALLENGE PROJECT

Dr. Charles W. Manry Jr., Dr. John R. Rockway, John Strauch, Darlene T. Wentworth Space and Naval Warfare Systems Center, San Diego San Diego, CA 92 152-500 I

ABSTRACT Each ship in the US Navy is part of a vast command, control, computer; and informational network. To meet this requirement more sophisticated communication systems are being added to the fleet. Integrated Topside Design (ITD) is one of the most important technology challenges for future Navy ship designs. This is due to dual mission requirements of increasing communication capability while reducing the overall signatures of a ship. Often these two goals are in conflict. Communication systems increase the radar signature of a ship. Low signature designs reduce the amount of real estate available for placement of antennas. Because of these conflicting design issues new and innovative techniques are being applied to this problem.

The ITD challenge is to ensure that new design concepts and products provide the best possible performance. In order to maximize performance accurate numerical modeling and simulation is required. By using modeling and simulation tools a thorough investigation of system performance can be obtained. This information can then used to make informed design decisions. State-of-the-art electromagnetic frequency-domain codes are used to perform these simulations. An example US Navy destroyer modeled using EIGER will be shown. Also the advantages of the HPCMO Challenge project will be covered.

INTRODUCTION Designing and optimizing a complex electromagnetic environment is slow, expensive, and error prone. To meet the challenge of 2 I It Century Integrated Topside Designs, advanced tools are required that isolate problems early in the design process. Eighty percent of the “affordability” decisions are made before a detailed design is available for a new platform. Thus the design tasks must be performed in a simulation based design environment. It is only through the application of concurrent engineering and its associated simulation based design environment that 21” Century Integrated Topside Designs can be implemented. A computational

This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

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based framework will reduce time to field new systems and ensure the application of improving technology.

The challenge to the integration of antennas in a topside design is that:

l All factors influencing an antenna system performance must be identified before an antenna site can be selected

. All factors influencing an antenna system performance cannot be determined before all antennas are located

Thus the design approach must support design synthesis through iterative analysis. Figure I describes the electromagnetic (EM) topside integration process required for antenna integration. The process is initiated with a proposed topside design and RF system design. These designs provide the description of the individual antenna systems. The electromagnetic environment (EME) analysis is used to provide the near fields for radiation hazard evaluation, the antenna impedance for RF circuit analysis, and the achieved isolation between topside systems. The electromagnetic compatibility (EMC) compares the achieved antenna isolation’of the EME analysis with the required antenna isolation generated by radio frequency (RF) circuit analysis for each transmit/receive antenna combination. The deficiency, if any, will indicate the additional isdlation required between systems for compatible operation. If deficiencies are found, mitigation techniques such as the addition of filtering, or the use of frequency, time, or power management will be suggested on the basis of the RF circuit analysis. It may also be necessary to modify the topside and/or the RF system design.

Once the system has been optimized within design constraints, an overall performance analysis is performed. An operational condition in which all transmitters are simultaneously in use is simulated. For communication systems each receiver’s resultant degraded articulation score or bit error rate can be compared to its interference-free performance. The EME analysis provides the antenna pattern for this performance analysis. Again, based on the results of this performance analysis, modifications to the proposed topside design and/or RF system design may

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be necessary. The EME analysis also provides the electromagnetic signature of the integrated topside design. A final evaluation can include the integrated performance of the topside design, including integrated combat system performance, integrated communication system performance, and estimates of overall signature.

The Electromagnetics and Advanced Technology Division of the Space and Naval Warfare Systems Center (SSC-SD) is developing an analysis framework that enables complexity to be treated concisely and efficiently. The design tool set provides a “total” integrated topside performance and EME analysis in a cost effective and timely manner. Advanced computational, visualization and optimization tools that exploit High Performance Computing are critical to these design tools.

EM ENVIRONMENT (EME) ANALYSIS Electromagnetic Environment (EME) analysis of a complex ship topside is essential to achieving a fully integrated design in a cost-effective manner. The Navy topsides of the future include composite materials. Thus ITD design and simulation tools must account for the presence of these materials. The analysis and evaluation algorithms to meet these needs that the SSC- SD EM topside integration process require are described in the following sections.

Several computational electromagnetics (CEM) codes have been developed to provide the electromagnetic environment (EME) analysis. In the microwave region the ship is many wavelengths in extent. Electromagnetic analysis tools have been developed to predict the performance of the systems in this frequency ray optic region. These codes include the Numerical Electromagnetic Code - Basic Scattering Code (NEC- BSC), the Reflector Antenna Code (NEC-REF), and the Periodic Moment Methods (NEC-PMM) Code. These codes will not be covered in this paper. In the resonant region the Electromagnetics Interactions GenERalized (EIGER) can be applied. This is where interactions are on the order of several wavelengths. In the HF range the ship is on the order of several wavelengths. Several of the antennas at higher frequencies are on the order of several wavelengths

The EIGER (Electromagnetic Interactions GenERalized) development is a multi-institutional collaboration that is bringing a variety of spectral domain analysis methods into a single integrated software tool set. Members from the SSC-SD, Lawrence Livermore National Laboratory, Sandia National Laboratory, and the University of Houston are collaborating to develop this package which has an unparalleled ability to take general purpose analysis

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methods and optimize the approach used for specific applications. New software engineering methods, specifically, object-oriented design, are being used to abstract the key components of spectral analysis methods so that the tools can be easily modified and extended to treat new classes of problems. This software design method yields a code suite that is more easily maintained than with standard designs.

The object-oriented design method enables the abstraction of the basic underlying components of computational electromagnetics to yield a suite of tools with unprecedented flexibility. The key components of the numerical analysis and their roles are elements (which are used to describe the geometry), expansion functions (which interpolate the unknowns, such as fields, locally), and operators (which are the underlying formulation of the physics used to propagate the energy or enforce fundamental principals). This is in contrast to a standard design procedure where entire codes are developed around a single element with a specialized basis function for a specific operator. Although such tools can be effectively used to model large classes of problems, it is often very difficult, if not intractable, to extend the tools beyond their initial design. Overcoming this limitation is one of the most compelling goals of the EIGER project. Indeed, the applicability of EIGER is significantly broadened as a variety of analytic treatments (e.g., Green’s functions) are cast into a form compatible with the numerical procedures in EIGER.

The principal EIGER features include:

. Unified representation of elements and basis functions independent of dimensionality and order (e.g., linear, quadratic, etc.),

. Higher order surface elements to more accurately resolve the geometry of curved objects,

. Compact operator notation that simplifies abstractions for both integral and partial differential equation formulations,

. Unified representations for Green’s functions and standard methods for resolving variety of boundary conditions,

. Object-oriented approach algorithms, encapsulated data, inheritance.

singular kernels, a

with abstracted and data objects

Because of its careful initial design, EIGER has, in a very short time, achieved a relatively mature status as a general electromagnetics-modeling tool. The essential High ‘Performance Computing implementation issues, which were addressed during the original software design, have been validated. The EIGER framework is

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now ready for acceleration in its application to advanced electromagnetic applications and as a test bed for new computational techniques.. New physics are continually being added. At this time EIGER includes:

. Generalized multi-layer geometry

. Periodic structures, including cavities

. Hybrid finite element/MoM treatments

. Thin material treatments

. Parallel High Performance Computing (HPC)

The EIGER workstation framework consists of four principal software components: EIGER-Build, EIGER- Solve, EIGER-Post and EIGER-Visual. This is shown in figure 2. The pre-processor, EIGER-Build, provides the means to fully define an EM model using output from a variety of commercial and in-house CAD/mesh generation packages. The computational engine, EIGER-Solve, computes the fundamental physical quantities such as currents and charges. The post- processor, EIGER-Post, calculates (using the EIGER- Solve engine) secondary quantities of interest such as antenna patterns, near fields, and impedances. EIGER- Visual provides scientific data visualization of these quantities.

The primary tasks for EIGER-Build are associating electromagnetic specifics with different parts of the model, associating numerical specifics with the underlying mesh, and providing diagnostics to the modeler. These are neither memory nor computationally intensive components of EIGER. The topological approach of partitioning a problem into pa@ regions, and domains has been validated, providing an object-oriented approach complementary to EIGER-Solve and EIGER-Post.

EIGER-Solve computes the fundamental quantities such as current or charge. The physics and numerics in EIGER include generalized multi-layer geometry, periodic structures, combined layered/periodic geometry, thin material treatments, and electrostatics/magnetostatics. EIGER-Post provides computation of secondary quantities such as impedances, near fields, and far fields. Both EIGER- Solve and EIGER-Post are objected-oriented electromagnetic analysis tools that are presently implemented in FORTRAN 90. The design of the code structure and the objects’ functionality and interactions were developed independently, and then the choice of the language was made. FORTRAN 90 is not a fully object-oriented language since it lacks direct polymorphism and inheritance. However, the actual implementation has been accomplished with relatively

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few limitations and enjoys the many benefits of FORTRAN 90 (i.e., efficient HPC compilers, array syntax, and a direct path to High Performance FORTRAN).

EXAMPLE SPRUANCE CLASS DESTROYER

As an example of some of the capabilities of EIGER a model of a Spruance class destroyer was created. This model is valid for the HF (3Mhz-30Mhz) band. All of the topside HF antennas were modeled. This includes the main fan antenna on the forward mast as well as five whip antennas. Using EIGER the currents were calculated for each of the five whip antennas. Each full set of the five HF whip antennas took approximately one wall-clock hour using I28 processors on the CEWES IBM-SP2 per frequency. A total of 21 frequencies, spaced every I MHz, from IOMHz to 30MHz were calculated. The case shown in figure 3 is when the starboard mid-ship dual whip antenna is excited at a frequency of IOMHz. This dual whip, and its port side twin, antenna has a length of I5 feet. These antennas operate in the frequency range calculated. In figure 3a the current magnitude is shown with both wire and surface currents. The currents are mapped to grayscale with the largest current value displayed in white and the smallest values displayed as black. Note in figure 3a that the largest current is on the antenna but currents on the other antennas and the masts are excited as well.

To see the interaction between the ship structure and other antennas it is often advantageous to use a logarithmic scale, which is shown in figure 3b. ‘In this figure the interactions can be more clearly seen. This is important because a large component of the antenna far field pattern is from currents excited on the ship structure. Note that the forward and aft guns are excited as well since their length is close to that of the excited antenna. A logarithmic scale also can show where strong interactions lead to EMC problems.

Once the currents are solved for, the antenna impedance and far field antenna patterns are calculated using EIGER-Post. In figure 4 the Smith chart impedance plot is shown with a Standing Wave Ratio (SWR) circle of 3 drawn. SPAWAR engineers use this plotting technique to design matching networks to minimize the amount of power reflected from the antenna back to the transmitter. In figure 5 a three-dimensional representation of the far field is shown for the excited starboard whip. In this figure the distance from the origin represents the strength of the antenna pattern. Also false color imaging is used to help in the interpretation of the pattern. For this antenna, the

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pattern is strongest to the starboard side of the ship. The port installed twin of this antenna has a similar pattern but its main coverage is to the port side. Together these two antennas provide the needed 360 degree coverage along the horizon for this communication system.

IMPACT OF DOD HPCMO CHALLENGE STATUS AND THE CEWES MSRC

For the fiscal year of 1999 the High Performance Modernization Office (HPCMO) as part of the Challenge initiative granted 202,000 CPU hours on an IBM-SP2. This machine is located at the US Army Corps of Engineers Waterways Experiment Station (CEWES) in Vicksburg, Mississippi. This is one of four Major Shared Resource Centers (MSRC) in the HPCMO. The IBM-SP2 at CEWES has 255 processing elements (PE) or CPUs. Other hardware at CEWES includes 540 PE CRAY T3E, I I2 PE SGI Origin 2000, another 126 PE IBM-SP2, a 16 PE Cray C90 (pk), and multiple mass storage devices.

Although any DOD user can obtain time at the four MSRC’s or at the five Distributed Centers (DC) the CPU time granted is somewhat limited. In order to support DOD users who have a recognizable need for large blocks of processing power the HPCMO created the Challenge projects instituted initially in FY 1997. These projects by definition are high-priority, computationally intensive and represent the highest priority DOD computational work. For these projects a minimum of 20% of the HPC resources are set aside. For FY1999 28 of these DOD Challenge Projects are currently supported. As more HPC are added and updated at the MSRC’s and DC’s the HMPCO is added to the number of Challenge projects that can be supported.

The ITD challenge meets the definition of a Challenge project. A US Navy ship is hundreds to thousands of wavelengths in size depending on the frequency band in question. The number of radiating systems (antennas, arrays, and radars) can number from 50 to over 100 systems. The large potential of cross interference and co-site problems creates the need for highly detailed models, which also add to the computational size of the ITD problem. As mentioned above, the destroyer example shown a single frequency requires one wall- clock hour using 128 processors on the CEWES IBM- SP2. Obtaining large hocks of CPU time to investigate problems of the interest to the Navy is paramount for solving the ITD challenge for the future. The need for HPC resources is clear.

Another benefit of having Challenge status is the full support of the ‘MSRC or DC you are working with.

This is because of the high profile nature of the Challenge projects have within HPCMO. In this project’s case the support from the CEWES staff has been exemplary. The EIGER team is currently working with the Scientific Visualization (SClVIS) staff at CEWES. The CEWES SCIVIS staff is not only interested in making grand presentations and videos but they want to understand the underlying physics of ITD and problems the Navy is facing. Our combined goal is to create visualization products and videos that will demonstrate the importance of the ITD challenge as well as the need for HPC and advanced visualization.

SUMMARY AND CONCLUSIONS

Concurrent engineering design, working within a simulation environment, is required to meet the integrated topside design challenge for current and future Navy designs. Design decisions must be made and thoroughly tested before construction is to achieve affordable and technologically superior communication systems. Accurate numerical modeling and simulation is required. Both state-of-the-art electromagnetic software codes and High Performance Computing resources are required to meet this need.

The computational electromagnetics code EIGER has an unparalleled ability to take general-purpose analysis methods and optimize the approach used for specific applications. This allows the best simulation method to be applied to each separate part of the design problem in an integrated fashion. By using object-oriented design the EIGER code suite is easily maintained and expandable and yields a suite of tools with unprecedented flexibility. As new modeling techniques are incorporated and integrated into EIGER the usefulness to designers today and in the future is guaranteed.

High Performance Computing resources are becoming more and more important to the success of topside design efforts. Without the HPCMO HPC current and future US Naval topside designs that take advantage of new technologies could not be completed. The HPCMO Challenge projects were created to address the Department of Defenses need for HPC resource to support these new designs.

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BIBLIOGRAPHY W. Johnson, R. Jorgenson, L. Warne, J. Kotulski, J. Grant, R. Sharpe, N. Champagne, D. Wilton, and D. Jackson, “Our Experiences with Object Oriented Design, FORTRAN 90, and Massively Parallel Computations,” 1998 IEEE AP-S/URSI Intl. Symposium, Atlanta, GA, June 1998.

R. Sharpe, J. Grant, N. Champagne, D. Wihon, D. Jackson, W. Johnson, R. Jorgenson, J. Rockway, and C. Manry, “Electromagnetic Interactions GeneRalized (EIGER): Algorithm Abstraction and HPC Implementation,” American Institute of Aeronautics and Astronautics (AIAA) Conference, Albuquerque, New Mexico, June 1998.

D. Wilton, D. Jackson, and N. Champagne, “Efficient Computation of Periodic and Nonperiodic Green’s Functions in Layered Media Using the MPIE,” Intl. Symposium Electromagnetic Theory, Thessaloniki, Greece, May 25-28, 1998.

D. Wilton, W. Johnson, R. Jorgenson, R. Sharpe, N. Champagne, and J. Grant, “EIGER: An object-oriented

approach to computational electromagnetics,” Intl. Conf. on Electromagnetics in Advanced Applications, Torino, Italy, Sept. 1997.

W. Brown, D. Wilton, “Higher Order Modeling of Surface Integral Equations,” IEEE AP-S/URSI Intl. Symposium, Montreal, July 1997.

R. Sharpe, J. Grant, N. Champagne, W. Johnson, R. Jorgenson, D. Wilton, W. Brown, and J. Rockway, “EJGER: Electromagnetic Interactions GEneRalized,” 1997 IEEE APS-International Symposium, Montreal, Canada, July 1997.

R. Graglia, D. Wilton, and A. Peterson, “Higher Order lnterpolatory Bases for Computational Electromagnetics,” IEEE Antennas and Propagation, vol. AP-45, March 1997.

D. Wilton, W. Johnson, R. Jorgenson, R. Sharpe, J. Rockway, “EIGER: A New Generation of Computational Electromagnetics Tools,” ElectroSft: Software for EE Analysis and Design, Miniato, Italy, 28-30 May 1996.

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Figure 1. EM Topside Integration Process.

Figure 2. EIGER Workstation Framework

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Figure 3. Currents on a Spruance Class Destroyer for (a) normal scale, and (b) logarithmic scale.

Figure 4. Mid Ship Starboard Whip Antenna Impedance.

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Fi we 5. Starboard Mid-Ship Antenna Pattern, both starboard view (top) and port \ riew (bottom).

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