AVAST Enhancements for Distributed Ray Tracing · AVAST Ray Tracing code found that the number of...

AVAST Enhancements for Distributed Ray Tracing

Michael Lichodzijewski, Dave Brennan and Dustin Pearson Lloyd's Register Applied Technology Group Prepared By: Lloyd's Register Applied Technology Group 1888 Brunswick Street, Suite 400 Halifax, Nova Scotia B3J 3J8 Contractor's Document Number: TR-16-50 Contract Project Manager: David Whitehouse, 902-425-5101 PWGSC Contract Number: W7707-145679/001/HAL Technical Authority: Layton Gilroy, 902-426-3100 Disclaimer: The scientific or technical validity of this Contract Report is entirely the responsibility of the Contractor and the contents do not necessarily have the approval or endorsement of the Department of National Defence of Canada.

Contract Report DRDC-RDDC-2016-C299 November 2016

© Her Majesty the Queen in Right of Canada, as represented by the Minister of National Defence, 2016

© Sa Majesté la Reine (en droit du Canada), telle que représentée par le ministre de la Défense nationale, 2016

Applied Technology Group tel. 902.425.5101

1888 Brunswick Street, Suite 400 fax. 902.421.1923 Halifax, Nova Scotia B3J 3J8 Canada email. [email protected]

www.lr.org/atg

WWorking together ffor a safer world

AVAST Enhancements for Distributed Ray Tracing

Technical Report # TR-16-50 Control Number: 14.28008.1142

November 2016

Prepared for:

Layton Gilroy DRDC Atlantic P.O. Box 1012 9 Grove Street

Dartmouth, Nova Scotia Canada B2Y 3Z7

Martec Limited is a member of the Lloyd’s Register Group, doing business as the Applied Technology Group

REVISION CONTROL

REVISION REVISION DATE 0 01 November 2016

PROPRIETARY NOTICE This report was prepared under Contract W7707-145679/001/HAL for Defence R&D Canada (DRDC) Atlantic. The information contained herein may be used and/or further developed by DRDC Atlantic for their purposes only. Complete use and disclosure limitations are contained in Contract W7707-145679/001/HAL, DRDC Atlantic.

EXECUTIVE SUMMARY The primary goal of the project was to make the ray tracing software capable of performing Target Echo Strength (TES) analyses involving a billion or more rays fired at a typical submarine model. In addition, the software was to be extended to provide the capability to perform monostatic TES out of the global axis plane and support was to be provided to the technical authority through the development of panelized and geometric AVAST models. To improve scalability, the software was modified and split into three components: the shell responsible for user interactions, the driver responsible for parallelization, and the ray tracer responsible for TES calculations. Changes to the user experience were minimized. The new software was tested using three different geometric models, a sphere, a cylinder, and a typical submarine model (BeTTSi). The tests demonstrated that the modified software produces the same results as the previous version, that it runs significantly faster, and that it can achieve scalability required to perform the analyses involving large numbers of rays.

TABLE OF CONTENTS 1.0 INTRODUCTION ......................................................................................................................................... 1 2.0 AVAST RAY TRACING PERFORMANCE IMPROVEMENTS ............................................................ 2

2.1 SUMMARY OF THE WORK PERFORMED ........................................................................................................ 2 2.2 THE SOFTWARE ARCHITECTURE .................................................................................................................. 3 2.3 THE ANALYSIS WORKFLOW ..................................................................................................................... 4 2.4 TESTING ....................................................................................................................................................... 4

2.4.1 Comparison of Results between Different Implementation ............................................................... 6 2.4.2 Comparison of Performance between Serial and Parallel Mode of Operation ................................. 6 2.4.3 Scalability Test Results ...................................................................................................................... 7

3.0 OUT-OF-PLANE MONOSTATIC TES ANALYSIS ................................................................................. 8 3.1 VERIFICATION OF OUT-OF-PLANE OPTION .................................................................................................... 8

4.0 MODELLING SUPPORT ............................................................................................................................ 9 4.1 PANELIZED MODELS .................................................................................................................................... 9 4.2 GEOMETRIC MODELS ................................................................................................................................. 12

5.0 ANALYSIS SUPPORT ................................................................................................................................ 15 6.0 CONCLUSIONS AND RECOMMENDATIONS ..................................................................................... 16 7.0 REFERENCES ............................................................................................................................................ 17 APPENDIX A: ISSUES IDENTIFIED BUT NOT ADDRESSED DURING THE PROJECT APPENDIX B: FILE FORMAT USED BY THE DRIVER AND RAY TRACING APPLICATIONS

LIST OF FIGURES FIGURE 2-1: THE BETTSI SUBMARINE MODEL. ........................................................................................................ 5 FIGURE 4-1: USER INTERFACE SUPPORT FOR OUT-OF-PLANE MONOSTATIC TES ANALYSIS. .................................. 8 FIGURE 4-2: MODEL USED TO VERIFY OF OUT-OF-PLANE MONOSTATIC TES ANALYSIS. ........................................ 9 FIGURE 4-3: VERIFICATION OF OUT-OF-PLANE MONOSTATIC TES ANALYSIS. ........................................................ 9 FIGURE 2-1: SIMPLE BENCHMARKING MODELS (REPRODUCED FROM (2)). ................................................................ 10 FIGURE 2-2: BENCHMARK MODEL 3-2 (REPRODUCED FROM (2)). ............................................................................. 11 FIGURE 2-3: COMPLEX BENCHMARK BETSSI SUBMARINE MODEL (REPRODUCED FROM (2)). .................................. 11 FIGURE 2-4: BETSSI SUBMARINE WITH INTERNAL STRUCTURE RBC TS. ................................................................. 13 FIGURE 2-5: BETSSI BOW IGES MODEL SHOWING VISUALIZED ENTITY (LEFT) AND ANALYZED ENTITY (RIGHT). .... 14 FIGURE 2-6: BETSSI SUBMARINE TS WITH MODIFIED BOW LONGITUDINAL BULKHEAD. .......................................... 14 FIGURE 3-1: AVAST CALCULATED TS USING KIRCHHOFF AND BIEM ANALYSIS METHODS ................................... 15

LIST OF TABLES TABLE 2-1: COMPARISON OF TES RESULTS. ............................................................................................................. 6 TABLE 2-2: COMPARISON OF EXECUTION TIMES WITH 1 LOGICAL PROCESSOR. ...................................................... 6 TABLE 2-3: COMPARISON OF EXECUTION TIMES WITH 8 LOGICAL PROCESSORS. ..................................................... 7 TABLE 2-1: CASING AND PRESSURE HULL TRANSMISSION AND REFLECTION COEFFICIENTS. .................................... 12

AVAST Enhancements for Distributed Ray Tracing 1

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1.0 INTRODUCTION

A recent investigation focused on the Target Echo Strength (TES) of cylinders analyzed using AVAST Ray Tracing code found that the number of rays required to achieve convergence for models having dimensions similar to the Victoria class submarine, and for ranges in excess of 1 km, would likely be between 500 million and 1 billion. The upper limit for the number of rays that could be processed by the software before completion of this project was reported to be about 2 million. The primary goal of the project was to modify the software to overcome this limit (SOW Task 2). The scope of work also included the addition of the capability to perform monostatic TES out of the global axis plane (SOW Task 1) and support to the technical authority through the development of panelized and geometric AVAST models (SOW Task 3). In addition to these tasks, an investigation was done in order to determine the feasibility of porting the ray-tracing code from the Microsoft Windows platform to Linux and into the applicability of Graphical Processing Unit (GPU) acceleration. In support of the BeTSSi IIb benchmark study (2), Lloyd’s Register Applied Technology Group (ATG) was contracted to provide modelling and analysis support. The benchmark study required each participating member to complete a set of monostatic and bistatic acoustic scattering analyses for each target. Defence Research and Development Canada (DRDC) Atlantic and ATG collaboratively contributed to the benchmarking conference by dividing the analysis tasks. Some examples of the modelling and analysis efforts completed by ATG are provided in the following sections. The following sections summarize the work that was performed.


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2.0 AVAST RAY TRACING PERFORMANCE IMPROVEMENTS

The primary goal of the project was to make the ray tracing software capable of performing TES analyses involving a billion or more rays fired at a typical submarine model. This section summarizes the work that was performed. It describes the resulting software architecture, outlines the analysis workflow, and presents results that prove its correctness and demonstrate improvements in its capabilities and performance.

2.1 SUMMARY OF THE WORK PERFORMED

The previous version of the AVAST ray tracing software was limited to about 2 million rays. In order to overcome this limit the software was modified. The modification was done in two stages. In the first stage, the existing AVAST ray tracing software was modified in the following ways:

- it was changed to be controlled via the command line; - a capability was added to automatically partition ray tracing problems into several

smaller problems; - a capability was added to launch multiple instances of the AVAST ray tracing software

with each instance assigned one of these smaller problems and to monitor these instances’ execution;

- a feature was added to collect, aggregate and present the results of the analysis once all instances of the ray tracing software completed.

These changes were implemented for both the bi-static and mono-static analyses. Test results indicated that the modified software could perform ray tracing noticeably faster, and that there was no overall reduction in overall system memory usage. However, due to limitations of the existing file format, it was generally difficult to ensure a problem definition that would be partitioned with exactly the same ray distribution and hence lead to the same results as the original unpartitioned problems. In the second stage of development, the existing AVAST ray tracing software was modified much more substantially. Prior to committing to the second round of modifications to the software, an investigation was made into the feasibility of eventually porting the software from the Microsoft Windows platform to the client’s High Performance Computing (HPC) platform. The biggest perceived risk to achieving this goal was the ability to build SMLib, which is used as the software’s geometric kernel, providing features for reading IGES data files, representing NURBS geometry, and performing geometric operations. To mitigate this risk, a virtual machine replicating the target platform (CentOS 6.7) was configured. After some modifications, SMLib 8.9.0 was eventually built, indicating that a future port is possible.


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2.2 THE SOFTWARE ARCHITECTURE

In the second round of modifications, the AVAST software was split into three components: the shell, the driver, and the ray tracing implementation. The shell is essentially the previous AVAST ray tracing software, and its purpose is to facilitate problem definition, analysis initiation, and results presentation. The shell exposes two new features. The first feature gives the user an option to choose between serial and parallel modes of operation. The serial mode uses what is effectively the previous ray tracing implementation; the only difference being a change to the ray generation algorithm, which now ensures that rays are distributed symmetrically about the centre of the projector eliminating the previous bias to generate rays towards to top left corner. The parallel mode makes use of the modified version of the ray tracing software via the driver. The second new feature simply reports on the duration of an analysis and has been used to gauge differences in solution speeds between the two modes of operation. The driver is a standalone command line application responsible for dividing a ray tracing problem into several smaller ray tracing problems, executing the smaller problems using multiple instances of the modified ray tracing implementation, and for collecting and aggregating the results after the instances have finished. For bi-static analysis the driver gives the user the option to choose the number of concurrent ray tracing processes to be executed. This number can be between 1 and the number of logical processors supported by the user’s computer. This option is currently not available for monostatic analyses, for which the maximum number of logical processors is used by default. The ray tracing implementation is a standalone command line application responsible for performing the actual TES calculations. It differs from the previous implementation in several respects. It does not rely on Microsoft Windows-only functionality, making it essentially platform independent. It uses a ray generation algorithm that ensures symmetry about the origin of the projector. It is configured to normally discard ray data once it is no longer required for TES calculations, although such data can be kept to help in troubleshooting and/or problem/analysis visualization. Functionality has been consolidated and simplified to improve performance, extensibility, and maintainability. Lastly, code abstraction has been used to reduce direct reliance on the SMLib geometric kernel. All software components, including SMLib 8.4.0 are written in C++ and the deliverable applications were built with Visual Studio 2015. Currently, the shell and the driver are Windows platform dependant, although the driver has been designed so as to make the replacement of operating system specific code relatively easy.


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2.3 THE ANALYSIS WORKFLOW

In the updated system, the basic workflows for bi-static and monostatic analyses are virtually the same as in the previous version. After having launched the AVAST Ray Tracing application (BEToolkit.exe), the first step is problem definition. The user specifies a problem definition (.ART) file to be read and after it has been read, uses the UI to modify the definition as need. The second step is the initiation of the specific analysis type. Bi-static analyses are initiated by pressing the ‘Bistatic (Fast)’ button. Monostatic analyses are initiated by pressing the ‘Monostatic’ button. At this point the user can select the mode of operation. If the user choses to run an analysis using the serial mode, the software effectively operates as it had in the previous version. If the user chooses to run an analysis using the parallel mode, the shell collects relevant input data and uses it to produce an input file for the driver. It then launches the driver (RayTracerDriverApp.exe) and passes it the path of the input file via command line. The driver reads the data file and determines the level of concurrency that is to be used. The default is to use the maximum number of logical processors. For bi-static analyses, this value can be modified by the user. For monostatic analyses this is not an option and the default value is used. Once the level of concurrency has been determined, the driver divides the original problem into smaller sub-problems. Each sub-problem is assigned roughly the same number of rays (+/- one ray). For each of these sub-problems, the driver generates a separate input file. The format for these input files is the same as the format of the input file that is used by the driver. The driver then launches an instance of the ray tracer application (RayTracerApp.exe) for each of the files, the name of the specific file having been passed via the command line. The ray tracer instances run concurrently and the driver waits until they all finish. Each of the ray tracer runs produces an output file that contains TES results for that run. The driver collects the data from these output files and aggregates it into a single result corresponding to the original problem, which then is written to another file. After this, the driver terminates. The shell, which had been waiting for the driver to terminate, then reads the output file and presents the results to the user just as if the software was run serially. For a bi-static analysis, the above steps are done once. For monostatic analysis, the shell repeats these steps for each projector/receiver position that it generates.

2.4 TESTING

The ray tracing algorithm has not changed significantly between the previous and current versions of the software. As such, the goal of testing was not to demonstrate the validity ray tracing as a method for TES analysis, but rather to demonstrate that the current version of the


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software produced the same or very similar results to the previous version, to demonstrate speed improvements, and to demonstrate scalability of the implementation to the point of being able to handle 1 billion rays fired at a typical submarine model. As shown below, the similarity of results, speed improvements, and scalability of the implementation have all been demonstrated. Some small differences in the results reported by the previous version of the software and the new serial version of the software were observed. These can be fully explained by the change in the algorithm used for generating the rays on the projector, which now ensures that the rays are symmetric about the projector’s origin and are not biased towards to projector’s top left corner as was the case previously. Some small differences between the new serial version and the new parallel version were also observed. These can be explained by code changes that consolidated some operations and re-implemented others to improve performance and maintainability. As can be seen in the test results, the differences between the two implementations are negligible.

Figure 2-1: The BeTTSi submarine model.


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2.4.1 Comparison of Results between Different Implementation

The cylinder model was used to demonstrate the correlation between the analytical results and the three different versions of the ray tracing implementation: the previous, modified (serial), and new (parallel) versions. For the tests, the projector and the receiver were centred about the y-axis, parallel to the zx plane, and set to be 0.1m wide and 1.0m high. Ray spacing was set to 0.01m producing 1000 rays. The acoustic centre was set to be at the global origin. The TES analysis was performed at 10m, 20m, 40m and 80m from the acoustic centre along the positive y-axis. The results are tabulated below.

Table 2-1: Comparison of TES results.

R (m)

TES Analytical

(dB)

TES Previous

(dB)

TES Modified

(dB)

TES New (dB)

% Error Previous

% Error Modified

% Error New

10 11.76 12.26 12.55 12.55 4.244 6.709 6.709 20 14.77 15.52 15.05 15.05 5.069 1.887 1.887 40 17.78 16.77 18.06 18.06 -5.689 1.566 1.566 80 20.79 18.02 21.07 21.07 -13.331 1.338 1.338

As can be seen in the table above, the results for all three implementations are relatively close to the expected value, with the correlation of the results produced using the implementations with the modified ray distribution (modified/serial and new/parallel) improving with distance from the acoustic centre. It can also be seen that the results for the serial and parallel implementation are the same. These results indicate that the ray tracing algorithm was not broken as a result of the modifications made.

2.4.2 Comparison of Performance between Serial and Parallel Mode of Operation

The sphere model was used to demonstrate relative differences in execution speed between the previous and modified implementations of the software. For the tests, the acoustic centre was placed at the global origin. The projector and the receiver were placed 40m from the acoustic centre along y-axis, centred about the y-axis, parallel to the zx plane, and set to be 1.0m wide and 1.0m high. Ray spacing was set to 0.1m, producing 100 rays, then to 0.01m, producing 10K rays, and finally at 0.001m producing 1 million rays. The modified software was first run using a single logical processor to demonstrate speed improvements resulting from the modifications. Then it was run using 8 logical processors to demonstrate speed improvements resulting from parallelization. The results are presented in the following two tables.

Table 2-2: Comparison of Execution Times with 1 Logical Processor.


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Spacing (m) Rays Time Modified (s) Time New (s) Acceleration Factor 0.1 100 1 3 0.3

0.01 10,000 40 8 5.0 0.001 1,000,000 3959 48 82.5

Table 2-3: Comparison of Execution Times with 8 Logical Processors.

Spacing (m) Rays Time Modified (s) Time New (s) Acceleration Factor 0.1 100 1 2 0.5

0.01 10,000 40 2 20.0 0.001 1,000,000 3959 13 304.5

As can be seen in the tables above, the serial version of the software runs faster than the parallel version for small problems. This can be explained by the extra overhead required for additional management of data in the parallel version. For larger numbers of rays the parallel version shows significant improvement, particularly when using the maximum number of logical processors.

2.4.3 Scalability Test Results

The BeTTSi submarine model was used to demonstrate the scalability of the new implementation. For the test, the acoustic centre was placed at the global origin. The projector and the receiver were placed 2000m from the acoustic centre along the y-axis, centred about the y-axis, parallel to the zx plane, and set to be 49.0m wide and 10.0m high. Ray spacing was set to 0.0007m, producing 999,950,000 rays. The test was run on a 64-bit Windows 7 machine with 12 Gb of RAM and 8 logical processors (Intel Xeon CPU E5-1620 0 @ 3.60 GHz). The test took 2 days, 21 hours, 42 minutes, and 58 seconds. The TES was calculated to be 38.65 dB.


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3.0 OUT-OF-PLANE MONOSTATIC TES ANALYSIS

Recent analysis tasks have required the monostatic target echo strength (TES) be calculated out of the global axis plane. In order to support this requirement, modifications have been made to the AVAST ray-tracing software and a new out-of-plane monostatic wizard has been added to the AVAST user interface. A screen shot of the out-of-plane monostatic wizard is provided below in Figure 3-1. The algorithm used to define the out-of-plane monostatic locations is based on the approach developed to define a ring of field points positioned in an arbitrary plane. In both cases the user is asked to define the following:

1. The starting, or initial, location of the projector; 2. The center of the arc used to position the projectors; 3. The global x-y-z direction cosines defining the plane used to position the projectors; 4. The number of projectors (points) to be generated; 5. The sweep angle.

Figure 3-1: User Interface Support for Out-of-Plane Monostatic TES Analysis.

3.1 VERIFICATION OF OUT-OF-PLANE OPTION

A “Cats Eye”, or corner reflector model (see Figure 3-2) was used to verify the TES estimates generated using the new out-of-plane modeling feature. Although the ray-tracing results provided below in Figure 3-3 are higher than those generated using other methods (i.e.:Kirchhoff techniques), they are consistent with the fundamental properties of a geometrically based method like ray-tracing, i.e.: unlike Kirchhoff methods, 100% of rays hitting a corner reflector will return to the receiver, leading to higher TES estimates.


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Figure 3-2: Model used to Verify of Out-of-Plane Monostatic TES Analysis.

Figure 3-3: Verification of Out-of-Plane Monostatic TES Analysis.

4.0 MODELLING SUPPORT

4.1 PANELIZED MODELS

The simple and complex targets shown in Figure 4-1 through Figure 4-3, respectively, were panelized for Kirchhoff and boundary element analysis methods (where possible). The


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panelized models suited for the Kirchhoff analysis method were set to 12.5 mm; corresponding to four elements per wavelength of a 30 kHz source frequency. Problems with hard walled boundary conditions (HWBC) were analysed using the boundary element method with models panelized with four elements per wavelength. A large portion of the benchmarking tasks calculated the scattering target strength (TS) of the models using realistic boundary conditions for water-backed (casing) or air-backed (pressure hull) steel plating. The transmission and reflection coefficients were calculated using a simplified Brekhovskikh (1) method and applied to the panelized models using the AVAST (3)user interface.

Figure 4-1: Simple benchmarking models (reproduced from (2)).


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Figure 4-2: Benchmark model 3-2 (reproduced from (2)).

Figure 4-3: Complex benchmark BeTSSi submarine model (reproduced from (2)).


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Table 4-1: Casing and pressure hull transmission and reflection coefficients.

Transmission Coefficient Frequency

(kHz) 1 3 10 30

Steel Thickness (mm) (water-

backed Re Im Re Im Re Im Re Im

20 0.9035 0.2949 0.5098 0.4989 0.0851 0.2755 0.9903 0.0098 10 0.974 0.1589 0.8063 0.3947 0.2722 0.4433 0.0393 0.1891 8 0.9832 0.1284 0.8667 0.3394 0.369 0.4811 0.0605 0.2341

Reflection Coefficient Frequency

(kHz) 1 3 10 30

Steel Thickness (mm) (water-

backed Re Im Re Im Re Im Re Im

20 0.0965 -0.2949 0.49016 -0.4989 0.915 -0.2755 0.9903 -0.0867 10 0.0257 -0.1589 0.1937 -0.3947 0.7278 -0.4433 0.9607 -0.1891 8 0.0168 -0.1284 0.1333 -0.3394 0.631 -0.4811 0.9395 -0.2341

4.2 GEOMETRIC MODELS

Efforts to improve the performance of geometric models were required during this task. The calculated TS of the BeTSSi submarine with internal structure is shown in Figure 4-4; using AVAST’s ray-tracing methodology (BT-RBC-AVAST 30kHz), Australia’s Department of Science and Technology Group (4) (DSTO) second order Kirchhoff methodology (BT-RBC-DSTO-30khz-20000m) and Beuth University of Applied Sciences (5) (BHT) (BT-RBC-BHT-30kHz) BEAM methodology (ray-tracing coupled with Kirchhoff method). The TS calculated by AVAST is in good agreement with the BHT TS from broadside (90o) to stern (180o). Some disagreement between the AVAST, DSTO and BHT results are observed in the forward region of the model from the bow (0o) to broadside (90o). Geometric modelling support in this task was focused on correcting the BeTSSi submarine geometric model and improving the agreement between the AVAST, DSTO and BHT TS results in the forward region of the model. The longitudinal bulkhead in the bow structure of the BeTSSi submarine shown in Figure 4-5 was causing the high TS in forward region of the vessel. The AVAST interface provides the analyst with the ability to view the geometric entity during the analysis. What is observed in the interface is not always what is analysed by the software. The original longitudinal bulkhead was modelled in such a way that it was showing the user the left image of Figure 4-5 and analysing the right image resulting in an over-prediction of the scattered TS. By adjusting the longitudinal bulkhead of the BeTSSi IGES entity, the calculated TS in the bow region of


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the vessel is reduced and in better agreement with DSTO and BHT. The TS of the modified BeTSSi model is shown in Figure 4-6 from bow (0o) to broadside (90o). Some peaks are observed in the TS at several positions indicating that a more refined ray density (< 0.1 m) is required.

Figure 4-4: BeTSSi submarine with internal structure RBC TS.


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Figure 4-5: BeTSSi bow IGES model showing visualized entity (left) and analyzed entity (right).

Figure 4-6: BeTSSi submarine TS with modified bow longitudinal bulkhead.


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5.0 ANALYSIS SUPPORT

A full set of Kirchhoff and BIEM TS analysis results were delivered to the technical authority prior to the BeTSSi IIb benchmarking study. An example of the TS calculated using the Kirchoff and boundary integral element methods (BIEM) are shown in Figure 5-1 for Model 2. Good agreement is observed between the Kirchhoff and BIEM methods in regions not affected by the multiple scattering bow section (270o to 350o) and stern bulkheads (90o to 160o and 190o to 265o). In the multiple scattering regions, the single reflective Kirchhoff method is unable to capture the multi-reflective behaviour of the acoustic wave. The BIEM is well suited to compute the effect of multi-reflective scattering; which is observed in Figure 5-1 by the positive TS in the bulkhead (90o to 160o and 190o to 265o) and bow (270o to 350o) multi-reflective regions.

Figure 5-1: AVAST calculated TS using Kirchhoff and BIEM analysis methods


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6.0 CONCLUSIONS AND RECOMMENDATIONS

Testing of the ray tracing software has shown that the modified version has achieved all of the explicit and implicit goals of the project: it produces results that are virtually identical to the results produced by the previous version; for large numbers of rays, it runs significantly faster than the previous version; it can solve problems involving significantly more rays than the previous version; and it has been coded in a way that should allow it to be ported to a non-Windows operating system such as Linux with relative ease. Recommended for future work are bug fixing, specifically in the shell, general code cleanup, cleanup of the data file formats, improvements to configurability, particularly for the purpose of troubleshooting, improvements to process management, study of benefits and drawbacks of using tessellated models in place of NURBS models, migration to Linux, and investigation of potential for and benefits and drawbacks of GPU acceleration. ATG provided modelling and analysis support of the BeTSSi IIb benchmarking study in a collaborative effort with DRDC Atlantic. The modelling tasks involved panelizing the simple and complex submarine structures as well as improving geometric IGES entities suitable for ray-tracing analysis. ATG contributed to the benchmarking study by providing target monostatic and bistatic results using the Kirchhoff and BIEM analysis methods.


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7.0 REFERENCES

(1) Brekhovskikh, L. 1960. Waves in Layered Media. Academic Press. New York.

(2) Ehrlich, Fillinger, Gilroy, Nijhof and Schafer. 2016. BeTSSi II B Benchmark Target Strength Simulation. Den Hague, Netherlands.

(3) Lloyd’s Register Applied Technology Group. 2015. AVAST. Halifax, N.S.

(4) MacGillivray, I. and A. Cave. 2014. BeTSSi II – The 2nd Benchmark Target Strength

Simulation Submarine Workshop. Defence Science and Technology Organization. Australia.

(5) Schafer, I., R. Burgschweiger, B. Nolte and M. Ochmann. 2014. Available methods for the determination of acoustic backscattering of underwater objects. Beuth University of Applied Sciences Berlin. Berlin.

APPENDIX A

ISSUES IDENTIFIED BUT NOT ADDRESSED DURING THE PROJECT

Several pre-existing, but out of scope, issues that impact the usability of the software have been identified. These issues are:

1) Under some conditions, data entered by the user either does not get set or resets within the UI

2) There exists a bug the calculation of receiver density for monostatic analyses, where the number of rays hitting the receiver rather than their intensity is used in the calculation

3) The .ART file format does not support persistence of the receiver dimensions

APPENDIX B

FILE FORMAT USED BY THE DRIVER AND RAY TRACING APPLICATIONS

# Version (v) v # Settings max hits, min intensity, attenuation (h, i, a) h i a # Acoustic centre coordinate (x, y, z) x y z # Projector centre coordinate (x, y, z) x y z # Projector up vector reference (x, y, z) x y z # Projector width and height (w, h) w h # Projector ray density (d) d # Indices of first and last ray projected (f, l) - if f and l are -1 then use all of the width and height f l # Receiver centre coordinate (x, y, z) x y z # Receiver up vector reference (x, y, z) x y z # Receiver width and height (w, h) w h #Body type t # IGES file path (p) p # Number of surfaces (n) n # Surface 1 state (active/inactive) reflectivity, transmissivity, dispersion angle, ray count (s, r, t, a, c) s r t a c ... # Surface n state (active/inactive) reflectivity, transmissivity, dispersion angle, ray count (s, r, t, a, c) s r t a c

# Version 1.0 1 0.0 0.0 0.0 0.0 0.0 0.0 10 0.0 0.0 0.0 1.0 1 1 0.5 -1 -1 0.0 10 0.0 0.0 0.0 1.0 1 1 iges C:\Dev\DRDC-A\AVAST Enhancements\Data\sphere.igs 1 1 15.0 1 0.0 1

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