Questions tagged [modeling]

Use this tag for questions about numerical or analytical modeling and simulation of engineered systems.

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24
votes
11answers
8k views

From an engineering point of view what are the downsides of a too accurate model?

I was wondering, from an engineering point of view, for what reasons can too much accuracy in modeling be detrimental? From a scientific point of view it seems like it's almost always a benefit, ...
21
votes
8answers
2k views

How do engineers really use numerical simulation?

Disclaimer I'm an applied mathematician by training, not an engineer. My work research primarily focuses on creating new "methods" to solve different PDE's related to solid deformation (elasticity) ...
17
votes
5answers
1k views

Meshing of complex geometrical domains

When using the finite element method, I have always used either already meshed domains or very simple ones. From what I've heard, meshing complex geometries is often outsourced to specialized ...
12
votes
3answers
4k views

Which turbulence models are suitable for CFD analysis on a streamlined vehicle body?

Many commercial and open-source CFD codes implement several closure methods for the non-linear convective acceleration term of the Reynolds-averaged Navier-Stokes (RANS) equations. Common methods (...
12
votes
1answer
3k views

Insufficiently constrained structural model in Ansys

I want to analyze this model that is stressed and deformed. I fixed the lowest of points in the x, y, and z directions, and I pulled top of points upward (y direction). When I run the model in Ansys I ...
10
votes
2answers
595 views

Differential equations of a (simplified) loading bridge

I am having trouble to calculate the differential equations of a simplified loading bridge. The system is build as shown in the picture below (just a sketch): If I use the Newton approach, I am ...
10
votes
1answer
263 views

Developing a stochastic differential equation model for concrete fibers

I am working on modeling concrete fibers (metallic fibers) as a mathematical model. My work is for my thesis. I am a PhD student of numerical analysis, but I am working on a real tunnel project. I ...
8
votes
6answers
544 views

Can two different modeling programs be used to confirm the results of each other?

Computer Models Computer modeling is used in various engineering fields. I am specifically considering structural analysis or finite element analysis (FEA). Sometimes models are used to speed up ...
7
votes
2answers
279 views

Modelling splashing water in FEA

I'm running an FEA on a vessel that has a "splashing water" effect with vibrations. The problem I'm really coming up against is what kind of Young's Modulus and Poisson's ratio to use for the fluids? ...
7
votes
1answer
209 views

Sending out a 12d Civil Design Model

My project team and I delivered the design of a 14ha urban infrastructure development in Sydney for a Client. The project was to hand over the development at a Tender level of design, which would be ...
7
votes
2answers
1k views

How do you model a real-life truss in structural analysis software?

I am trying to recreate the following model of a wooden roof truss provided to me by a truss manufacturer: My question is twofold: What is the common/correct way to model the boundary conditions and ...
7
votes
2answers
785 views

How do I use FEM to derive the torsional constant of an arbitrary shape?

In this question I ask about how to perform a first-principle derivation of the torsional constant of a section. It appears that there is no such analytical derivation for torsional constant, so my ...
7
votes
2answers
117 views

Adding a lubricant to an already lubricious material, how is CoF affected?

I have a dry film moly-graphite lubricant (CoF=.075) and a lubricious CVD coating (CoF=.05). The CoF of each of these lubricious materials was determined using the same ASME standardized test. The ...
7
votes
2answers
1k views

How can I model or simulate motion caused by an internal vibrating motor?

I have a vibration motor contained in an object. The motor looks similar to this: When the motor is running, I want to simulate the movement of the container object that results from the vibration of ...
7
votes
1answer
452 views

Boundary condition for a parallelogram-shaped excavation on an embankment

What we learn in engineering school is often idealistic, with textbook examples showing typical prismatic steel beams with a plastic section classification or excavation in a perfect sand or clay ...
6
votes
3answers
534 views

Is a distributed load in two parts equal to a full distributed load?

I have a structure like such: Due to my lack of knowledge of ANSYS, I have made the singular distributed loading (GI) represented as two distributed loadings (GH and HI). Would this be an accurate ...
6
votes
1answer
939 views

FEM modal analysis computing displacements

I have an FEM model that I am doing a modal analysis of. I wanted to check that how I am computing the physical displacement is the correct way, as I've read a lot of about normalizing modes, ...
6
votes
1answer
480 views

Differential equation of the vertical displacement of a cable

Given a cable (totally flexible) fixed at both ends, subjected to a vertical force $f(x)$ in his plane, with variable area $A(x)$, and variable elasticity $E(x)$ I want to find the differential ...
6
votes
1answer
188 views

Programmable parameter change of Pro/E simulation by using Excel VBA , Matlab, Labview or Pro/E own function

Now, I've been conducting beam simulation by using Pro/E. I would like to change payload(force) of beam step by step, and then plot the relation between deflection and payload(load range : 50kg to ...
5
votes
4answers
3k views

How to simulate car acceleration

I am a high school physics student and I've been trying to simulate the acceleration of a car as it fully accelerates from rest, but I'm finding it's much harder than I thought. Here was my first ...
5
votes
4answers
28k views

How to define Knurl on drawing?

I made this kind of knurl on shaft : but I am not sure how to be define on the drawing. I found some examples but not sure if they are correct. On the examples there type (GV) and depth of knurl and ...
5
votes
1answer
678 views

Discontinuity in mechanism simulation: is the mechanism jammed or is my analysis wrong?

I'm designing a compact mechanism for the deployment of a mast. The idea is that the linear actuator for the deployment is on the other side of the pivot, and a slider increases the lever arm to ...
5
votes
1answer
103 views

Would a partial space elevator work? [closed]

Background The normal space elevator (that reaches from the Earth's surface to a counterweight beyond geostationary) needs a material that's strength/weight ratio is better than any material we have ...
5
votes
2answers
2k views

Normalization and Non-Dimensionalization of a mass balance equation

I would like to ask what is the difference (if any) between normalization and non-dimensionalization. I will try to explain what I have done until now with an equation that I would like to work with ...
5
votes
1answer
126 views

System Identification 1-d altitude control

One dimensional altitude control of a hovercraft. The model's dynamic equations that I came up with are, I treat the hover craft as a rigid particle and my goal is to have it hover at or reach a ...
5
votes
2answers
638 views

Dynamic mass balance in plug flow reactor

So I would like to ask you about a problem I encountered. The case study goes like this: I want to study species distribution inside a packed bed reactor, at first at steady state but eventually what ...
5
votes
1answer
633 views

Coupling in a twin engine, tandem rotor power train

Consider a transmission for a tandem rotor helicopter with two engines and two main rotors such as the one below. Both engines are connected with sprag (one-way) clutches such that an engine's speed ...
5
votes
1answer
254 views

Questions regarding Cornering Stiffness for RC Car

I am a bachelor's level student tasked with modeling the vehicle dynamics of an RC Car that will be made to drive autonomously. I lack prior experience or particularly specific education with vehicle ...
4
votes
1answer
115 views

Modelling gas desorption from a still solution (e.g. a beer)

The common way to model or estimate gas (e.g. CO2) desorption rate from a liquid solution is by using an equation similar to this one $J_{CO_2} = -k_L a(H·C^G_{CO_2} - C^L_{CO_2})$ where $J_{CO_2}$ ...
4
votes
2answers
84 views

Viscosity of select species at atmospheric pressure for very large temperatures?

I'm dealing with hot combustion products flowing through heat exchangers and I'd like to perform some calculations regarding the flow properties (velocity, temperature, pressure and density) as it ...
4
votes
1answer
992 views

Heat Transfer coefficient calculation for hot air flow inside rectangular duct

I am working on modeling of air-heater component. A simplified representation of system is as follows: Cold air flow enters steel duct at one end. Inside duct is Calrod heating element shaped as ...
3
votes
2answers
70 views

connectedness between the output voltage and input voltage

Given this circuit I want to deduce the relationship between the output voltage $U_A(t)$ an d the input voltage $U_E(t)$ using Kirchhoff's current law. We're allowed to assume that $R$, $L $and $C_1$ ...
3
votes
1answer
408 views

Two dimensional plasticity with radial return

Note - This is a duplicate of the question I asked over on Physics which hasn't received any attention. What is the proper method to scale deviatoric stresses back to the yield surface in plane ...
3
votes
1answer
257 views

System model for motor controlled inverted pendulum with rotating motor body (used in camera stabilizer application)

I'm planning to build a head-mounted camera stabilizer for pro GoPro camera. The idea is that when I tilt my head the camera would stay at a user-set angle. I'm using an accelerometer and a gyro to ...
3
votes
2answers
39 views

How to estimate the time cost of interrupting a task and picking it up again later

In terms of personal productivity (single machine scheduling) when a task is interrupted before being done in order to switch to a different task, it incurres a 'tear down' time cost - putting tools, ...
3
votes
2answers
409 views

Specification of linear speed dampers

I'm looking at linear compression dampers and finding them most commonly specified only with a "Max Force" – e.g., 270 lbs. However, since the damping mechanism is provided by hydraulic or pneumatic ...
3
votes
2answers
185 views

Is it possible to apply different boundary conditions on the same model for different load cases?

Instead of creating multiple bridge models with different boundary conditions for differential settlement, and combining the forces output manually in Excel, is it possible to specify different ...
3
votes
1answer
301 views

Should sum of all joint reactions be zero when nodal displacement is applied?

I created a structural model of a laced strut using plate elements. To study second order effects of bow imperfection, I applied a joint displacement of 20 mm in a SAP 2000 v18 model. When the ...
3
votes
2answers
245 views

Modelling a DC motor

I am modellign some examples using the modelling language Modelica. Unfortunately, I am not an electrical engineer, so it is hard to understand the physical behavior of the following example (DC motor)...
3
votes
1answer
2k views

Shear area of atypical section

Shear areas have been obtained for a few different cross-sections. I-sections usually define their shear areas as equal to the product of the height of the section and the thickness of the web (...
3
votes
0answers
27 views

Solidworks Loft error (guide curve not intersecting with profiles)

I am trying to add 'finger grooves' to my model of a brake lever and want to use a loft to do so. I have created (to my knowledge) all required sketches for the loft but SW gives me an error when ...
3
votes
1answer
539 views

Torsional rigidity D vs torsional rigidity factor k vs torsion constant J

I have a physics background so apologize my ignorance. I'm confused by the constants $D$, $\kappa$, and $J$ when it comes to torsion of beams. From what I understand $\kappa$ and $J$ are the same ...
2
votes
2answers
1k views

Viscoelasticity and Hyperelastic model, history and difference

Actually, I see some papers use viscoelasticity or hyperelastic model for the same materials. It seems to me that those models were invented in different eras, and the hyperelastic is a newer model ...
2
votes
1answer
127 views

linearizing a non linear state space equation

I have this 1-DOF helicopter simulator. The motor's armature resistance is $R$, inductance $L$ and motor constant $K$ and reaction torque on the motor shaft is $τ$. $T$ is equal to $k_1w_2^2$ and $...
2
votes
1answer
56 views

Modeling the torque of a real motor

I am trying to control a real inverted pendulum by means of a DC motor, for this I must model the torque of the motor, the work I've done in this direction is the following (which I believe is right): ...
2
votes
2answers
29 views

Force Transmission in Flexible Tools such as this tool

In general, I want understand how the Power transmission in flexible tools works such as this flexible pick up tool in this link: https://www.youtube.com/watch?v=TLbCatz4Pnkv=q9AkmsTNLkY . ...
2
votes
1answer
144 views

Modelling a refrigeration cycle in Excel

Is it possible to model a heat pump cycle without using tools like EES, but using Excel? I am considering to use Refprop application as an add-in in Excel, and model a heat pump cycle. Another ...
2
votes
2answers
223 views

Mathematical modelling of the crank in a two-stroke (diesel) engine

I need to use a mathematical model of the crank in a two-stroke (diesel) engine. Since a real two-stroke engine endures anharmonic motion, I need to implement higher order harmonics - preferably into ...
2
votes
1answer
103 views

How are NPT hole features defined?

I'll be the first to admit that I have always been somewhat confused by best-practice dimensioning standards surrounding pipe threads. While there is a decent amount of literature available online, (...
2
votes
1answer
39 views

Can a system with a response Y(x) = ax + c be called linear?

I made a DC-DC converter its ideal transfer function is: $$ V_0(D) = DV_i $$ I took measurements of its response and then made a linear regression, I got this result: $$ V_0(D) = 0.98DV_i -0.42 $...