You can define the impedance condition on a surface. The impedance is applied to element edges in two dimensions and to element faces in three dimensions. The element-based surface (see “Defining element-based surfaces,” Section 2.3.2) contains the element and face information.

*SIMPEDANCE, PROPERTY=impedance property table name
surface name

Alternatively, you can define the impedance condition on element faces. The impedance is applied to element edges in two dimensions and to element faces in three dimensions. The edge or face of the element upon which the impedance is placed is identified by an impedance load type and depends on the element type (see Part VI, “Elements”).

*IMPEDANCE,  PROPERTY=impedance property table name
element number or set name, impedance load type label

Since the radiation boundary conditions for the different shapes are spatially local and do not involve discretization in the infinite exterior domain, an exterior boundary can consist of the combination of several shapes. The appropriate boundary condition can then be applied to each part of the boundary. For example, a circular cylinder can be terminated with hemispheres (see “Fully and sequentially coupled acoustic-structural analysis of a muffler,” Section 8.1.1 of the ABAQUS Example Problems Manual), or an elliptical cylinder can be terminated with prolate spheroidal halves. This modeling technique is most effective if the boundaries between surfaces are continuous in slope as well as displacement, although this is not essential.

When the mechanics of a fluid can be described as linear, the observed total acoustic pressure can be decomposed into two components: the known incident wave and the “scattered” wave that is produced by the interaction of the incident wave with structures and/or fluid boundaries. When this superposition is applicable, it may be common practice to seek the “scattered” wave field solution directly. Both acoustic and solid surfaces at the acoustic-structural interface should be loaded in this case.

*ACOUSTIC WAVE FORMULATION, TYPE=SCATTERED WAVE

The total wave formulation (see “Coupled acoustic-structural medium analysis,” Section 2.9.1 of the ABAQUS Theory Manual) is particularly applicable when the acoustic medium is capable of cavitation, rendering the fluid mechanical behavior nonlinear. It should also be used if the problem contains either a curved or a finite extent boundary where the pressure history is prescribed. Only the outer acoustic surfaces should be loaded with the incident wave in this case. Any impedance or radiation condition that may exist on this outer acoustic boundary applies only on the part of the acoustic solution that does not include the prescribed incident wave field. Thus, the applied incident wave loading will travel into the problem domain without being affected by the boundary conditions on the outer acoustic surface. In the total wave formulation the acoustic pressure degree of freedom stands for the total dynamic acoustic pressure, including contributions from incident and scattered waves and, in ABAQUS/Explicit, the dynamic effects of fluid cavitation. The pressure degree of freedom does not include the acoustic static pressure, which can be specified as an initial condition (see “Defining initial acoustic static pressure” in “Initial conditions,” Section 27.2.1). This acoustic static pressure is used only in determining the cavitation status of the acoustic element nodes and does not apply any static loads to the acoustic or structural mesh at their common wetted interface. It does not apply to analysis using ABAQUS/Standard.

*ACOUSTIC WAVE FORMULATION, TYPE=TOTAL WAVE

You must refer to a property definition for each prescribed incident wave.

Incident wave loads in ABAQUS may be either spherical or planar in shape. You select a planar incident wave (default) or a spherical incident wave in the incident wave property definition. The fluid and the solid surfaces where the incident loading acts are specified in the incident wave loading definition. The incoming wave load is further described by the locations of its source point and of a reference (“standoff”) point where the wave amplitude is specified. For information on how to specify these surfaces and the standoff point, see “Identifying the fluid and the solid surfaces for incident wave loading,” and “Selecting a standoff point” below. For a planar wave the specified locations of the source and the standoff points are used to define the direction of wave propagation.

The speed of the incident wave is prescribed by giving the properties for the incident wave-bearing acoustic medium. These specified properties should be consistent with the properties specified for the fluid discretized using acoustic elements.

For the preferred interface you must define nodes corresponding to the source and standoff points for the incident wave; the node numbers or set names must be specified for each incident wave definition. The node set names, if used, must contain only a single node. Neither the source node nor the standoff node should be connected to any elements in the model.

*INCIDENT WAVE INTERACTION PROPERTY, NAME=wave property name, TYPE=PLANE or SPHERE
speed of sound, fluid mass density
*INCIDENT WAVE INTERACTION, PROPERTY=wave property name
fluid surface name, source node, standoff node, reference magnitude

In the scattered wave formulation the incident wave loading must be specified on all fluid and solid surfaces that reflect the incident wave with two exceptions:

When the total pressure-based formulation is specified, the incident wave loading must be specified only on the fluid surfaces that border the infinite region that is excluded from the model. Typically, these surfaces have a nonreflecting radiation condition specified on them, and the implementation ensures that the radiation condition is enforced only on the scattered response of the modeled domain and not on the incident wave itself. See “Example: submarine close to the free surface,” and “Example: surface ship,” shown in Figure 27.4.5–2 and Figure 27.4.5–3, respectively.

In certain problems, such as blast loads in air, you may decide that the blast wave loads on a structure need to be modeled, but the surrounding fluid medium itself does not. In these problems the incident wave loading is specified only on the solid surfaces since the fluid medium is not modeled. The distinction between the scattered wave formulation and the total wave formulation for handling the incident wave loading is not relevant in these problems since the wave propagation in the fluid medium is of no interest.

The standoff point is a reference point used to specify the pulse loading time history: it is the point at which the user-defined pulse history is assumed to apply with no time delay, phase shift, or spreading loss. The standoff point should be defined so that it is closer to the source than any point on the surfaces in the model that would reflect the incident wave. Doing so ensures that all the points on these surfaces will be loaded with the specified time history of the source and that the analysis begins before the wave overtakes any portion of these surfaces. To save analysis time, the standoff point is typically on or near the solid surface where the incoming incident wave would be first deflected (see “Example: submarine close to the free surface,” shown in Figure 27.4.5–2). However, the standoff point is a fixed point in the analysis: if the loaded surfaces move before the incident wave loading begins, due to previous analysis steps or geometric adjustments, the surfaces may envelop the specified standoff point. Care should be taken to define a standoff point such that it remains closer to the incident wave source point than any point on the loaded surfaces at the onset of the loading.

When the total wave formulation is used and the incident wave loading is specified in the first step of the analysis in terms of pressure history, ABAQUS automatically initializes the pressure and the pressure rate at the acoustic nodes to values based on the incident wave loading. This allows the acoustic analysis to start with the incident waves partially propagated into the problem domain at time zero and assumes that this propagation had taken place with negligible effect of any volumetric dissipative sources such as the fluid drag. When the incident wave loading is specified in terms of the pressure values, the recommendations given above for selecting a standoff point are valid with the total wave formulation as well. However, when the incident wave loading is specified in terms of acceleration values, the automatic initialization is not done and the standoff point should be located near the exterior fluid boundary of the model such that the standoff point is closer to the source than any point on the exterior boundary. See “Example: submarine close to the free surface,” and “Example: surface ship,” shown in Figure 27.4.5–2 and Figure 27.4.5–3, respectively.

As previously mentioned, the time history to be specified by the user is that observed at the standoff point: histories at a point on the loaded surface are computed from the wave type and the location of that point relative to the standoff point. The time history of the acoustic source pulse can be defined either in terms of the fluid pressure values or the fluid particle acceleration values. Pressure time histories can be used for any type of element, such as acoustic, structural, or solid elements; acceleration time histories are applicable only for acoustic elements. In either case a reference magnitude is specified for any given incident-wave-loaded surface, and a reference to a time-history data table defined by an amplitude curve is specified. The reference magnitude varies with time according to the amplitude definition.

Currently the source pulse description in terms of fluid particle acceleration history is limited to planar incident waves acting on fluid surfaces. Further, if an impedance condition is specified on the same fluid surface along with incident wave loading, the source pulse is restricted to the pressure history type even for planar incident waves. The source pulse in terms of pressure history can be used without these limitations; i.e., pressure-history-based incident wave loading can be used with fluid or solid surfaces, with or without impedance, and for both planar and spherical incident waves.

When the source pulse is specified using pressure values and is applied on a fluid surface, the pressure gradient is computed and applied as a pressure-conjugate load on these surfaces. Hence, it is desirable to define the pulse amplitude to begin with a zero value, particularly when the cavitation in the fluid is a concern. If the structural response is of primary concern and the scattered formulation is being used, any initial jump in the pressure amplitude can be addressed by applying additional concentrated loads on the structural nodes that are tied to the acoustic mesh, corresponding to the initial jump in the incident wave pressure amplitude. Clearly, the additional load on any given structural node should be active from the instance the incident wave first arrives at that structural node. However, the scattered wave solution in the fluid still needs careful interpretation taking the initial jump into account.

*INCIDENT WAVE INTERACTION, PRESSURE AMPLITUDE=amplitude data table name
solid or fluid surface name, source node, standoff node, reference magnitude

*INCIDENT WAVE INTERACTION, ACCELERATION AMPLITUDE=amplitude data table name
fluid surface name, source node, standoff node, reference magnitude

An underwater explosion forms a highly compressed gas bubble that interacts with the surrounding water, generating an outward-propagating shock wave. The gas bubble floats upward as it generates these waves changing the relative positions of the source and the loaded surfaces. The loading effects due to bubble formation can be defined for spherical incident wave loading by using a bubble definition in conjunction with the incident wave loading definition.

The bubble dynamics can be described using a model internal to ABAQUS or by using tabulated data. ABAQUS has a built-in mechanical model of the bubble interacting with the surrounding fluid, which is simulated numerically to generate a set of data prior to running the finite element analysis. You can specify the explosive material parameters, ending time, and other parameters that affect the computation of the bubble amplitude curve used, as shown in Table 27.4.5–1.

Table 27.4.5–1 Parameters that define the bubble behavior.

Name	Dimensions	Description	Default
	FL–2(LM–1/3)1+A	Charge constant	None
	T/(MLB)	Charge constant	None
	Dimensionless	Similitude spatial exponent	None
	Dimensionless	Similitude temporal exponent	None
	F/L2	Charge constant	None
	Dimensionless	Ratio of specific heats for explosion gas	None
	M/L3	Charge material density	None
	M	Mass of charge	None
	L	Initial charge depth	None
	Dimensionless	X-direction cosine of the free surface normal	None
	Dimensionless	Y-direction cosine of the free surface normal	None
	Dimensionless	Z-direction cosine of the free surface normal	None
	L/T2	Acceleration due to gravity	None
	F/L2	Atmospheric pressure at free surface	None
	Dimensionless	Wave effect parameter	1.0
	Dimensionless	Bubble drag coefficient	0.0
	T	Maximum allowable time in bubble simulation	None
	Dimensionless	Maximum allowable number of steps in bubble simulation	1500
	Dimensionless	Relative error tolerance parameter for bubble simulation	1 × 10–11
	Dimensionless	Absolute error tolerance parameter for bubble simulation	1 × 10–11
	Dimensionless	Error control exponent for bubble simulation	0.2
	M/L3	Fluid mass density	None
	L/T	Fluid speed of sound	None

In an underwater explosion event a bubble migrates upward toward, and possibly reaches, the free water surface. If the bubble migration reaches the free water surface during the specified analysis time, ABAQUS applies loads of zero magnitude after this point.

Model data about the bubble simulation are written to the data (.dat) file. During an ABAQUS/Standard analysis history data are written each increment to the output database (.odb) file. The history data include the radius of the bubble and the bubble depth below the free water surface.

For the preferred interface the loading effects due to bubble formation can be defined for spherical incident wave loading using the UNDEX charge property definition. Because the bubble simulation uses spherical symmetry, the incident wave interaction property must define a spherical wave.

You can also specify incident wave loading due to bubble dynamics using tabulated data for the pressure and source migration. For the preferred interface you specify independent amplitude curves for the pressure at the standoff point and any source node location time histories. The source location amplitude names are referred to from boundary condition definitions for the source node.

*INCIDENT WAVE INTERACTION PROPERTY, TYPE=SPHERE,
NAME=wave property name*UNDEX CHARGE PROPERTY
data defining the UNDEX charge
*INCIDENT WAVE INTERACTION, UNDEX, 
PROPERTY=wave property name
fluid surface name, source node, standoff node, reference magnitude

*AMPLITUDE, DEFINITION=TABULAR, NAME=pressure
*INCIDENT WAVE INTERACTION, PRESSURE AMPLITUDE=pressure
solid or fluid surface name, source node, standoff node, reference magnitude

*AMPLITUDE, DEFINITION=TABULAR, NAME=name
*BOUNDARY, TYPE=DISPLACEMENT or VELOCITY,
AMPLITUDE=name 
source node, degrees of freedom

To model the effect of relative motion between a structure (such as a ship) and the wave source during the analysis using the preferred interface, the source node may be assigned a velocity. It is assumed that the entire fluid-solid model is moving at a velocity with respect to the source node during the loading and that the speed of the model's motion is low compared to the speed of propagation of the incident wave. That is, the effect of the speed of the source is neglected in the computation of the loads, but the change in position of the source is included. This is equivalent to assuming that the relative motion between the source and the model is at a low Mach number.

*BOUNDARY, TYPE=DISPLACEMENT or VELOCITY,  AMPLITUDE=name
source node, degrees of freedom

The waves emanating from the source may reflect off plane surfaces, such as seabeds or sea surfaces, before reaching the specified standoff point. Thus, the incident wave loading consists of the waves arriving from a direct path from the source, as well as those arriving from reflections off the planes. In ABAQUS an arbitrary number of these planes can be defined, each with its own location, orientation, and reflection coefficient.

If no reflection coefficient is specified, the plane is assumed to be “soft”; a zero total pressure condition is applied. If a reflection coefficient is specified, the magnitude of the reflected waves are modified by the reflection coefficient according to the formula:

The reflection planes are allowed only for incident waves that are defined in terms of fluid pressure values. Only one reflection off each plane is considered. If the effect of many successive reflections is important, these surfaces should be part of the finite element model. Reflection planes should not be used at a boundary of the finite element model if the total wave formulation is used, since in that case the incident wave will be reflected automatically by that boundary.

*INCIDENT WAVE REFLECTION

The acoustic pressure degree of freedom at nodes of acoustic elements can be prescribed using a boundary condition. However, since you can use the nodal acoustic pressure in an ABAQUS analysis to refer to the total pressure at that point or to only the scattered component, care must be exercised in some circumstances.

When the total wave formulation is used, a boundary condition alone is sufficient to specify a prescribed total dynamic pressure on a boundary.

In an analysis without incident wave loading, the nodal degree of freedom is generally equal to the total acoustic pressure at that point. Therefore, its value can be prescribed using a boundary condition in a manner consistent with other boundary conditions in ABAQUS. For example, you may set the acoustic pressure at all of the nodes at a duct inlet to a prescribed amplitude to analyze the propagation of waves along the duct. The free surface of a body of water can be modeled by setting the acoustic pressure to zero at the surface.

When incident wave loading is used, the scattered wave formulation defines the nodal acoustic degree of freedom to be equal to the scattered pressure. Consequently, a boundary condition definition for this degree of freedom affects the scattered pressure only. The total acoustic pressure at a node is not directly accessible in this formulation. Specification of the total pressure in a scattered formulation analysis is nevertheless required in some instances (for example, when modeling a free surface of a body of water). In this case, one of the following methods should be used.

If the fluid surface with prescribed total pressure is planar, unbroken, and of infinite extent, an incident wave reflection plane and a boundary condition can be used together to model the fact that the total pressure is zero on the free surface. A “soft” incident wave reflection plane coincident with the free surface will make sure that the structure is subjected to the incident wave load reflected off the free surface. A boundary condition setting the acoustic pressure in the surface equal to zero will make sure that any scattered waves emitted by the structure are reflected properly. The scattered wave solution in the fluid must be interpreted taking into consideration the fact that the incident field now includes a reflection of the source as well. If the fluid surface with prescribed total pressure is planar but broken by an object, such as a floating ship, this modeling technique may still be applied. However, the reflected loads due to the incident wave are computed as if the reflection plane passes through the hull of the ship; this approximation neglects some diffraction effects and may or may not be applicable in all situations of interest.

Alternatively, the free surface condition of the fluid can be eliminated by modeling the top layer of the fluid using structural elements, such as membrane elements, instead of acoustic elements. The “structural fluid” surface and the “acoustic fluid” surface are then coupled using either a surface-based mesh tie constraint (“Mesh tie constraints,” Section 28.3.1) or, in ABAQUS/Standard, acoustic-structural interface elements; and the incident wave loading must be applied on both the “structural fluid” and the “acoustic fluid” surfaces. The material properties of the “structural fluid” elements should be similar to those of the adjacent acoustic fluid. In ABAQUS/Explicit the thickness of the “structural fluid” elements must be such that the masses at nodes on either side of the coupling constraint are nearly equal. This modeling technique allows the geometry of the surface on which total pressure is to be prescribed to depart from an unbroken, infinite plane. As a secondary benefit of this technique, you can obtain the velocity profile on the free surface since the displacement degrees of freedom are now activated at the “structural fluid” nodes. If a nonzero pressure boundary condition is desired, it can be applied as a distributed loading on the other side of the “structural fluid” elements.

*BOUNDARY
*INCIDENT WAVE REFLECTION

*TIE
*INCIDENT WAVE or *INCIDENT WAVE INTERACTION

*BOUNDARY

Conceptually, the alternative interface is the same as the preferred interface; however, the usages are different. For conceptual information, see “Prescribing geometric properties and the speed of the incident wave.”

*INCIDENT WAVE PROPERTY, NAME=wave property name,
 TYPE=PLANE or SPHERE
data lines to specify the location of the acoustic source and the standoff point
*INCIDENT WAVE FLUID PROPERTY
bulk modulus, mass density
*INCIDENT WAVE, PROPERTY=wave property name

Conceptually, the alternative interface is the same as the preferred interface; however, the usages are different. For conceptual information, see “Defining the time history of the source pulse.”

*INCIDENT WAVE, PRESSURE AMPLITUDE=amplitude data table name
solid or fluid surface name, reference magnitude

*INCIDENT WAVE, ACCELERATION AMPLITUDE=amplitude data table 
name
fluid surface name, reference magnitude

Conceptually, the alternative interface is the same as the preferred interface; however, the usages are different. For conceptual information, see “Defining bubble loading for spherical incident wave loading.”

To define the bubble dynamics using a model internal to ABAQUS, you can specify a bubble amplitude. Use of the bubble loading amplitude is generally similar to the use of any other amplitude in ABAQUS.

*AMPLITUDE, DEFINITION=BUBBLE, NAME=name
*INCIDENT WAVE PROPERTY, TYPE=SPHERE, 
NAME=wave property name
*INCIDENT WAVE, PRESSURE AMPLITUDE=name
solid or fluid surface name, reference magnitude

To define the bubble dynamics using tabulated data for the pressure and source migration, you can specify independent amplitude curves for the pressure at the standoff point and any source location time histories. The source location amplitude names, or floating point data for source point coordinates that remain fixed, are referred to in the incident wave property definition. The amplitude name for the pressure amplitude is referred to in the incident wave loading definition in the usual manner.

*AMPLITUDE, DEFINITION=TABULAR, NAME=Pressure
*AMPLITUDE, DEFINITION=TABULAR, NAME=X
*AMPLITUDE, DEFINITION=TABULAR, NAME=Y
*AMPLITUDE, DEFINITION=TABULAR, NAME=Z
*INCIDENT WAVE PROPERTY, TYPE=SPHERE, 
NAME=wave property name
{standoff point data}
X, Y, Z
*INCIDENT WAVE, PRESSURE AMPLITUDE=Pressure
solid or fluid surface name, reference magnitude

Conceptually, the alternative interface is the same as the preferred interface; however, the usages are different. For conceptual information, see “Specifying the reflection effects.”

*INCIDENT WAVE REFLECTION

To model the effect of rigid motion of a structure such as a ship during the incident wave loading history, the standoff point can have a specified velocity. It is assumed that the entire fluid-solid model is moving at this velocity with respect to the source point during the loading and that the speed of the model's motion is low compared to the speed of propagation of the incident wave.

*INCIDENT WAVE PROPERTY, NAME=wave property name
data line to specify the velocity of the standoff point

Here the scattered wave response in the acoustic medium is of interest along with that of the structure to the incident wave loading. Cavitation in the fluid is not considered in a scattered wave formulation. Similarly, the initial hydrostatic pressure in the fluid is not modeled.

The zero dynamic acoustic pressure boundary condition on the free surface requires both a “soft” reflection plane coinciding with the free surface and a zero scattered pressure boundary condition at the nodes on this free surface. The incident wave loading is applied on the fluid surface, , and on the wet solid surface, . The incident wave loading can be only of pressure amplitude type since the loading includes a solid surface.

A good location for the standoff node is marked as A in Figure 27.4.5–2. This node is in the fluid, close to the structure, and closer to incident wave source S than any portion of the seabed or the free surface. The standoff node's offset from the loaded surfaces is exaggerated for emphasis in the figure.

The radiation condition is specified on the acoustic surface such that the scattered wave impinging on this boundary with the infinite medium does not reflect back into the computational domain. The seabed is modeled with an incident wave reflection plane on surface . The reflection loss at this seabed surface is modeled using an impedance property.

If the response of the structure in the nonlinear regime is of interest, the initial stress state in the structure should be established using ABAQUS/Standard in a static analysis. The stress state in the structure is then imported into ABAQUS/Explicit, and the loading on the solid surfaces causing the initial stress state is respecified in the acoustic analysis.

The following template schematically shows some of the ABAQUS input file options that are used to solve this problem using the scattered wave formulation:

*HEADING
…
*SURFACE, NAME= 
Data lines to define the acoustic surface that is wetting the solid
*SURFACE, NAME= 
Data lines to define the solid surface that is wetted by the fluid
*SURFACE, NAME= 
Data lines to define the acoustic surface separating the modeled region from the infinite medium
*INCIDENT WAVE INTERACTION PROPERTY, NAME=IWPROP
*AMPLITUDE, DEFINITION=TABULAR, NAME=PRESSUREVTIME
*TIE, NAME=COUPLING
,  
*STEP
** For an ABAQUS/Standard analysis:
*DYNAMIC
** For an ABAQUS/Explicit analysis:
*DYNAMIC, EXPLICIT
** Load the acoustic surface
*INCIDENT WAVE INTERACTION, PRESSURE AMPLITUDE=PRESSUREVTIME,
PROPERTY=IWPROP
, source node, standoff node, reference magnitude
*INCIDENT WAVE REFLECTION
Data lines for the reflection plane over the seabed , seabed_Q 
*INCIDENT WAVE REFLECTION
Data lines for a "soft" reflection plane over the free surface .
** Load the solid surface
*INCIDENT WAVE INTERACTION, PRESSURE AMPLITUDE=PRESSUREVTIME,
PROPERTY=IWPROP
, source node, standoff node, reference magnitude
*INCIDENT WAVE REFLECTION
Data lines for the reflection plane over the seabed ,  seabed_Q 
*INCIDENT WAVE REFLECTION
Data lines for a "soft" reflection plane over the free surface .
*BOUNDARY
** zero pressure boundary condition on the free surface
Set of nodes on the free surface , 8, 8, 0.0
*SIMPEDANCE
, 
*END STEP

Here the total wave response in the acoustic medium is of interest along with that of the structure to the incident wave loading. Cavitation in the fluid may be included. Similarly, a linearly varying initial hydrostatic pressure in the fluid can be specified.

The zero dynamic acoustic pressure boundary condition on the free surfaces requires only a zero pressure boundary condition at the nodes on this free surface. A reflection plane should not be included along the free surface. The incident wave loading is applied only on the fluid surface, , that separates the modeled region from the surrounding infinite acoustic medium. No incident wave should be applied directly on the structure surfaces. If the incident wave is considered planar, an acceleration-type amplitude can be used with the incident wave loading. Otherwise, a pressure-type amplitude must be used with the incident wave loading.

An ideal location for the standoff node depends on the type of amplitude used for the time history of the incident wave loading. The location A shown in Figure 27.4.5–2 can be used if the incident wave loading time history is of pressure amplitude type. Otherwise, the location B that is just on the boundary and closer to the source S than any part of either the seabed or the free surface can be used.

The nonreflecting impedance condition is specified on the acoustic surface, , such that the scattered part of the total wave impinging on this boundary with the infinite medium does not reflect back into the computational domain. The seabed is modeled with an incident wave reflection plane on the surface .

If the response of the structure in the nonlinear regime is of interest, the initial stress state in the structure should be established using ABAQUS/Standard in a static analysis. The stress state in the structure is then imported into ABAQUS/Explicit, and the loading on the solid surfaces causing the initial stress state is respecified in the acoustic analysis.

The following template schematically shows some of the input file options that are used to solve this problem using the total wave formulation:

*HEADING
…
*ACOUSTIC WAVE FORMULATION, TYPE=TOTAL WAVE
*MATERIAL, NAME=CAVITATING_FLUID
*ACOUSTIC MEDIUM, BULK MODULUS
Data lines to define the fluid bulk modulus
*ACOUSTIC MEDIUM, CAVITATION LIMIT
Data lines to define the fluid cavitation limit
…
*SURFACE, NAME= 
Data lines to define the acoustic surface that is wetting the solid
*SURFACE, NAME= 
Data lines to define the solid surface that is wetted by the fluid
*SURFACE, NAME= 
Data lines to define the acoustic surface separating the modeled region from the infinite medium
*INCIDENT WAVE INTERACTION PROPERTY, NAME=IWPROP
*AMPLITUDE, DEFINITION=TABULAR, NAME=PRESSUREVTIME
Data lines to define the pressure-time history at the standoff point
*TIE, NAME=COUPLING
,  
*INITIAL CONDITIONS, TYPE=ACOUSTIC STATIC PRESSURE
Data lines to define the initial linear hydrostatic pressure in the fluid
*STEP
*DYNAMIC, EXPLICIT
** Load the acoustic surface
*INCIDENT WAVE INTERACTION, PRESSURE AMPLITUDE=PRESSUREVTIME, 
PROPERTY=IWPROP
, source node, standoff node, reference magnitude
*INCIDENT WAVE REFLECTION
Data lines for the reflection plane over the seabed , seabed_Q 
*BOUNDARY
** zero pressure boundary condition on the free surface
Set of nodes on the free surface , 8, 8, 0.0
*SIMPEDANCE
, 
*END STEP