ActiveSEEP: Submittal Report

We were required to develop a software application revolving around a ‘visual’ component, namely one created/manipulated in the AutoCAD environment, and that would of course tackle a civil engineering application/problem. Accordingly, we took our time skimming through virtually all civil engineering problems involving an inherently ‘visual’ solution methodology to which we were exposed. That is, one that would make of the CAD environment a source of input to the problem under study, and not just a medium for illustrating results or reproducing maps/diagrams; hence making the 2-way interaction with AutoCAD the essence of such a VB/CAD application. Other selection criteria were the topic’s relative originality when compared to current and previous endeavors in this course and/or problem theme, it’s practicality by achieving a notable level of aid to the targeted user (through minimizing the amount of time & effort consumed in tackling the same problem using other means), it’s educational ‘multidimensionality’ that would have us benefit in multiple software development aspects in pursuing such an endeavor, and finally it’s concise and focused scope without which it would be impossible to develop a shrink-wrapped functional product given such limited time-frame and personal resources.

The topic we found most intriguing and readily satisfying to most, if not all, of the criteria just mentioned was developing a highly flexible drawing environment for defining numerous 2-D groundwater seepage setup variations to act as a CAD port to ‘LISA’, a finite element analysis engine. Supported problems can be defined in a matter of seconds, after which the user can choose among many of ActiveSEEP’s ‘meshing’ tools to draw/refine his desired finite element grid. The user can then choose to have his analysis results ‘visually’ presented in the form of colorful contour plots using the ‘LISA Graphic Explorer’, or have them reported in spreadsheet format for any additional statistical/numerical manipulation using ActiveSEEP’s export-to-Excel feature that uses a LISA output file-specific text trimming algorithm.

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Project Description

q Prelude to Deciding on Methodology

Originally, we aimed at using flow nets (as a solution to Laplace’s 2-D continuity equation in an isotropic medium) for calculating seepage and uplift pressure under hydraulic structures. In simplest terms, such an application, if successfully realized, was believed to remove the amount of subjectivity or inaccuracy in the cumbersome task of manually drawing a system of flow & equipotential lines that should be orthogonal and proportionally spaced. However, we then realized that by adopting such a solution mechanism we will have to limit our software application to not more than a few supported problem configurations (impervious structure combinations, number of soil layers, soil isotropy vs. anisotropy, etc…) due to the indispensable human-judgment involved in correctly drawing a system of flow & equipotential lines. Moreover, the final solution, had the ‘flow nets’ method been adopted, would only be approximate and farthest away from ‘exact’ when compared to the other mathematical/numerical methods used to solve the same problem.

Accordingly, we decided on using either the finite differences analysis (hereafter referred to as FDA) if we were to write the solution algorithms, or use the finite element analysis engine (hereafter referred to as FEA) of a commercial software that exposes its own algorithms or provides some sort of an ActiveX port to its object model. Hence the challenge was in either writing a less-accurate FDA code that accounts for all possible nodal boundary conditions and have it optimized to avoid draining the host system’s resources, or do an extensive search on available FEA software applications with sufficient documentation on how to access/manipulate their functions or object model. Being uncertain about realizing either of the methods with the limited time frame and resources allocated to the project, we embarked each in a separate direction; one set to deriving the FDA continuity equations for any node at any boundary in any soil layer of a certain seepage problem setup (which has been successfully derived), whereas the other was ‘exhaustively’ experimenting with ‘LISA’, a German FEA commercial software product with a viable license and adequate documentation.

Being able to subdue ‘LISA’, redirect its capabilities to serve our problem, and enforce a seamless CAD->LISA->Text Editor->EXCEL linkage, we finally decided on adopting ‘LISA’ as ActiveSEEP’s core FEA engine. Better put; ActiveSEEP becomes an AutoCAD port for 2-D FEM seepage modeling in ‘LISA’. ‘LISA’s OLE-Interface (object linking and embedding) is then invoked via its ActiveX port to solve the finite element grid produced by ActiveSEEP.

Of course, our initial attempt at deriving the necessary equations manually for an FDM solution did not go in vain. For, it provided us with insight on how ‘LISA’ works, what continuity & boundary conditions exist at different nodes/elements, and an appreciation for the amount of time, effort, and precision it takes to develop a complete FEM/FDM solver; all of which are definitely beyond the scope of this VBA for AutoCAD assignment.

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q Theory & Mechanism behind ActiveSEEP

A clear-cut line can be draw between the tasks solely carried out by ActiveSEEP:

§ Helping the user define his problem; recognizing what the user has drawn or intends on drawing; and/or checking the integrity of the defined problem before ‘meshing’ and, later on, analyzing the problem.

§ Providing the user with tools to define his grid/mesh; checking the grid/mesh integrity; sorting the grid/mesh nodes, combining them into ‘LISA’-specific elements, and assigning them boundary conditions (all in a manner that is to be compatible with ‘LISA’s input file requirements); passing the final grid/mesh to ‘LISA’ for analysis; and/or reproducing results in spreadsheet format for any further required statistical/numerical manipulation.

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q ActiveSEEP Features & Capabilities

Given the above two distinct sets of ActiveSEEP tasks, the following detailed overview of its features is meant to shed light on ActiveSEEP’s capabilities in a sequential manner (sequence of defining/analyzing a problem and sequence in which such tools are presented on ActiveSEEP’s custom 4-level menu bar):

§ Drawing Tools in Problem Definition – Defining a problem in ActiveSEEP can be done in one of two ways: (1) Using AutoCAD’s ‘Line’ command to draw the impervious layer, ground level, HGL(s), and soil layers as horizontal lines and then placing each set in its allocated ‘Layer’ (embedded in project drawing – ActiveSEEP.dwg); or (2) Using ActiveSEEP’s custom-menu tools “Problem Definition” tools to draw the necessary objects (here ActiveSEEP automatically sets the object entities, properties, and layers.)

The former alternative would serve a well-versed AutoCAD user best; for he can define his entire problem using a single ‘Line’ command (traversing multiple lines), trimming the unnecessary lines, and placing the rest in their corresponding ‘Layers’ (of course, ActiveSEEP will check the integrity of what he has before any analysis-related function.) On the other hand, an AutoCAD novice can just stick to the ActiveSEEP custom-menu to define his problem.

Nonetheless, when an impervious structure is to be defined, the custom-menu has to be used to select/insert a structure. Three impervious structures are provided:

o “Regular Dam”: This structure can sink below the ground level (or rest on it); is characterized by a much higher HGL on one side as compared to the other; and can coexist with another 2 “Pile” structures.

o “Earth Dam”: This structure cannot sink below the ground level (has to rest on it); is characterized by any HGL(s) at any heights on both sides; and can coexist with another 2 “Pile” structures

o “Pile”: This structure has to be below a dam’s bottom (if coexisting with dam); is rectangular and characterized by having any width-to-length ratio (i.e. not necessarily slender as the name ‘Pile’ might imply); and can coexist with any dam and another pile

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§ Mesh vs. Grid Tools – The user has the option of either manually defining his grid thus defining each and every aspect of it, or using ActiveSEEP’s “Auto Mesh” tool. (Hereafter, all such manual attempts will be referred to as those relating to a ‘grid’ definition, whereas the ‘mesh’ terminology will be used whenever the user opts to use the “Auto Mesh” tool.

When using the “Auto Mesh”, all the user needs to specify, once his problem definition is deemed ‘error-free’ by ActiveSEEP, is the number of horizontal & vertical nodes or lines in his mesh (a number above a lower limit required to draw the essential mesh elements, and below an upper plateau that would drain system resources and/or surpass ‘LISA’s allowed number of nodes under this free license of maximum 1300 nodes.) ActiveSEEP then produces a ‘3DPolygonMesh’ AutoCAD object of the required size and automatically adjusts the mesh by resizing its rectangular elements to engulf all impervious edges and seepage boundaries in order to capture the essence of the problem and automate the repetitive mesh element-sizing and boundary condition-assigning tasks usually carried out by the user.

Even when the user chooses to draw his own grid, ActiveSEEP still readily provides the user with the critical grid lines required to traverse problem boundaries and impervious edges. The “Draw Critical Elements” feature draws what we can consider the smallest possible grid (coarsest grid) required to properly (yet not sufficiently) simulate the seepage problem under study. In contrast with the rigid ‘3DPolygonMesh’ entity produced by “Auto Mesh”, the elements drawn by “Draw Critical Elements” are simple ‘Line’ entities placed in the predefined ‘Gridlines’ AutoCAD layer which the user can move, copy, paste, delete, or add to (refined the grid) using basic AutoCAD commands.

When using either grid/mesh definition technique, users needs not care about nodes in impervious regions; ActiveSEEP automatically detects such nodes and removes them from the node numbering procedure which places node numbers in their respective Autocad layer.

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§ Pre-Analysis Integrity Checking Tools – Since the user is granted the luxury of working outside the realm of ActiveSEEP and defining the entire problem – excluding impervious structure – using basic AutoCAD commands, continuous ‘checking & approval’ of what has been drawn and what still needs to be drawn is essential before passing the reins to ‘LISA’ for analysis. Of course, had this been intended to be processed in ‘batch’ format, a final overall ‘check’ before running ‘LISA’ would have done the job. However, the objective is giving ActiveSEEP an ‘interactive edge’, where it interferes, guides, alerts, restricts, and approves of whatever the user draws.

To achieve this, an integral component (procedure) that takes an “IsImplicit” argument was developed to check all problem definition-related errors (and not run-time errors). The “IsImplicit” argument is passed when other procedures want to implicitly use this ‘problem checker’ which most ActiveSEEP functions need to proceed. Moreover, it contains 30+ different checks with custom dialogs/message boxes used to caution or approve the user’s progress after which it automatically dimensions approved elements.

Another ‘checker’, specific to manually defined grids, is triggered to check the grid (entities used, skewness of gridlines, start/end points of gridlines, etc…) and provide grid-related statistics (number of nodes, horizontal gridlines, & vertical gridlines.)

The “Pre-Run Integrity Check” provided with the “Analysis” tools is used to run both checks on a supposedly complete problem setup (problem + grid/mesh.) Of course, all 3 checkers can be initiated by the user to track his progress/errors and are of course implicitly triggered by ActiveSEEP before performing any analysis-related tasks.

§ Defining Problem Properties – Properties in a seepage problem relate to the seeping fluid (reflected in its ability to permeate or seep, thus no fluid related properties are required), the porous media (soil layers; also reflected in the seepage constants, k_z & k_x; hence anisotropic conditions are supported), the desired system of units (metric and imperial), and finally the heights of the hydraulic grade lines on either side of the central impervious structure (extracted from drawing; to be overridden by the user at any time.) ActiveSEEP automatically reads the number of layers indicated in the drawing and asks for as many seepage constants.

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§ Embedded Sample Problems – ActiveSEEP ships with 3 predefined sample problems representing different seepage configurations to be modeled, and are also demonstrative of ActiveSEEP’s various drawing & ‘meshing’ techniques. The examples are constructed in run-time; all what remains for the user to do is trigger his desired analysis option. To maximize the benefit from such samples, the user is urged to modify, reassign properties, resize grids/meshes, etc… of the samples after being drawn (by using the regular ‘Erase’, ‘Line’, and ActiveSEEP commands); then re-running the analysis and monitoring the impact of the changes he enforced. The following is a brief description of each sample (an elaborate walkthrough of Sample Problem II is provided later on in this document):

o Sample Problem I: Composed of 1 earth dam resting on ground level and 1 underlying cut-off wall or pile; single layered soil; 1 HGL is at 0-level; anisotropic soil conditions prevail; a manual grid has been constructed.

o Sample Problem II: Composed of 1 regular dam sinking below ground level and 2 underlying cut-off walls or piles; single layered soil; isotropic soil conditions prevail; an “Auto Mesh” of 180 nodes has been constructed.

o Sample Problem III: Composed of 1 cut-off walls or piles central structure; multi-layered soil (3 layers); isotropic soil conditions prevail; an “Auto Mesh” of 80 nodes has been constructed.

§ Other Tools – Other tools under the ‘Clear’ and ‘View’ subsets are provided. The user can either delete the whole problem, all grid/mesh related items, or just the dimensions and notes properties written in text on his drawing by ActiveSEEP. Under ‘View’, the user can choose to remove all the displayed toolbars with the click of a button and retrieve them back whenever he desires. He can also turn on/off the node numbers on his grid/mesh.

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§ Analysis Tools – The procedure through which a problem is analyzed can be reduced to the following:

à ‘Problem Definition’ is approved by ‘Problem Checker’

à ‘Grid/Mesh’ is approved by ‘Grid/Mesh Checker’

à ‘Grid/Mesh’ is passed to a ‘Node Sorter’

à ‘Sorted Nodes’ are passed an ‘FEA Element Former’

à ‘ActiveSEEP’ passes ‘FEA Elements’ to ‘LISA FEA Modeler’

à ‘LISA FEA Modeler’ writes in .OUT format an ‘Output Text File’

à ‘ActiveSEEP’ trims/retrieves required results from ‘Output Text File’

à ‘ActiveSEEP’ sends results to customized ‘Excel Worksheet’

This port to Excel can be used to perform any extra statistical or numerical calculations or other operations (querying, sorting, and filtering) on the exported results. The results fall under fall fields/columns: node numbers, potential head, velocity in the x-direction, and velocity in the y-direction. The user can also use the ‘LISA Graphic Explorer’ to view the .GPH file produced when ‘LISA’ performs the analysis initially. In ‘LISA’, colorful contour plots of the head, x-velocity, and y-velocity are instantaneously rendered.

§ ActiveSEEP Help – An HTML Help file has been compiled to be distributed with ActiveSEEP. It follows that online assistance is readily provided; collapsible TOC entries, hyperlinks, and index keywords have been also included to facilitate users’ navigation through ActiveSEEP Help. Moreover, entries to the corresponding sections of the help file have been provided under distinct tool subsets on the menu bar to provide a sort of context-sensitive help. A link to the authors’ website is also provided for regular documentation updates and/or news on other projects or products.

§ About, Prelude, License, & Specs Form – This is a form that is loaded as ActiveSEEP loads. It contains the ActiveSEEP Logo, an ‘About ActiveSEEP’ & its developers tab, a ‘License, Disclaimer, & Terms of Use’ tab containing all proprietary notes for ActiveSEEP & ‘LISA’, and a tab containing their specs & limitations.

q Distinctive Merits of ActiveSEEP

ActiveSEEP tackles a specific problem and has focused objectives. It is in such a context and in such a context only that it would be reasonable to compare ActiveSEEP with other peer products. Given our limited undergraduate experience with FEA and FEA software applications, we have been only acquainted with ‘PCA Mat’ (for calculating stresses, deflections, and stresses under mat foundations) & ‘LISA’ as commercial FEA software products. Accordingly, we will be comparing the ‘meshing’ techniques in ActiveSEEP with those available in the former two products.

§ As compared to ‘PCA Mat’ – The way to draw a mesh over a mat model in ‘PCA Mat’ is by specifying the x-coordinates of the vertical grid lines and the y-coordinates of horizontal grid lines. This has to be done in a dialog box which in turn draws the grid lines on screen. Not any sort of direct edit/manipulation of those grid lines can be done on screen. To delete, alter location, or add grid lines, the same dialog box has to be reopened. Of course, the responsibility of properly defining grid lines to capture the mat boundaries and load application nodes/elements is solely that of the user. In ActiveSEEP, however, both the “Auto Mesh” (producing a single 3DPolygonMesh object) and the “Draw Critical Elements” (producing a series of essential grid line entities) auto adjust to all necessary boundaries. Also, the user can delete, add, copy, move, stretch, trim, extend, etc… a grid line at anytime without opening a special dialog box to do the job in an implicit manner. The benefit ‘PCA Mat’ & ActiveSEEP have over ‘LISA’ is that you don’t have to define the connectivity of nodes in elements (that is, specify in counter clockwise orientation the nodes an element connects.) However, this can be attributed to the fact that ‘LISA’ has an extensive library of elements to choose from including (and is not restricted to) triangular & 8-node 2D elements and cube & tetrahedron 3D elements for example, which makes the task of automating node connectivity very cumbersome.

§ As compared to ‘LISA’ – ‘LISA’ is a much more advanced FEA modeling tool that tackles a multitude of applications including structural, mechanical, dynamic, heat transfer, fluidmechanical, and dynamic response analysis applications in 2D and 3D model spaces along with numerous result plotting and streakline generation tools. However, it’s in this diversity of applications that ‘LISA’ becomes a ‘master of none’ by attempting to be a ‘master of all’; doing a bit of everything yet perfecting nothing. To define a custom problem in ‘LISA’, one has to define the coordinates of every node in the grid and then move to assigning the nodes to elements (in the required counter clockwise orientation), and then assign boundary conditions to nodes… a process that seems endless in the case of a large mesh. In fact, for the same problem, defining it in ‘LISA’ would take as much as 10 times more the time and effort to do that in ActiveSEEP (the more the number of nodes, the more exaggerated the time consumed differential shall be come.) But of course, ‘LISA’ can solve 3D seepage problems, skewed boundary & impervious edge conditions, unsteady-flow, etc… all of which require additional detail and patience from the ‘LISA’ user.

All in all, in ‘LISA’ and similar products, you define your model by defining its grid. The grid represents the model to be simulated. In ActiveSEEP, however, you define a simple problem for ActiveSEEP to read, understand, digest, and issue an appropriate mesh in return or guide you to construct one.

§ As compared to ‘flow nets’ method – As to the seepage problem itself, the only way to solve the problem besides using an FEA/FDA solver is using the ‘flow nets’ construction methodology. Results obtained using ‘flow nets’ vary from user to user, as there is a high degree of subjectivity and human judgment required in drawing an error-free system of flow & potential lines. Add to this the inaccuracy of the results obtained due to usually approximating the ratio of potential drops to number of flow lines by an integer. Moreover, flow net construction is arguably impossible in cases of layered soil and anisotropic conditions. Nevertheless, the ‘flow net’ technique remains the only manual way of solving a seepage problem.

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Software Tools Used

In developing ActiveSEEP, five major tools were used: AutoCAD, VBA, LISA, Excel Xp, and HTML Help Workshop, along with other minor tools such as FrontPage Xp, Paintbrush, Printscreen 2000, Notepad, Microsoft Visio 2002, and Word Xp:

q AutoCAD

AutoCAD is the host environment from which ActiveSEEP runs and links to all other applications involved. AutoCAD has been favored over other CADD software (computer-aided drafting & design), because of its popularity, ease of use, and built-in VBA. AutoCAD will serve as a medium for the user to define his problem and generate the desired grid/mesh, and as a tool for us as developers to automate the calling of various functions provided by AutoCAD through VBA to extract the necessary information needed to create an input file compatible with ‘LISA’s requirements. The embedded VBA also facilitated the link to other applications from the AutoCAD environment. The main disadvantage that we faced while using AutoCAD is the often bug-prone interface between AutoCAD & VBA, which suggests that VBA has yet to be improved before providing seamless compatibility with AutoCAD. Moreover, there are many AutoCAD functions not supported by VBA, which makes it, although superior to VisualLisp, still inferior to the much more capable ObjectARX that utilizes a C++ rather than BASIC core.

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q Visual Basic for Applications

Microsoft VBA is an object-oriented programming environment designed to provide rich development capabilities similar to those of Visual Basic (VB). The main difference between VBA and VB is that VBA runs in the same process space as AutoCAD, providing an AutoCAD-intelligent and extremely fast programming environment.

VBA also provides application integration with other VBA-enabled applications. This means that AutoCAD, using other application object libraries, can be an Automation controller for other applications such as Excel, which was used to report that analysis results in spreadsheet format.

The AutoCAD ActiveX/VBA interface represents several advantages over other AutoCAD API environments:

ü Speed: Running in-process with VBA, ActiveX applications are faster than either Auto LISP or ADS applications.

ü Ease of Use: The programming language and development environment are easy to use and come installed with AutoCAD.

ü Windows Interoperability: ActiveX and VBA are designed to be used with other Windows applications and provide an excellent path for communication of information across applications such as Microsoft office applications, and other ActiveX servers.

ü Rapid Prototyping: The rapid interface development of VBA provides the perfect environment for prototyping applications, even if those applications will eventually be developed in another language.

ü Programmer Base: AutoCAD ActiveX and VBA technology open up AutoCAD customization and application development for Visual Basic Programmers around the world.

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q LISA

LISA is a finite element analysis software, which allows software developers to call its function through an ActiveX Server. The Software Application that calls the function is called the ActiveX Client; hence in this case ActiveSEEP functions as the client, whereas ‘LISA’ is the ActiveX server. The advantage provided is that the developer can embed ‘LISA’ as a hidden engine and use it to run an FEM analysis. The main disadvantages encountered were trimming the output file, not being able execute to the ‘LISA’ application from AutoCAD, and the lack of documentation on the ActiveX functions of ‘LISA’.

To view the output file one can either open it as a text file using a text editor or by trimming it using VBA and displaying the output on excel, word etc… The trimming had to be curtailed to match the specific layout of the ‘LISA’ output file. The next disadvantage that we faced is failing to open ‘LISA’ from within the AutoCAD VBA, in order to display contour plots of results in its ‘Enhanced Graphic Explorer’. The user will have to open ‘LISA’, launch the ‘Enhanced Graphic Explorer’, and open the required “.GPH” file to view the potential head and velocity contour plots. As to the lack of documentation, we had to experiment (and sometimes guess) many of the variable/arguments needed to trigger a certain function and retrieve a certain ‘LISA’ object from its object model.

ActiveSEEP used the ‘LISA’ engine in a discrete manner unperceivable to the user to solver the seepage problems defined in AutoCAD. ActiveSEEP would extract the coordinates of the nodes from the AutoCAD drawing and use ‘LISA’ functions to generate the “*.vfd” file that is needed to create the input file. After creating the nodes, ActiveSEEP would call a different function that would create 4–nodal elements that are specific to fluid analysis through porous media. ActiveSEEP has to specify the nodes that are to be joined by the element when calling the ‘LISA’ function. The algorithm used is one that will look at the coordinates of the first and, depending on its position in the mesh, will specify what the other 3 nodes are. If the node is in an ‘impervious region’ then the ‘LISA’ function is not called and no element is formed, this is done to prevent having elements inside a sinking ‘Dam’ or ‘Pile’ structure. Boundary conditions and element properties are then extracted and assigned. All nodes that are located inside an ‘impervious region’ are removed from the “*.vfd” file through a ‘LISA’ delete function that is called after identifying the nodes by ActiveSEEP. The ‘LISA’ input file is generated next; this file is than analyzed by ‘LISA’ and an output file is generated “*.OUT”, which, in turn, is trimmed and exported to Excel.

Also a “*.GPH” file is produced. This file can be viewed using the ‘LISA’ ‘Enhanced Graphic Explorer’ that displays the equipotential lines in the problem under study. It also displays contour lines for the velocities (in the x-direction, and the y-direction).

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q Excel

Excel is a Microsoft Office application where by a user can perform calculations, analyze information, and manage lists in spread sheets. Excel, as well, uses VBA to facilitate automation and customization of the application; it also has its own application object library. This library can be accessed by either VBA or VB, thus we were able to integrate excel into AutoCAD. The user can choose to have the ‘LISA’s FEA results reported in spreadsheet format for any additional statistical/numerical manipulation using ActiveSEEP’s export-to-Excel feature that uses a LISA output file-specific text trimming algorithm. Now the results can be sorted, filtered, queried, and used generate various charts.

q HTML Help Workshop

This HTML Help compiler, a Microsoft product, was used to bind, edit, and compile the .html files meant to compose ActiveSEEP’s help file. Thus, online assistance is readily provided; collapsible TOC entries, hyperlinks, and index keywords have been also included to facilitate users’ navigation through ActiveSEEP Help.

q Other Tools

§ Microsoft Visio 2002: Microsoft Visio 2002 stencils were used to create ActiveSEEP’s logo.

§ Paintbrush & PrintScreen 2000: Those were used to capture snapshots of ActiveSEEP while running for documentation and sampling purposes.

§ Microsoft FrontPage Xp: FrontPage was used to create the .html pages needed by HTML Help Compiler to create our help file for ActiveSEEP. FrontPage will also be used convert all non-html documentation of ActiveSEEP to html and publish it the authors’ site along with uploading ActiveSEEP.

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Sample Problem

As mentioned in the ActiveSEEP Features & Capabilities section of this report, 3 examples are shipped with ActiveSEEP. Before the detailed demonstration of one of the samples, the reader should be familiar with the objects necessary in any ActiveSEEP seepage problem to be able to perform and FEA analysis:

ü An impervious bottom

ü A ground level

ü A supported combination of impervious structures

ü Hydraulic grade lines on both sides of the structure

ü Permeability of the soil layer(s) in the k_x and k_z direction

ü The grid/mesh for the FEM analysis

The second alternative for defining a problem, as mentioned in Drawing Tools in Problem Definition under ActiveSEEP Features & Capabilities, was using ActiveSEEP’s custom menu to draw the required objects.

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Figure 1: ‘Problem Definition’ submenu

As to grid/mesh definition techniques discussed earlier, the following ‘Finite Element Grid/Mesh’ submenu provides all of ActiveSEEP’s grid/mesh-related functionality.

Figure 2: ‘Finite Element Grid/Mesh’ submenu

The sample problem demonstrated herein is consists of a 50 m wide and 30 m high dam. The depth of the soil layer (1 soil layer) is 30 m and has properties of K_x = 0.5 m/sec and K_z = 0.5 m/sec (isotropic conditions). The hydraulic grade line to the right of the dam is 21 m above ground level and on the left is 4 m above ground level. Both piles are of a width of 1 m and a depth of 15 m and 18 m respectively. ‘Auto Mesh’ is used to draw a 10-row by 18-column mesh, thus consisting of 180 nodes.

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Figure 3: Sample Problem Setup

Then the analysis can be performed and the results viewed either in Excel or in ‘LISA’. The user can also perform an integrity check on his problem to make sure that all necessary components are present. Such functionality is provided in the ‘Analyze’ submenu:

Figure 4: ‘Analyze’ submenu

Before starting the analysis, ActiveSEEP checks the problem’s integrity and displays the properties form in which the system of units, HGL levels, and soil layer properties are specified. (The user has the option of automatically retrieving HGL levels from drawing or overriding them by his own values.)

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Figure 5: ActiveSEEP Properties Form

The analyses results can be either displayed in Excel or can be seen in ‘LISA’s ‘Enhanced Graphic Explorer’. The following figures show the results of the analysis in the alternative mediums:

Figure 6: Excel Report

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Figure 7: ‘LISA’ Potential Head Contour Plot

Figure 8: ‘LISA’ Horizontal Velocity Contour Plot

Figure 9: ‘LISA’ Vertical Velocity Contour Plot

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Specs & Limitations

It is important to differentiate between three distinct categories of specs and limitations as applied to ActiveSEEP:

q Conceptual Specs & Limitations

Ø Flow, in ActiveSEEP problems, is ideal, steady, and confined within known saturation boundaries. Soil layering (composite permeability, k, sections) and soil anisotropy (case of k_x not equal to k_z) are supported.

Ø Seepage problems defined in ActiveSEEP should be orthogonal. That is, subsurface inclinations or skewness in the ground level, impervious bottom, hydraulic grade line(s), soil layers, impervious structure(s), or mesh elements is not supported.

Ø At most, 3 impervious structures can coexist in a single problem; one of which (the center structure) must be either a regular or earth dam. Other combinations would include the cases of a single dam, a single pile, or a dam & a pile.

Ø An 'earth dam' cannot sink below the ground level, whereas the 'regular dam' could. The 'pile' structure can be used to simulate any rectangular impervious structure (any width/length), provided that the pile(s) is/are located within the dam's horizontal boundaries.

Ø The seeping fluid is not restricted to water; however, 'Fluid Properties' should be correctly modified to reflect those of the desired fluid.

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q Computational Specs & Limitations

Ø Numerous restraints have been implemented to guide the user throughout defining the problem geometry and characteristics. Such restrictions also help retain the integrity of the problem so as to generate a mesh compatible with LISA and reflective of user needs.

Ø Unexpected 'error in alignment' or 'line is not horizontal' alerts can be attributed to the use of AutoCAD's object snapping/tracking tools. In such a case, delete and redraw the line avoiding the user of such tools so as to enforce the required alignment or entity sizing.

Ø For code optimization purposes, a maximum displacement error of half the vertical element size under a layer's boundary (< 2%) might result when assigning new permeabilites to elements coinciding with the boundary. Such an error does not exist throughout a layer'(s) interior and is non-existent in the case of unlayered soils.

Ø When loading a saved drawing, nothing has to be redrawn; however, if an “Auto Mesh” was used to create the mesh, it should be retriggered because all variables were destroyed after closing your previous ActiveSEEP session.

Ø ‘LISA’ has to be closed when running any analysis-related feature in ActiveSEEP.

q Excel & Lisa-Related Specs & Limitations

Ø The license shipped with LISA's free version does not permit the analysis of more than a 1,300 node grid. However, it must be mentioned that constructing such relatively sophisticated grids (more than 500 nodes) would considerably drain your system resources and impair LISA's efficiency, without necessarily yielding results that are more accurate that those obtained using coarser meshes. Refer to LISA's extensive documentation (embedded with LISA) for further details.

Ø Refer to Excel's help file for a detailed overview of its specifications and limits. Those of relevance are Excel's "Worksheet & Workbook Specifications" and it's "Calculation Specifications".

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q Reasons Behind Limitations

None of the limitations mentioned above (besides those imposed by ‘LISA’s user license and AutoCAD’s unjustifiable glitches every now and then) exist because of our absolute incapacity to implement them, but because of our relative incapacity to implement them given the limited time frame allocated to this project. We believe “lack of technology” and “lack of experience” are direct consequences of “lack of time”; technology and experience are resources, and time makes resources. Given more time, one would make the technology he seems to need, as he would gain the experience he seems to lack.

q Source Code Propriety & Bug Reports

To our knowledge, ActiveSEEP source code is mostly error-free and serves its purpose with the minimal amount of sophistication required. Nonetheless, it was not designed to sit for a meticulous development appraisal and account for all the subtle glitches one might come to encounter after extensive and 'creative' usage. Yet again we stress, we know not of a single bug currently present; for we would not sign our names to an admittedly bug-prone application. We would highly appreciate you reporting any ‘inconsistencies’ (logical or run-time) you might come across while evaluating ActiveSEEP; for this would help us prepare a more perfected release.

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Epilogue

In short, ActiveSEEP is to be considered as an AutoCAD port for 2-D groundwater seepage modeling powered by ‘LISA's finite element analysis engine. ActiveSEEP is meant to provide a highly flexible CAD environment for the user to define his seepage problem and the corresponding finite element grid/mesh. ‘LISA's OLE-Interface (object linking and embedding) is then invoked via its ActiveX port to solve the finite element grid produced by ActiveSEEP.

The primary advantage of using ActiveSEEP is the convenience and speed with which one can setup a seepage problem, define a grid/mesh, and be able to ‘visualize’ results in the form of colorful potential head and velocity contour plots, or ‘spread’ them in a spreadsheet for further use and manipulation. Traditionally, the bulk of time was spent on preparing and defining the model leaving relatively little time for the analysis and interpretation of model results. By ActiveSEEP, we aim at shifting time allocation to post instead of pre-analysis.

Taking this a step further, we proposed working on an Applied Foundations course project that involves the experimental versus finite element modeling of a series of precisely defined groundwater seepage problem variations. We aim at experimentally defining each problem in the lab (using the ‘Seepage Tank’ available in the hydraulics lab) and in ActiveSEEP and reading/calculating the potential heads at various points in order to assess, quantify, and justify the error and deviation involved. The same problems will also be solved manually using the ‘flow nets’ adaptation of Laplace’s equation to check how far off are the approximate methods we employ.

All in all, are most grateful for and appreciative of the effort and time you are yet to pour into assessing ActiveSEEP and its accompanying documentation.

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References

§ Gibb, John W. and Kramer, Bill (1999). “AutoCAD VBA Programming Tools and Techniques”; Miller Freeman Books.

§ Clark, Jeffrey E. (2002). “VBA FOR AutoCAD 2002: Writing AutoCAD Macros”; Prentice Hall

§ MSDN Library Visual Studio 6.0a

§ LISA Help Documentation

§ Das, Braja M. (1998). “Principles of Geotechnical Engineering” 4^th Edition; PWS Publishing Company.

§ Al-Khafaji, Amir Wadi and Tooley John R. (1986). “Numerical Methods in Engineering Practice”; HOLT, RINEHART AND WINSTON.

§ “Introduction to Groundwater Modeling” (From FEA Library)

§ “Seepage, Drainage and Flow Nets” (From FEA Library)

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