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GeoMotions, LLC FAQ (Frequently Asked Questions)



Category: Main -> F.A.Q. For D-MOD2000

Question
·  How are program updates distributed?
·  Who developed the program?
·  How is D-MOD2000 different from D-MOD_2?
·  Who validated the program?
·  What makes D-MOD2000 different from other nonlinear programs?
·  What can I do with D-MOD2000 that I can't do with SHAKE2000?
·  How different are D-MOD2000 and DESRA-2?
·  What are the restrictions of the academic version of D-MOD2000?
·  How is porewater pressure controlled?
·  How is stress strain response controlled?
·  I have a composite soil profile. In the same analysis, can I simulate PWP generation in sand and ignore (disable) PWP generation in clay?
·  Do I need to uninstall an older version of D-MOD2000 before installing the new version with the USB Hardware Key?

Answer
·  How are program updates distributed?

An e-mail is sent to registered users informing them that an update of the program is available. A link to download the update file is included in the e-mail.

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·  Who developed the program?

D-MOD2000 was developed by GeoMotions, LLC; see also Genesis of the Program.

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·  How is D-MOD2000 different from D-MOD_2?

D-MOD2000 is the most recent iteration of D-MOD_2. D-MOD_2 was DOS-based while D-MOD2000 is Windows-based and integrated in fully-interactive graphic interface. D-MOD2000 also executes much faster than D-MOD_2 as many subroutines have been rewritten to enhance speed and numerical stability. D-MOD2000 is supported by GeoMotions, LLC while D-MOD_2 is not.

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·  Who validated the program?

The program was extensively validated during the Pacific Earthquake Engineering Research (PEER) Lifelines project1 2G02 – Benchmarking of Nonlinear Geotechnical Ground Response Analysis Procedures. The analytical work during the course of the 2G02 project was limited to the total-stress analysis. The validation included direct comparison with the closed form solutions for simple excitation cases by Kwok et al. (2007a), blind prediction of the site response in the 2004 Parkfield Earthquake Kwok et al. (2007b), and revisit to the La Cienega and Treasure Island case histories (Stewart et al. 2007).

Effective stress analyses by Matasovic (1993) conducted using early versions of D-MOD also showed reasonable agreements with recorded acceleration and pore water pressure time histories at the Wildlife, Owi Island, and Treasure Island sites. Zhai (2008, submitted for publication on the GEESD IV) recently compared D-MOD2000 and FLAC on F-type site and found excellent agreement in both acceleration and PWP responses. Additional work to validate the effective-stress analysis is ongoing in GeoSyntec Consultants (Dr. Matasovic), at the University of California at Berkeley (Prof. Jon Bray) and in several other institutions in U.S. and abroad.

1 The 2G02 project was sponsored by the PEER Center’s Program on Applied Earthquake Engineering Research of Lifeline Systems and supported by the State Energy Resources Conservation and Development Commission, the Pacific Gas and Electric Company, and the California Department of Transportation’s PEARL program.

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·  What makes D-MOD2000 different from other nonlinear programs?

  • D-MOD2000 is the only nonlinear site response program that already has effective-stress analysis built-in;
  • An extensive database or “ready-made” material parameters (for both nonlinear and effective-stress analysis) is available for D-MOD2000; and
  • D-MOD2000 has a familiar, proven interface (the same interface as SHAKE2000).

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·  What can I do with D-MOD2000 that I can't do with SHAKE2000?

Compared to SHAKE2000, D-MOD2000 has the following advantages: (i) no restrictions with the input acceleration level (D-MOD2000 incorporates a nonlinear constitutive model, while SHAKE2000 is based on an equivalent-linear model that typically extends up to 1% shear strain level. In large earthquakes/soft soils, shear strains in excess of 1.0% can be induced); (ii) D-MOD2000 can directly calculate soil liquefaction potential (D-MOD2000 is an effective stress program while SHAKE2000 is a total stress program); and (iii) D-MOD2000 accommodates for porewater pressure induced “soil softening” (reduction in shear modulus and strength) while SHAKE2000 does not.

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·  How different are D-MOD2000 and DESRA-2?

Very different. They have different stress strain models, different porewater pressure generation models, and different equation solvers. D-MOD2000 is WindowsTM based while DESRA-2 is not.

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·  What are the restrictions of the academic version of D-MOD2000?

In academic version of D-MOD2000, number of time steps is limited to 200. Cyclic degradation of clay option is disabled.

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·  How is porewater pressure controlled?

Porewater pressure generation in is controlled by semi-empirical models by Dobry and Vucetic (for sand) and Matasovic and Vucetic (for clay), with a computed porewater pressure used to degrade the backbone curve in a way that represents the softening and weakening of soils expected at lower effective confining pressures.

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·  How is stress strain response controlled?

At each time step, D-MOD2000 refers to the given stress-strain relation to obtain a value of shear stress (τ) from the current value of shear strain (γ). Because the shear stress is computed directly as a function of shear strain, the slope of the stress strain relationship, that is, the secant shear modulus (Gsec), does not have to be obtained explicitly. The new value of the shear modulus is then used in solving the equation of motion at the next time step. With this scheme mixed boundary conditions can be easily handled as the stresses, displacements or velocities at the boundaries are simply set to the required values (for the one dimensional shear wave propagation problem, the boundary conditions are different for the top and bottom layers but are otherwise the same for all intermediate layers).

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·  I have a composite soil profile. In the same analysis, can I simulate PWP generation in sand and ignore (disable) PWP generation in clay?

Yes.

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·  Do I need to uninstall an older version of D-MOD2000 before installing the new version with the USB Hardware Key?

Yes.

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