Empathy List Archives

CW

Christopher Wright

Tue, Apr 12, 2022 3:00 AM

On Apr 11, 2022, at 3:40 PM, Mohammad A Gharaibeh via Xansys xansys-temp@list.xansys.org wrote:

In conclusion, my dynamic amplification factor is the bending stiffness of
the plate I study.

I'm not entirely certain about the foregoing, 'In conclusion…'. Suggest you check a dynamics texts to make sure. The dynamic amplification isn't the same for all kinds of loads. For example the DAF for a particular load suddenly applied is 2. That includes the effect of the kinetic energy acquired as the structure deforms. I'm not sure I was entirely clear.

Christopher Wright
chrisw@skypoint.com
——
We are the Village Green Preservation Society.
God save Donald Duck, vaudeville and variety.
We are the Desperate Dan Appreciation Society.
God save strawberry jam and all the different varieties.

> On Apr 11, 2022, at 3:40 PM, Mohammad A Gharaibeh via Xansys <xansys-temp@list.xansys.org> wrote: > > In conclusion, my dynamic amplification factor is the bending stiffness of > the plate I study. I'm not entirely certain about the foregoing, 'In conclusion…'. Suggest you check a dynamics texts to make sure. The dynamic amplification isn't the same for all kinds of loads. For example the DAF for a particular load suddenly applied is 2. That includes the effect of the kinetic energy acquired as the structure deforms. I'm not sure I was entirely clear. Christopher Wright chrisw@skypoint.com —— We are the Village Green Preservation Society. God save Donald Duck, vaudeville and variety. We are the Desperate Dan Appreciation Society. God save strawberry jam and all the different varieties.

MA

Mohammad A Gharaibeh

Tue, Apr 12, 2022 1:58 PM

Perhaps I should have been more specific.

In my problem, a clamped plate (all edges) subjected to a half-sine wave
shock profile. I was able to identify the dynamic amplification factor to
be the equivalent bending stiffness of this plate.

Best,
Mohammad

On Tuesday, April 12, 2022, Christopher Wright chrisw@skypoint.com wrote:

On Apr 11, 2022, at 3:40 PM, Mohammad A Gharaibeh via Xansys <

xansys-temp@list.xansys.org> wrote:

In conclusion, my dynamic amplification factor is the bending stiffness

of

the plate I study.

I'm not entirely certain about the foregoing, 'In conclusion…'. Suggest
you check a dynamics texts to make sure. The dynamic amplification isn't
the same for all kinds of loads. For example the DAF for a particular load
suddenly applied is 2. That includes the effect of the kinetic energy
acquired as the structure deforms. I'm not sure I was entirely clear.

Christopher Wright
chrisw@skypoint.com
——
We are the Village Green Preservation Society.
God save Donald Duck, vaudeville and variety.
We are the Desperate Dan Appreciation Society.
God save strawberry jam and all the different varieties.

Xansys mailing list -- xansys-temp@list.xansys.org
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xansys-mod@tynecomp.co.uk and not to the list

--

---====
Mohammad A Gharaibeh, Ph.D.
Associate Professor
Department of Mechanical Engineering
The Hashemite University
P.O. Box 330127
Zarqa, 13133, Jordan
Tel: +962 - 5 - 390 3333 Ext. 4771
Fax: +962 - 5 - 382 6348

---====

Perhaps I should have been more specific. In my problem, a clamped plate (all edges) subjected to a half-sine wave shock profile. I was able to identify the dynamic amplification factor to be the equivalent bending stiffness of this plate. Best, Mohammad On Tuesday, April 12, 2022, Christopher Wright <chrisw@skypoint.com> wrote: > > > > On Apr 11, 2022, at 3:40 PM, Mohammad A Gharaibeh via Xansys < > xansys-temp@list.xansys.org> wrote: > > > > In conclusion, my dynamic amplification factor is the bending stiffness > of > > the plate I study. > > I'm not entirely certain about the foregoing, 'In conclusion…'. Suggest > you check a dynamics texts to make sure. The dynamic amplification isn't > the same for all kinds of loads. For example the DAF for a particular load > suddenly applied is 2. That includes the effect of the kinetic energy > acquired as the structure deforms. I'm not sure I was entirely clear. > > > Christopher Wright > chrisw@skypoint.com > —— > We are the Village Green Preservation Society. > God save Donald Duck, vaudeville and variety. > We are the Desperate Dan Appreciation Society. > God save strawberry jam and all the different varieties. > > _______________________________________________ > Xansys mailing list -- xansys-temp@list.xansys.org > To unsubscribe send an email to xansys-temp-leave@list.xansys.org > If you are receiving too many emails from XANSYS please consider changing > account settings to Digest mode which will send a single email per day. > > Please send administrative requests such as deletion from XANSYS to > xansys-mod@tynecomp.co.uk and not to the list -- ===================================== Mohammad A Gharaibeh, Ph.D. Associate Professor Department of Mechanical Engineering The Hashemite University P.O. Box 330127 Zarqa, 13133, Jordan Tel: +962 - 5 - 390 3333 Ext. 4771 Fax: +962 - 5 - 382 6348 =====================================

CW

Christopher Wright

Tue, Apr 12, 2022 6:40 PM

On Apr 12, 2022, at 8:58 AM, Mohammad A Gharaibeh via Xansys xansys-temp@list.xansys.org wrote:

In my problem, a clamped plate (all edges) subjected to a half-sine wave
shock profile. I was able to identify the dynamic amplification factor to
be the equivalent bending stiffness of this plate.

I question that finding only because the DAF is dimensionless. It's a pure number multiplier defined as the ratio of the maximum deformation under a given load dynamically applied to the deformation under the same load statically applied.It's not obvious to me how stiffness plays a part. Check this article: <https://en.wikipedia.org/wiki/Dynamic_amplification_factor https://en.wikipedia.org/wiki/Dynamic_amplification_factor> Of course if the deformation increases, the stress increases proportionately.

I've always thought the DAF reflects the inertia of the structure. A sudden deformation of (say) a spring-mass system structure imparts motion and therefore additional kinetic energy which adds to the strain energy of deformation. The overall deformation increases as the structure acquires velocity (momentum) 'overshoots' the deformed shape under purely static load. The ratio of the overshoot to the statical deformation is effectively the DAF.

I don't mean to put too fine a point on this, but you might want to refer to a set on statics or strength of materials. The bending stiffness of a structure is a constant physical property independent of loading; the dynamic amplification factor is the ratio of the deformation under a suddenly applied load under the same load applied statically. Bending stiffness is dimensional; the dynamic amplification factor is a pure number. I hop I haven't beaten this completely to death.

Christopher Wright
chrisw@skypoint.com
——
We are the Village Green Preservation Society.
God save Donald Duck, vaudeville and variety.
We are the Desperate Dan Appreciation Society.
God save strawberry jam and all the different varieties.

On Apr 12, 2022, at 8:58 AM, Mohammad A Gharaibeh via Xansys <xansys-temp@list.xansys.org> wrote: > > In my problem, a clamped plate (all edges) subjected to a half-sine wave > shock profile. I was able to identify the dynamic amplification factor to > be the equivalent bending stiffness of this plate. I question that finding only because the DAF is dimensionless. It's a pure number multiplier defined as the ratio of the maximum deformation under a given load dynamically applied to the deformation under the same load statically applied.It's not obvious to me how stiffness plays a part. Check this article: <https://en.wikipedia.org/wiki/Dynamic_amplification_factor <https://en.wikipedia.org/wiki/Dynamic_amplification_factor>> Of course if the deformation increases, the stress increases proportionately. I've always thought the DAF reflects the inertia of the structure. A sudden deformation of (say) a spring-mass system structure imparts motion and therefore additional kinetic energy which adds to the strain energy of deformation. The overall deformation increases as the structure acquires velocity (momentum) 'overshoots' the deformed shape under purely static load. The ratio of the overshoot to the statical deformation is effectively the DAF. I don't mean to put too fine a point on this, but you might want to refer to a set on statics or strength of materials. The bending stiffness of a structure is a constant physical property independent of loading; the dynamic amplification factor is the ratio of the deformation under a suddenly applied load under the same load applied statically. Bending stiffness is dimensional; the dynamic amplification factor is a pure number. I hop I haven't beaten this completely to death. Christopher Wright chrisw@skypoint.com —— We are the Village Green Preservation Society. God save Donald Duck, vaudeville and variety. We are the Desperate Dan Appreciation Society. God save strawberry jam and all the different varieties.

MA

Mohammad A Gharaibeh

Tue, Apr 12, 2022 7:15 PM

Thanks Chris! Maybe I need to dig deeper into this.

--

---====
Mohammad A Gharaibeh, Ph.D.
Associate Professor
Department of Mechanical Engineering
The Hashemite University
P.O. Box 330127
Zarqa, 13133, Jordan
Tel: +962 - 5 - 390 3333 Ext. 4771
Fax: +962 - 5 - 382 6348

---====

Thanks Chris! Maybe I need to dig deeper into this. -- ===================================== Mohammad A Gharaibeh, Ph.D. Associate Professor Department of Mechanical Engineering The Hashemite University P.O. Box 330127 Zarqa, 13133, Jordan Tel: +962 - 5 - 390 3333 Ext. 4771 Fax: +962 - 5 - 382 6348 =====================================

CW

Christopher Wright

Wed, Apr 13, 2022 2:17 AM

On Apr 12, 2022, at 2:15 PM, Mohammad A Gharaibeh via Xansys xansys-temp@list.xansys.org wrote:

Thanks Chris! Maybe I need to dig deeper into this.

I don't mean put too fine a point on it. There's a wide range of approaches to shock and vibrations problems of different sorts, using a range of conventions and assumptions depending on the class of problems and the use made of the results. I've done a fair amount of nuke plant related seismic analysis and some other odds and ends. It's really very cool work, but the connection to real-world dynamic loading is spotty. Lots of conventions are used—like the dynamic amplification factor we're presently about.

--

---====
Mohammad A Gharaibeh, Ph.D.
Associate Professor
Department of Mechanical Engineering
The Hashemite University
P.O. Box 330127
Zarqa, 13133, Jordan
Tel: +962 - 5 - 390 3333 Ext. 4771
Fax: +962 - 5 - 382 6348

---====

Xansys mailing list -- xansys-temp@list.xansys.org
To unsubscribe send an email to xansys-temp-leave@list.xansys.org
If you are receiving too many emails from XANSYS please consider changing account settings to Digest mode which will send a single email per day.

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Christopher Wright
chrisw@skypoint.com
——
We are the Village Green Preservation Society.
God save Donald Duck, vaudeville and variety.
We are the Desperate Dan Appreciation Society.
God save strawberry jam and all the different varieties.

On Apr 12, 2022, at 2:15 PM, Mohammad A Gharaibeh via Xansys <xansys-temp@list.xansys.org> wrote: > Thanks Chris! Maybe I need to dig deeper into this. I don't mean put too fine a point on it. There's a wide range of approaches to shock and vibrations problems of different sorts, using a range of conventions and assumptions depending on the class of problems and the use made of the results. I've done a fair amount of nuke plant related seismic analysis and some other odds and ends. It's really very cool work, but the connection to real-world dynamic loading is spotty. Lots of conventions are used—like the dynamic amplification factor we're presently about. > > -- > ===================================== > Mohammad A Gharaibeh, Ph.D. > Associate Professor > Department of Mechanical Engineering > The Hashemite University > P.O. Box 330127 > Zarqa, 13133, Jordan > Tel: +962 - 5 - 390 3333 Ext. 4771 > Fax: +962 - 5 - 382 6348 > ===================================== > _______________________________________________ > Xansys mailing list -- xansys-temp@list.xansys.org > To unsubscribe send an email to xansys-temp-leave@list.xansys.org > If you are receiving too many emails from XANSYS please consider changing account settings to Digest mode which will send a single email per day. > > Please send administrative requests such as deletion from XANSYS to xansys-mod@tynecomp.co.uk and not to the list Christopher Wright chrisw@skypoint.com —— We are the Village Green Preservation Society. God save Donald Duck, vaudeville and variety. We are the Desperate Dan Appreciation Society. God save strawberry jam and all the different varieties.

UD

Uffe Dal Eriksen

Wed, Apr 13, 2022 7:13 AM

Hi Mohammad,

"When I apply the equivalent static load using the ACEL command, the static displacements are 12 times higher than those of the transient analysis.
Keeping in mind that I am using a simple plate model with fixed boundary conditions at all edges."

A factor of 12 seems too high to be a DAF. Maybe a long shot, but your simple model (thin plate with fixed sides) makes me think of the old example showing the effects of small vs. large deflections. Could your static analysis be small deflection (where I assume the transient one is set to large deflection per default... NLGEOM,ON).

Kind regards

Uffe Dal Eriksen
Energy, Marine Structures
Ramboll Denmark

-----Original Message-----
From: Mohammad A Gharaibeh via Xansys xansys-temp@list.xansys.org
Sent: 10. april 2022 10:14
To: XANSYS Mailing List Home xansys-temp@list.xansys.org
Cc: Mohammad A Gharaibeh mgharai1@binghamton.edu
Subject: [Xansys] Replacing shock load by an equivalent static load

Dear XANSYS Members,

I am trying to obtain a methodology that uses an equivalent static loading in modeling shock impact.

In this methodology, I wanted to use static analysis to generate the same displacements of transient analysis at a certain instant of time. Using simple single-degree-of-freedom theory, I found that the equivalent static "input acceleration (Gst)" is equal to Gst = Xdyn*(wn)^2 where Xdyn is the displacement from transient solution at a time point (t), and wn is the natural frequency of the structure in rad/sec. This equation is also available in Harris' shock and vibration handbook, sixth edition (Equation 20.30).

When I apply the equivalent static load using the ACEL command, the static displacements are 12 times higher than those of the transient analysis.
Keeping in mind that I am using a simple plate model with fixed boundary conditions at all edges.

Is there anything I am missing here? I would appreciate your invaluable suggestions.

I hope that my problem description was clear and sound.

Best Regards,
Mohammad

---====
Mohammad A Gharaibeh, Ph.D.
Associate Professor
Department of Mechanical Engineering
The Hashemite University
P.O. Box 330127
Zarqa, 13133, Jordan
Tel: +962 - 5 - 390 3333 Ext. 4771
Fax: +962 - 5 - 382 6348

---====

Xansys mailing list -- xansys-temp@list.xansys.org To unsubscribe send an email to xansys-temp-leave@list.xansys.org If you are receiving too many emails from XANSYS please consider changing account settings to Digest mode which will send a single email per day.

Please send administrative requests such as deletion from XANSYS to xansys-mod@tynecomp.co.uk and not to the list

Hi Mohammad, "When I apply the equivalent static load using the ACEL command, the static displacements are 12 times higher than those of the transient analysis. Keeping in mind that I am using a simple plate model with fixed boundary conditions at all edges." A factor of 12 seems too high to be a DAF. Maybe a long shot, but your simple model (thin plate with fixed sides) makes me think of the old example showing the effects of small vs. large deflections. Could your static analysis be small deflection (where I assume the transient one is set to large deflection per default... NLGEOM,ON). Kind regards Uffe Dal Eriksen Energy, Marine Structures Ramboll Denmark -----Original Message----- From: Mohammad A Gharaibeh via Xansys <xansys-temp@list.xansys.org> Sent: 10. april 2022 10:14 To: XANSYS Mailing List Home <xansys-temp@list.xansys.org> Cc: Mohammad A Gharaibeh <mgharai1@binghamton.edu> Subject: [Xansys] Replacing shock load by an equivalent static load Dear XANSYS Members, I am trying to obtain a methodology that uses an equivalent static loading in modeling shock impact. In this methodology, I wanted to use static analysis to generate the same displacements of transient analysis at a certain instant of time. Using simple single-degree-of-freedom theory, I found that the equivalent static "input acceleration (Gst)" is equal to Gst = Xdyn*(wn)^2 where Xdyn is the displacement from transient solution at a time point (t), and wn is the natural frequency of the structure in rad/sec. This equation is also available in Harris' shock and vibration handbook, sixth edition (Equation 20.30). When I apply the equivalent static load using the ACEL command, the static displacements are 12 times higher than those of the transient analysis. Keeping in mind that I am using a simple plate model with fixed boundary conditions at all edges. Is there anything I am missing here? I would appreciate your invaluable suggestions. I hope that my problem description was clear and sound. Best Regards, Mohammad ===================================== Mohammad A Gharaibeh, Ph.D. Associate Professor Department of Mechanical Engineering The Hashemite University P.O. Box 330127 Zarqa, 13133, Jordan Tel: +962 - 5 - 390 3333 Ext. 4771 Fax: +962 - 5 - 382 6348 ===================================== _______________________________________________ Xansys mailing list -- xansys-temp@list.xansys.org To unsubscribe send an email to xansys-temp-leave@list.xansys.org If you are receiving too many emails from XANSYS please consider changing account settings to Digest mode which will send a single email per day. Please send administrative requests such as deletion from XANSYS to xansys-mod@tynecomp.co.uk and not to the list

K-

KARTHIK.S - Adv Engg

Wed, Apr 13, 2022 10:49 AM

Hello,

While performing a vibroacoustic analysis,
I am importing the electromagnetic forces from Maxwell to Harmonic system of Ansys.
While doing so, all the odd harmonics are exhibiting zero force values. This scenario is observed in different projects of same type of analysis.
Any ideas on this?

Regards,

Karthik
Dy. Mgr.
TVS,
Chennai.

Hello, While performing a vibroacoustic analysis, I am importing the electromagnetic forces from Maxwell to Harmonic system of Ansys. While doing so, all the odd harmonics are exhibiting zero force values. This scenario is observed in different projects of same type of analysis. Any ideas on this? Regards, Karthik Dy. Mgr. TVS, Chennai.

MA

Mohammad A Gharaibeh

Wed, Apr 13, 2022 1:01 PM

Hi Uffe Dal Eriksen,

Thanks for the reply and for the out of the box way of thinking. However, I
am not turning on the large deflections option.

I will have to set down this weekend and get my head into some books to
understand what’s going on further.

Thank you!

Best,
Mohammad

--

---====
Mohammad A Gharaibeh, Ph.D.
Associate Professor
Department of Mechanical Engineering
The Hashemite University
P.O. Box 330127
Zarqa, 13133, Jordan
Tel: +962 - 5 - 390 3333 Ext. 4771
Fax: +962 - 5 - 382 6348

---====

Hi Uffe Dal Eriksen, Thanks for the reply and for the out of the box way of thinking. However, I am not turning on the large deflections option. I will have to set down this weekend and get my head into some books to understand what’s going on further. Thank you! Best, Mohammad -- ===================================== Mohammad A Gharaibeh, Ph.D. Associate Professor Department of Mechanical Engineering The Hashemite University P.O. Box 330127 Zarqa, 13133, Jordan Tel: +962 - 5 - 390 3333 Ext. 4771 Fax: +962 - 5 - 382 6348 =====================================

HJ

Hozdic, Joseph C.

Thu, Apr 14, 2022 12:59 PM

Not to complicate this more, but have you looked into a Shock Response Spectrum (SRS) type analysis? It seems your main goal is to find a quicker (linear) solution.

This is something available in ANSYS, it takes into account the modal response as was previously discussed, and it can include some amplification factor (Q).
Very common in earthquake analysis for civil market, as well as explosive type shock events in aerospace industry (pyroshock)

The Q value is taken into account when transforming the input load into a SRS spectrum. A typical value is 10, but you can use whatever you deem appropriate.

Joseph Hozdic
Mechanical Engineer

Derrick Corporation
590 Duke Road
Buffalo, NY 14225 U.S.A.

Office: (716) 683-9010
Direct: (716) 683-1169 X574
Mobile: (716) 982-6758
www.Derrick.com

-----Original Message-----
From: Mohammad A Gharaibeh via Xansys xansys-temp@list.xansys.org
Sent: Tuesday, April 12, 2022 3:16 PM
To: XANSYS Mailing List Home xansys-temp@list.xansys.org
Cc: Mohammad A Gharaibeh mgharai1@binghamton.edu
Subject: [Xansys] Re: Replacing shock load by an equivalent static load

Thanks Chris! Maybe I need to dig deeper into this.

--

---====
Mohammad A Gharaibeh, Ph.D.
Associate Professor
Department of Mechanical Engineering
The Hashemite University
P.O. Box 330127
Zarqa, 13133, Jordan
Tel: +962 - 5 - 390 3333 Ext. 4771
Fax: +962 - 5 - 382 6348

---====

Xansys mailing list -- xansys-temp@list.xansys.org To unsubscribe send an email to xansys-temp-leave@list.xansys.org If you are receiving too many emails from XANSYS please consider changing account settings to Digest mode which will send a single email per day.

Please send administrative requests such as deletion from XANSYS to xansys-mod@tynecomp.co.uk and not to the list

Not to complicate this more, but have you looked into a Shock Response Spectrum (SRS) type analysis? It seems your main goal is to find a quicker (linear) solution. This is something available in ANSYS, it takes into account the modal response as was previously discussed, and it can include some amplification factor (Q). Very common in earthquake analysis for civil market, as well as explosive type shock events in aerospace industry (pyroshock) The Q value is taken into account when transforming the input load into a SRS spectrum. A typical value is 10, but you can use whatever you deem appropriate. Joseph Hozdic Mechanical Engineer Derrick Corporation 590 Duke Road Buffalo, NY 14225 U.S.A. Office: (716) 683-9010 Direct: (716) 683-1169 X574 Mobile: (716) 982-6758 www.Derrick.com -----Original Message----- From: Mohammad A Gharaibeh via Xansys <xansys-temp@list.xansys.org> Sent: Tuesday, April 12, 2022 3:16 PM To: XANSYS Mailing List Home <xansys-temp@list.xansys.org> Cc: Mohammad A Gharaibeh <mgharai1@binghamton.edu> Subject: [Xansys] Re: Replacing shock load by an equivalent static load Thanks Chris! Maybe I need to dig deeper into this. -- ===================================== Mohammad A Gharaibeh, Ph.D. Associate Professor Department of Mechanical Engineering The Hashemite University P.O. Box 330127 Zarqa, 13133, Jordan Tel: +962 - 5 - 390 3333 Ext. 4771 Fax: +962 - 5 - 382 6348 ===================================== _______________________________________________ Xansys mailing list -- xansys-temp@list.xansys.org To unsubscribe send an email to xansys-temp-leave@list.xansys.org If you are receiving too many emails from XANSYS please consider changing account settings to Digest mode which will send a single email per day. Please send administrative requests such as deletion from XANSYS to xansys-mod@tynecomp.co.uk and not to the list

CW

Christopher Wright

Thu, Apr 14, 2022 10:33 PM

On Apr 12, 2022, at 8:58 AM, Mohammad A Gharaibeh via Xansys xansys-temp@list.xansys.org wrote:

In my problem, a clamped plate (all edges) subjected to a half-sine wave
shock profile. I was able to identify the dynamic amplification factor to
be the equivalent bending stiffness of this plate.

That's what I thought you said. I don't see how the dynamic amplification factor—which is a dimensionless pure number applied to a static load—can be the same as the bending stiffness which is the ratio of the bending deformation to the corresponding load. Have I misunderstood your question?

Christopher Wright P.E. (ret'd)
chrisw@skypoint.com
——
We are the Village Green Preservation Society.
God save Donald Duck, vaudeville and variety.
We are the Desperate Dan Appreciation Society.
God save strawberry jam and all the different varieties.

On Apr 12, 2022, at 8:58 AM, Mohammad A Gharaibeh via Xansys <xansys-temp@list.xansys.org> wrote: > In my problem, a clamped plate (all edges) subjected to a half-sine wave > shock profile. I was able to identify the dynamic amplification factor to > be the equivalent bending stiffness of this plate. That's what I thought you said. I don't see how the dynamic amplification factor—which is a dimensionless pure number applied to a static load—can be the same as the bending stiffness which is the ratio of the bending deformation to the corresponding load. Have I misunderstood your question? Christopher Wright P.E. (ret'd) chrisw@skypoint.com —— We are the Village Green Preservation Society. God save Donald Duck, vaudeville and variety. We are the Desperate Dan Appreciation Society. God save strawberry jam and all the different varieties.

xansys-temp@list.xansys.org

[Mechanical] User defined result temperature difference