3-D Structural Surface Effect

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SURF154 Element Description

SURF154 is used for various load and surface effect applications in 3-D structural analyses. It can be overlaid onto an area face of any 3-D element. Various loads and surface effects may exist simultaneously. See SURF154 in the Mechanical APDL Theory Reference for more details about this element.

Figure 154.1:  SURF154 Geometry

SURF154 Geometry

SURF154 Input Data

The geometry, node locations, and the coordinate system for this element are shown in Figure 154.1: SURF154 Geometry. The element is defined by four to eight nodes and the material properties. A triangular element may be formed by defining duplicate K and L node numbers as described in Degenerated Shape Elements. The default element x-axis is parallel to the I-J side of the element.

The mass and volume calculations use the element thicknesses at nodes I, J, K, and L (real constants TKI, TKJ, TKK, and TKL, respectively). Thickness TKI defaults to 0.0, and thicknesses TKJ, TKK, and TKL default to TKI. The mass calculation uses the density (material property DENS, mass per unit volume) and the real constant ADMSUA, the added mass per unit area.

The stress stiffness matrix and load vector calculations use the in-plane force-per-unit length (input as real constant SURT). The elastic foundation stiffness (input as real constant EFS) uses pressure-per-length (or force-per-length-cubed) units. The foundation stiffness can be damped, either by using the material property BETD as a multiplier on the stiffness or by directly using the material property VISC.

See Nodal Loading for a description of element loads. Pressures may be input as surface loads on the element faces as shown by the circled numbers on Figure 154.2: Pressures. SURF154 allows complex pressure loads.

Faces 1, 2, and 3 [KEYOPT(2) = 0] Positive values of pressure on the first three faces act in the positive element coordinate directions (except for the normal pressure which acts in the negative y direction). For face 1, positive or negative values may be removed as requested with KEYOPT(6) to simulate the discontinuity at the free surface of a contained fluid. For faces 2 and 3, the direction of the load is controlled by the element coordinate system; therefore, the ESYS command is normally needed.

Faces 1, 2, and 3 [KEYOPT(2) = 1] Pressure loads are applied to the element faces according to the local coordinate system, as follows: face 1 in the local x direction, face 2 in the local y direction, and face 3 in the local z direction. A local coordinate system must be defined, and the element must be set to that coordinate system via the ESYS command; however, the loads specified in that local coordinate system do not follow the large displacements and/or rotations of the element. KEYOPT(6) does not apply.

Figure 154.2:  Pressures


Face 4 The direction is normal to the element and the magnitude of the pressure at each integration point is PI + XPJ + YPK + ZPL, where PI through PL are input as VAL1 through VAL4 on the SFE command, and X, Y, Z are the global Cartesian coordinates at the current location of the point. No input values can be blank. Face 4 can be used to apply hydrostatic ocean loading, with PL = -(vertical acceleration) * (water density). Positive or negative values may be removed as requested with KEYOPT(6) to simulate the discontinuity at the free surface of a contained fluid. The SFFUN and SFGRAD commands do not work with face 4.

Face 5 The magnitude of the pressure is PI, and the direction is where i, j, and k are unit vectors in the global Cartesian directions. The load magnitude may be adjusted with KEYOPT(11) and KEYOPT(12). No input values can be blank. When using the SFFUN or SFGRAD commands, the load direction is not altered but the load magnitude is the average of the computed corner node magnitudes. SFCUM,ADD should be used with caution, as this command also causes the load direction components to be added.

The effects of pressure load stiffness are automatically included for this element for real pressure on face 1 if KEYOPT(2) = 0 or on face 4. If an unsymmetric matrix is needed for pressure load stiffness effects, issue a NROPT,UNSYM command.

Temperatures may be input as element body loads at the nodes. Element body load temperatures are not applied to other elements connected at the same nodes. The node I temperature T(I) defaults to TUNIF. If all other temperatures are unspecified, they default to T(I). If all corner node temperatures are specified, each midside node temperature defaults to the average temperature of its adjacent corner nodes. For any other input temperature pattern, unspecified temperatures default to TUNIF. Temperatures are used for material property evaluation only.

When KEYOPT(4) = 0, an edge with a removed midside node implies that the displacement varies linearly, rather than parabolically, along that edge. See Quadratic Elements (Midside Nodes) in the Modeling and Meshing Guide for more information about the use of midside nodes.

KEYOPT(7) = 1 is useful when the element is used to represent a force. When KEYOPT(7) = 0, the force is input as a pressure times an area; however, if the area changes due to large deflections, the force also changes. When KEYOPT(7) = 1, the force remains unchanged even if the area changes.

KEYOPT(8) > 0 applies ocean loading on the element.

A summary of the element input is given in "SURF154 Input Summary". A general description of element input is given in Element Input.

SURF154 Input Summary

I, J, K, L if KEYOPT (4) = 1
I, J, K, L, M, N, O, P if KEYOPT (4) = 0
Degrees of Freedom


Real Constants
(Blank), (Blank), (Blank), EFS, SURT, ADMSUA,
See Table 154.1: SURF154 Real Constants for a description of the real constants
Material Properties


Surface Loads
Pressures -- 
face 1 (I-J-K-L) (in -z normal direction if KEYOPT(2) = 0; in local coordinate x direction if KEYOPT(2) = 1)
face 2 (I-J-K-L) (in tangential +x direction if KEYOPT(2) = 0; in local coordinate y direction if KEYOPT(2) = 1)
face 3 (I-J-K-L) (in tangential +y direction if KEYOPT(2) = 0; in local coordinate z direction if KEYOPT(2) = 1)
face 4 (I-J-K-L) (in -z normal direction, global taper)
face 5 (I-J-K-L) (oriented by input vector)
Body Loads
Temperatures -- 

T(I), T(J), T(K), T(L); also T(M), T(N), T(O), T(P) if KEYOPT(4) = 0

Special Features
Birth and death
Large deflection
Linear perturbation
Nonlinear adaptivity
Ocean loading
Stress stiffening

Pressure applied to faces 1, 2, and 3 according to coordinate system:

0 -- 

Apply face loads in the element coordinate system

1 -- 

Apply face loads in the local coordinate system


Midside nodes:

0 -- 

Has midside nodes (that match the adjacent solid element)

1 -- 

Does not have midside nodes


Applicable only to normal direction pressure (faces 1 and 4). This KEYOPT is valid only when KEYOPT(2) = 0.

0 -- 

Use pressures as calculated (positive and negative)

1 -- 

Use positive pressures only (negative set to zero)

2 -- 

Use negative pressures only (positive set to zero)


Loaded area during large-deflection analyses:

0 -- 

Use new area

1 -- 

Use original area


Specifies whether ocean loading is applied:

0 -- 

No ocean loading (default). This option applies even if the ocean-loading data is defined.

1 --

Ocean loading is applied if the ocean-loading data is defined. This option is valid when KWAVE = 8 or 101+ on the OCDATA command. For KWAVE = 101+, ocean loading is applied based on user subroutine userPanelHydFor computations.


Pressure applied by vector orientation (face 5):

0 -- 

On projected area and includes tangential component

1 -- 

On projected area and does not include tangential component

2 -- 

On full area and includes the tangential component


Effect of the direction of the element normal (element z-axis) on vector oriented (face 5) pressure:

0 -- 

Pressure load is applied regardless of the element normal orientation

1 -- 

Pressure load is not used if the element normal is oriented in the same general direction as the pressure vector.

Table 154.1:  SURF154 Real Constants

No. Name Description
1 ... 3(Blank)--
4EFSFoundation stiffness
5SURTSurface tension
6ADMSUAAdded mass/unit area
7TKIThickness at node I
8TKJThickness at node J (defaults to TKI)
9TKKThickness at node K (defaults to TKI)
10TKLThickness at node L (defaults to TKI)

SURF154 Output Data

The solution output associated with the element is in two forms:

A general description of solution output is given in Solution Output. See the Basic Analysis Guide for ways to view results.

The Element Output Definitions table uses the following notation:

A colon (:) in the Name column indicates that the item can be accessed by the Component Name method (ETABLE, ESOL). The O column indicates the availability of the items in the file Jobname.OUT. The R column indicates the availability of the items in the results file.

In either the O or R columns, “Y” indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.

Table 154.2:  SURF154 Element Output Definitions

Name Definition O R
ELElement NumberYY
EXTRA NODEExtra node (if present)YY
MATMaterial numberYY
AREASurface areaYY
XC, YCLocation where results are reportedY 1
VN(X, Y, Z)Components of unit vector normal to center of element-Y
PRESSURES(F/L2)Pressures P1 (includes hydrodynamic pressure), P2, P3, P4, and P5 at nodes I, J, K, L (Face indicated by PRES LOAD KEY) 2 -
PZ, PX, PYPressures at nodes in element coordinate system (P5 uses an average element coordinate system)- 2
DVX, DVY, DVZDirection vector of pressure P5 2 2

- Average normal pressure (P1AVG), including hydrodynamic ocean pressure when KEYOPT(8) > 1

- Average tangential-X pressure (P2AVG)

- Average tangential-Y pressure (P3AVG)

- Average tapered normal pressure (P4AVG)

- Effective value of vector oriented pressure (P5EFF)

2 2
AVERAGE OCEAN PRESSUREAverage normal hydrodynamic ocean pressure 3 3
TEMPSurface temperatures T(I), T(J), T(K), T(L), T(M), T(N), T(O), T(P) 4 4
DENSITYDensity 5 5
MASSMass of element 5 5
FOUNDATION STIFFNESSFoundation Stiffness (input as EFS) 6 6
FOUNDATION PRESSURESFoundation Pressures 6 6
SURFACE TENSIONSurface Tension (input as SURT) 7 7

  1. Available only at centroid as a *GET item

  2. If pressure load

  3. Only if KEYOPT(8) > 0

  4. If temperature load

  5. If dens > 0

  6. If EFS > 0

  7. If SURT > 0

Table 154.3: SURF154 Item and Sequence Numbers lists output available through the ETABLE command using the Sequence Number method. See The General Postprocessor (/POST1) of the Basic Analysis Guide and The Item and Sequence Number Table in this reference for more information. The following notation is used in Table 154.3: SURF154 Item and Sequence Numbers:


output quantity as defined in the Table 154.2: SURF154 Element Output Definitions


predetermined Item label for ETABLE command


sequence number for single-valued or constant element data


sequence number for data at nodes I, J, K, L

Table 154.3:  SURF154 Item and Sequence Numbers

Output Quantity Name ETABLE and ESOL Command Input
Item E I J K L
PZ (real)SMISC-1234
PX (real)SMISC-5678
PY (real)SMISC-9101112
PZ (imaginary)SMISC-27282930
PX (imaginary)SMISC-31323334
PY (imaginary)SMISC-35363738
P1AVG (real)SMISC13----
P2AVG (real)SMISC14----
P3AVG (real)SMISC15----
P4AVG (real)SMISC16----
P5EFF (real)SMISC17----
P1AVG (imaginary)SMISC39----
P2AVG (imaginary)SMISC40----
P3AVG (imaginary)SMISC41----
P4AVG (imaginary)SMISC42----
P5EFF (imaginary)SMISC43----
OCEAN PRESS (imaginary)SMISC44----

SURF154 Assumptions and Restrictions

  • The element must not have a zero area.

  • The surface-tension load vector acts in the plane of the element as a constant force applied to the nodes seeking to minimize the area of the surface. If the nodes of the element are not coplanar when using surface tension, equilibrium may be lost.

  • For structural large-deflection analyses, the loads are applied to the current size of the element, not the initial size.

  • Surface printout and foundation stiffness are not valid for elements deactivated (EKILL) and then reactivated (EALIVE). Surface printout does not include large strain effects.

  • Nodal hydrodynamic pressure output is not available.

  • For rezoning, only normal and tangential pressures applied on SURF154 are supported. (That is, rezoning support is available only for pressure on faces 1, 2 and 3.)

SURF154 Product Restrictions

When used in the product(s) listed below, the stated product-specific restrictions apply to this element in addition to the general assumptions and restrictions given in the previous section.

ANSYS Mechanical Pro 

  • Birth and death is not available.

  • Linear perturbation is not available.

  • Ocean loading is not available.

  • Rezoning is not available.

ANSYS Mechanical Premium 

  • Birth and death is not available.

  • Rezoning is not available.

Release 18.2 - © ANSYS, Inc. All rights reserved.