Application of Modeling and Simulation Methodologies to Enhance
Non-Combatant Naval Survivability
Margaret G. Nate (SNAME: AM)
Alion Science and Technology
[email protected]
David B. Goodfriend (SNAME: SM)
Virginia Tech
[email protected]
As the role of modern naval non-combatants evolves to include multi-mission ships increasing their exposure to
asymmetric threats and as damage can also occur accidentally outside of an intentional weapon impact, the
assessment of survivability of non-combatant ships becomes necessary to ensure fleet-wide mission capability. A
survivability enhancement case study was performed by modifying and applying traditional combatant survivability
methodology to the 145m non-combatant naval training and hospital vessel shown above. Thousands of tests were
conducted with each test randomly varying threat parameters and hit locations in order to capture the chaotic nature
of random unknowns, thus providing a probabilistically determined assessment of occurrences similar to real world
threat events. Structural, Mobility, Damage Control, and Self Defense mission areas with limited inherent
survivability are identified and expert recommendations proposed based on analysis of initial damage in addition to
“through time” performance results and from expert design review. In cases where design recommendations are not
feasible or difficult to implement, then the recommendations made focus in improving operational survivability
through crew actions and training.
KEY WORDS: Survivability, Susceptibility, Vulnerability,
Recoverability, Non-combatant, AIREX, Crew Egress
INTRODUCTION
Throughout the history of naval warfare a consistent pattern has
evolved between the development of anti-ship threats and the
development of shipboard protective measures against those
threats. Since the 1980’s, the combination of ship-board
Nate
protective measures has been colloquially referred to as
‘survivability’ and is defined more accurately as the measure of
a vessel’s ability to complete its mission after an attack. The
measure of survivability considers one or more of the following
aspects: susceptibility (ability to avoid being hit), vulnerability
(level of damage when hit) and recoverability (ability to recover
from a given level of damage). (OPNAVIST 9071.1A 2012)
Consideration of all three aspects (susceptibility, vulnerability
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
1
and recoverability) independently by separate analyses is
referred to as ‘Total Survivability’ and the consideration of all
three aspects within a single assessment of the vessel is referred
to as ‘Total Integrated Ship Survivability’.
While historically the enhancement of ship survivability has
been primarily associated with naval combatants; as the role of
modern naval non-combatants evolves to include additional
missions as with the LCS, and as the possibility of asymmetric
threats places these ships at increased risk, the assessment of
survivability of non-combatant ships becomes necessary to
ensure fleet-wide mission capability.
The authors have performed a survivability enhancement case
study by modifying and applying traditional combatant
survivability methodology to a 145m non-combatant naval
training and hospital vessel. Within this paper, the authors will
identify areas with limited inherent survivability and propose
design recommendations based on the case study with a focus
on separation and redundancy of vital equipment, passive and
active fire protection, and crew egress/evacuation capability.
PRINCIPLES OF SURVIVABILITY
Survivability is the capacity of a total ship system to avoid and
withstand damage while maintaining mission integrity over
time. Total ship survivability metrics are separated into a
combination of several factors focusing on Susceptibility (avoid
damage), Vulnerability (withstand damage), and Recoverability
(control damage). Depending on the size and mission of a ship,
all three survivability branches or specific combinations may be
assessed to examine inherent survivability performance. For
example, it is important for submarine survivability to focus
most on susceptibility as avoiding detection is a submarine’s
first line of defense especially during covert and reconnaissance
missions. Although inherent susceptibility protection typically
increases as the size of the vessel decreases due to naturally
smaller signatures, inherent vulnerability and recoverability
protection decreases due to reduction in space available for
separation and redundancy. However, with the introduction of
multi-mission ships, modern surface warfare vessels should
focus on an optimized combination of all three survivability
elements in order to ensure the success of each individual
mission.
Susceptibility
The first layer of a ship’s defense system is susceptibility or a
ship’s ability to avoid detection by an enemy, usually defined by
management of visual, infrared, acoustic, radar cross section,
magnetic, and other detectable signature systems.
The
susceptibility portion of a survivability analysis considers the
structural design of the ship and technology incorporated to
reduce these signatures. Assessment of any signature involves
evaluating the strength of the signal at the receiver of interest,
and comparing that signal strength to the background "noise" in
the expected operating environment.
Signature analysis
indicates how easily a given threat can detect, track, target, and
home in on the ship system. By assessing the system signatures,
Nate
the probabilities of these early events (detect, track and target)
in the "kill chain" can be calculated for a given threat. (Sajdak
2014) Lower signatures decrease the probability of all of these
events, thereby decreasing susceptibility. Beyond evaluation of
the capability for the threat to detect, track, and target the ship
system, the impact of factors such as countermeasures,
environmental conditions, tactics, and threat system
performance must also be assessed. Countermeasures including
threat suppression, maneuvering tactics, radar decoys, and
strategic topside antenna arrangement are commonplace
techniques to decrease the susceptibility of a vessel.
Susceptibility analyses are conducted using software which
considers design parameters of the ship such as shape and
emissions to determine the ships ability to avoid detection. A
susceptibility review is primarily conducted during the detail
design phase of a project as structural elements are finalized
during this stage while topside and equipment arrangements
remain flexible.
As an example of a generic susceptibility analysis, a radar
signature is input for the ship system, and a hit probability curve
is generated. The resultant probability curve determines the
probability the threat has of detecting, tracking, and targeting
the ship system for that given signature. This probability data is
unique for each threat, and is usually determined through a
combination of experimental and empirical methods. Similar
probability curves exist for all events in the kill chain.
Combining these probabilistic calculations with simulated
elements, e.g. threat and ship system motions, and running the
mission scenario multiple times varying the inputs by randomly
selecting each input based on its probabilistic distribution, gives
a number of times the ship system was unable to avoid or defeat
the threat attack out of a total number of simulations at any
simulation analysis time. For example if the susceptibility is
measured as 253 hits to the ship system in a total of 1000
analyses, the probability that the ship system was unable to
avoid or defeat the threat attack is 25.3%.
Vulnerability
The second layer of defense is measured as vulnerability, or a
ship’s probability of mission capability loss given a hit. More
specifically, vulnerability measures the ship’s inherent
capability to withstand damage.
Examining the varying
methods by which damage may be imparted on the ship system
and subsequently quantifying the type and amount of the
ensuing system damage yields the determination of a ship
system’s vulnerability. Methods by which damage may be
inflicted on a ship system include shock and overpressure
caused by internally or externally detonating explosions in air
(Airex) or external underwater explosions (Undex), ballistic
projectile and fragmentation damage, and shape charge jetting.
Additionally, damage may be progressive such as with fire
spread or flooding.
Vulnerability can be managed in several ways including
separation and redundancy of equipment, ballistic armoring of
critical spaces, shock hardening of components, etc.
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
2
Redundancy involves the duplication of critical components in
order to avoid loss of primary and secondary systems following
an event. However, implementing duplicates of equipment is
only useful if the equipment is properly separated. By utilizing
both separation and redundancy simultaneously, the vessel is
less likely to lose critical systems that support primary mission
capability. For example, if an event occurs causing loss of
starboard power cabling then port cabling should remain intact
and no electrical functionality would be lost due to separation
and redundancy. Hardening and armoring is used to mitigate
damage from blast, fragmentation, direct projectile impact, fire,
and/or shock. However, the type of protection implemented
must be carefully considered as the parameters necessary for
prevention of damage can be counterintuitive. For example, the
mitigation of shock damage requires increased ductility of
surfaces while mitigation of fragmentation requires a harder,
less penetrable material.
Vulnerability is typically investigated at both basic or detail
design stages. As more detailed equipment, structure, and
system diagrams are available, more detailed vulnerability
analysis can be conducted. In recent years there has been a shift
to operationally oriented vulnerability requirements where the
vulnerability of the system is measured by its lack of ability to
perform a specified capability, such as a mission or operation,
based on the residual strength or functionality of the system as
damage is applied. By employing system deactivation diagrams,
the ship system vulnerability is measured and assessed by
following the progression of failures through the deactivation
diagram to determine the most vulnerable areas of the system
architecture.
Recoverability
Following the preventative susceptibility and vulnerability
measures, recoverability is a ship’s ability to control damage
and remain functional after an event occurs. A system may
regain capability by reconfiguration, repair, or replacement of
components or subsystems. Reconfiguration is a means to
reactivate a failed sub-system by modifying the existing subsystem architecture to work through an alternate path. For
example, a fractured fuel line has required that the engine shut
down resulting in the failure of the ship system to achieve
required speed. Reconfiguring the engine’s fuel system to allow
it to draw fuel from a path not containing the fractured line will
allow the vessel to regain the required speed capability. System
reactivation may also be accomplished via the repair or
replacement of a failed vital component such as the fractured
fuel line.
Mitigation of progressive damage is imperative to maintain all
onboard ship functionality, the most universal of which is active
fire containment, fire suppression, and firefighting. Fire
containment systems include securing ventilation fans, shutting
ventilation dampers, shutting doors/hatches, installing fire
curtains and blankets to prevent spread of smoke and manning
hoses at fire boundaries to prevent fire spread. Fire suppression
systems such as Sea Water, Water Mist, and Foam sprinkling
Nate
systems can be installed and employed to combat fires that
might arise from threat damage or accidental damage in noncombat scenarios. Manual crew firefighting can also prevent
further damage through strategic placement of fire plugs and
hose reels throughout the ship. Fire Zones that employ fire
retardant bulkheads with fire rated insulation (such that fire
cannot spread from one fire zone to another) and the use of
insensitive munitions are passive ways to ensure that damage is
controlled and increase recoverability. Watertight zones limit
flooding capability in a collision or external hull damage event
while washdown systems and decontamination stations are vital
to maintaining collective protection system zones in the event of
a chemical/biological/radiological attack.
Damage Casualty Isolation Instruction (DCII) cards are
typically generated during the detail design phase to decrease
crew response times and serve as a tool to identify distributed
systems existing in a compartment and location of accessible
valves outside of each compartment in order to rapidly set fire
and flooding boundaries and to isolate damaged distributive
systems. Recoverability assessments primarily focus on damage
control system availability and crew response times in order to
restore mission capabilities. System recoverability is measured
and assessed by following the progression of repairs,
replacements, and reconfigurations through a reactivation
diagram to determine the most recoverable areas of the system
architecture. System reactivation diagrams are essentially the
reverse of the system’s deactivation diagrams.
TOTAL INTEGRATED SHIP SURVIVABILITY
Total ship survivability requires a balanced and integrated
consideration of the differing facets of ship design including
signature control and self-defense weapon systems
(susceptibility reduction) and post hit damage mitigation
(vulnerability reduction and recoverability enhancement). The
significant weight, volume and cost penalties associated with
survivability features such as thicker armor and rapid-response
damage control systems may often be outweighed by the simple
fact that the probability of the ship getting hit by the threat is
minimal. Consequently, an integrated probabilistic approach to
the determination and evaluation of a measure of a system’s
total survivability is required in order to provide a true measure
of mission capability and success for any systems engineering
acquisition program.
To mitigate mission system failures, and consequently mission
failures, designers and systems engineers analyze the system
functionality, be it intact or in a damaged state to determine the
system effectiveness in achieving a quantified performance or a
“performance based requirement”. The analysis of a system’s
functionality for the purpose of evaluating the probability of
mission success is called a survivability analysis. With regard to
ship systems, survivability is one of the most important aspects
of design and systems engineering because it is one of the most
influential factors in determining combat ship system mission
effectiveness.
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
3
Further within the disciplined system engineering process,
concept, systems and lifecycle designers employ an integrated
total ship survivability assessment program in those areas from
performance requirement definition in concept development
through detail drawing design of ship systems. In all design and
requirement definition aspects, designers and systems engineers
using a survivability analysis methodology coupled with
reliability analysis will be able to provide development of
quantitative performance requirements for survivability
conditions, and sub conditions yielding mission success.
reports as shown in Figure 1. Vulnerability measures are the
predicted probabilities of ships meeting selected levels of
mission performance after sustaining a hit while Recoverability
measures are the probability distribution of the time required to
stop the spread of damage and to return to a
preselected/optimum capability after such a hit. The topside
assessment however, is primarily used to analyze the
susceptibility of a ship. Susceptibility measures are defined as
the predicted probability of a ship to avoid and/or defeat and
attack by a weapon threat.
To ensure mission success, survivability analysis methodology
being with accessing the design of the vessel, evaluating the
threat environment, and selecting the design threats based on the
CONOPS. The ship structure, equipment, distributed systems,
and threat distribution should be modeled in a 3D environment.
Using the threat distribution, 1000’s of hit scenarios should be
simulated against the vessel using validated Modeling and
Simulation software to maintain statistical significance of
damage results. Mission performance can be evaluated by
applying the quantified hit probability to survivability
performance requirement criteria selected at concept design.
Based on the results of the performance requirements,
survivability
weaknesses
can
be
identified
and
recommendations made to enhance the design of the vessel. In
cases where design recommendations are not feasible or
difficult to implement, then the recommendations made focus in
improving operational survivability through crew actions and
training.
The specific Survivability Analysis Process depicted in Figure 1
was developed at Alion Science and Technology to represent an
industry standardized survivability lifecycle flow from project
conception through detail design and beyond if operational
maintenance is required. Figure 1 also demonstrates the
progression of how initial vulnerability results generated at
concept design are used to determine susceptibility scores and
“through time” recoverability results at basic design which in
turn are used to generate operational guidelines at detail design.
Many institutes provide guidance for designing “survivable”
ship systems by reviewing threats, discussing survivability and
damage control concepts, and acknowledging the tradeoff
process. Most institutes however only emphasize one aspect of
survivability, be it susceptibility, vulnerability, or recoverability.
To quantify system survivability and provide a true measure of
ship system’s effectiveness, a methodology beyond those
presented within the current literature must be employed. This
method must integrate all three aspects of survivability:
susceptibility, vulnerability, and recoverability, and must also
achieve verification, validation and accreditation (VV&A) such
that the designer has the proper tool in order to develop and
determine an accurate single measure of total integrated system
survivability. (DoD Instruction 5000.61 2009)
Application to Naval Vessels
An essential element of ship design is the integrated
measurement of a ship’s susceptibility and vulnerability to
specific weapons threats, as well as the ability to recover from a
weapon event. Advanced survivability efforts generally include
generating platform specific survivability requirements as well
as simulating and analyzing the effective performance capability
of the ship against weapon threats.
A typical approach to a ship’s survivability assessment begins
with the acquisition of the ships ICD/CONOPS/DRM, from a
Navy which initiates the generation of the series of models and
Nate
Figure 1 Survivability Analysis Process
To ensure an affordable and effective military system, one that
will achieve a high probability of mission success, the
Department of Defense DOD 5000.2R requires that any
acquisition project use a disciplined systems engineering
process to be applied throughout the concept, systems and
lifecycle designs. Within the disciplined systems engineering
process, such as that of the intended acquisition of a navy
warship, integrated product teams (IPT) are defined for many
tasks including survivability and / or live fire test and evaluation
(LFT&E). The survivability or LFT&E IPT, through the use of
an integrated total ship survivability assessment program,
evaluates, compares, and investigates design growth and
emerging design features and cost.
Modifications Required for Non-combatant Application While
historically the enhancement of ship survivability has been
primarily associated with naval combatants; as the role of
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
4
modern naval non-combatants evolves to include additional
missions, and as the possibility of asymmetric threats places
these ships at increased risk, the assessment of survivability of
non-combatant ships becomes necessary to ensure fleet-wide
mission capability. The design of “multi-mission ships” and
emphasis on fleet-wide standardization has advanced
survivability practices on both combatants and non-combatants
in the 21st century.
Additionally, it is important to recognize that damage can occur
outside of a weapon impact. Fire initiation and flooding can be
caused by overheated machinery equipment, faulty wiring,
equipment cable sparking due to poor maintenance practices,
repair activities such as welding or cutting, accidental hazardous
material spillage, oil used in cooking, smoking paraphernalia or
arson. Accidental flooding can be associated with hull breach
due to a collision or grounding incident or deluged pipe rupture
due to poor maintenance practices. These occurrences can
occur unexpectedly on both combatants and non-combatants
alike and are vital to simulate to ensure the vessel is designed to
withstand accidental damage as well as intentional damage.
MODELING AND SIMULATION SOFTWARE
OVERVIEW
As a probabilistic indication of a ship’s ability to maintain a
designated capability or performance level, survivability is a
quantifiable description of designated ship capabilities or
performance measures as defined and assessed against a threat.
Full quantification of a complex system is not feasible leading
to the need to perform a statistical determination to provide
probabilistic representation of a ship’s survivability. Advanced
survivability methods include generating platform specific
survivability requirements as well as simulating and analyzing
the effective performance capability of a ship against various
weapon threats.
Integrated survivability tools such as MOTISS (Measure of
Total Integrated Ship Survivability) are utilized to provide
probabilistic representations of survivability by combining
initial damage effects with recovery analysis into a single
software suite that assists in survivability design, design
evaluation, requirements assessment, and resource allocation.
Thousands of tests are conducted with each test randomly
varying threat parameters and hit locations in order to capture
the chaotic nature of random unknowns, thus providing a
probabilistically determined assessment of occurrences similar
to a real world threat event.
MOTISS utilizes a 3D physical representation of systems
coupled with detailed logic models of selected subsystems.
Structural modeling is performed using Rectilinear Mapping to
allow for more rapid processing over traditional modeling and
simulation methods while still maintaining simulation accuracy
for large structures. Component and system modeling is
performed using Axis-Aligned Bounding Box (AABB) space
and weight formulation to allow for rapid component modeling
enabling a total system simulation of the vessel performance.
Nate
Incorporated within MOTISS is the methodology for internal
overpressure, ballistic and fragment penetration, linear jet theory
for shaped charges, hull rupture and holing, rule based
component lethality including shock impulse, acceleration,
kinetic impact, temperature and saturation failures, fault tree
analysis and network decision theory for system deactivation
and reactivation re-evaluation, zonal fire spread, solid and liquid
fuel loads allowing for thermal pulse ignition, options for
sprinkling, water-mist, foam agent and gas agent fire
suppression systems, progressive flooding, tank loading, and the
inclusion of firewater release and education. (MOTISS Ver. 3.0
User and Theory Manual 2011)
MOTISS is built as a federation of software subroutines or
modules linked by a common physical model and controlled by
a single master routine as shown in Figure 2. The “one model
and one tool” approach enables through-time integrated failure
effect and consequence classification analyses across all barriers
(technical, operational, and procedural). The benefits of this
approach include reduced costs to perform the analysis through
the use of less software and the development of fewer separate
system models, reduced time to conduct analysis by requiring
fewer models to be built and less total run-time to generate
results, and enhanced capability and understanding of the total
system of systems through significantly enhanced integration of
efforts and a greater understanding of system complexities.
Figure 2 MOTISS Analysis Assessment Process
NON-COMBATANT CASE STUDY
Mission and Specifications
CONOPS The concept of operations (CONOPS) for the case
study defines the vessel as a hospital ship during wartime and
training and humanitarian support vessel during peacetime. The
vessel is ~145m length overall, ~130m length waterline, ~20m
maximum beam, ~10m depth to Main Deck, ~5m design draft,
and ~6,000 tons displacement.
The vessel has a crew
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
5
compliment of 120 but is able to accommodate up to 320 total
trainees and/or passengers.
Propulsion The vessel is equipped with a CODOG (Combined
Diesel or Gas) system. Two controllable pitch propellers each
connect to an individual shaft with each shaft connecting to a
reduction gear driven by individual diesel engines or a single
gas turbine.
Ship Service Power Ship service power system is composed of
four ship service diesel generators (SSDGs), two main
switchboards, and two power load centers (PLCs).
Figure 4 Vessel Fire Zones
Equipment Model A total of 891 Vital Components and 2712
pipes and cables were modelled to incorporate 696 pieces of
equipment with 767 network deactivation logic systems to
represent 42 survivability performance requirements shown
below in Figure 5.
Scantlings The vessel has 600mm frame spacing and is
constructed using high tensile Grade A steel (355MPa Yield),
high tensile Grade E steel (355MPA Yield), and Aluminum as
shown below in Figure 3.
Figure 5 Vital Component and Distributed System Model
Figure 3 Plate Material
Inherent Mission Capabilities In accordance with ships
required inherent mission capabilities, the vessel is expected to
fulfill the following: Air Capable Ship (ACS), Search and
Rescue (SAR) using Rigid-hulled Inflatable Boats (RHIBs) or
aircraft, Humanitarian support, and Medical support through
sick bays.
Secondary Mission Capabilities Although the ship is not
expected to engage directly within a combat zone it is required
to perform the following specific roles/duties: Identify Friend or
Foe (IFF) detection, Anti-Surface Ship Warfare (ASU)
engagement, and Anti-Air Warfare (AAW) engagement. It is
important to note that the self-defense equipment listed here can
be used with dummy detonators for training purposes or loaded
with active charges to use in a wartime environment if
necessary.
Requirement Model Survivability requirements can be
separated into two categories: compliance based and
performance based. Compliance based requirements are the
minimum survivability design requirements to be met. Some
requirements can be waived based on the type and size of the
ship. These requirements are not performance based and are
assessed for compliance solely through design review (i.e.
visual inspection and confirmation of design data) to ensure
“Good Survivability Practice” to be followed.
Performance based requirements can be assessed against the
specific MOTISS probability of encounter evaluation criteria
given in Table 1 which allows a vessel to be ‘scored’ based on a
probabilistic remaining design capability post impact. The
performance requirements can be separated into four (4) levels
defined in Table 1. For purposes of this case study, only
performance requirements will be addressed. A total of 42
survivability performance requirements were assessed against
the case study vessel.
Model Description
Structural Model Based on general arrangement drawings the
model was refined to include 1029 Axis Aligned Bounding Box
(AABB) zones and 7057 structural plate elements (with
associated stiffening and thermal insulation) in order to
represent 586 compartments (with associated environmental
conditions, fuel, and tankage loadings prescribed) within the 4
Pressure Zones and 4 Fire Zones (shown in Figure 4).
Table 1 Survivability Performance Level Descriptions
Nate
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
6
Threat Model In order to properly assess the overall
survivability of the case study vessel, the model was subjected
to 1,000 impingements across four threats. The threats were
selected using an Analytical Hierarchy Process (AHP) (Saaty
1994) and include a Man Portable Rocket, Naval Artillery
Round, and two Anti-Ship Missiles (ASMs). Each threat is then
categorized as “over matching”, “equivalently matching”, and
“under matching” as shown in Table 2. A threat is defined as
“Under matched” if the vessel is designed to withstand an
impact and still maintain full mission capability (SP4 level
capability). A threat is defined as “equivalently matched” if the
vessel is designed to withstand an impact and be able to return
to port safely under its own power (SP2 level capability). A
threat is defined as “under matched” if the vessel is designed to
withstand an impact and be able to remain afloat (SP1 level
capability).
Table 2 Threat Descriptions
MOTISS Simulation Assumptions
For each threat analysis the vulnerability and recoverability
performance of the vessel was evaluated over a 15 minute
duration (analysis length) at a 30 second time increment (global
time step). Within all analyses, the primary weapon effects
(blast, thermal pulse, and fragmentation), and secondary effects
(secondary detonations, progressive flooding, progressive fire
and system network deactivation / reactivation) were assessed.
Within these assessments, only passive and installed Firefighting systems were permitted as Man-in-the-Loop-Operations
(MITLO) were assumed to only initiate at 16 minutes post
impact (conservatively assumed as twice the ideal DC on-sight
action team response time). Crew were allowed to activate
installed firefighting systems as well as perform limited system
isolation or equipment activation / deactivation functions prior
to the 16 minute condition.
Preliminary Survivability Performance
Assessment
As tabulated in Table 3, the case study vessel was incapable of
providing system recovery of lost capability post initial
automated reconfigurations. For example, uninterrupted power
supply (UPS) and automatic bus transfer (ABT) restoration
functions which occur instantaneously function where
appropriate provided that the equipment remains undamaged.
However auxiliary system reconfiguration to regain limited
functional capability in the absence of damaged equipment and
MITLO is not possible.
The remaining case study vessel concerns, as determined by a
root cause analysis of the deficiencies, and identified by the
vessel’s MOTISS assessment, all relate to power distribution
and unsuppressed fire propagation. Additionally, in scenarios
Nate
for which unsuppressed fires spread along the Main Deck,
sufficient passenger egress routes may be unavailable to safely
muster or evacuate vessel passengers. This is particularly
concerning in scenarios where the total number of passengers
exceeds the minimum (120) number of crew members as is
possible in inherent Humanitarian and Medical support
missions. The case study vessel has sufficient redundancy and
separation to assure post damage power generation capacity (i.e.
the case study vessel can produce power and assures casualty
power connections are intact), however, the design is incapable
of distributing power sufficiently throughout the vessel in a
damage event.
Table 3 Case Study Vessel Threshold Survivability Scores
Power Distribution Power cabling on the case study vessel was
modeled from the SSDGs to the Switchboards, PLCs, ABTs,
MBTs, power panels, and controllers and includes 440V, 220V,
and 115V power systems as shown below in Figure 6.
Figure 6 Power Distribution
As can be seen in Figure 6, the primary power system is not
designed using a Port-High Starboard-Low configuration but
clearly runs zonally below the damage control deck. However,
the survivability of the overall power system is limited due to
exceedingly long cable segments that act as the sole power
source to vital loads.
As an example, Figure 7 depicts a scenario in which any event
that induces the loss of the power cable availability between
frames 98 and 162 (shown in blue) will cause loss of the
Emergency Radio Room 220V power panel. The loss of this
panel directly results in failure of a survivability control
requirement necessary for damage control communications.
Loss of damage control communications can limit the amount of
time available for damage control response teams to respond to
progressive damage such as fire and flooding.
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
7
In order to reduce the vulnerability of this run, without
changing the designs distribution methodology, an additional
transformer would need to be installed in the area of the
Emergency Radio Room. However, the cabling needed to run
from the 220V Radio Feeder Panel to the Emergency Radio
Room and the transformer required to service this space would
be roughly the same weight (around 70 kg).
Separating these critical spaces from this vertical zone should
increase the case study vessel’s survivability when impacted in
this location. However, this examination of power distribution
shows that even if the “Vulnerable L” is populated with less
critical spaces, this does no good if critical systems (like power
and communications) are still routed through the “Vulnerable
L” region. Not only is it imperative to relocate critical
compartments to outside of the “Vulnerable L”, but system
arrangements much be changed as well.
Unsuppressed Fire Spread The root cause of failure analysis
discussed previously analysis also indicated that the case study
vessel is unable to contain fire from progressing outside of the
primary damage zone resultant from the naval artillery and
ASM missile strikes without Man-in-the-Loop operations (i.e.
manual firefighting). The standard naval interpretation assumes
that the Primary Damage Zone (PDZ) encompasses only the
compartments directly influenced by the impact of the weapon –
the compartment containing the hit location and any
compartments open to the blast. The system logic for limiting
the fire spread therefore stipulates that any compartment not a
part of the Primary Damage Zone (PDZ), and on fire, fails the
performance requirement.
Figure 7 Power Supply to Emergency Radio Power Panel
The application of Mil-C-24640 ‘A’ or Mil-C-24643 ‘A’
armored wire / braided armor cables (in minimum compliance
with IEEE-45-2002) in lieu of the non-armored (Mil-C-24640
‘U’ or Mil-C-24643 ‘U’) cables that are presently applied to the
case study vessel would improve power distribution availability
without requiring additional equipment or secondary power
sources.
Based on the power generation results discussed above, and area
has been identified that is referred to the “Vulnerable L” which
designates an “L shaped” susceptibility and vulnerability
problem aboard the case study vessel. The main reason for
concern with the ‘Vulnerable L” is that vital spaces relating to
command and control functions are stacked and/or adjacent
along the “L” configuration. Any impacts between frames 76
and 94 could affect more than one of these vital spaces, leading
to multiple survivability performance requirement failures as
shown in Figure 8.
However, the recent International Maritime Organization (IMO)
Safe Return to Port (SRtP) as dictated by Safety Of Life At Sea
(SOLAS) regulations, has defined the PDZ as any compartment
within a vertical fire zone containing the weapons affect (i.e. the
Main Vertical Zone or MVZ). To account for the IMO SRtP
definition within Fire Limited to PDZ requirement, vertical
damage zones were superimposed and aligned with the watertight separation and failure of the performance requirement was
updated to “Fire Limited to MVZ”. This updated performance
requirement is set to fail when a single compartment outside the
MVZ is on fire – i.e. the requirement would fail as soon as the
fire spreads from the vertical zone that contained the primary
weapon effect to any other vertical zone.
By modifying survivability performance requirement definition
from the standard naval PDZ definition to comply with IMO
SRtP (coinciding therefore with accepted practice for passenger
vessels, hospital ships and training vessels), the performance of
the case study vessel shown in Table 4 increases by as much as
10%.
Table 4 Affect MVZ Definition on Fire Spread Requirement
As indicated by Table 4, the revised SP1-14 PDZ definition
(accepted practice for passenger vessels, hospital ships and
training vessels) results in only an approximate 4% (41 of 1000)
of threat weapon impacts breaching the vertical WT zones
thereby violating IMO Safe Return to Port (SRtP) regulations
and failing the MOTISS SP1-14 (Fire Limited to MVZ
requirement). The particular statistics by threat are:
Figure 8 “Vulnerable L” Location
Nate
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
8




0 of 250 (0%) were Man Portable Rocket threats
(where 44 impacts induced conflagration)
32 of 250 (12.8%) were Naval Artillery threats (where
183 impacts induced conflagration)
3 of 250 (1.2%) were ASM 2 threats (where 237
impacts induced conflagration)
6 of 250 (2.4%) were ASM 1 threats (where 241
impacts induced conflagration)
38 of the 41 of IMO SRtP violations of the Fire Limited to MVZ
requirement, the primary cause is the unmitigated progression of
fire along breached passageways (e.g. fire is initiated within a
passage which then burns unmitigated across a non-tight
boundary). An example of this is illustrated by a fire initiated
from a naval artillery hit shown in red in Figure 9.
Figure 9 Fire Progression 600s Post Artillery Impact on Main
Deck
In this case, a naval artillery impact breaches command and
control, pressure lock, and collective protection system (CPS)
fan room doors initiating the fire in the starboard Main Deck
Passageway. The failure of the pressure lock door causes a
breach in the Fire Zone Boundary and enables fire to spread
from the MVZ into the CPS fan room (which is only accessible
from the pressure lock). Despite the spread of fire from one Fire
Zone to another, fire spreads to no other compartments in Fire
Zone 1 before 15 minutes and no secondary detonations result
though the fire does spread unmitigatedly aft through the
starboard main deck passage and continues aft and athwart ship
as there is no installed firefighting with these compartments.
While MITLO actions were not permitted in analyses described
here, it is important to note that the damage scenario described
in Figure 9 resulted in loss of a “single point of failure”
seawater firefighting branch to the deckhouse therefore severely
limiting manual and installed damage control capability. Based
on this damage and potential inability to mitigate fire
progression in the deckhouse and above thereby further
affecting the evacuation capability especially since the life boats
are located on the deckhouse levels.
Crew Egress and Emergency Evacuation As the case study
vessel is a multi-mission ship, including hospital, training, and
conference hosting capabilities, much of the service life will be
spent with significant numbers of untrained people on board.
This makes easy and fast egress an important function that the
ship must be able to support. Even if all people on board can
safely egress, emergency evacuation stalled if either the forward
deckhouse or the aft deckhouse (where the lifeboats are located)
is inaccessible.
According to a National Research Lab study on the ex-USS
Shadwell, the decision to abandon ship must be made within 7
minutes of fire ignition or flooding progression in order to
ensure that all crew and passengers on board can egress safely
because crew in spaces adjacent to a total flashover environment
will become disoriented at 7 minutes. (Williams 1999)
However, the command crew need to quickly determine and
assess all damage information in order to make an evacuation
decision, and utilizing investigators and verbal communication
may not be sufficient. Therefore, the installed casualty
management system needs to have ample sensors and input, as
well as a survivable layout, in order to quickly provide the
command crew with the information needed to make a timely
abandon ship decision.
To investigate the egress and evacuation of the case study
vessel, the post damage availability of egress routes from each
of the crew manned spaces as well as the lecture halls (which
can pose a “choke point” problem in the event of an emergency
evacuation) to any one of the six lifeboat muster stations (red
highlighted compartments in Figure 10) was examined. Within
this analysis, the condition of evacuation (e.g. do all passengers
egress safely?) was not initially examined, however, the
possibility of evacuation (i.e. does a safe route to any lifeboat
muster station exist?) was examined.
A route (from a green manned or lecture space to a red muster
space in Figure 10) was determined unsafe if:
1. The hot air temperature along any route exceeded 100
degrees Celsius which would result in human
incapacitation within 30 minutes if egress is not
possible (Williams 1999)
2. Flooding along any route exceeded 50 cm in depth as
all personnel would require the use of egress aids such
as handrails, human assistance, etc. that may not be
installed/available on the vessel to evacuate from a
confined space at this flooding depth (Ishigaki 2008)
3. Any door/hatch necessary for egress of a compartment
in which crew are stationed was inoperable
As indicated in Figure 9 the rate of fire spread along passages is
not immediate. The average breach or flashover time from
primary weapon damage compartment is approximately 5
minutes. Therefore, fire containment aboard the case study
vessel is functionally dependent on Man-in-the-Loop Operation
(MITLO) actions and that limited manning is not recommended
for this vessel.
Nate
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
9
Propulsion, and Navigation. These requirements and their
specific parameters vary by ship type and mission but can
include:
 Structural damage limited to XX% length waterline
 Flooding limited to X number of watertight zones
 Maintain damage stability in sea state X
 Fire limited to Main Vertical Zones
 Maintain XX% residual strength given a damaged state
Of the 14 out of 1000 (less than 2%) total weapon impact events
affecting the Damage Stability, Fire Protection, Power,
Propulsion, and Navigation categories of survivability
performance requirements, an example representative analyses
(shown Figure 11) was selected for a crew evacuation study.
Figure 11 Artillery Damage Illustration at 300s Post Impact
Figure 10 Manned Compartments and Muster Stations
Based on the post damage availability of egress routes, egress
route loss as shown is primarily due to two reasons:
1. The compartment of origin exceeds 100 degrees
Celsius making the space uninhabitable and causing
route loss
2. A space near the compartment of origin along the
egress route exceeded 100 degrees Celsius where the
passage is required for all egress such that when access
to this passage is lost, all egress routes specific
compartments in the deckhouse are lost
Following the conclusion of the egress route availability
assessment (e.g. is an egress route available for all passengers?),
a crew egress safety study to determine the condition of the
evacuation (e.g. can all passengers egress safely given a
damaged state?) was also considered. For the crew egress safety
study, the vessel was subjected to several weapon impact
analyses affecting primary function and damage control
performance requirement categories that would be vital to safe
evacuation including Damage Stability, Fire Protection, Power,
Nate
In this scenario, a naval artillery shell detonates in a port
passageway on the Main deck, igniting a fire and rupturing an
Operation Room. Additionally, doors and hatches fail that
connect the First Platform and Main Deck passages as well as
Operation Room and Main Deck passage. The fire slowly heats
the surrounding passages spreading as it spreads through the
Main Deck port passageway. By 660 seconds, all open First
Platform passages as well as the Main Deck passage above the
failed hatch are ignited and fire spread is stopped on the 1st
Platform at the watertight bulkheads (fore and aft). From 660 to
810 seconds, the fire continues to spread through the Main Deck
passages.
However, in this scenario no other performance requirements
other than Fire Limited to MVZ are affected by the scenario
described above, though the functionality of several fireplugs
and installed firefighting systems are lost (including Diesel
Engine Room watermist functionality). Although, this is not an
issue that requires a design change if the fire does not spread to
this machinery space.
Within the crew egress simulations, crew and passengers were
modelled in each accessible compartment. A base crew speed of
1.36 m/s was used based on the average of the four crew speeds,
minimum and maximum, female and male, on page 36 of
International Maritime Organization (IMO), Guidelines for
Evacuation Analysis for New and Existing Passenger Ships,
MSC.1/Circ.1238, 30 October 2007. However, in order to
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
10
account for factors that would affect crew speed during
evacuation such as; injury, littering, lighting effects, queuing
effects, etc. a reduced speed of 0.40 m/s was assumed based on
corrective factors as defined within the International Maritime
Organization (IMO), Guidelines for Evacuation Analysis for
New and Existing Passenger Ships, MSC.1/Circ.1238, 30
October 2007. Additionally, a set time of 300 seconds (5
minutes) post weapon event was assumed as the time at which
evacuation initiates based on the Time to Alert from
International Maritime Organization (IMO), Guidelines for
Evacuation Analysis for New and Existing Passenger Ships,
MSC.1/Circ.1238, 30 October 2007.
The primary forward and aft lifeboat muster stations were taken
as the evacuation muster locations for these analysis and each
crew member was assigned a single muster location (i.e. 1 of 6)
based on their location within the ship.
Based on the route check assessment and confirmed by crew
evacuation study, the evacuation of the case study vessel post
weapon impact initiated no later than 7 minutes post impact in
order to reduce the probability of loss of life.
As shown in Table 5, the average time to evacuate from any
manned compartment to a muster location is approximately 100
seconds, with the maximum time approaching 4 minutes (240
seconds). As previously discussed, the primary evacuation
failure is delay of reaction due to temperature at the time the call
to evacuate is first given.
Related to the rate of fire spread along passages, the fires do not
spread immediately (i.e. less than 60 seconds). The average
breach or flashover time from primary weapon damage
compartment is approximately 5 minutes. Therefore, fire
containment aboard the case study vessel is functionally
dependent on Man-in-the-Loop Operation (MITLO) actions and
that limited manning is not recommended for this vessel.
Based on the route check assessment and confirmed by crew
evacuation study, the evacuation of the case study vessel to
muster stations initiate no later than 7 minutes post impact if the
damage is not under control by this time in order to reduce the
probability of loss of life. The consideration of a non-combatant
vessels power distribution system design, ability to resist fire
propagation through both systems and MILTO response, and
available egress routes combine to ensure full mission capability
of training, humanitarian and medical support in non-aggravated
environment but also self-defense capabilities in wartime
scenarios.
The authors intend for this technical report to serve as the first
in a series highlighting survivability related to ship design and
crew operations. Future publications within this series will
examine the applicability of standards developed as part of
LFT&E regulations for mid-size naval surface combatants to
other case studies such as small patrol craft, offshore oil
platforms, passenger vessels, and modernizations from flight to
flight.
Following publications will then concentrate on
incrementally adding complexity to the survivability simulations
such as electrifying flooded water, considering the effect of
Firefighting Ensembles (FFEs) on crew tolerances, and
implementation of updated regulatory framework developed by
inter-governmental and/or non-governmental organizations.
ACKNOWLEDGEMENTS
Table 5 Average Time to Evacuation
CONCLUSIONS
Based on the power generation results discussed above, and area
has been identified that is referred to the “Vulnerable L” which
designates an “L shaped” susceptibility and vulnerability
problem aboard the case study vessel. The main reason for
concern with the “Vulnerable L” is that vital spaces relating to
command and control functions are stacked and/or adjacent
along the “L” configuration. Separating these critical spaces
from this vertical zone should increase the case study vessel’s
survivability when impacted in this location. However, this
examination of power distribution shows that even if the
“Vulnerable L” is populated with less critical spaces, this does
no good if critical systems (like power and communications) are
still routed through the “Vulnerable L” region. Not only is it
imperative to relocate critical compartments to outside of the
“Vulnerable L”, but system arrangements much be changed as
well.
Nate
The authors would like to acknowledge both Dr. Alan Brown of
Virginia Tech and Dr. John Waltham-Sajdak of Alion Science
and Technology. Their continued mentorship and support is
integral in expanding the authors’ survivability research. This
technical paper is resultant of their encouragement to share the
authors’ findings with peers in the maritime community
worldwide and raise awareness for combatant and noncombatant survivability alike. The authors also wish to express
their gratitude to the Republic of Korea Navy for their extensive
support and collaboration on international survivability projects.
REFERENCES
Germanischer Lloyd. Preliminary Guidelines for Safe Return to
Port Capability of Passenger Ships. Hamburg, 2009.
International Maritime Organization. Guidelines for Evacuation
Analysis for New and Existing Passenger Ships. 2007.
Ishigaki, T., Y. Onishi, Y. Asai, K. Toda, and H. Shimada.
“Evacuation Criteria during Urban Flooding in
Underground Space.” presented at the 11th
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
11
International Conference on Urban Drainage.
Edinburgh, Scotland, UK, 2008.
MOTISS User and Theory Manual, Version 3.0, Alion Science
and Technology, Alexandria, VA, 2011.
Saaty, T.L. Fundamentals of Decision Making and Priority
Theory with the AHP. Pittsburgh: RWS Publications,
1994.
United States. Department of Defense. DoD 5000.2-R:
Mandatory Procedures for Major Defense Acquisition
Programs (MDAPS) and Major Automated Information
System (MAIS) Acquisition Programs. Washington DC,
2002
United States. Department of Defense. DoD Instruction
5000.61: DoD Modeling and Simulation (M&S)
Verification, Validation, and Accreditation (VV&A).
Washington DC, 2009.
United States. Department of the Navy. Office of the Chief of
Naval Operations. OPNAVIST 9070.1A: Survivability
Policy and Standards for Surface Ships and Craft of
the U.S. Navy. Washington DC, 2012.
United States. Naval Research Laboratory. Williams, F.W., J.L.
Scheffey, S.A. Hill, T.A. Toomey, R.L. Darwin, J.T.
Leonard, and D.E. Smith. Post-Flashover Fires in
Shipboard Compartments Aboard ex-USS Shadwell:
Phase V — Fire Dynamics. Washington DC, 1999.
Waltham-Sajdak, J.A., A. Shechter, and M. Shechter.
“Quantification of Naval Combatant's Susceptibility as
a Means of Survivability.” presented at the 17th Naval
Ship Technology Seminar. Republic of Korea, 2014.
Nate
Application of Modeling and Simulation Methodologies to Enhance Non-Combatant Naval Survivability
12