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.

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