Benjamin Du's Activities

Dynamic superelement force file generation through dynamic time history wave, wind force analysis type.

Benjamin Du — Mon, 07 Jun 2021 06:33:04 GMT

When using SACS for creaction of dynamic superelement, it contains structural file (matrix, mass and damping etc,) and force file. Now it has been verified that the structural file can be OK. My question is on the force file.

In the user manual, it teaches a way t generate the force file through dynamic wave response analysis, which can output 'dsefrc' file for the next step. The key problem here is for the offshore jacket substructure with inclined tube, as it can convert the direction of upper load, namely the gravity from tower, turbine and itself weight, whose direction are vertical but will cause horizontal load at the mudline tube. Then in the real dynamic wave response, the horizontal load of tube at the mudline will combine this converted load with wave load.

So in order to consider this converted load, dynamic time history wave, wind force analysis type was used, with gracity and turbine bending momont from the upper part added at the substructure top. However, the dynamic superelement force file had no change. In another words, the dynamic superelement point at the substructure top considered solely the wave force, and neglected the converted load from the structural weight.

If it is a UC check analysis, I know after the dynamic wave response, it needs a post calculation which could combine the load coming from different source. But here is a dynamic superelement creaction calculation, I don't know how to do it. Or, does SACS can provide another way to have dynamic superelement force file? If so, I could combine the above two loads by hand and input for calculation.

Last, in my own viewpoint, the dynamic superelement force file is mainly an external load. In all the other structural analysis, the SACS could only give a structural internal load, which are used to UC check. How to examine the external load of structure except wave load?

Water pressure in the gap between pile and soil

Benjamin Du — Sat, 18 Sep 2021 08:18:35 GMT

Hello, I have a doubt whether the Plaxis-3D could simulate the water pressure in the gap between pile and soil. The background of this is when cyclic load applied at the offshore monopile, the gap would appear at least on one side of pile, which would reduce the lateral capacity of soil. I know in the Plaxis-3D, gap closure is setup to adjust the interface condition, where compression takes effect until there is contact between the pile and the soil, when the load is reversed. But in the process of this, dose water pressure in the gap will take effect, as I marked in the above picture? If so, how could be proved?

How to import Craig-bampton super element in a dynamic SACS analyses ?

Guillaume Luria — Thu, 04 Oct 2018 14:10:25 GMT

I created a Craig-Bampton dynamic super element as per methodology described in "SACS Dynamic Superelement" document.

I created a wave response file so as to have be able to create a reduced force vector.

Spectral check is directly done in the listing file of the super element calculation, however I would like to proceed with a spatial check of my super element.

Thus, I would like to compare interface joint displacement of the super element while I apply the same wave on it than on the full model (a jacket).

However, I cannot find a wat to import the Craig-Bampton super element into SACS.

Could you please explain me how to proceed ?

semi-coupled offshore foundation calculation

Benjamin Du — Fri, 07 Aug 2020 07:59:12 GMT

I noticed that the new edition SACS gives a new function, which enable user input time history displacement instead of load from the upper load effect of wind turbine. When combining this with the wave load, dynamic behavior can be obtained. When have a try, I realized that the sacs failured to read the displacement I input, and the errror is like below. It seems that sacs only can be available when inputting the time history load.

*** ERROR IN READING THLOAD FILE RECORD AS FOLLOWS
THDISP 1UNI 0.02 ABC MMN 1.0 1.0

Can anyone give some advice how to input time history displacement correctly?

波浪谱疲劳分析提取结构特定位置的疲劳荷载（荷载幅值和循环次数）？

Benjamin Du — Fri, 29 May 2020 03:41:49 GMT

如题，是否可以在结构波浪谱疲劳分析计算中，提取结构特定位置的疲劳荷载（荷载幅值和循环次数）？

SACS-SCF

JAYAN VARGHESE — Thu, 30 Jan 2020 08:09:49 GMT

Has Lotsberg's update to Efthymiou SCF been implemented in SACS?

SACS读取时序风机载荷错误

Benjamin Du — Fri, 22 May 2020 02:37:46 GMT

海上风机时序波浪、风机载荷动力响应时，在SACS输入基础顶的风机载荷（6个自由度载荷）。在计算文件WVRNCF查看输入的时程载荷，发现FX\FY\FZ\MZ都和输入载荷完全匹配，但是MX/MY载荷出现不匹配。这是什么原因造成的？突然发现两年前的一次模拟也有类似现象。相关证据如下：

第一幅图以MX载荷示例，A处数据为bladed提供的基础顶载荷，B处为force time history input file文件载荷，C处为WVRNCF文件的载荷。A和B相同，说明我输入SACS没有问题，和C有区别说明SACS读取出现错误。同样，也可以从MX两个时程图的峰值发现两者的差异。

第二幅图以MZ显示为例，数据完全吻合。

关于风机机头叶轮的模拟问题

wuxmei@sh163.net — Tue, 26 Mar 2019 01:20:03 GMT

关于风机机头叶轮的模拟问题：在风机-基础结构计算过程中，风机机头叶轮一般通过添加质量点的方式进行模拟，但是这样就忽略了机头与叶轮的转动特性，如何在sacs中添加结构的转动惯量呢？（只有质量点，无实体模型；转动惯量已经计算得出）

SACS软件中LRFD和WSD，在设置上有哪些主要区别？

中油奥特雷勇 — Mon, 25 Mar 2019 07:39:12 GMT

海上升压站的结构设计规定使用荷载抗力系数法（如LRFD API RP2A 1st）。请问SACS软件中应用LRFD和WSD，在设置上有哪些主要区别？

effect of flooded on frequency

Benjamin Du — Tue, 20 Aug 2019 01:32:37 GMT

当前考虑海洋结构物的模态计算法为一致质量方法（consistent approach）。浸没在水下的杆件要设置为flooded，这个设置对模态有一定影响。请问，管内的水是如何参与到模态计算当中的，是当作结构的一部分吗？跟Bladed对比，Bladed当中也有flooded设置，此外还有一个sealed的概念，即水在管内是封闭的还是可以自由进出的。发现这些设置对同样模型下的频率有影响。

桩土文件中土参数和p-y曲线混用

Benjamin Du — Thu, 18 Jul 2019 08:07:23 GMT

尝试，在桩土文件中土参数的输入和p-y曲线的输入是可以共存计算的。

请问是否确认过这样计算土反力和桩变形的准确性？

桩基竖向承载力计算的问题

wuxmei@sh163.net — Tue, 19 Feb 2019 08:21:51 GMT

PSI帮助文件中提供了如下三种计算竖向承载力的方法，请问在psiinp文件中分别是如何体现的？（相关设置参数在哪里？）

使用SACS axial adhesion(即输入各土层侧摩阻力值)计算出来的桩基竖向承载力（抗力）与使用规范手动计算（侧摩阻力乘以面积）的承载力相差较大，请问出现这种情况的原因？